The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm,...The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm, the power-law process was used to simulate the wind speeds at a hub height of 60 m. The Weibull and Rayleigh distributions were chosen to express the wind speeds at two different heights. The parameters in the model were estimated via the least square(LS) method and the maximum likelihood estimation(MLE) method, respectively. An adjusted MLE approach was also presented for parameter estimation. The main indices of wind energy characteristics were calculated based on observational wind speed data. A case study based on the data of Hexi area, Gansu Province of China was given. The results show that MLE method generally outperforms LS method for parameter estimation, and Weibull distribution is more appropriate to describe the wind speed at the hub height.展开更多
The effects of environmental vertical wind shear （VWS） on the intensity and rainfall asymmetries in Tropical Storm （TS） Bilis （2006） have been analyzed based on TRMM/TMI-estimated surface rainfall data, QuikSCAT...The effects of environmental vertical wind shear （VWS） on the intensity and rainfall asymmetries in Tropical Storm （TS） Bilis （2006） have been analyzed based on TRMM/TMI-estimated surface rainfall data, QuikSCAT wind fields, 850- and 200-hPa winds of the NCEP-NCAR reanalysis, precipitation data at 5-min intervals from automatic weather stations over China's Mainland, and the best track data of TS Bilis （2006）. The results show that the simultaneous and 6-hour-lagged correlation coefficients between VWS and storm intensity （the minimum central sea level pressure） are 0.59145 and 0.57438 （P 〈0.01）, respectively. The averaged VWS was found to be about 11 m s-1 and thus suppressed the intensification of Bilis （2006）. Distribution of precipitation in Bilis （2006） was highly asymmetric. The azimuthally-averaged rainfall rate in the partial eyewall, however, was smaller than that in a major outer rainband. As the storm intensified, the major rainband showed an unusual outward propagation. The VWS had a great impact on the asymmetric distribution of precipitation. Consistent with previous modeling studies, heavy rainfall generally occurred downshear to downshear-left of the VWS vector both near and outside the eyewall, showing a strong wavenumber-one asymmetry, which was amplified as the VWS increased.展开更多
In this study,the effect of vertical wind shear(VWS)on the intensification of tropical cyclone(TC)is investigated via the numerical simulations.Results indicate that weak shear tends to facilitate the development of T...In this study,the effect of vertical wind shear(VWS)on the intensification of tropical cyclone(TC)is investigated via the numerical simulations.Results indicate that weak shear tends to facilitate the development of TC while strong shear appears to inhibit the intensification of TC.As the VWS is imposed on the TC,the vortex of the cyclone tends to tilt vertically and significantly in the upper troposphere.Consequently,the upward motion is considerably enhanced in the downshear side of the storm center and correspondingly,the low-to mid-level potential temperature decreases under the effect of adiabatic cooling,which leads to the increase of the low-to mid-level static instability and relative humidity and then facilitates the burst of convection.In the case of weak shear,the vertical tilting of the vortex is weak and the increase of ascent,static instability and relative humidity occur in the area close to the TC center.Therefore,active convection happens in the TC center region and facilitates the enhancement of vorticity in the inner core region and then the intensification of TC.In contrast,due to strong VWS,the increase of the ascent,static instability and relative humidity induced by the vertical tilting mainly appear in the outer region of TC in the case with stronger shear,and the convection in the inner-core area of TC is rather weak and convective activity mainly happens in the outer-region of the TC.Therefore,the development of a warm core is inhibited and then the intensification of TC is delayed.Different from previous numerical results obtained by imposing VWS suddenly to a strong TC,the simulation performed in this work shows that,even when the VWS is as strong as 12 m s-1,the tropical storm can still experience rapid intensification and finally develop into a strong tropical cyclone after a relatively long period of adjustment.It is found that the convection plays an important role in the adjusting period.On one hand,the convection leads to the horizontal convergence of the low-level vorticity flux and therefore leads to the enhancement of the low-level vorticity in the inner-core area of the cyclone.On the other hand,the active ascent accompanying the convection tends to transport the low-level vorticity to the middle levels.The enhanced vorticity in the lower to middle troposphere strengths the interaction between the low-and mid-level cyclonical circulation and the upper-level circulation deviated from the storm center under the effect of VWS.As a result,the vertical tilting of the vortex is considerably decreased,and then the cyclone starts to develop rapidly.展开更多
The effects of vertical wind shear on tropical cyclone(TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006.First,the...The effects of vertical wind shear on tropical cyclone(TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006.First,the influence of wind shear between different vertical levels and averages in different horizontal areas are compared.The results indicate that the effect of wind shear between 200 and 850 hPa averaged within a 200-800 km annulus on TC intensity change is larger than any other calculated vertical wind shear.High-latitude and intense TCs tend to be less sensitive to the effects of VWS than low-latitude and weak TCs.TCs experience time lags between the imposition of the shear and the weakening in TC intensity.A vertical shear of 8-9 m/s(9-10 m/s) would weaken TC intensity within 60 h(48 h).A vertical shear greater than 10 m/s would weaken TC intensity within 6 h.Finally,a statistical TC intensity prediction scheme is developed by using partial least squares regression,which produces skillful intensity forecasts when potential predictors include factors related to the vertical wind shear.Analysis of the standardized regression coefficients further confirms the obtained statistical results.展开更多
The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency （PE） were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 20...The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency （PE） were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 2007. Vertical wind shear affected PE by changing the kinetic energy conversion between the mean and perturbation circulations. Clou^radiation interaction impacted upon PE, but the relationship related to cloud radiative effects on PE was not statistically significant. The reduction in deposition processes as- sociated with the removal of ice microphysics suppressed efficiency. The relationships related to effects of vertical wind shear, radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget.展开更多
The effect of vertical wind shear(VWS)directions on the change in western North Pacific tropical cyclone(TC)intensity is revisited in this study.Results show that the differences in the correlations between VWS in dif...The effect of vertical wind shear(VWS)directions on the change in western North Pacific tropical cyclone(TC)intensity is revisited in this study.Results show that the differences in the correlations between VWS in different orientations and the change in TC nondimensional intensity highly diminish,although slight differences are still present.The subtle differences in the correlations are likely associated with different synoptic-scale patterns at upper and lower levels.This result suggests that,in addition to thermodynamic effects,dynamic roles of the synoptic-scale patterns associated with the VWS should also be taken into account when the authors examine how VWS in different directions affects TC intensity change.展开更多
This study investigates the effects of vertical wind shear on the torrential rainfall response to the large-scale forcing using a rainfall separation analysis of a pair of two-dimensional cloud-resolving model sensiti...This study investigates the effects of vertical wind shear on the torrential rainfall response to the large-scale forcing using a rainfall separation analysis of a pair of two-dimensional cloud-resolving model sensitivity experiments for a pre-summer heavy rainfall event over southern China from 3-8 June 2008 coupled with National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS) data.The rainfall partitioning analysis based on the surface rainfall budget indicates that the exclusion of vertical wind shear decreases the contribution to total rainfall from the largest contributor,which is the rainfall associated with local atmospheric drying,water vapor divergence,and hydrometeor loss/convergence,through the reduction of the rainfall area and reduced rainfall during the rainfall event.The removal of vertical wind shear increases the contribution to total rainfall from the rainfall associated with local atmospheric drying,water vapor convergence,and hydrometeor loss/convergence through the expansion of the rainfall area and enhanced rainfall.The elimination of vertical wind shear enhances heavy rainfall and expands its area,whereas it reduces moderate rainfall and its area.展开更多
Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertic...Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.展开更多
Using tropical cyclone （TC） best track and intensity of the western North Pacific data from the Joint Typhoon Warning Center （JTWC） of the United States and the NCEP/NCAR reanalysis data for the period of 1992-200...Using tropical cyclone （TC） best track and intensity of the western North Pacific data from the Joint Typhoon Warning Center （JTWC） of the United States and the NCEP/NCAR reanalysis data for the period of 1992-2002, the effects of vertical wind shear on TC intensity are examined. The samples were limited to the westward or northwestward moving TCs between 5°N and 20°N in order to minimize thermodynamic effects. It is found that the effect of vertical wind shear between 200 and 500 hPa on TC intensity change is larger than that of the shear between 500 and 850 hPa, while similar to that of the shear between 200 and 850 hPa. Vertical wind shear may have a threshold value, which tends to decrease as TC intensifies. As the intensifying rate of TC weakens, the average shear increases. The large shear has the obvious trend of inhibiting TC development. The average shear of TC which can develop into typhoon （tropical depression or tropical storm） is below 7 m s^-1 （above 8 m s^-1）.展开更多
Super Typhoon Halyan （1330）, which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan w...Super Typhoon Halyan （1330）, which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network, typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 m s-1, the storm had the largest lightning density in the inner core, compared with other intensity stages. In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear （VWS） on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the ralnbands.展开更多
Vertical wind shear fundamentally influences changes in tropical cyclone （TC） intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not .well und...Vertical wind shear fundamentally influences changes in tropical cyclone （TC） intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not .well understood. We present a new statistical study of all named TCs in this region during the period 2000- 2006 using a second-generation partial least squares （PLS） regression technique. The results show that the lower-layer （between 850 hPa and 10 m above the sea surface） wind shear is more important than the commonly analyzed deep-layer shear （between 200 and 850 hPa） for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low θe air into the boundary layer from above, significantly reducing values of θe in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 m s-1, and the critical value of lower-layer shear for TC intensification is approximately ±1.5 m s-1.展开更多
The variation of the spectral structure of the internal inertio-gravity waves (ⅡGWs) propagating in the atmospheric wind shear environments is discussed in this paper. From the hydrodynamic equation set in Boussinesq...The variation of the spectral structure of the internal inertio-gravity waves (ⅡGWs) propagating in the atmospheric wind shear environments is discussed in this paper. From the hydrodynamic equation set in Boussinesq approximation, a spectral propagation equation ⅡGWs satisfy is derived, then the spectral correspondence in the upper atmosphere is numerically calculated, after a forced spectrum is given as a Van- Zandt one at the lower boundary. The results show that if ⅡGWs do not encounter the critical-layer absorp- tion, then their spectral structure may be not changed significantly; otherwise it may be changed greatly, and a few of spectral components are filtered. Also the isotropy of the assumed VanZandt spectrum is distorted in upward-propagating process. That is the directional filtering effect of the atmospheric wind on the gravity wave spectrum.展开更多
In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examine...In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method.Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward,resulting in the lowestθ_(e)in the downshear-left boundary layer.Quantitative estimations ofθ_(e)recovery indicate that air parcels,especially those originating from the downshear-left outer core,can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically.As a result,the maximumθ_(e)is observed in the downshear-right quadrant of a highly sheared TC.The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement ofθ_(e)in the downshear-left outer core.In particular,the former plays a leading role in suchθ_(e)enhancements,while the latter plays a secondary role.As a result,moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.展开更多
The characteristics of tropical cyclone(TC) tilts under vertically varying background flows were preliminarily examined in this study based on numerical simulations with the Tropical Cyclone Model version 4(TCM4).The ...The characteristics of tropical cyclone(TC) tilts under vertically varying background flows were preliminarily examined in this study based on numerical simulations with the Tropical Cyclone Model version 4(TCM4).The tilt magnitudes presented a linearly decreasing tendency in the simulation with the environmental wind speed vertically varying throughout the troposphere and in the simulation with the vertical wind shear concentrated in the lower troposphere,while the vortex tilt showed a linearly increasing tendency in magnitude in the simulation where the vertical shear was concentrated in the upper troposphere.The change in tilt magnitude was found to be related to the evolution of the penetration depth near the eyewall.When the shear was concentrated in the lower troposphere,the vortex tended to tilt downshear right during the early integration and underwent more precession processes.When the shear was concentrated in the upper troposphere,the vortex rapidly tilted downshear left during the early simulation and vortex precession was less frequently observed.The storms simulated in all experiments were finally in downshear-left tilt equilibrium.展开更多
In this paper,the authors present the statistical characteristics of the buoyancy of outer-core convective-scale updrafts in numerically simulated sheared tropical cyclones(TCs).The total buoyancy is predominantly pos...In this paper,the authors present the statistical characteristics of the buoyancy of outer-core convective-scale updrafts in numerically simulated sheared tropical cyclones(TCs).The total buoyancy is predominantly positive in weak-to-strong ambient vertical shears,whereas much of the total buoyancy under an extreme shear environment becomes negative.Thermal buoyancy positively contributes to the total buoyancy value.For weakly and moderately sheared TCs,the updraft buoyancy is statistically significantly stronger downshear but smaller upshear.Such a downshear preference of strong buoyancy becomes less evident as the shear magnitude increases.The total buoyancy of updrafts shows a decreasing tendency with radius.Both thermal and dynamic buoyancy do not significantly correlate with vertically averaged vertical mass fluxes.This also leads to no significant correlation between the total buoyancy and vertical mass fluxes of outer-core updrafts.展开更多
The monsoon trough （MT） is one of the large-scale patterns favorable for tropical cyclone （TC） formation over the western North Pacific （WNP）. This study re-examines TC formation by treating the MT as a large-sc...The monsoon trough （MT） is one of the large-scale patterns favorable for tropical cyclone （TC） formation over the western North Pacific （WNP）. This study re-examines TC formation by treating the MT as a large-scale background for TC activity during May-October. Over an 11-year （2000-10） period, 8.3 TC formation events on average per year are identified to occur within MTs, accounting for 43.1% of the total TC formation events in the WNP basin. This percentage is much lower than those reported in previous studies. Further analysis indicates that TC formation events in monsoon gyres were included at least in some previous studies. The MT includes a monsoon confluence zone where westerlies meet easterlies and a monsoon shear line where the trade easterlies lie north of the monsoon westerlies. In this study, the large-scale flow pattern associated with TC formation in the MT is composited based on the reference point in the confluence zone where both the zonal and meridional wind components are zero with positive vorticity. While previous studies have found that many TCs form in the confluence zone, the composite analysis indicates that nearly all of the TCs formed in the shear region, since the shear region is associated with stronger low-level relative vorticity than the confluence zone. The prevailing easterly vertical shear of zonal wind and barotropic instability may also be conducive to TC formation in the shear region, through the development of synoptic-scale tropical disturbances in the MT that are necessary for TC formation.展开更多
Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subt...Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subtle differences in initializations of(a)500-850-h Pa environmental winds,and(b)midlevel moisture and ventilation.We then describe how these differences impact on the evolving convective organization,storm structure,and the timing of RI.As expected,ascent,diabatic heating and the secondary circulation near the inner-core are much stronger in the member that best forecasts the RI.The evolution of vortex cloudiness from this member is similar to the actual imagery,with the development of an inner cloud band wrapping inwards to form the eyewall.We present evidence that this structure,and hence the enhanced diabatic heating,is related to the tilt and associated dynamics of the developing inner-core in shear.For the most accurate ensemble member:(a)inhibition of ascent and a reduction in convection over the up-shear sector allow moistening of the boundary-layer air,which is transported to the down-shear sector to feed a developing convective asymmetry;(b)with minimal ventilation,undiluted clouds and moisture from the down-shear left quadrant are then wrapped inwards to the up-shear left quadrant to form the eyewall cloud;and(c)this process seems related to a critical down-shear tilt of the vortex from midlevels,and the vertical phase-locking of the circulation over up-shear quadrants.For the member that forecasts a much-delayed RI,these processes are inhibited by stronger vertical wind shear,initially resulting in poor vertical coherence of the circulation,lesser moisture and larger ventilation.Our analysis suggests that ensemble prediction is needed to account for the sensitivity of forecasts to a relatively narrow range of environmental wind shear,moisture and vortex inner-structure.展开更多
This paper analyzes the characteristics of super typhoons （STYs） over the western North Pacific （WNP） from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and...This paper analyzes the characteristics of super typhoons （STYs） over the western North Pacific （WNP） from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and the E1 Nifio-Southern Oscillation （ENSO） as well as the possible reason for the influence of the ENSO on STY activity are also investigated. The results showed that about one fifth of the tropical cyclones （TCs） over the WNP could reach the rank of STY. Most STYs appeared from July to November while there was a highest ratio between number of STYs and total number of TCs in November. Most STYs appeared east of the Philippine Sea. In E1 Nino years, affected by sea surface temperature （SST）, monsoon trough and weak vertical wind shear, TC formation locations shifted eastward and there were more STYs than in La Nifia years when the affecting factors changed.展开更多
It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive a...It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.展开更多
Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </...Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Southwestern Indian Ocean (SWIO). This study analyzed the dynamics and the impacts of the Tropical Cyclone (TC) Idai (4</span><sup><span style="font-family:Verdana;">th</span></sup><span style="font-family:Verdana;">-21</span><sup><span style="font-family:Verdana;">st</span></sup><span style="font-family:Verdana;"> March, 2019) which devastated most of the SWIO countries. The study used the Reanalysis 1 products of daily zonal (u) and meridional (v) winds, Sea Surface Temperatures (SSTs), amount of Precipitable Water (PRW), </span></span><span style="font-family:Verdana;">and relative humidity</span><span style="font-family:Verdana;"> (Rh). The dynamics and movements of Idai w</span><span style="font-family:Verdana;">ere</span><span style="font-family:Verdana;"> analyzed using the wind circulation at 850, 700, 500 and 200 mb, where the TC dynamic variables like vertical wind shear, vorticity, and the mean zonal wind were calculated using u and v components. Using the open Grid Analysis and Display System (GrADS) software the data was processed into three</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">time epochs of pre, during and post;and then analyzed to feature the state of the atmosphere before (pre), during and post TC Idai using all datasets. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">amount of precipitable water was used to map the rainfall on pre, during, and post Idai as well as during its landfall. The results revealed that dynamics of TC Idai was intensifying the weather (over Mozambique) and clearing the weather equatorward or southward of 12<span style="white-space:nowrap;">°</span>S, with low vertical wind shear over the landfall areas (</span><span style="white-space:nowrap;font-family:Verdana;">-</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">3 to 3 m/s) and higher shear values (10 - 40 m/s) northward and southward of the Mozambican channel. Higher moisture content (80 - 90%) and higher PRW (40 - 60 mm/day) mapped during Idai over the lowland areas of Mozambique propagating westward. Higher low</span></span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">level vorticity values were also mapped over the landfall areas. More results revealed that countries laying equatorward of 12<span style="white-space:nowrap;">°</span>S</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> e.g.</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the northern coastal areas of Kenya (Turkana and Baringo) and Tanzania, Idai disrupted the 2019 March to May (MAM) seasonal rainfall by inducing long dry spell which accelerated the famine over the northeastern Kenya (Turkana). Moreover, results revealed that the land falling of Idai triggered intensive flooding which affected </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">wide spectrum of socio</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">economic livelihoods including significant loss of lives, injuries, loss of material wealth, infrastructure;indeed, people were forced to le</span><span style="font-family:Verdana;">ave</span><span style="font-family:Verdana;"> their houses for quite </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">longtime;water</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">born</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> diseases like malaria, cholera among others were experienced. Furthermore, results and reports revealed that </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">large amount of funds were raised to combat the impacts of Idai. For instance, USAID/OFDA used about $14,146,651 for human aid and treatment of flood</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">prone diseases like Cholera in Mozambique ($13,296,651), Zimbabwe ($100,000), and Malawi ($280,000), respectively. Also a death toll of about 602 in Mozambique and 344 in Zimbabwe, and more than 2500 cases of injured people were reported</span><span style="font-family:Verdana;">.</span><span style="font-family:Verdana;"> Conclusively the study has shown that TCs including Idai and other are among the deadliest natural phenomenon which great affects the human and his environments, thus extensive studies on TCs frequency, strength, tracks as well </span><span style="font-family:Verdana;">as </span><span style="font-family:Verdana;">their coast benefit analysis should be conducted to reduce the societal impacts of these TCs.</span>展开更多
基金Project(51165019)supported by the National Natural Science Foundation of ChinaProject(1308RJYA018)supported by Gansu Provincial Natural Science Fund,ChinaProject(2013-4-110)supported by Lanzhou Technology Development Program,China
文摘The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm, the power-law process was used to simulate the wind speeds at a hub height of 60 m. The Weibull and Rayleigh distributions were chosen to express the wind speeds at two different heights. The parameters in the model were estimated via the least square(LS) method and the maximum likelihood estimation(MLE) method, respectively. An adjusted MLE approach was also presented for parameter estimation. The main indices of wind energy characteristics were calculated based on observational wind speed data. A case study based on the data of Hexi area, Gansu Province of China was given. The results show that MLE method generally outperforms LS method for parameter estimation, and Weibull distribution is more appropriate to describe the wind speed at the hub height.
基金supported by the National Natural Science Foundation of China under the Grant Nos.40828005the National Natural Science Foundation of China under the Grant Nos.40921160382+7 种基金the National Natural Science Foundation of China under the Grant Nos.40775060the Key Project of the Ministry of Education of China,Grant No.02109the State Key Basic Research Program 2009CB421500the State Key Basic Research Program 2006BAC02B03the State Key Basic Research Program GYHY200706033supported by National Science Foundation of UAS Grants ATM-0427128National Science Foundation of UAS Grants ATM-0754039the ONR Grant 00014-06-10303
文摘The effects of environmental vertical wind shear （VWS） on the intensity and rainfall asymmetries in Tropical Storm （TS） Bilis （2006） have been analyzed based on TRMM/TMI-estimated surface rainfall data, QuikSCAT wind fields, 850- and 200-hPa winds of the NCEP-NCAR reanalysis, precipitation data at 5-min intervals from automatic weather stations over China's Mainland, and the best track data of TS Bilis （2006）. The results show that the simultaneous and 6-hour-lagged correlation coefficients between VWS and storm intensity （the minimum central sea level pressure） are 0.59145 and 0.57438 （P 〈0.01）, respectively. The averaged VWS was found to be about 11 m s-1 and thus suppressed the intensification of Bilis （2006）. Distribution of precipitation in Bilis （2006） was highly asymmetric. The azimuthally-averaged rainfall rate in the partial eyewall, however, was smaller than that in a major outer rainband. As the storm intensified, the major rainband showed an unusual outward propagation. The VWS had a great impact on the asymmetric distribution of precipitation. Consistent with previous modeling studies, heavy rainfall generally occurred downshear to downshear-left of the VWS vector both near and outside the eyewall, showing a strong wavenumber-one asymmetry, which was amplified as the VWS increased.
基金Natural Science Foundation of China(40921160382,40730948 and 40830958)State Key Basic Program of China(2009CB421502)
文摘In this study,the effect of vertical wind shear(VWS)on the intensification of tropical cyclone(TC)is investigated via the numerical simulations.Results indicate that weak shear tends to facilitate the development of TC while strong shear appears to inhibit the intensification of TC.As the VWS is imposed on the TC,the vortex of the cyclone tends to tilt vertically and significantly in the upper troposphere.Consequently,the upward motion is considerably enhanced in the downshear side of the storm center and correspondingly,the low-to mid-level potential temperature decreases under the effect of adiabatic cooling,which leads to the increase of the low-to mid-level static instability and relative humidity and then facilitates the burst of convection.In the case of weak shear,the vertical tilting of the vortex is weak and the increase of ascent,static instability and relative humidity occur in the area close to the TC center.Therefore,active convection happens in the TC center region and facilitates the enhancement of vorticity in the inner core region and then the intensification of TC.In contrast,due to strong VWS,the increase of the ascent,static instability and relative humidity induced by the vertical tilting mainly appear in the outer region of TC in the case with stronger shear,and the convection in the inner-core area of TC is rather weak and convective activity mainly happens in the outer-region of the TC.Therefore,the development of a warm core is inhibited and then the intensification of TC is delayed.Different from previous numerical results obtained by imposing VWS suddenly to a strong TC,the simulation performed in this work shows that,even when the VWS is as strong as 12 m s-1,the tropical storm can still experience rapid intensification and finally develop into a strong tropical cyclone after a relatively long period of adjustment.It is found that the convection plays an important role in the adjusting period.On one hand,the convection leads to the horizontal convergence of the low-level vorticity flux and therefore leads to the enhancement of the low-level vorticity in the inner-core area of the cyclone.On the other hand,the active ascent accompanying the convection tends to transport the low-level vorticity to the middle levels.The enhanced vorticity in the lower to middle troposphere strengths the interaction between the low-and mid-level cyclonical circulation and the upper-level circulation deviated from the storm center under the effect of VWS.As a result,the vertical tilting of the vortex is considerably decreased,and then the cyclone starts to develop rapidly.
基金National Natural Science Foundation of China(41405060,41475082,41305049,41275067,41475059)
文摘The effects of vertical wind shear on tropical cyclone(TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006.First,the influence of wind shear between different vertical levels and averages in different horizontal areas are compared.The results indicate that the effect of wind shear between 200 and 850 hPa averaged within a 200-800 km annulus on TC intensity change is larger than any other calculated vertical wind shear.High-latitude and intense TCs tend to be less sensitive to the effects of VWS than low-latitude and weak TCs.TCs experience time lags between the imposition of the shear and the weakening in TC intensity.A vertical shear of 8-9 m/s(9-10 m/s) would weaken TC intensity within 60 h(48 h).A vertical shear greater than 10 m/s would weaken TC intensity within 6 h.Finally,a statistical TC intensity prediction scheme is developed by using partial least squares regression,which produces skillful intensity forecasts when potential predictors include factors related to the vertical wind shear.Analysis of the standardized regression coefficients further confirms the obtained statistical results.
基金supported by projects of the National Natural Sciences Foundation of China(Grant Nos.41075044,41275065,and 41075079)
文摘The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency （PE） were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 2007. Vertical wind shear affected PE by changing the kinetic energy conversion between the mean and perturbation circulations. Clou^radiation interaction impacted upon PE, but the relationship related to cloud radiative effects on PE was not statistically significant. The reduction in deposition processes as- sociated with the removal of ice microphysics suppressed efficiency. The relationships related to effects of vertical wind shear, radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget.
基金This work was jointly supported by the National Key Research and Development Program of China[grant numbers 2018YFC1507103 and 2017YFC1501601]the Key Program of the Ministry of Science and Technology of China[grant number 2017YFE0107700]National Natural Science Foundation of China[grant numbers 41875054,41730961,41730960,and 41775065].
文摘The effect of vertical wind shear(VWS)directions on the change in western North Pacific tropical cyclone(TC)intensity is revisited in this study.Results show that the differences in the correlations between VWS in different orientations and the change in TC nondimensional intensity highly diminish,although slight differences are still present.The subtle differences in the correlations are likely associated with different synoptic-scale patterns at upper and lower levels.This result suggests that,in addition to thermodynamic effects,dynamic roles of the synoptic-scale patterns associated with the VWS should also be taken into account when the authors examine how VWS in different directions affects TC intensity change.
基金supported by the National Key Basic Research and Development Project of China under Grant 2011CB403405the Chinese Special Scientific Research Project for Public Interest under Grant GYHY200806009+1 种基金the National Natural Science Foundation of China under Grants 41075039 and 41175065the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘This study investigates the effects of vertical wind shear on the torrential rainfall response to the large-scale forcing using a rainfall separation analysis of a pair of two-dimensional cloud-resolving model sensitivity experiments for a pre-summer heavy rainfall event over southern China from 3-8 June 2008 coupled with National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS) data.The rainfall partitioning analysis based on the surface rainfall budget indicates that the exclusion of vertical wind shear decreases the contribution to total rainfall from the largest contributor,which is the rainfall associated with local atmospheric drying,water vapor divergence,and hydrometeor loss/convergence,through the reduction of the rainfall area and reduced rainfall during the rainfall event.The removal of vertical wind shear increases the contribution to total rainfall from the rainfall associated with local atmospheric drying,water vapor convergence,and hydrometeor loss/convergence through the expansion of the rainfall area and enhanced rainfall.The elimination of vertical wind shear enhances heavy rainfall and expands its area,whereas it reduces moderate rainfall and its area.
基金supported by the National Natural Science Foundation of China(Grant number 42075072)support from The Startup Foundation for Introducing Talent of the Nanjing University of Information Science and Technology.
文摘Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 4995014, 40275018, and 40333025.
文摘Using tropical cyclone （TC） best track and intensity of the western North Pacific data from the Joint Typhoon Warning Center （JTWC） of the United States and the NCEP/NCAR reanalysis data for the period of 1992-2002, the effects of vertical wind shear on TC intensity are examined. The samples were limited to the westward or northwestward moving TCs between 5°N and 20°N in order to minimize thermodynamic effects. It is found that the effect of vertical wind shear between 200 and 500 hPa on TC intensity change is larger than that of the shear between 500 and 850 hPa, while similar to that of the shear between 200 and 850 hPa. Vertical wind shear may have a threshold value, which tends to decrease as TC intensifies. As the intensifying rate of TC weakens, the average shear increases. The large shear has the obvious trend of inhibiting TC development. The average shear of TC which can develop into typhoon （tropical depression or tropical storm） is below 7 m s^-1 （above 8 m s^-1）.
基金Supported by the National Key Basic Research Program of China(2014CB441401)National Natural Science Foundation of China(41475002)
文摘Super Typhoon Halyan （1330）, which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network, typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 m s-1, the storm had the largest lightning density in the inner core, compared with other intensity stages. In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear （VWS） on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the ralnbands.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2009CB421502)China Meteorological Administration Special Public Welfare Research Fund(GYHY201006007)+2 种基金National Natural Science Foundation of China(40905020)State Key Laboratory of Severe Weather(2011LASW-B11)Funds for the Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutions
文摘Vertical wind shear fundamentally influences changes in tropical cyclone （TC） intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not .well understood. We present a new statistical study of all named TCs in this region during the period 2000- 2006 using a second-generation partial least squares （PLS） regression technique. The results show that the lower-layer （between 850 hPa and 10 m above the sea surface） wind shear is more important than the commonly analyzed deep-layer shear （between 200 and 850 hPa） for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low θe air into the boundary layer from above, significantly reducing values of θe in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 m s-1, and the critical value of lower-layer shear for TC intensification is approximately ±1.5 m s-1.
文摘The variation of the spectral structure of the internal inertio-gravity waves (ⅡGWs) propagating in the atmospheric wind shear environments is discussed in this paper. From the hydrodynamic equation set in Boussinesq approximation, a spectral propagation equation ⅡGWs satisfy is derived, then the spectral correspondence in the upper atmosphere is numerically calculated, after a forced spectrum is given as a Van- Zandt one at the lower boundary. The results show that if ⅡGWs do not encounter the critical-layer absorp- tion, then their spectral structure may be not changed significantly; otherwise it may be changed greatly, and a few of spectral components are filtered. Also the isotropy of the assumed VanZandt spectrum is distorted in upward-propagating process. That is the directional filtering effect of the atmospheric wind on the gravity wave spectrum.
基金jointly supported by the National Key Research and Development Program of China under Grant No. 2017YFC1501601the National Natural Science Foundation of China under Grant Nos. 42175005 and 41875054
文摘In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method.Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward,resulting in the lowestθ_(e)in the downshear-left boundary layer.Quantitative estimations ofθ_(e)recovery indicate that air parcels,especially those originating from the downshear-left outer core,can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically.As a result,the maximumθ_(e)is observed in the downshear-right quadrant of a highly sheared TC.The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement ofθ_(e)in the downshear-left outer core.In particular,the former plays a leading role in suchθ_(e)enhancements,while the latter plays a secondary role.As a result,moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.
基金jointly supported by the National(Key)Basic Research and Development(973)Program of China(No.2015CB452803)the National Natural Science Foundation of China(Nos.41475058 and 41375068)+1 种基金the Open Project of the State Key Laboratory of Severe Weather(No.2016LASW-B08)the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions(TAPP)
文摘The characteristics of tropical cyclone(TC) tilts under vertically varying background flows were preliminarily examined in this study based on numerical simulations with the Tropical Cyclone Model version 4(TCM4).The tilt magnitudes presented a linearly decreasing tendency in the simulation with the environmental wind speed vertically varying throughout the troposphere and in the simulation with the vertical wind shear concentrated in the lower troposphere,while the vortex tilt showed a linearly increasing tendency in magnitude in the simulation where the vertical shear was concentrated in the upper troposphere.The change in tilt magnitude was found to be related to the evolution of the penetration depth near the eyewall.When the shear was concentrated in the lower troposphere,the vortex tended to tilt downshear right during the early integration and underwent more precession processes.When the shear was concentrated in the upper troposphere,the vortex rapidly tilted downshear left during the early simulation and vortex precession was less frequently observed.The storms simulated in all experiments were finally in downshear-left tilt equilibrium.
基金supported by the National Key Research and Development Program of China [grant numbers 2017YFC1501601 and 2015CB452803]the National Natural Science Foundation of China [grant numbers41475058,41730961,and 41875054]+1 种基金the Basic Research Fund of the Chinese Academy of Meteorological Sciences[grant number 2016Z003]the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions(TAPP)
文摘In this paper,the authors present the statistical characteristics of the buoyancy of outer-core convective-scale updrafts in numerically simulated sheared tropical cyclones(TCs).The total buoyancy is predominantly positive in weak-to-strong ambient vertical shears,whereas much of the total buoyancy under an extreme shear environment becomes negative.Thermal buoyancy positively contributes to the total buoyancy value.For weakly and moderately sheared TCs,the updraft buoyancy is statistically significantly stronger downshear but smaller upshear.Such a downshear preference of strong buoyancy becomes less evident as the shear magnitude increases.The total buoyancy of updrafts shows a decreasing tendency with radius.Both thermal and dynamic buoyancy do not significantly correlate with vertically averaged vertical mass fluxes.This also leads to no significant correlation between the total buoyancy and vertical mass fluxes of outer-core updrafts.
基金supported by the National Basic Research Program of China (Grant Nos. 2013CB430103, 2015CB452803)the National Natural Science Foundation of China (Grant No. 41275093)the project of the "Specially-Appointed Professorship" of Jiangsu Province
文摘The monsoon trough （MT） is one of the large-scale patterns favorable for tropical cyclone （TC） formation over the western North Pacific （WNP）. This study re-examines TC formation by treating the MT as a large-scale background for TC activity during May-October. Over an 11-year （2000-10） period, 8.3 TC formation events on average per year are identified to occur within MTs, accounting for 43.1% of the total TC formation events in the WNP basin. This percentage is much lower than those reported in previous studies. Further analysis indicates that TC formation events in monsoon gyres were included at least in some previous studies. The MT includes a monsoon confluence zone where westerlies meet easterlies and a monsoon shear line where the trade easterlies lie north of the monsoon westerlies. In this study, the large-scale flow pattern associated with TC formation in the MT is composited based on the reference point in the confluence zone where both the zonal and meridional wind components are zero with positive vorticity. While previous studies have found that many TCs form in the confluence zone, the composite analysis indicates that nearly all of the TCs formed in the shear region, since the shear region is associated with stronger low-level relative vorticity than the confluence zone. The prevailing easterly vertical shear of zonal wind and barotropic instability may also be conducive to TC formation in the shear region, through the development of synoptic-scale tropical disturbances in the MT that are necessary for TC formation.
基金partially supported by the National Natural Science Foundation of China (Grant Nos. 41365005, 41765007 and 41705038)the Hainan Key Cooperation Program (Grant No. ZDYF2019213)the Natural Science Foundation of Hainan Province of China (Grant No. 417298)
文摘Diagnostics are presented from an ensemble of high-resolution forecasts that differed markedly in their predictions of the rapid intensification(RI)of Typhoon Rammasun.We show that the basic difference stems from subtle differences in initializations of(a)500-850-h Pa environmental winds,and(b)midlevel moisture and ventilation.We then describe how these differences impact on the evolving convective organization,storm structure,and the timing of RI.As expected,ascent,diabatic heating and the secondary circulation near the inner-core are much stronger in the member that best forecasts the RI.The evolution of vortex cloudiness from this member is similar to the actual imagery,with the development of an inner cloud band wrapping inwards to form the eyewall.We present evidence that this structure,and hence the enhanced diabatic heating,is related to the tilt and associated dynamics of the developing inner-core in shear.For the most accurate ensemble member:(a)inhibition of ascent and a reduction in convection over the up-shear sector allow moistening of the boundary-layer air,which is transported to the down-shear sector to feed a developing convective asymmetry;(b)with minimal ventilation,undiluted clouds and moisture from the down-shear left quadrant are then wrapped inwards to the up-shear left quadrant to form the eyewall cloud;and(c)this process seems related to a critical down-shear tilt of the vortex from midlevels,and the vertical phase-locking of the circulation over up-shear quadrants.For the member that forecasts a much-delayed RI,these processes are inhibited by stronger vertical wind shear,initially resulting in poor vertical coherence of the circulation,lesser moisture and larger ventilation.Our analysis suggests that ensemble prediction is needed to account for the sensitivity of forecasts to a relatively narrow range of environmental wind shear,moisture and vortex inner-structure.
基金supported by the National Natural Science Foundation of China(Grant No.s 40975038 and10735030)the State Key Development Program for Basic Research of China(973 Program)(Grant Nos.2006CB403603 and 2005CB422301)111 Project(Grant No.B07036)
文摘This paper analyzes the characteristics of super typhoons （STYs） over the western North Pacific （WNP） from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and the E1 Nifio-Southern Oscillation （ENSO） as well as the possible reason for the influence of the ENSO on STY activity are also investigated. The results showed that about one fifth of the tropical cyclones （TCs） over the WNP could reach the rank of STY. Most STYs appeared from July to November while there was a highest ratio between number of STYs and total number of TCs in November. Most STYs appeared east of the Philippine Sea. In E1 Nino years, affected by sea surface temperature （SST）, monsoon trough and weak vertical wind shear, TC formation locations shifted eastward and there were more STYs than in La Nifia years when the affecting factors changed.
基金Plan Project of Wenzhou Science and Technology (S20080030)Open Study Special Project of Meteorological Science and Technology of Zhejiang Province (KF2008004)+1 种基金Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (708051)Natural Science Foundation of China (40875068)
文摘It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.
文摘Tropical Cyclones (TCs) are among the atmospheric events which may trigger/enhance the occurrence of disasters to the society in most world basins including <span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">Southwestern Indian Ocean (SWIO). This study analyzed the dynamics and the impacts of the Tropical Cyclone (TC) Idai (4</span><sup><span style="font-family:Verdana;">th</span></sup><span style="font-family:Verdana;">-21</span><sup><span style="font-family:Verdana;">st</span></sup><span style="font-family:Verdana;"> March, 2019) which devastated most of the SWIO countries. The study used the Reanalysis 1 products of daily zonal (u) and meridional (v) winds, Sea Surface Temperatures (SSTs), amount of Precipitable Water (PRW), </span></span><span style="font-family:Verdana;">and relative humidity</span><span style="font-family:Verdana;"> (Rh). The dynamics and movements of Idai w</span><span style="font-family:Verdana;">ere</span><span style="font-family:Verdana;"> analyzed using the wind circulation at 850, 700, 500 and 200 mb, where the TC dynamic variables like vertical wind shear, vorticity, and the mean zonal wind were calculated using u and v components. Using the open Grid Analysis and Display System (GrADS) software the data was processed into three</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">time epochs of pre, during and post;and then analyzed to feature the state of the atmosphere before (pre), during and post TC Idai using all datasets. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">amount of precipitable water was used to map the rainfall on pre, during, and post Idai as well as during its landfall. The results revealed that dynamics of TC Idai was intensifying the weather (over Mozambique) and clearing the weather equatorward or southward of 12<span style="white-space:nowrap;">°</span>S, with low vertical wind shear over the landfall areas (</span><span style="white-space:nowrap;font-family:Verdana;">-</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">3 to 3 m/s) and higher shear values (10 - 40 m/s) northward and southward of the Mozambican channel. Higher moisture content (80 - 90%) and higher PRW (40 - 60 mm/day) mapped during Idai over the lowland areas of Mozambique propagating westward. Higher low</span></span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">level vorticity values were also mapped over the landfall areas. More results revealed that countries laying equatorward of 12<span style="white-space:nowrap;">°</span>S</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> e.g.</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> the northern coastal areas of Kenya (Turkana and Baringo) and Tanzania, Idai disrupted the 2019 March to May (MAM) seasonal rainfall by inducing long dry spell which accelerated the famine over the northeastern Kenya (Turkana). Moreover, results revealed that the land falling of Idai triggered intensive flooding which affected </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">wide spectrum of socio</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">economic livelihoods including significant loss of lives, injuries, loss of material wealth, infrastructure;indeed, people were forced to le</span><span style="font-family:Verdana;">ave</span><span style="font-family:Verdana;"> their houses for quite </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">longtime;water</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">born</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> diseases like malaria, cholera among others were experienced. Furthermore, results and reports revealed that </span><span style="font-family:Verdana;">a </span><span style="font-family:Verdana;">large amount of funds were raised to combat the impacts of Idai. For instance, USAID/OFDA used about $14,146,651 for human aid and treatment of flood</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">prone diseases like Cholera in Mozambique ($13,296,651), Zimbabwe ($100,000), and Malawi ($280,000), respectively. Also a death toll of about 602 in Mozambique and 344 in Zimbabwe, and more than 2500 cases of injured people were reported</span><span style="font-family:Verdana;">.</span><span style="font-family:Verdana;"> Conclusively the study has shown that TCs including Idai and other are among the deadliest natural phenomenon which great affects the human and his environments, thus extensive studies on TCs frequency, strength, tracks as well </span><span style="font-family:Verdana;">as </span><span style="font-family:Verdana;">their coast benefit analysis should be conducted to reduce the societal impacts of these TCs.</span>
