An average of eight snowfall events occur each year in the eastern Lesotho Highlands.These snowfall events are typically associated with cut-off low(CoLs)systems and mid-latitude cyclones.However,the moisture sources ...An average of eight snowfall events occur each year in the eastern Lesotho Highlands.These snowfall events are typically associated with cut-off low(CoLs)systems and mid-latitude cyclones.However,the moisture sources of the snowfall are unclassified and unclear.The Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model,an air mass back trajectory model,has been used to evaluate moisture source waters locally in southern Africa and internationally in China and Europe.This study uses HYSPLIT to determine the source moisture of snow in Lesotho.A list of all 82 snowfall events in Lesotho spanning 2017 to 2022 was compiled using the Snow Report SA Instagram page,including the date and location of snowfall.A 72-hour back trajectory for each snowfall event was initiated for both Afriski and the whole of Lesotho.This amounts to models of moisture source trajectories for 28 and 82 snowfall days,respectively.These air mass pathways are classified according to their frequency per snowfall event,per month in the snow season,per year and for the full period.From this,associated moisture source regions and dominant air mass trajectories were identified.This study reports that the air mass trajectories associated with Afriski and Lesotho as a whole are very similar.The most common pathway of air mass trajectories transporting snow-bearing moisture to Lesotho was an inland trajectory from the northern regions of southern Africa.This pathway makes up 16.6%of all trajectories reported and is associated with the Angola Low,the Congo Air Boundary and the St.Helena High Pressure.展开更多
Meteorological conditions are vital to PM_(2.5)and ozone(O_(3))complex pollution.Herein,the T-mode principal com-ponent analysis method was employed to objectively classify the 925-hPa geopotential height field of Don...Meteorological conditions are vital to PM_(2.5)and ozone(O_(3))complex pollution.Herein,the T-mode principal com-ponent analysis method was employed to objectively classify the 925-hPa geopotential height field of Dongying from 2017 to 2022.Synoptic patterns associated with four pollution types-namely,PM_(2.5)-only pollution,O_(3)-only pollution,Co-occurring of PM_(2.5)and O_(3)pollution,Non-occurring of PM_(2.5)and O_(3)pollution-were characterized at different time scales.The results indicated that synoptic classes conducive to PM_(2.5)-only pollution were“high-pressure top front”,“offshore high-pressure rear”,and“high-pressure inside”,while those conducive to O_(3)-only pollution were“offshore high-pressure rear”,“subtropical high”,and“high and low systems”.The Co-occurring of PM_(2.5)and O_(3)pollution were influenced by high pressure,and the Non-occurring of PM_(2.5)and O_(3)pollution were linked to precipitation and strong northerly winds.The variation in dominant synoptic patterns is crucial in the frequency changes of the four pollution types,which was further validated through the analysis of typical cases.Under the favorable meteorological conditions of high-pressure control with strong northerly winds or a subtropical high and inverted trough both with strong precipitation,there is potential to achieve coordinated control of PM_(2.5)and O_(3)in Dongying.Additionally,measures like artificially manipulating local humidity could be adopted to alleviate pollution levels.This study reveals the importance of comprehending the meteorological factors contributing to the formation of PM_(2.5)and O_(3)complex pollution for the improvement of urban air quality in the Bohai Rim region of China when emissions are high and the concentration of air pollutants exhibits high meteorological sensitivity.展开更多
This research work involves a comparative study of satellite rainfall and synoptic observations in the Republic of Guinea over a 30-year period.The methodology used consists,firstly,in assessing rainfall trends over t...This research work involves a comparative study of satellite rainfall and synoptic observations in the Republic of Guinea over a 30-year period.The methodology used consists,firstly,in assessing rainfall trends over the study period in Guinea’s four natural regions,using the temporal averages of the three stations located in each region.Secondly,we calculated the correlations between synoptic and satellite observation data,in order to determine the links between them on the basis of data analysis.The results for synoptic stations on average seasonal rainfall cycles and satellite products show that in Lower Guinea,the CRU(Climatic Research Unit)and GPCC(Global Precipitation Climatology Center)data are good estimates of observations.In the Fouta Djallon region,they also estimate observations well,but at two synoptic stations,with the exception of Mamou,they underestimate them.In Upper Guinea,during the monsoon period,satellites give a good estimate of rainfall in this area.In the forest region,these products show highly variable behavior,sometimes underestimating and sometimes overestimating observations,depending on the stations in the zone.展开更多
An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes...An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage(June 13-15) was the frontal heavy rainfall caused by cold air(brought by an East Asian trough)from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet(SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage(June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet(BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.展开更多
Here,we analyze the characteristics and the formation mechanisms of low-level jets(LLJs)in the middle reaches of the Yangtze River during the 2010 mei-yu season using Wuhan station radiosonde data and the fifth genera...Here,we analyze the characteristics and the formation mechanisms of low-level jets(LLJs)in the middle reaches of the Yangtze River during the 2010 mei-yu season using Wuhan station radiosonde data and the fifth generation of the European Centre for Medium-Range Weather Forecasts(ERA5)reanalysis dataset.Our results show that the vertical structure of LLJs is characterized by a predominance of boundary layer jets(BLJs)concentrated at heights of 900-1200 m.The BLJs occur most frequently at 2300 LST(LST=UTC+8 hours)but are strongest at 0200 LST,with composite wind velocities>14 m s^(-1).Synoptic-system-related LLJs(SLLJs)occur most frequently at 0800 LST but are strongest at 1100LST,with composite wind velocities>12 m s^(-1).Both BLJs and SLLJs are characterized by a southwesterly wind direction,although the wind direction of SLLJs is more westerly,and northeasterly SLLJs occur more frequently than northeasterly BLJs.When Wuhan is south of the mei-yu front,the westward extension of the northwest Pacific subtropical high intensifies,and the low-pressure system in the eastern Tibetan Plateau strengthens,favoring the formation of LLJs,which are closely related to precipitation.The wind speeds on rainstorm days are greater than those on LLJ days.Our analysis of four typical heavy precipitation events shows the presence of LLJs at the center of the precipitation and on its southern side before the onset of heavy precipitation.BLJs were shown to develop earlier than SLLJs.展开更多
Accurate meteorological predictions in the Arctic are important in response to the rapid climate change and insufficient meteorological observations in the Arctic.In this study,we adopted a high-resolution Weather Res...Accurate meteorological predictions in the Arctic are important in response to the rapid climate change and insufficient meteorological observations in the Arctic.In this study,we adopted a high-resolution Weather Research and Forecasting(WRF)model to simulate the meteorology at two Arctic stations(Barrow and Summit)in April 2019.Simulation results were also evaluated by using surface measurements and statistical parameters.In addition,weather charts during the studied time period were also used to assess the model performance.The results demonstrate that the WRF model is able to accurately capture the meteorological parameters for the two Arctic stations and the weather systems such as cyclones and anticyclones in the Arctic.Moreover,we found the model performance in predicting the surface pressure the best while the performance in predicting the wind the worst among these meteorological predictions.However,the wind predictions at these Arctic stations were found to be more accurate than those at urban stations in mid-latitude regions,due to the differences in land features and anthropogentic heat sources between these regions.In addition,a comparison of the simulation results showed that the prediction of meteorological conditions at Summit is superior to that at Barrow.Possible reasons for the deviations in temperature predictions between these two Arctic stations are uncertainties in the treatments of the sea ice and the cloud in the model.With respect to the wind,the deviations may source from the overestimation of the wind over the sea and at coastal stations.展开更多
To analyze a new heavy rain case over China during the year 2022, by using the data from NCC-CMA and NCEP, a heavy rain weather process in most areas of China from July 26 to 30, 2022 was analyzed. Synoptic methods we...To analyze a new heavy rain case over China during the year 2022, by using the data from NCC-CMA and NCEP, a heavy rain weather process in most areas of China from July 26 to 30, 2022 was analyzed. Synoptic methods were used in this research and results show that under the influence of low vortex and wind shear, the abundant water vapor supply brought by the southeast airflow in the lower level and the lifting of the Taihang Mountain, heavy rain weather occurred in the northern part of Henan, China. In the west of Liaoning and Jilin, the rainfall process had the characteristics of frontal rainfall and the stable precipitation resulted in heavy rain weather. To sum up, the rainfall process was mainly affected by the upper-level trough, low-level wind shear and low-level jet.展开更多
An extensive rainfall occurred in central and eastern China during 23-24 April, 2021. This research mainly uses the reanalysis data of NCEP/NCAR every 6 hours to analyze this heavy rainfall weather process. The result...An extensive rainfall occurred in central and eastern China during 23-24 April, 2021. This research mainly uses the reanalysis data of NCEP/NCAR every 6 hours to analyze this heavy rainfall weather process. The results show that the main reason for this precipitation process is the shear formed between the cold air and the warm and humid air flow in the southwest. The low temperature on the ground allows the warm and humid air flow to lift up to form precipitation. The shear system is strengthened to a low vortex, which greatly strengthens the vertical ascent movement. Good water vapor and dynamic conditions form a large range of heavy rainfall.展开更多
As global warming increasingly affects vulnerable regions such as Central East Africa, it is crucial to understand future changes in rainfall variability to reduce vulnerability. Despite the importance of rainfall var...As global warming increasingly affects vulnerable regions such as Central East Africa, it is crucial to understand future changes in rainfall variability to reduce vulnerability. Despite the importance of rainfall variability, it has received less attention compared to changes in mean and extreme rainfall. This study evaluates the amplification of synoptic (weekly) to annual variability of East African Monsoon (EAM) Long Rainfall (March to May) by climatic extremes. Using band-pass filtered daily rainfall data, we found that EAM rainfall variability is anticipated to increase by 20% - 60% across the region under global warming conditions. The majority of the intermodal variability in Long Rain EAM rainfall forecasting is explained by differences in mean rainfall. Our results show that the synoptic variability of Long Rain for EAM rainfall is likely to amplify, resulting in more extreme rainfall events and longer dry spells under global warming. This amplification is attributed to the warming of the Indian Ocean and the associated changes in atmospheric circulation patterns. The projected increase in synoptic to annual variability of Long Rain for EAM rainfall has significant implications for water resources management and agriculture in the region, challenging policymakers to develop adaptive strategies that can mitigate the impacts of these extreme events. This study emphasizes the potential impacts of projected climate changes in rainfall variability on the East African region at all periods and underscores the need for effective adaptation strategies to ensure sustainable development.展开更多
In order to evaluate the precipitation forecast performance of mesoscale numerical model in Northeast China,mesoscale model in Liaoning Province and T213 model,and improve the ability to use their forecast products fo...In order to evaluate the precipitation forecast performance of mesoscale numerical model in Northeast China,mesoscale model in Liaoning Province and T213 model,and improve the ability to use their forecast products for forecasters,the synoptic verifications of their 12 h accumulated precipitation forecasts of 3 numerical modes from May to August in 2008 were made on the basis of different systems impacting weather in Liaoning Province.The time limitations were 24,36,48 and 60 h.The verified contents included 6 aspects such as intensity and position of precipitation center,intensity,location,scope and moving velocity of precipitation main body.The results showed that the three models had good forecasting capability for precipitation in Liaoning Province,but the cupacity of each model was obviously different.展开更多
Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall...Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.展开更多
By using regular meteorological data and Doppler radar data,causes for a hail storm over northern area of Dalian on Oct.13,2009 were analyzed from several aspects,including synoptic background,T-LnP charts and the cha...By using regular meteorological data and Doppler radar data,causes for a hail storm over northern area of Dalian on Oct.13,2009 were analyzed from several aspects,including synoptic background,T-LnP charts and the characteristics of radar reflectivity factor evolution.The results showed that the hail storm occurred in downstream of 500 hPa trough.The 500 hPa cold trough turned zonally and triggered the formation of shear line on lower level.Before the hail event,instability energy and moisture supply were observed.The shear line on lower level intensified the atmospheric instability,promoted the release of potential energy,caused the hail event.The cooperation of upper and lower level jet streams provided favorable dynamic condition for strong convection development.The Doppler radar analysis showed that strong convection was comprised of multiple convection cells,which demonstrated 'L' and 'V' shapes during mature stage,with peak intensity of 50-60 dBz.展开更多
In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert ...In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert Subjective Method （ESM）, the Objective Synoptic Analysis Technique （OSAT） for partitioning TC precipitation was developed by analyzing the western North Pacific （WNP） TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM, by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation （D0） and the TC size （D1）, into variable parameters.Case verification for OSAT was also carried out by applying CMORPH （Climate Prediction Center MORPHing technique） daily precipitation measurements, which is NOAA＇s combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.展开更多
Knowledge of the statistical characteristics of inversions and their effects on aerosols under different large-scale synoptic circulations is important for studying and modeling the diffusion of pollutants in the boun...Knowledge of the statistical characteristics of inversions and their effects on aerosols under different large-scale synoptic circulations is important for studying and modeling the diffusion of pollutants in the boundary layer. Based on results gen- erated using the self-organizing map （SOM） weather classification method, this study compares the statistical characteristics of surface-based inversions （SBIs） and elevated inversions （EIs）, and quantitatively evaluates the effect of SBIs on aerosol condensation nuclei （CN） concentrations and the relationship between temperature gradients and aerosols for six prevailing synoptic patterns over the the Southern Great Plains （SGP） site during 2001-10. Large-scale synoptic patterns strongly influ- ence the statistical characteristics of inversions and the accumulation of aerosols in the low-level atmosphere. The activity, frequency, intensity, and vertical distribution of inversions are significantly different among these synoptic patterns. The verti- cal distribution of inversions varies diurnally and is significantly different among the different synoptic patterns. Anticyclonic patterns affect the accumulation of aerosols near the ground more strongly than cyclonic patterns. Mean aerosol CN con- centrations increase during SBIs compared to no inversion cases by 16.1%, 22.6%, 24.5%, 58.7%, 29.8% and 23.7% for the six synoptic patterns. This study confirms that there is a positive correlation between temperature gradients and aerosol CN concentrations near the ground at night under similar large-scale synoptic patterns. The relationship is different for different synoptic patterns and can be described by linear functions. These findings suggest that large-scale synoptic patterns change the static stability of the atmosphere and inversions in the lower atmosphere, thereby influencing the diffusion of aerosols near the ground.展开更多
ABSTRACT During a sea-fog field observation campaign on Donghai Island in the spring of 2011, fog-water, visibility, meteorological elements, and fog droplet spectra were measured. The main cations and anions in 191 ...ABSTRACT During a sea-fog field observation campaign on Donghai Island in the spring of 2011, fog-water, visibility, meteorological elements, and fog droplet spectra were measured. The main cations and anions in 191 fog-water samples were Na＋, NH2, H＋, NO3, C1- and SO] , and the average concentrations of cations and anions were 2630 and 2970 p-eq L 1, respectively. The concentrations of Na＋ and C1- originated from the ocean were high. The enhancement of anthropogenic pollution might have contributed to the high concentration of NH＋, H＋, and NO^-3. The average values ofpH and electrical conductivity （EC） were 3.34 and 505 uS cm-1, respectively, with a negative correlation between them. Cold fronts associated with cyclonic circulations promoted the decline of ion loadings. Air masses from coastal areas had the highest ion loadings, contrary to those from the sea. The ranges of wind speed, wind direction and temperature corresponding to the maximum total ion concentration （TIC） were 3.5-4 m s-1, 79°-90° and 21°C-22°C, respectively. In view of the low correlation coefficients, a new parameter Lr was proposed as a predictive parameter for TIC and the correlation coefficient increased to 0.74. Based on aerosol concentrations during the sea-fog cases in 2010, we confirmed that fog-water chemical composition also depended on the species and sizes of aerosol particles. When a dust storm passed through Donghai Island, the number concentration of large aerosol particles （with diameter 〉 1 p-m） increased. This caused the ratio of CaZ＋/Na＋ in fog-water to increase significantly.展开更多
A robust anomalous anticyclonic circulation (AAC) was observed over Northeast Asia and the Japan Sea in boreal win-ter 1997/98 and over the Japan Sea in spring 1998. The formation mechanism is investigated. On the bac...A robust anomalous anticyclonic circulation (AAC) was observed over Northeast Asia and the Japan Sea in boreal win-ter 1997/98 and over the Japan Sea in spring 1998. The formation mechanism is investigated. On the background of the vertically sheared winter monsoonal flow, anomalous rainfall in the tropical Indo-Western Pacific warm pool excited a wave train towards East Asia in the upper troposphere during boreal winter of 1997/98. The AAC over Northeast Asia and the Japan Sea is part of the wave train of equivalent barotropic structure. The AAC over the Japan Sea persisted from winter to spring and even intensified in spring 1998. The diagnostic calculations show that the vorticity and temperature fluxes by synoptic eddies are an important mechanism for the AAC over the Japan Sea in spring 1998.展开更多
In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November throug...In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November through March), using NCEP/NCAR reanalysis datasets for the time period of 1948/49-2000/01. High-frequency signals are defined as those with timescales shorter than three weeks and measured in terms of variance, for each winter for each grid. The correlations between monthly mean AO index and high-frequency variance are conducted. A predominant feature is that several regional centers with high correlation show up in the middle to high latitudes. Significant areas include mid- to high-latitude Asia centered at Siberia, northern Europe and the middle-latitude North Atlantic east of northern Africa. Their strong correlations can also be confirmed by the singular value decomposition analysis of covariance between mean SLP and high-frequency variance. This indicates that the relationship of AO with daily Sea Level Pressure (SLP) is confined to some specific regions in association with the inherent atmospheric dynamics. In middle-latitude Asia, there is a significant (at the 95% level) trend of variance of-2.26% (10 yr)-1. Another region that displays a strong trend is the northwestern Pacific with a significant rate of change of 0.80% (10 yr)-1. If the winter of 1948/49, an apparent outlier, is excluded, a steady linear trend of +1.51% (10 yr)-1 shows up in northern Europe. The variance probability density functions (PDFs) are found to change in association with different AO phases. The changes corresponding to high and low AO phases, however, are asymmetric in these regions. Some regions such as northern Europe display much stronger changes in high AO years, whereas some other regions such as Siberia show a stronger connection to low AO conditions. These features are supported by ECMWF reanalysis data. However, the dynamical mechanisms involved in the AO-high frequency SLP variance connection have not been well understood, and this needs further study.展开更多
Fogs observed over Incheon international airport （IIA） in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal ext...Fogs observed over Incheon international airport （IIA） in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature （T ） and the SST, i.e., cold sea fog if TSST = T -SST 〉 0~0C and warm sea fog if TSST 〈 0~0C. The numbers of coastal, cold, and warm sea fog cases are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea fogs occur mostly in summer and warm sea fogs are observed from January to May but not in November and December. On average the air gets colder by 1.6~0C during the three hours leading up to the coastal fog formation, and an additional cooling of 1.1~0C occurs during the fog. The change in the dew point temperature （T_d） is minimal except during the fog （0.6~0C）. Decreases in T for the cold and warm sea fogs are relatively smaller. The average Td is higher than SST during the cold sea fog periods but this T_d is more than 4~0C higher than that for the corresponding non-fog days, suggesting that cold sea fogs be formed by the cooling of already humid air （i.e., T_d〉SST）. Increases of T_d are significant during the warm sea fog periods （1.4~0C）, implying that effcient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.展开更多
Summer precipitation over the Yangtze River basin(YRB)in 2020 experienced a strong subseasonal and synoptic fluctuation in addition to contributing to an exceptionally large seasonal mean precipitation.The cause of th...Summer precipitation over the Yangtze River basin(YRB)in 2020 experienced a strong subseasonal and synoptic fluctuation in addition to contributing to an exceptionally large seasonal mean precipitation.The cause of this higher-frequency fluctuation is examined based on observational analyses.Apart from the continuous northward movement of the climatological mei-yu rainband,the mei-yu rainbelt in the summer of 2020 experienced multiple northward and southward swings.The cause of the swings was attributed to the subseasonal variability of southerly winds to the south and northeasterly winds to the north of the YRB.In addition,synoptic-scale variability,characterized by the eastward propagation of low-level cyclonic vorticity and precipitation anomalies,was also commonplace in the summer of 2020.While the strengthening of both the subseasonal and synoptic variabilities in the summer of 2020 was attributed to the increase of the background mean moisture,the synoptic variability was greatly affected by the subseasonal rainfall variability.As a result,both the synoptic-scale and subseasonal variabilities contributed to the north-south swings of the rainbelt.The large-scale modulations by both the seasonal mean and subseasonal anomalies provide insight regarding the optimization of issuing accurate,extended-range forecasts of extreme weather events.展开更多
基金the University of the Witwatersrand Friedel Sellschop Grantthe WitsUCL strategic partnership grant
文摘An average of eight snowfall events occur each year in the eastern Lesotho Highlands.These snowfall events are typically associated with cut-off low(CoLs)systems and mid-latitude cyclones.However,the moisture sources of the snowfall are unclassified and unclear.The Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model,an air mass back trajectory model,has been used to evaluate moisture source waters locally in southern Africa and internationally in China and Europe.This study uses HYSPLIT to determine the source moisture of snow in Lesotho.A list of all 82 snowfall events in Lesotho spanning 2017 to 2022 was compiled using the Snow Report SA Instagram page,including the date and location of snowfall.A 72-hour back trajectory for each snowfall event was initiated for both Afriski and the whole of Lesotho.This amounts to models of moisture source trajectories for 28 and 82 snowfall days,respectively.These air mass pathways are classified according to their frequency per snowfall event,per month in the snow season,per year and for the full period.From this,associated moisture source regions and dominant air mass trajectories were identified.This study reports that the air mass trajectories associated with Afriski and Lesotho as a whole are very similar.The most common pathway of air mass trajectories transporting snow-bearing moisture to Lesotho was an inland trajectory from the northern regions of southern Africa.This pathway makes up 16.6%of all trajectories reported and is associated with the Angola Low,the Congo Air Boundary and the St.Helena High Pressure.
基金jointly supported by the Ministry of Ecology and Environment of the People’s Republic of China[grant number DQGG202121]the Dongying Ecological and Environmental Bureau[grant number 2021DFKY-0779]。
文摘Meteorological conditions are vital to PM_(2.5)and ozone(O_(3))complex pollution.Herein,the T-mode principal com-ponent analysis method was employed to objectively classify the 925-hPa geopotential height field of Dongying from 2017 to 2022.Synoptic patterns associated with four pollution types-namely,PM_(2.5)-only pollution,O_(3)-only pollution,Co-occurring of PM_(2.5)and O_(3)pollution,Non-occurring of PM_(2.5)and O_(3)pollution-were characterized at different time scales.The results indicated that synoptic classes conducive to PM_(2.5)-only pollution were“high-pressure top front”,“offshore high-pressure rear”,and“high-pressure inside”,while those conducive to O_(3)-only pollution were“offshore high-pressure rear”,“subtropical high”,and“high and low systems”.The Co-occurring of PM_(2.5)and O_(3)pollution were influenced by high pressure,and the Non-occurring of PM_(2.5)and O_(3)pollution were linked to precipitation and strong northerly winds.The variation in dominant synoptic patterns is crucial in the frequency changes of the four pollution types,which was further validated through the analysis of typical cases.Under the favorable meteorological conditions of high-pressure control with strong northerly winds or a subtropical high and inverted trough both with strong precipitation,there is potential to achieve coordinated control of PM_(2.5)and O_(3)in Dongying.Additionally,measures like artificially manipulating local humidity could be adopted to alleviate pollution levels.This study reveals the importance of comprehending the meteorological factors contributing to the formation of PM_(2.5)and O_(3)complex pollution for the improvement of urban air quality in the Bohai Rim region of China when emissions are high and the concentration of air pollutants exhibits high meteorological sensitivity.
文摘This research work involves a comparative study of satellite rainfall and synoptic observations in the Republic of Guinea over a 30-year period.The methodology used consists,firstly,in assessing rainfall trends over the study period in Guinea’s four natural regions,using the temporal averages of the three stations located in each region.Secondly,we calculated the correlations between synoptic and satellite observation data,in order to determine the links between them on the basis of data analysis.The results for synoptic stations on average seasonal rainfall cycles and satellite products show that in Lower Guinea,the CRU(Climatic Research Unit)and GPCC(Global Precipitation Climatology Center)data are good estimates of observations.In the Fouta Djallon region,they also estimate observations well,but at two synoptic stations,with the exception of Mamou,they underestimate them.In Upper Guinea,during the monsoon period,satellites give a good estimate of rainfall in this area.In the forest region,these products show highly variable behavior,sometimes underestimating and sometimes overestimating observations,depending on the stations in the zone.
基金National Natural Science Foundation of China(42075014)Science and Technology Key Project of Guangdong Meteorological Bureau(GRMC2020Z02,GRMCGS202101)+1 种基金Natural Science Foundation of Guangdong Province,China(2021A1515011539)Forecasters Project of China Meteorological Administration(CMAYBY2019-080)。
文摘An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage(June 13-15) was the frontal heavy rainfall caused by cold air(brought by an East Asian trough)from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet(SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage(June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet(BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.
基金supported by the National Natural Science Foundation of China(Grant Nos.42230612,41620104009,41705019,42075186,and 41975058)the Projects of the S&T Development Foundation of the Hubei Meteorological Bureau(Grants No.2021Q04 and 2020Y04)。
文摘Here,we analyze the characteristics and the formation mechanisms of low-level jets(LLJs)in the middle reaches of the Yangtze River during the 2010 mei-yu season using Wuhan station radiosonde data and the fifth generation of the European Centre for Medium-Range Weather Forecasts(ERA5)reanalysis dataset.Our results show that the vertical structure of LLJs is characterized by a predominance of boundary layer jets(BLJs)concentrated at heights of 900-1200 m.The BLJs occur most frequently at 2300 LST(LST=UTC+8 hours)but are strongest at 0200 LST,with composite wind velocities>14 m s^(-1).Synoptic-system-related LLJs(SLLJs)occur most frequently at 0800 LST but are strongest at 1100LST,with composite wind velocities>12 m s^(-1).Both BLJs and SLLJs are characterized by a southwesterly wind direction,although the wind direction of SLLJs is more westerly,and northeasterly SLLJs occur more frequently than northeasterly BLJs.When Wuhan is south of the mei-yu front,the westward extension of the northwest Pacific subtropical high intensifies,and the low-pressure system in the eastern Tibetan Plateau strengthens,favoring the formation of LLJs,which are closely related to precipitation.The wind speeds on rainstorm days are greater than those on LLJ days.Our analysis of four typical heavy precipitation events shows the presence of LLJs at the center of the precipitation and on its southern side before the onset of heavy precipitation.BLJs were shown to develop earlier than SLLJs.
基金funded by the National Key Research and Development Program of China(Grant no.2022YFC3701204)the 2023 Outstanding Young Backbone Teacher of Jiangsu“Qinglan”Project(Grant no.R2023Q02)the National Natural Science Foundation of China(Grant no.41705103).
文摘Accurate meteorological predictions in the Arctic are important in response to the rapid climate change and insufficient meteorological observations in the Arctic.In this study,we adopted a high-resolution Weather Research and Forecasting(WRF)model to simulate the meteorology at two Arctic stations(Barrow and Summit)in April 2019.Simulation results were also evaluated by using surface measurements and statistical parameters.In addition,weather charts during the studied time period were also used to assess the model performance.The results demonstrate that the WRF model is able to accurately capture the meteorological parameters for the two Arctic stations and the weather systems such as cyclones and anticyclones in the Arctic.Moreover,we found the model performance in predicting the surface pressure the best while the performance in predicting the wind the worst among these meteorological predictions.However,the wind predictions at these Arctic stations were found to be more accurate than those at urban stations in mid-latitude regions,due to the differences in land features and anthropogentic heat sources between these regions.In addition,a comparison of the simulation results showed that the prediction of meteorological conditions at Summit is superior to that at Barrow.Possible reasons for the deviations in temperature predictions between these two Arctic stations are uncertainties in the treatments of the sea ice and the cloud in the model.With respect to the wind,the deviations may source from the overestimation of the wind over the sea and at coastal stations.
文摘To analyze a new heavy rain case over China during the year 2022, by using the data from NCC-CMA and NCEP, a heavy rain weather process in most areas of China from July 26 to 30, 2022 was analyzed. Synoptic methods were used in this research and results show that under the influence of low vortex and wind shear, the abundant water vapor supply brought by the southeast airflow in the lower level and the lifting of the Taihang Mountain, heavy rain weather occurred in the northern part of Henan, China. In the west of Liaoning and Jilin, the rainfall process had the characteristics of frontal rainfall and the stable precipitation resulted in heavy rain weather. To sum up, the rainfall process was mainly affected by the upper-level trough, low-level wind shear and low-level jet.
文摘An extensive rainfall occurred in central and eastern China during 23-24 April, 2021. This research mainly uses the reanalysis data of NCEP/NCAR every 6 hours to analyze this heavy rainfall weather process. The results show that the main reason for this precipitation process is the shear formed between the cold air and the warm and humid air flow in the southwest. The low temperature on the ground allows the warm and humid air flow to lift up to form precipitation. The shear system is strengthened to a low vortex, which greatly strengthens the vertical ascent movement. Good water vapor and dynamic conditions form a large range of heavy rainfall.
文摘As global warming increasingly affects vulnerable regions such as Central East Africa, it is crucial to understand future changes in rainfall variability to reduce vulnerability. Despite the importance of rainfall variability, it has received less attention compared to changes in mean and extreme rainfall. This study evaluates the amplification of synoptic (weekly) to annual variability of East African Monsoon (EAM) Long Rainfall (March to May) by climatic extremes. Using band-pass filtered daily rainfall data, we found that EAM rainfall variability is anticipated to increase by 20% - 60% across the region under global warming conditions. The majority of the intermodal variability in Long Rain EAM rainfall forecasting is explained by differences in mean rainfall. Our results show that the synoptic variability of Long Rain for EAM rainfall is likely to amplify, resulting in more extreme rainfall events and longer dry spells under global warming. This amplification is attributed to the warming of the Indian Ocean and the associated changes in atmospheric circulation patterns. The projected increase in synoptic to annual variability of Long Rain for EAM rainfall has significant implications for water resources management and agriculture in the region, challenging policymakers to develop adaptive strategies that can mitigate the impacts of these extreme events. This study emphasizes the potential impacts of projected climate changes in rainfall variability on the East African region at all periods and underscores the need for effective adaptation strategies to ensure sustainable development.
文摘In order to evaluate the precipitation forecast performance of mesoscale numerical model in Northeast China,mesoscale model in Liaoning Province and T213 model,and improve the ability to use their forecast products for forecasters,the synoptic verifications of their 12 h accumulated precipitation forecasts of 3 numerical modes from May to August in 2008 were made on the basis of different systems impacting weather in Liaoning Province.The time limitations were 24,36,48 and 60 h.The verified contents included 6 aspects such as intensity and position of precipitation center,intensity,location,scope and moving velocity of precipitation main body.The results showed that the three models had good forecasting capability for precipitation in Liaoning Province,but the cupacity of each model was obviously different.
基金National Key Fundamental Project for Research Development and Plan (2004CB418301)Natural Science Foundation of China (40575018, 40675033)
文摘Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.
文摘By using regular meteorological data and Doppler radar data,causes for a hail storm over northern area of Dalian on Oct.13,2009 were analyzed from several aspects,including synoptic background,T-LnP charts and the characteristics of radar reflectivity factor evolution.The results showed that the hail storm occurred in downstream of 500 hPa trough.The 500 hPa cold trough turned zonally and triggered the formation of shear line on lower level.Before the hail event,instability energy and moisture supply were observed.The shear line on lower level intensified the atmospheric instability,promoted the release of potential energy,caused the hail event.The cooperation of upper and lower level jet streams provided favorable dynamic condition for strong convection development.The Doppler radar analysis showed that strong convection was comprised of multiple convection cells,which demonstrated 'L' and 'V' shapes during mature stage,with peak intensity of 50-60 dBz.
文摘In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert Subjective Method （ESM）, the Objective Synoptic Analysis Technique （OSAT） for partitioning TC precipitation was developed by analyzing the western North Pacific （WNP） TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM, by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation （D0） and the TC size （D1）, into variable parameters.Case verification for OSAT was also carried out by applying CMORPH （Climate Prediction Center MORPHing technique） daily precipitation measurements, which is NOAA＇s combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.
基金sponsored by the U.S. Department of Energy (DOE)supported by the Ministry of Science and Technology of China (Grant Nos. 2010CB950804 and 2013CB955801)+1 种基金the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No. XDA05100300)the National Natural Science Foundation of China (Grant No. 41305011)
文摘Knowledge of the statistical characteristics of inversions and their effects on aerosols under different large-scale synoptic circulations is important for studying and modeling the diffusion of pollutants in the boundary layer. Based on results gen- erated using the self-organizing map （SOM） weather classification method, this study compares the statistical characteristics of surface-based inversions （SBIs） and elevated inversions （EIs）, and quantitatively evaluates the effect of SBIs on aerosol condensation nuclei （CN） concentrations and the relationship between temperature gradients and aerosols for six prevailing synoptic patterns over the the Southern Great Plains （SGP） site during 2001-10. Large-scale synoptic patterns strongly influ- ence the statistical characteristics of inversions and the accumulation of aerosols in the low-level atmosphere. The activity, frequency, intensity, and vertical distribution of inversions are significantly different among these synoptic patterns. The verti- cal distribution of inversions varies diurnally and is significantly different among the different synoptic patterns. Anticyclonic patterns affect the accumulation of aerosols near the ground more strongly than cyclonic patterns. Mean aerosol CN con- centrations increase during SBIs compared to no inversion cases by 16.1%, 22.6%, 24.5%, 58.7%, 29.8% and 23.7% for the six synoptic patterns. This study confirms that there is a positive correlation between temperature gradients and aerosol CN concentrations near the ground at night under similar large-scale synoptic patterns. The relationship is different for different synoptic patterns and can be described by linear functions. These findings suggest that large-scale synoptic patterns change the static stability of the atmosphere and inversions in the lower atmosphere, thereby influencing the diffusion of aerosols near the ground.
基金provided by the Meteorology Fund of the Ministry of Science and Technology [Grant No.GYHY(QX)2007-6-26]the National Natural Science Foundation of China (Grant Nos.41275151 and 41375138)+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Graduate Student Innovation Plan at the Universities of Jiangsu Province
文摘ABSTRACT During a sea-fog field observation campaign on Donghai Island in the spring of 2011, fog-water, visibility, meteorological elements, and fog droplet spectra were measured. The main cations and anions in 191 fog-water samples were Na＋, NH2, H＋, NO3, C1- and SO] , and the average concentrations of cations and anions were 2630 and 2970 p-eq L 1, respectively. The concentrations of Na＋ and C1- originated from the ocean were high. The enhancement of anthropogenic pollution might have contributed to the high concentration of NH＋, H＋, and NO^-3. The average values ofpH and electrical conductivity （EC） were 3.34 and 505 uS cm-1, respectively, with a negative correlation between them. Cold fronts associated with cyclonic circulations promoted the decline of ion loadings. Air masses from coastal areas had the highest ion loadings, contrary to those from the sea. The ranges of wind speed, wind direction and temperature corresponding to the maximum total ion concentration （TIC） were 3.5-4 m s-1, 79°-90° and 21°C-22°C, respectively. In view of the low correlation coefficients, a new parameter Lr was proposed as a predictive parameter for TIC and the correlation coefficient increased to 0.74. Based on aerosol concentrations during the sea-fog cases in 2010, we confirmed that fog-water chemical composition also depended on the species and sizes of aerosol particles. When a dust storm passed through Donghai Island, the number concentration of large aerosol particles （with diameter 〉 1 p-m） increased. This caused the ratio of CaZ＋/Na＋ in fog-water to increase significantly.
基金supported by the Ministry of Science and Technology of China(National Basic Research Program of China(Grant No.2012CB955602))the National Key Program for Developing Basic Science(Grant No.2010CB428904)the Natural Science Foundation of China(Grant Nos.40830106,40921004,41176006)
文摘A robust anomalous anticyclonic circulation (AAC) was observed over Northeast Asia and the Japan Sea in boreal win-ter 1997/98 and over the Japan Sea in spring 1998. The formation mechanism is investigated. On the background of the vertically sheared winter monsoonal flow, anomalous rainfall in the tropical Indo-Western Pacific warm pool excited a wave train towards East Asia in the upper troposphere during boreal winter of 1997/98. The AAC over Northeast Asia and the Japan Sea is part of the wave train of equivalent barotropic structure. The AAC over the Japan Sea persisted from winter to spring and even intensified in spring 1998. The diagnostic calculations show that the vorticity and temperature fluxes by synoptic eddies are an important mechanism for the AAC over the Japan Sea in spring 1998.
文摘In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November through March), using NCEP/NCAR reanalysis datasets for the time period of 1948/49-2000/01. High-frequency signals are defined as those with timescales shorter than three weeks and measured in terms of variance, for each winter for each grid. The correlations between monthly mean AO index and high-frequency variance are conducted. A predominant feature is that several regional centers with high correlation show up in the middle to high latitudes. Significant areas include mid- to high-latitude Asia centered at Siberia, northern Europe and the middle-latitude North Atlantic east of northern Africa. Their strong correlations can also be confirmed by the singular value decomposition analysis of covariance between mean SLP and high-frequency variance. This indicates that the relationship of AO with daily Sea Level Pressure (SLP) is confined to some specific regions in association with the inherent atmospheric dynamics. In middle-latitude Asia, there is a significant (at the 95% level) trend of variance of-2.26% (10 yr)-1. Another region that displays a strong trend is the northwestern Pacific with a significant rate of change of 0.80% (10 yr)-1. If the winter of 1948/49, an apparent outlier, is excluded, a steady linear trend of +1.51% (10 yr)-1 shows up in northern Europe. The variance probability density functions (PDFs) are found to change in association with different AO phases. The changes corresponding to high and low AO phases, however, are asymmetric in these regions. Some regions such as northern Europe display much stronger changes in high AO years, whereas some other regions such as Siberia show a stronger connection to low AO conditions. These features are supported by ECMWF reanalysis data. However, the dynamical mechanisms involved in the AO-high frequency SLP variance connection have not been well understood, and this needs further study.
基金supported by Grant No. R01-2008-000-12073-0 from the Basic Research Program of Korea Science & Engineering Foundation
文摘Fogs observed over Incheon international airport （IIA） in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature （T ） and the SST, i.e., cold sea fog if TSST = T -SST 〉 0~0C and warm sea fog if TSST 〈 0~0C. The numbers of coastal, cold, and warm sea fog cases are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea fogs occur mostly in summer and warm sea fogs are observed from January to May but not in November and December. On average the air gets colder by 1.6~0C during the three hours leading up to the coastal fog formation, and an additional cooling of 1.1~0C occurs during the fog. The change in the dew point temperature （T_d） is minimal except during the fog （0.6~0C）. Decreases in T for the cold and warm sea fogs are relatively smaller. The average Td is higher than SST during the cold sea fog periods but this T_d is more than 4~0C higher than that for the corresponding non-fog days, suggesting that cold sea fogs be formed by the cooling of already humid air （i.e., T_d〉SST）. Increases of T_d are significant during the warm sea fog periods （1.4~0C）, implying that effcient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.
基金This work was jointly supported by China National Key R&D Program 2018YFA0605604,NSFC grants(Grant No.42088101,41875069),NSF AGS-2006553NOAA NA18OAR4310298.This is SOEST contribution number 11413,IPRC contribution number 1541,and ESMC number 357.
文摘Summer precipitation over the Yangtze River basin(YRB)in 2020 experienced a strong subseasonal and synoptic fluctuation in addition to contributing to an exceptionally large seasonal mean precipitation.The cause of this higher-frequency fluctuation is examined based on observational analyses.Apart from the continuous northward movement of the climatological mei-yu rainband,the mei-yu rainbelt in the summer of 2020 experienced multiple northward and southward swings.The cause of the swings was attributed to the subseasonal variability of southerly winds to the south and northeasterly winds to the north of the YRB.In addition,synoptic-scale variability,characterized by the eastward propagation of low-level cyclonic vorticity and precipitation anomalies,was also commonplace in the summer of 2020.While the strengthening of both the subseasonal and synoptic variabilities in the summer of 2020 was attributed to the increase of the background mean moisture,the synoptic variability was greatly affected by the subseasonal rainfall variability.As a result,both the synoptic-scale and subseasonal variabilities contributed to the north-south swings of the rainbelt.The large-scale modulations by both the seasonal mean and subseasonal anomalies provide insight regarding the optimization of issuing accurate,extended-range forecasts of extreme weather events.
