降水,尤其是强降水(暴雨),对国家经济发展、社会建设以及人民生活影响巨大,然而由于同降水相关的物理过程非常复杂,因此,对降水的研究与预测十分困难。过去有关降水的研究大多关注水汽及水汽辐合(输送)的影响,对与降水有关的水汽收支研...降水,尤其是强降水(暴雨),对国家经济发展、社会建设以及人民生活影响巨大,然而由于同降水相关的物理过程非常复杂,因此,对降水的研究与预测十分困难。过去有关降水的研究大多关注水汽及水汽辐合(输送)的影响,对与降水有关的水汽收支研究较多。Gao et al.(2005a)率先将大气中水汽和云中水凝物(云水、雨水、云冰、雪及霰等)的变化方程结合起来,得到一个地面降水诊断方程,从而可以将与降水有关的大气中水汽和云的演变过程在同一框架下定量地分析研究。本文利用一套21天长度的热带云分辨尺度模拟资料,通过计算地面降水诊断方程中的局地水汽变化、水汽辐合辐散率、地面蒸发率以及云的变化率等各项,分析了这些物理过程对降水的贡献,指出局地水汽和云的变化率、水汽辐合率,地面蒸发率等均对地面降水有重要贡献。区域平均资料分析表明,若水汽辐合与局地大气变干共存,则产生强降水;若存在水汽辐合但局地大气增湿或者存在水汽辐散但局地大气变干,则引起中等强度降水;若水汽辐散与局地大气增湿共存,则造成弱降水。将降水划分成对流和层状降水进行分析发现,对流降水率一般大于层状降水率,水汽辐合是对流降水最主要的水汽源,而局地大气变干则是层状降水最主要的水汽源。区域平均局地大气变干主要发生在降水性层状云区,而最强的局地大气增湿则发生在对流云区和晴空区;最强的局地云的消散发生在层状云区,而最强的局地云的发展发生在对流云区。展开更多
Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy t...Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy transformation, moisture transfer, midlatitude baroclinic frontal zones and ambient wind fields, Chen et al.Le et al.and Zeng et al.studied the sustaining mechanism of TCs that have made landfall. Li et al.also pointed out that the intensification of TCs during transition was associated with the disturbance and downward transportation of high-level potential vortexes, low-level frontal zones and low-pressure circulation around TCs, after explaining the difference in TCs transition following the theory of wet potential vortexes. With large-scale diagnostic study of two types of TCs that unexpectedly weaken or enhance just before landfall in southern China, Hu et al.noted that enhancing TCs were usually to the southwest or south of the subtropical high with low levels featured by well-defined southwesterly inflow inside TCs and sufficient supply of water vapor. Liang et al.not only analyzed the changes in convective cloud bands, precipitation, track and temperature and humidity structure in the course of TC Vongfang landfall, but the effect of cold air and Southwest Monsoon on its intensity in particular. As also shown in numerical experiments conducted both at home and abroad and relevant studies,saturated humidity and large-sized bodies of water are favorable for the maintenance and enhancement of landfall TCs circulation. All of the above research achievements not only help broaden the understanding of the patterns by which TCs behave but are positive in improving the forecast of the track, winds and rains after landfall. It is.however, not much addressed in the field or evounon of landfall TCs when they are with special underlying surface and circulation background. TC Rananim （0414） was the most serious typhoon that ever affected Zhejiang province after landfall in the 48 years from 1956 to 2004, which was also the storm that caused heavy rains in the most widespread area in Jiangxi province in the past 20 years. There are two points about Rananim that stand out from the other storms. The first was the sudden westward turning of its track and the second the significant enhancement of precipitation after moving above the Boyang Lake.What kind of mechanism caused such remarkable change in the storm？ With 6-hourly 1×1°NECP global reanalysis data, real-time upper-level observations and TCs location reports by the Central Observatory, the above two points and possible causes are studied in terms large-scale circulation background, underlying surface, cold air and diagnosis of physical quantity fields. New understanding has been made about the behavioral pattern of landfall TCs and related results will offer effective help in operational forecast.展开更多
Soil management matters in semiarid lands are key to have acceptable yields and to preserve diversity. After the major agricultural intensification underwent in the semiarid lands of Monegros, NE Spain, custom tailore...Soil management matters in semiarid lands are key to have acceptable yields and to preserve diversity. After the major agricultural intensification underwent in the semiarid lands of Monegros, NE Spain, custom tailored tools are needed to reconcile agriculture with habitats conservation. The objectives of this study were to quantify the effect of soil properties of two distinctly colored soils, white patches （WP） and dark patches （DP）, dominant in the arid landscape of the central Ebro Basin, Spain on winter cereal grain yield and to prove that superficial soil color could be used as a visual diagnostic criterion for evaluation of agricultural practices in arid lands. Significant differences between WP and DP soils were found in gypsum, carbonate contents, available water holding capacity and infiltration rate. The grain yield ranged from 51 to 5 713 kg ha-1. Significantly lower yields （P 〈 0.01） and precipitation-use efficiency （P 〈 0.05） were attained in the WP soils for the three seasons studied. This difference increased with the average rainfall due to the significantly lower soil water infiltration （P 〈 0.01） and water holding capacity （P 〈 0.05） found in the gypseous soils. Our results show that mapping the soil surface color at farm scale can be a low=cost tool for optimizing agricultural practices and recovering the natural vegetation. This approach can be advantageous in similar arid or semiarid environments around the world.展开更多
文摘降水,尤其是强降水(暴雨),对国家经济发展、社会建设以及人民生活影响巨大,然而由于同降水相关的物理过程非常复杂,因此,对降水的研究与预测十分困难。过去有关降水的研究大多关注水汽及水汽辐合(输送)的影响,对与降水有关的水汽收支研究较多。Gao et al.(2005a)率先将大气中水汽和云中水凝物(云水、雨水、云冰、雪及霰等)的变化方程结合起来,得到一个地面降水诊断方程,从而可以将与降水有关的大气中水汽和云的演变过程在同一框架下定量地分析研究。本文利用一套21天长度的热带云分辨尺度模拟资料,通过计算地面降水诊断方程中的局地水汽变化、水汽辐合辐散率、地面蒸发率以及云的变化率等各项,分析了这些物理过程对降水的贡献,指出局地水汽和云的变化率、水汽辐合率,地面蒸发率等均对地面降水有重要贡献。区域平均资料分析表明,若水汽辐合与局地大气变干共存,则产生强降水;若存在水汽辐合但局地大气增湿或者存在水汽辐散但局地大气变干,则引起中等强度降水;若水汽辐散与局地大气增湿共存,则造成弱降水。将降水划分成对流和层状降水进行分析发现,对流降水率一般大于层状降水率,水汽辐合是对流降水最主要的水汽源,而局地大气变干则是层状降水最主要的水汽源。区域平均局地大气变干主要发生在降水性层状云区,而最强的局地大气增湿则发生在对流云区和晴空区;最强的局地云的消散发生在层状云区,而最强的局地云的发展发生在对流云区。
文摘Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy transformation, moisture transfer, midlatitude baroclinic frontal zones and ambient wind fields, Chen et al.Le et al.and Zeng et al.studied the sustaining mechanism of TCs that have made landfall. Li et al.also pointed out that the intensification of TCs during transition was associated with the disturbance and downward transportation of high-level potential vortexes, low-level frontal zones and low-pressure circulation around TCs, after explaining the difference in TCs transition following the theory of wet potential vortexes. With large-scale diagnostic study of two types of TCs that unexpectedly weaken or enhance just before landfall in southern China, Hu et al.noted that enhancing TCs were usually to the southwest or south of the subtropical high with low levels featured by well-defined southwesterly inflow inside TCs and sufficient supply of water vapor. Liang et al.not only analyzed the changes in convective cloud bands, precipitation, track and temperature and humidity structure in the course of TC Vongfang landfall, but the effect of cold air and Southwest Monsoon on its intensity in particular. As also shown in numerical experiments conducted both at home and abroad and relevant studies,saturated humidity and large-sized bodies of water are favorable for the maintenance and enhancement of landfall TCs circulation. All of the above research achievements not only help broaden the understanding of the patterns by which TCs behave but are positive in improving the forecast of the track, winds and rains after landfall. It is.however, not much addressed in the field or evounon of landfall TCs when they are with special underlying surface and circulation background. TC Rananim （0414） was the most serious typhoon that ever affected Zhejiang province after landfall in the 48 years from 1956 to 2004, which was also the storm that caused heavy rains in the most widespread area in Jiangxi province in the past 20 years. There are two points about Rananim that stand out from the other storms. The first was the sudden westward turning of its track and the second the significant enhancement of precipitation after moving above the Boyang Lake.What kind of mechanism caused such remarkable change in the storm？ With 6-hourly 1×1°NECP global reanalysis data, real-time upper-level observations and TCs location reports by the Central Observatory, the above two points and possible causes are studied in terms large-scale circulation background, underlying surface, cold air and diagnosis of physical quantity fields. New understanding has been made about the behavioral pattern of landfall TCs and related results will offer effective help in operational forecast.
基金Supported by the Project of Spanish Government(No.AGL2009-08931)
文摘Soil management matters in semiarid lands are key to have acceptable yields and to preserve diversity. After the major agricultural intensification underwent in the semiarid lands of Monegros, NE Spain, custom tailored tools are needed to reconcile agriculture with habitats conservation. The objectives of this study were to quantify the effect of soil properties of two distinctly colored soils, white patches （WP） and dark patches （DP）, dominant in the arid landscape of the central Ebro Basin, Spain on winter cereal grain yield and to prove that superficial soil color could be used as a visual diagnostic criterion for evaluation of agricultural practices in arid lands. Significant differences between WP and DP soils were found in gypsum, carbonate contents, available water holding capacity and infiltration rate. The grain yield ranged from 51 to 5 713 kg ha-1. Significantly lower yields （P 〈 0.01） and precipitation-use efficiency （P 〈 0.05） were attained in the WP soils for the three seasons studied. This difference increased with the average rainfall due to the significantly lower soil water infiltration （P 〈 0.01） and water holding capacity （P 〈 0.05） found in the gypseous soils. Our results show that mapping the soil surface color at farm scale can be a low=cost tool for optimizing agricultural practices and recovering the natural vegetation. This approach can be advantageous in similar arid or semiarid environments around the world.
