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1.
The effects of sea surface temperature(SST) and its diurnal variation on diurnal variation of rainfall are examined in this study by analyzing a series of equilibrium cloud-resolving model experiments which are imposed with zero large-scale vertical velocity.The grid rainfall simulation data are categorized into eight rainfall types based on rainfall processes including water vapor convergence/divergence,local atmospheric drying/moistening,and hydrometeor loss/convergence or gain/divergence.The rainfall contributions of the rainfall types with water vapor convergence are insensitive to the increase in SST from 27°C to 29°C during the nighttime,whereas they are decreased during the daytime.The rainfall contributions of the rainfall types with water vapor convergence are decreased as the SST increases from 29°C to 31°C but the decreases are larger during the nighttime than during the daytime.The rainfall contributions of the rainfall types with water vapor convergence are decreased by the inclusion of diurnal variation of SST with diurnal difference of 1°C during the nighttime,but the decreases are significantly slowed down as the diurnal difference of SST increases from 1°C to 2°C.The rainfall contributions of the rainfall types with water vapor convergence are insensitive to the inclusion of diurnal variation of SST during the daytime.  相似文献   

2.
In this study,two convective-stratiform rainfall partitioning schemes are evaluated using precipitation and cloud statistics for different rainfall types categorized by applying surface rainfall equation on grid-scale data from a two-dimensional cloud-resolving model simulation.One scheme is based on surface rainfall intensity whereas the other is based on cloud content information.The model is largely forced by the large-scale vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment(TOGA COARE).The results reveal that over 40% of convective rainfall is associated with water vapor divergence,which primarily comes from the rainfall type with local atmospheric drying and water hydrometeor loss/convergence,caused by precipitation and evaporation of rain.More than 40% of stratiform rainfall is related to water vapor convergence,which largely comes from the rainfall type with local atmospheric moistening and hydrometeor loss/convergence attributable to water clouds through precipitation and the evaporation of rain and ice clouds through the conversion from ice hydrometeor to water hydrometeor.This implies that the separation methods based on surface rainfall and cloud content may not clearly separate convective and stratiform rainfall.  相似文献   

3.
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.  相似文献   

4.
Effects of time-dependent large-scale forcing, solar zenith angle, and sea surface temperature on time-mean rainfall during the Tropical Ocean Global Atmosphere Coupled Ocean?CAtmosphere Response Experiment (TOGA COARE) are examined through a partitioning analysis of a series of sensitivity cloud-resolving model experiment data based on surface rainfall budget. The model is forced by time-dependent large-scale forcing (LSF), solar zenith angle (SZA), and sea surface temperature (SST) in the control experiment and is forced only by either time-dependent LSF, SZA, or SST while others are replaced with their time averages in the sensitivity experiments. The rainfall associated with water vapor divergence and local atmospheric drying and hydrometeor loss/convergence has the largest contribution to total rainfall among eight rainfall types. The largest rainfall contribution is increased in the simulations where either time-dependent LSF, SZA, or SST is replaced with its average, whereas it is decreased in the simulation where COARE-derived large-scale vertical velocity is replaced with zero vertical velocity. The contribution of the rainfall associated with water vapor convergence to total rainfall is decreased in the simulations with time-mean LSF, SZA, and SST, whereas it is increased in the simulation without large-scale vertical velocity.  相似文献   

5.
Water vapor, cloud, and surface rainfall budgets associated with the landfall of Typhoon Krosa on 6--8 October 2007 are analyzed based on a two-dimensional cloud-resolving model simulation. The model is integrated with imposed zonally-uniform vertical velocity, zonal wind, horizontal temperature, and vapor advection from NCEP/Global Data Assimilation System (GDAS) data. The simulation data that are validated with observations are examined to study physical causes associated with surface rainfall processes during the landfall. The time- and domain-mean analysis shows that when Krosa approached the eastern coast of China on 6 October, the water vapor convergence over land caused a local atmospheric moistening and a net condensation that further produced surface rainfall and an increase of cloud hydrometeor concentration. Meanwhile, latent heating was balanced by advective cooling and a local atmospheric warming. One day later, the enhancement of net condensation led to an increase of surface rainfall and a local atmospheric drying, while the water vapor convergence weakened as a result of the landfall-induced deprivation of water vapor flux. At the same time, the latent heating is mainly compensated the advective cooling. Further weakening of vapor convergence on 8 October enhanced the local atmospheric drying while the net condensation and associated surface rainfall was maintained. The latent heating is balanced by advective cooling and a local atmospheric cooling.  相似文献   

6.
邢书强  李小凡 《气象科学》2021,41(4):427-440
以2010年6月19日发生在浙闽赣地区的一次强降水过程为例,利用中尺度WRF模式进行模拟,用模拟资料对该地区降水收支特征和冰云热力作用进行分析。依据局地水汽/热量变化项、水汽/热量辐合辐散项和云凝物辐合辐散项这3个因子可将降水分为8类,其中局地水汽变干和大气变暖、水汽辐合和热量辐散以及云凝物辐合时,降水强度(雨强)最强,而局地水汽变湿和大气变冷、水汽辐合和热量辐散以及云凝物辐合时,降水覆盖率最大。冰云热力效应包括辐射和潜热两部分。基准试验与敏感性试验对比分析表明冰云辐射减弱降水,而冰云潜热增强降水。热量收支对比分析发现冰云辐射造成辐射冷却的减弱在对流层中低层随高度增加,减弱大气不稳定和降水;而冰云潜热造成潜热增强在对流层中高层随高度减小,增强大气不稳定和降水。  相似文献   

7.
Two experiments were carried out using a two-dimensional cloud-resolving model to study the effects of diurnally varying sea surface temperature (SST) on diurnal variations of tropical convective and stratiform rainfall. Experiment SST29 is imposed by a constant SST of 29°C, whereas experiment SST29D is imposed by a diurnally varying SST with a time-mean of 29°C and a diurnal difference of 1°C. Both experiments are also zonally uniformly imposed by a zero vertical velocity and a constant zonal wind, and are integrated for 40 days to reach quasi-equilibrium states. The model domain mean surface rain rate is larger in SST29D than in SST29 in the late afternoon, when the ocean surface is warmer in SST29D. Convective-stratiform rainfall partitioning analysis reveals that the late-afternoon convective rainfall is larger in SST29D than in SST29, whereas the stratiform rainfalls are similar in both experiments. Further analysis of surface rainfall and cloud microphysical budgets over convective regions shows that, in the late afternoon, the larger amount of water vapor is pumped into the non-raining region through the larger surface evaporation associated with the warmer SST. This water vapor is then transported into convective regions to produce more vapor condensation and greater collection of cloud water by raindrops and larger convective rainfall in SST29D than in SST29.  相似文献   

8.
A lag correlation analysis is conducted with a 21-day TOGA COARE cloud-resolving model simulation data to identify the phase relation between surface rainfall and convective available potential energy (CAPE) and associated physical processes. The analysis shows that the maximum negative lag correlations between the model domain mean CAPE and rainfall occurs around lag hour 6. The minimum mean CAPE lags mean and convective rainfall through the vapor condensation and depositions, water vapor convergence, and heat divergence whereas it lags stratiform rainfall via the transport of hydrometeor concentration from convective regions to raining stratiform regions, vapor condensation and depositions, water vapor storage, and heat divergence over raining stratiform regions.  相似文献   

9.
In this study,the effects of key ice microphysical processes on the pre-summer heavy rainfall over southern China during 3-8 June 2008 were investigated.A series of two-dimensional sensitivity cloud-resolving model simulations were forced with zonally uniform vertical velocity,zonal wind,horizontal temperature,and water vapor advection data from the National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS).The effects of key ice microphysical processes on the responses of rainfall to large-scale forcing were analyzed by comparing two sensitivity experiments with a control experiment.In one sensitivity experiment,ice crystal radius,associated with depositional growth of snow from cloud ice,was reduced from 100 μm in the control experiment to 50 μm,and in the other sensitivity experiment the efficiency of the growth of graupel from the accretion of snow was reduced to 50% from 100% in the control experiment.The results show that the domain-mean rainfall responses to these ice microphysical processes are stronger during the decay phase than during the onset and mature phases.During the decay phase,the increased mean rain rate resulting from the decrease in ice crystal radius is associated with the enhanced mean local atmospheric drying,the increased mean local hydrometeor loss,and the suppressed mean water vapor divergence.The increased mean rain rate caused by the reduction in accretion efficiency is related to the reduced mean water vapor divergence and the enhanced mean local hydrometeor loss.  相似文献   

10.
The short-term tropical surface rainfall processes in rainfall regions (raining stratiform and convective regions) and rainfall-free regions (non-raining stratiform and clear-sky regions) are investigated based on the hourly data from a two-dimensional cloud-resolving model simulation. The model is integrated over a 21-day period with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapor advection, and sea surface temperature from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). The analysis of the model domain-mean surface rainfall budget reveals that surface rainfall is mainly associated with water vapor convergence and local atmospheric drying. The mean surface rainfall lags the mean water vapor convergence by 3?h. The convective?Cstratiform rainfall separation analysis shows that convective rainfall is associated with water vapor convergence, whereas stratiform rainfall is related to the local atmospheric drying and hydrometeor loss/convergence. The transport of water vapor from rainfall-free regions to rainfall regions creates the main water vapor source for rainfall while it balances local atmospheric drying in rainfall-free regions. Surface evaporation plays a minor role in short-term surface rainfall processes.  相似文献   

11.
The diurnal cycles of precipitation over north China during summer in four strong rainfall years are examined using two-dimensional cloud-resolving modeling data. The diurnal signals are analyzed in terms of precipitation budget, fractional rainfall coverage and rain intensity over convective and stratiform rainfall area. The analysis of precipitation budget shows that the diurnal cycles of convective and stratiform precipitation mainly correspond respectively to those of water vapor convergence and transport of hydrometeor from convective rainfall area to stratiform rainfall area in 1964, 1994 and 1995, whereas they mainly correspond to those of water vapor convergence in 2013. The diurnal cycles of convective and stratiform precipitation are mainly associated with those of rain intensity in 1964, 1994 and 1995. In 2013, the diurnal cycle of stratiform precipitation is mainly related to that of fractional rainfall coverage over stratiform rainfall area. The multiple peaks of convective precipitation mainly correspond to the rain intensity maxima associated with strong water vapor convergence.  相似文献   

12.
Both water vapor and heat processes play key roles in producing surface rainfall.While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies,the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform,constant,large-scale zonal wind and zero large-scale vertical velocity.The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate.Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions,whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions.The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions,which is,in turn,offset by the radiative cooling over rainfall-free regions.The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions.  相似文献   

13.
利用1961—2017年中国地面观测站日降水资料、全球大气多要素和海表温度月资料,分析华南区域持续性强降水过程的气候特征,诊断并比较与华南前汛期、后汛期区域持续性强降水年际变化相关的大气环流和海表温度异常特征。结果表明,3—12月华南都可能出现持续性强降水过程,其中汛期4—9月的占了94.4%。伴随着区域持续性强降水的年际变化,华南本地垂直上升运动显著异常是前汛期和后汛期的共同点,但前汛期、后汛期在华南及周边环流异常、水汽输送来源以及海温异常分布等方面都存在一定差异。在前汛期华南区域持续性强降水偏重年,赤道西太平洋区域海温偏低,由于大气罗斯贝波响应使西太平洋副热带高压偏强,热带西太平洋向华南区域水汽输送加强,从而有利于区域持续性强降水偏重。后汛期华南区域持续性强降水偏重年的海温异常分布是赤道中东太平洋区域正异常、东印度洋至西太平洋暖池区负异常,海温异常通过西北太平洋副热带高压、南海热带季风强度、水汽输送和垂直环流等多方面,导致后汛期区域持续性强降水偏重。   相似文献   

14.
基于低阶大气环流谱模式，本文设计了太平洋及印度洋４个不同海域的海表温度异常试验，去研究大气环流及降水对热带海表温度异常强迫作用的“同时”性响应。结果表明尽管暖性的海表温度异常均激发出低空辐合及高空辐散，但在不同海域所激发的异常流场却差异甚大。不过降水异常均发生在海表温度异常区及其毗邻处。它在对称的ＳＳＴＡ区的分布一般是非对称的。对水汽收支的分解分析表明，海表温度异常区异常降水的大小主要由异常的低空辐合决定，而异常降水的分布形态则由异常的水汽平流过程所决定。由于异常的低空辐合及异常的水汽平流过程主要发生在海表温度异常区及毗邻处，因此，降水对热带海表温度异常的响应基本Ｌ是一种邻域响应。它发生在气候平均低空气流沿海表温度异常的下风方向，或在海表温度异常所激发的低空异常气流沿气候平均海温降低的方向。  相似文献   

15.
The responses of vertical structures,in convective and stratiform regions,to the large-scale forcing during the landfall of tropical storm Bilis(2006) are investigated using the data from a two-dimensional cloud-resolving model simulation.An imposed large-scale forcing with upward motion in the mid and upper troposphere and downward motion in the lower troposphere on 15 July suppresses convective clouds,which leads to ～100% coverage of raining stratiform clouds over the entire model domain.The imposed forci...  相似文献   

16.
为了利用人工增雨技术合理开发六盘山地区空中水资源,首先需要了解该地区水汽场、地形对当地降水的影响和空中水资源的特征及典型降水过程中云系的降水效率。本文采用欧洲中期天气预报中心(ECMWF)发布的高时空分辨率ERA5再分析数据集和中分辨率成像光谱仪(MODIS)数据,通过统计分析研究了该地区水汽的输送、地形强迫作用下的辐合抬升状况和地形云参量特征,并分别利用WRF模式数值模拟的输出结果和ERA5再分析数据,估算2016~2017年夏季自西向东移经该山区的多次混合降水云系的水凝物降水效率。研究结果表明:位于西北地区东部的六盘山地区具有较为丰沛的大气可降水量和更强的水汽输送。受亚洲季风影响,夏季偏南风向六盘山地区输送了丰沛的水汽,山区成为相对湿度高值区;春、夏、秋季午后山区云量(CF)达70%及以上,夏季云水路径(CWP)和云光学厚度(COT)均明显大于周边地区。在夏季降水过程中,地形引起的动力场对降水有明显的影响,在日降水量5 mm以上强度的过程中,气流遇迎风坡地形产生明显辐合抬升,且辐合抬升越强时降水强度越大。夏季典型降水系统中,山区水凝物降水效率平均约为48.1%,空中还有较大部分的水凝物未能成为降水。因此作为水源涵养地的六盘山地区夏季空中水资源相对丰富而降水量不足,空中水资源具有一定开发空间。  相似文献   

17.
The surface rainfall processes associated with the torrential rainfall event over Hubei,China,during July 2007 were investigated using a two-dimensional cloud-resolving model.The model integrated the large-scale vertical velocity and zonal wind data from National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS) for 5 days.The time and model domain mean surface rain rate was used to identify the onset,mature,and decay periods of rainfall.During the onset period,the descending motion data imposed in the lower troposphere led to a large contribution of stratiform rainfall to the model domain mean surface rainfall.The local atmospheric drying and transport of rain from convective regions mainly contributes to the stratiform rainfall.During the mature periods,the ascending motion data integrated into the model was so strong that water vapor convergence was the dominant process for both convective and stratiform rainfall.Both convective and stratiform rainfalls made important contributions to the model domain mean surface rainfall.During the decay period,descending motion data input into the model prevailed,making stratiform rainfall dominant.Stratiform rainfall was mainly caused by the water vapor convergence over raining stratiform regions.  相似文献   

18.
Effects of vertical wind shear, radiation, and ice clouds on cloud microphysical budget associated with torrential rainfall during landfall of severe tropical storm Bilis (2006) are investigated by using a series of analysis of two-day grid-scale sensitivity experiment data. When upper-tropospheric upward motions and lower-tropospheric downward motions occur on 15 July 2006, the removal of vertical wind shear and ice clouds increases rainfall contributions from the rainfall type (CM) associated with positive net condensation and hydrometeor loss/convergence, whereas the exclusion of cloud radiative effects and cloud-radiation interaction reduces rainfall contribution from CM. The elimination of vertical wind shear and cloud-radiation interaction increases rainfall contribution from the rainfall type (Cm) associated with positive net condensation and hydrometeor gain/divergence, but the removal of cloud radiative effects and ice clouds decreases rainfall contribution from Cm. The enhancements in rainfall contribution from the rainfall type (cM) associated with negative net condensation and hydrometeor loss/convergence are caused by the exclusion of cloud radiative effects, cloud-radiation interaction and ice clouds, whereas the reduction in rainfall contribution from cM results from the removal of vertical wind shear. When upward motions appear throughout the troposphere on 16 July, the exclusion of all these effects increases rainfall contribution from CM, but generally decreases rainfall contributions from Cm and cM.  相似文献   

19.
利用NCEP再分析资料和WRF模式,对2013年6月26—29日江西大范围暴雨过程进行了数值模拟分析。结果表明,西太平洋副热带高压脊线稳定维持在21°N附近,副高北侧强盛西南气流将水汽向江南北部地区输送是暴雨产生和稳定维持的主要原因。超低空偏南急流的建立、发展和维持是这次连续暴雨过程产生的一个重要因素,同时低空低涡南侧出现一串近似东西向排列的30～60km更小尺度的强对流系统,它们与大暴雨区相吻合;整层水汽通量密集区的南北界位置和暴雨区南北界位置基本吻合,整层水汽的大值中心的范围和大暴雨中心的范围具有明显的正相关关系;水汽通量散度最大辐合中心为暴雨的产生输送了大量的水汽,水汽辐合中心与暴雨的落区有很好的一致性;强降水落区与假相当位温最大值区相对应。  相似文献   

20.
陈冬冬  戴永久 《大气科学》2009,33(6):1247-1258
利用中国气象局信息中心提供的西北地区1951～2005年夏季月平均资料集和1958～2002年ERA40资料, 分析近五十年来西北地区夏季降水场的主要变化特征, 及与之相关的大尺度水汽输送和环流场变化, 讨论大尺度环流指数如涛动、 极涡、 赤道太平洋Niño3.4区海温与西北地区夏季降水的相关性。结果表明, 近五十年西北西部尤其是南疆的降水增多, 与西伯利亚 (50°N～60°N, 40°E～70°E) 上空位势高度增加和伊朗高原 (35°N～42.5°N, 60°E～75°E) 上空位势高度减少有很大关系。1987年后, 西北西侧水汽辐合也是该区降水增多的一个重要因素。西北东部降水受海温影响大。此外, 北大西洋涛动、 极涡面积可以反映近几十年来西北降水西增东减的年际波动。极涡面积大小与西北降水第一模态相关性尤其突出, 可以作为考察西北降水变化的一个重要指标。  相似文献   

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