Rainfall responses to doubled atmospheric carbon dioxide concentration were investigated through the analysis of two pairs of two-dimensional cloud-resolving model sensitivity experiments. One pair of experiments simulated pre-summer heavy rainfall over southern China around the summer solstice, whereas the other pair of experiments simulated tropical rainfall around the winter solstice. The analysis of the time and model domain mean heat budget revealed that the enhanced local atmospheric warming was associated with doubled carbon dioxide through the weakened infrared radiative cooling during the summer solstice. The weakened mean pre-summer rainfall corresponded to the weakened mean infrared radiative cooling. Doubled carbon dioxide increased the mean tropical atmospheric warming via the enhanced mean latent heat in correspondence with the strengthened mean infrared radiative cooling during the winter solstice. The enhanced mean tropical rainfall was associated with the increased mean latent heat.
Surface rainfall and cloud budgets associated with three heavy rainfall events that occurred over eastern China during the mei-yu season in June 2011 were analyzed using 2D cumulus ensemble model simulation data. Model domain mean rainfall showed three peaks in response to three prescribed ascending motion maxima, primarily through the mean moisture convergence during the torrential rainfall period. Prescribed ascending motion throughout the troposphere produced strong convective rainfall during the first(9 June) and third(17–18 June) rainfall events, whereas strong prescribed ascending motion in the mid and upper troposphere and weak subsidence near the surface generated equally important stratiform and convective rainfall during the second rainfall event(14 June). The analysis of surface rainfall budgets reveals that convective rainfall was associated with atmospheric drying during the first event and moisture convergence during the third event. Both stratiform and convective rainfall responded primarily to moisture convergence during the second event. An analysis of grid data shows that the first and third mean rainfall maxima had smaller horizontal scales of the precipitation system than the second.
A mixed rain-snow storm associated with a strong burst of cold air and development of an extratropical cyclone occurred over North China from 3 to 5 November 2012.This early snowfall event was characterized by a dramatic drop in temperature,strong winds,high precipitation intensity,broad spatial extent,and coexistence of multi-phase precipitating hydrometeors.This study investigates the multi-scale interactions between the large-scale circulation background and the synoptic-scale weather systems associated with the storm.The results are as follows.(1)The Arctic Oscillation(AO)had been in its negative phase long before the event,leading to southward advection of cold air into North China in advance of the storm.(2)The large-scale atmospheric circulation experienced a decreased number of long waves upstream of North China prior to the storm,resulting in reduced wave velocity and an almost stagnant low pressure system(extratropical cyclone)over North China.(3)An-shaped blocking high over East Asia and the western Pacific obstructed the eastward movement of an upstream trough,allowing the corresponding surface cyclone to stabilize and persist over Beijing and its neighboring areas.This blocking high was a major factor in making this event a historically most severe precipitation event in autumn in Beijing for the past 60 years.(4)Baroclinic instability at lower levels gave rise to rapid development of the cyclone under the classical"second type"development mechanism for extratropical cyclones.(5)Moisture originated from the Yellow Sea entered the slowly-moving cyclone in a steady stream,creating fairly favorable water vapor supply for the heavy rainfall-snowfall,especially during the later stage of the cyclone development.(6)Moisture transport and frontal lifting triggered low-level instability and updrafts.Intensification of the front enhanced the vertical wind shear,causing conditional symmetric instability(CSI)to expand upward within the unstable lower troposphere,and to eventually gear into the CSI region of the
利用华东区域实况自动观测资料和全球预报系统的FNL再分析资料对一次爆发性气旋及其引发的大风天气进行诊断分析,结果发现,由高空急流调整导致叠加在气旋上空的中层辐散区,中高层干冷空气伴随正涡度,沿西北气流下传并在低层侵入气旋后部,气旋前部850 h Pa西南急流输送的暖湿气流和气旋西侧槽前西南急流输送的暖湿气流通过潜热释放共同促成气旋的爆发性发展;同时在气旋发展初期,高层高湿位涡区的向下传输,也加速了气旋的快速发展。气旋第三象限的大风由动量下传触发强对流并形成大风叠加所致,低层西北干冷气流切断低层的增湿,使大风区降雨很弱。低层切变线与地面带状CAPE高值区重合,该区域未来1~2 h将出现大风,对预报有明显的指示意义。
A mesoscale torrential rainfall event that occurred over eastern China in June 2013 is analyzed by using observational data.The results show that a mesoscale convergence line and a weak convective cloud line formed over the northern part of the Hangzhou Bay during the onset of the torrential rainfall event.A meso-vortex appeared over the confluence point of northeasterly flow associated with the Yellow-Sea high,easterly flow from rainfall area,and southeasterly flow from the Hangzhou Bay.The meso-vortex with a horizontal scale of 10-20 km lasted for about 1 h for stable surface circulations.The analysis of radar retrieval reveals that the meso-vortex in the boundary layer occurred at the south of strong radar echo.The formation of the meso-vortex turned to enhance convergence and cyclonic vorticity in the lower troposphere,which strengthened updrafts that are tilted into convective clouds and caused torrential rainfall.Thus,the occurrence of the meso-vortex in boundary layer is one of the mechanisms that are responsible for the enhancement of convective development.
A large number of in-situ measurements of cloud-precipitation microphysical properties have been made since 1960, including measurements of particle size distribution, particle concentration, and liquid water content of clouds and rain. These measurements have contributed to considerable progress in understanding microphysical processes in clouds and precipitation and significant improvements in parameterizations of cloud microphysics in numerical models. This work reviews key findings regarding cloud-precipitation microphysics over China. The total number concentrations of various particles vary significantly, with certain characteristic spatial scales. The size distributions of cloud droplets in stratiform clouds can generally be fit with gamma distributions, but the fit parameters cover a wide range. Raindrop size distributions(RSDs)associated with stratiform clouds can be fit with either exponential or gamma distributions, while RSDs associated with convective or mixed stratiform-cumuliform clouds are best fit with gamma distributions.Concentrations of ice nuclei(IN) over China are higher than those observed over other regions, and increase exponentially as temperature decreases. The particle size distributions of ice crystals, snow crystals, and hailstones sampled at a variety of locations can be reliably approximated by using exponential distributions,while aerosol particle size distributions are best described as the sum of a modified gamma distribution and a Junge power-law distribution. These results are helpful for evaluating and improving the fidelity of physical processes and hydrometeor fields simulated by microphysical parameterizations. The comprehensive summary and analysis of previous work presented here also provide useful guidelines for the design of future observational programs.
