Abstract
Aiming to investigate the weather characteristics and mesoscale system in the heavy rainstorm process on Jul 26, 2017 of Yellow River, the conventional observations and mesoscale numerical model (WRF) and its assimilation system 3DVAR was utilized to simulate the major precipitation period. The difference between the results of model with assimilation observation date of meteorological observation stations and without assimilation were also discussed. the results indicates that upper at 500hPa and shear line at 850hPa form the forward-titling trough which provides favorable instability conditions for generation of rainstorm. stability of subtropical high is beneficial to the water flux transporting to main precipitation zone. the wind shear at 850hPa and surface cyclone are the mesoscale systems. By comparing the simulations with and without assimilation, the result showed that the simulation with assimilation improved obviously the location of heavy rain and spatial distribution of different levels of precipitation. Of which the region with precipitation below 10mm simulated by experiment with assimilation was greatly improved. At the factors of atmospheric circulation field, the intensities of water vapor transportation and surface cyclone have strengthened after assimilation, thus can support more favorable conditions for development of convection's system. its implied that simulations after assimilation improve the spatial structure of initial field, and have an essential effect on simulating mesoscale convective system's structure.
Highlights
IntroductionRainstorm over China and its damage were the one of the major natural calamity in China. emphases and difficulties always consist in lie in the heavy rain forecasts and researches for the complexity of rainstorm physics mechanism. there were many intentional researches concerning the heavy rain forecast skill after years of research. but the forecast skills about heavy rainfall area and the predictability time were barely satisfactory. at the same time, observation ability and temporal-spatial resolution of data restricted the weather system identification to a certain degree(Zheng et al 2009). all the more so when referring to local heavy rain with small spatial scale, short life and complicated. heavy rainfall was the result of interaction among multi-scale weather systems. the large scale circulation provideed advantage condition for moisture transport, and the meso-micro scale weather system made a direct contribution to the heavy rainfall(Jiang et al 2009). there were some important conditions resulting heavy rainfall, of which triggering mechanism with regional difference played the key role(Tao et al 1979; Zhang et al, 2012; Shi et al 2011). many studies about heavy rainfall in Northern China showed that vertical shear, invasion of cold air in mid troposphere, cold front and topography forcing and so on were the most influential factors(Guo et al, 2006; Li et al 2011)
The hindcast experiments using WRFV3.5 was to the analysis the strong heavy rainfall period of NO 1 flood of Yellow River. the experiments included two tests, the one test was with data assimilation, another without assimilation. the evolving and structure of mesoscale weather system was analyzed and discussed
Wu ding valley located in front of low-pressure and back of high-pressure. after six hours, the pressure gradient field improved significantly. strong cyclonic shear developed in Wu ding valley(Figure not shown)
Summary
Rainstorm over China and its damage were the one of the major natural calamity in China. emphases and difficulties always consist in lie in the heavy rain forecasts and researches for the complexity of rainstorm physics mechanism. there were many intentional researches concerning the heavy rain forecast skill after years of research. but the forecast skills about heavy rainfall area and the predictability time were barely satisfactory. at the same time, observation ability and temporal-spatial resolution of data restricted the weather system identification to a certain degree(Zheng et al 2009). all the more so when referring to local heavy rain with small spatial scale, short life and complicated. heavy rainfall was the result of interaction among multi-scale weather systems. the large scale circulation provideed advantage condition for moisture transport, and the meso-micro scale weather system made a direct contribution to the heavy rainfall(Jiang et al 2009). there were some important conditions resulting heavy rainfall, of which triggering mechanism with regional difference played the key role(Tao et al 1979; Zhang et al, 2012; Shi et al 2011). many studies about heavy rainfall in Northern China showed that vertical shear, invasion of cold air in mid troposphere, cold front and topography forcing and so on were the most influential factors(Guo et al, 2006; Li et al 2011). But the forecast skills about heavy rainfall area and the predictability time were barely satisfactory. At the same time, observation ability and temporal-spatial resolution of data restricted the weather system identification to a certain degree(Zheng et al 2009). Heavy rainfall was the result of interaction among multi-scale weather systems. The maximum flood peak of many hydrologic stations in Wu ding river reached a new high. The maximum flood peak occurred reached to 6010 m2/s in Long men station of Yellow River at 01(Beijing) 27jul 2017. High-resolution numerical models was the powerful tool to study mid-scale heavy rain. Because of the time and space uneven distribution of observation records, numerical weather prediction errors came from the initial condition. The hindcast experiments using WRFV3.5 was to the analysis the strong heavy rainfall period of NO 1 flood of Yellow River. The hindcast experiments using WRFV3.5 was to the analysis the strong heavy rainfall period of NO 1 flood of Yellow River. the experiments included two tests, the one test was with data assimilation, another without assimilation. the evolving and structure of mesoscale weather system was analyzed and discussed
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