摘要
针对弱环境场下局地对流性降水难于准确预报问题,本文以长江下游地区两次局地对流性降水过程为例,通过调整WRF模式中两类边界层参数化方案(YSU和ACM2)的湍流垂直混合强度,探究改善降水预报准确度的一种可行途径。结果表明:在模式默认的垂直混合强度下,YSU方案模拟的对流发展较缓,对流触发时间略晚;ACM2方案则由于垂直混合过强,模拟的对流弱于YSU方案,对流触发时间晚于观测1~2 h。无论是YSU还是ACM2方案,减弱边界层内垂直混合强度能够更准确模拟对流触发及其发展演变。不同垂直混合主要通过影响边界层内位温、水汽混合比、风的垂直分布和能量输送来影响对流过程模拟:减弱垂直混合后,对流前期边界层内更湿冷,风速和垂直风切变增大,同时对流有效位能(Convective Available Potential Energy,CAPE)增加,这些因素利于更早触发对流,模拟的对流强度也更强。
Aiming at the predicting difficulty of local convective precipitation in weak environmental field,two local convective precipi⁃tation cases in the lower Yangtze River region were took as examples,and YSU and ACM2 parameterization schemes in WRF model were selected to explore feasible way to improve this problem by adjusting the vertical mixing intensity in the boundary layer.The re⁃sults show that the development of convection simulated by YSU scheme is relatively slow and the triggering of convection is slightly later under the default vertical mixing intensity,while the convection simulated by ACM2 scheme is weaker than that of YSU scheme,and the triggering of convection is about 1-2 hours later than the observation due to too strong vertical mixing.Reducing vertical mixing intensity could get more accurate convective triggering time and its evolution in YSU and ACM2 schemes.The vertical distribution of potential temperature,water vapor ratio and wind,the transport of energy are affected mainly by different vertical mixing intensity,so that get varies of simulation results.There is colder and wetter in the boundary layer,stronger wind speed and wind shear from surface to the top of the boundary layer in the early stage of the convection,and larger CAPE(Convective Available Potential Energy),all of them are conductive to trigger convection earlier,at the meanwhile,the intensity stronger.
作者
孙明燕
张述文
SUN Mingyan;ZHANG Shuwen(College of Atmospheric Sciences,Lanzhou University,Lanzhou 730000,China)
出处
《干旱气象》
2023年第2期290-300,共11页
Journal of Arid Meteorology
基金
国家自然科学基金项目(42275088)
国家重点研发计划(2017YFC1502101)共同资助。
关键词
WRF模式
边界层方案
垂直混合强度
局地热对流模拟
WRF model
boundary layer parameterization schemes
vertical mixing intensity
simulations of local thermal convection