边界层湍流垂直混合强度对局地热对流模拟影响的个例研究

doi:10.11755/j.issn.1006-7639(2023)-02-0290

摘要/Abstract

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。

关键词: WRF模式, 边界层方案, 垂直混合强度, 局地热对流模拟

Abstract:

Aiming at the predicting difficulty of local convective precipitation in weak environmental field, two local convective precipitation 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 results 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.

Key words: WRF model, boundary layer parameterization schemes, vertical mixing intensity, simulations of local thermal convection

中图分类号:

P435+.1

孙明燕, 张述文. 边界层湍流垂直混合强度对局地热对流模拟影响的个例研究[J]. 干旱气象, 2023, 41(2): 290-300.

SUN Mingyan, ZHANG Shuwen. Cases study of numerical simulation influences of turbulent vertical mixing intensity on local thermal convection in boundary layer[J]. Journal of Arid Meteorology, 2023, 41(2): 290-300.

图/表 10

图1 模式嵌套区域设置

Fig.1 The setting of model domain

表1 两个方案试验设置及命名

Tab.1 Experiment settings and naming of two schemes

试验名称	试验设置	试验名称	试验设置
YSU10	p=1.00	ACM10	p=1.00
YSU15	p=1.50	ACM15	p=1.50
YSU20	p=2.00（模式默认值）	ACM20	p=2.00（模式默认值）
YSU25	p=2.50	ACM25	p=2.50
YSU30	p=3.00	ACM30	p=3.00

图2 2016年7月29日南通站雷达组合反射率演变（单位：dBZ）

Fig.2 Evolution of radar composite reflectivity at Nantong station on 29 July 2016（Unit： dBZ）

图3 不同垂直混合强度下YSU方案模拟的2016年7月29日雷达组合反射率演变（单位：dBZ）

Fig.3 Evolution of simulated radar composite reflectivity under different vertical mixing intensities of YSU scheme on 29 July 2016 （Unit： dBZ）

图4 不同垂直混合强度下ACM2方案模拟的2016年7月29日雷达组合反射率演变（单位：dBZ）

Fig.4 Evolution of simulated radar composite reflectivity under different vertical mixing intensities of ACM2 scheme on 29 July 2016 （Unit： dBZ）

表2 不同垂直混合强度下两种方案模拟的雷达组合反射率FSS值

Tab.2 FSS of simulated radar composite reflectivity under different vertical mixing intensities of two schemes

试验名称	13：00	14：00	15：00	16：00	试验名称	14：30	15：00	16：00	17：00
YSU10	0.000	0.000	0.170	0.099	ACM10	0.000	0.032	0.284	0.103
YSU15	0.000	0.072	0.176	0.006	ACM15	0.000	0.135	0.196	0.118
YSU20	0.000	0.371	0.205	0.044	ACM20	0.073	0.273	0.236	0.163
YSU25	0.003	0.480	0.275	0.054	ACM25	0.211	0.337	0.221	0.013
YSU30	0.144	0.336	0.175	0.056	ACM30	0.303	0.403	0.307	0.007

图5 不同垂直混合强度下YSU（a）和ACM2（b）方案模拟的2016年7月29日区域平均边界层高度随时间变化

Fig.5 The time series of simulated regional mean boundary layer height under different vertical mixing intensities of YSU （a） and ACM2 （b） schemes

图6 不同垂直混合强度下两种方案模拟的2016年7月29日不同时刻区域平均纬向风（u）、经向风（v）、位温（θ）及水汽混合比（q）垂直廓线（横坐标正负表示风向，向东和向北为正，向西和向南为负）

Fig.6 The vertical profile of simulated regional mean zonal wind （u）， meridional wind （v）， potential temperature （θ） and water vapor mixing ratio （q） at different time on 29 July 2016 under different vertical mixing intensities of two schemes （The positive and negative on the horizontal axis indicate the wind direction， which are positive to the east and the north， and negative to the west and the south）

图7 不同垂直混合强度下YSU（a、b）和ACM2（c、d）方案模拟的2016年7月29日区域平均CAPE（a、c）和CIN（b、d）随时间变化

Fig.7 The times series of simulated regional mean CAPE （a， c） and CIN （b， d） on 29 July 2016 under different vertical mixing intensities of YSU （a， b） and ACM2 （c， d） schemes

图8 观测和不同垂直混合强度下两种方案模拟的2013年8月16日南京地区雷达组合反射率演变（单位：dBZ）

Fig.8 Evolution of observed and simulated radar composite reflectivity at Nanjing on 16 August 2013 under different vertical mixing intensities of two schemes （Unit： dBZ）

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