不同风场结构下贺兰山地形降水的理想数值试验

doi:10.13866/j.azr.2024.08.02

摘要/Abstract

摘要：

地形降水是我国西北地区最主要的降水类型之一，加深其形成机理的认识对提高预报能力有重要意义。本文以贺兰山东麓地区20次暴雨过程中的高空环境参数为基础构建不同类型风场垂直分布结构，利用WRF模式中的em_hill2d_x模块开展不同类型风场对降水模态影响的理想数值试验。结果表明：（1）有/无风垂直切变的两种不同类型干气流过山后其迎风坡均表现为地形对迎风坡气流的抬升作用，而背风坡波动表现出明显不同的变化特征，单层均一气流条件下背风坡主要表现为沿垂直方向传播的过山波，低空存在风切变的风场条件下背风侧主要体现背风波的特征，重力波呈水平与垂直传播共存的特征，且随着低空风切变增强水平传播的背风波特征越来越明显。（2）单层均一湿气流条件下模拟的降水主要位于迎风侧，背风侧在较强的下坡风影响下，降水强度相对较弱。当风速增大至10 m·s^-1以上时，迎风侧云水含量大值区向山顶汇集，降水强度显著增强。低空存在风切变湿气流过山试验结果显示在迎风侧与背风侧均存在较强的降水中心，背风坡存在一深对流系统，随着风速增大，两侧降水均增强。（3）在低空东风高空西风的条件下，背风侧降水显著减弱，降水更加集中于上游山顶附近，强度也有一定的增强，这与高空西风的出现使迎风坡上升气流加强，且不利于水汽向下游的输送有关，这是贺兰山脉两侧降水特征存在显著差异的主要原因之一。

关键词: 地形降水, 理想试验, 重力波, 对流系统, 贺兰山

Abstract:

Topographic precipitation is one of the main types of precipitation in northwest China. It is therefore of great significance to achieve a deeper understanding of the mechanism of topographic precipitation formation to improve forecasting ability. In this study, the vertical distribution structure of different types of wind fields was constructed based on the high-altitude environmental parameters during 20 heavy rains around the eastern foothills of Helan Mountain, and the em_hill2d_x module of WRF model was used to conduct ideal numerical experiments on the influence of different types of wind field on precipitation distribution. The results show that: (1) The dry air flow of two different types of wind fields (with/without wind shear) on the windward slope of the mountain range has an uplift effect of terrain on the windward slope air flow. The leeward slope fluctuation showed different characteristics; under the condition of single layer uniform flow, the leeward slope is mainly represented by a mountain wave propagating in the vertical direction. Under the wind field with low-level wind shear, the leeward side mainly reflects the characteristics of the dorsal wave, and the gravity wave has the characteristics of coexisting horizontal and vertical propagation. With the increase in low-level wind shear, the characteristics of the horizontal propagation of the dorsal wave become increasingly obvious. (2) The simulated precipitation under the condition of a single layer of uniform wet airflow is mainly located on the windward side, and the precipitation intensity is relatively weak on the leeward side under the influence of strong downhill wind. When the wind speed increases to more than 10 m·s^-1, the large cloud water content area on the windward side converges to the top of the mountain, and the precipitation intensity increases significantly. In the presence of low-level wind shear flow moving over the mountains, the test result shows that both the windward and leeward side there is a strong rainfall center, with a deep convective system on the leeward slope, and the precipitation on both sides increases with the increase in wind speed. (3) The simulation results under the condition of low-altitude east wind and high-altitude west wind show that the appearance of high-altitude west wind strengthens the updraft on the windward slope and is not conducive to the transport of water vapor downstream; the precipitation on the leeward side is significantly weakened; the precipitation is more concentrated near the upper reaches of the mountain peak; and the intensity also increases to a certain extent. This is one of the main reasons for the significant difference in precipitation characteristics between the two sides of the Helan Mountain.

Key words: topographic precipitation, ideal test, gravity wave, convection system, Helan Mountain

李超, 隆霄, 曹怡清, 韩子霏, 王号, 郑景元. 不同风场结构下贺兰山地形降水的理想数值试验[J]. 干旱区研究, 2024, 41(8): 1272-1287.

LI Chao, LONG Xiao, CAO Yiqing, HAN Zifei, WANG Hao, ZHENG Jingyuan. Ideal numerical tests of topographic precipitation around the Helan Mountain under different wind field structures[J]. Arid Zone Research, 2024, 41(8): 1272-1287.

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暴雨时段（北京时）	持续时间/h	最大雨量/mm
2009年7月7日8:00—8日7:00	24	汝箕沟107.6
2012年7月29日20:00—30日11:00	16	滚钟口174.3
2015年9月3日4:00—4日1:00	21	小口子65.9
2015年9月8日1:00—8日20:00	20	八顷村69.6
2016年7月24日5:00—12:00	8	灵武煤矿89.5
2016年8月13日15:00—14日14:00	24	王老滩110.2
2016年8月21日19:00—22日8:00	14	滑雪场241.7
2016年8月22日22:00—23日6:00	9	路家营子村57
2017年6月4日15:00—5日10:00	20	黄旗口沟116.5
2017年7月25日20:00—26日2:00	6	窑子圈64.4
2017年7月5日3:00—18:00	16	滑雪场114.4
2018年7月19日3:00—10:00	8	明长城136.2
2018年7月1日9:00—2日1:00	17	牛首山84.3
2018年7月22日19:00—23日7:00	13	滑雪场277.6
2018年7月23日12:00—20:00	9	红翔新村89.3
2018年8月31日19:00—9月1日17:00	23	苦水沟136.9
2018年8月6日12:00—7日16:00	29	马莲口119.1
2018年8月9日12:00—10日13:00	26	临河镇71.4
2019年8月2日18:00—3日0:00	7	暖泉农场71
2020年8月11日7:00—12日8:00	26	五渠村142.5

	试验名称	N/s^-1	比湿/（g·g^-1）	风场结构	东风/（m·s^-1）	西风/（m·s^-1）	试验目的
干过程（WRF-dry）	D1	N = 0.007	0	（Ⅰ）	u₀：-4、-6、-8、-10、-13、-15	-	重力波特征
干过程（WRF-dry）	D2	N = 0.007	0	（Ⅱ）	u_shear：-8、-10、-12、-15	-	重力波特征
湿过程（WRF-moist）	M1	以20次降水过程的平均位温阔线作为初始场	以20次降水过程的平均比湿阔线作为初始场	（Ⅰ）	u₀：-4、-5、-6、-7、-8、-9、-10、-11、 -12、-13、-14	-	重力波特征、降水分布特征
	M2			（Ⅱ）	u_shear：-8、-9、-10、-11、-12、-13、-14、 -15、-16、-17、-18、-19、-20、-22	-
	M3			（Ⅲ）	u₁：-14	u₂：5、10、20、 30、40