The Tropical Diurnal Cycle Under Varying States of the Monsoonal Background Wind
The Tropical Diurnal Cycle Under Varying States of the Monsoonal Background Wind
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DOI：
10.1175/jas-d-22-0045.1
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发表时间：
2022-10
影响因子：
3.1
通讯作者：
M. Natoli;E. Maloney
中科院分区：
文献类型：
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作者：
M. Natoli;E. Maloney
本文用观测资料和理想模式研究了环境背景风对热带岛屿附近日变化的影响。菲律宾北方的吕宋岛被用作观测测试案例。根据ERA 5纬向风廓线的第一经验正交函数（ERA 1）构造了CMORPH降水的合成日变化。一个强降水的日周期和明显的离岸传播在背风方向往往发生在一个弱，离岸盛行风的日子。强烈的背景风，特别是在向岸方向，与一个压抑的昼夜循环。理想化的高分辨率2-D云模型1（CM 1）模拟测试环境风速和风向的昼夜循环的依赖性轻推模型的基本状态对复合配置文件来自再分析纬向风指数。这些模拟可以定性地复制所观察到的发展，强度和海上传播的日生成的对流在不同的风况。在强背景风作用下，海陆对比度减弱，导致海风环流强度和降水日变化显著减弱。较弱的近海盛行风有利于较强的日周期和近海背风传播，传播方向对低层自由对流层的背景风高度敏感。海上传播速度似乎与密度流理论相一致，而不是直接耦合到一个单一的重力波模式，虽然重力波可能有助于海上环境的不稳定。
The impact of the environmental background wind on the diurnal cycle near tropical islands is examined in observations and an idealized model. Luzon Island in the northern Philippines is used as an observational test case. Composite diurnal cycles of CMORPH precipitation are constructed based on an index derived from the first empirical orthogonal function (EOF) of ERA5 zonal wind profiles. A strong precipitation diurnal cycle and pronounced offshore propagation in the leeward direction tends to occur on days with a weak, offshore prevailing wind. Strong background winds, particularly in the onshore direction, are associated with a suppressed diurnal cycle. Idealized high resolution 2-D Cloud Model 1 (CM1) simulations test the dependence of the diurnal cycle on environmental wind speed and direction by nudging the model base-state toward composite profiles derived from the reanalysis zonal wind index. These simulations can qualitatively replicate the observed development, strength, and offshore propagation of diurnally generated convection under varying wind regimes. Under strong background winds, the land-sea contrast is reduced, which leads to a substantial reduction in the strength of the sea-breeze circulation and precipitation diurnal cycle. Weak offshore prevailing winds favor a strong diurnal cycle and offshore leeward propagation, with the direction of propagation highly sensitive to the background wind in the lower free troposphere. Offshore propagation speed appears consistent with density current theory rather than a direct coupling to a single gravity wave mode, though gravity waves may contribute to a destabilization of the offshore environment.