Westerlies Affecting the Seasonal Variation of Water Vapor Transport over the Tibetan Plateau Induced by Tropical Cyclones in the Bay of Bengal

IF 6.5 2区地球科学 Q1 METEOROLOGY & ATMOSPHERIC SCIENCES Advances in Atmospheric Sciences Pub Date : 2024-03-21 DOI:10.1007/s00376-023-3093-7

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Abstract

This study investigates the activity of tropical cyclones (TCs) in the Bay of Bengal (BOB) from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly (MMBA) over the southern boundary of the Tibetan Plateau (SBTP). May and October–December are the bimodal phases of BOB TC frequency, which decreases month by month from October to December and is relatively low in May. However, the contribution rate to the MMBA is the highest in May. The seasonal variation in the meridional position of the westerlies is the key factor affecting the contribution rate. The relatively southern (northern) position of the westerlies in November and December (May) results in a lower (higher) contribution rate to the MMBA. This mechanism is confirmed by the momentum equation. When water vapor enters the westerlies near the trough line, the resultant meridional acceleration is directed north. It follows that the farther north the trough is, and the farther north the water vapor can be transported. When water vapor enters the westerlies from the area near the ridge line, for Type-T (Type-R) TCs, water vapor enters the westerlies downstream of the trough (ridge). Consequently, the direction of the resultant meridional acceleration is directed south and the resultant zonal acceleration is directed east (west), which is not conducive to the northward transport of water vapor. This is especially the case if the trough or ridge is relatively south, as the water vapor may not cross the SBTP.

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西风影响孟加拉湾热带气旋诱导的青藏高原水汽输送的季节变化

摘要本研究调查了1979-2018年孟加拉湾（BOB）热带气旋（TC）的活动情况，以发现影响青藏高原南缘经向水分预算异常（MMBA）贡献率的机制。5月和10-12月是BOB TC频率的双峰阶段，10-12月TC频率逐月降低，5月相对较低。然而，5 月份对 MMBA 的贡献率最高。西风经向位置的季节变化是影响贡献率的关键因素。11 月和 12 月（5 月）西风位置相对偏南（偏北），导致对 MMBA 的贡献率较低（较高）。动量方程证实了这一机制。当水汽进入波谷线附近的西风带时，所产生的经向加速度会指向北方。由此可见，波谷越靠北，水汽越能向北输送。当水汽从山脊线附近进入西风带时，对于 T 型（R 型）热气旋，水汽会从槽（山脊）下游进入西风带。因此，所产生的经向加速度方向是向南的，所产生的带状加速度方向是向东（西）的，这不利于水汽向北输送。尤其是当槽或脊相对偏南时，水汽可能无法穿过 SBTP。

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来源期刊

Advances in Atmospheric Sciences 地学-气象与大气科学

CiteScore

9.30

自引率

5.20%

发文量

154

审稿时长

6 months

期刊介绍： Advances in Atmospheric Sciences, launched in 1984, aims to rapidly publish original scientific papers on the dynamics, physics and chemistry of the atmosphere and ocean. It covers the latest achievements and developments in the atmospheric sciences, including marine meteorology and meteorology-associated geophysics, as well as the theoretical and practical aspects of these disciplines. Papers on weather systems, numerical weather prediction, climate dynamics and variability, satellite meteorology, remote sensing, air chemistry and the boundary layer, clouds and weather modification, can be found in the journal. Papers describing the application of new mathematics or new instruments are also collected here.