Atmospheric Thermal and Dynamic Vertical Structures of Summer Hourly Precipitation in Jiulong of the Tibetan Plateau

Yonglan Tang,Guirong Xu,Rong Wan,Ping Li,Junchao Wang,Xiaofang Wang

doi:10.3390/atmos12040505

Abstract

It is an important to study atmospheric thermal and dynamic vertical structures over the Tibetan Plateau (TP) and their impact on precipitation by using long-term observation at representative stations. This study exhibits the observational facts of summer precipitation variation on subdiurnal scale and its atmospheric thermal and dynamic vertical structures over the TP with hourly precipitation and intensive soundings in Jiulong during 2013–2020. It is found that precipitation amount and frequency are low in the daytime and high in the nighttime, and hourly precipitation greater than 1 mm mostly occurs at nighttime. Weak precipitation during the daytime may be caused by air advection, and strong precipitation at nighttime may be closely related with air convection. Both humidity and wind speed profiles show obvious fluctuation when precipitation occurs, and the greater the precipitation intensity, the larger the fluctuation. Moreover, the fluctuation of wind speed is small in the morning, large at noon and largest at night, presenting a similar diurnal cycle to that of convective activity over the TP, which is conductive to nighttime precipitation. Additionally, the inverse layer is accompanied by the inverse humidity layer, and wind speed presents multi-peaks distribution in its vertical structure. Both of these are closely related with the underlying surface and topography of Jiulong. More studies on physical mechanism and numerical simulation are necessary for better understanding the atmospheric phenomenon over the TP.

Highlights

The Tibetan Plateau (TP), known as the “roof of the world” and “the third pole,” is the highest plateau in the world with an average altitude higher than 4000 m
Precipitation amount, frequency and intensity present obvious diurnal variations, especially in the two grades of [1, 5) mm and [5, 10) mm. Both precipitation amount and frequency present a similar unimodal pattern in diurnal variation, in which the value is low during the day and high at night with a maximum of 22 Local Standard Time (LST). It is generally low during the day and high at night, a bimodal pattern was found for hourly precipitation greater than 1 mm, with the main peak at 22 LST and the second peak at 09 LST
During the observational experiment period in Jiulong, hourly precipitation of less than 1 mm can occur during the day, while hourly precipitation greater than 1 mm mostly occurs at night and is the main contributor to the nighttime precipitation amount

Summary

Introduction

The Tibetan Plateau (TP), known as the “roof of the world” and “the third pole,” is the highest plateau in the world with an average altitude higher than 4000 m. Based on the hourly geostationary meteorological satellite (GMS) infrared brightness temperature observation and the sounding data of five stations along the YR, Zhuo et al [9] studied a heavy precipitation process caused by the eastward moving convective cloud cluster over the TP in 1998, and pointed out that the main causes of the heavy precipitation were the occurrence, development and eastward movement of the wet core cyclone over the TP This is promoted by the divergence of upper air flow and the convergence of lower air flow, as well as the guidance of high and low level jet and the instability of atmospheric stratification in the troposphere. As the vortex system continues to move eastward out of the plateau, the large-scale dynamic background of potential vortex advection increases with height in the middle and lower reaches of the YR, which leads to the development of ascending motion and heavy rainfall

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Conclusion