Abstract
A sudden rainstorm that occurred in the northeast Sichuan Basin of China in early May 2017 was associated with a southwest low-level jet (SWLJ) and a mountainous low-level jet (MLLJ). This study investigates the impact of the double low-level jets (LLJs) on rainfall diurnal variation by using the data from ERA5 reanalysis, and explores the characteristics of water vapor transport, including the main paths and sources of moisture, by using the HYSPLIT-driven data of the ERA—interim, GDAS (Global Data Assimilation System), and NCEP/NCAR reanalysis data. The analysis shows that the sudden rainstorm in the mountain terrain was located at the left side of the large-scale SWLJ at 700 hPa, and at the exit region of the meso-scale MLLJ at 850 hPa. The double LLJs provide favorable moisture conditions, and the enhancement (weakening) of the LLJs is ahead of the start (end) of the rainstorm. The capacity of the LLJ at 850 hPa with respect to moisture convergence is superior to that at 700 hPa, especially when the MLLJ and the southerly LLJ at 850 hPa appear at the same time. The HYSPLIT backward trajectory model based on Lagrangian methods has favorable applicability in the event of sudden rainstorms in mountainous terrain, and there is no special path of moisture transport in this precipitation event. The main moisture sources of this process are the East China Sea–South China Sea, the Arabian Sea–Indian Peninsula, the Bay of Bengal, and the Middle East, accounting for 38%, 34%, 17% and 11% of the total moisture transport, respectively. Among them, the moisture transport in the Bay of Bengal and the South China Sea–East China Sea is mainly located in the lower troposphere, which is below 900 hPa, while the moisture transport in the Arabian Sea–Indian Peninsula and the Middle East is mainly in the middle and upper layers of the troposphere. The moisture changes of the transport trajectories are affected by the topography, especially the high mountains around the Sichuan Basin.
Highlights
Heavy rainfall is the most serious meteorological disaster in the Sichuan Basin, and it has always been a hot topic in extreme weather research
With respect to the definition of sudden rainstorms in mountainous terrain, this is given by the Wuhan Rainstorm Research Institute of the China Meteorological Administration, who suggest that a sudden rainstorm has the following characteristics: it takes place in the western mountainous region of China, the precipitation area is less than 200 km in diameter, the cumulative rainfall is more than 20 mm in one hour, and the cumulative rainfall is more than 50 mm in 3 h
We analyzed the effect of double level jets (LLJs) on moisture convergence during a sudden rainstorm in the northeast Sichuan Basin of China on 2–3 May 2017
Summary
Heavy rainfall is the most serious meteorological disaster in the Sichuan Basin, and it has always been a hot topic in extreme weather research. Taking an extreme precipitation event in the Sichuan Basin in 2013 as an example, they found that the water vapor was mainly from the Arabian Sea, followed by the Indian Peninsula and the Bay of Bengal-South China Sea. Tao et al [42] pointed out in the previous work that LLJs of different scales do not exist in isolation; most researchers only give one jet center, because they designate different standards for LLJs. With the increase in data accuracy, it is necessary to think about how the free-atmospheric LLJs at different altitudes can affect the moisture convergence of the rainstorm area.
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