The Roles of Low-level Jets in “21·7” Henan Extremely Persistent Heavy Rainfall Event

An extremely heavy rainfall event lasting from 17 to 22 July 2021 occurred in Henan Province of China, with accumulated precipitation of more than 1000 mm over a 6-day period that exceeded its mean annual precipitation. The present study examines the roles of persistent low-level jets(LLJs) in maintaining the precipitation using surface station observations and reanalysis datasets. The LLJs triggered strong ascending motions and carried moisture mainly from the outflow of Typhoon In-fa(2021). The varying directions of the LLJs well corresponded to the meridional shifts of the rainfall. The precipitation rate reached a maximum during 20-21 July as the LLJs strengthened and expanded vertically into double LLJs, including synoptic-weather-system-related LLJs(SLLJs) at 850–700 hPa and boundary-layer jets(BLJs)at ~950 hPa. The coupling of the SLLJ and BLJ provided strong mid-and low-level convergence on 20 July, whereas the SLLJ produced mid-level divergence at its entrance that coupled with low-level convergence at the terminus of the BLJ on21 July. The formation mechanisms of the two types of LLJs are further examined. The SLLJs and the low-pressure vortex(or inverted trough) varied synchronously as a whole and were affected by the southwestward movement of the WPSH in the rainiest period. The persistent large total pressure gradient force at low levels also maintained the strength of low-level geostrophic winds, thus sustaining the BLJs on the synoptic scale. The results based on a Du-Rotunno 1D model show that the Blackadar and Holton mechanisms jointly governed the BLJ dynamics on the diurnal scale.

A Statistical Algorithm for Retrieving Background Value of Absorbing Aerosol Index Based on TROPOMI Measurements

The ultraviolet aerosol index(UVAI) is essential for monitoring the absorbing aerosols during aerosol events. UVAI depends on the absorbing aerosol concentration, the viewing geometry, and the temporal drift of radiometric sensitivity. To efficiently detect absorbing aerosols with the highest precision and to improve the accuracy of long-term UVAI estimates,the background UVAI must be examined through the UVAI retrieval. This study presents a statistical method that calculates the background value of UVAI using TROPOspheric Monitoring Instrument(TROPOMI) observation data over the Pacific Ocean under clear-sky scenes. Radiative transfer calculations were performed to simulate the dependence of UVAI on aerosol type and viewing geometry. We firstly applied the background UVAI to reducing the effects of viewing geometry and the degradation of the TROPOMI irradiance measurements on the UVAI. The temporal variability of the background UVAI under the same viewing geometry and aerosol concentration was identified. Radiative transfer calculations were performed to study the changes in background UVAI using Aerosol Optical Depth from the Moderate Resolution Imaging Spectroradiometer(MODIS) and reflectance measurements from TROPOMI as input. The trends of the temporal variations in the background UVAI agreed with the simulations. Alterations in the background UVAI expressed the reflectance variations driven by the changes in satellite state. Decreasing trends in solar irradiance at 340 and 380 nm due to instrument degradation were identified. Our findings are valuable because they can be applied to future retrievals of UVAI from the Environmental Trace Gases Monitoring Instrument(EMI) onboard the Chinese GaoFen-5 satellite.

Three-Year Observations of Ozone Columns over Polar Vortex Edge Area above West Antarctica

Ozone vertical column densities(VCDs)were retrieved by Zenith Scattered Light-Differential Optical Absorption Spectroscopy(ZSL-DOAS)from January 2017 to February 2020 over Fildes Peninsula,West Antarctica(62.22°S,58.96°W).Each year,ozone VCDs started to decline around July with a comparable gradient around 1.4 Dobson Units(DU)per day,then dropped to their lowest levels in September and October,when ozone holes appeared(less than 220 DU).Daily mean values of retrieved ozone VCDs were compared with Ozone Monitoring Instrument(OMI)and Global Ozone Monitoring Experiment 2(GOME-2)satellite observations and the Modern-Era Retrospective analysis for Research and Applications Version 2(MERRA-2)reanalysis dataset,with correlation coefficients(R2)of 0.86,0.94,and 0.90,respectively.To better understand the causes of ozone depletion,the retrieved ozone VCDs,temperature,and potential vorticity(PV)at certain altitudes were analyzed.The profiles of ozone and PV were positively correlated during their fluctuations,which indicates that the polar vortex has a strong influence on stratospheric ozone depletion during Antarctic spring.Located at the edge of polar vortex,the observed data will provide a basis for further analysis and prediction of the inter-annual variations of stratospheric ozone in the future.

Flash translation layer:a review and bibliometric analysis

Purpose-The purpose of this paper is to make an overview of 474 publications and 512 patents of FTL from 1987 to 2020 in order to provide a conclusive and comprehensive analysis for researchers in this field,as well as a preliminary knowledge of FTL for interested researchers.Design/methodology/approach-Firstly,the FTL algorithms are classified and its functions are introduced in detail.Secondly,the structures of the publications are analyzed in terms of the fundamental information and the publication of the most productive countries/regions,institutions and authors.After that,co-citation networks of institutions,authors and papers illustrated by VOS Viewer are given to show the relationship among those and the most influential of them is further analyzed.Then,the characteristics of the patent are analyzed based on the basic information and classification of the patent and the most productive inventors.In order to obtain research hotspots and trends in this field,the time-line review and citation burst detection of keywords carried out by Cite Space are made to be visual.Finally,based on the above analysis,it draws some other important conclusions and the development trend of this field.Findings-The research on FTL algorithm is still the top priority in the future,and how to improve the performance of SSD in the era of big data is one of the research hotspots.Research limitations/implications-This paper makes a comprehensive analysis of FTL with the method of bibliometrics,and it is valuable for researchers can quickly grasp the hotspots in this area.Originality/value-This article draws the structural characteristics of the publications in this field and summarizes the research hotspots and trends in this field in recent years,aiming to inspire new ideas for researchers.