In order to improve the practical prediction ability of refined grid precipitation,the performance of ECMWF(EC),CMA-MESO,SXWRF and SCMOC precipitation forecast products in Shaanxi Province during the rainy season of 2021 are compared and evaluated,and the correction effect of Kalman dynamic frequency matching method on different models is discussed.Then,for the shortcomings of this method,based on the optimal TS scoring threshold method and SCMOC's judgment of weather process,the small-magnitude precipitation is revised for the second time.Finally,the heavy precipitation is revised by using the precipi-tation sub process modeling and the improved Kalman dynamic frequency matching method which is based on image similarity recognition technology.The results show that SCMOC has the highest accuracy of sun-ny and rainy forecast and the highest TS score of heavy precipitation,which are 81.60％and 0.30 respec-tively.The Kalman dynamic frequency matching method can significantly improve the accuracy of sunny and rainy forecast of EC,CMA-MESO and SXWRF precipitation forecast products,but the improvement effect of heavy rainfall forecast is unstable.The improvement ranges of the EC model sunny and rainy fore-cast accuracy and the TS score of rainstorm forecast are the largest,6.35％and 6.99％respectively.This correction method is more suitable for EC model.Compared with the EC model modified by Kalman dy-namic frequency matching method,the accuracy of sunny rain and light rain prediction of EC model after the second correction of sunny rain spaced elimination is improved by 0.51％and 0.64％,respectively.The correction of the precipitation sub process modeling can further improve the TS score of EC model heavy precipitation,which is 1.05％higher than the TS score of heavy precipitation without sub process correction.Other scoring indicators of heavy precipitation are also better.The improved Kalman dynamic frequency matching method can significantly further improve the TS score of EC precipitation of all magni-tudes,especially the TS score of heavy precipitation,improved by 2.79％.
PM2.5 and O3 which interact with each other have become the most important pollutants in the cities of Fenwei Plain.The pollution often occurs simultaneously in warm seasons and is closely related to meteorological conditions.Based on the daily PM2.5 and O3 concentration data,surface meteorological ob-servation data and ERA5 high-altitude reanalysis data of 12 cities in the Fenwei Plain from 2015 to 2021,the spatio-temporal characteristics of PM2.5 and O3 in the Fenwei Plain,as well as the relationship between PM2.5 and O3 when compound pollution occurs are analyzed.Besides,the impact of local meteorological conditions and synoptic situation on compound pollution is also studied.The results show that the average annual PM2.5 and MDA8 O3(maximum daily 8 h average ozone)concentrations in the Fenwei Plain began to decline continuously in 2017 and 2018,respectively,and the number of compound pollution days also be-gan to decrease continuously after 2019.Compound pollution mainly occurs in March to September,fre-quently seen in the cities of eastern Fenwei Plain,mostly in condition of high temperature and low humidi-ty.Finally,the synoptic circulation situation of compound pollution is divided into four types by principal component analysis with the T-PCA algorithm,featured with the northwest or westerly air flow in high-al-titude and the southerly wind or breeze in the low-level warm zone.These findings could provide some ba-sis for controlling pollution in the Fenwei Plain and are of great significance for cooperative governance of PM2.5 and O3 pollution.
Based on the EAR5 reanalysis data in June from 1979 to 2016,the moist thermodynamic advec-tion parameter,thermal helicity,divergence flux,moisture divergence flux and the thermodynamic wave-activity density are selected as five comprehensive factors.The probability prediction model of regional persistent rainstorm in Hunan is constructed by the means of nuclear density estimation and based on the optimal factor and weight combination which is established with the best TS score as the test standard.The results show that the average TS of independent samples from 2017 to 2019 reaches 29.9％,which is a positive skill relative to the European Centre for Medium-Range Weather Forecasts(ECMWF)fine grid forecast(with an average TS score of 22.4％).During the two regional persistent rainstorm operational experiments in the 2021 and 2022 flood seasons,the rainstorm forecast with a 24 h leadtime by the Hunan regional perisistent rainstorm probability prediction model is superior to the forecasts of ECMWF and CMA-GFS large-scale model as well as CMA-SH and CMA-GD regional mesoscale model.Therefore,the Hunan regional persistent rainstorm prbability prediction model has a strong ability to forecast the regional persistent rainstorm in Hunan.
Based on the hourly precipitation data in the wet season during 2011-2020 from the gradient ob-servation system between Cangshan Mountain and Erhai Lake of Dali National Climate Observatory,the diurnal variation characteristics of precipitation at the mountain top,hillside and dam area are analyzed.The results show that the diurnal variation of rainfall amount at the dam station presented one peak,while that at mountain side and hilltop stations presented two peaks.The diurnal variation of rainfall frequency at dam and hilltop stations displayed a single peak,while that at the hillside station was relatively stable.All hourly rainfall amount and rainfall frequency for a whole day basically increased with the rise of alti-tudes.The diurnal variation of rainfall intensity at hilltop station exhibited double peaks,while that the hillside and dam stations showed remarkable fluctuation with small values in the afternoon and large values over night.There were no significant differences in rainfall intensity from 14:00 BT to 17:00 BT among the three stations,but the rainfall intensities at the hillside and dam stations were obviously greater than that at the hilltop station during other periods.The rainfall amount with a duration of 2-16 h over night was a large value area,which maintained a longer duration with the rise of altitude.The rainfall amount with a duration of less than 6 h during the daytime was a large value area,and the occurrence of the large value was delayed with the increase of altitude.The rainfall frequencies at all the three stations had a large value area during the day(night)when the rainfall duration was less than 6 h,while that at the hilltop sta-tion only had a large value area at night when the duration was 7-18 h.The rainfall frequencies over night were greater than that during the day at the dam and hilltop stations,while there was little difference in the rainfall frequency during the day and night at the hillside station.The accumulated rainfall amount and frequency of long(medium and short)duration increased(decreased)with the increase of altitudes.The contribution of long duration rainfall amount(long duration rainfall frequency)to accumulated rainfall amount(accumulated rainfall frequency)at each station was the largest,but the contribution of short du-ration rainfall amount(medium duration rainfall frequency)was the least.
A large-scale extremely severe convective weather named"5·17"severe convection occurred in Shandong Province on 17 May 2020,and the hail coverage was the largest in the resent 10 years.The convective storms were highly organized.The regional supercell clusters and a strong squall line over 500 km in length caused this extremely severe convection.Based on ERA5 reanalysis data,automatic weather station data and Doppler weather radar data,the ambient conditions of this extremely severe convective weather are analyzed.The results show as follows.The cold vortex was located in the key area which was most conducive to the Shandong severe convection.The large-scale weather system forcing was strong,and the unusually strong cold air in the middle troposphere moved southward impacting the previously abnormally warm Shandong Province and resulting in the"5·17"extremely severe convection weather.The anomaly of weather system is more representative of the intensity of dynamic and thermal forcing,and when anoma-ly level is above 2σ,the extremely severe convection would be caused.When the intensity of the cold vor-tex weakened during its southward moving,accompanied by increasing anomaly,it may still cause ex-tremely severe convective weather in its southeast quadrant.The strong deep vertical wind shear was con-ducive to storms organization and development.The long axis of the squall line orientated the same direc-tion as the 0-6 km vertical wind shear vector.The area where new cells were generated,developed and merged was located in the front of the large value center of the wind vector difference.The low-level warm and moist advection continuously transported warm and humid air to Shandong,which was the mechanism of CAPE reconstruction and the main energy source for the long-term maintenance of supercell group and long squall line.
