Abstract:We quantify the changes of anthropogenic carbon emissions and major air pollutants during the COVID-19 epidemic in China by analyzing data from economic sectors,1 580 surface monitoring sites,and 6 satellite retrievals.Compared to the first quarter of 2019,national carbon emissions decreased by 9.8% in 2020 with the maximum reduction of 43.4% in transportation sector.Compared to the average of February-March in 2019,surface ozone concentrations increased by 1.9 nL/L(5%) during the epidemic on the country level,with major reductions in North China Plain but enhancements in the Southeast.Surface PM_2.5 concentrations decreased by 12.6 μg·m^-3(24.9%) with the maximum reduction in Yangtze River Delta(YRD).For NO₂, both the surface concentrations and tropospheric column density showed consistent reductions of 20%-30% in Beijing-Tianjin-Hebei,Pearl River Delta,and YRD.Surface CO concentrations declined by 17% while tropospheric column CO increased by 2.5%,likely because the transportation of air pollutants from biomass burning outside China enhances CO density at high levels in southern China.Aerosol optical depth significantly decreased in the middle and eastern China,leading to an increased surface shortwave radiation by 11.6 W·m^-2(9.6%).

Abstract:Understanding the bias in reanalysis water vapor data is very conducive to studying the stratosphere and troposphere water vapor transport,particularly over the Tibetan Plateau (TP),which is an important water vapor source in the extratropical region where it is located.In this paper,the Aura MLS satellite observations taken over the TP are used to evaluate the upper troposphere and lower stratosphere (UTLS) water vapor data from the ERA-I,MERRA,JRA-55,CFSR and NCEP2 reanalysis data taken during the period of August 2004 to December 2013.The results reveal that the water vapor data from ERA-I and MERRA are superior to the other reanalysis data.In addition,the water vapor spatial and temporal distributions in ERA-I and MERRA are further compared by MLS satellite observations.The contrast results show that all of the reanalysis data used are wetter in terms of UTLS compared to the MLS satellite observations.Specifically,the ERA-I,MERRA,JRA-55 and CFSR reanalysis data overestimated the upper tropospheric (215 hPa) water vapor content by up to 165% compared to the MLS observations,while the water vapor data from ERA-I and MERRA bore small differences with the MLS observations.Overall,the water vapor data from ERA-I and MERRA were closer to the MLS observations compared to the other reanalysis data.Further contrast results show that the water vapor horizontal and vertical structures in ERA-I and MERRA are consistent with the MLS observations over the TP in winter and summer.In the MLS observations,the water vapor maximum in the latitude and longitude occurred over the TP in summer,and that there is a strong meridional gradient of water vapor near tropopause and westerly jet in winter.These observations were also made in ERA-I and MERRA,yet the spatial distribution is better in MERRA.The water vapor content over the TP exhibited significant seasonal changes,being lowest in January and February,and highest in July and August,while the seasonal variability was greatest at 200~300 hPa.The seasonal changes in ERA-I and MERRA resembled the MLS observations,but the seasonal variability was slightly larger (smaller) in ERA-I and MERRA in the upper troposphere (lower stratosphere).According to the daily water vapor time series,there upward and poleward water transport were present near the tropopause in the MLS observations over the TP.The upward and poleward transport were also observed in the ERA-I and MERRA daily water vapor data time series;however,compared to the MLS results,the upward higher water vapor transport was superior in ERA-I,while the poleward transport of the higher water vapor was more obvious in MERRA in the lower stratosphere (100 hPa).In summary,although the water vapor contents in ERA-I and MERRA exhibited significant differences with the MLS observation in the upper troposphere,the spatial and temporal distributions are more similar to the MLS observations,and for this reason the ERA-I and MERRA water vapor data can be used to study the water vapor transport over the TP in UTLS.

Abstract:Based on high-resolution satellite observations and NCEP-CFSR reanalysis results,this study investigates the sub-seasonal variation of the winter gap wind over the eastern Pacific and its associated air-sea interaction.It is observed that gap wind displays a significant sub-seasonal cycle during the period of 4-16 days.In the sub-seasonal cycle,the relationship between the gap wind anomaly and its underlying sea surface temperature(SST) anomaly undergoes a significant transition when the gap wind reaches its peak phase.Before the peak phase,their relationship is negative,indicating an atmospheric-to-oceanic forcing.During this period,the increasing northerly winds blow toward the Gulfs with a dry and cold air flow,enhancing the surface net heat fluxes loss,in turn leading to the SST decreased.After the peak phase ends,the relationship between gap wind anomaly and its underlying SST anomaly turns positive,corresponding to an oceanic-to-atmospheric forcing,and particularly worth noting is that the negative SST anomalies can last for 6 days.The associated cold SST anomaly in turn suppresses the turbulent mixing,causing the sea surface wind speed to decrease.In addition,the atmospheric circulation anomalies over the eastern Pacific toward North America may exert an influence on the sub-seasonal variation of the gap wind.Positive sea level pressure anomalies over the North Pacific move southeastward as the gap wind increases,and reach Mexico Bay when the gap wind reaching its peak.The sea level pressure anomalies over Mexico Bay enhance the North American High,so as to enlarge the pressure differences between the east and west side of the Gulfs,thereby contributing to the gap wind peak.

Abstract:Based on various oceanographic and atmospheric reanalysis data from 1979 to 2015,this paper analyzed anomalous distribution characteristics of summer rainfall in the middle and lower reaches of the Yangtze River during different phase years of PJ (Pacific-Japan) teleconnection pattern and discussed possible causes of asymmetric precipitation changes.Result shows that the asymmetry of anomalous precipitation distribution includes asymmetric position and intensity.In the negative PJ phase year (corresponding to the next year of El Niño),precipitation in the middle and lower reaches of the Yangtze River increases significantly,with two maximum precipitation centers located in the Changjiang-Huaihe River Basin and southern Japan.In the positive PJ phase year (corresponding to the next year of La Niña),precipitation decrease is not obvious in the middle and lower reaches of the Yangtze River.The previously winter SST anomalies closely relate to PJ teleconnection pattern are similar to distribution characteristics of ENSO.It shows that during the negative PJ phase year,positive SST anomalies in the eastern and central Pacific,Indian Ocean and South China Sea are stronger than negative SST anomalies in the positive PJ phase year.In the negative PJ phase year,warmer SST in Indian Ocean excites an abnormal anticyclone over the Philippine Sea and an abnormal cyclone over the middle and lower reaches of the Yangtze River.It is vice versa in the positive PJ phase year.In the negative PJ phase year,the abnormal anticyclone over the Philippine Sea and the abnormal cyclone over the middle and lower reaches of the Yangtze River are stronger than the abnormal cyclone over the Philippine Sea and the abnormal anticyclone over the middle and lower reaches of the Yangtze River in the positive PJ phase year.It leads to the asymmetric response of precipitation position and intensity anomalies in the middle and lower reaches of the Yangtze River.Based on the general circulation model ECHAM4.8,the sensitivity numerical simulation results show that even though the positive and negative SST anomalies over the Indian Ocean are equal,the abnormal anticyclone over the Philippine Sea induced by the positive SST anomalies in the Indian Ocean is obviously stronger than the abnormal cyclone excited by the negative SST anomalies.It causes the increase degree of precipitation in the middle and lower reaches of the Yangtze River in the negative PJ phase year greater than the decrease degree in the positive PJ phase year.It is confirmed that the prediction skill of more summer precipitation in the middle and lower reaches of the Yangtze River in the negative PJ phase year is higher than that of less summer precipitation in the positive PJ phase year.

Abstract:In this study,using the ensemble forecast data of ECMWF and moving SVD methods,the sensitive areas of sea level pressure in the processes of two cyclonic rainstorm cases in Jiangsu Province are identified and compared.One case occurred along the Yangtze River and southern areas of Jiangsu,and the other in Huaibei District of Jiangsu.The main results are as follows:1)The sensitive signals can be locked two days prior,and propagate eastward with phase transition occurring.2)The signals first appeared in northern Jiangxi and northwestern Hunan Provinces.In the case of rainstorms along the Yangtze River and southern areas of Jiangsu,the signals then generally spread downstream along the Yangtze River.The phase transition from positive to negative signal corresponds to the southward adjustment of the rain belt,while the consistent negative signals cause an increase in precipitation as a whole,and vice versa.3)In the case of rainstorms occurring in Huaibei,the uncertainty of the forecast results originates from the east central coast of Jiangsu,namely both its positive and negative perturbation in northern Hubei may have led to the anomalous rain belt exhibiting a northeast-southwestward distribution with positive-negative signals.At the same time,the positive perturbation in western Hubei may have caused a decrease in precipitation throughout region,and vice versa.However,all of these signals were distributed along the trajectory of Hubei-Henan-Anhui-Jiangsu.4)The sensitive areas of the first two modes in each rainstorm are relatively complementary in terms of covering the high value region of the ensemble dispersion.

Abstract:Based on a typical case of sea breeze under the cloudy weather in Hainan Island,this paper simulates the structure of local sea breeze circulation by using the WRF model(Version 3.7),analyzes the evolution characteristics of sea breeze circulation,and explores the influence of the complex topography on the structures of local sea breeze circulation and the distribution of cloud water by designing the sensitivity experiments with different terrain heights in Hainan Island.Results show that the topography can significantly affect the structure of sea breeze circulation and the distribution of cloud water mixing ratio.The steep mountain area in the western Hainan Island results in the forced lifting of sea breeze.The southerly background wind causes obvious high-altitude back-flow in the northern Hainan Island.A nearly complete structure of sea breeze is revealed in the western and northern Hainan Island.The higher the terrain height is,the stronger the blocking effect of mountain area in the southern Hainan Island is,the more significant the high-altitude back-flow characteristics of sea breeze in the western Hainan Island,and the further the position of cloud water mixing ratio in the western and northwestern Hainan Island is in the inland.Under the influence of the South China Sea monsoon,compared with the clear weather,the maximum wind speed of the whole island is slightly larger in the strong period of sea breeze and the height of sea breeze in the vertical direction is higher under the cloudy weather.After moving the terrain,the average wind speed of the whole island under the cloudy weather only decreases by 2-3 m·s^-1,while under the clear weather,the wind speed of the whole island is greatly weakened,that is to say,the influence of the topography on the horizontal structure of sea breeze circulation under the cloudy weather is weaker than that under the clear weather.

Abstract:The Lorenz cycle diagnosis is a powerful approach to the understanding of the internal dynamics within atmospheric events.Local Lorenz cycle energetics,however,are mostly restrained from usage due to their ambiguity in transport-transfer separation.Recently,this issue has been resolved through the introduction of a new functional analysis tool,namely the multiscale window transform (MWT),and the resulting energy transfer is known as canonical transfer.In the present study,using an MWT-based localized multiscale energetics analysis,and according to the resulting local Lorenz cycle diagnostics,the 2009 sudden stratospheric warming (SSW) is investigated so as to achieve an understanding of the underlying dynamics.The fields are first reconstructed onto three scale windows,i.e.mean window,sudden warming window or SSW window,and synoptic window.It is observed that the explosive growth of temperature has an intrinsic dynamic origin;it is due to a strong baroclinic instability,which results in a large canonical transfer of available potential energy from the mean window to the SSW window.The accumulated SSW-scale potential energy is then converted into SSW-scale kinetic energy,which,together with a barotropic instability prior to the warming,lead to the reversal of the night jet.

Abstract:There have previously been many mergences during the squall line formation process,after which its intensity enhanced and caused 9-and 10-scale thunderstorm gales in Zhangqiu and Ningyang in Shandong Province in the afternoon of 18 August 2012.Based on the retrieved wind from Doppler weather radar and automatic weather station(AWS) data,this paper analyzes the effect of propagation moving on the convective storm mergence during the squall line developmental process.The results show the following:1)The gust front prior to the surface cold pool was intensive,its vertical thickness reached up to 2 km,under its influence the squall propagated eastward while moving eastward(forward propagation),and the north of squall line changed to bow echo.2)The bow echo and cell E both possessed independent vertical circulations,and all propagated forward.The propagation velocity of the squall line located upstream was faster than that of the cell E,thus they emerged in the end and their vertical circulation combined.3)During the mergence process,the horizontal and upward wind speed were all significantly increased,and the pressure in the air column was reduced.Under the influence of pressure gradient force,a small scale low pressure column with strong rotating updrafts was formed,after which thunderstorm gales were produced in Zhangqiu.4)Due to the fact that there was abundant vapor present in the end of the squall line,the warm and moist air were lifted by the gust front,so that new cells were produced continually and their strength increased in the case of mergence,resulting in the squall line propagating southwestward(back propagation).5)The downstream convective cells propagated in the opposite direction of the advection direction,generating a cloud bridge at a height of 3 km,and eventually merged with the upstream cells.The convective storms at the tail of the squall line merged several times,and the strength continued increasing,thereby causing the Ningyang thunderstorm gales.

Abstract:In this study,using the northern Indian Ocean storms data collected since 1972 and released by JTWC,along with NCEP/NCAR monthly reanalysis data and JMA mean monthly SST data,we analyzed the relationship between the early summer storm activity in the Bay of Bengal and the previous Indian Ocean SST.The results show that the TS activity in April and May of the Bay of Bengal and the SST of the Indian Ocean to the west of Australia have a significant negative correlation,namely the outbreak time of TS in the Bay of Bengal is late or the TS does not occur when the SST in the key areas is high.In addition,when the SST of the important areas is low,there are two scenarios for storm activity.If the Indian Ocean SST north of 30°S is slightly cold (warm) and that of the southeast and southwest Indian Ocean is slightly warm (cold),then the early summer TS appears less frequently or not at all (multiple and early).Further analysis shows that the local circulation changes caused by the high (low) SST in the key area,i.e.the Indian Ocean,leads to the weak (strong) Maschlin high and weak (strong) transequatorial current in the Eastern Hemisphere,which are likely the main reasons for the occurrence time of TS being late (early) and the TS frequency being lower (higher) in early summer.Moreover,when the Somali-equatorial flow and the New Guinea-equatorial airflow undergo weak antipodean synergistic changes,there is a better indication of TS in the Bay of Bengal.

Abstract:The study evaluates the rainfall estimates from ground radar network against Early and Final Run Integrated Multi-Satellite Retrievals for Global Precipitation Mission (IMERG) during an extreme precipitation storm over Yancheng Tornado on June 23,2016.The statistics indexes used in this study were as follows:correlative coefficient (CC),relative bias (RB) and root mean square error (RMSE),probability of detection (POD),critical success index (CSI) and false alarm ratio (FAR).From the results,the following were shown:1)the radar quantitative precipitation estimates (RQPE) and three IMERG can all capture the spatial pattern of storm cumulative rainfall with high CC from 0.91-0.98,and the RQPE was highly correlated with the gauge measurement (CC~0.98);2)the radar and satellite products can capture the rainfall center in Jiangsu Province;3)all the satellite products significantly overestimated the hourly area-mean cumulative precipitation from 46.32% to 60.11%, thus indicating a significantly deviation between the time series of IMERG and observation in the heavy rain storm;4)the RQPE agrees well with the trend of gauge observations before and after the peaks of rainfall,yet underestimates the maximum rainfall;5)the RQPE can effectively capture the trend of rainfall intensity in terms of space and time,but performs less effectively in estimating heavy rain and torrential rain (>5 mm/h);and 6)the POD,CSI and FAR values of RQPE are much higher than IMERG.IMERG can barely detect the occurrence of heavy precipitation (40 mm/h),while RQPE has the lowest value in the range of 40~45 mm/h.Overall,the radar outperforms the satellite in estimating precipitation during extreme rainfall storms,yet still requires improvement to capture the intensive rainfall peaks.

Abstract:This study investigates the trend and mutation analysis of extreme precipitation based on the annual maximum of daily precipitation(AMP) data in the Haihe River Basin during the period of 1951 to 2010.The frequency estimates and spatial characteristics of extreme precipitation can be further calculated and analyzed by using the Regional L-Moments method described in this paper.The results indicate that the AMP series of most sites exhibit no linear trends and mutation at the 90% confidence level;however,there is a distinctive decrease trend among the remaining sites with significant confidence,especially in the Beijing-Tianjin-Tangshan region.The shift analysis of the mean and variance shows that the AMP of most sites exhibits a linear decrease shift,which is distributed in the Luanhe River and Beisanhe River sub-basins.The comprehensive analysis of the trend and shift provides a more reasonable judgment for the drought caused by extreme precipitation.The spatial patterns of the frequency estimates are similar to the different return periods,which show high agreement with the terrain.The quantile values gradually decrease from southeast to northwest,and from coastal to inland.The center of extreme precipitation mainly concentrated in the Zunhua and Qinglong stations of the Luanhe River sub-basin.Frequency estimates of the 50-year return period are in agreement with the maximum observations of the AMP series at most of the stations,which can provide a more quantitative and scientific basis for future decision making.

Abstract:By using TBB(Black Body Temperature) data of FY-2E satellite,statistical research of Meso-α Convective System(MαCS) and Meso-β Convective System(MβCS) occurred over East China in summer(from June to August) during the year of 2010 to 2014 is carried out respectively,which finds two scales of MCS are nocturnal that mainly occurred in Anhui,Jiangsu,Jiangxi and Zhejiang area and moved from west to the east.Based on the reanalysis data of NCEP-CFSR and NCEP-CFSV2 every 6 hours,the causes of MCS were analyzed by principal component analysis(PCA) and K-means clustering analysis.Secondly,the analysis of the formation cause of two kinds of MCS shows the shear line and low-level jet at 850 hPa,subtropical high and short wave trough in middle latitude at 500 hPa and upper-level jet at 200 hPa are the main impact systems before MCS formed.The water vapor supply in the middle and lower troposphere,atmospheric instability in the low layer and the power structure of convergence at low level and divergence at upper level are the necessary conditions for the formation of MCS.The weather situation before initiation of MαCS can be divided into two categories:(1)the formation position is in the western part of the low level jet and the southern part of the cyclonic circulation at 850 hPa,and affected respectively by the southwest airflow in front of trough at 500 hPa and anti-cyclonic circulation at 200 hPa;(2) westerly flow in the south of the shear line at 850 hPa and westerly flow at 500 hPa cooperated with the upper-level jet at 200 hPa.In the two types of circulation situations before the occurrence of MβCS,the westerly in the southern part of the shear line at 850 hPa controls is the first type,while the southwest flow in the southern part of the shear line and low level jet in east of the formation position belongs to the second category.Both of them correspond to short wave trough in the eastern part of the formation position at 500 hPa and westerly jet at 200 hPa.

Abstract:Based on the daily maximum ground temperature data in Anhui Province from 1961 to 2017,the mutation analysis of high temperature events in Anhui Province was carried out by using Mann Kendall method,and it was found that the high temperature events increased significantly after 2000.In order to analyze the characteristics and mechanism of the extreme hot weather in Anhui Province,35-37℃ high temperature weather cases were selected for comparative analysis.The results showed that:(1) location of subtropical high in the Western Pacific at 500 hPa and temperature at 850 hPa were the best indicators for surface high temperature prediction.(2) As the center of the western Pacific subtropical high was at different locations,the warming mechanism in Anhui Province was obviously different.If the area was controlled by the center of the subtropical high,the heat caused by solar radiation was much larger than that from the airflow subsidence,thus Anhui Province was prone to experience extreme hot weather.When the center of the western Pacific subtropical high was over the sea and Anhui Province was near its ridge,the intensity of high temperature weather was much weaker in Anhui Province.Based on case study and composite average analysis,the paper summarized the forecast indexes of extreme hot weather in Anhui Province.

Abstract:Taking a wind farm in Zhangjiakou as the experimental site,the Wind3D 6000 and WindMast WP350 Doppler lidars were used to measure the wake and incoming wind speeds of wind turbines respectively,and three working conditions of full wake,half wake and independent wake were studied.Results show that the wake width increases with the development of the wake,while the depth and velocity decay of the wake decreases with the development of the wake under the three working conditions.Under the full wake and half wake conditions,the presence of the upstream wind turbine will increase the wake width of the downstream wind turbine,and the increase of the full wake is greater than that of the half wake.Under the full wake and half wake conditions,compared with the upstream wind turbine,the wake depth and velocity attenuation of the downstream wind turbine are smaller.