Abstract:In recent years, extreme weather and climate events have occurred frequently, and are often compound extreme events formed by the interweaving of a variety of events.They have attracted extensive attention and research due to their serious hazards.In order to better understand compound extreme events, IPCC AR6 evaluated the latest research results of compound extreme events based on existing new evidence, and obtained some new understandings.The definition of compound extreme events is expanded.Focusing on heatwave and drought compound extreme events, compound floods and wildfires, the variation characteristics of compound extreme events are evaluated, the dependence among multiple factors of compound extreme events is discussed, the attribution analysis of the impact of human activities is carried out, and the possible projection in the future is given.These assessment results have enriched the current basic understanding of compound extreme events.However, according to the existing assessment, it can be seen that there are still insufficient understandings of the mechanism of occurrence and development of compound extreme events.At the same time, it is still necessary to further improve cross-disciplinary, cross-departmental and cross-regional research, strengthen the assessment of formation mechanism and projection of compound extreme events and their impact and risk on ecosystem, economy and society, and improve the adaptability to regional climate change in the future.

Abstract:In August 2021, the Intergovernmental Panel on Climate Change (IPCC) released the Summary for Policymakers of the Physical Science Basis in the Sixth Assessment Report (AR6), which mainly made a systematic assessment of the scientific research progress of climate change since the Fifth Assessment Report (AR5) in 2013, and used the new generation climate model to project future climate change under the new shared socio-economic path scenario.Based on the materials of relevant chapters in AR5 and AR6, this paper interpreted the assessment conclusion of drought change.

Abstract:In August 2021, the Working Group Ⅰ(WGI) report of the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) was released.The report has concluded that human activities have warmed the atmosphere, ocean and land.Widespread and rapid changes in the atmosphere, ocean, cryosphere and biospherehave occurred.This paper presents the main conclusions of the report on the impact of human activities on the climate system, including the impact of human activities on the atmosphere and surface, the cryosphere, the ocean, the biosphere and the climate variability.It is clear that based on recent literatures in the filed of climate change detection and attribution, anthropogenic forcing signal, which is dominated by greenhouse gases, has been detected in multivariable changes in the climate system.The uses of the newest observational data, the latest generation of climate models and the updated attribution methods provide solid basis for these conclusions.

Abstract:This article introduces the new advances in air quality-climate interactions in the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC).AR6 presented emission-based estimates of the effective radiative forcing (ERF) of major air pollutants or their precursors, which have important implications for understanding the climatic effects of air pollution control measures.AR6 quantified the changes in global mean surface air temperature (GSAT) by anthropogenic emissions.Over 1750-2019, anthropogenic ERF was estimated to lead to change in GSAT by 1.29 (0.99-1.65)℃, in which changes in well-mixed greenhouse gases, O₃, and aerosols contributed 1.58 (1.17-2.17)℃、0.23 (0.11-0.39)℃、-0.50 (-0.22——0.96)℃, respectively.Changes in emissions of SO₂ since 1750 have made a dominant contribution to the effective radiation forcing (ERF) of aerosols through aerosol-cloud interactions (high confidence), which partially offset the warming caused by anthropogenic emissions of greenhouse gases (high confidence).AR6 assessed for the first time the sensitivity of surface ozone concentration to temperature, which is -0.2——2 nL·L^-1·℃^-1 in remote areas and 0.2-2 nL·L^-1·℃^-1 in polluted regions.With respect to the impact of climate change on PM_2.5, model results show low consistency about wheather climate change increases or decreases PM_2.5.

Abstract:Since the release of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), the international scientific community has made a number of significant progresses in the field of climate system change, which deepen our understanding on climate change.These scientific progresses and findings have been assessed objectively and comprehensively in the Working Group I (WGI) report of the Sixth Assessment Report (AR6)of IPCC.Given that temperature is the most direct indicator of global climate change, this paper briefly reviews the scientific cognition of the observed changes, attribution and projection from AR5 to AR6 from the perspective of changes in surface temperature.Compared to AR5, AR6 further confirms the objective fact of global warming since 1850 with stronger evidence, and the signals of human influenceon global warming are much clearer.The future amplitude of global warming depends on the efforts of greenhouse gas emission reduction.

Abstract:The severe torrential rain attacked Henan province during July 17-22 in 2021 (abbreviation "21·7") whenever the process total rainfall amount reaches 1 122.6 mm and the hourly rain intensity at Zhengzhou national observation is up to 201.9 mm/h which broke through the meteorological record of hourly rain intensity extreme value in Chinese inland since 1951.The precipitation features and abnormality of atmospheric circulations and the environmental physical quantities were analyzed with the comparative analysis of physical quantities in the process of heavy rain over 50 mm in Zhengzhou and Hebi since 1981 based on the national and regional automatic meteorological observation data and the high resolution European central atmospheric reanalysis (ERA5).As shown by the results, the "21·7" severe rainfall process presents significant extremes in terms of cumulative precipitation, heavy rainfall coverage, daily rainfall, and hourly rainfall intensity.The eastern foot of Taihang Mountain and the windward slope of eastern Funiu Mountain are the only two locations with accumulated precipitation over 400 mm, which are closely related to topography.Anomalies in atmospheric circulation such as the enhancement and eastward extension of the South Asian high, the northward anomaly of the subtropical high, and the low-value system in low-latitude regions are responsible for the stable and lasting water vapor transport to Henan province.Water vapor convergence along Taihang and Funiu Mountain was below -10σ, showing significant extremes.Dynamic conditions are also apparent in the "21·7" process.With a deviation of 2σ-5σ from the historical climate, the divergence centers are located along the eastern foothills of Taihang Mountain and Funiu Mountain in 200 hPa.The deviation of 850 hPa vorticity from the climate state along Funiu Mountain is higher than that on the eastern foot of Taihang Mountain while the deviation of 700 hPa vertical velocity from the climate is more extreme on the eastern foot.For the same region since 1981, the standard deviation of 850 hPa vorticity and 700 hPa vertical velocity is the largest (least) or the secondary maximum (minimum) in the process of "21·7", which indicates the extreme rain.In the eastern foot of Taihang Mountain and Funiu Mountain, the deviations of 850 hPa convergence and 700 hPa vertical velocity are consistently greater than 3σ(-3σ) on average, positively correlated with daily rainfall.

Abstract:The "7·20" Zhengzhou severe heavy rain broke the Zhengzhou observed station's 1-hour precipitation record (201.9 mm) as well as the daily precipitation record (552 mm).In addition, there was a catastrophic rainfall process that left hundreds dead and dozens missing.High intensity, wide-coverage, and terrain-specific distribution were characteristics of this severe rainfall.This study used gauge precipitation observations, geostationary satellite observations, reanalysis data, and multiple numerical model forecasts to analyze the models' forecast deviations and Jiangsu Precision Weather Analysis and Forecasting System's (PWAFS) ability in forecasting extreme rainfall events.Here are the main conclusions:1) The heavy rain was caused by a strengthened easterly flow between the westward extended subtropical high and typhoon "In-fa", combined with a topographic lift.2) In terms of heavy rain, the European Center for Medium-range Weather Forecasts (ECMWF) and the Global Forecast System(GFS) performed well, but the precipitation center was slightly northerly biased and the intensity was noticeably lower than observation.PWAFS had a better performance in precipitation intensity forecasting and a distribution pattern along the terrain.However, PWAFS shows isolated rain centers that are biased to the west.3) Based on the PWAFS forecasts and reanalysis data, it was found that on 20 July over the heavy rain area, a shear line eventually developed into a deep low-pressure system, which provided favorable dynamic conditions for convective development.

Abstract:Typhoon In-fa (202106) formed on July 18, 2021, and became an extratropical cyclone on July 30, with a life history of 13 d.It affected 14 provinces and cities in eastern China.Its main characteristics are slow moving speed, long retention time on land and large accumulated rainfall.Based on multi-channel observations and products from geostationary meteorological satellites, polar-orbiting meteorological satellites and global precipitation measurement satellites, this paper analyzes the influence process of Typhoon In-fa.Results show that the spatial scale of Typhoon In-fa is large, with the maximum radius of about 350 km.Before landing, the convection is deep and the spiral characteristics of the cloud system are significant.After landing, the cloud system structure is destroyed and the medium convection is densely distributed but unorganized.When Typhoon In-fa is on the ocean surface, the liquid water and ice water are rich and show asymmetric distribution.After landing, the liquid and ice water are mainly concentrated on the right side of forward direction of the typhoon.Based on microwave imager, the retrieved precipitation rate show that the precipitation mainly locates in the spiral rain belt around the typhoon, and the position and area are in good agreement with the observations.Although there is a certain deviation between the estimated precipitation and the observed precipitation, it is still useful for precipitation forecasting, especially in regions where the conventional data are scarce.

Abstract:The echo characteristics of Jiangxi subtropical high edge mesoscale thunderstorm gale on July 11, 2020 were examined using MICAPS conventional weather map data, ground automatic weather station data, lightning data and radar mosaic data, for the study of weather evolution and radar mosaic echo characteristics.The results show that:1) under the control or edge of subtropical high, the northeast wind is at 100 hPa and the southwest wind is at 500 hPa over Jiangxi, and the upper layer of T-lnP is unstable and CAPE area is large, which is beneficial to strong convective weather;Because of the different wind directions on the upper and lower floors, the movement of thunderstorm echo system is inconsistent with the extension direction of cloud anvil of echo system, which intensifies the convection rising movement and makes thunderstorm echo system develop, strengthen and maintain.2) At the initial stage of echo generation, it is the local convection single echo, and the echo short band in the north-south direction is formed by using the new generation and a single combination.As the echo short band forms vigorously, it will produce thunderstorms with multiple stations and windy weather.3) The main echo feature of a thunderstorm gale is the short echo band in the north-south direction.Despite the low echo intensity of 55 dBZ (60-70 km), the echo travels at speed, resulting in the gale.The multiple radar storm tracking information STI (Storm Tracking Information) is superimposed on Jiangxi WebGIS radar mosaic, which can clearly show the moving direction and speed of storms, and will be more useful if STI dense areas are used.4) The "forward" or "extended" echo reflects the high-altitude wind direction over the echo system and the cloud anvil drifting away from cumulonimbus clouds.In some ways, the "extended" echo shows the strength of the thunderstorm echo system at the edge of the subtropical high.It provides a basis for improving the early forecasting and early warning of mesoscale thunderstorm gales at the edge of subtropical highs.

Abstract:With 10 m wind speed, geopotential height field, temperature, and wind field from ERA-Interim from 1979 to 2018, HadISST reanalyzed Sea Surface Temperature (SST) from the Hadley Center, applying SVD analysis and synthetic analysis methods.We examined the relationship between the Western Pacific Warm Pool SST and the 10 m daily maximum wind speed anomaly in summer (June-August) in Eastern China offshore waters.The SVD analysis results show there is a significant negative correlation between the 10 m wind speed changes in the offshore waters of East China and the SST in the east of the Philippines.The correlation coefficient of the left and right spatial vectors of the first mode is 0.58, which passes the 95% confidence test.When the SST of the Western Pacific Warm Pool is in a positive anomaly year, the SST of the warm pool area increases, the Northwest Pacific Subtropical High (NPSH) strengthens, and the subtropical high ridge usually moves northward, where the correlation coefficient of the latitude of the NPSH ridge and the SST from warm pool reached 0.46, passing the 95% confidence test.At this time, the offshore waters of East China are under the control of the subtropical high, and the sinking motion has increased over the offshore waters, the vertical temperature profile of the troposphere has generally increased, and the 10 m wind shows north wind abnormal over the offshore waters.The reduction of sea surface wind speed has accounted for about 30% of the mean wind speedover the past 40 years.When the warm pool SST is negative, the subtropical high retreats to the southeastward.The activity of cold air in the offshore waters of East China has strengthened.The vertical temperature profile has a significant cooling phenomenon.The increase in wind speed has accounted for more than 20% of the averagewind speed over the past 40 years.This study further demonstrates that the SST anomaly in the warm pool is an effective predictor, which can be used to predict the sea surface wind speed in the offshore waters of Eastern Chinaand to guide economic production and maritime activities in related fields.

Abstract:Surface ozone(O₃) pollution poses a very serious threat to human health.O₃ pollution in China has been deteriorating since 2013.To evaluate the O₃ pollution change and its health effect in China from 2014 to 2018, this paperutilized a novel data fusion method that combinedsurface monitoring observations, air quality model predictionsand satellite retrieval data to obtain the mass concentration and spatial distributionof surface O₃, and then used the Environmental Benefits Mapping and Analysis Program-Community Edition (BenMAP-CE) model to estimate the number of O₃-related premature mortality in China in 2014 and 2018.Results show that the annual average value of the maximum daily 8-hour average O₃(O₃-MDA8) mass concentration in 2018 (98.0 μg/m³) increases by 11.5%, compared to that in 2014 (87.9 μg/m³), among which O₃-MDA8 mass concentration increases most significantly in Anhui, Shanxi and Shandong Provinces.The number of O₃-related premature mortality in 2014 and 2018 is 174 000 and 267 000 respectively, and the growth rate of premature mortality numberis about 57%.Among the nine regions in China, Central China has the largest increase in O₃ mass concentration and O₃-related premature mortalitynumber compared with the other regions, and the regions with population density of about 1 000 people/km² have the largest increase in premature mortality number.The number of O₃-related premature mortality increases more in Henan, Hebei and Sichuan Provinces than in other provinces.In recent years, the increase of health hazards of surface atmospheric O₃ in China is much greater than that of O₃ mass concentration.The control of O₃ pollution should be strengthened as soon as possible.

Abstract:In order to study the deviation of low-level temperature in squall line simulated by WRF (Weather Research and Forecasting) model, a squall line case in North Jiangsu Province on June 14, 2009 was selected for analysis.The simulation results show that the WRF has defects in simulating the diurnal variation of low-level temperature, which mainly show that the simulated daily maximum temperature lags behind the observation for 2-3 h, and the cooling range of simulated low-level temperature in the evening is 2-3℃ lower than the observation.Comparative experiments show that by changing the parameterization scheme of the boundary layer, the temperature exchange between the boundary layer and the free atmosphere is weakened, and then the simulation results are improved to a certain extent, that is, the simulated squall line intensity and low-level temperature are more similar to the observations.Without changing the boundary layer scheme, by adding the ground automatic encryption observation station data into the simulation, it can also improve the simulation results.

Abstract:Using ocean reanalysis data, this paper studies the variation of sea surface salinity (SSS) in the North Pacific and its relationship with fresh water flux (FWF).Results show that SSS has an increasing trend from 1914 to 2013, with a periodic change of 25-30 a;From 1979 to 2013, SSS decreases first and then increases, with a periodic change of 7-12 a.The active areas of SSS variation in the North Pacific are located in the Kuroshio and its extension area (Area A) and the eastern central North Pacific (Area B).SSS in Area A and Area B shows a decreasing trend before 2000 and an obvious increasing trend from 2000 to 2009.Variations of SSS in Area A and Area B are significantly correlated with variation of FWF in the North Pacific.SSS in Area A is greatly affected by local FWF (The maximum correlation coefficient is 0.56 when FWF leads 16 months), and SSS in Area B is less affected by local FWF (The maximum correlation coefficient absolute value is 0.21 when FWF leads 20 months).Correlation between FWF in the North Pacific and SSS in Area A shows that there is a large range of positive correlation area, which is mainly located in the extension area of Kuroshio (east of Area A), and the high value area of positive correlation moves eastward with the shortening of FWF lead time.Corresponding to the interdecadal variation of temperature in the North Pacific, SSS also has significant interdecadal variation, and the variation of SSS in key areas of the North Pacific can characterize the North Pacific climate variability, which can be used as an alternative index of the North Pacific climate variability.

Abstract:Based on the 160 stations monthly rainfall data provided by National Climate Center of China Meteorological Administration, the all-India monthly rainfall data provided by Indian Institute of Tropical Meteorology and the NCEP/NCAR reanalysis data, this study is made to investigate the summer Eurasian teleconnection (EU) effect on the relationship between the Indian summer monsoon (ISM) and North China summer rainfall (NCSR) from interannual and interdecadal scales respectively, as well as the associated mechanism.Based on the -0.078 correlation coefficient, the EU and ISM are independent of each other.When it comes to the positive EU phase, the relationship between the ISM and NCSR becomes weak, but strong when it comes to the negative EU phase.During negative EU phases, an anticyclonic circulation appears over Lake Baikal area which is extremely conducive to the northerly wind south of Lake Baikal area, thereby controlling the circulation over North China.As a result, when the ISM is strong, warm moist air from the southwest meets northerly winds and forms a front, which can give rise to North China's rainfall.However, during weak ISM, the circulation over North China is completely dominated by northerly winds, and the water vapor transport channel is completely blocked, which makes rainfall impossible.A strong relationship between ISM and NCSR has resulted from the negative EU phase.In contrast, the ISMR-NCSR relationship is weak during the positive EU phase.

Abstract:The method of the subjective and objective combination was used to detect and track Northeast China cold vortexes (NECVs) in May-September, based on 30-year NCEP/NCAR reanalysis data and MICAPS observation data provided by China Meteorological Administration.Over the past 30 years, the number of NECVs has steadily increased.NECV processes lasted 3 to 5 days on average in northeast China each year.In May, the frequency was highest, while in August and September, it was lowest.May-July, the longest time influenced by NECVs can exceed 19 days, with an annual average of 9.9 days, 8.8 days, and 7.0 days, respectively.NECVs can be categorized according to their characteristics:north, middle, and south cold vortices (NCV, MCV, and SCV) as well as strong and weak cold vortices.SCVs mostly occur in May and June.Weak NECVs occurred about 1.2 times as often as strong NECVs.The NCVs in late spring and early autumn, as well as the weak MCVs in summer, occurred frequently.Researchers found that when NCVs occur in late spring and early autumn, the upper-level westerly jets are stronger, strengthening the divergence in the upper troposphere and the vortex circulation.During the upper and lower levels of circulation, strong jets cooperated with the circulation fields, enabling the cold vortices to develop and grow constantly.Other than the jets and circulation, the lower central potential height coupled with the obvious cold-core and stronger ascending motions were conducive to the development of NCV.Furthermore, the dry invasion was strongly promoted by lower-level cold advection and the downward intrusion of high potential vorticity (PV).The MCVs happened in the summer when the opposite was true.

Abstract:In this study, two Tornado disasters occurred in northern Jiangsu, Chinafrom 2009 to 2016 were studiedvia numerical simulation.The objective of the study was to explore the reasons of the northern Jiangsu coastal plain area as the most frequent place of strong tornados in China in spring and summer.The mechanism of tornado formation due to emergence of double front systems in the area was discussed.The results showed that the tornado events in northern Jiangsu accounted for 58.6% of that of the whole province.Particularly, Yancheng and Xuzhou are two cities with high incidence of tornadoes.In spring and summer, the intensities of cold, warm, dry, and wet air masses are similarin the area, forming many mesoscale front systems.Thus, the area is prone to local strong convection tornadoscaused by the convergence of two frontsystems.Analysis of two typical strong convection tornado sites in Yancheng (2016) and Xuzhou (2009) showed that the Yancheng tornado was due to the convergence of a cyclone front and a shore front, while the Xuzhou tornado was a result of a deformation field frontogenesis and a sea-breeze front.The WRF simulation results showed that the convergence of the two frontal systems and the encounter of the frontal secondary circulation caused vertical torsion of the local horizontal wind and horizontal shear of the vertical wind, which increased the regional positive vorticity.The superposition of the vertical ascending branches of the double front secondary circulation produced strong systematic uplift in flat areas, resulting in an area favorable for the development of tornados.Moreover, all of the common strong convection indices showed strong local characteristics, which need to be used for reference according to local statistical characteristics.

Abstract:Despite the high temperatures associated with the warming climate, there are also occurrences of low temperatures.A persistent low temperature in summer 2014 is typical of recent years.The three-dimensional structure of the low temperature and anomaly in large-scale circulation is investigated using station observations of temperature over China, NOAA observations of sea surface temperature, and NCEP/NCAR reanalysis data.It has been shown that the low temperature anomalies in the near-surface layer are not only regionally located in the Yangtze River Basin, but can extend to the ocean in a large-scale belt pattern.The abnormality belt is not only visible near the surface, but also at all atmospheric levels (925-500 hPa).Based on the analysis, the low temperature in the atmosphere is largely due to anomalous systems at high latitudes.In the geopotential height field, the belt-like positive anomalies at 60°N may induce the inflow of colder-than-normal air in its southern region from the north or northeast.At all levels, the geopotential height shows positive anomalies.Accordingly, there are negative geopotential anomalies at low latitudes (40°N).A region of low temperatures lies between them, and all levels exhibit this distribution pattern.There is an overall tilt in these systems from the near surface to the upper levels, resulting in a large-scale front-like vertical cross-section, which a simple conceptual model can explain.The vertical structure may be maintained by the interaction between the dynamics and thermodynamics in the atmosphere.