Consistency of Tropospheric Water Vapor between Reanalyses and Himawari-8/AHI Measurements over East Asia

High spatiotemporal resolution radiances from the advanced imagers onboard the new generation of geostationary weather satellites provide a unique opportunity to evaluate the abilities of various reanalysis datasets to depict multilayer tropospheric water vapor(WV),thereby enhancing our understanding of the deficiencies of WV in reanalysis datasets.Based on daily measurements from the Advanced Himawari Imager(AHI)onboard the Himawari-8 satellite in 2016,the bias features of multilayer WV from six reanalysis datasets over East Asia are thoroughly evaluated.The assessments show that wet biases exist in the upper troposphere in all six reanalysis datasets;in particular,these biases are much larger in summer.Overall,we find better depictions of WV in the middle troposphere than in the upper troposphere.The accuracy of WV in the ERA5 dataset is the highest,in terms of the bias magnitude,dispersion,and pattern similarity.The characteristics of the WV bias over the Tibetan Plateau are significantly different from those over other parts of East Asia.In addition,the reanalysis datasets all capture the shift of the subtropical high very well,with ERA5 performing better overall.

Analysis of Precipitation Anomaly and a Failed Prediction During the Dragon-boat Rain Period in 2022

This study investigates the possible causes for the precipitation of Guangdong during dragon-boat rain period(DBRP) in 2022 that is remarkably more than the climate state and reviews the successes and failures of the prediction in2022. Features of atmospheric circulation and sea surface temperature(SST) are analyzed based on several observational datasets for nearly 60 years from meteorological stations and the NCEP/NCAR Global Reanalysis Data. Results show that fluctuation of the 200-h Pa westerly wind as well as the westerly jet is strengthened due to the propagation of wave energy, leading to strong updraft over southern China. Activities of a subtropical high and a shear line provide favorable conditions for the transport of moisture to Guangdong. With the support of powerful southwest winds, extreme precipitation is induced. ENSO is a good indicator of atmospheric circulation at mid-and high-levels during the DBRP in2022 but it performs badly at low levels. During recent years, the influence of ENSO on precipitation during the DBRP has decreased obviously. The SSTA of tropical southeast Atlantic(SEA) in spring may become the key indicator. During the years with warm SEA, wave trains propagate from northwest to southeast over Eurasia with energy enhancing the westerly jet, conducive to updraft over southern China and the occurrence of heavy precipitation. Meanwhile, the Rossby wave is triggered over Maritime Continent by heat sources of southern Atlantic-western Indian Ocean through the Gill response. Thus, strong transport of moisture and heavy rainfall occur.

Diurnal Variations of Precipitation over North China Regulated by the Mountain-plains Solenoid and Boundary-layer Inertial Oscillation

The mountain-plains solenoid(MPS) and boundary-layer inertial oscillation(BLO) are two typical regional forcings at the diurnal time scale. Their relative role in regulating the diurnal variations of summer rainfall over North China and their change under different monsoon conditions are studied using a 19-yr archive of satellite rainfall and reanalysis data. It is shown that both a strong MPS and BLO can increase nocturnal rainfall in the North China plains but exhibit evident regional differences. The MPS-induced nocturnal rainfall is relatively confined to the plains adjacent to mountains from late night to morning, due to the upward branch of the nighttime MPS. In contrast, the BLO-induced nocturnal rainfall strengthens from early evening and is more extensive in early morning over the open plains further east. The contrasting effect in the evening is related to the convergent(divergent) easterly anomaly in the plains under the BLO(MPS). The BLO also induces the relatively strong enhancement of moisture convergence and high humidity by the southerly anomaly at late night. On strong monsoon days, the nocturnal rainfall amount associated with the MPS and BLO increases considerably in the plains.Both regional forcings become effective in regulating the rainfall diurnal cycle with enhanced moisture convergence under monsoon conditions. Their induced diurnal amplitudes of moisture convergence can be comparable to the daily mean by monsoon flow. The regional forcings thus couple with monsoon flow to strengthen rainfall in the plains, particularly from late night to morning. The results highlight that a combination of regional and large-scale forcings can strongly regulate the warm-season climate.

Sub-seasonal Prediction of the South China Sea Summer Monsoon Onset in the NCEP Climate Forecast System Version 2

This study depicts the sub-seasonal prediction of the South China Sea summer monsoon onset(SCSSMO)and investigates the associated oceanic and atmospheric processes,utilizing the hindcasts of the National Centers for Environmental Prediction(NCEP)Climate Forecast System version 2(CFSv2).Typically,the SCSSMO is accompanied by an eastward retreat of the western North Pacific subtropical high(WNPSH),development of the cross-equatorial flow,and an increase in the east-west sea surface temperature(SST)gradient.These features are favorable for the onset of westerlies and strengthening of convection and precipitation over the South China Sea(SCS).A more vigorous SCSSMO process shows a higher predictability,and vice versa.The NCEP CFSv2 can successfully predict the onset date and evolution of the monsoon about 4 pentads(20 days)in advance(within 1–2 pentads)for more forceful(less vigorous)SCSSMO processes.On the other hand,the climatological SCSSMO that occurs around the 27th pentad can be accurately predicted in one pentad,and the predicted SCSSMO occurs 1–2 pentads earlier than the observed with a weaker intensity at longer leadtimes.Warm SST biases appear over the western equatorial Pacific preceding the SCSSMO.These biases induce a weaker-thanobserved WNPSH as a Gill-type response,leading to weakened low-level easterlies over the SCS and hence an earlier and less vigorous SCSSMO.In addition,after the SCSSMO,remarkable warm biases over the eastern Indian Ocean and the SCS and cold biases over the WNP induce weaker-than-observed westerlies over the SCS,thus also contributing to the less vigorous SCSSMO.

Recent Progress in Dual-Polarization Radar Research and Applications in China

Dual-polarization(dual-pol)radar can measure additional parameters that provide more microphysical information of precipitation systems than those provided by conventional Doppler radar.The dual-pol parameters have been successfully utilized to investigate precipitation microphysics and improve radar quantitative precipitation estimation(QPE).The recent progress in dual-pol radar research and applications in China is summarized in four aspects.Firstly,the characteristics of several representative dual-pol radars are reviewed.Various approaches have been developed for radar data quality control,including calibration,attenuation correction,calculation of specific differential phase shift,and identification and removal of non-meteorological echoes.Using dual-pol radar measurements,the microphysical characteristics derived from raindrop size distribution retrieval,hydrometeor classification,and QPE is better understood in China.The limited number of studies in China that have sought to use dual-pol radar data to validate the microphysical parameterization and initialization of numerical models and assimilate dual-pol data into numerical models are summarized.The challenges of applying dual-pol data in numerical models and emerging technologies that may make significant impacts on the field of radar meteorology are discussed.

On the Second-Year Warming in Late 2019 over the Tropical Pacific and Its Attribution to an Indian Ocean Dipole Event

After its maturity,El Niño usually decays rapidly in the following summer and evolves into a La Niña pattern.However,this was not the case for the 2018/19 El Niño event.Based on multiple reanalysis data sets,the space-time evolution and triggering mechanism for the unusual second-year warming in late 2019,after the 2018/19 El Niño event,are investigated in the tropical Pacific.After a short decaying period associated with the 2018/19 El Niño condition,positive sea surface temperature anomalies(SSTAs)re-intensified in the eastern equatorial Pacific in late 2019.Compared with the composite pattern of El Niño in the following year,two key differences are evident in the evolution of SSTAs in 2019.First,is the persistence of the surface warming over the central equatorial Pacific in May,and second,is the re-intensification of the positive SSTAs over the eastern equatorial Pacific in September.Observational results suggest that the re-intensification of anomalous westerly winds over the western and central Pacific,induced remotely by an extreme Indian Ocean Dipole(IOD)event,acted as a triggering mechanism for the second-year warming in late 2019.That is,the IOD-related cold SSTAs in the eastern Indian Ocean established and sustained anomalous surface westerly winds over the western equatorial Pacific,which induced downwelling Kelvin waves propagating eastward along the equator.At the same time,the subsurface ocean provided plenty of warm water in the western and central equatorial Pacific.Mixed-layer heat budget analyses further confirm that positive zonal advection,induced by the anomalous westerly winds,and thermocline feedback played important roles in leading to the second-year warming in late 2019.This study provides new insights into the processes responsible for the diversity of El Niño evolution,which is important for improving the physical understanding and seasonal prediction of El Niño events.

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines.A recent eruption occurred on 12 January 2020(Fig.1a),and this volcano is still active with the occurrence of volcanic earthquakes.The eruption has become a deep concern worldwide,not only for its damage on local society,but also for potential hazardous consequences on the Earth’s climate and environment.

Science and Prediction of Heavy Rainfall over China:Research Progress since the Reform and Opening-Up of New China

This paper reviews the major progress on development of the science and prediction of heavy rainfall over China since the beginning of the reform and opening-up of new China(roughly between 1980 and 2019).The progress of research on the physical mechanisms of heavy rainfall over China is summarized from three perspectives:1)the relevant synoptic weather systems,2)heavy rainfall in major sub-regions of China,and 3)heavy rainfall induced by typhoons.The development and application of forecasting techniques for heavy rainfall are summarized in terms of numerical weather prediction techniques and objective forecasting methods.Greatly aided by the rapid progress in meteorological observing technology and substantial improvement in electronic computing,studies of heavy rainfall in China have advanced to investigating the evolution of heavy-rain-producing storms and observational analysis of the cloud microphysical features.A deeper and more systematic understanding of the synoptic systems of importance to the production of heavy rainfall has also been developed.Operational forecast of heavy rainfall in China has changed from subjective weather event forecasts to a combination of both subjective and objective quantitative precipitation forecasts,and is now advancing toward probabilistic quantitative precipitation forecasts with the provision of forecast uncertainty information.

Characteristics of Pre-summer Daytime Cloud Regimes over Coastal South China from the Himawari-8 Satellite

Using the high spatiotemporal resolution(2 km-and-10 min)data from the Advanced Himawari Imager onboard the Himawari-8 satellite,this study documents the fine-scale characteristics of daytime cloud regimes(CRs)over coastal South China during the pre-summer rainy season(April–June).Six CRs(CR1–CR6)are identified based on the joint frequency distribution of cloud top brightness temperature and cloud optical thickness,namely,the optically thin-to-moderate cloud mixture,optically thin warm clouds with cirrus,optically thick warm clouds,weak convective cloud mixture,strong convective clouds,and extreme,deep convective clouds.The optically thick warm clouds are the major CR during April and May,with higher frequencies over land,especially along the urban agglomeration,rather than the offshore which may be an indicator of the higher aerosol concentrations being a contributing factor over the cities.The CRs with weak convective cloud mixtures and strong convective clouds appear more frequently over the land,while the two CRs with optically thinner clouds occur mainly offshore.Synoptic flow patterns(SPs)are objectively identified and examined focusing on those favoring the two major rainproducing CRs(CR5 and CR6)and the highly reflective CR with optically thick warm clouds(CR3).The two SPs favoring CR5 and CR6 are characterized by abundant moisture with low-level jets after monsoon onset,and a northwest highsoutheast low pattern with strong dynamic convergence along the coastline,respectively.The non-convective CR3 with high reflectance is related to a SP that features the western North Pacific subtropical high extending more westward,leading to a moderate moisture supply and a wide range of convective available potential energy,but also,large convective inhibition.

Isentropic Analysis of Regional Cold Events over Northern China

From the perspective of cold air mass(CAM)analysis,we examine the characteristics and mechanisms of regional cold events(RCEs)over northwestern and northeastern China in the past 58 years(1958/59-2015/16).The RCEs in northwestern(northeastern)China are shown to have an average duration of 6.8(4.7)days with a moderate(sharp)temperature drop.We quantitatively estimate the RCE-related CAM,for the first time,using an isentropic analysis method.Before an RCE in northwestern China,CAM is accumulated in western Siberia with convergent CAM flux under a blocking pattern in the Urals region.During RCE outbreak,CAM penetrates the valleys of the Tianshan-Altay Mountains to the Tarim Basin and Hexi Corridor.The CAM moves slowly because of the blocking pattern and orographic effect,which explains the relatively long duration of RCEs.Comparatively,during RCEs in northeastern China,the CAM depth anomaly originates more to the east and quickly passes the Mongolian Plateau guided by an eastward-moving trough.Diagnostic analyses further show that adiabatic processes play a crucial role in regulating the local change of CAM depth during the two kinds of RCEs.The advection term of adiabatic processes mainly increases the CAM depth during RCE outbreak,while the convergence term increases(reduces)CAM depth before(after)RCE outbreak.Both terms are relatively strong during RCEs in northeastern China,resulting in the rate of change in CAM depth being^50%larger than for those in northwestern China.Therefore,the variations of RCEs in duration and intensity can be well explained by the different evolution of CAM depth and flux.

Effects of local and non-local closure PBL schemes on the simulation of Super Typhoon Mangkhut(2018)

With the convection-permitting simulation of Super Typhoon Mangkhut(2018)with a 3 km resolution for 10.5 days using mesoscale numerical model,Weather Research and Forecasting Model Version 4.1(WRFV4.1),the influences of local closure QNSE planetary boundary layer(PBL)scheme and non-local closure GFS planetary boundary layer scheme on super typhoon Mangkhut are mainly discussed.It is found that in terms of either track or intensity of typhoon,the local closure QNSE scheme is better than the non-local closure GFS scheme.Local and non-local closure PBL schemes have a large influence on both the intensity and the structure of typhoon.The maximum intensity difference of the simulated typhoon is 50 hPa.The intensity of typhoon is closely related to its variations in structure.In the rapid intensification stage,the typhoon simulated by the QNSE scheme has a larger friction velocity,stronger surface latent heat flux,sensible heat flux and vapor flux,related to a higher boundary height and stronger vertical mixing.The latent heat flux and sensible heat flux on the surface conveyed energy upward for the typhoon while the water vapor was transported upward through vertical mixing.While the water vapor condensed,the latent heat was released,which further warmed the typhoon eyewall,strengthening the convection.The stronger winds also intensified the vertical mixing and the warm-core structure,further strengthened the typhoon.The differences in surface layer schemes dominated the differences between the two simulations.

Sea-Salt Aerosol Effects on the Simulated Microphysics and Precipitation in a Tropical Cyclone

We investigate the effects of sea-salt aerosol(SSA) activated as cloud condensation nuclei on the microphysical processes, precipitation, and thermodynamics of a tropical cyclone(TC). The Weather Research and Forecasting model coupled with Chemistry(WRF-Chem) was used together with a parameterization of SSA production. Three simulations, with different levels of SSA emission(CTL, LOW, HIGH), were conducted. The simulation results show that SSA contributes to the processes of autoconversion of cloud water and accretion of cloud water by rain,thereby promoting rain formation. The latent heat release increases with SSA emission, slightly increasing horizontal wind speeds of the TC. The presence of SSA also regulates the thermodynamic structure and precipitation of the TC.In the HIGH simulation, higher latent heat release gives rise to stronger updrafts in the TC eyewall area, leading to enhanced precipitation. In the LOW simulation, due to decreased latent heat release, the temperature in the TC eye is lower, enhancing the downdrafts in the region; and because of conservation of mass, updrafts in the eyewall also strengthen slightly; as a result, precipitation in the LOW experiment is a little higher than that in the CTL experiment.Overall, the relationship between the precipitation rate and SSA emission is nonlinear.

Turbulent flows over real heterogeneous urban surfaces:Wind tunnel experiments and Reynolds-averaged Navier-Stokes simulations

Wind tunnel experiment and steady-state Reynolds-averaged Navier-Stokes(RANS)approaches are used to examine the urban boundary layer(UBL)development above Kowloon Peninsula,Hong Kong Special Administrative Region(HKSAR).The detailed urban morphology is resolved by computational fluid dynamics(CFD)and is fabricated by 3D-printing(reduced scale)for wind tunnel experiments.Different from the majority existing results based on idealized,homogeneous urban geometries,it was found that the wind and turbulence in the UBL over downtown Kowloon are characterized by the wake behind several high-rise buildings.In particular,local maxima of turbulence kinetic energy(TKE)and shear stress are found at the roof level of those high-rise buildings.In the downstream region where the flows are already adjusted to the urban surfaces,the urban roughness sublayer(URSL)can be further divided into two layers based on the structures of the mixing length/m,effective drag Dx and dispersive stress.In the lower URSL(z<100 m),lm is rather uniform,and the Reynolds stress and dispersive stress are comparable.In the upper URSL(100 m z s 300 m),on the contrary,lm is peaked at the mid-height and the magnitude of dispersive stress is smaller than that of the Reynolds stress(<30%).The effective drag Dx is negligible in the upper URSL.

Constraining the Emergent Constraints

An accurate estimate of equilibrium climate sensitivity(ECS)is pivotal to humankind’s responses,including both the mitigation and adaptation,to future global climate change(not necessarily that of a distant future).However,the uncertainty in estimates of ECS remains large,as shown in the past assessments by the Intergovernmental Panel on Climate Change(IPCC)(see IPCC,2013),though the level of understanding on the physics and dynamics of Earth’s climate system has improved considerably during the past four decades since the appearance of the Charney report(Charney et al.,1979).

珠三角秋季硝酸盐气溶胶致霾污染的区域性特征

为研究珠三角地区大气霾污染特征和形成机制,于2014年秋季在区域内三个典型观测站同步开展了细颗粒物外场观测。结果表明,三个站点大气细颗粒物及其化学组分质量浓度的时间变化趋势高度一致,呈现出区域性特征。结合气象因素分析,发现珠三角区域霾污染的形成受到中尺度的静态天气形势的影响。随着霾污染过程的发展,细颗粒物中硝酸盐的比例显著增加,移动源的贡献较大。结合后向气流轨迹和卫星火点分布,证实区域内的生物质燃烧会加剧大气霾污染的强度。为进一步改善珠三角的空气质量,建议在区域尺度上实施联防联控的减排方案。

Shipborne oceanic high-spectral-resolution lidar for accurate estimation of seawater depth-resolved optical properties

Lidar techniques present a distinctive ability to resolve vertical structure of optical properties within the upper water column at both day-and night-time.However,accuracy challenges remain for existing lidar instruments due to the ill-posed nature of elastic backscatter lidar retrievals and multiple scattering.Here we demonstrate the high performance of,to the best of our knowledge,the first shipborne oceanic high-spectral-resolution lidar(HSRL)and illustrate a multiple scattering correction algorithm to rigorously address the above challenges in estimating the depth-resolved diffuse attenuation coefficient Kd and the particulate backscattering coefficient bbp at 532 nm.HSRL data were collected during day-and night-time within the coastal areas of East China Sea and South China Sea,which are connected by the Taiwan Strait.Results include vertical profiles from open ocean waters to moderate turbid waters and first lidar continuous observation of diel vertical distribution of thin layers at a fixed station.The root-mean-square relative differences between the HSRL and coincident in situ measurements are 5.6%and 9.1%for Kd and bbp,respectively,corresponding to an improvement of 2.7-13.5 and 4.9-44.1 times,respectively,with respect to elastic backscatter lidar methods.Shipborne oceanic HSRLs with high performance are expected to be of paramount importance for the construction of 3D map of ocean ecosystem.

Winter extreme precipitation over the Tibetan Plateau influenced by Arctic sea ice on interdecadal timescale

The Tibetan Plateau(TP)and the Arctic are the most sensitive regions to global climate change.However,the interdecadal varibility of winter extreme precipitation over the TP and its linkage with Arctic sea ice are still unclear.In this study,the characteristics and mechisnems of the TP extreme precipitation(TPEP)influenced by Arctic sea ice on interdecadal timescale are studied based on the daily precipitation,monthly sea ice concentration and ERA5 reanalysis data from 1980 to 2018.We found that the dominant mode of the TPEP in winter mostly exhibits a uniform spatial variation on the interdecadal timescale,with an opposite weak variation in the southeastern TP,and the Arctic sea ice concentration(SIC)before 2002 are larger than that after 2003.The interdecadal variation of TPEP is affected by two teleconnection wave trains regulated by the Barents and Kara Sea ice.In the light ice years,a remarkable positive geopotential height(HGT)anomaly appears over the Barents-Kara Sea and a remarkable negative HGT anomaly is located over the Lake Baikal.Two wave trains originating over the Barents-Kara Sea can be observed.The southern branch forms a wave train through the North Atlantic along the subtropical westerly jet stream,showing a‘+-+-+'pattern of HGT anomalies from Arctic to the TP.Negative HGT anomaly controls the western TP,which creates dynamic and water vapor conditions for the TPEP.The northern branch forms a wave train through the Lake Baikal and the southeast of the TP,showing a‘+-+'HGT anomaly distribution.Positive HGT anomaly controls the southeastern TP,which is not conducive to precipitation in the region.When the SIC in the Barents-Kara Sea increases,the situation is opposite.The above analysis also reveals the reason for the difference in the east-west distribution of the TPEP.

Climatology of tropical cyclone tornadoes in China from 2006 to 2018

We surveyed the occurrence of tropical cyclone(TC) tornadoes in China from 2006 to 2018. There were 64 cataloged TC tornadoes, with an average of five per year. About one-third of the landfalling TCs in China were tornadic. Consistent with previous studies, TC tornadoes preferentially formed in the afternoon shortly before and within about 36 h after landfall of the TCs. These tornadoes mainly occurred in coastal areas with relatively flat terrains. The maximum number of TC tornadoes occurred in Jiangsu and Guangdong provinces. Most of the TC tornadoes were spawned within 500 km of the TC center. Two notable characteristics were found:(1) TC tornadoes in China mainly occurred in the northeast quadrant(Earth-relative coordinates) rather than the right-front quadrant(TC motion-relative coordinates) of the parent TC circulation;and(2) most tornadoes were produced by TCs with a relatively weak intensity(tropical depressions/storms), in contrast with the United States where most tornadoes are associated with stronger TCs. Further analyses showed that TC tornadoes in China tend to be spawned in an environment with large low-level storm relative helicity and large convective available potential energy taking entrainment effects into account. TC tornadoes were particularly active in 2018, with 24 reported tornadoes accounting for 37.5% of the total surveyed samples. The first recorded tornado outbreak in the modern history of China occurred in the envelope of TC Yagi(2018), in which 11 tornadoes were reported in association with significant midlevel intrusions of dry air and the interaction of Yagi with an approaching midlatitude midlevel trough.

Shifting of summertime weather extremes in Western Europe during 2012-2020

Over the past decades,droughts and heatwaves frequently appeared in Western Europe(45°-65°N,10°W-20°E)during boreal summer,causing huge impacts on human society and ecosystems.Although these extremes are projected to increase in both frequency and intensity under a warming climate,our knowledge of their interdecadal variations and causes is relatively limited.Here we show that the droughts and heatwaves in Western Europe have shifted in their trends in the last decade:for 1979-2012,wind speed and precipitation have both strengthened in Western Europe;for 2012-2020,however,Western Europe have experienced declined wind speed,decreased precipitation,and higher air temperature,leading to more frequent droughts and heatwaves there.Recent changes in the WE climate and extremes are related to the variations of the North Atlantic westerly jet stream.In 1979-2012(2012-2020),the westerly jet stream shifted equatorward(poleward),which enhanced(reduced)transportation of water vapor fluxes from the North Atlantic Ocean to the European land areas,resulting in wetter(drier)surface in Western Europe.Further analysis suggests that phase changes in the Pacific Decadal Oscillation could have played a key role in regulating the position of the jet stream,providing important implications for decadal predictions of the Western Europe summertime climate and weather extremes.