Abstract:Climate feedback reflects the adaptation process of the climate system to external interference, and affects the prediction of future climate change to a great extent.This paper summarizes the content on climate feedback in the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC).In AR6, the understanding of cloud feedback has been improved greatly compared with that in AR5, especiallythe feedback of low clouds over the Subtropical Ocean.The net cloud feedback parameter is assessed to be positive with high confidence in AR6, which plays an amplification effect on climate change..However, the uncertainty range of cloud feedback is still the largest in all feedback mechanisms.Apart from Planck feedback, all the other feedbacks (water vapor, temperature lapse rate, land surface albedo, cloud, bio-geophysical and non-CO₂ biogeochemical feedback) are positive or near zero, generally amplifying climate change.The estimate of general climate feedback parameter in AR6 is -1.16 W·m^-2·℃^-1, with a 5%—95% confidenceinterval of [-1.81, -0.51] W·m^-2·℃^-1.With global warming, the climate feedback parameters are likely to be closer to the positive value.

Abstract:CMIP6 has endorsed the Land Use Model Intercomparison Project (LUMIP) to further understand the impacts of land-use and land-cover change (LULCC) and land management on climate and biogeochemical processes.The LUMIP experimental design consists of two phases.During Phase 1, an idealized coupled deforestation scenario and land-only model simulations are used to advance understanding of LULCC impacts on climate, as well as to quantify model sensitivity to potential land-cover and land-use changes.During phase two, experiments will quantify the historical impacts of land use and determine the potential for future land management decisions to help mitigate climate change.The purpose of this paper is to describe the scientific background, experimental protocol, and involved models of the LUMIP, and to evaluate its importance and significance.In this paper, we hope to provide a quick overview of its relevant research highlights and development directions.

Abstract:In early October, 2021, northern China experienced an unprecedented autumn flood in history.From October 3 to 6, persistent extreme heavy rainstorm maintained stably in the regions centered along the middle-lower reaches of the Yellow River and Hai River (including the south of central Shaanxi-Shanxi-Beijing-Tianjin-Hebei-Liaoning and the north of Shandong).The flood caused huge economic losses and serious casualties.Based on the observed precipitation in China, the NCEP/NCAR and ERA5 reanalysis datasets, the extreme of this heavy rainfall case is diagnosed in this paper.Results show that the rainstorm process shows the characteristics of typical northern summer rainstorm and atmospheric circulation in terms of precipitation intensity, duration and meridional water vapor transport.The regional average 4-day accumulative rainfall intensity of the above five provinces and two cities is much higher than that of other rainstorms in autumn from 1961 to 2020, and ranks second even in summer.Its extreme intensity is closely related to the long-term persistency of heavy precipitation center in the above areas.The regional average precipitation of the above five provinces and two cities exceeds 15 mm for four consecutive days, which has never occurred in the history of autumn.In addition to the strong extremes of the process, the abnormally abundant precipitation in Shanxi and other places in September also superimposes the autumn flood in early October.The atmospheric circulation corresponding to this autumn flood presents a typical circulation pattern in the main rainy season in summer in northern China, which is manifested by a much stronger and more westward/northward western Pacific subtropical high, and the meridional water vapor transport in the west of the subtropical high is also extremely strong.At the same time, a strong cold air process invades northern China from October 4 to 6, and the cold dry and warm wet air flows converge in the above areas.The calculation of water vapor budget shows that the meridional water vapor transport intensity of this process is the highest in autumn history, and even exceeds that of most rainstorm processes in northern China in midsummer.Above results show that even in mid-autumn, the circulation pattern and water vapor transport conducive to extreme persistent rainstorm in northern China can also be triggered, resulting in severe autumn flood.

Abstract:Based on the station data, reanalysis data and dynamic climate model hindcast data, a dynamic-statistical downscaling prediction method of annual precipitation anomaly in the Yangtze River Basin and its application skill are discussed by using the empirical orthogonal decomposition (EOF) iteration and interannual increment method.Results show that based on the annual scale circulation field of reanalysis data, a statistical downscaling prediction scheme for annual scale precipitation anomaly increment over the Yangtze River Basin is established.The average anomaly correlation coefficient (ACC) of 26-year hindcast test can reach 0.6, which proves that the scheme has high predictability.A dynamic-statistical downscaling prediction scheme of annual precipitation anomaly increment is furth erestablished by using the annual scale circulation predicted by the model.The average ACC is 0.42, showing a high hindcast skill.The skill is much better than that of the directly output precipitation of the model.By analyzing the factors affecting the skill of annual precipitation prediction, it shows that when the annual average SST anomaly in equatorial central and eastern Pacific is negative, the prediction skill is higher, and the average ACC is more than 0.5.Under the cold water background of La Niña development year or La Niña duration year, more eigenvectors are selected by EOF iteration, which are incorporated into the multi-scale atmospheric circulation information as the prediction signal, and the prediction skill of annual precipitation anomalyis improved.

Abstract:Using the optimum path dataset of typhoons in the Northwest Pacific provided by China Meteorological Administration, the ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the astronomical data of the HORIZONS system of NASA, the tidal force on each node of the tropical cyclone path generated in the Northwest Pacific from 1949 to 2019 was analyzed by statistical method, and the relationship between tidal force and atmospheric circulation is diagnosed.The results show that:1) When the upward vertical tidal force was greater, the number of tropical cyclones was more, the speed of strengthening was faster, and the westward moving speed of tropical cyclones also increased. When the azimuth of the horizontal tidal force was close to the forward movement direction of the tropical cyclone, the effect of the vertical tidal force enhancement was more obvious. 2) During the active period of tropical cyclones in the Northwest Pacific (July to October), the upward vertical tidal force is conducive to the upward movement of air masses, leading to convergence (divergence) in the middle (upper) troposphere, and forming a circulation configuration that was favourable to the development of tropical cyclones.

Abstract:Northwest Pacific is the most active area for tropical cyclones(TCs).Intensified TCs usually cause natural disasters, leading to tremendous losses in life and property.Statistical analyses of the historical records of tropical cyclones are crucial to the risk assessment of TCs.However, current historical records of TCs are out of the requirement of a refined risk assessment in coastal area.In this study, the climatic properties (including annual frequency, location, path movement and intensity change, etc.) of TCs derived from the International Best-Track Archive for Climate Stewardship(IBTrACS) database have been analyzed, and a synthetic model of the TC tracks over Northwest Pacific has been developed.The model includes four parts:genesis model, movement model, lysis model and intensity model.The model is evaluated by comparing an ensemble of simulations to the historical records from the perspective of spatial track density, annual landfall rate and frequency distribution of maximum landfall wind speed.Results show that the model performs well according to a few of diagnostics, and the simulations and observations are statistically indistinguishable.Therefore, the model can be used to generate synthetic tropical cyclones for a refined risk assessment of TCs over Northwest Pacific, and can improve the reliability of cyclone risk disaster assessment.

Abstract:Extreme temperature events are one of the causes of climate risk, and they often exert severe impacts on human health and leave large socioeconomic damages.It is therefore vital to investigate the regional climate response to different global warming levels for highly sensitive area vulnerable to climate change.Based on the CORDEX-EAS experiments, this paper evaluates the projected changes of extremetemperature in Chengdu-Chongqing Economic Zone and its surrounding areas under 1.5 ℃ and 2.0 ℃ global warming levels (GWLs).Results show that at the two GWLs, the extreme high temperature indices show an obvious upward trend, and the extreme low temperature indices show a downward trend in Chengdu-Chongqing Economic Zone and its surrounding areas.Extreme cold and warm events have the characteristics of local symmetry, and the change amplitude of extreme warm events is greater than that of extreme cold events.The responses ofextreme temperature indices to the two GWLs are different.Except for daily temperature range, variation ranges of other indices are greater at 2.0 ℃ GWL than those at 1.5 ℃ GWL.In addition, the intensity and frequency of extreme temperature events will increase in a warmer future, indicating that the extreme temperature events are highly sensitivity to the additional 0.5 ℃ warming (from 1.5 ℃ to 2.0 ℃).This paper comprehensively investigates the future evolution of extreme temperature in Chengdu-Chongqing Economic Zone and its surrounding areas under 1.5 ℃ and 2.0 ℃ GWLs, emphasizing the necessity of restricting mean global warming to less than 1.5 ℃.

Abstract:On the basis of NCEP/NCAR reanalysis data and daily surface climate data for China from 1965 to 2015, the finite-mixed-model-based clustering algorithms were utilized to group tracks of cold wave intrusion over China.A statistical analysis was conducted on the relationship between the active variation of the Eurasian teleconnection pattern (EU) and the frequency of cold waves in China.In addition, the pattern variation probably affects the selection of tracks of cold waves.According to the results, total cold waves had increased relatively, meridional circulation tended to be enhanced, and cold air moved southward;this typical circulation pattern led to more times of total and strong cold waves events for Cluster-2 of north tracks during a positive EU winter.Contrary to this, in the negative EU phase, zonal circulation had increased relatively with the advent of moist cold air, and there was a higher frequency of strong cold waves events within Cluster-3 and Cluster-4.

Abstract:Buoyancy frequency is an important concept in atmospheric dynamics.Based on NCEP/NCAR reanalysis data, the data of four times a day, daily average and monthly average are used as inputs to calculate, and the temporal and spatial changes of buoyancy frequency at different scales are analyzed.It is found that the spatial distribution of buoyancy frequency is related to latitude and altitude, ocean and land, mountains and terrain.It is generally believed that the buoyancy frequency depends on the temperature difference between the upper and lower layers.Through the deduction of its expression, it is pointed out that the buoyancy frequency is not only related to the temperature difference between the upper and lower layers, but also related to the temperature itself, which can be expressed as a nonlinear function of the two.The relative importance of air temperature and vertical temperature difference in the temporal and spatial variations of buoyancy frequency is studied by a statistical fitting method.Results show that for some temporal and spatial variations of the buoyancy frequency, the variation of air temperature itself is also very important in some areas, and its influence can even exceed the effect of temperature difference between the upper and lower layers.

Abstract:The radiosonde data is the most basic routine observation data in meteorological data assimilation and plays an important role in the effective improvement of assimilation analysis and forecast.Due to the low spatial resolution and uneven distribution of the existing radiosonde stations, only two observations per day and the small quantity, the accurate reproduction ability of their analysis field to the small and medium-sized atmospheric state is limited.After the L-band radar-digital radiosonde in our country has been updated, the radiosonde observation could obtain the atmospheric profile data 4 times a day with second-level and minute-level vertical resolution.In this paper, the WRF mesoscale numerical model is used to analyzethe sensitivity of intensive temporal radiosonde observationdata to the assimilation analysis and forecast quality through the effective assimilation of 06 UTC intensive radiosonde data and 12 UTC conventional radiosonde data.The results show that:the quality of afternoon rainstorm forecast by assimilating 06 UTC intensive radiosonde data is better than that of 12 UTC conventional radiosonde data.To be specific, the forecast skill of heavy rain and rainstorm by assimilating 06 UTC intensive radiosonde data are more accurate than by assimilating 12 UTC conventional radiosonde data.The root mean square error of prediction fields such as geopotential height, temperature and wind field is more effective at higher levels.The assimilation of the intensive radiosonde data at 06 UTC contributes more to the forecast quality of upper-level jet stream and lower-level water vapor flux divergence.Batch tests further confirm that assimilating 06 UTC intensive radiosonde data is of positive significance for both analysis fields and numerical forecasting.

Abstract:Based on the sea surface temperature (SST) from Hadley Center, the precipitation data of GPCP, NCEP-DOE reanalysis data, the variability of boreal spring south tropical Atlantic (STA) SST anomaly (SSTA) and its association with boreal summer precipitation in the Asian-Australian monsoon region are investigated by using statistical analysis methods.The results indicate a significant negative (positive) relationship between boreal spring STA SSTA and subsequent summer precipitation anomalies in the tropical western Pacific-South China Sea (the sea between eastern Australia and the tropical eastern Indian Ocean).The spring positive STA SSTA can cause an anomalous vertical circulation over the equatorial Atlantic and tropical Pacific.The anomalous descending and low-level divergence over the tropical central Pacific can generate anomalous easterly conditions in the tropical western Pacific, which can result in a negative SSTA in the tropical central eastern Pacific.In the tropical central and eastern Pacific, the SSTA can be enhanced by the Bjerknes positive feedback mechanism from boreal spring to summer.During boreal summer, two anomalous anticyclones are induced over the western Pacific as a result of the Rossby wave response to the negative SSTA in the tropical central eastern Pacific.The tropical western Pacific and South China Sea (seas to eastern Australia and tropical eastern Indian Ocean) are experiencing anomalous easterly winds in 850 hPa, resulting in less (more) precipitation for tropical west Pacific and South China Sea.

Abstract:Based on the monthly precipitation data of 1 767 stations in China, NOAA sea surface temperature data of Extended Reconstructed SST V3b and NCEP/NCAR atmospheric reanalysis data in recent 30 years, this paper studies the influence mechanism of Northeast Pacific sea surface temperature anomaly on the extreme drought event in Southwest China in summer (from June to August) 2011.Results show that the precipitation in Southwest China is extremely below normal in summer 2011.The regional average precipitation anomaly is -270 mm, less than negative twice standard deviations.The minimum area of negative precipitation anomaly is mainly located at the junction of Yunnan, Guizhou and Guangxi Provinces.In summer 2011, the extreme negative precipitation anomaly in Southwest China is closely related to the negative phase of Northeast Pacific SSTA dipole (NEPD), which presents the negative SSTA in the tropical Northeast Pacific [5°—20°N, 90°—120°W] and the positive SSTA in the mid-latitude North Pacific [37°—45°N, 150°—170°W].The negative phase of NEPD event causes anomalous easterlies in the lower troposphere over the tropical central and eastern Pacific, causes the positive geopotential height anomaly in the Far East by triggering the propagation of the quasi-stationary Rossby wave train from west to east, and weakens the western Pacific subtropical high, which is not conducive to the transportation of warm and humid air from the southwest to Southwest China.Meanwhile, Southwest China is controlled by abnormal downdraft with the lower tropospheric divergence and upper tropospheric convergence.The above conditions together cause the extreme negative anomaly of summer precipitation in Southwest China in 2011.

Abstract:Besides the well-known AMO (Atlantic Multidecadal Oscillation) with a period of 70 years in North Atlantic, longterm climatic records such as Central England Temperature (CET) and net snow accumulation from Greenland ice core also show a distinctive 20-year oscillation. The counterclockwise rotational mode of SST dipole in subpolar North Atlantic is obtained based on extended empirical orthogonal function (EEOF) method with 10-50-year bandpassed SST from piControl simulation of Community Climate System Model version 4 (CCSM4). The rotational mode of SST dipole shows quasi-20-year period which is consistent with the period of the surface air temperature (SAT) over England and Greenland. It may be possible to infer that the rotational mode of SST dipole with 20-year period can affect the climatic variability in the vicinity. The realtionship is verified by the sensitive experiments with the community atmosphere model version 4 (CAM4) which is forced by the rotational mode of SST dipole with quasi-20-year period.

Abstract:The microphysical characteristics observation test of advection fog was carried out in Tianjin in the winter of 2016/2017.Combined with the droplet spectrum at a height of 66 m above the ground and the atmospheric boundary layer data of 255 m meteorological tower, the development stages of two consecutive advection fog processes after heavy haze were objectively divided by means of change-point detection and trend consistency nonparametric test, which reveals the observation facts of droplet microphysical characteristics and size distribution characteristics at a certain height in the fog, and discusses the evolution law of its generation and disappearance.The results show that with the southwest warm and humid advection, the saturated layer first appears in the air and extends to the ground.During the fog process, the temperature rises within the observation height range in the mature stage, and the fog layer is in a neutral or weakly unstable stratification state.At the height of 66 m, large fog droplets persist, and the microphysical characteristics change quasi synchronously with the ground visibility.The high value of number concentration appears in the early stage of maturity, while the high value of water content and characteristic diameter appears in the late stage of maturity, corresponding to the decrease of fog droplet number concentration and a small jump in ground visibility in the late stage of maturity.In the dissipation stage, the number concentration of each size decreases synchronously due to droplet evaporation.

Abstract:Based on the monthly sea surface temperature (SST) data derived from HadISST, this paper studied the tropical Indo-Pacific SST modes and their combination modes.Results show that the negative precipitation anomalies appear in the eastern tropical Indian Ocean and maritime continent and the Walker circulation weakens over Indo-Pacific region during the eastern Pacific (EP) and symmetric central Pacific (CPⅠ) El Niño developing years, which results in the surface easterly anomalies off Java-Sumatra.Under the Bjerknes feedback, the abnormal easterlies lead to negative SST anomalies off Java-Sumatra, which is favorable for the formation of positive Indian Ocean Dipole (IOD) events.But, the asymmetric central Pacific El Niño events (CPⅡ) are not related to the IOD events.The relationship between SST modes and their combination modes over Indo-Pacific region and autumn precipitation anomalies in southern China were further investigated by the composite analysis method.Results show that during the developing years of single EP El Niño, single CPⅠ El Niño, combination of EP El Niño and positive IOD (PIOD), and combination of CPⅠ El Niño and PIOD, the autumn precipitation anomaly in southeastern China is positive due to the effect of warm and moist air from equatorial Indian Ocean and tropical Pacific.Under the Indo-Pacific SST modes, the moisture related to positive autumn precipitation anomaly in southeastern China is contributed by zonal transport from west to east, except the EP＆PIOD modes.During the EP＆PIOD developing years, the western Pacific subtropical high (WPSH) further extends westward, which results in the moisture transport northward into southeastern China along the southwest boundary of WPSH, therefore, the moisture related to the positive autumn precipitation anomaly in southeastern China is contributed by meridional transport.The negative autumn precipitation anomaly appears in southern China during the CPⅡ El Niño developing years.In addition, the positive (negative) autumn precipitation anomaly occurs in southwestern (southeastern) China during the single PIOD developing years.