Abstract:From January 10th to February 2nd, 2008, four rare low-temperature rain, snow and freezing weather events occurred consecutively in southern China.This disaster was characterized by a wide range, high intensity and long duration, thereby resulting in extremely serious economic losses and casualties.In addition, freezing rain, sleet, supercooled fog and other factors caused serious typical icing and secondary disasters, which in turn led to the lodging of electricity transmission and communication line towers, and interruption of power supply and communication and traffic transportation.Therefore, since 2009, the research team of this paper have carried out field experiments on wire icing and road icing, the results of which have progressed the research of wire icing from the traditional observation of icing meteorological conditions to a new highlight of comprehensive observation research regarding icing meteorological conditions and cloud and precipitation micro physics in icing weather events.The present paper reveals the micro physical mechanism of icing accretion, studies the icing accretion growth rate and its influencing factors, and establishes the icing accretion growth model, so as to better simulate the icing accretion growth process.Furthermore, observations on the temperature of the three underlying surfaces of asphalt, cement and soil and the temperature changes of different subgrade depths of expressways and bridges are carried out, and explanations are made from the perspective of energy balance.Based on the achievements of the research team, this paper studies and organizes the relevant representative research results, including the spatial and temporal distribution of ice accretion frequency, microphysical characteristics of icing weather, growth rate of ice and its influencing factors, meteorological conditions of icing, construction of ice growth model, and law of road icing growth and prediction, and proposes suggestions for the future research of wire icing.

Abstract:Based on the global Emergency Events Database (EM-DAT), using Mann-Kendall trend test method and Pettitt, Buishand and SNHT abrupt change test methods, this paper analyzed the trend and abrupt change characteristics of global and Chinese meteorological and hydrological disasters from 1990 to 2019.Results show that:1) The frequencies of global flood disasters and extreme temperature disasters increase significantly in recent 30 years.Global annual death toll caused by flood disasters shows a significant decreasing trend, while global annual economic loss caused by storm disasters shows a significant increasing trend.2) The annual frequencies of global extreme temperature disasters and flood disasters change abruptly in 1999.Since 2000, the average frequency of extreme temperature disasters and flood disasters is about twice that of the first 10 years (1990-1999).3) In the past 30 years, the frequency of flood disasters in China has changed from less to more around 1999, but the annual death toll displays an opposite transition around 1999.Compared with the world, the annual death toll caused by storm disasters and flood disasters in China has a more significant decreasing trend in recent 30 years.Similar to the world, the annual economic loss caused by storm disasters in China shows a long-term increasing trend, but the increasing trend is more significant.The abrupt change of economic loss caused by storm disasters in China occurs in 2012.

Abstract:In this study, a set of reconstructed black carbon (BC) data is used to analyze the relationship between BC over southern China (SC) and the South China Sea (SCS) summer monsoon (SCSSM) on the interannual time scale.An abrupt change of the relationship appears at around 2000.Before 2000, there is a negative correlation between them, namely larger BC concentration corresponding to weaker SCSSM, while positive correlation begins in 2000.By means of composite and contrast analyses, it is found that a major climate effect of BC over SC is attributed to the indirect radiative forcing during the first period (1988-1999):Namely, the reduced cloud particle radiuses related to BC over SC suppress the spring precipitation, yet increase the cloud lifetime, which decreases the amount of solar radiation, thus leading to a cooling at the surface and in the lower atmosphere.The negative air temperature anomalies excite an anomalous anticyclone with easterly anomalies over the SCS.In summer, the anomalous easterlies weaken the SCSSM and decrease the precipitation over the SCS.During the second period (2000-2010), the main BC climate effect is direct radiative forcing:The warmer atmosphere associated with the larger BC concentration enhances the spring precipitation, while decreasing the number of rain days, which in turn increases the amount of solar radiation, thus leading to a greater warming at the surface and in the lower atmosphere.The positive air temperature anomalies excite an anomalous cyclone with westerly anomalies over the SCS.In summer, the anomalous westerlies enhance the SCSSM and the precipitation over the SCS.

Abstract:In the present study, a new local breeding growth mode (LBGM) method is used to conduct convection-allowing ensemble prediction experiments regarding two typical squall line cases.Next, by comparing the results with the traditional breeding growth mode (BGM) method, the actual forecast effect of the LBGM is tested.The simulations of precipitation are performed using the probability-matched mean (PMM) method, then compared with the observational data.Finally, the fraction skill score (FSS) is used to replace the traditional equitable threat score (ETS), so as to reasonably evaluate the precipitation prediction.We obtained the following results:(1) The LBGM is observed to be superior to the BGM in the forecast of the precipitation in the squall line.(2) The FSS better represents the convection-allowing ensemble prediction capability better than ETS, particularly for extremely severe rain assessments.(3) The precipitation scoring results show that the EM is superior to the PMM method for light, moderate and heavy rainfall, whereas the PMM method is better for severe and extremely severe rainfall.

Abstract:Using the sounding data as a reference, taking the COSMIC occultation pressure from 1 January to 31 December 2014 as a GPS test sample, China was divided into four climate zones.The GPS occultation pressure was evaluated from the perspectives of double weight average, double weight standard deviation and correlation coefficient, and the quality control was carried out according to the statistical results.Results show that compared with the traditional method, the double weight average and the double weight standard deviation are less susceptible to abnormal data, and the evaluation resultsare more accurate.The differences of double weight average values of atmospheric pressure among the four climate zones are small.The doubleweight standard deviation is smaller in the subtropical monsoon climate zone (less than 6 hPa) and larger in the temperate monsoon climate zone (up to 15 hPa).With the sounding data as a reference, the statistics of atmospheric pressure deviation show that there is a positive deviation from the lower troposphereto the upper troposphere in the subtropical monsoon climate zone(about 0.8 hPa), and there are mostly negative deviation below 6 km and a positive deviation above 6 km in the other three climate zones (about 0.5 hPa).According to the statistics of correlation coefficient, the correlation coefficient is determined to be 0.80.According to the different statistical results in each climate zone, the threshold interval is divided.Quality control results show that the error points are mostly distributed in the areas where there is a big difference between GPS occultation pressure and sounding pressure.The percentage of error data produced by the two-step quality control is mostly less than 5%.Comparing the correlation coefficients between GPS occultation pressure and sounding pressure before and after quality control, it shows that the correlation between them is significantly improved after quality control.

Abstract:Based on the hourly temperature data derived from 48 708 surface automatic weather stations in China, the CLDAS-V2.0 temperature data in October 2017, January 2018, April 2018 and July 2018 (resolution:0.062 5°) were analyzed by using the evaluation indexes such as mean deviation (Bias), correlation coefficient, root mean square error (RMSE) and mean absolute error (MAE).This paper studied the correlation and deviation distribution characteristics between CLDAS and station temperature in spring, summer, autumn and winter in eight zones of China.Results show that:(1) CLDAS temperature reflects the interannual variation of temperature in China, and the average correlation coefficients of non-independence test, independence test and station temperature are 0.995 and 0.991 respectively.The correlation coefficient is the highest in Northeast China and the lowest in Southwest China.(2) The Bias of CLDAS and station temperature is -0.011℃, RMSE and MAE of non-independence test are 1.275℃ and 1.645℃, and RMSE and MAE of independence test are 0.867℃ and 1.089℃, respectively.In general, CLDAS has small temperature error and high reliability.(3) The deviation in spring and autumn is less than that in summer and winter.The deviation in Northeast, North China, Jianghuai and South China is smaller than that in Northwest and Southwest China.In 84.6% stations, the cold deviation or warm deviation is within 1℃, and the spatial distribution of cold and warm deviation is uniform.(4) The maximum temperature of CLDAS has cold deviation, the minimum temperature has warm deviation, and the maximum deviation of maximum temperature in summer is -0.59℃.(5) The diurnal variation of mean deviation of CLDAS is -0.23-0.07℃, colder in the daytime and warmer in the night.The diurnal variation of mean deviation of CLDAS is significant in summer, and the diurnal range of deviation is 0.26℃.The maximum diurnal variation of summer mean deviation in the eight zones of China is 1.06℃, and the variation ranges in autumn, winter and spring are similar.The diurnal variation of mean deviation is the largest in Southwest China and the smallest in Jianghuai.

Abstract:Based on the S-band dual polarization Doppler weather radar of Xuzhou and Nanjing, the single polarization radar of Suqian and Huaian, and the reanalysis data, the paper analyzes the circulation background, instability mechanismdynamic, uplift conditions, radar echo and the evolution characteristics of dual polarization radar parameters and the wind inversion technology of dual radar of a wide range hailstorm process accompanied by a thunderstorm and short-term excessive rainfall occurred in Jiangsu Xuzhou, Suqian, Huaian, Nanjing and Changzhou on July 6, 2019.The results show that a wide range of strong convective weather occurredwhen the cold vortex falling on high level and horizontal trough swing south, the trough line swept across Jiangsu from north to south before midnight on the 6th, the lower layer warm and humid air flow moved northward, under the background of strong unstable circulation on upper and lower layers, and the low pressure slowly moved eastward and the South pressure provided the convergence and uplift conditions.Generally, the intensity of radar echo is over 50 dBZ and the echo top is always above 10 km in this procedure.Additionally, it appears that there are significant Three Body Scattering Spikes, cyclonic convergence and storm top divergence.A hail storm can be identified by its polarization parameters (such as the Z_DR, CC, K_DP).Hail storm usually exist in the area with strong reflectivity、low value of Z_DR, and CC.The typical value of Z_DR is usually between -1.0 and 0.2 and the value of CC is less than 0.85.Additionally, Z_DR and K_DP columns help identify hail, thunderstorms, and short-term heavy rainfall.The characteristics of the two polarization parameters above can be used for the prediction of strong convection and hail recognition.As a result of study of the hail period using double radar wind inversion technology, a noticeable downdraft is found.In the three-dimensional flow field structure of the hailstorm supercell, the cyclonic air flow forms at the front of the storm, and then gradually inclines to the top of the storm to form the anticyclonic air flow, which forms the downdraft;in the weakening stage of the system, there is a strong downdraft, strong echo bottom and ground.Due to dual radar's ability to retrieve fine structure of three-dimensional wind, it is possible to deepen the understanding of hailstorm cloud structure and improve the prediction and early warning capability of severe convective weather, such as hailstorms.

Abstract:In order to study the modulation effect of large-scale background field on the relationship between ENSO and Indian summer monsoon precipitation, and to better predict the interannual variation of Indian summer monsoon precipitation under the climate warming background, this paper studies the relationship between ENSO and Indian summer monsoon precipitation in the past 500 years based on ten sets of reconstructed ENSO indices and Indian precipitation data, the reasons for its existence and how to understand this phenomenon.This paper mainly focuses on the influence of ENSO on Indian summer monsoon.Results show that, firstly, the relationship between ENSO and Indian summer monsoon precipitation is not immutable in the past 500 years (1470-1999), generally shows a negative correlation.The negative correlation is weak during Little Ice Age (LIA) and strengthened during Current Warm Period (CWP), but begins to weaken after the 1980s.Secondly, the relationship between Indian summer monsoon precipitation anomaly and ENSO in the past 500 years is certain, not random.Thirdly, the relationship between the Indian summer monsoon precipitation anomaly and the amplitude and cycle of Niño indices are very different during LIA and CWP.The amplitude and cycle of ENSO during CWP are significantly larger than those during LIA, which leads to a stronger negative correlation between Indian summer monsoon and ENSO during CWP.But the average states of the two periods are almost same.

Abstract:Based on the observed precipitation data from 312 stations in Southwest China, NCEP/NCAR reanalysis data and sea surface temperature data from 1961 to 2018, the summer SPI (Standardized Precipitation Index) index was used to study the variation characteristics of summer drought in Southwest China and its relationship with circulation anomalies.Results indicate that Southwest China has a drying trend in summer, especially in Yunnan and southeast Sichuan.In the typical dry summers, Southwest China is characterized by the lower troposphere divergence and upper troposphere convergence, and the water vapor transport to the area is less.The reason of drought maintenance in Southwest China can be attributed to the abnormal atmospheric wave activity and the abnormal sea surface temperature forcing.The former disperses energy downstream through the disturbance of the westerly zone, which provides the necessary disturbance energy accumulation for the formation and maintenance of the circulation anomalies of lower troposphere divergence and upper troposphere convergence in Southwest China.The latter forces the atmosphere through anomalous heat sources in the tropical Northwest Pacific, causing the lower (upper) troposphere in the region to form an abnormal convergence (divergence), and an oblique vertical circulation to be formed in Southwest China and the tropical Northwest Pacific, which makes Southwest China controlled by the sinking airflow, thus forming conditions conducive to the occurrence and maintenance of significantly less precipitation and drought.These results are helpful to understand the formation mechanism of drought in Southwest China and provide useful clues for prediction.

Abstract:Using ERA-Interim reanalysis data from 1980 to 2000, this study calculates the Eliassen-Palm (EP) flux and its divergence of the planetary wave in the Northern Hemisphere winter (December-February).In the following sections, this study examines the characteristics of decadal changes in stratospheric temperature and zonal wind, as well as changes in planetary wave activity during different winter months.The results show that the changes for decadal temperature show a significant warming trend in the high-latitude mid-to-lower stratospheres in December, followed by a weak cooling trend in January, and an apparent cooling trend in February.Zones of significant deceleration in the mid-to-high latitude stratosphere in December deceleration and acceleration weak intensities in January, and significant acceleration in February, are alternately distributed in the stratosphere every month.Planetary waves propagating into the tropopause along with the low-latitude waveguide weaken in December, while those propagating along with the polar waveguide into the stratosphere strengthen.During January, both propagations along two waveguides are unchanged, but their intensities are declining.As for February, it turns into an evident strengthened tendency along the low-latitude waveguide and a noticeable weakened tendency along with the polar waveguide.In addition, December and February remain transitional months for EP flux divergence, while January is decadal.Therefore, the annual decadal changes of Arctic stratospheric temperature, zonal winds, and EP flux present an evolution from the NAM (Northern Hemisphere Annular Mode) index negative polarity tendency to positive polarity tendency throughout the winter.

Abstract:In this study, the performance of Coupled Model Intercomparison Project Phase 6 (CMIP6) models in simulating the temperature extremes, including the annual maximum of daily maximum temperature (TXx) and annual minimum of daily minimum temperature (TNn) over the mid-high latitudes of Asia are comprehensively assessed, as are their future changes.The main findings are as follows:1) The observed spatial distributions of extreme temperatures that decreases from south to north and west to east over the mid-high latitude of Asia are reasonably reproduced by most CMIP6 models, but the cold bias is still obvious over the Tibetan Plateau.Additionally, the higher skill is generally observed for the climate mean simulation of TNn rather than TXx, while a relatively higher skill is for the TXx of the trend simulation.The multimodel ensemble mean (MME) generally outperforms the individual models.2) The results of future projection indicate that both TXx and TNn show a significant increasing trend in the 21st century, but the increase in magnitude of TNn is shown to be much greater than that of TXx.Under the SSP5-8.5 scenario, both TXx and TNn are projected to increase by approximately 7.0℃ and 9.6℃ by the end of the 21st century, with respect to the current state (1995-2014).The projection uncertainty is estimated to increase with time and scenarios, and the increase of TXx shows a higher model agreement.

Abstract:Using the ERA-Interim reanalysis database and the tropical cyclone (TC) best-track dataset from both China Meteorological Administration (CMA) and Joint Typhoon Warning Center (JTWC) during the period of 1979-2017, this study analyzes the relationship between Intraseasonal Oscillation (ISO) of East Asian upper-level (200 hPa) zonal wind and the interannual variation in the frequency of tropical cyclone landfall over mainland China during boreal summer.
The TC frequencies of landfall in July-August present a significant interannual variation.In addition, an East Asian Westerly Jet Index (EAWJI), which represents the meridional migration of the westerlies, is defined based on the two regions where significant correlations exist between TC landfall frequencies and 200 hPa zonal wind.The EAWJI and TC landfall exhibit a significant negative correlation.That signifies that when a negative (positive) anomaly appears, westerlies appear in the northern (southern) position, and the TC landfall frequency may increase (decrease).When the westerly jet moves to the north, the troposphere in the TC active region presents anomalous easterly winds, thereby resulting in abnormal easterly shear, which is conducive to maintaining the TC landfall process and increasing the frequency of TC landfall in mainland China.
The high similarity in both standard deviation and EOF modes regarding the East Asian upper-level zonal wind's ISO variation and interannual variation indicates that they are governed by a common mode of spatial variability.This signifies that the asymmetric frequency of north (south) conditions would generate residual deviations and alter the seasonal mean.In Landfall High-Frequency years, ISO-filtered EAWJI exhibits a higher frequency of north conditions, which cause the convergence of ISO-scale transient eddy flux in the south of the westerly jet exit, and lead the westerly jet to drift northward.Therefore, by modulating the large-scale circulation which affects the process of TC landfall, the ISO of the 200 hPa zonal wind can be indirectly connected with the interannual variation of the TC landfall frequency.

Abstract:In the present study, a heavy precipitation process of the Yangtze Valley River Basin during the period of 30 June to 4 July 2016 is simulated by using a Weather Forecast modeling system. The effects of the microphysics schemes are dividedinto two groups of nine single-moment and seven double-moment schemes. Next, using the time series of observational precipitation to simulate single-moment and double-moment schemes, FY-2G and Cloudsat cloud product were also used to evaluate the simulation different microphysics schemes of the cloud macroscale and microscale characteristics, such as total cloud fraction and vertical struction of the cloud fraction and cloud water content in the precipitation process. The results revealedthe following:the simulation of different microphysics schemes can present the rain belt position and central rainfall intensity of the process, yet the simulation of the cloud macroscale and microscale characteristics are significantly different. With the exception of the Kessler scheme by the warm cloud scheme of single-moment scheme, in which, due to the insufficient description of the ice cloud process causing the simulation of total cloud fraction to be significantly higher, all of the other single-moment and double-parameter schemes can simulate the temporal and spatial evolution characteristics of the total cloud cover during the heavy precipitation process. From the vertical distribution characteristics of cloud coverage and cloud water content, the simulation stability of the group of single-moment schemes to the middle and low level warm clouds below 600 hPa are slightly better than the group of the double-moment schemes. In addition, the simulation results of the ice cloud between 200-500 hPa were reversed, and the group of double-moment schemes was more concentrated than the single-moment group. The comparison of the simulation cloud fraction of each layer with the Cloudsat cloud product showed that for the low level warm cloud precipitation process using the WSM3 scheme of single-moment scheme the cloud fraction is closer to the observation than the double-moment schemes. However, the deep convection process which took the cold cloud precipitation process as the main movement characteristics, when using the WDM5 or WDM6 scheme of double-moment schemes, the high cloud fraction is more stable and the error is smaller.

Abstract:Based on the hourly observation data of black carbon (BC) and ozone (O₃) at Nanjing ground station from 2016 to 2017, the relationship between BC and near surface O₃ in different seasons was analyzed.Results shows that the O₃ value under the influence of high BC (higher than average) is significantly lower than that under the influence of low BC (lower than average).The inhibition effect is obviously stronger in autumn and winter than in spring and summer, and the negative correlation between BC and O₃ is significantly higher in autumn and winter than in spring and summer, while the negative correlation between PM_2.5 and O₃ is not significant.Based on the WRF-Chem model, the numerical simulations of BC feedback effect on O₃ are carried out for the cases in December 2017, and the results confirm that BC has negative feedback effect on O₃.The influencing mechanisms are as follows:BC can reduce the photochemical production of ozone (VOCs control area) by inhibiting the development of boundary layer and accumulating NO_x near the ground;BC can reduce the downward turbulent transport of high O₃ in the upper part of the boundary layer by suppressing the vertical turbulent exchange in the boundary layer, so as to reduce O₃ near the ground;BC can reduce the advection input of O₃ from upwind region by reducing the near ground wind speed, so as to reduce the ground O₃.The main control factors of the cases are different and should be analyzed in detail.

Abstract:Soil moisture is an important parameter of ecological environment and an important part of water cycle.The retrieval of surface soil moisture based on multi-source remote sensing data is a hotspot and trend in recent years.As a new generation of Sentinel satellites, the Sentinel-1 SAR data combined with the Sentinel-2 optical data have broad application prospects.Taking Salamanca, Spain as the research area, a BP neural network soil moisture retrieval model is constructed by combining the Sentinel-1 backscatter coefficient and incidence angle information, the vegetation index extracted from the Sentinel-2 optical data, and the ground observation data, and the model is applied to retrieve the soil moisture in the area.Finally, the model retrieval results are tested and evaluated.Results show that:(1) Based on the Sentinel-1 satellite VV and VH polarization radar backscatter coefficients and radar incidence angles and the Sentinel-2 vegetation index data, the BP neural network soil moisture retrieval model can realize high-precision retrieval of soil moisture in Salamanca area;(2) In the joint retrieval of soil moisture of optical and microwave data in vegetation coveragearea, the NDVI, NDWI1 and NDWI2 indices from the Sentinel-2 can be used to weaken the influence of vegetation on soil moisture retrieval, but the NDWI1 based on SWRI1 band can obtain more accurate soil moisture retrieval results (RMSE=0.049 cm³/cm³, ubRMSE=0.048 cm³/cm³, Bias=0.008 cm³/cm³, r=0.681);(3) Comparing with the Sentinel-1 VH polarization model, the Sentinel-1 VV polarization model shows greater advantages in soil moisture, indicating that the Sentinel-1 VV polarization model is more suitable for soil moisture retrieval.