Abstract:By using the mesoscale numerical model of WRF,this study compared and analysed Morrison and Milbrandt-Yau two-moment microphysical schemes by using them to numerically simulate a heavy rainfall in Liaoning Province on July 20-21,2010.The purpose was to compare their simulation capability and difference in microphysical process by analysing surface cumulative precipitation,rainfall intensity and raindrop cloud microphysical quantity.The results showed that in terms of the simulation capability of rain belt location and the number of strong precipitation centers,Morrison performed better than Milbrandt-Yau scheme.However,in terms of the simulation capability of the center of heavy rainfall intensity,Milbrandt-Yau scheme was superior to Morrison.Their diffiences in macro characteristics of strong precipitation reflected,to some extent,the differences in microphysical characteristics they described.Compared with MY scheme,MOR scheme simulated a higher vertical water vapor flux than that of MY scheme,which enhanced the snow sublimation growth and touch growth.It brought the high content of snow and the low content of ice crystals in MOR scheme,which produced a large amount of graupel through rime attachment of ice ctystals.The attachment process consumed much could water and made the cloud droplets(cold water) decrease.The raindrop diameter remained 1mm from 600 hPa to the surface in Morrison scheme,which was obviously inconsistent with the reality.So it needs further improvement.

Abstract:To evaluate the effect of various schemes on rainstorm forecast in summer in Hubei and its surrounding areas,eight microphysical schemes and six cumulus parameterization schemes of WRFV3.6 are used to forecast 12 rainstorm cases.The results show that the prediction effects of different schemes are not the same on different scales.For the eight microphysical schemes (Lin,WSM6,Thompson,Morrison 2-mom,CAM5.1,WDM5,WDM6 and NSSL 2-mom) and KF cumulus parameterization scheme,combined with TS scores,anomaly correlation coefficient(ACC) and root mean square error(RMSE),it can be concluded that CAM5.1 is better than others,followed by Morrison 2-mom.Under the condition of CAM5.1,the sensitivity test results of six cumulus parameterization schemes (KF,BMJ,GD,SAS,G3D and Tiedtke) indicate that the six schemes both have advantages and disadvantages in the precipitation prediction of different magnitudes.GD,SAS and Tiedtke are better than the other through synthetical consideration.On these bases,the ensemble forecasting experiments are carried out by the ensemble mean (EMN).The results show that the method can reduce the forecast error and the uncertainty of individual member forecasts.

Abstract:On the assumption that the topographic correlation function is approximately equal to the terrain height function,the constant analytical solutions of the mesoscale motion under the influence of some typical terrains are obtained by using an analytical method,and the movement of airflow is discussed correspondingly.The main conclusions are as follows:The airflow does not present any fluctuation on the windward side of the terrain,and jet streams and rotors cannot form in the lower terrain.For the terrains with a certain height(depth),when the Froude number F_r>1/π,the atmospheric fluctuation only occurs near the terrain,the low-level streamlines are close to the terrain,and the strength of fluctuation decreases with the increase of the height;when 1/π>F_r>1/(2π),the fluctuation not only occurs near the terrain,but also on its leeward side.The wave length depends only on the background field,rather than the horizontal scale of the terrain,and the fluctuation decreases gradually with the increase of the height;when F_r<1/(2π),a jet stream forms in the middle atmosphere of the leeward side of the terrain,then it divides into two branches,one locates in the upper atmosphere and the other locates in the lower atmosphere,and they finally converge in the middle atmosphere;rotors appear on one or both sides of the jet stream.There is a sharp increase in the disturbance due to a discontinuity in the singular value F_r=(nπ)^-1.

Abstract:Based on the OLR (outgoing longwave radiation) data from NOAA and the NECP/NCAR reanalysis data along with CMAP precipitation data,using composite analysis and other methods,this paper has investigated the interdecadal change in relations of convective activities between the tropical Northwest Pacific(10°-20°N,125°-140°E) and the tropical Southeast India ocean(5°-15°S,90°-105°E).The results demonstrate that there are significant interdecadal variations in relations of convective activities between the tropical Northwest Pacific and the tropical Southeast Indian Ocean,with a significant positive correlation period from 1980s to 1990s,and a significant negative correlation period from 1990s to early twenty-first century,and another positive correlation period after 2004.When the convective activities in the tropical Northwest Pacific and the tropical Southeast Indian Ocean are positively correlated,there are two anti-cyclonic circulations over the two regions,which lead to weak convective activities and negative precipitation anomalies in the two places.When the convective activities in the tropical Northwest Pacific and the tropical Southeast Indian Ocean are negatively correlated,the distinctly different circulation anomalies are observed in the two regions.Accordingly,during the negative correlation period,the positive sea temperature anomalies are found in the tropical Southeast Indian Ocean,where the upper level divergence and lower level convergence facilitate the anomalous strong convection activities and more than normal precipitation.This scenario is opposite in the tropical Northwest Pacific.The slanted vertical circulation between the tropical Northwest Pacific and the tropical Southeast Indian Ocean connects the two regions,which induces the negative correlation between convection activities over the two regions.

Abstract:In this research study,historical SST data provided by the Japan Meteorological Agency and Hadley Center,along with NCEP/NCAR reanalysis data,and the ten-day precipitation data in Jiangnan (25°-28°N,110°-120°E;112 stations),were used to examine the relationship between the yearly precipitation in Jiangnan from April to June(Jiangnan rainy season(JRS),also referred to as the first flood period in South China) and the preceding heat content anomalies over the western Pacific Ocean warm pool.Next,the possible mechanism for this relationship was investigated.In this study,consideration was given to the depth of the lower boundary of the thermocline,and the mean temperature in the 0 to 400 m range was defined as the value of the heat content in the upper level of the ocean.Due to the interdecadal increases in the SST,the linear trends of the calculated heat content and precipitation during the Jiangnan rainy season(JRS) were removed,and only the interannual relationship was discussed.Furthermore,the statistical methods which were used in this study included time-delay correlations,regression,and synthetic analyses.The results showed that the precipitation levels during the Jiangnan rainy seasons were negatively related to the heat content anomalies over the warm pool of the western Pacific Ocean.It was found that the heat content over the key areas (3.5°-11.5°N,130.5°-150.5°E) during the months of July and August could be regarded as a good precursor of the winter rainfall.The preceding heat content was found to have important influences on the precipitation and circulation from the month of April until the following June.During the cold years,it was been observed to be negative over northern Pacific Ocean and positive over the western Pacific Ocean warm pool at 500 hPa,which has been referred to as the anti-WP teleconnection waves or the enhancement of the subtropical highs.These are controlled by the anomalous anticyclone activities around the Philippines,and the anomalous cyclone activities at high latitudes over the western Pacific Ocean at the 850 hPa wind field,with distributions of significant anomalous anticyclonic water vapor flux around the Philippines.The anomalous anticyclone activities over the Phillipines tend to intensify the western extensions of the subtropical highs,which subsequently strengthen the transportation of the warm and wet water vapor flow from the west side of the anticyclone regions to Jiangnan.Also,with the divergences in the upper troposphere,the anomalous convective rising motions become enhanced in Jiangnan,and vice versa.These enhancement trends indicate that the precipitation which occurs during the Jiangnan rainy season will be more(less) during the cold(warm) years.In regard to the mechanism,the strong westerly anomalies to the south of the key areas during the previous summer will result in the development of anomalous anticyclone activities in the Philippines during the late autumn months,and cold(warm) SSTs to the west(east) of the key areas.Up until the month of April,the upwelling of the subsurface cold water will sustain the cold SSTA and enhance the anticyclone activities,which continuously transports water vapor to Jiangnan.Meanwhile,the anomalous zonal vertical circulations tend to become enhanced in the tropical Indian Ocean with the development of warm SSTs in the western Indian Ocean,and easterly anomalies in the Equatorial regions.Then,the sinking branch in the western Pacific Ocean sustains the anomalous anticyclone activities,which further induces the water vapor convergence and rising motions in Jiangnan.Moreover,the upper strong divergences which are induced by the southward movements of the subtropical westerly jet stream also favor the increasing convective rising motions in Jiangnan.Therefore,the above-mentioned processes lead to increased (lower) rainfall levels during the Jiangnan rainy season,which are known to be related to the preceding negative (positive) heat content anomalies over the key areas.

Abstract:In this study,based on site data for the Tibetan Plateau(TP) and the south of the Yangtze River Region during the period of 1980-2015,and by utilizing EOF,wavelet analysis and other statistical methods,the sensible heat fluxes over the TP and its subareas in April were calculated and analyzed.In addition,the precipitation in the south of the Yangtze River Region was also analyzed,and its correlations with sensible heat flux were determined.It was observed that sensible heat flux over the Himalayan Region,the sensible heat flux over the crucial district which can be defined as Tibet Plateau sensible heat index(TPSHI),can be treated as a precursor for the summer precipitation in the south of the Yangtze River Region.The exception is that sensible heat flux over the TP in April and summer precipitation in the south of the Yangtze River Region shows the same 4a primary period and 8a secondary period,with the turning point being around 1998 and 2011.Favorable negative correlations exist between the sensible heat over the TP,area E,area G in April and precipitation in the south of the Yangtze River Region in summer,especially in area E,due to the negative correlation of sensible heat over the TP and areas E and G in April related to precipitation in the south of the Yangtze River Region in summer.This signifies that when the sensible heat flux is weaker in April,the south of the Yangtze River Region will undergo drastic precipitation in summer.However,when the sensible heat flux is strong,the opposite will be true.When the sensible heat flux over the critical area is weak,the south of the Yangtze River Region is in front of the deep trough(850 hPa).With the shear line system,the baroclinicity is very strong and the relative humidity is very high,which jointly contribute to the precipitation.If the opposite is true,it will not be conducive to precipitation.

Abstract:Based on the Advanced Research Weather Research and Forecast(ARW-WRF) model simulations with the grid size of 2 km,the development mechanism of the convective cells in spiral rainbands and the inner rainbands in super Typhoon Chanchu(2006) was examined.Results show that the WRF model can well reproduce the track and intensity of the typhoon.Development mechanism of inner rainbands that exist only on the lateral side of the eye wall is not related with the gravity waves,the vortex Rossby waves and the mixed Rossby-Gravity Waves,and it may be only associated with the low-level radial outflow,the horizontal wind field and the deformation wind field.The convective cells of inner rainbands are advected radially outward by the low-level radial outflows and deformed into spiral shapes by the low-level horizontal and deformation wind fields.In terms of the development mechanism of fine convective cells in the spiral rainbands,they acquire vertical vorticity through the tilting of horizontal vorticity and the stretching of vertical vorticity based on the quantitative analysis of vorticity budget equation.With advection transport,the convective cells in different spiral rainbands are merged and converged near the eye wall.

Abstract:In this study,the accuracies of the final products of Integrated Multi-satellite Retrievals for Global Precipitation Measurement(GPM)(IMERG),from September 2014 to August 2015 over mainland China(MLC),are evaluated through the quantitative and classification scoring methods using the China Gauge-Based Daily Precipitation Analysis(CGDPA) products,developed by the National Meteorological Information Center.The results are as follows:1)The IMERG can display the spatial distribution characteristics of the precipitation over MLC with relatively high accuracy,although the accuracy is lower than that obtained by the CGDPA over some areas.The spatial distribution of the IMERG seasonally averaged precipitation has a rather high consistency with that obtained by the CGDPA,especially over the central,eastern and southern parts of MLC.2)The correlation coefficients retrieved by the daily precipitation of the IMERG and CGDPA range between 0.2 and 0.5 over most areas of MLC,except for a small number of areas where they exceed 0.6,and are even negative over some areas.3)Although the accuracies of the IMERG over eastern part of MLC are significantly higher than those over the west,the daily precipitation estimation of the IMERG is as much as 10%-30% lower than the daily precipitation of the CGDPA over the east.4)The largest difference of the probability density between the IMERG and CGDPA is small-amount precipitation,followed by moderate rain,while the differences between the two in the other precipitation intensities are very minor.5)None of probabilities of detections(PODs) of precipitation events for the IMERG in any of the four seasons are significantly high,while the false alarm ratios(FARs) are relatively high.In addition,the critical success indexes(CSIs) are relatively low.

Abstract:A Meiyu front torrential rain event occurred over the middle and lower reaches of the Yangtze River on 26-28 June 2015.The organization modes and initiation conditions of Mesoscale Convective Systems(MCS) are analyzed by using the conventional meteorological observation data,the dense surface automatic meteorological stations data,Doppler weather radar data and the simulated data from WRF(Weather Research and Forecast) model.The results are as follows:(1)many types of organization modes are found in the development of the linear MCS.Constantly back building of the east-west oriented rainbands and subsequent echo-training of convective cells are the main development modes of the MCS in the initial stage.The convection cells develop in the direction of NE-SW and form several short parallel convective rainbands in a nearly NE-SW direction in the mature stage.Two scales of convective organization modes are found:one is northeastward echo-training of new convective cells along individual rainbands,and the other is eastward band-training of the NE-SW oriented short rainbands along the linear MCS.(2)The continuous enhancement of low-level jet provides the conditional instability and convective available potential energy for the generation and development of convections.The southerly warm and moist air is lifted to the level of free convection,releasing the unstable energy and triggering convection at the convergence of wind speed.(3)The consistent interactions between the cold outflow of convective cells and the low-level southwest warm and moist air are favorable for the generation and development of new cells,maintaining the rainbands.

Abstract:In this study,the anomalies of summer precipitation in China,and the atmospheric circulation over East Asia,were compared during the spring(SP) and summer(SU) El Niño developing and decaying years,in order to improve the understanding of the relationship between the El Niño events and climate anomalies in China,and to provide references for climate predictions.The percentages of the precipitation anomalies in China;horizontal wind anomalies at 850 hPa;geopotential height anomalies at 500 hPa;velocity potential anomalies;and divergent wind anomalies at 850 hPa and 200 hPa,respectively,were also analyzed.This study utilized the monthly precipitation data of 160 stations in China for the period ranging from 1950 to 2016,which were provided by the National Climate Center of China Meteorological Administration.The monthly geopotential height,wind,and specific humidity data were provided by the American National Centers for Environmental Prediction.The Niño 3.4 index data were provided by the American Climate Prediction Center.
The results obtained in the study were as follows:
1) During the SP El Niño developing years,the majority of China experienced below-normal precipitation levels,and displayed a "higher northern-lower southern" rain trend during the decaying years.During the SU El Niño developing years,the precipitation anomalies were observed to be "sandwich" formations,in which the regions receiving more rain were larger during the decaying years;
2) It was determined that at 850 hPa during the SP El Niño developing years,the summer monsoons were strong,and had maintained strong levels up to the decaying years.However,during the SU El Niño developing years,the East Asian summer monsoon were observed to be weak,before turning stronger in the decaying years;
3) It was found in this study that at 500 hPa during the SP El Niño developing years,the influences of the East Asian summer monsoons on China's climate were weaker,and the warm and moist water from the low latitude regions was insufficient to become transported to the mainland China.However,during the decaying years,the warm and moist water from the low latitude regions was affected by the stronger summer monsoons,and was easily transported to the hinterland of China.During the SU El Niño developing years,having been affected by the relatively active cold air movements,it was observed that the Inner Mongolia and northern China regions had experienced above-normal rain levels.However,during the decaying years,having been affected by the strong summer monsoons,the cold and warm air had intersected north of the Yellow River;
4) This study's comparison results of the lower and upper levels of the troposphere revealed the following:During the SU El Niño developing years,there were sinking anomalies observed over China,with the exceptions of Inner Mongolia and Northeast China;During the decaying years,there were rising anomalies observed over China.During the SU El Niño developing years,there were significant subsidence anomalies observed over China,and during the decaying years,there were weaker subsidence anomalies evident.However,having been affected by stronger summer monsoons,the regions which had experienced below-normal precipitation became larger.

Abstract:Based on the daily ground observations in meteorological stations of Jilin Province during April-July 1997-2015,taking temperature,air pressure,relative humidity,water vapor pressure and wind speed as covariates,this paper established a statistical prediction model of daily precipitation based on self-organizing maps(SOM).This paper studied major synoptic patterns in Jilin Province and the relationship between daily precipitation and the patterns,and based on this relationship,proposed a Monte Carlo simulation method for daily precipitation.Results demonstrate that SOM has high classification quality of synoptic patterns,and the accumulative probability distributions of adjacent synoptic patterns are similar,while those of synoptic patterns far away are quite different.The correlation coefficient between the probability of no precipitation and the corresponding width of daily precipitation interval in the synoptic patterns is -0.94,and the significance level is less than 0.01.According to the accumulative probability distribution of precipitation,20 types of synoptic patterns are divided into four categories,which match the occurrence rate of precipitation and the daily precipitation.On this basis,this paper carried out Monte Carlo simulation of daily precipitation in 24 stations of Jilin Province,and analyzed the forecast performance.The median values of MAE(mean absolute error),RMSE(root mean square error),S_Brier and S_sig are 3.12 mm,6.13 mm,0.06 and 0.51,respectively,which indicates that the method has a good forecast performance in general.The distribution of MAE and RMSE is large in the southeast and small in the northwest,and all stations have smaller errors after removing the effect of the natural fluctuation of precipitation.S_Brier and S_sig have no obvious spatial distribution characteristics.

Abstract:This study analyzed the observational data;ECMWF Era-interim datasets;data of wind towers located along the Jiangsu coast line;assimilated precipitation data;sea/land breezes (SLB);and sea-breeze fronts (SBF) in the Jiangsu coastal regions,and the stimulating processes of the SBF for strong convections were numerically simulated.The results showed that the SBFs mainly appeared under high pressure systems,or in the edge parts of high-pressure systems where there were steady weather backgrounds.The SBFs were classified into two types as follows:The SBF Type I were located around the westward extending parts of subtropical highs over the sea;and the SBF Type Ⅱ were located under continental high-pressure systems entering the sea,in which their circulations usually had several more local systems and were accompanied by strong convective systems.The vertical cross-sections of the SBF events showed that the u-component of the east winds at low levels formed the frontal edges of the cold air masses from sea.This impacted the positions and intensities of the lifting motion of the SBF fronts.The secondary circulation of the SBF formed unstable environments.It was observed that when the SBF in coastal areas met the inland convective systems,it stimulated and enhanced the local convection.The data analyses of wind towers showed that the features of the time series of the SBF winds included sudden changes in wind directions and increases in wind speeds.The local systems' convective available potential energy (CAPE) showed that the meeting of the CAPE high value inland and SBF could potentially increase the local CAPE values.When a vapor convergence center was present,a local stimulating condition was built for the SBF acting on the convective systems.The numerical simulation showed that the horizontal distribution of the CAPE,and the release which met the SBF and strong convection inland.Meanwhile,the vertical profiles of the CAPE indicated the increase,release,and duration of the strong convection energy stimulated by the SBF.It was determined that the release action was fast,and the duration was approximately two hours.

Abstract:For the breeding of the growing mode (BGM),how to choose the scale-down factor in the process of dynamic propagation is very important because it is directly related to the forecast effect.Using the Weather Research and forecasting (WRF) meso-scale numerical prediction model,on the basis of analyzing the error growth mechanism of various physical quantities during the numerical simulation of the squall line system,this paper finds that almost all the physical quantity errors in the moist convection zone grows faster than in the other places,so it puts forward an improved Breeding of the Growing Mode that obtains an initial perturbation scheme based on spatial and temporal distributions of moist convection zone.The scheme adjusts the horizontal structure of small perturbation in the process of dynamic propagation,which reinforces the disturbance of moist convection zone,and it can capture the small perturbation on the direction of the fastest growing way.After that,the small perturbation can be used as the initial disturbance.Based on the results of multiple experiments with different perturbations,the following conclusions are obtained:Compared to the other schemes,the improved scheme,which makes the initial disturbance based on the amount of precipitation,has larger disturbance energy,each member in the ensemble system performances more differently,and the ensemble mean forecast has smaller error than the other schemes.The horizontal distribution and precipitation intensity of heavy precipitation are simulated by the improved scheme based on the amount of precipitation,showing that the method forecasts the heavy precipitation range well and its rainfall score of rainstorm is higher.Meanwhile,using the improved method,the forecasts of meridional and zonal wind profiles and water vapor field are closer to the observations,which improve the ensemble forecast effects.

Abstract:In this research study,ground-based GPS Perceptible Water Vapor(PWV) data,which was based on routine observational data,satellite images,and NECP 1°×1° reanalysis data,were used to examine a large-scale severe precipitation process which had occurred in Chengdu from September 23rd to 26th of 2008.It was found that the storm had been caused by a combination of cold air from the north,warm moist air from the Bay of Bengal,and the high and low torrents from a "Hagupit" typhoon.Prior to the rainstorm,the water vapor of the middle and lower troposphere was observed to be sufficient,and the atmospheric stratification was extremely unstable.In addition,vertical wind shear had been obvious.During the rainstorm period,the majority of the water vapor was concentrated in the 900 to 500 hPa layers,and was mainly composed of the warm wet air brought in by the southwest monsoons and cold air originating from a "Hagupit" typhoon in the South China Sea.The results of this study's comparison of the satellite cloud data indicated that the heavy ground precipitation center was not only related to the entire layer of the water vapor transmission center,but also had a close relationship with the water vapor transmission intensity.It was observed that the larger the water vapor flux was,the greater the precipitation would be.Meanwhile,the GPS-PWV was also found to be sensitive to the strength of the water vapor transmission.For example,when the water vapor had reached a baseline,the probability of precipitation was greater.Also,the longer the water vapor amount had been maintained at a high-value stage,the longer the duration of the precipitation and the stronger the intensity would be.It was also determined that the maximum amount of precipitation was not necessarily consistent with the time that the peak precipitation had been reached.However,it was observed that the heaviest rainfall had usually occurred when the precipitation was in the fastest rising stage.The results of this study indicated that before and after the rainstorm event,the precipitation could be divided into increasing and decreasing stages,respectively.Therefore,the high temporal resolution observations of the ground-based GPS were able obtain the rapidly changing information of the water vapor,along with certain indications of the occurrence time and strength of the rainstorm event.This type of information could potentially play an important role in the real-time monitoring of the occurrences and development of rainstorm events in the future,and also provide important references for the future construction of ground-based GPS stations in the Chengdu area.In this study,when the findings were combined with the results of the mesoscale numerical simulation WRF,it was found that the examined rainstorm event was more dependent on various dynamical and thermodynamic conditions than on the values of the PWV.Furthermore,the strength of the moisture convergence had played a crucial role in the examined rainstorm event.

Abstract:The area around the Taihu Lake is quick and sensitive in response to climate elements changes,such as temperature and precipitation with regard to complex and variable climate,special geographical location and landform morphology.Therefore the study in this area is profound and significant for explaining the local special climate changes and laying the foundations for the research about the impact of urbanization on the climate changes around the Taihu Lake area in the future.Based on the daily mean temperature and daily precipitation data of 9 meteorological stations around the Taihu Lake area from 1971 to 2010,the methods of linear regression,EOF analysis,Morlet wavelets analysis and Mann-Kendall Test were used in this paper to analyze the spatial and temporal pattern and characteristics of climate changes.The results are as follows:(1)During the period 1971-2010,the air temperature around the Taihu Lake area has been increasing in general,and the precipitation distribution had an increasing tendency in the northern part of the area and a reducing tendency in the southern part.There is a spatial difference of seasonal heating rate in the area around the Taihu lake area,the air temperature in the northwest area increased significantly in spring and summer,while there was a significantly heating rate in autumn and winter in the southeast area.Besides,there was a completely opposite spatial-distribution in heating rate around the year of 1990.In the whole area the precipitation was increasing generally in winter,the spatial precipitation distribution differs widely in spring and summer.(2)The annual mean temperature fluctuated significantly with an interval of 16 years or 17 years,and fluctuated with the intervals of 6 years and 26 years in the small scale of the whole area around the Taihu Lake area.The annual precipitation in the area fluctuated significantly with interval of 15 years or 16 years and 24 years.Whereas,there were some differences in intensity of the annual mean temperature fluctuation and the annual precipitation fluctuation in terms of different regions.(3)During the period 1992-1993,there was an abrupt climate change from low temperature to high temperature for all stations in this area.