Abstract:This paper retrieves and studies the three-dimensional wind fields of the heavy rain on 26th-27th June 2003 in the Huaihe river basin,using the volume scan data of the dual-Doppler radar located in Hefei and Maanshan cities.The meso-β-scale convective system(MβCS) and the meso-γ-scale system on the MβCS played important role in this heavy rainfall.The wind retrieval shows that the heavy rainfall was triggered and maintained by the meso-β-scale convergence line at the low-middle level,and the strong convergence and positive vorticity areas in the low-middle layer of the MβCS superposed over the surface intense rainfall centers.The three-dimensional kinematic structure model of the heavy rain is also given.

Abstract:Using the monthly mean data from GISST2.3b dataset and CMAP precipitation data from 1979 to 1999,the relationships between tropical SSTA of Indian Ocean and summer rainfall in southern China have been studied.By defining the pure Indian Ocean Dipole(IOD) index and pure Nino3 index,the results demonstrate that both IOD and the tropical middle Indian Ocean SSTA from Jun to August have significant positive correlations with summer rainfall in southern China.About 60% summer rainfall anomalies in southern China can be explained by the interannual variations of tropical Indian Ocean SSTA in May,which is a very useful clue to rainfall prediction.When the IOD index is positive(negative),summer rainfall increases(reduces) in southern China,due to the anomalous ascent(subsidence) and water vapor convergence(divergence) caused by tropical Indian Ocean SSTA.

Abstract:Using the NCEP/NCAR reanalysis data of 500hPa geopotential height during January 1948 to March 2005,the nonlinear characters of teleconnections of the general circulation during winters over the northern hemisphere are investigated in this paper by the means of EOF and Nonlinear Principal Component Analysis.It is concluded that the NLPCA is obvious superior to the EOF in abstracting the lower-dimensional structer in datasets when comparing the results of the two methods with the observational reality.Teleconnections of the general circulation during winters,especially EU and PNA over the northern hemisphere have the clear nonlinear structures.When the NLPC adopts the maximum and minimum values,EU and PNA don't show the complete antisymmetric responses both in spatial pattern and intensity.When the NLPC takes the minimum value,the pattern of EU locates west of the position when the NLPC takes the maximum value,and in particular the negative anomaly center over the central Eurasia has a stronger intensity than its counterpart-the positive anomaly center.And When the NLPC takes the positive value,the four anomalies of PNA are more concentrative than those of PNA when the NLPC takes the negative value;and the positive anomaly center over the extratropical Pacific Ocean and the negative anomaly center over North Pacific have a stronger intensity than their counterpart centers and locate east of their counterpart center positions.

Abstract:The characters of inter-annual and inter-decadal variations of summer precipitation over the mid-and low-reaches of Yangtze River have been statistically analyzed from 1951 to 2002.Results indicate that the 1960's and 1970's are dry-spells and the 1990's a wet-spell,and the 1980's is a transition period of drought alternating with flood.Drought and flood are determined by the polarities of the inter-annual and inter-decadal changes.On this basis,simultaneous temporal and time-lagged realtions of the composite latent heat and sensible heat flux anomalies with the atmospheric circulation anomalies on the inter-annual and inter-decadal scales are analyzed.Results show that the heat flux anomalous mode in the T and R areas in the preceding spring is a presage for the summer rain anomaly in the mid-and low-reaches of Yangtze River.

Abstract:The mesoscale structure and organization of a stratiform cloud precipitation system occurring during April 4 to 5,2002,in Henan province are simulated by using nonhydrostatic mesoscale numerical model MM5(v3.5),and analysed by contrasting the simulated results with the observations.The results show that there were a low vortex at 850hPa and a low trough at 500hPa and 700hPa,and a cloud system formed and developed from 0800BST April 4 to 2000BST April 5,and displayed inhomogeneous structual character.The simulation results show the rain cores' appearing,growing,and disappearing within the cloud bodies of columned structure on 10-100km horizontal scale in the cloud system,where ice crystals form in the upper layer,ice phase particles and supercooled water coexist in the middle layer,and liquid water as well as strongest ascending airflow dominates in the low layer.Snow and graupel contribute most to rain's forming.The simulated results also reveal the key impacts of the mesoβ low vortex at 850 hPa and the vapor transportation on the rain cores.

Abstract:Based on the Arctic sea ice concentration data and the NCEP/NCAR reanalysis data,the contemporaneous relationship of the winter sea ice in the sea of Okhotsk and its adjacent sea areas with the northern Pacific storm track is investigated by statistical analysis methods.It is found that the anomalous sea ice area over the southwest part of the sea of Okhotsk,together with the associated northern Pacific SST anomaly,can exert crucial influence on the variability in the vigor and NW-SE extension(contraction) of the Pacific storm track,while the sea ice area anomalies over the area of northeastern part of the sea of Okhotsk and the gulf of Shelikhow,together with its associated North Pacific SSTA,mainly impact the strength and south-north movement of the storm track.

Abstract:In this study,the variation characteristics of extreme drought and flood events during the past 500 years were analyzed using the early-summer dryness indices series reconstructed by tree ring width chronologies of Huashan Pine sampled at the Huashan Mountain.Comparisons between the dryness indices and the Palmer indices show that the dryness indices could be used to figure out the drought and flood events in the central Shaanxi plain.There were 18 extreme droughts and 11 extreme floods events in early-summer detected in this area during the past 500 years.Most of the events could be found in the historical documents,except that a flood event was detected from the dryness index but a drought event was recorded in the historical documents in A.D.1521.There are also four events which have no corresponding records in the historical documents in A.D.1513,1574,1675 and 1945,respectively.Nine continuous drought periods and ten continuous flood periods are significant in the past 500 years.The drought and flood events occurred with high frequency in the sixteenth and the nineteenth centuries,but were less in the seventeenth and eighteenth centuries.The drought events are obvious more than the flood events in the twentieth century.

Abstract:Chinese meteorological satellite FY-1D acquires global data through four spectral channels which include visible and infrared channels.2366 snow and ice samples,2024 cloud samples,1602 land samples and 1648 water body samples were selected randomly from arctic imageries.Land,water and some clouds can be detected by spectral features.Snow-ice and cloud can be further classified by a Bayes classifier based on textural features.By synthesizing five days class result of arctic snow and ice cover area,we can get complete arctic snow and ice cover area.The result agrees with the NOAA/NESDIS IMS products up to 70%.

Abstract:Using the summertime(JJA) sea surface temperature from GISST data and the wind at 850hPa from the NCEP/NCAR reanalysis data during 1958 to 1999,we analyse the air-sea interactions over the Indian Ocean with the SVD method.Our results demonstrate that the two leading SVD modes explain large parts of the Indian Ocean-atmosphere coupled variabilities.The first mode(SVD1) displays the one-year-lag response of the Indian Ocean to El Nino in Pacific.However,the second mode(SVD2) exhibits the air-sea coupled phenomenon characterized with a dipolar pattern in Indian Ocean.We also discuss the relationships of these two modes(SVD1 and SVD2) with the summertime climate variations in China.The negative correlations have been observed between the mono-polar mode in the Indian Ocean SSTA and the summertime rainfall in southern China,while the positive correlations have been observed between the SVD1 and the rainfall in Changjiang River region.The correlation of the dipolar SSTA in the Indian Ocean as resprented by SVD2 and the rainfall of China is not evident.

Abstract:The analytic solution to the evolution of the axisymmetric vortex in a weakly secondary shear ambient flow is obtained using the Green's function method.The result indicates:when the weakly secondary shear grows(decays),the maximum value of the perturbation kinetic energy also grows(decays),and the change of the energy accelerates(slows).The range of the vortex also has impact on the perturbation kinetic energy and its change rate.

Abstract:Currently,wind retrieval with Single-Doppler radar data is still a difficult issue,and the retrieved wind is in low quality and difficult to apply.This is due to the low quality of radar data itself and the deficiency of retrieval methods.Based on a newly developed retrieval method Extended-VAP,several quality control methods including extremal check,spatial continuity check and temporal consistency check were developed and applied to the retrieval of wind field.Results show that most of the points which contain obvious errors could be corrected,the modified field seems more reasonable and consistent with Dual-Doppler radar retrieved field,and therefore the quality is much improved.However how to determine a proper correction threshold and extra model-related procedure needs further investigation.

Abstract:With diabatic heating completely considered and based on a primitive equation,derived are an expression of modified ageostrophic wet Q-vector(Q^q) and the ageostrophic ω equation with the Q^q divergence as a forcing term.The modified ageostrophic wet Q-vector is then applied to diagnoses a heavy rain event.The results show that:the ability of simultaneously reflecting precipitation of Q^q is enhanced significantly in contrast to Yue Caijun's modified wet Q-vector(QM),original ageostrophic wet Qvector(Q^*) and ageostrophic Q-vector(Q^#);throughout the Meiyu front rainstorm process,the convergence intensity and center of 500 hPa Q^q divergence field are good indicators for the intensity and location of precipitation;and the vertical distribution of Q^q reveals the direction and intensity of the secondary circulation,and the heavy rain may occur around the uprising leg of the secondary circulation.

Abstract:Based on the monthly mean temperature and precipitation data of 155 stations covering 1961-1999 in eastern and northern China,and using the Thornthwaite formula,the water requirement and the moisture index in study area are calculated in this paper.The-20 and 0 moisture index isolines are defined as the front and back boundaries of monsoon's boundary zone.The boundaries' interdecadal positions and their fluctuations are also analyzed,and results show that in the 39 years,the motion of the monsoon's boundaries in the east of China has an obvious regional character,and the fluctuation of the back boundary also has a conspicuous interdecadal variability.The interdecadal variation characteristics of rainfall in the study area are analyzed too,and it is found that the trends of precipitation in the three subareas,i.e.the east of Northwest China,North China,and Northeast China,are generally in agreement with the respective trends of the boundary fluctuations of monsoon.

Abstract:A new diagnostic quantity-moisture helicity is derived from the moisture equation,and the difinition of helicity,and its influence factors are analyzed in details by the dimensional analysis.The simulated results by the numerical model MM5 of the rainstorm process on 4th to 5th July 2003 are diagnostically analyzed,and results show that the moisture helicity is well correlated.Both the helicity flux divergence and the humid helical divergence have indication for heavy rain,and the former has better indicating effect for both the location and intensity of heavy rainfall,while the latter is only better correclated with the intensity of heavy rainfall.

Abstract:The water vapour flux,apparent heat source(Q₁) and apparent moist sink(Q₂) of a severe rainstorm in South China during 17th-21st July were calculated and analyzed by using the NCEP/NCAR global reanalysis grid data(4 times perday) and their vertical structures were studied.The results show that the moisture and latent heat were closely related to the heavy rain event.The Bay of Bengal,South China Sea and West Pacific were the water vapour sources in the rainstorm process.During this process,the water vapor came in mostly from the southern boundary and went out from the northern boundary of the heavy rainfall region.The inflows of water vapor of the southern and the eastern boundaries happen principally in the lower layer,and that of the western boundary in the lower and middle layers.The higher value regions of Q1and Q2 basically corresponded with the heavy rainfall region.The variances of the Q₁,Q₂ and vertical velocity were well in agreement with the evolution of the precipitation.The peak value of Q₁ located at 400hPa,and that of Q₂ respectively at 700hPa and 450hPa.The vertical advection term was the main contributor of the Q₁ and Q₂.

Abstract:The index for identifing the hail clouds was obtained based on the data fitting of heights of 45dBZ radar echo and the monthly averaged heights of zero-temperature level for 231 convective clouds in 165 days from 1991 to 2003 at Baoji radar observation.The index is defined that if the height of 45dBZ echo of a developing convective cloud at 0800BST ≥ 2.9km of monthly averaged zero-temperature level height,then the hail will occur.The analysis of radar echoes of hail-bearing clouds show that the higher the base of 45dBZ radar echo,the earlier the hail clouds can be identified,and the higher the top of 45dBZ radar echo,the sooner the hail occurs.The formation of hails generally started in the middle part of hail cloud,supper cell,and multi-cell,and then extended upwards and downwards.With the proposed index,the averaged early time indentification is 12 minutes for hail clouds,and 18 minutes for supercell storms,and 22 minutes for multi-cell storms and supercell storms of squall lines.Those times will be helpful for preparation of hail suppression operation.

Abstract:Temporal and spatial distributions and its geographical causes of the heat index at 125 stations in Yunnan From 1971-2003 were analyzed by the PCA method,statistic analysis and the non-integer technique of power spectrum.The results show that(1)the barrier and passage effects of longitudinal range-gorge break the law of zonal distribution of air temperature in Yunnan,the law of longitudinal distribution of air temperature is obvious and the spatial distribution is very zonally asymmetry;(2)under the effect of longitudinal range-gorge,the distributive pattern of thermal resources in Yunnan is that heat resources are abundant in the south area of Yunnan,deficient in the north area,more abundant in the west area than the east area,with the most abundant in the river valley regions and the poorest in the northwest area and mountain areas;(3)heat resources are the most abundant in June and July each year in Yunnan,the poorest in January,and in-between in spring and autumn with the former's greater than the latter's;(4)Yunnan annual mean temperature has obviously increasing trend with obvious 7a,11a,18a and weak 3a,5a periodic oscillations during the past 30-year;(5)the PCA1 of annual mean air temperature in Yunnan shows the same change trend over the most areas but the PCA2 displays opposite trends in the east and west areas,respectively.

Abstract:Based on the temperature data at 20 stations in Ningxia in 1961-2004 and the NCEP/NCAR monthly global reanalysis data in the same period,trends of temperature in the recent 44 years in Ningxia are analyzed,and the characters of background circulation fields for warm and cold periods and the circulation differences between typical warm and cold years are compositely analyzed in this paper.The analysis results show that since 1961,temperature in Ningxia has generally increased,with the 1960s being a colder period,and the 1990s being a rapid warming period.The seasonal temperature increased most in winter,but least in summer.The station number of high temperature has increased gradually since 1986,remarkably after 1998.On the other hand,the station number of low temperature were more from the 1960s to the mid 1980s.In the warm years,the Ural cold low was relatively weak,the main cold air in northern Asia located north of normal,the easterly flow dominated over Ningxia,and therefere Ningxia was in the positive temperature departure area;but in the cold years,the cold air from the polar region and the Baikal lake region was piled up in Mongolia,the westerly wind over Ningxia was clearly strengthened,and Ningxia was in the bottom area of the negative departure of temperature.

Abstract:The conception of the natural process of aridity is put forward in this paper.The "natural process of aridity(NPA)" is defined as the relative precipitation-deficit period between two consecutive continuous precipitation processes with its accumulative rainfall equal to 25mm or more in May to September,and the aridity index(AI) is then synthetically defined by the duration of a NPA and the ratio of precipitation to evaporation in the NPA and its early stage of 60 days immediately preceding the NPA.The ensemble of aridity prediction models for four station points in Zhenjiang were established using the stepwise regression,and their predictions are integrated by optimal weights.Computed AIs agree well with the historical documents of droughts,and the forecasts of aridity made using the ensemble of aridity prediction models in 2000-2004 are all correct.

Abstract:Orbit error is a very important error source of water vapor sounding used in GPS.In order to deal with the orbit interpolation in realtime water vapor sounding.The orbit errors effect on water vapor sounding is analysed and the feasibility of precisely predicting ephemeris using Neville algorithm is studied.It is shown that the Neville algorithm can meet precisely predicted ephemeris interpolation on near real-time and lay a foundation for water vapor sounding.