Abstract:The two important modes of standardized wintertime zonal-mean zonal wind in Northern extratropics are extracted using the method of empirical orthogonal function (EOF).The leading mode (explaining 34% of the variance)is characterized by anomalous westerly (easterly) in high-middle latitudes and anomalous easterly (westerly) in mid-latitudes,and the antiphase variations of SLP anomalies between polar regions and high-middle latitudes.The leading mode is Arctic Oscillation (AO).The second mode defined as sub-tropical oscillation (STO) (explaining 21% of the variance) emerges as anomalous westerly (easterly) in mid-latitude regions and easterly (westerly) in middle-low latitude regions and shows opposite variations of SLP anomalies between sub-polar regions and sub-tropics.The spatial structure of STO is studied.The results indicate that STO shows a prominent zonally symmetric structure in the horizontal and a quasi-barotropic structure in the vertical.The zonal-mean temperature field associated with a positive phase of STO shows negative anomalies in high-middle latitudes and positive anomalies in sub-tropics,and the enhanced Ferrel moves equator-ward.We still concluded that STO can both be found in winter or the whole winter half year,but not in the summer half year.

Abstract:A scheme of Fourier analysis for tropically climatological wind field (V) is put forward.850hPa tropically climatological wind field (V) is investigated from 30°S to 30°N in January,the results show that is characterized by low dimension and low order;the first nine wave components (|m|=0,4) fit 92.4% of modular square.The most important wave component V₀ (m=0),which fits 56.4% modular square of,characterizes the configuration of mean zonal trade winds.The stationary wave (V^*),fitting 43.6% modular square of,is also low-dimensional and low-order;the first eight wave components (|m|=1,4) of which the stationary wave wind field (V₄^*) consists,fit 82.6% of V^* modular square.The similar coefficient between V₄^* and the original stationary wave field (V^*) is 0.909,so that the V₄^* describes the major circulation systems of V^*.Therefore,Fourier analysis is very effective method to investigate the tropically climatological wind field.

Abstract:This paper carries out a numerical experiment on a flash-flood-producing rainstorm process from 3 to 5 September 2004 in Sichuan province,using NCEP/NCAR data and regional observational data as the background field.Because of the good precipitation simulation,the model outputs are used to analyze the non-linear convective symmetric instability of the storm.The results show that joint action of conditional instability and topographic forcing on the near-surface layer triggered the convection,then conditional symmetric instability at middle and high levels further promotes the convection.This process produced the vigorously developed deep moist convection and resulted in such a heavy and long-lasting rainstorm.

Abstract:The climatorological and anomalous features of the intraseasonal oscillation (ISO) in the Pacific domain have been investigated using the NMC (National Meteorological Center) sea surface temperature (SST),winds at 10m and monthly mixed layer depth (mld) from 1981 through to 2002.Three centers of strong ISO in the SST are detected in the Pacific.The center of SST ISO in the eastern equatorial Pacific can be detected in all the year,however,the other two centers in the northwest and the southwest Pacific respectively are season-dependent.In the summer hemisphere,the intensity of ISO seems much stronger than that in the winter hemisphere.These three strong ISO regions are closely related to the variations of the oceanic mld.The thinner the mld,the more active the ISO.This suggests that the ISO in the Pacific involves the ocean dynamical processes.On the other hand,the SVD1 mode of the SST and the winds at 10m above the ocean surface shows that the ISO is coupled with the surface air motion through a negative feedback between the atmosphere and the Ocean,and exists in the sea area where the mld is thinner.Which explains the existence of SST intraseasonal oscillation in the North Pacific.

Abstract:Based on the NCEP/NCAR monthly mean reanalysis data (1948-2005),four indexes are defined to describe the position,area and intensity characteristics of Siberian high (SH).By analyzing the indexes,the features of the SH’s normal and anomalous variations are examined.The main conclusions are given as follows.The SH’s indexes had obvious interannual and interdecadal variations.In the past 58 years,the SH exhibited a temporal trend of weakning/shrinking and then fluctuatedly strengthening/expanding.Its position showed a latitudianal variation trend of westward withdrawing eastward advancing and westward withdrawing again after 1999.Besides,the SH slowly moved southwards.Anomalous variations of SH’S various indices had different variabilities:the intensity and area anomaly indices had 24yr and 14yr periods on interdecadal time scale,and 8yr and 4-6yr periods on interannual time scale.The longtitude and latitude indexs showed quasi-30yr and 12-14yr periods on interdecadal time scale,and furthermore,they had 3-6yr significant interannual variability.

Abstract:The relation between summer south and north branch rainbands over the Changjiang River basin and spring Pacific sea surface temperature (SST) is numerically investigated using the NCAR/CAM 3.0 global atmospheric circulation model.The results show that spring (MAM) SST anomaly in the eastern equatorial Pacific (EEP;5°S-5°N,150-90°W) has important impact on summer (JJA) precipitation over the two branch rainbands:when spring SST anomaly in the EEP is positive,summer rainfall of south branch rainband is deficit,and that of north branch raindand is not obvious affected;and when the spring SST anomaly is negative,summer rainfall of south branch rainband is excessive,and that of north branch rainband is deficit.Anomalous spring SST forcing can trigger teleconnection wavetrains in the troposphere of Northern Hemisphere,which affect summer precipitation of both south and north branch rainbands in the Changjiang River basin,but with more obvious influence on the precipitation of the former.

Abstract:Diagnostic analyses are carried out for the rainstorm from 2000 BST 5th to 0800 BST 12th July 2005 and WRF model is applied to simulate the precipitation process from 0800 BST 6th to 2000 BST 7th July 2005.Results show that: (1)The rainstorm process can be divided into two periods,nonlinear subcritical symmetric instability might be the main mechanism. (2)The strengthening of zonal disturbance wind component u and meridional v are respectively in advance of precipitation’s enhancement,and the peaks of u and v disturbances as well as peaks of ageostrophic intensity and cold or warm air’s peak indicate the precipitation peak which emerges after 12 or 24h. (3)The space-time allocation among peaks of upper jet,lower jet,upper disturbance wind,lower disturbance wind and precipitation is revealed. (4)It is depicted that at earlier stage of rainfall,space-time allocations relate among upper level vorticity,divergence and lower level vorticity,divergence.The new physical mechanism that nonlinear subcritical symmetric instability stimulates rainstorm is shown by the above 4 points and the situation of vertical upward current.

Abstract:In this paper,the numerical simulation and the diagnostic ananlysis of the structure and characteristic of spiral rain bands around the typhoon "Haitang" during the period of 19th to 20th July 2005 is carried out by using the WRF meso-scale model.The results are as follows.The coastal rain caused by this typhoon corresponds with the activity of the principal and secondary rain bands.The principal band caused by vortex Rossby waves is related well to the 850hPa positive vorticity band and has heavy rainfall.Its low level convergence lies in somewhere of the maximum gradient of temperature and azimuthal winds,however the convergence level of the secondary band is higher than the former.Its maximum gradients of temperature and equivalent potential temperature θ_e occur above 700hPa level without the coordination of the distinct gradient of azimuthal winds.It mainly corresponds with the ladder-shape frontal zone of θ_e near the center of the typhoon.The mergence of the two rain bands brings the strengthening of rainfall.During the period of the landing of Haitang,there exists the break of spiral rain bands.The divergence fields in the middle-low levels west and northwest of the typhoon center result in the strengthening of cyclonic streamline at higher levels.The cyclonic streamline at the high levels and the cyclonic flow of the low-pressure to the west of the typhoon merge into one,producing the mass convergence in this area,which splits the spiral rain bands.When the low pressure at higher levels produces the obvious cyclonic shear,which may also breaks down the spiral rain bands in the down-stream.

Abstract:Based on the soil temperature data collected at the soil site covered with broomcorn millet over the Loess plateau during the period from August 21 to 23,2005,we calculate the thermal diffusivity (2.950×10^-7～3.015×10^-7m²·s^-1) and the liquid water flux density (1.738×10^-6～2.197×10^-6m³·s^-1·m^-2) via the method of coupled thermal conduction and convection transfer at the depths 0.05m to 0.1m in this area.The soil temperatures are therefore modeled by using the method of coupled thermal conduction and convection transfer,as well as the traditional method of thermal conduction alone.The result shows the latter overestimates both the amplitude (0.42K) and phase shift (0.1407 rad) of soil temperature,and the covariances of two schemes are 2.99 and 2.14,respectively,because it does not consider the soil water vertical movement,while the covariance of the former is 2.13,which makes a reasonable estimate of soil temperature.

Abstract:The rainfall distributive characteristics of strong tropical storm Bilis (2006) after the landfall and its possible formation mechanism are analyzed based on the NCEP/NCAR 1°×1° grid reanalysis data,the TBB data from FY-2C,and the precipitation data at 740 observational stations in China.The main results are as follows: (1)The strong precipitation centers of Bilis lay in the Northwest side of its surface center during its landfalling,and the heavy rain mainly occurred in Fujian and Zhejiang province;and after the landfall,those centers shifted to the West side and latter to the southwest side of Bilis’ surface center,and the heavy rain occurred in the Northeast of Guangdong Province,Fujian Province,Jiangxi Province,and the South of Hunan Province. (2)The stable and motionless Northwest Pacific subtropical high provided a stable large scale circulation background field for Bilis’ persistent precipitation during its westward movement over land. (3)The development and strengthening of the Southwest monsoon to the Southwest of Bilis greatly enhanced the moisture transfer to Bilis’ precipitation areas. (4)The interaction between storm vortex and meso-and small-scale vortices,which were resulted from the mergence of vortices and self-excitation,might be the possible formation mechanism for Bilis’ strong precipitation after its landfall.

Abstract:In this paper,the far distant rainstorm of Typhoon Matsa in Shandong Province on August 5,2005 was analyzed.Based on several factors leading to the rainstorm far distant from the typhoon,relations were first analyzed between the strong rainstorm process and the westerly systems,and the rainstorm’s type was judged.The concept of removal entropy index (I_RE) was introduced on the basis of the theory of dissipative structure.Afterward the association of removal entropy index and the rainstorm in Shandong Province on August 5,2005 was analyzed.The results are as follows:the rainstorm was caused by the interaction between a westerly trough and the far distant typhoon (0509;Matsa);the non-zonal SE high-level jet and the SE low-level jet played an important role in this rainstorm process and the negative entropy change (I_RE <0) corresponded to the large-scale heavy rain,and the rain location of far distant rainstorm was consistent with the confluence of negative entropy change areas.The removal entropy index is able to provide very useful information for the forecasting of far distant typhoon rainstorm.

Abstract:Baesd on Palmer drought index,a flood/drought index series from 1951 to 1996 in the Tianmu Mountain area was established,and this dynamic index can reflect the persistent character of floods/droughts.The tree α-cellulose δ¹³C time series from 1835 to 1997 was obtained based on cross-dating tree rings age from the Tianmu Mountain,Zhejiang Province.After removing the long-term decrease trend,which is related to atmospheric CO₂ concentration of the δ¹³C series,we analyzed the correlation between the δ¹³C and the flood/drought index of different periods.The results suggest that both the same year and the next year tree ring δ¹³C are distinctly related with the spring and summer drought indices,showing that the δ¹³C better responsed to the spring and summer flood/drought.Based this better correlation and using the multiple regression method,we reconstructed the historical spring and summer flood/drought index from 1835 to 1996.The reconstructed series shows obvious decadal variability,and thus provides a reliable reference for the local climatic change study.

Abstract:Based on the 711-digital weather radar data in Weibei area of Shaanxi Province between May and September from 2000 to 2006,335 cases of mesoscale convective systems (MCS) were classified into three categories (cell,linear and areal MCS) and nine sub-categories (slightly moving cell,moving cell,merging cell,trailing stratiform (TS),leading stratiform (LS),parallel stratiform (PS),broken linear,broken areal and embedded areal MCS).The primary characteristics including frequency,diurnal variation,duration,horizontal scale and moving speed of echo,of each category were also statistically analyzed in this paper.In particular,differences in hail disasters (hail occurrence and damage) among MCSs of different categories were analyzed.The results show that the linear MCS has a maximum probability for hails,and the cell MCS possesses a minimum probability;and the TS MCS tends to bring about severest weather disaster,and the slightly moving cell MCS produces lightest disaster.

Abstract:By using the daily precipitation data of 81 stations in Northeast China during 1959-2004,we analyze the spatial and temporal distribution characteristics and variations of annual rainfall,precipitation-concentration degree (PCD) and precipitation-concentration period (PCP).The result shows that there is a close positive correlation between annual PCD and annual rainfall over Northeast China,which indicates that Northeast China,especially the significant correlation areas,are vulnerable to floods in excessive rainfall years.The average PCD of annual rainfall is quite big and the average PCP is later.Viewing from the long-term change,PCD,PCP and annual rainfall all display a decreasing trend,but they have obvious regional differences in magnitude.Morlet wavelet analysis indicates that the periodic oscillations of annual rainfall,PCD and PCP are basically consistent with each other.

Abstract:The method of Z-I regression is used to estimate the rainfall in two cumulostratus precipitation processes in 2006.It is found changes of regression parameters A and b that there is heteroskedasticity in the Z-I relation due to its nonlinearity and instability,and the methods of weighted least square and best criterion function are proposed to slove this problem.Comparing analysis is performed among the methods of weighted least squares,ordinary least squares,robust least squares,best criterion function,and weighted best criterion function.The results show that the instability of heteroskedasticity is suppressed,and the absolute errors of radar rainfall estimation is minimized when the weighted best criterion function is used.

Abstract:Using the data set of monthly mean temperature and precipitation at 34 stations in Chongqing in 1959-2003,the utilizable precipitation was calculated based on the Takahashi’s evaporation equation.Then the main distributive patterns were analyzed using the EOF method and their variation characters were discussed.Finally the utilizable precipitation in future 10yr (2006-2015) were projected using the MGF-BP neural network multi-step prediction model in Chongqing District.The results show that the distributions of annual utilizable precipitation may be divided into four kinds of distributive patterns roughly,namely entire region pattern,west-east pattern,north-south pattern and central pattern,among them the entire region pattern is the primary distributive one.Each distributive pattern has remarkably interdecadal variations.The utilizable precipitation may decrease when temperature is higher and precipitation is less;and vice versa.The preliminary projection indicates that the utilizable precipitation may be overally less from 2006 to 2011,but more from 2012 to 2015.

Abstract:The ECMWF and NCEP reanalysis data are compared of monthly mean temperatures in lower stratosphere using Lorenz circulation decomposition.The results are given as follow:in DJF and JJA,the zonal mean temperature of 30°S～30°N is a cold band at 100hPa.In this area,the climatological temperature normals of ECMWF reanalysis are lower than those of NCEP reanalysis significantly,and the interannual variances of ECMWF reanalysis are smaller than the ones of NCEP reanalysis.Several high and low centers in midlatitudes reveal some shortcomings in NCEP temperature stationary waves.But the thermal anomaly of NCEP reanalysis is superior to ECMWF reanalysis,because ECMWF reanalysis fails to capture the marked warming in stratosphere (100hPa and 10hPa) after three strong volcanic eruptions.

Abstract:The TREC (tracking radar echoes by correlation) method is used to estimate the TREC wind on CAPPI (constant altitude plan position indicating).The horizontal storm streamline field on CAPPI is first estimated from single radar observation data at two successive observation times,and then the motion direction of the whole echo field is extrapolated.The case experiments of typhoon,rainstorm,and boundary clear air echoes are performed,and the results suggest that the horizontal structure of the meso-scale systems is better revealed,thus favorable to the nowcasting of meso-scale systems.Besides,in the boundary clear air echo experiment,the interference of large ground targets with TREC vectors can be controlled by adjusting the correlation coefficient threshold.

Abstract:In this paper,we consider a semilinear parabolic system,and deal with the blow-up estimates of the position solution with the Scaling method,Green fuction and Schauder estimates,yielding the upper and lower bounds of blow-up rates.Moreover we give the impacts of nonlinear reaction terms and boundary absorption terms on the blow-up estimates.

Abstract:We deal with the matrix equation A^TXA=D and establish the perturbation bounds by using the patitioned matrix and the properties of the matrix norms.The results can be used in numerical calculation in model updating.