Abstract:This paper presents a Fourier analysis scheme on a sequence of monthly anomalous wind {V'(t)} in the tropical field. The analysis of tropical(30°S-30°N) {V'(t)} at 850 hPa in January from 1948 to 2005 shows that:1)Module square of steady wave abnormalities S'^* is much larger than that of the trade wind abnormalities[S']. It is significantly different from the spectral structure of module square S of climatological wind, which is mainly about the trade wind. 2){V'(t)} is characterized by low dimension and low order. The first 13 wave components(|m|=0, 6) fit 87.2% of {V'(t)} module square. 3)The module square of all-terrain abnormal steady wave S'_|m|^*decreases with the increase of|m|, and V'_|m|^*(|m|=1, 2) fit the 44.4% of S'^*, which is the most important component of {V'^*}. The accumulated module square fitting rate P'_|m|^*(φ) of abnormal steady wave varies with latitudes φ. The high value belt mainly lies from equator to 10°S and another locates in the region to the north of 20°N. 4)Module squares of {V'^*} in the entire domain and at φ latitude, and the sum of module squares of|m|=1, 2 have significant interannual variations;and they are closely related to the strong ENSO events since 1980s. Therefore, Fourier analysis method is very effective to study the spatial-temporal structure of the tropical anomalous wind fields.

Abstract:Seasonal surface air temperature(SAT) anomalies over China from 1951 to 2003 is investigated by applying a neural-network-based nonlinear principal component analysis(NLPCA) method. The results of the first NLPCA mode show that the seasonal SAT anomalies have some nonlinear characters;its nonlinearity is stronger in spring(MAM) and summer(JJA), and weaker in autumn(SON) and winter(DJF). The SAT approximation by 1-D NLPCA is closer to the observations than that by 1-D PCA.

Abstract:Based on the multiple-spectral data of NOAA satellite, the effective radius(r_e) of particles on the cloud tops was retrieved via the reflectance of channel centered at 3.7 μm, and the microphysical properties of clouds were displayed and analyzed by means of visualized RGB microphysical schemes. The satellite retrieval methodology proposed by Rosenfeld was used to mainly infer the microphysical properties and processes for different cumuli according to the temperature(T) versus r_e relations for different microphysical processes. The analyses show that the bases of continental cumuli in high and middle latitudes have the deep zone of condensation growth with much smaller effective radius and lower initial temperature of glaciation growth. Compared with the clouds in the high and middle latitudes, the cumuli in the low latitude near the island or the sea have larger effective radius, rather stronger coalescence and rather higher initial temperature of glaciation growth with the microphysical properties transiting from the continental to the maritime. The maritime cumuli have the largest effective radius in the cloud bases, higher initial temperature of glaciation growth and rather deep zone of precipitation formation among the three kinds of cumuli.

Abstract:A cold air index(CAI) is defined as the cold air activity days weighted with respect to the temperature and 24 h temperature change at 850 hPa over Austrilia. The intraseasonal and interannual features of Australian cold air activity are studied using CAI. Results show that the key region of cold air activity is located in the southwest of Australia in May, and its center and influence range display a gradual northward shift in July and August with the main activity region expanding towards the east part of Australia. Australian cold air activity has no obvious interannual difference over the whole winter(JJA), but it has distinct interannual variation in May, June, July and August, respectively.

Abstract:Using the dipole mode index(DMI), Nino3 index, and five East Asian summer monsoon(EASM) indices, the interdecadal variations of interannual relationships of East Asian summer monsoon(EASM) with Indian Ocean dipole(IOD) and ENSO are examined, respectively, in the present paper. There is appreciable positive correlation between EASM and IOD in the most of time-periods except the 1980s and the beginning of the 1990s. IOD and ENSO have opposite effects on EASM. When the correlation between IOD and EASM is strongly positive, the ENSO-EASM correlation is weaker. However, when the IOD-EASM correlation weakens in the end of the 1970s and early 1980s, the ENSO-EASM correlation is noticeable. The obvious difference of sea surface temperatures between the period of 1972-1982 and that of 1983-1993, may result in changes of the period and pattern of circulation in the air-sea interaction process, thus leading to the interdecadal variations of relationships of East Asian summer monsoon with IOD and ENSO.

Abstract:Based on NCEP/NCAR 1°×1°final analysis(FNL) data, we calculated the helicity of Typhoon Sepat, and analyzed the relations between the horizontal helicity at different vertical height levels and the temporal variation of storm rainfall, between the horizontal helicity and the location of storm rainfall, and between the temporal variation of vertical helicity with occurring and development of the strong storm rainfall. Results show that the 700 hPa helicity has a strongest power to portray the evolution of strong storm rainfall;the location of big positive helicity center and its neighborhood is consistent with the falling area of storm rainfall;the central strength of helicity in a region has a close relation with the rainfall strength there;if the horizontal helicity at high-and low-levels all changes from negative to positive, the storm rainfall will happen, and v. v.;using of horizontal helicity has more predictable time than that of vertical helicity, divergence or vertical velocity for the prediction of typhoon storm rainfall;using of vertical helicity has more advantages than that of horizontal helicity for the precipitation intensities variation of typhoon storm rainfall;if the vertical helicity is used to correct the typhoon storm rainfall predicted by horizontal helicity, it will help to improve the prediction accuracy rate of typhoon storm rainfall.

Abstract:In order to evaluate the characteristics and application value of meteorological data compiled by China Meteorological Administration(CMA data), the significance of differences in climatic averages and interannual variances of 100 hPa and 500 hPa geopotential height fields in July and sea level pressure field in January among CMA data and NCEP/NCAR, ECMWF reanalysis data sets are checked by using statistical methods respectively, with the interannual variability and correlations of the area and intensity indices of main active centers of the atmosphere compared in January and July in the Northern Hemisphere. Results show that:1)The climatic mean values of ECMWF 100 hPa and 500 hPa geopotential fields in July are all evidently smaller than those of CMA data, with their long term mean values smaller than 1 660 and 588 dagpm respectively, so that the ECMWF data are not adequate to study the South Asian high and the subtropical high. 2)The CMA data, which are directly read from the single level isobaric charts, are closer to observations in situ and more suited to diagnoses of pressure systems on the single isobaric level. 3)The interannual variabilities of the Mongolia high and the Aleutian low in winter are more consistent than those of the South Asian high and the subtropical high in summer among the three data sets.

Abstract:Based on the NCEP/NCAR daily reanalysis data, the onset dates of the South China Sea summer monsoon(SCSSM) and Indian summer monsoon(ISM) are investigated, in such a way that the great and small difference years are defined by using the difference of the two onset dates. Results show that the difference has obvious interannual variations. In the small difference years, when the SCSSM bursts, the westerly has prevailed over Indian Peninsula, and therefore the two summer monsoons burst almost synchroneously. However in the great difference years, the ISM bursts(i. e. the westerly is prevailing over Indian Peninsula) in about the seveth pentad after the onset of the SCSSM, so the onset of the ISM is much later than that of the SCSSM. The analysis on mechanisms of monsoon onset shows that ISM onset is mainly related with the turning of meridional temperature gradient, while SCSSM onset is associated with the turning of zonal temperature gradient;the two onset dates are relatively independent from each other. The zonal temperature gradient turning is more important for the differences of the two onset dates. The two temperature gradient turnings depend on the appearance of the intensive belt of accumulated temperature contours.

Abstract:Based on the NCEP/NCAR reanalysis data, outgoing long-wave radiation(OLR) data and precipitation observed by satellite and meteorological stations, the convective activity, general circulation and precipitation before and after South China Sea summer monsoon(SCSSM) onset of 2007 are analyzed. Results show that the convective heating first appears in the east coast of Bay of Bengal, then extending to South China Sea in 2007. Meanwhile, the subtropical high withdraws eastward and northward, and SCSSM breaks out in the last two dekads of May(the 29th pentad) in 2007. After the monsoon onset, South China Sea area is controlled by southwest air current, and the meridional temperature difference and wind shear reverse in Asian mid-low latitudes areas. During the SCSSM period of 2007, the enhancement of water vapor transportation and monsoon surge lead to the precipitation increase in eastern China.

Abstract:Weighted mean temperatures(WMT) of Zhangjiakou, Beijing and Xingtai are calculated by using different methods. Results indicate that there are some systematic errors in the WMTs of North China obtained using the common calculation methods. Based on the relationship between the WMT and local surface meteorological elements, single factor and multi-factor regression equations for WMT are developed, and these local regression equations are able to satisfy the requirements of real time use and high accuracy for the retrieval of precipitable water from ground-based GPS remote sensing data.

Abstract:The landfalling tropical cyclone precipitation(TCP) over East China was partitioned from the daily rainfall observations at 129 stations during 1954-2004 by the Objective Synoptic Analysis Technique and its advanced scheme. The climate characteristics of TCP were analyzed with variance analysis, trend coefficient and linear regression technique, followed by comparison with those of annal total rainfall in East China. Results show that the spatial distribution of TC rainfall is not uniform in East China with the highest rainfall occurring in southeast Fujian Province, and the decreasing feature of TCP from southeast to northwest is related with the terrain and other factors. The interannual oscillation of TCP volume is evident with marked 9-year and 15-year periods, and the inter-decadal variability of TCP is that the maximum occurred in the 1950s, and then decreased before the 1970s, which is 10 years earlier than the time in North China. The climate characteristic of total precipitation is greatly different from that of TCP. Thus it makes sense to extract TCP from total precipitation before making long-range precipitation prediction.

Abstract:The normalized sunshine hours, effective accumulative temperature and normalized precipitation are calculated by use of daily meteorological data, yields of winter wheat and physiological meteorological indicators of winter wheat of its growth period. Based on path analysis, the contribution ratios of sunshine, temperature and precipitation to winter wheat meteorological yield are calculated, respectively. The influence coefficients, which reflect the impact of dekadly sunshine hours, effective accumulative temperature and normalized precipitation on winter wheat yield, are obtained by means of integration regression method, thus a quantitative estimation model for meteorological factors' influences on winter wheat yield is established. The example analysis indicates that the above influence coefficients of meteorological factors, calculated by use of the path analysis and the integral regression, can precisely reflect the relationship between the growth course of winter wheat and the meteorological conditions. The evaluation model can quantitatively estimate the effects of meteorological factors on the yield of winter wheat in the entire growth period, so that it is of higher scientificity and accuracy. The technique lines of the quantitative evaluating of meteorological factors provides a favorable technique foundation for developing related operational service.

Abstract:Characteristics of rain belts and precipitation cores in a mixed stratiform and convective clouds system(MSCCS), which was affected by a low trough-cold front and a Jianghuai cyclone, are studied in this paper based on TRMM(the tropical rainfall measuring mission) satellite data. The results show that the cloud structure in different parts of the cold front was very inhomogeneous;the clouds can be sorted into three types, i. e. typical MSCCS, homogeneous stratus and weak MSCCS. In the typical MSCCS over the south of Henan there were many short echo band structures(embeded with many precipitation cores), with an average length about 63.0 km, a width about 19.4 km and an average rainfall rate of 14.54 mm/h. In the homogeneous stratus over the north of Henan, the precipitation rate ranged generally from 1 to 2 mm/h, with the stronger rate of 2 to 7 mm/h in some embeded rainbands, showing a clod-front rainband structure. In the weak MSCCS over the middle part of Henan, cold-front rainbands and warm-sector rainbands dominated, and the cold-front rainbands were embeded with many precipitation core structures. Meanwhile, the vertical profiles of precipitation rete show different charecters in cloud areas of different properties, i. e. short echo band, precipitation core and stratus areas.

Abstract:A severe rainstorm occurred in southwest part of Leizhou Peninsula for the period of August 8 to 11, 2007, with both daily and hourly rainfalls exceeding the maximum of historical observations. This paper analyzes the characteristics of total, daily and hourly rainfall, discussing the relationships of the heavy rain with paths of tropical cyclones "Pabuk" and "Wutip", weather pattern, variations of satellite cloud images and radar echo, respectively. The results show that this heavy rain is characteristic of high intensity, long duration, large amount and concentrative location. In the early stage, heavy rain occurred in Leizhou Peninsula on account of the effects of the "Pabuk" circulation and its outer region cloud system. In the subsequent stage after the early morning August 10 the track of "Pabuk" turned, the circulation adjusted, and the center of rainstorm sustained and swayed over southwest part of Leizhou Peninsula for a long period of time as a consequence of the interactions of the "Pabuk" circulation, the outer region cloud system and the cold vortex cloud clusters over the Beibu Gulf. Such a weather situation was in favor of the convergence of a huge amount of energy and water vapor, and the southern and northern convective cloud systems and radar echoes meeted in southwest part of Leizhou Peninsula, leading to a severe flood disaster.

Abstract:Based on the meteorological observations at Nanjing Meterological Observatory and other five suburban meteorological stations(Jiangpu, Luhe, Lishui, Jiangning and Gaochun) during 1961-2006, the climatological characteristics of fogs in Nanjing and their relationships with various meteorological parameters are analyzed. Results show that, depending on the topography and the nature of underlying surface, the occurrences of fog events at these six locations are different. The fog processes are more likely to happen at Lishui, Luhe and Nanjing than at other three places(Jiangpu, Jiangning and Gaochun) with the highest frequency of fogs(34.9 days annually) at Lishui. Fog events at six stations show the same seasonal characteristics with the maximum frequency in winter and autumn, the next in spring and the minimum in summer. It is also found that the annual fog days at Lishui, Gaochun and Jiangpu are increasing and an opposite tendency occures at Nanjing, Jiangning and Luhe. Results reveal that the fog events are more likely to occur under the conditions of weak surface wind, high humidity and weak high system.

Abstract:By the principal component analysis(PCA) and correlation analysis, it is found that the main information of Fujian spring precipitation in the last 40 years concentrates on the first two principal components, which account for 83.8% of the total variance. Meanwhile, the correlation coefficients between the first two principal components and the reconstructed spring precipitation of Fuzhou and Xiamen are both significant at a more than the 0.01 confidence level. Therefore, two new precipitation sequences can be constructed by using the sum/difference of Fuzhou and Xiamen rainfall in March and April in recent 100 years to represent the first/second components of Fujian spring precipitation, respectively, and the length of data can be extend to 100 years. Then the multi-time scale features of the reconstructed spring precipitation series are explored by the continuous and orthogonal wavelet analyses and the power spectrum. Results indicate that the first principal component corresponding to the sum serial denotes the drought/flood trend consistent over the whole province with marked quasi-4-year and 24-26-year periods;the second principal component corresponding to the difference serial describes the difference of spring precipitation between southern and morthern Fujian with quasi-2-year and quasi-11-year periods;and in spring drought years, precipitaton over the southern is less than that over the northern. The amount of spring rainfall was remarkably less than the normal in the 1950s-1960s but more in the 1980s. At present it is in the period of normal-less rainfall with less precipitation in the southern than in the northern.

Abstract:Land surface temperature(LST) of Nanjing was retrieved from the Advanced Spacebome Thermal and Emission and Reflection Radio meter(ASTER) data at 1030 BST 21 August 2002 with the split-window algorithm, and the retrieved results are compared with that from the synchronous MODIS data and the observations. Results show that:(1)The LST derived from ASTER is 0.9℃ higher than the observation, and its spatial distribution pattern is well consistent with that from the MODIS data;(2)On 21 August 2002, the retrieval LST from ASTER data is between 23℃ to 56℃ in Nanjing, and there are marked spatial differences in LSTs over different land surfaces;the LST of city is generally higher than 35℃ and little lower between 30℃ to 35℃ in the parks, but for Yangtze river water body it is lower than 30℃;(3)The urban heat island(UHI) effect is obvious in summer daytime in Nanjing, and the spatial distribution of UHI intensity is related to the development and planning of the city.

Abstract:Focusing on the detection of snow cover from the image data of Earth Observation System/Moderate Resolution Imaging Spectroradiometer(EOS/MODIS), this paper introduces a new classification model of remote sensing images based on Support Vector Machines(SVMs). Firstly, the feature extraction and selection are analyzed of snow cover detection process, then a new classification method is established for remote sensing images based on SVMs, and at last a snow cover detection experiment is performed to validate the model. The results suggest that the feature selection is effective for the snow cover detection, which also certifies the predominance of SVMs method in remote sensing image classification. The new method is worth to further popularize and apply.

Abstract:The computational principle of the Morlet wavelet power spectrum W(t, k) of a meteorological time-series p={P(t), t=1, n}is intuitively illuminated using the geometric analysis in phase space, and a scheme of Monte Carlo significance test for W(t, k) is presented in this paper, that is convenient and simple because the generation of the random series is unrelated to the theoretical distribution of the analyzed series. Significance test is performed for wavelet power spectrum of the intensity index series of 100 hPa South Asia High in June, the results show that the scheme can sufficiently reveal the temporal evolution of interannual and interdecadal oscillations of p, thus it is of practical application value.

Abstract:According to the concept of optimum space-matching between ground rain rate, I, and radar reflectivity factor, Z, for a certain vertical reflectivity profile, this paper presents a method to determine the optimally matched vertical profile of reflectivity for estimating stratiform cloud precipitation in ground clutter areas. The unblocked part of the vertical profile of reflectivity in ground clutter area is first used to find a best partial correlated vertical profile of mean reflectivity from the unblocked areas, and the both are combined to estimate the surface precipitation in the ground clutter area. The varification of estimation error against the raingauge-observed rain rate in the ground clutter area in the stratiform cloud precipitation event on June 18, 2004 in Anhui Province suggest that the method is applicable in operational rain estimation.

Abstract:The problem of multiple periodic solutions of a class of differential delay equations with perturbations is considered. The existence of multiple periodic solutions of the equations is gotten by using convex Hamiltonian theory and Morse index theory.