Spatio-Temporal Analysis of Drought in the North-Eastern Coastal Region of Vietnam Using the Standardized Precipitation Index (SPI)

Spatio-temporal analysis of drought provides valuable information for drought management and damage mitigation. In this study, the Standardized Precipitation Index at the time scale of 6 months (SPI-6) is selected to reflect drought conditions in the North-Eastern coastal region of Vietnam. The drought events and their characteristics from 1981 to 2019 are detected at 9 meteorological stations and 10 Chirps rainfall stations. The spatio-temporal variation of drought in the study region is analyzed on the basis of the number, duration, severity, intensity, and peak of the detected drought events at the 19 stations. The results show that from 1981 to 2019 the drought events mainly occurred with 1-season duration and moderate intensity and peak. The number, duration, severity, and peak of the drought events were the greatest in the period 2001-2010 and were the smallest in the period 2011-2019. Among the 19 stations, the drought duration tends to decrease at 11 stations, increase at 7 stations, and has a slight variant at 1 station;the drought severity tends to decrease at 14 stations, increase at 4 stations, and has not a significant trend at 1 station;the drought intensity tends to decrease at 17 stations, increase at 1 station, and has a slight variant at 1 station;and the drought peak tends to decrease at 18 stations and increase at 1 station.

The GNSS PWV retrieval using non-observation meteorological parameters based on ERA5 and its relation with precipitation

The pressure and temperature significantly influence precipitable water vapor(PWV) retrieval. Global Navigation Satellite System(GNSS) PWV retrieval is limited because the GNSS stations lack meteorological sensors. First, this article evaluated the accuracy of pressure and temperature in 68 radiosonde stations in China based on ERA5 Reanalysis data from 2015 to 2019 and compared them with GPT3model. Then, the accuracy of pressure and temperature calculated by ERA5 were estimated in 5 representative IGS stations in China. And the PWV calculated by these meteorological parameters from ERA5(ERA5-PWV) were analyzed. Finally, the relation between ERA5-PWV and precipitation was deeply explored using wavelet coherence analysis in IGS stations. These results indicate that the accuracy of pressure and temperature of ERA5 is better than the GPT3 model. In radiosonde stations, the mean BIAS and MAE of pressure and temperature in ERA5 are-0.41/1.15 hpa and-0.97/2.12 K. And the mean RMSEs are 1.35 hpa and 2.87 K, which improve 74.77% and 40.58% compared with GPT3 model. The errors of pressure and temperature of ERA5 are smaller than the GPT3 model in bjfs, hksl and wuh2, and the accuracy of ERA5-PWV is improved by 18.77% compared with the GPT3 model. In addition, there is a significant positive correlation between ERA5-PWV and precipitation. And precipitation is always associated with the sharp rise of ERA5-PWV, which provides important references for rainfall prediction.

Cluster analysis on summer precipitation field over Qinghai-Tibet Plateau from 1961 to 2004

The summer day-by-day precipitation data of 97 meteorological stations on the Qinghai-Tibet Plateau from 1961 to 2004 were selected to analyze the temporal-spatial distribution through accumulated variance,correlation analysis,regression analysis,empirical orthogonal function,power spectrum function and spatial analysis tools of GIS.The result showed that summer precipitation occupied a relatively high proportion in the area with less annual precipitation on the Plateau and the correlation between summer precipitation and annual precipitation was strong.The altitude of these stations and summer precipitation tendency presented stronger positive correlation below 2000 m,with correlation value up to 0.604（α=0.01）.The subtracting tendency values between 1961-1983 and 1984-2004 at five altitude ranges（2000-2500 m,2500-3000 m,3500-4000 m,4000-4500 m and above 4500 m）were above zero and accounted for 71.4%of the total.Using empirical orthogonal function, summer precipitation could be roughly divided into three precipitation pattern fields：the Southeast Plateau Pattern Field,the Northeast Plateau Pattern field and the Three Rivers＇ Headstream Regions Pattern Field.The former two ones had a reverse value from the north to the south and opposite line was along 35°N.The potential cycles of the three pattern fields were 5.33a,21.33a and 2.17a respectively,tested by the confidence probability of 90%.The station altitudes and summer precipitation potential cycles presented strong negative correlation in the stations above 4500 m,with correlation value of-0.626（α=0.01）.In Three Rivers Headstream Regions summer precipitation cycle decreased as the altitude rose in the stations above 3500 m and increased as the altitude rose in those below 3500 m.The empirical orthogonal function analysis in June precipitation,July precipitation and August precipitation showed that the June precipitation pattern field was similar to the July＇s,in which southern Plateau was positive and northern Plateau negative.But positive value area in July precipitation pattern field was obviously less than June＇s.The August pattern field was totally opposite to June＇s and July＇s.The positive area in August pattern field jumped from the southern Plateau to the northern Plateau.

The SIA method for spatial analysis of precipitation in the upper-middle reaches of the Yangtze River

Using geographic information system (GIS) techniques and the newest seasonal and annual average precipitation data of 679 meteorological stations from 1971 to 2000, the multiple regressions equations of the precipitation and topographical variables are established to extract the effect of topography on the annual and seasonal precipitation in the upper-middle reaches of the Yangtze River. Then, this paper uses a successive interpolation approach (SIA), which combines GIS techniques with the multiple regressions, to improve the accuracy of the spatial interpolation of annual and seasonal rainfall. The results are very satisfactory in the case of seasonal rainfall, with the relative error of 6.86%, the absolute error of 13.07 mm, the average coefficient of variation of 0.070, and the correlation coefficient of 0.9675; in the case of annual precipitation, with the relative error of 7.34%, the absolute error of 72.1 mm, the average coefficient of variation of 0.092, and the correlation coefficient of 0.9605. The analyses of annual mean precipitation show that the SIA calculation of 3-5 steps considerably improves the interpolation accuracy, decreasing the absolute error from 211.0 mm to 62.4 mm, the relative error from 20.74% to 5.97%, the coefficient of variation from 0.2312 to 0.0761, and increasing the correlation coefficient from 0.5467 to 0.9619. The SIA iterative results after 50 steps identically converge to the observed precipitation.

Analysis of the Characteristics of Inertia-Gravity Waves during an Orographic Precipitation Event

A numerical experiment was performed using the Weather Research and Forecasting（WRF） model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods（Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis）were applied. During the storm, inertia-gravity waves appeared at heights of 10-14 km, with periods of 80-100 min and wavelengths of 40-50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15-20 m s^（-1）. Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.

Analysis on the Variation Characteristics of Temperature and Precipitation in Benxi Area under the Background of Climate Warming

[Objective] The research aimed to study the variation characteristics of temperature and precipitation in Benxi area under the background of climate warming.[Method] Based on the monthly mean temperature and precipitation data of four routine meteorological stations in Benxi area from 1953 to 2010,by using linear tendency rate,linear regression equation,wavelet analysis,Mann-Kendall detection and so on,the variation characteristics of temperature and precipitation under the background of climate warming in the area were analyzed.[Result] The annual average temperature during 1953-2010 in Benxi area presented rise trend,and the linear tendency rate was 0.28 ℃/10 a.It was temperature increase trend in four seasons.The temperature rise rate in winter was the maximum and was the minimum in summer.The annual rainfall presented decrease trend,and the linear tendency rate was-18.16 mm/10 a.Except in spring,it was decrease trend in other seasons.Mann-Kendall mutation detection showed that the mutation of annual average temperature in Benxi area in recent 58 years appeared in 1986.There was no mutation phenomenon in summer.Spring mutation appeared in 1974,and autumn mutation appeared in 1987.Winter mutation was in 1981.The annual and seasonal precipitation didn’t have the mutation phenomenon.The wavelet analysis found that the annual average temperature had the periodic variations of 12-14,5-6 and 2 years in Benxi area in recent 58 years.The annual rainfall had the periodic fluctuations of 8-12,5-6 and 2 years.[Conclusion] The research provided the scientific basis for exploration and sustainable development of the climate resources in the mountain area.

Complexity analysis of precipitation in changing environment in Chien River Basin,China

The hydrological processes influenced by the multiple factors of climate, geography, vegetation, and human activities are becoming more and more complex, which is an important characteristic of hydrological systems. The different complexity distributions of precipitation processes of the Chien River Basin （a sub-basin of the Minjiang Basin） in two periods （from 1952 to 1980, and from 1981 to 2009） are illustrated using the fractal based on the continuous wavelet transform （CWT）. The results show that （1） at the basin scale the precipitation process in the latter period is more complex than in the former period; （2） the maximum value of the complexity distribution moved from the east to the middle; and （3） through analysis of the time-information and space-information concealed in this complexity change, the precipitation characteristics in the changing environment in the basin can be illuminated. This study could provide a reference for research on disaster pre-warning in changing environments and for integrated water resources management in the local basin.

SEOF Analysis on the Precipitation and Temperature in China during 1951-1999

[Objective] The research aimed to study the seasonal variation characteristics of precipitation and temperature in China during 1951-1999. [Method] Based on the monthly average precipitation and temperature data in 160 stations from January, 1951 to February, 1999, which were provided by China Meteorological Administration, the spatial-temporal variation characteristics of precipitation and temperature in 48 years were studied by using SEOF method. [Result] SEOF analysis of precipitation:SEOF analysis of the first modal showed the four-season propulsion of rain belt in China from south to north. Seen from the time coefficient, as a whole, the precipitation in China decreased slightly during the 1960s-1970s. After the 1970s, the precipitation had the increase trend and was the decrease trend after the 1980s. SEOF analysis of temperature:the first modals of precipitation and temperature configured well in the space. In the dry zone where the precipitation was less, the temperature variation was obvious. Seen from the time sequence, the temperature in China during 1951-1999 was low, and it was the low temperature period in the 1950s. The temperature rose slightly during the 1950s-1960s, and it entered into the low temperature period again from the middle and latter periods of 1960s to early the 1970s. From the metaphase of 1970s to the end of 1990s, the temperature increased relatively and stably. [Conclusion] The research provided the theory basis for studying the climate variation in China.

Rietveld Quantitative Analysis of Carbides Precipitation in Normalized-tempered 2.25Cr-1Mo-0.25V Steel

The quantitative determination of the mass fractions of precipitates in steels is very difficult using traditional materials characterization techniques. The Rietveld full-pattern fitting algorithm was introduced to solve this problem. The precipitated multicomponents’ mass fraction of M3C, MC, M7C3 and M23C6 were evaluated precisely and relatively quickly. It is found evolution of carbides apparently occurs during tempering at high temperatures, and a two-step transformation mechanism is proposed for M7C3 during early tempering treatment. The method is an effective way on the investigation of precipitation kinetics, which may play a promising role in propertities’ enhancement and design of the heat-resistant steels.

EFFECT OF TROPICAL CYCLONE PRECIPITATION ON ALLEVIATING THE DROUGHT SITUATION IN THE SOUTHEAST COASTAL REGIONS OF CHINA DURING SUMMER AND AUTUMN:USING THE IMPROVED OBJECTIVE SYNOPTIC ANALYSIS TECHNIQUE

To quantitatively study the role of tropical cyclone precipitation(TCP) on alleviating the drought in the southeast coastal region of China(SCR) during summer and autumn,the objective synoptic analysis technique(OSAT),improved for consistency and rationality,was used to separate the TCP data on the summers and autumns of 1963-2005 on the basis of daily precipitation data from stations and tropical cyclone best track data.After defining the season drought index,the actual drought distribution and the assumed drought distribution without TCP were acquired.The results showed that within 1 000 km from the southeast coastline of China,TCP accounted for 11.3%of natural precipitation(NP).Without TCP,the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions.The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions.The TCP proportion(TCPP) showed a significant negative correlation with the drought index in many regions of the southeast,and the significant region is wider in autumn than in summer.TCP relieved the drought most significantly within a range of 0-500 km from the southeast coastline.This drought relief showed different characteristics for the interannual variability in summer and autumn,and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2-4-year time scales.In particular,there was a significant effect during the summers of 1977-1985 and in the autumns following that of 1985.Therefore,TCP has indeed largely alleviated drought in the SCR during summer and autumn.

Analysis on Precipitation Variation in Anyang and Nanyang in Recent 57 Years

[Objective] The aim was to analyze precipitation variation in Anyang and Nanyang in recent 57 years. [Method] Based on the data of annual precipitation in Anyang and Nanyang from 1953 to 2009, the changes of precipitation in Anyang and Nanyang were compared by means of mathematical statistics, regression analysis and wavelet analysis. [Result] In recent 57 years, annual precipitation in Anyang and Nanyang showed decrease trend, especially Anyang with obvious decrease trend; from seasonal variation, average precipitation in spring and winter went up in Anyang and went down in Nanyang, while average precipitation in summer and autumn reduced in two cities; from periodic variation, when the time scale of precipitation in Anyang was 12-15 years, there was a catastrophe point in 1970, and Nanyang had two catastrophe points in 1965 and 1997 when the time scale of precipitation was 15 years and 4 catastrophe points in 1968, 1978, 1987 and 1999 when time scale was 7-10 years. [Conclusion] The study could provide theoretical foundation for the forecast of local climate changes.

Stress-Induced Precipitation of Fineγ'-Phase and Thermodynamics Analysis

The microstructures of a single crystal Ni-base superalloy with [001] orientation were observed by means of TEM. Results showed that the fine γ’ particles were precipitated in the γ matrix channels during the tensile deformation of the alloy. Thermodynamics analysis indicated that the solubility of elements M(Al,Ta) within the γ matrix may be changed when the alloy was deformed by the external applied stress. The tensile stress reduced the solubility of elements Al and Ta so as to occur the over-saturation and agglomeration of them, which promoted the precipitation of fine γ’-phase in the γ matrix.

The Analysis on the Temporal and Spatial Variation of Strong Precipitation Caused Flood and Agricultural Disaster Loss in Huaihe River Basin of Anhui Province during Meiyu Period of 2007

[Objective] The research aimed to analyze temporal and spatial variation of strong precipitation caused flood and agricultural disaster loss in Huaihe River basin of Anhui Province during Meiyu period of 2007.[Method] On the basis of rainfalls of each station in Huaihe River basin of Anhui,rainfall data during Meiyu period of 2007 and flood disaster data in the same period,the temporal and spatial distribution characteristics of strong precipitation caused flood during Meiyu period of 2007 and its harm on agriculture were analyzed.The variation rule,distribution characteristics of strong precipitation during Meiyu period in Huaihe River basin of Anhui and its relationship with agricultural disaster loss were discussed.[Result] During Meiyu period of 2007 in Huaihe River basin of Anhui,the rainstorm was more,and the rainfall was large.The precipitation variation showed 'three-peak' trend.Rainfall in Huaihe River basin during Meiyu period of 2007 was greatly more than that homochronously in Yangtze River basin.The rain area over 400.0 mm during Meiyu period mainly located in Huaihe River basin,and the rain area over 600.0 mm mainly located from area along Huaihe River to central Huaibei.The rainfall during Meiyu period gradually decreased toward south and north by the north bank of Huaihe River as the symmetry axis.The rainfall in area along Huaihe River showed wavy distribution in east-west direction.The flood disaster loss index and disaster area of crops in Huaihe River basin of Anhui both increased as rainfall in Meiyu period.[Conclusion] The research provided theoretical basis for flood prevention,disaster reduction and agricultural flood-avoiding development in Huaihe River basin.

Analysis on Temporal and Spatial Variation Characteristics of the Precipitation in Hexi Corridor in Recent 58 Years

[ Objective] The research aimed to analyze temporal and spatial variation characteristics of the precipitation in Hexi Corridor in the past 58 years. [Method] Based on monthly rainfall data in Hexi Corridor from 1951 to 2008, by using moving average, wavelet analysis and climate trend coefficient, variation rule of the precipitation in Hexi Corridor in the past 58 years was analyzed. [ Result] Average rainfall in Hexi Corridor in the past 58 years was 130.4 mm. Precipitation mainly concentrated in summer, occupying 59.08% of the annual rainfall. From June to September, it occupied 72.57% of the annual precipitation. Interdecadal change of the precipitation in Hexi Corridor wasn＇t severe. Average rainfall in each dec- ade was from 120.8 to 139.0 mm. The precipitation series had periods of the 5, 10, 21 and 32 years in Hexi Corridor from 1951 to 2008. in the fu- ture, annual, spring, summer and winter precipitation would have small increase tendency. Increase amplitude of the annual precipitation in Shule River basin was the biggest （5.231 -0.062 mm/10 a）. The increase amplitude in the south and southeast of the Heihe River basin was bigger than that in the northwest. The smallest increase amplitude of the annual precipitation was 3.280 -0.098 mm/10 a in Shiyang River basin. [ Conclusion] This research could provide beneficial reference for coordinated development between local social economy and ecological environment.

Analysis of Extreme Precipitation Events over Central Plateau of Iran

This paper describes the results of an analysis of extreme rainfall events in the central plateau of Iran. To study the extreme events, daily records of eighteen stations’ rainfalls in the region for different initial dates up to 2005 gathered from the bureau of meteorology. Then, the extreme rainfall threshold was calculated for each individual station using the statistical index of Gamble type I. Lastly, 22 mm was determined as the extreme rainfall value for the entire stations, and eventually 17 out of 169 extreme precipitation events were extracted in accordance with three factors including a) days with precipitation in not less than 50% of the stations, b) maximum rainfall is 22 mm or more in at least one of the stations, and c) mean precipitation of the basin is more than 3 mm. In the next step to analyze the synoptic features, the relevant meteorological data i.e. relative vorticity, geopotential height, sea level pressure, u and v wind components, relative humidity, vertical velocity, and precipitable water content at multiple levels of the atmosphere were examined from the NCEP/NCAR reanalysis dataset. The synoptic findings indicate that two patterns of deep trough and high ridge of the eastern Mediterranean were responsible for making the heavy precipitation events over the central plateau of Iran. The most and severest rainfall events occurred via deep tough pattern, which covered 76% of days with extreme precipitations during the examined period. Furthermore, the results suggest that the main moisture resources, which identified by HYSPLIT model’s outputs and moisture convergence/divergence zones for the rainy systems in the first pattern (deep trough) including Persian Gulf, Oman Sea, Indian Ocean, and Red Sea, while for the second pattern (high ridge) Persian Gulf and Red Sea play a significant role in feeding the storms in the central regions of Iran. Moreover, the southward movement of Polar Vortex is also considered as those important factors to produce extreme precipitation events over the central plateau of Iran. In general, the HYSPLIT trajectories model’s outputs confirmed the observed synoptic features in particular for the systems’ moisture feeding discussed in the patterns.

A Case Study of Impact of FY-2C Satellite Data in Cloud Analysis to Improve Short-Range Precipitation Forecast

Chinese FengYun-2C(FY-2C) satellite data were combined into the Local Analysis and Prediction System(LAPS) model to obtain three-dimensional cloud parameters and rain content. These parameters analyzed by LAPS were used to initialize the Global/Regional Assimilation and Prediction System model(GRAPES) in China to predict precipitation in a rainstorm case in the country. Three prediction experiments were conducted and were used to investigate the impacts of FY-2C satellite data on cloud analysis of LAPS and on short range precipitation forecasts. In the first experiment, the initial cloud fields was zero value. In the second, the initial cloud fields were cloud liquid water, cloud ice, and rain content derived from LAPS without combining the satellite data. In the third experiment, the initial cloud fields were cloud liquid water, cloud ice, and rain content derived from LAPS including satellite data. The results indicated that the FY-2C satellite data combination in LAPS can show more realistic cloud distributions, and the model simulation for precipitation in 1–6 h had certain improvements over that when satellite data and complex cloud analysis were not applied.

VARIABILITY OF DAILY PRECIPITATION IN CHINA(1980-1993): PCA AND WAVELET ANALYSIS OF OBSERVATION AND ECMWF REANALYSIS DATA

In this study, principal component analysis(PCA) and complex Morlet wavelet transform were used with daily rainfall in China for the period 1980-1993(1 May-31 Dec.) from observation and ECMWF reanalysis to study its variability and evaluate the validation of reanalyzed precipitation. The results showed that northward movement of the summer rain belt was a wavelike propagation, which was always accompanied by rainfall breaks and could be treated as one event under time scale of about 1 month only. The first 4 EOFs accounted for 28% and 35% of total variance from observation and reanalysis, respectively, and were roughly consistent with each other. The first and third EOFs for observation mainly represented interweekly, interseasonal and interannual variations and contained some summer intraseasonal fluctuations also. The second and fourth ones mainly represented some rather strong summer intraseasonal fluctuations for a paticular year and contained interweekly, interseasonal and interannual variations also. Although there is still room for improvement, the ECMWF reanalysis is the best available dataset with global coverage and daily variability.

AN ANALYSIS OF DISTRIBUTION AND MESOSCALE STRUCTURE OF PRECIPITATION ABOUT LANDFALL TROPICAL CYCLONE KOPPU(0915)

Observation from automatic weather stations, radars and TRMM satellites are employed to investigate the precipitation distribution of tropical cyclone(TC) Koppu(0915) that made landfall on Guangdong province in 2009.The results show that the precipitation of landfall TC Koppu is featured by significant asymmetry and mesoscale structure, and occurs mainly to the left of its moving path. By examining the sea surface temperature(SST), water vapor flux, Q vector, vertical wind shear of environment etc., it is found out that the distribution of SST, water vapor convergence, low-level convective ascending and vertical wind shear facilitates the TC precipitation to take place to the left of the TC moving path. The mesoscale structure separated by Barnes band-pass filter presents that the precipitation of landfall KOPPU has some organized mesoscale spiral structures, which is around the TC center and composed of the form of belts or blocks. The heavy local rainfall of landfall TC Koppu is primarily associated with the rainfall due to mesoscale spiral structure.

The Construction of Daily Fine Clim atic Analysis Field for Precipitation in Zhejiang Province

We successfully developed a set of technical methods constructing fine climatic analysis field for regional precipitation considering terrain influence based on PRISM monthly climatic precipitation analysis field and DEM. By using harmonic analysis and Shepard inverse distance interpolation,we quantitatively analyzed precipitation observation data at 68 reference weather stations of Zhejiang Province in recent 50 years,and established climatic analysis field of daily precipitation at 1 km grid of Zhejiang Province considering terrain influence. Systemic cross-examination of the method was conducted. Result showed that the established fine climatic field for precipitation could reproduce rapid seasonal evolution characteristics of precipitation induced by monsoon migration and typhoon landing with better quantitative accuracy.