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28 April 2019, Volume 38 Issue 2   
  • Characteristics of Atmospheric Water Vapor over the Qinghai-Tibetan Plateau in Summer with Global Warming
  • CHANG Shuting;LIU Yuzhi;HUA Shan;JIA Rui
  • 2019 Vol. 38 (2): 227-236.  DOI:10.7522/j.issn.1000-0534.2018.00080
  • Abstract ( ) HTML PDF (9791KB) ( )
  • The Qinghai-Tibetan Plateau (QTP), which is aptly called as the "Asian water tower", acknowledged as the water source of the rest region in China, may profoundly have an significant impact on the regional and global atmospheric water vapor cycle, climate change and incidents of drought, disastrous weather and climate evolution in China and of the world, as a whole. In this paper, combined with the reanalysis data of ERA-Interim, MERRA2 (second Modern-Era Retrospective analysis for Research and Applications), JRA-55 (Japanese 55-year Reanalysis), and the GLDAS-2.0 (Global Land surface Data Asimilation System), the precipitation and temperature daily grid data from CMA (China Meteorological Administration) were used to investigate the characteristics of spacial distribution and variation tendency of precipitation, temperature, atmospheric water vapor, and the atmospheric water vapor transport in summer over the QTP in summer during the period of 1979-2010 in this study. The results showed that the surface temperature over the QTP had increasing trend while the precipitation showed a decreasing trend during the period of 1979-1998. Otherwise, during the period of global warming deceleration (1999-2010), the surface temperature and the precipitation showed a more significant increasing trend than those during the period of 1979-1998. The atmospheric water vapor over the QTP showed an increasing trend during the period of 1979-2010. On the contrary, based on the further analysis, the inward transport of atmospheric water vapor showed a decreasing trend year by year. Especially, after the year of 1998, due to the sharp weakening of the intensity of southwest monsoon, the net inward atmospheric water vapor transport was reduced more significantly in this period. The results indicated that the surface evapotranspiration over the plateau showed an increasing trend significantly, which may be a major cause of the increased atmospheric water vapor over the QTP.
  • Surface Diabatic Heating Mode of the Qinghai-Tibetan Plateau and Its Relationship with the Anomalous Circulation in Northern China
  • YU Han;ZHANG Jie;LIU Shimeng
  • 2019 Vol. 38 (2): 237-252.  DOI:10.7522/j.issn.1000-0534.2018.00079
  • Abstract ( ) HTML PDF (35613KB) ( )
  • Based on the estimation of the surface heat transfer coefficient and the effective surface radiation under the EOF analysis of the Qinghai-Tibetan Plateau (QTP), the surface diabatic heating data of the QTP were calculated since 2000, and the diabatic heating data from 1958 to 2013 were reconstructed. The surface diabatic heating index of the QTP was obtained, which is used to indicate the surface thermal conditions for different climatic regions of QTP. According to the results of EOF, the QTP was divided into four climatic regions. The effects of QTP on the circulation anomalies in the northern China from the perspective of the propagation of wave energy were analyzed. The following conclusions were obtained:the surface diabatic heating index in the western edge of QTP (regionⅠ)has a weak increasing trend, except for winter with a slight decline trend. The surface diabatic heating index in the mid-west hinterland of QTP (regionⅡ) is decreasing in all seasons. The surface diabatic heating index in the northeast of the QTP (region Ⅲ) has a weak increasing trend, except for winter with a slight decline trend. However, the surface diabatic heating index in the southeast of QTP (region Ⅳ) shows a declining tendency in all seasons. The high altitude is a wave energy divergence area of QTP at 200 hPa, when the surface diabatic heating index with abnormal increasing in the western edge of QTP. The enhancement of wave energy convergence of northern China in early summer benefits to the precipitation, which weakened drought. However, the wave energy divergence in northern China in midsummer, which makes more drought. When the surface diabatic heating index anomalies increase in the northeast of QTP, there is an energy divergence area at high altitude as well. Whether in early summer or midsummer, convergence in northern China will contribute to weakening the drought. However, divergence will appear in the northeast of China and drought will be intensified. These conclusions provides a reference for the understanding of the spatial and temporal distribution of surface diabatic heating of QTP, which effects on the anomalous circulation in northern China.
  • Characteristics of Long-term Surface Heat Source and Its Climate Influence Factors in Nagqu Alpine Meadow
  • YAN Xiaoqiang;HU Zeyong;SUN Genhou;XIE Zhipeng;WANG Yidan;ZHENG Huixuan
  • 2019 Vol. 38 (2): 253-263.  DOI:10.7522/j.issn.1000-0534.2018.00091
  • Abstract ( ) HTML PDF (4418KB) ( )
  • Based on multi-level AWS data during 2001 to 2015 and eddy covariance data during 2011 to 2014 from Nagqu Station of Plateau Climate and Environment, the turbulent fluxes were calculated by a surface energy balance combination (CM) and eddy covariance method (EC). The EC fluxes are compared to the CM fluxes. Therefore, a long-term heat fluxes and surface heat source were obtained. The further results are also obtained:The energy closure ratio is close to 1 in spring, summer, autumn and throughout the year. In winter, the energy closure ratio is 1.34, because radiation observation value is small. From 2002 to 2015, sensible heat flux shows a ascend trend, while latent heat flux shows a descend trend. The surface heat sourceshows a descend trend. The analysis of the surface heat source indicates that it has a significant relationship withnet radiationflux, surface temperature, soil moisture and wind speed. Particularly, thesurfaceheat source has a significant response to net radiationflux throughout the year, the great influence of surface temperatureon the surface heat source in spring autumn and winter is strong, the great influence of soil moisture on the surface heat source in spring summer and autumn is strong, and the influence of wind speedson surface heat source isstrong in spring. The annual variation of sensible heat flux and latent heat flux are obvious. Sensible heat flux reaches the maximum value of the year in April and the minimum value in July, however, latent heat flux shows the maximum value in July and the minimum value in January.
  • Climate Trend of Upper Troposphere Temperature Revealed by Satellite Data over the Qinghai-Tibetan Plateau
  • MING Shaohui;QIN Zhengkun;HUANG Yu
  • 2019 Vol. 38 (2): 264-277.  DOI:10.7522/j.issn.1000-0534.2018.00120
  • Abstract ( ) HTML PDF (18005KB) ( )
  • Satellite data has been an important database of climate research because of its global coverage. Based on the MSU/AMSU-A temperature data from 1982 to 2016, this paper analyzes the climate trend and its evolution of air temperature on the upper troposphere over the Tibetan Plateau, the ERA-Interim and NCEP-R2 reanalysis datasets are also included for the comparison. Results show that the air temperature on the upper troposphere is gradually warming over the Qinghai-Tibetan Plateau, which is in good agreement with the changes of atmospheric temperature at the corresponding levels of the two reanalysis datasets. Nonlinear trend analysis based on ensemble empirical mode decomposition (EEMD) reveals that the warming of the upper tropospheric bright temperature over the Tibetan Plateau starts from the central of the Qinghai-Tibetan Plateau, as the time evolved, the warming trend gradually spread to the periphery of the Tibetan Plateau, and eventually lead to the temperature become warmer for the whole study area. For the ERA-Interim data, the evolution of the climate trend for atmospheric temperature at 300 hPa has good similarity with that of the satellite observations, the warming phenomenon is first observed near the Qinghai-Tibetan Plateau and the warming trend gradually expands to surrounding areas. However, there are significantly differences between the trend of observations and that of the NCEP-R2 data, temperature at 300 hPa of the NCEP-R2 has obvious cooling trend in the first 20 years of the research period, the warming phenomenon only exists in the last 10 years.
  • The Characteristics of COSMIC Radio Occultation Data Biases over Qinghai-Tibetan Plateau
  • YU Xiaojia;YANG Shengpeng;JIANG Xi
  • 2019 Vol. 38 (2): 288-298.  DOI:10.7522/j.issn.1000-0534.2018.00162
  • Abstract ( ) HTML PDF (5346KB) ( )
  • COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) RO (Radio Occutaion) data are collocated in space and time with ECMWF (European Centre for Medium-Range Weather Forecasts) analyses during 7 year period from 2007 to 2013 over Qinghai-Tibetan Plateau and its surrounding areas. Atmospheric refractivity, temperature and relative humidity derived from COSMIC GPS ROs are compared with those of the ECMWF analysis. It is found the COSMIC GPS RO refractivity observations are systematically greater than the refractivity calculated from ECMWF analyses in summer and autumn. The fractional refractivity bias over Qinghai-Tibetan Plateau is larger than that over southwest monsoon area and plain with the value of 0.7%. In winter and spring the refractivity bias over Qinghai-Tibetan Plateau is positive, while that over southwest monsoon area and plain is negative. Temperature and water vapor of GPS RO are derived from refractivity. The positive bias of refractivity is highly correlated with positive water vapor bias and negative temperature bias. The bias of relative humidity and temperature are 7% and 0.5℃, respectively over Qinghai-Tibetan Plateau. It is noted that relative humidity bias can reach 11% at the top of troposphere over southwest monsoon area.The lower tropospheric negative refractivity biases are related to the multi-path effect, and the positive biases in the middle and lower troposphere are the result of the influence of cloud. The occurrence of relative humidity bias near the tropopause is due to the inaccuracy of the ECMWF mode results.
  • Characteristics of Surface Land Heating in the Qinghai-Tibetan Plateau Vortex Source Regions along with the Departure Plateau Vortex and Non-departure Plateau Vortex
  • YU Shuhua;GAO Wenliang
  • 2019 Vol. 38 (2): 299-313.  DOI:10.7522/j.issn.1000-0534.2018.00086
  • Abstract ( ) HTML PDF (42854KB) ( )
  • Using daily average latent heat flux and sensible heat flux of NCEP/DOE reanalysis data, historical weather graphs of MICAPS, and Qinghai-Tibetan Plateau vortex and shear line year books from 1998 to 2016, the Qinghai-Tibetan Plateau Vortex (QTPV) source regions and characteristics of the Plateau surface land heating were analyzed by statistics methods. The seasonal variation of source regions to Departure Qinghai-Tibetan Plateau Vortex (DQTPV) and Non-Departure Qinghai-Tibetan Plateau Vortex (NDQTPV) and the Plateau surface land heating were contrastively analyzed. The Plateau surface land heating characteristics of DQTPV and NDQTPV and the relationship between the generation of QTPV with the surface land heating were also analyzed. The results show that the seasonal variation of source distribution to QTPV, NDQTPV and DQTPV are similar from winter-to-spring-to-summer, along with the source generation area gradually expands. And in summer-to-autumn-to-winter phase, it just has the opposite variation mode, and the DQPTV has obviously smaller area than the QTPV and NDQTPV. And the seasonal variation of QTPV's generation center location are different to QTPV, DQTPV and NDQTPV. Second, the seasonal variations of the surface land sensible heat, the surface land latent heat and the surface land heat sources in distribution are similar. In winter-to-spring-to-summer they are all clearly strengthening and are weakened in summer-to-autumn-to-winter. And the rapid enhancement, the attenuation of heat sources and their seasonal variation had big difference in two stages. The surface latent heat is especially strengthened in spring to summer, which is highly consistent with the obvious increase numbers of the DQTPVs. Third, the value range of surface land heating to DQTPV and NDQTPV are different in Spring, Summer and Autumn, and the value of DQTPV is higher than NDQTPV's in Summer. The reliance of DQTPV to surface land heating is stronger than that of the NDQTPV. Fourth, the source regions of DQTPV and NDQTPV locate in positive correlation area with the Plateau surface land heating. And their obvious positive correlation area is bigger with the surface land latent heat than that with the sensible heat, which is especially clear in DQTPV. The surface latent heat has vital role in generation of QTPV, with more important influence to the generation of DQTPV.
  • Application of Doppler Spectral Density Data in Vertical Air Motions and Drop Size Distribution Retrieval in Cloud and Precipitation by Ka-band Millimeter Radar
  • MA Ningkun;LIU Liping;ZHENG Jiafeng
  • 2019 Vol. 38 (2): 325-339.  DOI:10.7522/j.issn.1000-0534.2018.00127
  • Abstract ( ) HTML PDF (17293KB) ( )
  • Vertically pointing Ka-band Millimeter Radar has a good detection sensitivity and high temporal-spatial resolution. The Doppler spectral density data can be utilized to retrieve the detailed cloud structure and micro-physical parameters. In this study, a stratiform precipitation case in 2016 CAMs South China Precipitation Test is used to retrieve the vertical air velocity in clouds and drop size distribution, and compare the DSD results with Distrometer and MRR. First, Liquid droplets trace methods is used to get the vertical airspeed which can obtain Doppler spectral in static air. Then we retrieve DSD from the translated Doppler spectrum by a V-D relation. Last, Normalized Gamma Distribution is used to fit the retrieved DSD. Several conclusions are get from the case study:(1)Weak downwards flow dominates the vertical air motions in cloud between the height from 1 km to the 0℃ level height. The clear-air echo caused by plankton contamination and noisy echo influence the Doppler spectral, as well as the phenomenon of saturation in Z existing near surface layer and affect the results of vertical air motions too. (2) Differences in Z is found in the detection of CR、MRR and Distrometer. MRR's Z data has a smaller difference with Distrometer than CR. In stable stratiform precipitation, Doppler spectral of CR and MRR are almost consistent. (3) In the comparison test of CR and MRR, DSD retrieval results are highly sensitive to the introduction of vertical Airspeed. Because of airspeed changing with height, DSD from CR has an overall increasing number concentration and decreasing value of average radium. DSDs retrieved by the two instruments' spectrum have a similar distribution along all heights, demonstrating the validity of retrieving DSD from Doppler spectral. (4) In the comparison of Gamma fitting parameters of CR and distrometer, the DSD of CR introducing vertical air motions results in has a smaller Dm and a same Nw magnitude comparing to Distrometer.
  • The Temporal and Spatial Characteristics of Convective Precipitation in Xinjiang among the Summer and Causes Analysis
  • JIANG Huimin;LIU Chunyun;JIA Jian;ZHAO Delong;FENG Jingjie
  • 2019 Vol. 38 (2): 340-348.  DOI:10.7522/j.issn.1000-0534.2018.00087
  • Abstract ( ) HTML PDF (9684KB) ( )
  • In order to study the temporal and spatial distribution characteristics of convective precipitation and the causes of circulation in the Xinjiang area in summer, the ERA-Interim reanalysis data are utilized in this article, including precipitation products such as convective precipitation, large-scale precipitation and total precipitation, and meteorological variables such as geopotential height, relative humidity, specific humidity, temperature and winds. The results of the analysis indicate that:(1)On the characteristics of average precipitation in summer, average total precipitation and the proportion of convective precipitation show spatial distribution with the terrain. The accumulated total summer precipitation in Kunlun and Tianshan Mountains is above 200 mm on average, but for basin region it is below 40 mm. The proportion of convective precipitation in most basin region is more than 70%, while it is less than 50% for Kunlun Mountains and 50%~60% for Tianshan Mountains. (2)The Emprical orthogonal function(EOF) method is used to analyse the temporal and spatial distribution of convective precipitation in summer. The first mode from EOF analysis shows that there are a positive phase in the western moutainous area of Tarim basin and a negative phase in Ili region and the northern part of Tianshan Mountains, which indicates that the main spatial-temporal characteristic of the above two regions is anti-phase change. The time coefficients of this pattern show 5a and 10a main period before 2000s. Since 1995, there has been a sudden change, convective precipitation decreases in the west of Tarim Basin, while increases in Ili region and the northern foot of Tianshan Mountains. And this pattern is different from the first mode of large-scale precipitation which shows the same phase in the southern Tarim Basin and Tianshan Mountains. (3)On the analysis based on the anomalies of whole layer water vapour fluxes, precipitable water and geopotential heights fields, it is found that the blocking system in Eurasian mid-high latitude are stronger in typical low years of convective precipitation PC1 compared with the high years. The northern part of Xinjiang lies between the Ural Trough and the Baikal Lake high pressure, which weakens the northward water vapor transport in Xinjiang and leads to less water vapor transport across and around the Tianshan Mountains to the southern basin of Xinjiang, and more water vapor accumulates in the northern part of Tianshan Mountains. Under the background of this large-scale circulation, the vertical warming range of the lower layer in Ili region is larger and wetter than that in the western tarim basin, which makes the former's stratification instability condition stronger. The difference in both the water vapor condition and the stratification unstable condition leads to the change of the opposite phases of the convective precipitation in that two regions.
  • Statistical Downscaling Modeling Analysis of Summer Precipitation in Southwest China
  • SHU Jianchuan;JIANG Xingwen;HUANG Xiaomei;WU Qing
  • 2019 Vol. 38 (2): 349-358.  DOI:10.7522/j.issn.1000-0534.2018.00078
  • Abstract ( ) HTML PDF (1800KB) ( )
  • Based on the BP-CCA method and the results of state-of-the-art climate prediction models, this paper discusses how to establish a statistical downscaling model with high predictive skills for summer precipitation in southwest China, and also investigates the predictability sources of the statistical downscaling mode. The predictive ability of the statistical downscaling model taking tropical sea surface temperature as the predictor is superior to that of 500 hPa geopotential height in Asia and the tropics as the predictor. When taking the tropical sea surface temperature as predictor, the predictive ability of statistical downscaling model is highly influenced by the second EOF mode of the tropical sea surface temperature, which is characterized by positive loading values in the tropical South-East Indian and Western Pacific regions, and negative loading centers in the tropical Middle and East Pacific region. This mode of the tropical sea surface temperature is highly correlated with the convection over Philippine Sea and the western Maritime Continent, which plays an important role in the Southwest China summer precipitation. The ECMWF and NCEP climate prediction model has high predictability of the second EOF mode of the tropical sea surface temperature. This feature helps to enhance the predictability of summer precipitation in Southwest China from the statistical downscaling model that taking the tropical sea surface temperature as the predictor.
  • Analysis on the Characteristic of Radar Echo and the Causes of a Strong Hail in Tianshui City of Gansu Province
  • WANG Yanfeng;HUANG Wubin;WANG Jujie;HUANG Yuxia;DUAN Bolong;YANG Yong
  • 2019 Vol. 38 (2): 368-376.  DOI:10.7522/j.issn.1000-0534.2018.00077
  • Abstract ( ) HTML PDF (21830KB) ( )
  • Using normal surface meteorological data、weather radar data and NCEP FNL reanalysis datasets on 18 May 2017, the radar echo structure evolution characteristics and the causes of a strong hail in Tianshui city of Gansu province was analyzed. The results showed that:(1)The low-level reflectivity factor of the convective cells showed obvious "V" gap, the strongest echo appears in the low-level and the value got to 63 dBz. The vertical cross-sections of reflectivity factors showed typical BWER, overhanging echo. The corresponding the vertical cross-sections of radial velocity showed low-level radial wind with obvious characteristic of convergence and high-level to divergence, especially at storm near the top. (2)The background conditions of the convective cells occuring was low vortex and its adjacent cold area from Hetao region to Hedong east and high pressure ridges and cold pool of northeastern in middle of Hexi in the centre of the troposphere, a cold vortex at the border of Gansu and Ningxia provide favorable condition for high-level dry and cold air coming and low-level updrafts pushed by the warm moist southerly flow in the lower troposphere, respectively. High values of the CAPE and low values of the CIN are conducive to strong convection. At the same time the configuration of the deep updrafts airflow in the center and lower troposphere and sinking airflow in the centre of the troposphere, strong convective updrafts above 0℃layer in favor of water vapor transport, generating, develop and maintaining of the convective cells. 0℃ layer height apart from above ground is about 2600~2900 meters, which provides environmental conditions for large hail floor. (3)Maximum reflectivity reaches 55 dBz, VIL value over 25 kg·m-2 and VIL density over 2. 3 kg·m-2 can be taken as early warning radar parameterized indicators of hail.
  • Spatio-temporal Characteristics of the Occurrence Timing of Extreme Precipitation in the Huai River Basin from 1960 to 2014
  • PAN Xin;YIN Yixing;WANG Xiaojun
  • 2019 Vol. 38 (2): 377-385.  DOI:10.7522/j.issn.1000-0534.2018.00076
  • Abstract ( ) HTML PDF (6660KB) ( )
  • Based on the daily precipitation data of 25 stations which are almost uniformly distributed in the Huai River basin during 1960-2014, the spatio-temporal characteristics of the occurrence timing in the Huai River basin were analyzed by using the methods of linear trend method, circular statistics, EOF analysis and so on. The main results are listed as follows:(1) The occurrence timing of extreme precipitation in the Huai River basin mainly concentrates in the mid and late July every year, and the time series of the occurrence timing shows obvious interannual oscillation. The time series of occurrence timing of extreme precipitation in the Huai River basin shows an advancing trend on the numerical value, but the advancing trend of occurrence timing of extreme precipitation does not reach 0. 05 significant level. The time series of the Concentration degree of the occurrence timing of extreme precipitation in the Huai River basin rises with time rising, and the rising trend has reached 0. 05 significant level by using the test of significance. All in all, the possibility of extreme precipitation happens in the July is increasing. (2)In space, the occurrence timing of extreme precipitation in the Huai River basin is gradually postponed from southwest to northeast in the Huai River basin, and most of the sites in the Huai River basin show the slightly advancing linear trend but do not reach 0. 05 significant level; the spatial distribution of Huai River basin is relevant to the changes of Meiyu and typhoon of Huai River basin, while to some degree the advancing trend may be due to the fact that the main rain belt of China has been moving northward from the original position since the 1990s. (3)The EOF analysis results of occurrence timing of extreme precipitation indicates:the typical spatial field of the first mode of the occurrence timing shows the anti-phase distribution between the northwest and the southeast in the Huai River basin, while the time coefficient series of the first mode shows the declining trend which do not reach 0. 05 significant level; the typical spatial field of the second mode of the occurrence timing is uniformly distributed in the Huai River basin, while the time coefficient series of the second mode shows the rising trend which do not reach 0. 05 significant level. And the results reveals the differential and approximately consistent spatial characteristics of occurrence timing of extreme precipitation in the Huai River basin.
  • Accuracy Assessment for Two Satellite Precipitation Products: Case Studies in the Yarlung Zangbo River Basin
  • LIU Jiangtao;XU Zongxue;ZHAO Huan;HE Jingyi
  • 2019 Vol. 38 (2): 386-396.  DOI:10.7522/j.issn.1000-0534.2018.00092
  • Abstract ( ) HTML PDF (6385KB) ( )
  • Precipitation plays a very important role in the hydrological cycle and energy balance in many basins.In the Qinghai-Tibet Plateau, good quality precipitation data are unavailable and not easily accessible.Satellite precipitation data are being extensively used for alternative data sources for the ungauged basin.The uncertainties of satellite products over a certain region are largely unknown for systematic and random error.Therefore, satellite products need extensive validation before using in water resources research and streamflow simulation.Based on daily precipitation data of meteorological stations in the Yarlung Zangbo River Basin during 1998-2015, the accuracy was assessed and compared between PERSIANN-CDR (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record) and TRMM 3 b42 V7 (Tropical Rainfall Measuring Mission 3B42 V7) satellite precipitation products against quantitative indices and classification indices.The volumetric classification indices including VHI (Volumetric Hit Index, VHI), VFAR (Volumetric False Alarm Ratio, VFAR), and VMI (Volumetric Miss Index, VMI) are used to evaluate precipitation products in the Yarlung Zongbo River Basin for the first time.The results show that:(1) The deviation of light and heavy precipitation is the main expression for the deviation of satellite products, and the satellite data always overestimate precipitation in areas where precipitation is small and underestimates precipitation in areas where precipitation is great.The deviation of PERSIANNT is smaller than the deviation of TRMM.(2) The correlation coefficient of PERSIANN precipitation satellite data is 0.663, and the deviation is 0.845.The correlation coefficient of TRMM precipitation satellite data is 0.666, and the deviation is 0.579.The accuracy for PERSIANN and TRMM satellite data are similar only by using quantitative indices.(3) Overall, the values of POD, VHI, FAR, VFAR, and VMI are 0.830, 0.927, 0.54, 0.33, and 0.073 respectively for PERSIANN.The values of POD, VHI, FAR, VFAR, and VMI are 0.674, 0.833, 0.50, 0.31, and 0.167 respectively for TRMM.PERSIANN satellite has better performance than TRMM satellite on each site against classification indices.The evaluation system considering volumetric indices provides additional information beyond the traditional quantitative indices that can be useful in evaluating satellite products in plateau alpine region.This study is very meaningful and it could provide useful information for water resource management, water allocations and hydrologic simulation in the Yarlung Zangbo River Basin.
  • Analysis of the Characteristics of Temporal and Spatial Changes and Influencing Factors of Frost Season in Gansu Province
  • MA Shangqian;ZHANG Bo;LIU Lili;SHI Xiaoting;YANG Wenyi;YANG Mei;JIAO Wenhui;WEI Huaidong;CUI Yanqiang;HUANG Hao;LUO Hongdong
  • 2019 Vol. 38 (2): 397-409.  DOI:10.7522/j.issn.1000-0534.2018.00132
  • Abstract ( ) HTML PDF (2554KB) ( )
  • Under the background of global warming, a comprehensive understanding of the changing rules of the frost period will warnfrost damage earlier, protect the regional environment, and promote the rational development of climate resources in Gansu province.Ground 0 cm daily minimum temperature data collected at 61 meteorological stations combined with the linear propensity estimates method were used to obtainclimate tendency rate of frost date.Meanwhile, the Mann-Kendall and the sliding t-test methodwere used to detect the time of frost date which may change suddenly, thus building the impact range of frost in frost stations.Then stability of frost date was calculated by the standard deviation and predictions to future frost date were also made with the Hurst index method.Moreover, the correlation analysis method was used to analyze the influential factors of frost date.The following main results were obtained:(1) The mutation years of the first frost date, the last frost date, and the frost-free period were 2002, 1996, and 1999 respectively.(2)The change rate of frost period with a descending order is frost-free period, first frost date, last frost date.The change rate of Hexi was higher than that of Hedong, which had a greater contribution to the change of the frost period in whole province.(3)The descending order of the stability of frost date in Gansu province is first frost date, last frost date and frost-free period.The stability of frost date of Hexi was better than that of Hedong.(4) The spatial distribution patterns of the first frost date, the last frost date, and the frost-free period follow the rules as "Northern early and southern late, Western early and Eastern late", "Northern late and Southern early, Western late and Eastern early" and "Northern short and Southern long, Western Short and eastern long"respectively.5)The changes in the predicted frost period are roughly the delay of the first frost date, the advance of the last frost date, and the prolonged frost-free period.But there is a slight difference in the magnitude of the change with the descending order of frost-free period, last frost date and first frost date.The last frost date in Hexi may reach the average level of the province in advance, and the frost-free period of this area may exceed that of Hedong in the future.The conclusions can be drawn that the date of occurring, the length and the stability of the frost period are the results of the combined effects of the first and last frost date, altitude, latitude and longitude, in which the dominant factors were significantly different.Meanwhile, the prolonged frost-free period was caused by the deterioration of the stability of the first and last frost date.
  • The Comparative Study of Initial Field and Cloud Microphysical Parameter Scheme in the Numerical Simulation of Squall Line
  • ZHANG Chi;WANG Yongqing;LIAO Yue;SHEN Xinyong;LI Xiaofan
  • 2019 Vol. 38 (2): 410-420.  DOI:10.7522/j.issn.1000-0534.2018.00084
  • Abstract ( ) HTML PDF (13385KB) ( )
  • The paper adopts the CM1 model to simulate the process of a squall line under the background of Northeast Cold Vortex with a high precision horizontal grid distance of 200 m. Comparative experiment was carried out with a horizontal grid spacing of 1 km to explore the influence of grid spacing on squall line, and the influence of unstable energy and vertical wind shear on the squall line is studied through the replacement and modification of the sounding data. It is found that the increase of horizontal grid spacing mainly slows down the evolution of the system, and the strength of system is also weakened. The decrease of unstable energy of the initial field will cause the squall line to weaken obviously and the squall line can not be generated when the unstable energy is reduced to 0. The vertical wind shear has little effect on the formation of the squall line, which mainly changes the structure of the squall line, and when there is no vertical wind shear in the initial field, the squall line is more loosely in structure. Finally, the sensitivity test studied the influence of seven cloud microphysical parameter schemes on the distribution of water particles in squall line. It is found that different schemes of cloud microphysical parameters will change the content and distribution of water particles and further affect the precipitation of solid and liquid, and lead to different precipitation intensity. The solid water particles of the NASA-Goddard version of LFO (NA) scheme used in the simulation of squall line are mainly snow, and has the highest ice and snow content in the upper layer, however, due to snow and ice did not fall to the surface, and the content of rain, hail and graupel are less than other schemes, the accumulated precipitation is minimal.
  • Characteristics of Meteorological Disaster in Ordos Plateau during the Ming and Qing Dynasties
  • XI Xiumei;DUAN Shuguo
  • 2019 Vol. 38 (2): 421-427.  DOI:10.7522/j.issn.1000-0534.2018.00082
  • Abstract ( ) HTML PDF (951KB) ( )
  • By collecting and sorting the meteorological disasters of historical literature in Ordos Plateau region during the Ming and Qing Dynasty, and analyzing the frequency and periodicity characteristics of the meteorological disasters such as drought, wind and sand, frost and snow, hail and flood by statistical analysis and wavelet transform. The results show that the drought frequency is relatively high in this region during the Ming and Qing Dynasty. All kinds of meteorological disasters tend to increase with time. The phases of frequent meteorological disasters occurrences include from the late fifteenth century to the early sixteenth century, the middle of seventeenth century to the middle of eighteenth century and the early twentieth century. In different time scales, the cycles of meteorological disaster occurrences are 3~9, 17~21 and 28~42 years, respectively. The climate of the Ming and Qing Dynasties in the Ordos Plateau was divided into two major stages, the warm and wet period was 1368-1659 years, the 1660-1911 year was the cold dry period, the cold dry was the main, and the climate fluctuation of the following level was experienced:warm wet, warm dry, warm wet, cold dry, cold wet, cold dry, respectively. In the period of meteorological disaster outbreak, the environment deteriorated in this area in Ordos Plateau region during the Ming and Qing Dynasty.
  • Variations of Surface Roughness on Different Underlying Surface at Nagqu Area over the Qinghai-Tibetan Plateau
  • LIU Xiaoran;LI Maoshan;HU Wenbin
  • 2019 Vol. 38 (2): 428-438.  DOI:10.7522/j.issn.1000-0534.2018.00083
  • Abstract ( ) HTML PDF (23047KB) ( )
  • Using the MODIS satellite data and three site turbulent data of the Nagqu region in northern Qinghai-Tibetan plateau in 2008, 2010 and 2012, with the Massman inversion model and an independent method to determine aerodynamic surface roughness, calculate and analyze the dynamic change laws of aerodynamic roughness length and verify the inversion model.The results show that the aerodynamic roughness length has a dynamic monthly change.From February to August, Z0m increases constantly with the ablation of snow and vegetation growth, and the maximum value of sites reaches 4~5 cm.From September to February, due to the post-monsoon over the plateau, Z0m gradually decreased, and the values decreased to about 1~2 cm.Snowfall is the main reason why Z0m during this period is significantly lower than normal.The underlying surface can be divided into four categories according to the different values of Z0m:ice and snow, sparse grassland, lush grassland, and urban.Among them, sparse grassland and lush grassland account for 62.49% and 33.74% of underlying surface of the region respectively, and they are the main categories, whose Z0m fluctuate between 2~6 cm and 1~4 cm.The results obtained by the two calculation methods are positively related to each other.Due to the average sliding effect, the inversion results are smaller than the site calculation results.Overall, the way of calculating Z0m using satellite data in an inversion method is feasible and can be applied to improve the land surface model parameters, the accuracy of the model simulation, and better reveal the heat flux exchange.
  • Composition Analysis of Condensation Water in Biological Soil Crusts Covering Area in Alpine Sandy Lands
  • CHENG Long;JIA Xiaohong;WU Bo;LI Yuanshou;ZHAO Xuebin;ZHOU Hong
  • 2019 Vol. 38 (2): 439-447.  DOI:10.7522/j.issn.1000-0534.2018.00089
  • Abstract ( ) HTML PDF (4519KB) ( )
  • As an important source of moisture in arid and semi-arid regions, condensation water has significant ecological effect to the biological soil crust.For describing the source of condensation water in 5 cm of biological soil crust, we used micro-lysimeters to measure the amounts of condensation water in different types of biological soil crust and moving sand in Qinghai Gonghe basin.The results show that, condensation water generated almost every day except the windy and rainy days.In alpine sandy lands, the condensate water at different land cover types were significant different, and the condensate water was increasing with the development of crust:moss crusts > algae crusts > physical crusts > sand.The amount of condensation water in biological soil crust was significantly higher than that in moving sand, which proving that the biological soil crusts were beneficial to the production of condensation water.The condensate source was divided into two parts:the first was the air water vapor near the ground, including the natural moisture in the atmosphere and the moisture of the evapotranspiration in the plant and the soil, the natural moisture in the atmosphere and the moisture of the evapotranspiration condensed on the surface of the earth, the other was the water vapor in the soil gap, and the water vapor moved upwards in the lower layer of soil due to the temperature gradient of the night.The condensation water in biological soil crust was made up of three parts, hygroscopic and condensate water, atmospheric vapor condensate water, soil condenses water.During the observation period, no significant difference was found in daily soil condenses water in different types of biological soil crusts.And the hygroscopic and condensate water was significantly higher than soil condenses water(P < 0.05).The contribution rate to condensation water of hygroscopic and condensate water and soil condenses water had a fluctuated trend.The composition of condensate in the alpine sand lands was closely related to the relative humidity in the near formation at night, the peak air relative humidity in the near stratum was less than 80% at night, and the ratio of the contribution rate of the moisture absorption water and the atmospheric water vapor condensate to the soil condensate was about 2:1, and the contribution rate of the moisture absorption water and the atmospheric water vapor condensate to the soil condensate was about 4:1 when the relative humidity was higher than 80%.