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28 December 2019, Volume 38 Issue 6   
  • Impact of High-Resolution Atmospheric Forcing and Plant Functional Types Datasets on Soil Temperature Simulation in the Qinghai-Tibetan Plateau
  • SHEN Runping;GUO Qian;CHEN Pingping;LI Xinhui;WANG Shaowu;SHI Chunxiang
  • 2019 Vol. 38 (6): 1129-1139.  DOI:10.7522/j.issn.1000-0534.2018.00159
  • Abstract ( ) HTML PDF (9830KB) ( )
  • Soil temperature is a key physical quantity in the land-atmosphere interaction, and also an important parameter in the research of land surface model simulation. However, it is very difficult to obtain the spatiotemporal continuous data in high resolution, especially in the Qinghai-Tibetan Plateau of China with high altitude and harsh environment. Land surface model simulation with fusion of remote sensing data sets provides a feasible and effective way to obtain soil temperature information with high spatial and temporal resolution. Meanwhile, atmospheric forcing data and plant functional type's data are both important input data of Community Land Model (CLM), and their quality affects the accuracy and reliability of simulation results. In this paper, a new surface plant functional types data (MVEG) was produced, based on multi-source remote sensing data fusion. And then several simulation experiments were carried out which focused on the simulation study of soil temperature (0~10 cm) on the Tibetan Plateau in 2015. These experiments were all about Community Land Model, but different atmospheric forcing data and plant functional type's data were inputted. The latest High Resolution China Meteorological Administration Land Data Assimilation System Version1.0 (HRCLDAS V1.0, 1 km, 1 h) was used to improve the spatial and temporal resolution of model simulation. And its influence on soil temperature simulation was explored, as well as its synergistic effect with MVEG. The results showed that HRCLDAS-V1.0 atmospheric forcing data (1 km, 1 h) had a great improvement effect, it could significantly reduce the error of model simulation. MVEG could improve the simulation of extremes and at the same time, the spatial distribution of soil temperature turned out to be more reasonable. The simulated value of CLDAS/CLM (6 km, 1 h) was larger than observation overall(about 1℃). In contrast, HRCLDAS/CLM (1 km, 1 h) could improve the simulation results. The absolute value of annual mean bias and RMSE of soil temperature (0~10 cm) in the HRCLDAS/CLM simulation experiment were reduced by 0.82℃, 0.18℃, respectively. The simulated value by HR-MVEG/CLM (1 km, 1 h, improved plant functional types) was the most close to the observed value with the RMSE of HR-MVEG/CLM decreased by 0.27℃. Moreover, HR-MVEG/CLM could reflect the detailed characteristics of soil temperature spatial distribution.
  • Numerical Simulation of the Variation of the Turbulent Fluxes on the Qinghai-Tibetan Plateau and its Surrounding Area from 2004 to 2013
  • LI Maoshan;YIN Shucheng;LIU Xiaoran;Lü Zhao;SONG Xingyu;MA Yaoming;SUN Fanglin
  • 2019 Vol. 38 (6): 1140-1148.  DOI:10.7522/j.issn.1000-0534.2018.00145
  • Abstract ( ) HTML PDF (21766KB) ( )
  • The mesoscale model WRF with improved surface roughness is used to simulate the variation characteristics of surface turbulent flux over the Qinghai-Tibetan Plateau and its surrounding areas from 2004 to 2013. The results show that sensible heat flux in the central and southeastern parts of the Qinghai-Tibetan Plateau has increased by 9.952 W·m-2·(10a)-1 and 14.595 W·m-2·(10a)-1 since 2004 to 2013, respectively, sensible heat in other regions of the Qinghai-Tibetan Plateau decreased by -4.473 W·m-2·(10a)-1. The Hengduan Mountains increased by 9.928 W·m-2·(10a)-1, the Yunnan-Guizhou Plateau increased by 9.868 W·m-2·(10a)-1 and the Jiangnan Hilly Region increased by 15.177 W·m-2·(10a)-1; The sensible heat in other surrounding areas decreased, the order of magnitude is -10.26 W·m-2·(10a)-1. The latent heat increased weakly in the eastern part of the Qinghai-Tibetan Plateau[1.175 W·m-2·(10a)-1], and decreased in other parts of the Qinghai-Tibetan Plateau[-3.762 W·m-2·(10a)-1], and weakened in the Sichuan Basin on the eastern side of the Qinghai-Tibetan Plateau, the Bay of Bengal on the southern side and the surrounding northern areas, respectively, -0.27, -2.416 and -2.287 W·m-2·(10a)-1; The latent heat flux increased in different degrees in the surrounding areas. There were strong increases in Jiangsu and Zhejiang provinces in southeastern China[11.385 W·m-2·(10a)-1], increased in Indian Peninsula[2.988 W·m-2·(10a)-1], in Myanmar[9.287 W·m-2·(10a)-1] and in Loess Plateau[1.160 W·m-2·(10a)-1], but decreased in Yunnan-Guizhou Plateau[-2.705 W·m-2·(10a)-1].
  • Relationship between Atmospheric Heat Source over Qinghai-Tibetan Plateau and Its Surrounding Area and Rainstorm in Sichuan Basin during Summer
  • CHEN Dan;ZHOU Changyan;QI Dongmei
  • 2019 Vol. 38 (6): 1149-1157.  DOI:10.7522/j.issn.1000-0534.2019.00041
  • Abstract ( ) HTML PDF (4084KB) ( )
  • Based on the observed daily precipitation data and NCEP/NCAR reanalysis data from 1960 to 2016, the relationship between atmospheric heat source in Qinghai-Tibetan Plateau and its surrounding area and rainstorm in Sichuan Basin in summer were discussed. The main conclusions are as follows:The key region with significant positive correlations between rainstorm in Sichuan Basin and atmospheric heat sources in Qinghai-Tibetan Plateau is located in the south-central and the southern side of the plateau, while the significant negative correlations region is located in the east-central and the eastern side of the plateau. And then the Thermal Contrast Index (Itc) of these two regions is proposed. The index can reflect the difference between eastern and western regions of the Sichuan Basin in summer rainstorm frequency. In the years of high thermal difference index, the position of subtropical high shifts westward and northward, and the water vapor transport in the Arabian Sea and the Bay of Bengal is significantly enhanced. Due to the blocking of the subtropical high, the water vapor accumulates in the western part of the basin and converges with the water vapor from the Southeast coast. At the same time, the trough or the low pressure on the west side of Lake Baikal is westward, and the path of the gathered cold air to the south is westward. Then the water vapor convergence in the western part of Sichuan Basin increased abnormally, and there were more rainstorms. In the eastern part of the basin, water vapor transport in the southwest side is blocked, and the water vapor diverged westward, so the water vapor content in the eastern part of Sichuan Basin is low and the rainstorm is obviously less. In the years of low thermal difference index, the location of the subtropical high is eastward, and the water vapor transport in the Arabia Sea and the bay of Bengal is significantly weaker. Water vapor transport in Sichuan Basin mainly comes from the Southeast coast and increases in the eastern part of Sichuan Basin, but it is difficult to reach the western part of the basin. At the same time, the multi-blocking situation in the south side of Baikal makes the path of the cold air to south is eastward, and the water vapor converges increase in the east of the basin, resulting in more rainstorms. At this time, the water vapor content in the west of the basin is on the low side and the rainstorm is on the low side.
  • Characteristics of the Intraseasonal Oscillation of Qinghai-Tibetan Plateau Monsoon
  • CHEN Yue;LI Wenkai;GUO Weidong
  • 2019 Vol. 38 (6): 1158-1171.  DOI:10.7522/j.issn.1000-0534.2019.00001
  • Abstract ( ) HTML PDF (36037KB) ( )
  • The intraseasonal variability of Qinghai-Tibetan Plateau monsoon (QTPM) has been largely ignored. Based on the ERA-Interim reanalysis data, the characteristics of the intraseasonal oscillation of QTPM revealed by QTPM index (QTPMI) are analyzed by using Ensemble Empirical Mode Decomposition, spectrum and composite analysis. The results show that:(1) The intraseasonal component (10~90 days) of QTPM is dominant for total variability. The intraseasonal component explains approximate 26% of the total variability, and even more dominant in summer (37%). (2) The intraseasonal variability of QTPM variability is associated with the eastward movement of the low-frequency atmospheric circulation anomalies (i. e., the middle-and upper-tropospheric anomalous cyclones and anticyclones) over the plateau. During the eastward propagation of the anomalous signal, the intensity of the anomalous signal has the evolutional characteristics of strengthening-weakening-strengthening-weakening (for example, strengthening before reaching the plateau, weakening eastward on the plateau, strengthening after moving out of the plateau, and weakening when moving eastward into the sea). (3) There is consistency between the circulation and the atmospheric heat source during summer QTPM, showing the relationship between the summer QTPM strengthening (weakening) and the atmospheric heat source strengthening (weakening) over the Qinghai-Tibetan Plateau.
  • Analysis of the Influence of the Qinghai-Tibetan Plateau Surface Energy Change on the Formation of the Plateau Vortex in Summer
  • LI Li;Lü Shihua;FAN Guangzhou
  • 2019 Vol. 38 (6): 1172-1180.  DOI:10.7522/j.issn.1000-0534.2018.00154
  • Abstract ( ) HTML PDF (15077KB) ( )
  • To analyze the climate characteristics of Qinghai-Tibetan Plateau surface heat flux and plateau vortex, study the effects of surface heat flux on the vortex activity in the Qinghai-Tibetan Plateau, the spatial and temporal distribution characteristics of surface sensible heat flux, surface latent heat flux and plateau vortex were analyzed by using the ERA-Interim reanalysis data from 1986 to 2015 (four times a day). By means of correlation analysis and synthesis analysis, this paper selected the key area of the summer plateau vortex generation (30.75°N-36°N, 81°E-91.5°E), and discussed the possible connection between the surface sensible heat flux, surface latent heat flux and the frequency of plateau vortex generation. The result shows that:from the characteristics of time variability, in the last 30 years, there were 915 summer plateau vortex generated, with an average of 30.5 times a year, of which 697 were generated in the key area, accounting for 76.18% of the total, and the climate trend rate of it was -0.598 every 10 years, showing a significant downward trend. In the key area, the surface sensible heat flux generally declined, with an decrease rate of -0.704 W·m-2·(10a)-1, while the latent heat flux shows a weak upward trend, with an increase rate of 0.04 W·m-2·(10a)-1. From the perspective of spatial variability, the plateau vortex were mainly distributed in the northern of Tibet and the southwest of Qinghai, the key area corresponds to the larger value region of the surface sensible heat flux average and the smaller value region of the surface latent heat flux average. In summer, the frequency of plateau vortex is positively correlated with surface sensible heat flux and negatively correlated with surface latent heat flux in the west and north of the plateau (especially in the key area). The distribution of surface energy in the key area is obviously different in the years of more plateau vortex and less. When the surface sensible heat flux in the key area is stronger than the climate average, it is easier to produce plateau vortex; however, when the surface latent heat flux in the key area is stronger than the climate average, it is more difficult to produce plateau vortex, and vice versa. Therefore, both in time and space, the relation between the plateau vortex generating frequency was positively correlated with the surface sensible heat flux, and negatively correlated with the surface latent heat flux in summer.
  • The Variation Characteristics of Planetary Boundary Layer Height in Northwest China: Based on Radiosonde and ERA-Interim Reanalysis Data
  • ZHAO Cailing;LI Yaohui;LIU Yuanpu;ZHOU Ganlin;ZHANG Tiejun;SUN Xuying
  • 2019 Vol. 38 (6): 1181-1193.  DOI:10.7522/j.issn.1000-0534.2018.00152
  • Abstract ( ) HTML PDF (16370KB) ( )
  • The planetary boundary layer height (PBLH) are calculated by using the radiosonde sounding data of 38 L-band operational sites during September 2015 to August 2016 in Northwest China. The radiosonde sounding data of 6 intensive sounding sites are also used. The diurnal and seasonal variations of PBLH have been analyzed by using the radiosonde sounding data and ERA-Interim Daily data. The PBLH-OBS (PBLH derived from of sounding data) shows that in Northwest China, the PBLH-OBS is highest in winter at 08:00 (Beijing time, the same as after). And the PBLH-OBS is highest in spring at 20:00 and decreased significantly from west to east. Compared to the PBLH-OBS, the PBLH-ERA (PBLH of ERA-Interim Daily data) are all lower except the PBLH of 20:00 in summer. The annual PBLH are lower 160 m (170 m) at 08:00 (20:00). The PBLH-ERA of 08:00 (20:00) is lower significantly in winter (summer). PBLH-ERA can basically show the regional distribution of PBLH in Northwest China. The correlation between the PBLH and the lower tropospheric stability (LST), the near surface temperature (Ts) and the 10 m wind speed (WS) is more significant at 08:00. And the PBLH is more related to LST and relative humidity (RH) at 20:00. The intensive sounding data shows that the PBLH-ERA of convective/neutral boundary layer is significantly higher in July 2016. The lower LST, RH and higher WS may be the cause of the higher PBLH-ERA. The stable boundary layer height of PBLH is lower, which is related to lower LST and Ts, but the influencing factors are more complex.
  • Analysis on Precipitation and Cloud of Transverse Shear Line Cases in Summer over Qinghai-Tibetan Plateau based on TRMM PR and VIRS Detection
  • SUN Lilu;WANG Rui;TAN Ruiting;YAO Xiuping;FU Yunfei
  • 2019 Vol. 38 (6): 1194-1207.  DOI:10.7522/j.issn.1000-0534.2018.00160
  • Abstract ( ) HTML PDF (26136KB) ( )
  • The characteristics of precipitation and cloud of two transverse shear line cases in the Qinghai-Tibetan Plateau on June 22, 1998 (orbit number:03257) and July 3, 2011 (orbit number:77642) were investigated based on combining measurements of the tropical rainfall measuring mission (TRMM) precipitation radar (PR) and visible and infrared scanner (VIRS) together with European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis data. Results indicate that storm top height in the region near the transverse shear line over the Qinghai-Tibetan Plateau varies from 4 km to 10 km and only in some region the storm top height reaches about 12 km. Approximately 85% rain rate near the transverse shear line region over Qinghai-Tibetan Plateau varies from 0.5 mm·h-1 to 2.5 mm·h-1 and greater than 20 mm·h-1 only in small scale area. It is apparent that the area is mostly sprinkle. The spectral distributions of effective particle radius (Re) and liquid water path (LWP) are different. The distribution of cloud particle dimension, namely the effective particle radius of cloud particle is evenly distributed, mostly varies in 10~30 μm and the maximum of effective particle radius is 16 μm. And the sizes of cloud particle is 5 μm smaller than that in oceanic cloud system in a general way. It is noticed that the effective particle radius of cloud particle may up to 30 μm in some region. For the LWP (liquid water path), the maximum is 1.5 kg·m-2. And according to the previous work, it is known that the LWP is 0.3 kg·m-2 less than that in frontal precipitation cloud system in eastern China. The storm top height can reaches about 17 km and the maximum echo of near surface rain rate is 50 dBZ, the precipitation echo mainly exist in 6~10 km and 17~25 dBZ. The differences in precipitation vertical structure between shallow precipitation, deep weak convective precipitation and deep strong convective precipitation are evident in the transverse shear line region over Qinghai-Tibetan Plateau and show different near surface rain rate. There also some differences exist in precipitation vertical structure of precipitation cloud with different phases near the cloud top, but the differences in near surface rain rate are not evident.
  • Nudging Radar Data Impact on Southern China Rainstorm Short-term Forecast
  • ZHANG Lan;XU Daosheng;HU Dongming;ZHANG Yufei;LI Huaiyu;LIANG Zhiyan;TIAN Congcong
  • 2019 Vol. 38 (6): 1208-1220.  DOI:10.7522/j.issn.1000-0534.2018.00147
  • Abstract ( ) HTML
  • Based on one kilometer resolution short-term forecast model in Southern China, we adopt the Nudging method to assimilate wind and water substances from radar retrieve. Two typical rainfall cases of pre-flood season in Southern China are conducted in order to study different influence on precipitation forecast of short-term forecast model after improving wind and water substances at initial moment. The results show that the retrieve method is reasonable basically. And then Nudging radar retrieve results to forecast model and compare with control test (Test-ctl). The results show that:(1)The test of only Nudging water substances (Test-qcqr) can improve precipitation forecast during 0~7 h, especially for making rainfall which is less than normal data at 0~2 h better. (2)The test of only Nudging wind (Test-uv) makes better on 3~7 h forecast, but the improvement rate is generally small. (3)The test of both Nudging radar retrieve wind and water substances (Test-qcqr-uv) is best. It has significant improvement on 0~10 h precipitation forecast. From the vertical distribution of micro-physical point, we obtain that the main source of precipitation in the early stage is from water substances, so both test-qcqr and test-qcqr-uv are better obviously for pre-rainfall forecast. Nudging radar retrieve wind can quickly regulate bias of convergence lines at the lower level, but it must be with water substances. In general, Nudging water substances is most significant on short-term forecast, while Nudging radar retrieve wind can make better improvement on precipitation forecast after 3 hours on the base of the former.
  • Potential Vorticity Diagnose on a Heavy Rainstorm under Deformation Field
  • PEI Kunning;WANG Lei;LI Xiehui;CHEN Deyuan
  • 2019 Vol. 38 (6): 1221-1228.  DOI:10.7522/j.issn.1000-0534.2019.00021
  • Abstract ( ) HTML PDF (17460KB) ( )
  • Rainstorm under a background of deformation field occurred in northern Henan from the night of 8 July 2016 to the next morning. We studied the process from the perspective of potential vorticity with Hourly precipitation data from China automatic meteorological station and CMORPH fusion and NCEP's six-hour reanalysis data. The results show that as the high potential vorticity and cold air move to the southeast the potential vorticity values in north of Henan increase gradually from 20:00 on 8 July to 08:00 on 9 July. The meeting of dry cold air and warm wet air causes the heavy rainfall. When the potential vorticity in northern Henan has decreased and typhoon has weakened, the rainfall attenuates consequently due to the continuous eastward movement of the high potential vorticity and the landing of the typhoon at 14:00 on 9 July. The high potential vorticity near 111°E is transmitted eastward and downward, which increases the potential vorticity over the rainstorm area from 02:00 to 08:00 on July 9. Meanwhile, there is strong water vapor convergence on the surface. The maximum value is located at the upwind slope of Taihang Mountain at the height of 900 hPa. In addition, secondary circulation forms from 400 hPa to surface over rainstorm area and the rising branch corresponds to the rainstorm area. The diagnostic analysis of the potential vortity budget equation shows that the local potential vorticity in the rainstorm area at the height of 500 hPa at 08:00 on July 9 increases, and only the horizontal potential vorticity advection provides a positive contribution.
  • Evaluation of Seasonal Prediction for Summer Rainfall in China based on BCC Second-Generation Short-range Climate Forecast Systerm
  • ZHANG Danqi;SUN Fenghua;ZHANG Yaocun
  • 2019 Vol. 38 (6): 1229-1240.  DOI:10.7522/j.issn.1000-0534.2018.00149
  • Abstract ( ) HTML
  • The model ability to predict summer precipitation at seasonal time scale in China is evaluated by using the re-forecast data during 1996-2015 from the BCC second-generation short-range climate forecast system with the lead time of 1~3 months, and the interannual differences of model's prediction ability are analyzed. The possible causes of model prediction errors are also discussed. The results show that the model has a certain seasonal forecasting ability for summer precipitation in China, it has high seasonal forecasting skill over southwest China, the middle and lower reaches of the Yangtze River, west of Huanghuai Plain, North China and Northern Tibet Plateau. Generally speaking, the model has good prediction ability for precipitation anomalies in China. The anomaly sign consistency is high in middle and lower reaches of the Yangtze river, Huanghuai area, South China, Northwest China and northern part of North China. However, there are also some deviations, which are mainly manifested in the less precipitation in East China predicted by the model, the limited forecasting skills for summer precipitation anomalies and the large differences of prediction ability in different years. The predicted high temperature areas in western Pacific and Indian Ocean SST is limited, the intensity of the subtropical high and water vapor convergence is significantly weak, which lead to the less precipitation in East China. Judging from the interannual differences in model's prediction ability, when the precipitation in South China is more than normal years, and the precipitation in the middle and lower reaches of the Yangtze River and North China is less, the model has higher prediction skills. On the contrary, the forecast skill is lower. The analyses of the relationship between summer precipitation in East China and sea surface temperature show that the Northwest Pacific Ocean, the tropical western Pacific and the North Indian Ocean are three key areas for summer precipitation prediction in East China and the SST biases in the Northwest Pacific Ocean have important effects on the model's forecasting skills. The mutual configuration of SST, geopotential height, wind field and water vapor flux divergence field leads to the distribution and intensity difference of summer precipitation in East China, but the model cannot reasonably capture the relationship between them, thus reduce the model's ability to predict summer precipitation in East China. Therefore, accurate prediction on the relationship between external forcing factors and precipitation anomalies is important for the improvement of the precipitation forecasting skills in China.
  • Response of Summer Precipitation in Eastern Part of Northwest China to the Surface Sensible Heat in Early Spring
  • WANG Rui;WANG Hui;LI Dongliang
  • 2019 Vol. 38 (6): 1241-1250.  DOI:10.7522/j.issn.1000-0534.2018.00153
  • Abstract ( ) HTML PDF (15817KB) ( )
  • The monthly sensible heat flux calculation data of 74 conventional meteorological stations in Northwestern China, the monthly precipitation data of 155 conventional meteorological stations in the northwest of China, and the monthly average reanalysis data of NCEP/NCAR from 1961 to 2015 were selected. Mathematical statistical analysis methods such as empirical orthogonal function decomposition (EOF), linear regression analysis, and singular value decomposition (SVD) were used to analyze relationship between the anomalous temporal and spatial evolution characteristics of precipitation in midsummer (July-August) in the eastern part of Northwest China and the surface sensible heat anomalies in the early spring (March-April) of the Northwestern China. The results show that:(1) The precipitation in the eastern part of Northwestern China decreases from southeast to northwest with an overall decadal decline. The most obvious areas for reduction are northern Ningxia and central and southern Inner Mongolia. Its spatial anomaly is mainly characterized by a consistent increase (decrease) in the whole region and a "-+-" change in the northwest-southeast direction. (2) When the surface sensible heat flux is relatively strong (weak) in the early spring in Northwestern China, in midsummer (July-August), the height field over the southern part of Baikal Lake and northern China during midsummer is abnormally high (low), the water vapor divergence (convergence) in Northwestern China is strengthened, and the precipitation in the Ningxia Plain in the northwestern part of the northwest is abnormally low (above average); while in the southwest of Shaanxi, the convergence (diverging) of water vapor is strengthened, which is (not) conducive to the occurrence of precipitation in this region.
  • Research of Inner Mongolia Urban Heat (Cold) Island Effection based on MODIS Data Time Series
  • SU Yue;YU Shan;Duwala;LIN Hongjin;SHAGDAR Gantiganbold
  • 2019 Vol. 38 (6): 1263-1271.  DOI:10.7522/j.issn.1000-0534.2018.00156
  • Abstract ( ) HTML PDF (6832KB) ( )
  • The surface temperature was retrieved based on MODIS remote sensing satellite data, and the spatial distribution and seasonal variation characteristic of urban heat island in Inner Mongolia were studied. The results showed that:(1)The urban heat island effect is weak in western Inner Mongolia during the daytime. Except for Jining, the probability of urban heat island effect in the central region has half-and-half trend, which is not as strong as that in the eastern region. The urban heat island effect in the eastern region has the highest probability, especially in Chifeng and Tongliao. The urban heat island effect is more likely to appear at night than the day, some cities even reaching 100% probability. (2) Inner Mongolia urban heat island effect does not show uniform seasonal variation. In daylight, Xilinhaote, Hailar, Jining and Tongliao are likely to have urban heat island effect in winter. Huhhot and Wulanhaote are likely to have urban heat island effect in summer. In nighttime, Huhhot, Jining, Tongliao, Wuhai, Wulanhaote and Xilinhaote are experienced urban heat island effect yearly. Linhe has urban heat island effect only in spring and not other seasons. Chifeng and Dongsheng have urban heat island effect only in autumn and not other seasons. Bayanhaote, Hailaer, Baotou have seasonal variation. (3) On June, July and August, Huhhot shows obvious urban heat island effect, summer is also the season owns the most serious urban heat island effect. Urban heat island effect also shows in winter, and the nighttime urban heat island effect is more serious. (4) Except cold island effect in May, July and December, the rest months in Jining are heat island effect. A weak cold island effect is showed in daylight on July, and the temperature difference between the urban and suburbs is only 0.58℃. A heat island effect is showed in nighttime on July, and the temperature difference between the urban and suburbs is only 1.42℃. Urban heat island effect is showed in daylight in December. In December, the weak cold island effect is observed in nighttime.
  • Idealized Numerical Simulation of Local Mountain-Valley Winds over Complex Topography
  • JIANG Ping;LIU Xiaoran;ZHU Haonan;ZHU Yu;ZENG Wenxin
  • 2019 Vol. 38 (6): 1272-1282.  DOI:10.7522/j.issn.1000-0534.2019.00019
  • Abstract ( ) HTML PDF (12393KB) ( )
  • This study used observational data to carry out a high-resolution simulation on mountain-valley winds over complex topography with a computational fluid dynamics model. Results show that the thermal contrast by topography could form the mountain-valley winds. During daytime (T16), the temperature at mountain top increases faster than the foot by the solar radiation, which result in thermal contrast at a same level, and thus forms a clear valley-wind circulation. The near-surface wind is strong at both edges of mountain ridge, and the magnitude can reach 0.15 m·s-1. However, the winds at flat areas of mountain top and valley are not observable. In the evening (T04), the valley keeps warm and mountain top cools by radiation, which forms the mountain wind blowing from the valley. The simulated mountain winds are similar to valley wind, but with a smaller magnitude (~0.1 m·s-1) and an opposite direction. Two sensitive tests show that enlarging the amplitude of the thermal difference between mountain top and valley could enhance valley winds at daytime. The near-surface winds can be as large as 0.4 m·s-1, and the corresponding vertical winds and boundary layer height both increase obviously. However, the mountain-wind circulation do not show similar variations.
  • Analysis of Continuous High Temperature Process and Its Anomalous Atmospheric Circulation Characteristics over Gansu Province in August 2016
  • YE Peilong;LIU Xinwei;ZHAO Wenjing;YANG Xiaojun;LI Yan;LIU Weiping
  • 2019 Vol. 38 (6): 1283-1292.  DOI:10.7522/j.issn.1000-0534.2019.00006
  • Abstract ( ) HTML PDF (11007KB) ( )
  • Based on the daily temperature data at 81 stations of Gansu province and the NCEP/NCAR reanalysis data from 1960 to 2016, the general characteristics and the possible anomalous atmospheric circulation effect of continuous heat wave occurred in Gansu province during the August of 2016 had been analyzed and investigated. The results were shown as follows:(1) The number of high temperature days was significantly more than the historical average during the summer of 2016, and most stations in eastern of Gansu province increased by about 5 days; in particular, the high temperature process from the end of July to the late August, which was rarely occurred in history no matter the intensity or the range of high temperature. (2) The South Asia High became stronger and the center position located to 5~10 degree north to the average, South Asia High center slightly shifted to the east, thus, the cold air was not conducive to move towards South areas. The East Asia Subtropical westerly jet was significantly strong and shifted to the North, about 3~5 degree north, meanwhile, its distribution pattern changed from latitudinal to meridional, enhanced the downdraft on south of jet axis, which played an important role in the maintenance and development of high temperature. (3) Affected by the anomalous South Asia High and East Asia Subtropical westerly jet, the continental warm high pressure was extremely strong and stable, meanwhile, the frequency of Ural blocking was about more than 10 days, and the meridional pattern inhibited the eastward movement of ridge-trough system, which was difficult to form effective cooling and precipitation weather. (4) Although the moisture was twenty percent more than normal, particularly in western region, the moisture divergence was strong, therefore, it is difficult to form the effective precipitation; in addition, the downdraft was more significant than the average, caused the warmer air by descending draft in the middle and upper stratosphere, which was conducive to develop and maintain the high temperature weather. Based on the daily temperature data at 81 stations of Gansu province and the NCEP/NCAR reanalysis data from 1960 to 2016, the general characteristics and the possible anomalous atmospheric circulation effect of continuous heat wave occurred in Gansu province during the August of 2016 had been analyzed and investigated. The results were shown as follows:(1) The number of high temperature days was significantly more than the historical average during the summer of 2016, and most stations in eastern of Gansu province increased by about 5 days; in particular, the high temperature process from the end of July to the late August, which was rarely occurred in history no matter the intensity or the range of high temperature. (2) The South Asia High became stronger and the center position located to 5~10 degree north to the average, South Asia High center slightly shifted to the east, thus, the cold air was not conducive to move towards South areas. The East Asia Subtropical westerly jet was significantly strong and shifted to the North, about 3~5 degree north, meanwhile, its distribution pattern changed from latitudinal to meridional, enhanced the downdraft on south of jet axis, which played an important role in the maintenance and development of high temperature. (3) Affected by the anomalous South Asia High and East Asia Subtropical westerly jet, the continental warm high pressure was extremely strong and stable, meanwhile, the frequency of Ural blocking was about more than 10 days, and the meridional pattern inhibited the eastward movement of ridge-trough system, which was difficult to form effective cooling and precipitation weather. (4) Although the moisture was twenty percent more than normal, particularly in western region, the moisture divergence was strong, therefore, it is difficult to form the effective precipitation; in addition, the downdraft was more significant than the average, caused the warmer air by descending draft in the middle and upper stratosphere, which was conducive to develop and maintain the high temperature weather.
  • Sensitivity of Soil Evapotranspiration to Climate Change in the Permafrost Area
  • LI Yuanshou;JIA Xiaohong;QI Yanjun;CHENG Long;WANG Genxu
  • 2019 Vol. 38 (6): 1293-1299.  DOI:10.7522/j.issn.1000-0534.2019.00077
  • Abstract ( ) HTML PDF (1143KB) ( )
  • The sensitivity of evapotranspiration to climate change, which varies in different regions, may lay a foundation for understanding the relationship between permafrost, climate change and hydrological cycle during permafrost activity. This paper calculated the soil evapotranspiration amount and its climatic sensitivity coefficient by Penman-Monteith equation based on the observation data of meteorological stations and analyzed the soil evapotranspiration in typical permafrost regions of the Qinghai-Tibetan Plateau. The results show that soil evapotranspiration is most sensitive to relative humidity (-1.291), followed by wind speed (0.658), and lowest was air temperature (0.248). The sensitivity of soil evapotranspiration to climate was highest in vegetation growth period while lowest in vegetation withering period. The sensitivity of soil evapotranspiration to climate change reached the highest value in August and the lowest value in January or December. The sensitivity of soil evapotranspiration to air temperature and relative humidity varied with the change in vegetation growth. But the change in the sensitivity of soil evapotranspiration to wind velocity was complex and related with transformation in soil freezes and melts.
  • Evaluation of Drought Condition in the Whole Growth Period of Winter Wheat in Rain-Fed Agricultural Area by Using Long Sequence NDVI Data
  • GUO Ni;LU Yaling;HAN Lanying;ZHANG Moucao
  • 2019 Vol. 38 (6): 1300-1308.  DOI:10.7522/j.issn.1000-0534.2019.00059
  • Abstract ( ) HTML PDF (2622KB) ( )
  • Drought is a widespread climate phenomenon throughout the world, as well as one of the natural disasters that seriously impact agricultural. The frequency, intensity and impact of drought are increasing with the global warming, which bring severe challenges to food and ecological security. It is significant for global food and ecological security and sustainable development to strengthen the research and development of drought monitoring and assessment technology to improve the level of drought monitoring and early drought warning. Satellite remote sensing technology can obtain drought information widely, quickly and dynamically; Meanwhile it can cover the shortage of discontinuous and point-to-area of discrete ground sites monitoring space on the ground effectively. In this paper, we select the Longdong rain-fed agricultural area with precipitation of 400~600 mm in the semi-humid climate area in Gansu Province, Northwest China, to evaluate the drought situation of winter wheat in different years using satellite remote sensing data objectively and quantitatively. Based on NASA GIMMS NDVI data from 1981 to 2006 together with precipitation, soil moisture and winter wheat yield data of the same period, the characteristics of winter wheat NDVI and the relationship with precipitation, soil moisture and growth period in these 25 years were analyzed. Furthermore, a new index WWDI (Winter Wheat Drought Index) is proposed, which can objectively and quantitatively evaluate the winter wheat drought situation during the whole growth period. This index considers the slow development of drought and the gradual accumulation of impacts on crops, and implies the robustness of crop growth. The accuracy of WWDI was tested use meteorological data, winter wheat yield and historical Yearbook data. The results showed that:(1) The WWDI can monitor the drought degree of winter wheat during whole growth period. 1995, 2000 and 1992 were the worst drought years that winter wheat suffered in the study area, and the drought degree of winter wheat was corresponding with its meteorological conditions and actual agricultural production. (2) The WWDI has a very significant correlation with winter wheat yield (p < 0.001) and WWDI can be used as an index to evaluate quantitatively the drought status of winter wheat during the whole growth period.
  • Properties of Ice Clouds under Different Optical Depth over China based on DARDAR Data
  • CHEN Wenfeng;ZHENG Youfei;WANG Liwen;ZHENG Qian;LIN Tong
  • 2019 Vol. 38 (6): 1309-1319.  DOI:10.7522/j.issn.1000-0534.2019.00051
  • Abstract ( ) HTML PDF (11996KB) ( )
  • Ice clouds are crucial to the Earth's radiation balance. Two active sensors, the CloudSat radar and the CALIPSO lidar, provide the opportunity to detect ice clouds over the global region. Data DARDAR (liDAR/raDAR) combines these two active sensors advantages to derive ice cloud products, which make obtain optical thin and thick ice cloud vertical properties possible. Based on the data product DARDAR from January 2013 to December 2016, the ice cloud occurrence frequency, horizontal and vertical distribution, seasonal variation and microphysical properties of various optical depth ice clouds in China were analyzed. The results show that the occurrence frequency of ice clouds is 52% over the last four years, which is higher in spring and summer than in autumn and winter and the occurrence height is mainly between 5 and 10 km. The mean ice cloud optical depth, ice water path, and effective radius of China are approximately 4, 157 g·m-2 and 51 μm, respectively. The properties of ice cloud in China not only have obvious regional and seasonal variation characteristics, but also related to the type of ice cloud defined by different optical depth τ values. Optically thin ice clouds (0.03 < τ < 0.3) and opaque ice clouds (0.3 < τ < 3) are the most frequently observed in China which account for approximately 65% of all ice cloud samples and the high concentration area is in the Qinghai-Tibet Plateau. Except for the subvisual ice clouds (τ < 0.03), the main occurrence height of other types of ice clouds decreases with the increase of optical depth. Seasonal changes of different types of ice clouds are not obvious except for thicker ice clouds (τ>20). The more thick ice clouds with τ>3 are more occurred in summer while the thin ice cloud with τ < 3 are more occurred in winter. In terms of microphysical properties, the ice water content (IWC) are changing with the variation of optical depth. The Probability Distribution Function (PDF) of subvisual ice clouds accumulate with the IWC distribution. However, the range of PDF increases with optical depth increasing and both of the IWC distribution range and mode value increase. The relationship between the effective particle radius and height of the ice cloud is more closely related to the optical depth. According to the vertical frequency distribution analysis, all types of ice cloud effective radius increases with height decreasing significantly, optically thinner ones (τ < 3) frequency distribution almost unanimously, while thicker ones (τ>3) effective radius is generally larger.
  • Analysis of the Relationship between Lightning Flashes and Radar Echo based on Terrain Difference
  • SUN Yuting;LAI Anwei;WANG Minghuan;WANG Zhibin;ZHU Chuanlin;SUN Jing
  • 2019 Vol. 38 (6): 1320-1331.  DOI:10.7522/j.issn.1000-0534.2018.00146
  • Abstract ( ) HTML PDF (23428KB) ( )
  • By utilizing the Severe Weather Automatic Nowcast System (SWAN) 3D mosaic products and lightning locating data from 2014 to 2018, the relationship between lightning activity and radar echo characteristics in Central China is investigated and their functional fits under two different terrains of plains and mountains are established for calculating lightning-proxy reflectivity. It was found that the frequency and area of lightning have strong linear correlations with the areas of 40~45 dBZ and 45~50 dBZ reflectivity and the maximum reflectivity, and little correlations with the areas of 50~55 dBZ reflectivity. Under the two terrain conditions of mountain and plain, the fitted S-shape curve of column maximum reflectivity as a function of lightning ground stroke densities are effective. On 13 km grid, a S-shape curve in plain areas is distinctly above that in mountain areas. The fitting values of the two curves are larger than those of the preliminary linear and non-linear relationships within the cloud analysis of the Grid point Statistical Interpolation (GSI) analysis package (developed by NCEP), whereas the growth rates of the two S-shape curves are close to that of linear relationship in the GSI cloud analysis system. On 3 km grid, the S-shape curve in the plain slightly exceeds that in the mountain. By using S-shape curve fitting formulas and the GSI empirical formulas to estimate radar echo, the lightning-proxy reflectivity derived by S-shape curve fitting is very corresponding to the high frequency region of lightning flashes and the strong radar echo field. And the new proxy reflectivity intensity on 13 km grid, which is less accurate than that on 3-km grid, is larger than the reflectivity derived via the preliminary empirical formulas within the GSI and is closer to the observed radar reflectivity value. If the difference of the terrains is not considered, the radar reflectivity values are often underestimated in plain areas and overestimated in mountain areas.
  • Pollution Distribution and Source Analysis of a Haze Process in Beijing-Tianjin-Hebei Area
  • SHEN Xinyong;CHEN Yizhi;GUO Chunyan;LI Xiaofan
  • 2019 Vol. 38 (6): 1332-1343.  DOI:10.7522/j.issn.1000-0534.2018.00157
  • Abstract ( ) HTML PDF (20447KB) ( )
  • To investigate the pollution process from 3 to 6 in November 2016 in Beijing, Tianjin and Hebei region, a simulations with anthropogenic emissions are conducted by using WRF-Chem V3.5 (Weather Research and Forecasting Model coupled to Chemistry Version 3.5). The effective simulated results shows that the atmospheric stability index can effectively quantify the atmospheric stable status in the process of pollution, both the K index and the TT index are more accurate than the other two indices. It is a powerful basis for discussing the causes of the occurrence and development of haze. There are three high value centers of pollution. They are Beijing Tianjin area, northeast Hebei and southern Hebei. The horizontal distribution of PM2.5, PM10 and SO2 pollutants has a more obvious diurnal variation, while CO and NO2 are not changed obviously. The pollution begin on 3 and end on 6 in November, all pollutants are obviously affected by the cold air except NO2, and the concentration suddenly drops on 6 in November. The pollution in Beijing and Tianjin is mainly derived from the external pollution of industry and transport in southern Hebei, while the pollution in the northeast of Hebei and southern Hebei is an endogenous pollution mainly affected by local emissions. With the classification of chemical composition, the main pollutants are CO, and with the classification of the particle size of the pollutants, the size of PM2.5 and PM10 are similar and their concentration is not very different, all of which have great contribution to the pollution.
  • Situation and Influencing Factors of Ground-level Ozone Pollution in China from 2015 to 2017
  • LI Ping;YU Ye;ZHAO Suping;DONG Longxiang;YAN Ming
  • 2019 Vol. 38 (6): 1344-1353.  DOI:10.7522/j.issn.1000-0534.2019.00066
  • Abstract ( ) HTML PDF (3652KB) ( )
  • Based on hourly concentration of ozone (O3) and other three pollutants (fine particles with a diameter of 2.5 μm or less (PM2.5), carbon monoxide (CO), nitrogen dioxide (NO2)) released by the Chinese Ministry of Environmental Protection from 2015 to 2017, and the meteorological data archived by National Climatic Data Center, the situation of ground-level O3 pollution in China was analyzed. The factors influencing summer ground-level O3 in heavily polluted areas was evaluated by stepwise regression. The results showed that the annual mean of daily maximum 8-hour average ozone concentration (O3 MDA8) in China during the years of 2015-2017 were 83.02±16.79, 87.05±14.32 and 94.70±13.89 μg·m-3 respectively. The exceeding rates of O3 MDA8 were 6.61%±6.47%, 6.74%±6.25% and 8.95%±7.61% respectively. The ground-level O3 pollution in China is very heavy and the situation is becoming worse. The concentration of O3 MDA8 increased (growth rate was 14.07%) from 2015 to 2017, with the fastest increase in winter (growth rate ranged from 14.67% to 34.32%) and the slowest increase in summer (growth rate ranged from 2.32% to 14.16%), which could be attributed to the growing concentration of O3 in background. Summer was the most polluted season of ground-level O3, with exceeding rate of 14.93%±16.31%, while the exceeding rate were 8.92%±9.27% in spring, 5.49%±6.80% in autumn and 0.28%±1.27% in winter. The ground-level O3 pollution in the five most developed areas of China, i. e. Jinjingji, Yangtze River delta, Shangdong Peninsula, Chuanyu and Central China regions, was heavier than other areas. Temperature, relative humidity and PM2.5 were the main factors affecting O3 MDA8 in these five heavily polluted areas. In addition, the O3 MDA8 in Jinjingji and Chuanyu were more affected by NO2 compared to the other three heavily polluted areas, which could be explained by the large number of vehicles in these two areas. The O3 MDA8 in Central China regions were more affected by CO than in other areas, which could be attributed to the large usage of coal in this area. This study is helpful to deeply understand the current situation of O3 pollution in China, and provides a reference for policy maker to formulate targeted prevention and control measures.