Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic（AVISO） data using a sea level anomaly（SLA）-based eddy identification. A geographical d...Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic（AVISO） data using a sea level anomaly（SLA）-based eddy identification. A geographical distribution and an eddy polarity, an eddy lifetime and propagation distances, eddy origins and terminations,eddy propagation directions and trajectories, eddy kinetic properties, the evolution of eddy properties,seasonal and interannual variabilities of eddy activities are analyzed in this area. Eddies exist principally in the western Bay of Bengal and most of them propagate westward. The polarity distribution of eddies shows cyclones prefer to occur in the northwest and south of the Bay of Bengal, while anticyclones mainly occur in the east of the bay. Five hundred and sixty-five cyclones and 389 anticyclones with the lifetime that exceeds 30 d are detected during the 22 a period, and there is a preference for the cyclones for all lifetime and propagation distances. The kinetic properties of all observed eddies show the average amplitude of the cyclones is larger than that of the anticyclones, whereas that is opposite for average radius, and their average velocities are basically the same. Moreover, the evolution of eddies properties reveals that the eddies with a long lifetime that exceeds 90 d have a significant double-stage feature of the former 50 d growth period and the dying period after 50 d. For the seasonal variability of the eddies, the cyclones occur more often in spring while the anticyclones occur more often in summer. The analysis of long-lived eddy seasonal distributions shows that there is the obvious seasonal variation of the eddy activities in the Bay of Bengal. The interannual variability of an eddy number shows an obvious negative correlation with the EKE variation.展开更多
Precipitation is the dominant factor that controls vegetation growth and land-use practices in the arid and semiarid Mongolian Plateau(MP), so the spatiotemporal heterogeneity of precipitation change has been an impor...Precipitation is the dominant factor that controls vegetation growth and land-use practices in the arid and semiarid Mongolian Plateau(MP), so the spatiotemporal heterogeneity of precipitation change has been an important scientific question in the region. This study investigated the spatiotemporal characteristics of annual and seasonal precipitation across the entire MP based on monthly precipitation data from 136 meteorological stations during 1961–2014 by using a modified Mann–Kendall test, Sen's slope, Morlet Wavelet Transform, and geostatistical methods. Results show the following: 1) Annual precipitation decreased slightly from 1961 to 2014.Stations with positive and negative trends were 41.9%and 58.1%, respectively. Significant positive trends were mainly in the southwestern and northeastern regions of the plateau, whereas significant negative trends were in the northern and southeastern regions.2) Precipitation decreased at rates of-5.65 and-0.41 mm/decade in summer and autumn, respectively, but increased at 1.91 and 0.51 mm/decade in spring and winter. The contribution of spring and winter precipitation to the annual amount increased significantly, but that of summer precipitation decreased significantly. 3) A large majority of stations(80.2%) showed decreasing trends in summer,whereas 89.7% and 83.1% of stations showed increasing trends in spring and winter. The spatial distribution of trend magnitude in seasonal precipitation amount was strongly heterogeneous. 4)By climatic zones, precipitation increased in humid and arid zones, but decreased in a semiarid zone. On the whole, the MP experienced a drying trend, with significant regional differentiation and seasonal variations.展开更多
干旱区绿洲春季土壤盐渍化问题十分严重。以新疆第二师31团灌区为例,在GIS技术的支持下,运用经典统计学和地统计学方法,对春季灌区内不同深度土层的盐渍化特征与空间分布格局进行分析,探讨了这一地区土壤盐渍化规律,为当地农业生产和土...干旱区绿洲春季土壤盐渍化问题十分严重。以新疆第二师31团灌区为例,在GIS技术的支持下,运用经典统计学和地统计学方法,对春季灌区内不同深度土层的盐渍化特征与空间分布格局进行分析,探讨了这一地区土壤盐渍化规律,为当地农业生产和土壤改良提供了理论依据。结果显示:春季灌区内土壤pH值范围在8.01~8.32,总体呈碱性;土壤盐分呈表聚型,盐分阳离子以K^(+)和Na^(+)为主,阴离子在耕地土壤以SO_(4)^(2-)、在非耕地土壤以Cl^(-)为主;盐分类型耕地以氯化物-硫酸盐型为主,非耕地以硫酸盐-氯化物型为主。不同深度土层土壤盐分含量在水平方向均具有较强的变异性且大多具良好的空间相关性;其中,40~60 cm土层土壤盐分含量空间相关性强烈,0~20 cm、20~40 cm、80~100 cm土层空间相关性中等。在垂直方向上,0~20 cm、40~60 cm土层土壤盐分含量较高,在1.59~8.91 g kg^(-1)之间;20~40 cm、80~100 cm土层盐分含量相对较低,在2.44~3.95 g kg^(-1)之间。在水平方向上,不同深度土层的土壤盐分含量空间分布状况基本一致,研究区中部及东北部盐分含量相对较高,且由中部向两侧逐渐递减。中部荒漠化程度高,地势低洼之处盐分含量达3.00~8.91 g kg^(-1);西北和东南部盐分含量相对较低,在1.59~3.00 g kg^(-1)之间。展开更多
In this study, significant rainfall microphysical variability is revealed for the extremely heavy rainfall event over Henan Province in July 2021(the “21·7” Henan EHR event) using a dense network of disdrometer...In this study, significant rainfall microphysical variability is revealed for the extremely heavy rainfall event over Henan Province in July 2021(the “21·7” Henan EHR event) using a dense network of disdrometers and two polarimetric radars.The broad distributions of specific drop size distribution(DSD) parameters are identified in heavy rainfall from the disdrometer observations, indicating obvious microphysical variability on the surface. A K-means clustering algorithm is adopted to objectively classify the disdrometer datasets into separate groups, and distinct DSD characteristics are found among these heavy rainfall groups. Combined with the supporting microphysical structures obtained through radar observations, comprehensive microphysical features of the DSD groups are derived. An extreme rainfall group is dominantly formed in the deep convection over the plain regions, where the high number of concentrations and large mean sizes of surface raindrops are underpinned by both active ice-phase processes and efficient warm-rain collision-coalescence processes in the vertical direction. Convection located near orographic regions is characterized by restricted ice-phase processes and high coalescence efficiency of liquid hydrometeors, causing the dominant DSD group to comprise negligible large raindrops. Multiple DSD groups can coexist within certain precipitation episodes at the disdrometer stations, indicating the potential microphysical variability during the passage of convective system on the plain regions.展开更多
基金The National Natural Science Foundation of China under contract No.41576176the National High Technology Research and Development Program(863 program)of China under contract No.2013AA122803the Project of ESA-MOST Dragon-3 Cooperation Programme
文摘Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic（AVISO） data using a sea level anomaly（SLA）-based eddy identification. A geographical distribution and an eddy polarity, an eddy lifetime and propagation distances, eddy origins and terminations,eddy propagation directions and trajectories, eddy kinetic properties, the evolution of eddy properties,seasonal and interannual variabilities of eddy activities are analyzed in this area. Eddies exist principally in the western Bay of Bengal and most of them propagate westward. The polarity distribution of eddies shows cyclones prefer to occur in the northwest and south of the Bay of Bengal, while anticyclones mainly occur in the east of the bay. Five hundred and sixty-five cyclones and 389 anticyclones with the lifetime that exceeds 30 d are detected during the 22 a period, and there is a preference for the cyclones for all lifetime and propagation distances. The kinetic properties of all observed eddies show the average amplitude of the cyclones is larger than that of the anticyclones, whereas that is opposite for average radius, and their average velocities are basically the same. Moreover, the evolution of eddies properties reveals that the eddies with a long lifetime that exceeds 90 d have a significant double-stage feature of the former 50 d growth period and the dying period after 50 d. For the seasonal variability of the eddies, the cyclones occur more often in spring while the anticyclones occur more often in summer. The analysis of long-lived eddy seasonal distributions shows that there is the obvious seasonal variation of the eddy activities in the Bay of Bengal. The interannual variability of an eddy number shows an obvious negative correlation with the EKE variation.
基金funded by the China National Key R&D Program(Grant No.2016YFA0600303)CAS International ProgramClimate Change Observation and Synthesis along B&R(Grant No.34111KYSB20160010)the National Natural Science Foundation of China(Grant No.61661045)
文摘Precipitation is the dominant factor that controls vegetation growth and land-use practices in the arid and semiarid Mongolian Plateau(MP), so the spatiotemporal heterogeneity of precipitation change has been an important scientific question in the region. This study investigated the spatiotemporal characteristics of annual and seasonal precipitation across the entire MP based on monthly precipitation data from 136 meteorological stations during 1961–2014 by using a modified Mann–Kendall test, Sen's slope, Morlet Wavelet Transform, and geostatistical methods. Results show the following: 1) Annual precipitation decreased slightly from 1961 to 2014.Stations with positive and negative trends were 41.9%and 58.1%, respectively. Significant positive trends were mainly in the southwestern and northeastern regions of the plateau, whereas significant negative trends were in the northern and southeastern regions.2) Precipitation decreased at rates of-5.65 and-0.41 mm/decade in summer and autumn, respectively, but increased at 1.91 and 0.51 mm/decade in spring and winter. The contribution of spring and winter precipitation to the annual amount increased significantly, but that of summer precipitation decreased significantly. 3) A large majority of stations(80.2%) showed decreasing trends in summer,whereas 89.7% and 83.1% of stations showed increasing trends in spring and winter. The spatial distribution of trend magnitude in seasonal precipitation amount was strongly heterogeneous. 4)By climatic zones, precipitation increased in humid and arid zones, but decreased in a semiarid zone. On the whole, the MP experienced a drying trend, with significant regional differentiation and seasonal variations.
文摘干旱区绿洲春季土壤盐渍化问题十分严重。以新疆第二师31团灌区为例,在GIS技术的支持下,运用经典统计学和地统计学方法,对春季灌区内不同深度土层的盐渍化特征与空间分布格局进行分析,探讨了这一地区土壤盐渍化规律,为当地农业生产和土壤改良提供了理论依据。结果显示:春季灌区内土壤pH值范围在8.01~8.32,总体呈碱性;土壤盐分呈表聚型,盐分阳离子以K^(+)和Na^(+)为主,阴离子在耕地土壤以SO_(4)^(2-)、在非耕地土壤以Cl^(-)为主;盐分类型耕地以氯化物-硫酸盐型为主,非耕地以硫酸盐-氯化物型为主。不同深度土层土壤盐分含量在水平方向均具有较强的变异性且大多具良好的空间相关性;其中,40~60 cm土层土壤盐分含量空间相关性强烈,0~20 cm、20~40 cm、80~100 cm土层空间相关性中等。在垂直方向上,0~20 cm、40~60 cm土层土壤盐分含量较高,在1.59~8.91 g kg^(-1)之间;20~40 cm、80~100 cm土层盐分含量相对较低,在2.44~3.95 g kg^(-1)之间。在水平方向上,不同深度土层的土壤盐分含量空间分布状况基本一致,研究区中部及东北部盐分含量相对较高,且由中部向两侧逐渐递减。中部荒漠化程度高,地势低洼之处盐分含量达3.00~8.91 g kg^(-1);西北和东南部盐分含量相对较低,在1.59~3.00 g kg^(-1)之间。
基金jointly supported by the National Natural Science Foundation of China (Grant Nos. 42025501, 42005009, 41875053, U2142203)the National Key Research and Development Program of China (Grant No. 2017YFC1501703)+1 种基金the Basic Research Fund of CAMS (Grant No. 2021Z003)the Open Research Program of the State Key Laboratory of Severe Weather (Grant No. 2020LASW-A01)。
文摘In this study, significant rainfall microphysical variability is revealed for the extremely heavy rainfall event over Henan Province in July 2021(the “21·7” Henan EHR event) using a dense network of disdrometers and two polarimetric radars.The broad distributions of specific drop size distribution(DSD) parameters are identified in heavy rainfall from the disdrometer observations, indicating obvious microphysical variability on the surface. A K-means clustering algorithm is adopted to objectively classify the disdrometer datasets into separate groups, and distinct DSD characteristics are found among these heavy rainfall groups. Combined with the supporting microphysical structures obtained through radar observations, comprehensive microphysical features of the DSD groups are derived. An extreme rainfall group is dominantly formed in the deep convection over the plain regions, where the high number of concentrations and large mean sizes of surface raindrops are underpinned by both active ice-phase processes and efficient warm-rain collision-coalescence processes in the vertical direction. Convection located near orographic regions is characterized by restricted ice-phase processes and high coalescence efficiency of liquid hydrometeors, causing the dominant DSD group to comprise negligible large raindrops. Multiple DSD groups can coexist within certain precipitation episodes at the disdrometer stations, indicating the potential microphysical variability during the passage of convective system on the plain regions.
