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62.
1951～2008年西南地区夏季旱涝的环流特征 总被引：1，自引：0，他引：1
本文利用西南地区多个站点所取得的1951~2008年逐月降水量资料,结合1948~2008年的17层高度场和风场资料,重点取200hPa与700hPa两个层次,分析了与西南地区夏季旱涝年对应的环流异常特征,结果表明:欧亚地区中高纬地区环流(特别是乌山和贝湖附近高度距平的变化)以及西南地区上空伴随高度场出现的气旋性环流和反气旋性环流是直接影响我国西南地区夏季降水的重要环流因子。 相似文献
63.
为了进一步认识北极涛动与行星波之间的关系,利用NCEP/NCAR再分析资料并借助谐波分析、相关分析等方法讨论了北极涛动异常下行星波的活动情况。结果表明:在北极涛动指数强(弱)值年,纬向平均风场在中纬度明显减小(增大),在中高纬度明显增大(减小);行星波1波振幅在低纬度对流层中层和中纬度平流层明显增大(减小),在高纬度平流层明显减小(增大);2波振幅在中纬度对流层明显减小(增大),在高纬度平流层有所增大(减小)。E-P通量反映出在北极涛动强(弱)值年,行星波1波在中高纬度从地面向上传播显著增强(减弱),低纬度波导显著增强(减弱),极地波导显著减弱(增强);2波在中高纬度从地面向上传播显著减弱(增强),低纬度波导和极地波导变化不明显。 相似文献
64.
Regional distribution and diurnal variation of deep convective systems over the Asian monsoon region 总被引：2，自引：0，他引：2
Using 12 years of data from the Tropical Rainfall Measuring Mission(TRMM)-based Precipitation Radar(PR),spatial and diurnal variations of deep convective systems(DCSs)over the Asian monsoon region are analyzed.The DCSs are defined by a 20 dBZ echo top extending 14 km.The spatial distribution of DCSs genesis is also discussed,with reference to the National Centers for Environmental Prediction(NCEP)reanalysis data.The results show that DCSs occur mainly over land.They concentrate in south of 20°N during the pre-monsoon season,and then move distinctly to mid-latitude regions,with the most active region on the south slope of the Himalayas during monsoon season.DCSs over the Tibetan Plateau are more frequent than those in central-eastern China,but smaller in horizontal scale and weaker in convective intensity.DCSs in central-eastern China have more robust updrafts and generate more lightning flashes than in other Asian monsoon regions.The horizontal scale of DCSs over the ocean is larger than that over the other regions,and the corresponding minimum infrared(IR)brightness temperature is lower,whereas the convective intensity is weaker.Continental DCSs are more common from noon through midnight,and DCSs over the Tibetan Plateau are more frequently from noon through evening.Oceanic DCSs frequency has a weaker diurnal cycle with dawn maximum,and diurnal variation of DCSs over the tropical maritime continent is consistent with that over the continent. 相似文献
65.
In this study, sensible heat (H) calculation using remote sensing data over an alpine grass landscape is conducted from May to September 2010, and the calculation is validated using LAS (large aperture scintillometers) measurements. Data from two remote sensing sensors (FY3A-VIRR and TERRA-MODIS) are analysed. Remote sensing data, combined with the ground meteorological observations (pressure, temperature, wind speed, humidity) are fed into the SEBS (Surface Energy Balance System) model. Then the VIRR-derived sensible heat (VIRR_SEBS_H) and MODIS-derived sensible heat (MODIS_SEBS_H) are compared with the LAS-estimated H, which are obtained at the respective satellite overpass time. Furthermore, the similarities and differences between the VIRR_SEBS_H and MODIS_SEBS_H values are investigated. The results indicate that VIRR data quality is as good as MODIS data for the purpose of H estimation. The root mean square errors (rmse) of the VIRR_SEBS_H and MODIS_SEBS_H values are 45.1098 W/m2 (n = 64) and 58.4654 W/m2 (n = 71), respectively. The monthly means of the MODIS_SEBS_H are marginally higher than those of VIRR_SEBS_H because the satellite overpass time of the TERRA satellite lags by 25 min to that of the FT3A satellite. Relative evaporation (EFr), which is more time-independent, shows a higher agreement between MODIS and VIRR. Many common features are shared by the VIRR_SEBS_H and the MODIS_SEBS_H, which can be attributed to the SEBS model performance. In May–June, H is over-estimated with more fluctuations and larger rmse, whereas in July–September, H is under-estimated with fewer fluctuations and smaller rmse. Sensitivity analysis shows that potential temperature gradient (delta_T) plays a dominant role in determining the magnitude and fluctuation of H. The largest rmse and over-estimation in H occur in June, which could most likely be attributed to high delta_T, high wind speed, and the complicated thermodynamic state during the transitional period when bare land transforms to dense vegetation cover. 相似文献
66.
利用雨滴谱和Ka波段毫米波云雷达等资料,针对2020年7月21日发生在那曲地区的一次对流云降水过程进行特征分析。结果表明:此次强对流云降水过程表现出明显的日变化特征,对流云在傍晚达到最强。强对流区内存在明显的上升气流和下沉气流,降水最强时雷达回波达到40 dBZ以上,降水过程中最大云顶高度为12 km,最小为720 m。那曲地区Gamma分布相对于M-P分布更适用于对流云小直径粒子（0~1 mm）的雨滴谱拟合,随着粒子直径增大,降水越来越不稳定。 相似文献
67.
Record ozone loss was observed in the Arctic stratosphere in spring 2020. This study aims to determine what caused the extreme Arctic ozone loss. Observations and simulation results are examined in order to show that the extreme Arctic ozone loss was likely caused by record-high sea surface temperatures(SSTs) in the North Pacific. It is found that the record Arctic ozone loss was associated with the extremely cold and persistent stratospheric polar vortex over February–April, and the extremely cold vortex was a result of anomalously weak planetary wave activity. Further analysis reveals that the weak wave activity can be traced to anomalously warm SSTs in the North Pacific. Both observations and simulations show that warm SST anomalies in the North Pacific could have caused the weakening of wavenumber-1 wave activity, colder Arctic vortex, and lower Arctic ozone. These results suggest that for the present-day level of ozone-depleting substances, severe Arctic ozone loss could form again, as long as certain dynamic conditions are satisfied. 相似文献
68.
69.
The Role of Stationary and Transient Planetary Waves in the Maintenance of Stratospheric Polar Vortex Regimes in Northern Hemisphere Winter 总被引：1，自引：1，他引：0
Using 1958-2002 NCEPNCAR reanalysis data, we investigate stationary and transient planetary wave propagation and its role in wave-mean flow interaction which influences the state of the polar vortex (PV) in the stratosphere in Northern Hemisphere (NH) winter. This is done by analyzing the Eliassen-Palm (E-P) flux and its divergence. We find that the stationary and transient waves propagate upward and equatorward in NH winter, with stronger upward propagation of stationary waves from the troposphere to the stratosphere, and stronger equatorward propagation of transient waves from mid-latitudes to the subtropics in the troposphere. Stationary waves exhibit more upward propagation in the polar stratosphere during the weak polar vortex regime (WVR) than during the strong polar vortex regime (SVR). On the other hand, transient waves have more upward propagation during SVR than during WVR in the subpolar stratosphere, with a domain of low frequency waves. With different paths of upward propagation, both stationary and transient waves contribute to the maintenance of the observed stratospheric PV regimes in NH winter. 相似文献
70.