热带山区高时空分辨率NDVI融合精度及其影响因素分析     

高书鹏  刘晓龙  宋金玲  史正涛  杨磊  郭利彪 《地球信息科学学报》2022,24(2):405-419

高时空分辨率NDVI时序数据作为遥感应用中的重要数据源,对土地覆被动态变化监测具有重要意义,特别是在地表高程变化显著、气候条件复杂、景观异质性强烈的热带山区。虽然当前学者们提出了诸多时空数据融合模型,但针对这些模型在热带山区的NDVI数据融合精度及其影响因素分析尚不多见。对此,本文选取3类时空数据融合方法（权重函数法、概率统计法和多种混合法）中具有代表性的4个模型：STARFM（Spatial and Temporal Adaptive Reflectance Fusion Model）、RASTFM（Spatial and Temporal Adaptive Reflectance Fusion Model）、ESTARFM（Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model）、BSFM（Bayesian Spatiotemporal Fusion Model） （STARFM、ESTARFM为权重函数法;BSFM为概率统计法;RASTFM为多种混合法）,选择位于我国热带山区的纳板河流域作为研究区。对融合模型的数据源选择、研究区的地形及景观空间异质性、融合模型、以及薄云和雾霾等大气条件等影响因素进行分析,研究结果表明：① 数据融合精度随输入影像之间的时间间隔及其相对变化量增加而降低;融合中输入的高、低空间分辨率数据光谱匹配度越高,融合精度越高（OLI优于Sentinel-2; MODIS优于VIIRS）;经过BRDF校正的数据能够有效提高各模型的融合精度;② 地形及空间异质性对融合结果精度影响显著,融合精度与空间异质性呈负相关,本研究中融合精度随着坡度的增大而减小,但坡向对融合精度的影响较小;地形对RASTFM的影响较其他模型低;③ 融合模型中输入的高质量影像越多,模型的融合精度往往越高;④ 薄云和雾霾会对融合精度产生显著负面影响。本研究的结果对于改进热带山地地区的高时空数据融合模型,生产热带山区复杂地理环境的高精度高时空分辨率NDVI数据集具有重要的参考价值。  相似文献   

The Record-breaking Mei-yu in 2020 and Associated Atmospheric Circulation and Tropical SST Anomalies※     

Yihui DING  Yunyun LIU  Zeng-Zhen HU 《大气科学进展》2021,38(12):1980-1993

The record-breaking mei-yu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the mei-yu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.  相似文献   

Western North Pacific Tropical Cyclone Database Created by the China Meteorological Administration   总被引：19，自引：0，他引：19  

Xiaoqin LU  Hui YU  Ming YING  Bingke ZHAO  Shuai ZHANG  Limin LIN  Lina BAI  Rijin WAN 《大气科学进展》2021,38(4):690-699

This paper describes the access to, and the content, characteristics, and potential applications of the tropical cyclone(TC) database that is maintained and actively developed by the China Meteorological Administration, with the aim of facilitating its use in scientific research and operational services. This database records data relating to all TCs that have passed through the western North Pacific(WNP) and South China Sea(SCS) since 1949. TC data collection has expanded over recent decades via continuous TC monitoring using remote sensing and specialized field detection techniques,allowing collation of a multi-source TC database for the WNP and SCS that covers a long period, with wide coverage and many observational elements. This database now comprises a wide variety of information related to TCs, such as historical or real-time locations(i.e., best track and landfall), intensity, dynamic and thermal structures, wind strengths, precipitation amounts, and frequency. This database will support ongoing research into the processes and patterns associated with TC climatic activity and TC forecasting.  相似文献   

The Key Supply Source of Long-Distance Moisture Transport for the Extreme Rainfall Event on July 21, 2012 in Beijing     

李娟  徐祥德  李跃清  赵天良  吴翀 《热带气象学报(英文版)》2021,27(1):34-47

In this study, the Weather Research and Forecasting (WRF) model and meteorological observation data were used to research the long-distance moisture transport supply source of the extreme rainfall event that occurred on July 21, 2012 in Beijing. Recording a maximum rainfall amount of 460 mm in 24 h, this rainstorm event had two dominant moisture transport channels. In the early stage of the rainstorm, the first channel comprised southwesterly monsoonal moisture from the Bay of Bengal (BOB) that was directly transported to north China along the eastern edge of Tibetan Plateau (TP) by orographic uplift. During the rainstorm, the southwesterly moisture transport was weakened by the transfer of Typhoon Vicente. Moreover, the southeasterly moisture transport between the typhoon and western Pacific subtropical high (WPSH) became another dominant moisture transport channel. The moisture in the lower troposphere was mainly associated with the southeasterly moisture transport from the South China Sea and the East China Sea, and the moisture in the middle troposphere was mainly transported from the BOB and Indian Ocean. The control experiment well reproduced the distribution and intensity of rainfall and moisture transport. By comparing the control and three sensitivity experiments, we found that the moisture transported from Typhoon Vicente and a tropical cyclone in the BOB both significantly affected this extreme rainfall event. After Typhoon Vicente was removed in a sensitivity experiment, the maximum 24-h accumulated rainfall in north China was reduced by approximately 50% compared with that of the control experiment, while the rainfall after removing the tropical cyclone was reduced by 30%. When both the typhoon and tropical cyclone were removed, the southwesterly moisture transport was enhanced. Moreover, the sensitivity experiment of removing Typhoon Vicente also weakened the tropical cyclone in the BOB. Thus, the moisture pump driven by Typhoon Vicente played an important role in maintaining and strengthening the tropical cyclone in the BOB through its westerly airflow. Typhoon Vicente was not only the moisture transfer source for the southwesterly monsoonal moisture but also affected the tropical cyclone in the BOB, which was a key supply source of long-distance moisture transport for the extreme rainfall event on July 21, 2012 in Beijing.  相似文献   

Assimilation of Polarimetric Radar Data Using an Ensemble Kalman Filter for the Analysis and Forecast of Tropical Storm Ewiniar     

黎慧琦  刘显通  肖辉  万齐林 《热带气象学报(英文版)》2021,27(2):94-108

This study explores the potential for directly assimilating polarimetric radar data (including reflectivity Z and differential reflectivity ZDR) using an ensemble Kalman filter (EnKF) based on the Weather Research and Forecasting (WRF) model to improve analysis and forecast of Tropical Storm Ewiniar (2018). Ewiniar weakened but brought about heavy rainfall over Guangdong, China after its final landfall. Two experiments are performed, one assimilating only Z and the other assimilating both Z and ZDR. Assimilation of ZDR together with Z effectively modifies hydrometeor fields, and improves the intensity, shape and position of rainbands. Forecast of 24-hour extraordinary rainfall ≥250 mm is significantly improved. Improvement can also be seen in the wind fields because of cross-variable covariance. The current study shows the possibility of applying polarimetric radar data to improve forecasting of tropical cyclones, which deserves more researches in the future.  相似文献   

Influence of Sea Surface Temperature on the Predictability of Idealized Tropical Cyclone Intensity     

钟权加  李建平  李舒文  王羱  丁瑞强  张立凤 《热带气象学报(英文版)》2021,27(4):355-367

The role of sea surface temperature (SST) forcing in the development and predictability of tropical cyclone (TC) intensity is examined using a large set of idealized numerical experiments in the Weather Research and Forecasting (WRF) model. The results indicate that the onset time of rapid intensification of TC gradually decreases, and the peak intensity of TC gradually increases, with the increased magnitude of SST. The predictability limits of the maximum 10 m wind speed (MWS) and minimum sea level pressure (MSLP) are ~72 and ~84 hours, respectively. Comparisons of the analyses of variance for different simulation time confirm that the MWS and MSLP have strong signal-to-noise ratios (SNR) from 0-72 hours and a marked decrease beyond 72 hours. For the horizontal and vertical structures of wind speed, noticeable decreases in the magnitude of SNR can be seen as the simulation time increases, similar to that of the SLP or perturbation pressure. These results indicate that the SST as an external forcing signal plays an important role in TC intensity for up to 72 hours, and it is significantly weakened if the simulation time exceeds the predictability limits of TC intensity.  相似文献   

Role of external forcing on the seasonal and interannual variability of mixed layer depth over the Bay of Bengal using reanalysis datasets during 1980–2015     

《Dynamics of Atmospheres and Oceans》2021

The monsoon reversal winds in different seasons and high influx of freshwater from various rivers make the Bay of Bengal (BoB) a unique region. Thus, the knowledge of the dynamics of the mixed layer over this region is very important to assess the climatic variation of the Indian subcontinent. A comprehensive study of the role of external forcing on the seasonal and interannual mixed layer depth (MLD) variability over the BoB is carried out for 36 years (1980–2015) using reanalysis products. A weak and strong seasonality of MLD is observed over the northern and the southern BoB (NBoB and SBoB) respectively. The partial correlation suggests that the net heat flux (Qnet) is the major contributor to the deepening of MLD over the NBoB, whereas the wind stress controls the deepening over the SBoB. The seasonal variability reveals the deepening of MLD during summer and winter monsoon and the shallowing during pre- and post-monsoon over the BoB. The relation of the interannual MLD variability and the different phases of the Indian Ocean Dipole (IOD) reveals that the negative phase of IOD is associated with deeper MLD over BoB while the positive phase of IOD depicts shallower MLD. In addition, the opposing characteristic of MLD is highly prominent during October-December. This is majorly contributed by variations related to the second downwelling Kelvin and associated Rossby waves over BoB for the opposing phases of the IOD years.  相似文献   

A study of track deflection associated with the landfall of Tropical Cyclone Sidr (2007) over the Bay of Bengal and Bangladesh     

《Dynamics of Atmospheres and Oceans》2021

In this study, the dynamics of track deflection associated with Tropical Cyclone (TC) Sidr (2007) are explored using a numerical weather prediction model. It is found that (a) the simulated track of Sidr is sensitive to flow, orographic, and model vertical structure that change the environmental steering flow leading to the track deflection. In particular, the track of TC Sidr is deflected northwestward for cases with lower domain height, horizontal domain covering only part of Himalaya mountains, and varying mountain heights; (b) the simulated track of TC Sidr, when compared with GFS reanalysis data, is mainly controlled by its deep-layer environmental steering flow as a point vortex; (c) the northwestward deflection with lower domain height is caused by an artificially larger high pressure at lower levels in the vicinity of the Himalayas, due to the upward propagation of wave energy being reflected by the upper domain boundary; (d) the significant northwestward deflection associated with the varying mountain height cases is due to the cyclone vortex being advected by the northeasterly monsoonal flow, which is blocked by the mountains in the corresponding cases with mountains; (e) the northeastward track deflection after the landfall of Sidr is explained by the addition of the frictional force.In summary, the model vertical domain height and the Himalaya mountain representation play key roles in influencing the accuracy of TC Sidr track simulation, compared with other factors, such as the vertical resolution, at least for TC Sidr.  相似文献   

Effects of vertical wind shear and storm motion on tropical cyclone rainfall asymmetries over the North Indian Ocean     

《Dynamics of Atmospheres and Oceans》2021

Tropical cyclone (TC) rainfall asymmetry is often influenced by vertical wind shear and storm motion. This study examined the effects of environmental vertical wind shear (200-850 hPa) and storm motion on TC rainfall asymmetry over the North Indian Ocean (NIO): the Bay of Bengal (BoB) and the Arabian Sea (AS). Four TC groups were used in this study: Cyclonic Storm (CS), Severe Cyclonic Storm (SCS), Very Severe Cyclonic Storm (VSCS) and Extreme Severe Cyclonic Storm (ESCS). The Fourier coefficients for wave number-1 was used to analyze the structure of TC rainfall asymmetry. Results show that the maximum TC rainfall asymmetry was predominantly in the downshear left quadrant in the BoB, while it placed to downshear right quadrant in the AS, likely due to the different primary circulation strength of the TC vortex. For the most intense cyclone (ESCS), the maximum TC rainfall asymmetry was in the upshear left quadrant in the BoB, whereas it was downshear right quadrant in the AS. It is evident for both basins that the magnitude of TC rainfall asymmetry declined (increased) with TC intensity (shear strength). This study also examined the collective effects of vertical wind shear and storm motion on TC rainfall asymmetry. Here, the analysis in case of the strong shear environment (>7 m s^-1) omitted for the AS because the maximum value for this basin was about 7 m s^-1. The result showed that the downshear left quadrant was dominant in the BoB for the maximum TC rainfall asymmetry. In a weak shear environment (<5 m s^-1), on the other hand, downshear right quadrant is evident for the maximum TC rainfall asymmetry in the BoB, while it placed dominantly downshear left quadrant in the AS. In the case of motion-relative wavenumber-1, the maximum TC rainfall asymmetry was dominantly downshear for both basins.  相似文献   

1949—2019 年影响山东的热带气旋时空分布及极端降水和大气环流异常          下载免费PDF全文

欧阳婧怡  黄菲  许士斌  曹倩 《山东气象》2021,41(4):1-10

使用中国气象局热带气旋资料中心的热带气旋最佳路径数据集和NCEP/NCAR再分析资料提供的月平均数据,对北上影响山东的热带气旋（tropical cyclone,TC）及其造成的极端降水进行统计分析,并揭示了有利于 TC北移影响山东的大气环流特征。结果表明：影响山东的 TC主要出现 于 6—9 月,其中盛夏时节（7、8 月）TC对山东影响最大;TC影响山东时,强度主要为台风及以下等 级,或已发生变性;TC会引发山东极端降水事件,TC极端降水多出现在夏秋季（7—9 月）,其中8月的占比最大,9月次之,TC降水在极端降水事件中的占比约为 10%,但年际变化大,有些年份占比达60%以上,特别是1990 年以来 TC对极端降水的贡献显著增强;影响山东的 TC主要生成于西 北太平洋,多为转向型路径;当500 hPa位势高度异常场呈太平洋一日本遥相关型的正位相时,TC更易北上影响山东,此时西北太平洋副热带高压位置偏北,其外围气流会引导TC北上转向,对华东地区造成影响;850 hPa上,南海至西北太平洋存在异常气旋式环流,对流活跃,夏季风环流和季风槽加强,有利于TC的生成和发展,同时,华东、华南上空有异常上升运动,涡度增大,垂直风切变减小,水汽充沛,TC登陆后强度能得到较好的维持。  相似文献