Venus Express observations of ULF and ELF waves in the Venus ionosphere: Wave properties and sources     

C.T. Russell  H. Leinweber  R.A. Hart  H.Y. Wei  R.J. Strangeway  T.L. Zhang 《Icarus》2013

Electrical activity in a planetary atmosphere enables chemical reactions that are not possible under conditions of local thermodynamic equilibrium. In both the Venus and terrestrial atmospheres, lightning forms nitric oxide. Despite the existence of an inventory of NO at Venus like the Earth’s, and despite observations of the signals expected from lightning at optical, VLF, and ELF frequencies, the existence of Venus lightning still is met with some skepticism. The Venus Express mission was equipped with a fluxgate magnetometer gradiometer system sampling at rates as high as 128 Hz, and making measurements as low as 200 km altitude above the north polar regions of Venus. However, significant noise levels are present on the Venus Express spacecraft. Cleaning techniques have been developed to remove spacecraft interference at DC, ULF, and ELF frequencies, revealing two types of electromagnetic waves, a transverse right-handed guided mode, and a linearly polarized compressional mode. The propagation of both types of signals is sensitive to the magnetic field in ways consistent with propagation from a distant source to the spacecraft. The linearly polarized compressional waves generally are at lower frequencies than the right-handed transverse waves. They appear to be crossing the usually horizontal magnetic field. At higher frequencies above the lower hybrid frequency, waves cannot enter the ionosphere from below when the field is horizontal. The arrival of signals at the spacecraft is controlled by the orientation of the magnetic field. When the field dips into the atmosphere, the higher frequency guided mode above the lower hybrid frequency can enter the ionosphere by propagating along the magnetic field in the whistler mode. These properties are illustrated with examples from five orbits during Venus Express’ first year in orbit. These properties observed are consistent with the linearly polarized compressional waves being produced at the solar wind interface and the transverse guided waves being produced in the atmosphere.  相似文献   

A data assimilation approach to discharge estimation from space     

Jeffrey Neal  Guy Schumann  Paul Bates  Wouter Buytaert  Patrick Matgen  Florian Pappenberger 《水文研究》2009,23(25):3641-3649

River discharge is currently monitored by a diminishing network of gauges, which provide a spatially incomplete picture of global discharges. This study assimilated water level information derived from a fused satellite Synthetic Aperture Radar (SAR) image and digital terrain model (DTM) with simulations from a coupled hydrological and hydrodynamic model to estimate discharge in an un‐gauged basin scenario. Assimilating water level measurements led to a 79% reduction in ensemble discharge uncertainty over the coupled hydrological hydrodynamic model alone. Measurement bias was evident, but the method still provided a means of improving estimates of discharge for high flows. The study demonstrates the potential of currently available synthetic aperture radar imagery to reduce discharge uncertainty in un‐gauged basins when combined with model simulations in a data assimilation framework, where sufficient topographic data are available. The work is timely because in the near future the launch of satellite radar missions will lead to a significant increase in the volume of data available for space‐borne discharge estimation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Adjoint Assimilation in Marine and an Example of Application   总被引：1，自引：1，他引：0  

XU Qing  LIU Yuguang  and LU Xianqing Physical Oceanography Laboratory  Ocean University of China  Qingdao  P.R.China 《中国海洋大学学报(英文版)》2005,4(1):14-20

This paper aims at a review of the work carried out to date on the adjoint assimilation of data in marine ecosystem models since 1995. The structure and feature of the adjoint assimilation in marine ecosystem models are also introduced. To illustrate the application of the adjoint technique and its merits, a 4-variable ecosystem model coupled with a 3-D physical model is established for the Bohai Sea and the Yellow Sea. The chlorophyll concentration data derived from the SeaWiFS ocean colour data are assimilated in the model with the technique. Some results are briefly presented.  相似文献   

STUDY ON THE MIGRANT LABOUR FORCE OF CHINA IN RECENT YEARS──A Case Study of Nanhai City of Guangdong Province     

阎小培 《中国地理科学(英文版)》1997,(1)

I.INT~IOWFOralOngthe,thesyStemofPermanentresidencempistrationhasdividedChineseampleintOthO8ewith"tirbanresidence"andthOSehaving"rUralresidence".TherationingsyStem,underwhichedibleoilandgrainwasdistributedonlytOthOSewith"urbanresidence"Calds,hasbeendondnant.Bothsystems,beingcentraltorestrictingthegrowthofurbanpopulation,havestagnatedrUral-tirbaningration.Duringthe30yearsbefore1978,thestatedidsPOnsorpopulationmovementsfromrUraltourbanareasbymeansofenrollingnewworkers,butingeneral,thiss…  相似文献   

2006-2016年昆明市雷电致灾因素分析及易损性风险区划     

刘平英  张腾飞  周清倩 《气象科学》2018,38(6):824-831

基于近11 a（2006-2016）云南省闪电定位监测数据以及雷电灾害汇编资料,运用ArcGIS对闪电数据与地理信息进行叠加,分析昆明市地闪活动规律和雷电灾害时空分布特征,结合地理环境、人口分布和经济社会发展情况,研究雷电致灾成因机制。从灾害系统理论和综合易损性出发,构建评价指标体系及权重判断矩阵,计算雷电灾害风险综合评价指数R值并进行分级,形成昆明市雷电灾害易损性风险区划。结果表明：频繁活跃的地闪活动是导致雷电灾害多发的主要致灾影响因子,雷电灾害的时空分布与地闪活动的变化特征存在较好的对应关系。全市有雷电灾害高易损区3个,次高易损区2个,中易损区4个,次低易损区4个,低易损区1个,建立雷电灾害易损性区划,能够为确定雷电防护重点和防范等级提供必要的参考依据,通过完善雷电防护措施,可以增强承灾体抵御雷电灾害的能力。  相似文献   

不同同化方案在一次梅雨锋暴雨预报中的应用研究     

梅疏影  闵锦忠 《气象科学》2018,38(4):432-441

基于ATOVS辐射率资料和GTS常规观测资料融合,通过不同化任何观测资料的控制试验、3DVAR同化试验和ETKF-3DVAR混合同化试验,对2013年7月4—5日一次梅雨锋暴雨天气过程进行模拟分析。结果表明:混合同化方案能够明显地提高暴雨预报准确率,且有效改善了风场、温度场和相对湿度场等各个气象要素的初始场结构,而这些气象要素对于暴雨的预报准确性具有重要作用。且混合同化方案对于中低层大气改进效果较为明显。在数值积分过程中,随着时间的推移,混合同化方案的优势逐渐减弱。  相似文献   

Assimilation of Feng-Yun-3B Satellite Microwave Humidity Sounder Data over Land     

Keyi CHEN  Niels BORMANN  Stephen ENGLISH  Jiang ZHU 《大气科学进展》2018,35(3):268-275

The ECMWF has been assimilating Feng-Yun-3B(FY-3B) satellite microwave humidity sounder(MWHS) data over ocean in an operational forecasting system since 24 September 2014. It is more difficult, however, to assimilate microwave observations over land and sea ice than over the open ocean due to higher uncertainties in land surface temperature, surface emissivity and less effective cloud screening. We compare approaches in which the emissivity is retrieved dynamically from MWHS channel 1 [150 GHz(vertical polarization)] with the use of an evolving emissivity atlas from 89 GHz observations from the MWHS onboard NOAA and EUMETSAT satellites. The assimilation of the additional data over land improves the fit of short-range forecasts to other observations, notably ATMS(Advanced Technology Microwave Sounder) humidity channels, and the forecast impacts are mainly neutral to slightly positive over the first five days. The forecast impacts are better in boreal summer and the Southern Hemisphere. These results suggest that the techniques tested allow for effective assimilation of MWHS/FY-3B data over land.  相似文献   

A Prototype Regional GSI-based EnKF-Variational Hybrid Data Assimilation System for the Rapid Refresh Forecasting System:Dual-Resolution Implementation and Testing Results     

Yujie PAN  Ming XUE  Kefeng ZHU  Mingjun WANG 《大气科学进展》2018,35(5):518-530

A dual-resolution(DR) version of a regional ensemble Kalman filter(EnKF)-3D ensemble variational(3DEnVar) coupled hybrid data assimilation system is implemented as a prototype for the operational Rapid Refresh forecasting system. The DR 3DEnVar system combines a high-resolution(HR) deterministic background forecast with lower-resolution(LR) EnKF ensemble perturbations used for flow-dependent background error covariance to produce a HR analysis. The computational cost is substantially reduced by running the ensemble forecasts and EnKF analyses at LR. The DR 3DEnVar system is tested with 3-h cycles over a 9-day period using a 40/13-km grid spacing combination. The HR forecasts from the DR hybrid analyses are compared with forecasts launched from HR Gridpoint Statistical Interpolation(GSI) 3D variational(3DVar)analyses, and single LR hybrid analyses interpolated to the HR grid. With the DR 3DEnVar system, a 90% weight for the ensemble covariance yields the lowest forecast errors and the DR hybrid system clearly outperforms the HR GSI 3DVar.Humidity and wind forecasts are also better than those launched from interpolated LR hybrid analyses, but the temperature forecasts are slightly worse. The humidity forecasts are improved most. For precipitation forecasts, the DR 3DEnVar always outperforms HR GSI 3DVar. It also outperforms the LR 3DEnVar, except for the initial forecast period and lower thresholds.  相似文献   

Ten Years of Science Based on the Canadian Precipitation Analysis: A CaPA System Overview and Literature Review†     

V. Fortin  G. Roy  T. Stadnyk  K. Koenig  N. Gasset  A. Mahidjiba 《大气与海洋》2018,56(3):178-196

Near real-time quantitative precipitation estimates are required for many applications including weather forecasting, flood forecasting, crop management, forest fire prevention, hydropower production, and dam safety. Since April 2011, such a product has been available from Environment and Climate Change Canada for a domain covering all North America. This product, known as the Regional Deterministic Precipitation Analysis, is generated using the Canadian Precipitation Analysis (CaPA) system. Although it was designed for near real-time use, an archive of pre-operational and operational products going back to 2002 is now available and has been used in numerous studies. This paper presents a review of the various scientific publications that have reported either using or evaluating CaPA products. We find that the product is used with success both for scientific studies and operational applications and compares well with other precipitation datasets. We summarize the strengths and weaknesses of the system as reported in the literature. We also provide users with information on how the system works, how it has changed over time, and how the archived and near real-time analyses can be accessed and used. We finally briefly report on recent and upcoming improvements to the product based, in part, on the results of this literature review.  相似文献   

Estimating the Correlated Observation-Error Characteristics of the Chinese FengYun Microwave Temperature Sounder and Microwave Humidity Sounder     

Ting WANG  Jianfang FEI  Xiaoping CHENG  Xiaogang HUANG  Jian ZHONG 《大气科学进展》2018,35(11):1428-1441

In operational data assimilation systems, observation-error covariance matrices are commonly assumed to be diagonal.However, inter-channel and spatial observation-error correlations are inevitable for satellite radiances. The observation errors of the Microwave Temperature Sounder(MWTS) and Microwave Humidity Sounder(MWHS) onboard the FengYun-3A(FY-3A) and FY-3B satellites are empirically assigned and considered to be uncorrelated when they are assimilated into the WRF model's Community Variational Data Assimilation System(WRFDA). To assimilate MWTS and MWHS measurements optimally, a good characterization of their observation errors is necessary. In this study, background and analysis residuals were used to diagnose the correlated observation-error characteristics of the MWTS and MWHS. It was found that the error standard deviations of the MWTS and MWHS were less than the values used in the WRFDA. MWTS had small inter-channel errors, while MWHS had significant inter-channel errors. The horizontal correlation length scales of MWTS and MWHS were about 120 and 60 km, respectively. A comparison between the diagnosis for instruments onboard the two satellites showed that the observation-error characteristics of the MWTS or MWHS were different when they were onboard different satellites. In addition, it was found that the error statistics were dependent on latitude and scan positions.The forecast experiments showed that using a modified thinning scheme based on diagnosed statistics can improve forecast accuracy.  相似文献