Features of marine wind fields over New Zealand waters from ERS‐1 scatterometer data.

Wind data from the ERS‐1 scatterometer have been processed for New Zealand waters. These show spatial features of marine wind fields which have previously been difficult to resolve using conventional surface‐based measurements. Winds across the western access to Cook Strait, delineated by a corridor between Farewell Spit and western Taranaki, were analysed and profiles of wind stress extracted. These show characteristic structures for south‐easterly events in which the stress steadily increases from Farewell Spit towards the Taranaki Coast. In westerly or north‐westerly events the structure is more uniform. The mean stress across this corridor has been compared to that calculated from surface‐based measurements at Farewell Spit and the Maui‐A oil and gas production platform off Cape Egmont. The Farewell spit data lead to underestimates of the stress, which partially reconciles previous attempts to model wind‐driven currents off the west coast of the South Island from these data. In these the currents were underestimated. The Maui‐A data are unbiased in westerly events but give overestimates in southeasterly winds. An improved estimate of the mean stress can be derived from using a combination of wind data from these two stations.     

水体颗粒后向散射系数测量一致性对比实验研究

颗粒后向散射系数是水体最重要的固有光学参量之一,也是海洋水色卫星遥感的核心参数。现场准确测量水体颗粒后向散射数据,对于水色遥感模型构建以及水色遥感产品真实性检验至关重要。本文针对常用的3种水体颗粒后向散射系数原位测量仪(HydroScat6,VSF3和BB9),通过比测实验,对三者测量结果的一致性进行了比较分析。结果表明,在清洁水体中3种仪器对颗粒后向散射系数测量具有较好的一致性;但在浑浊水体中,HydroScat6和BB9测量值会比VSF3高,三者偏差显著增大。同时,数值模拟和实验结果均表明,颗粒形状会对测量结果产生影响,3种仪器对球形颗粒的后向散射系数测量结果的一致性显著好于野外颗粒结果。     

ASCAT散射计风场在我国近海的初步检验与应用

为了弥补中国近海海区缺乏洋面风场观测资料,提高海洋气象预报能力,对MetOP-A极轨卫星搭载的ASCAT散射计反演风场资料和中国气象局在近海布设的18个浮标站测风资料进行对比。结果表明,离岸较远的海域中ASCAT反演风场的质量要优于离岸较近的海域,在较远的海域中,ASCAT风速和浮标观测风速的平均偏差为0.9 m·s~(-1),ASCAT的风速高于浮标站的风速,平均绝对偏差和均方根误差分别为1.2和1.4 m·s~(-1),风速的相关系数为0.94。统计特征分析结果显示,ASCAT散射计风场资料在中国近海有较好的可信度,在高风速的时候,ASCAT和浮标资料一致性较好,而低风速时候,ASCAT比浮标略偏大。目前,中央气象台正在逐步开展ASCAT资料的业务应用,ASCAT洋面的MICAPS格式产品和图形产品现已实现准实时运行。     

Annual and interannual variability of scatterometer ocean surface wind over the South China Sea

To investigate the annual and interannual variability of ocean surface wind over the South China Sea (SCS), the vector empirical orthogonal function (VEOF) method and the Hilbert-Huang transform (HHT) method were employed to analyze a set of combined satellite scatterometer wind data during the period from December 1992 to October 2009. The merged wind data were generated from European Remote Sensing Satellite (ERS)-1/2 Scatterometer, NASA Scatterometer (NSCAT) and NASA’s Quick Scatterometer (QuikSCAT) wind products. The first VEOF mode corresponds to a winter-summer mode which accounts for 87.3% of the total variance and represents the East Asian monsoon features. The second mode of VEOF corresponds to a spring-autumn oscillation which accounts for 8.3% of the total variance. To analyze the interannual variability, the annual signal was removed from the wind data set and the VEOFs of the residuals were calculated. The temporal mode of the first interannual VEOF is correlated with the Southern Oscillation Index (SOI) with a four-month lag. The second temporal interannual VEOF mode is correlated with the SOI with no time lag. The time series of the two interannual VEOFs were decomposed using the HHT method and the results also show a correlation between the interannual variability and El Niño-Southern Oscillation (ENSO) events.     

ERS风散射计反演地表参数——一种混合像元方法

基于混合像元的方法,利用ERS风散射计(WSC)数据估算植被覆盖率和同时期NDVI有较高的相关性(0.78),计算出的垂直入射菲涅耳反射系数的空间分布状况也比较合理。     

Early prediction of onset of south west monsoon from ERS-1 scatterometer winds

Detailed analysis of the surface winds over the Indian Ocean derived from ERS-1 scatterometer data during the years 1993 and 1994 has been used to understand and unambiguously identify the onset phase of south-west monsoon. Five day (pentad) averaged wind vectors for the period April to June during both years have been examined to study the exact reversal of wind direction as well as the increase in wind speed over the Arabian Sea in relation to the onset of monsoon over the Indian west coast (Kerala). The related upper level humidity available from other satellites has also been analysed. The results of our analysis clearly show a consistent dramatic reversal in wind direction over the western Arabian Sea three weeks in advance of the onset of monsoon. The wind speed shows a large increase coinciding with the onset of monsoon. These findings together show the dominant role of sea surface winds in establishing the monsoon circulation. The study confirms that the cross equatorial current phenomenon becomes more important after the onset of monsoon.     

SeaWinds散射计风矢量解空间中图像椭圆总灰度值对风矢量反演误差的约束效应

已有的SeaWinds散射计反演结果误差评价包括两种方法:一是与其他数据来源进行对比,如与数值气象预报产品或浮标风场数据对比;二是从风场反演结果的空间一致性进行判断.文中采用二维几何中心矩定量描述象元解空间中模糊解区域(与真解最接近的模糊解区域)的图谱特征,如图像椭圆的主轴倾角、长短轴比以及总灰度值;研究了总灰度值与风矢量反演误差的关系.结果表明,当总灰度值大于某一阈值时,风矢量反演误差将被限制在一个较小的范围之内.根据图像椭圆总灰度的这一特性,设计了一种新的基于总灰度约束特性的滤波算法.通过与浮标风矢量     

Growth of Wind Waves with Fetch in the Sea of Japan under Winter Monsoon Investigated Using Data from Satellite Altimeters and Scatterometer

By using wind vector fields observed by the NASA Scatterometer (NSCAT) and significant wave heights observed by the TOPEX/POSEIDON and European Remote Sensing Satellite-2 (ERS-2) altimeters, one-dimensional fetch growth of wind waves has been investigated under conditions of strong wind and high waves caused by the East Asian winter monsoon in the Sea of Japan. The evolution of fetch-limited wind waves can be observed by the altimeters along their ground tracks. The fetch is estimated by using vector wind fields observed by NSCAT. The derived growth characteristics of wind waves are compared with empirical relationships between the non-dimensional fetch and significant wave height proposed by previous studies. Good agreement is discernible with Toba's fetch graph formula normalized by the friction velocity, while Wilson's well-known formula normalized by the wind speed at a height of 10 m tends to underestimate the wave height under such severe conditions of high wind and very long fetch. This discrepancy is explained by the wind-speed dependence of the drag coefficient. A simple correction to Wilson's formula for the high wind conditions is proposed and compared with the observed data.     

Impact of wind/wind-stress field in the North Pacific constructed by ADEOS/NSCAT data

Data sets of surface wind and wind-stress fields in the North Pacific from September 1996 to June 1997 have been constructed using NASA Scatterometer (NSCAT) data on-board ADEOS to investigate their variability and implications for the wind-driven oceanic circulation. Using a weighting function decreasing with the distance between each grid and data points, and of Gaussian type for time, daily, 10-day and monthly averages are calculated for each 1°×1° grid. Products are validated by comparison with those calculated from in-situ measurement data at oceanic buoys around Japan (JMA) and in the equatorial area (TAO). The RMS differences for wind direction and speed never exceed 20° and 2 ms⁻¹, respectively, for the TAO buyos. This does not hold for data taken by JMA buoys, suggesting that the reliability in the mid-latitudes is not good for time averages shorter than several days. Zonal integration of the Sverdrup transport in a zone of 28°–30°N calculated from the monthly-mean products ranges between 25 and 60×10⁶ m³s⁻¹ (Sv) around its mean of 38 Sv. These are not so different from the Kuroshio transport values calculated from oceanic measurements.     

HY-2B卫星散射计神经网络多区间风速反演

以欧洲中期天气预报中心ECMWF(European Centre for Medium Range Weather Forecasts)的ERA5风场数据为真实风速参考值,利用HY-2B卫星散射计L2A数据,使用反向传播神经网络方法对风速进行了反演,分别建立了中高风速、中低风速和全风速反演模型.与基于NSCAT-4地球...