Study of the ability of SWOT to detect sea surface height changes caused by internal solitary waves

Surface Water and Ocean Topography(SWOT)is a next-generation radar altimeter that offers high resolution,wide swath,imaging capabilities.It has provided free public data worldwide since December 2023.This paper aims to preliminarily analyze the detection capabilities of the Ka-band radar interferometer(KaRIn)and Nadir altimeter(NALT),which are carried out by SWOT for internal solitary waves(ISWs),and to gather other remote sensing images to validate SWOT observations.KaRIn effectively detects ISW surface features and generates surface height variation maps reflecting the modulations induced by ISWs.However,its swath width does not completely cover the entire wave packet,and the resolution of L2/L3 level products(about 2 km)cannot be used to identify ISWs with smaller wavelengths.Additionally,significant wave height(SWH)images exhibit blocky structures that are not suitable for ISW studies;sea surface height anomaly(SSHA)images display systematic leftright banding.We optimize this imbalance using detrending methods;however,more precise treatment should commence with L1-level data.Quantitative analysis based on L3-level SSHA data indicates that the average SSHA variation induced by ISWs ranges from 10 cm to 20 cm.NALTs disturbed by ISWs record unusually elevated SWH and SSHA values,rendering the data unsuitable for analysis and necessitating targeted corrections in future retracking algorithms.For the normalized radar cross section,Ku-band and four-parameter maximum likelihood estimation retracking demonstrated greater sensitivity to minor changes in the sea surface,making them more suitable for ISW detection.In conclusion,SWOT demonstrates outstanding capabilities in ISW detection,significantly advancing research on the modulation of the sea surface by ISWs and remote sensing imaging mechanisms.

The Kuroshio Transport East of Taiwan and the Sea Surface Height Anomaly from the Interior Ocean

The relationship between the Kuroshio transport to the east of Taiwan and the SSHA (Sea Surface Height Anomaly) field is studied based on the World Ocean Circulation Experiment (WOCE) PCM-1 moored current meter array observation, the satellite altimeter data from the MSLA (Map of Sea Level Anomaly) products merged with the ERS and TOPEX/POSEIDON (T/P) data sets, and the WOCE satellite-tracked drifting buoy data. It is confirmed that the Kuroshio transport across PCM-1 array highly correlates with the SSHA upstream (22°-24°N, 121.75°-124°E). The SSHA is not locally generated by the developed Kuroshio meandering but is from the interior ocean and is propagating westward or northwestward. During the period from October 1992 to January 1998, two events of the northwestward propagating negative SSHA occurred, during which the SSHA merged into the Kuroshio and caused the remarkable low transport events in contrast to the normal westward propagating negative SSHA. It is also shown that the lower Kuroshio transport event would be generated in different ways. The negative anomaly in the upstream of PCM-1 array can reduce the Kuroshio transport by either offshore or onshore Kuroshio meandering. The positive anomaly, which is strong enough to detour the Kuroshio, can cause an offshore meandering and a low transport event at the PCM-1 array.

POSSIBLE RELATIONSHIP BETWEEN THE INTERANNUAL ANOMALY OF THE TROPICAL PACIFIC SEA SURFACE HEIGHT AND SUMMER PRECIPITATION IN CHINA

By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations between SSH and summer rainfall are discussed.The results are shown as follows:(1) The tropical Pacific SSH takes on a "V" pattern in the climatic field with an eastward opening,and it is higher in the western part(in the northwestern part) than in the eastern part(in the southwestern part).The high-value areas are more stable in the northwest,and the value range(greater than 0.8 m) is larger in spring and summer than in autumn and winter.The high-value area in the southwestern part is the largest(smallest) and more northerly(southerly) in spring(summer).SSH is higher in spring and autumn than in summer and winter over the equatorial zone.(2) The interannual anomalies of the SSH are the strongest over the tropical western and southwestern Pacific and are stronger in winter and spring than in summer and autumn.The interannual anomalies are also strong over the equatorial middle and eastern Pacific.The distribution ranges are larger and the intensities are stronger in the autumn and winter.There is a close relationship between the SSH interannual anomalies and ENSO events in autumn,winter and spring.(3) When ENSO events take place in winter,according to the simultaneous relationship among the tropic Pacific SSH,850 hPa wind fields and the summer precipitation of China,it can be predicted that the precipitation will be significantly more than normal over the south of the Yangtze River,especially over Dongting Lake and Poyang Lake region,eastern Qinghai-Tibet Plateau,Yangtze-Huai River Valley,eastern part of Inner Mongolia and less than normal over the area of Great Band of Yellow River,North China and South China in successive summers.

Prediction of Gravity Anomalies Over the South China and Philippine Seas from Multi-satellite Altimeter Sea Surface Heights

t Gravity anomalies on a2.5 ×2.5 arc-minute grid in a non-tidal system were derived over the South China and Philippine Seas from multi-satellite altimetry data. North and east components of deflections of the vertical were computed from altimeter-derived sea surface heights at crossover locations, and gridded onto a 2.5 × 2.5 arc-minute resolution grid. EGM96-derived components of deflections of the vertical and gravity anomalies gridded into 2.5 × 2.5 arc-minute resolutions were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Inverse Vening Meinesz formula via the 1D-FFT technique to predict the gravity anomalies over the South China and Philippine Seas from the gridded altimeter-derived components of deflections of the vertical. Statistical comparisons between the altimeter-derived and the shipboard gravity anomalies showed that there is a root-mean-square agreement of 5.7 mgals between them.

基于ICESat-2多波束激光测高数据的全球海洋重力异常反演分析

卫星测高技术是获取精细海洋重力数据的重要技术手段之一。常规卫星测高反演海洋重力异常主要是利用沿轨测高数据,而跨轨数据因较长的时间间隔或者稀疏的地面轨间距往往不能用于海洋重力异常反演,进而影响了海洋重力异常模型精度的进一步改善。新型激光测高ICESat-2能够同时获得3对光束观测数据,相邻激光束的地面间距约为3 km,为结合跨轨数据改善海洋重力异常模型提供了可能。本文首先给出了集成沿轨和跨轨数据反演海洋重力异常的处理策略;然后,分别利用沿轨数据和集成的数据构建了ICESat-2全球海洋重力异常模型(IS2Gra_alo和IS2Gra_alo_acr),结果表明通过补充跨轨数据能够有效提高沿轨数据反演海洋重力异常的精度,并验证了ICESat-2测高数据反演全球海洋重力异常的可靠性。此外,本文还探讨了ICESat-2不同跨轨数据组合对海洋重力异常模型反演精度的影响,在沿轨数据的基础上集成适当距离的跨轨观测数据能够有利于改善海洋重力异常模型的精度。本文研究为后续SWOT宽刈幅测高数据和我国双星跟飞模式测高数据反演海洋重力异常模型提供了参考意义。

DATA ASSIMILATION ON SEASONAL CYCLE OF SEA SURFACE HEIGHT ANOMALY IN THE SOUTH CHINA SEA

The Sea Surface Height Anomaly (SSHA) from the TOPEX/Poseidon altimeter data in 1994 is assimilated into a high-resolution model of the South China Sea (SCS) with nudging method. The model results can reveal the seasonal variations of SSHA and its time-space migration characters,at the same time,verify the effect of assimilation.Compared with non-assimilation results,assimilation results can show the seasonal variations of SSHA better,particularly in winter.Futhermore,it can distinguish temporal-spatial migration characters of SSHA clearly,i.e. cold signal of SSHA in northern SCS propagating westward and warm signal of SSHA in central SCS propagating eastward.It shows that as an easy and effective method,data assimilation of the SSHA with nudging method could make the simulated results closer to the available observations.

Sea surface height and transport stream function of the South China Sea from a variable-grid global ocean circulation model

A fine-grid model (1/6) covering the South China Sea (SCS), East China Sea and Ja-pan/East Sea, which is embedded into a coarse-grid (3) global model, was established to study the SCS circulation. In the present paper, we report the model-produced monthly and annual mean transport stream functions and sea surface heights(SSH) and their anomalies of the SCS. Com-parison to the TOPEX/Poseidon data shows that the model-produced monthly sea surface height anomalies (SSHA) are in good agreement with altimeter measurements. Based on the results, the circulation of the SCS, especially the upper layer circulation, is discussed. In the surface layer, the western Philippine Sea water intrudes into the SCS through the Luzon Strait in autumn, winter and spring, but not in summer. However, as far as the whole water column is concerned, the water in-trudes into the SCS through the Luzon Strait all the year round. This indicates that in summer the water still intrudes into the SCS in the subsurface and intermediate layers. The area near the northern continental slope of the SCS is dominated by a cyclonic circulation all the year round. The SCS Southern Anticyclonic Gyre, SE Vietnam Off-Shore Current in summertime and SCS South-ern Cyclonic Gyre in wintertime are reproduced reasonably. The difference between the monthly averaged SSH and SSHA is significant, indicating the importance of the mean SSH in the SCS circulation.

亚丁湾附近海域海洋中尺度涡的时空特征分析

亚丁湾附近海域中尺度涡过程活跃,了解和掌握其分布特征与变化规律,对于研究区域海洋动力学过程具有重要意义。利用CMEMS提供的多星融合海面高度异常资料,采用海面高度异常等值线法,对2003~2021年间亚丁湾附近海域中尺度涡进行了识别和追踪,并对其时空分布和移动特征进行了统计分析。结果表明,19年间亚丁湾附近海域共出现147个中尺度涡,这些涡旋几乎均在亚丁湾以东海域生成,并主要以3种不同路径向西移动。其移速存在明显的季节变化,夏季风期间移动缓慢,呈准静止状态,冬季风及季风转换期以约平均5~8 cm/s的速度向西移动。

卫星跟踪浮标和卫星遥感海面高度中的南海涡旋结构

选择 4个南海卫星跟踪Argos漂流浮标及同期的TOPEX/Poseidon卫星遥感海面高度资料 ,研究了南海海域涡旋的活动及空间结构。这 4个Argos漂流浮标的轨迹除了基本符合各季节海盆尺度环流趋势外 ,分别在菲律宾以西、越南外海、南海中部等海域呈现出中尺度旋转轨迹。这些中尺度涡旋现象在同期的TOPEX卫星遥感海面高度异常 (SSHA)分布中得到了准确的印证 ,并在诊断得到的地转流场中对应了一系列瞬变的中尺度涡旋活动。

1985国家高程基准的系统差

基于异常位、高程异常差以及海面地形模型 3种方法 ,分别求出了 1985国家高程基准相对于全球大地水准面的垂直偏差 。

T/P,Jason-1测量风速及有效波高的验证与比较

选取与T/P(TOPEX/POSEIDON)卫星高度计同步的浮标资料以及月平均浮标资料对T/P卫星高度计测量结果进行验证,结果表明:选取较窄的空间窗口以及较长的资料序列,可以减小浮标测量结果和高度计测量结果之间的误差;在所选浮标海域,浮标测量获得的有效波高与T/P测得有效波高存在0.3m的系统误差。T/P卫星高度计和Jason-1卫星高度计测量结果的比较显示,由于受海浪成长状态和仪器噪声的影响,二者测量获得的标准化雷达后向散射截面在低风速时相差较大,在高风速时符合较好。T/P和Jason-1卫星高度计测量获得的有效波高和海面高度异常的均方根误差分别为0.21m和0.05m。

海洋暖涡对“威马逊”(2014)影响的观测和模拟研究

本文利用多元卫星遥感资料和上海台风所的最佳路径资料,分析了南海暖涡对超强台风"威马逊"的影响,观测表明:"威马逊"在快速加强期间,先后从两个暖涡(WOE1和WOE2)的边缘穿过,中心最低气压在30 h内下降了60 hPa,对应暖涡的区域,海平面温度(SST)高于30℃,海表高度异常(SSHA)大于30 cm,热带气旋潜热(TCHP)大于100 kJ/cm^2,并具有70 m以上的深厚暖层。进一步采用中尺度大气模式WRF与区域海洋模式POM构造的中尺度海气耦合模式,模拟研究了海洋暖涡对"威马逊"的影响。与观测结果对比,尽管模拟台风最大强度与观测比较仍有一定差距,但模拟结果能较合理地模拟出台风中心气压和最大风速的变化特征。对比敏感性试验结果表明,虽然暖涡的存在并不是台风快速加强的充分条件,但暖涡使得海洋向大气输送的表面热通量增加,特别是对应近岸的WOE1海域,具有更高的SSHA和热带气旋潜热,台风中心区域的平均潜热通量也增加了40%以上,是使台风快速加强能达到更大强度的重要影响因子。

利用卫星高度计资料对台湾海峡流量变化的诊断分析

利用AVISO的MSLA海面高度距平资料和NCEP风场资料,应用张庆华等导出的渠道流的解,诊断计算了1993—2001年台湾海峡流量及其变化。结果表明,台湾海峡的年平均流量为 1.27 Sv,夏季最大,平均为 2.27Sv;秋季最小,平均为0.46 Sv,季节变化明显。分析认为,台湾海峡流量变化的决定性因素是台湾海峡南北方向海平面倾斜。局地风的驱动是次要因素,它所产生的流量变化具有显著的规律性,基本为南向流。

南海海面高度异常与厄尔尼诺和大气环流的关系

利用经验正交函数分解和相关分析等方法分析研究了南海和赤道太平洋的海面高度异常、海面温度异常和风异常之间的相关关系。得出南海海面高度异常EOF第一模态为ENSO模态,方差贡献达到44.7%。在厄尔尼诺(El Nio)期间,整个南海海面下降,SSHA呈现不同的分布状态,本文讨论了爆发与下半年的El Nio期间南海SSHA呈现的典型分布状态。El Nio的先兆阶段南海中部为SSHA低值区,鼎盛阶段南部SSHA增大形成南高北低的分布状态,恢复阶段SSHA分布与El Nio过后是否发生La Nia密切相关。南海海面高度异常与大气环流存在明显的相关关系。El Nio期间,Hadley环流的加强使得南海东部和赤道西太平洋水交换加强,水温的降低和海水的流失使南海海面下降,Walker环流结构和强度的变化则进一步促进了南海SSH的下降。El Nio期间,南海海面高度会较常年偏低。

2006年西南大西洋鱿钓渔场与表温和海面高度距平值的关系

根据2006年1-6月中国鱿钓船在西南大西洋的生产统计和表面水温（SST）、海面高度距平值（SSHA）的资料，利用海洋地理信息系统软件Marine explorer 4．0绘制了各月产量、日产量与SST和SSHA的关系图，推测出各月渔场的最适SST和SSHA值，并经K-S检验。结果表明：1—3月中心渔场主要分布在45°S、60°W附近海域，各月最适SST分别为11～12℃、12～13℃、12～13℃；4-6月中心渔场主要分布在42°S、58°W附近海域，各月最适SST分别为11～13℃、9～11℃、8～9℃。中心渔场主要分布在SSHA=0附近海域。中心渔场分布与SST和SSHA关系极为密切，可作为渔情分析指标。

印度洋西北部公海鸢乌贼资源特征及其与海况的关系

根据2004年9月~2005年4月我国鱿钓船在印度洋西北部12°N^21°30′N,58°E^65°E获得的鸢乌贼资源调查资料,对其资源特征及其与海况关系进行了分析。研究认为,调查海域内鸢乌贼均有一定的分布,其中以14°30′N、60°E^63°E附近海域CPUE为最高。渔获物胴长范围为163~560 mm,优势胴长组为280~440 mm,占总数的70.51%,平均胴长为365.0 mm。渔获个体组成随纬度变化差异显著,而随经度变化差异不明显。16°N以南海域,雌性个体一般以Ⅰ、Ⅱ期为主;16°N以北海域,则以Ⅲ~Ⅴ期为主。分析还认为,鸢乌贼分布与表温、海面高度距平关系密切,9~11月适宜表温为27~28℃,12月~翌年3月为26~27℃,高产渔场大都分布在海面高度距平SSHA≤0的附近海域。

卫星测高数据的沿轨迹重力异常反演法及其应用

本文给出了一套基于直角坐标系下的垂线偏差求解重力异常公式 ,并将之发展成为一套新的沿轨迹重力异常求解公式。与其他方法相比 ,本方法无须求解交叠点处沿轨迹和跨轨迹方向的海面高斜率 ,仅需计算沿轨迹方向的海面高斜率 ,因而更为简洁、有效 ,而且分辨率可以更高并可与真正的沿航迹实际船测重力相比较、验证。据此 ,利用 Geosat/GM、ERS-1 /35天及TOPEX/Poseidon三种测高数据 ,反演了南中国海域 (0°～ 2 5°N,1 0 5°～ 1 2 2°E)的 2′× 2′重力异常—— IGG-S。通过与实际船测资料和国际同行提供的重力模型相比 ,IGG-S总体精度达到1 0× 1 0 - 5ms- 2。

热带太平洋海平面高度的年代际异常及其与中国东部夏季降水的关系

利用美国国家海洋和大气管理局的GODAS逐月海平面高度资料、NCEP/NCAR 850 h Pa逐月风场再分析资料和中国160站逐月降水资料,分析了热带太平洋海平面高度(Sea Surface Height,SSH)年代际异常的时空特征,并进一步分析了夏季热带太平洋SSH、850 h Pa风场与中国东部夏季降水年代际异常的相关关系。结果表明:1)从秋到冬,热带太平洋SSH年代际异常主要空间形态向类"ENSO"型异常发展,从春到夏,类"ENSO"型异常逐渐减弱直到消失。1996前后热带太平洋SSH发生一次显著年代际转折,转折之后热带太平洋SSH呈东低西高特征,不同季节有所差异。2)1990年前后夏季热带太平洋SSH发生的一次弱波动,持续影响夏季大气环流,使得1992年前后东亚夏季风出现减弱趋势,造成中国东部黄河以南地区,特别是华南夏季降水显著异常偏多,四川盆地和东北大部降水异常偏少;1996年SSH的实质性转折加剧了中国夏季降水的年代际异常趋势。

热带太平洋海平面高度年际异常及其与中国夏季降水的关系

利用1980—2009年共30a的NCEP逐月GODAS海平面高度(sea surface height,SSH)和中国160站降水资料,系统分析了热带太平洋海平面高度季节变化及年际异常特征,初步探讨了海平面高度年际异常与中国夏季降水年际异常之间的相关关系。结果表明:1)热带太平洋海平面高度气候场总体呈"V"型分布,西高东低、西北部高于西南部;西北部高值区稳定少动,春夏季大于0.8m的范围较秋冬季略有扩大;西南部高值区春季范围最大且偏北,夏季最小且偏南;赤道区域海平面高度春秋季高于冬夏季。2)多年平均而言,热带西太平洋、西南太平洋的海平面高度年际异常最强,且冬春季较夏秋季更强,赤道中东太平洋年际异常也较大,且秋冬季异常强度和范围都更大,秋、冬和春季海平面高度年际异常与ENSO事件关系密切。3)当冬季发生ENSO事件,可利用热带太平洋海平面高度异常与中国夏季降水异常之间的同期相关关系,预测次年(ENSO事件衰减年)夏季江南地区特别是洞庭湖和鄱阳湖流域、青藏高原东部、江淮流域、内蒙东部降水可能偏多,黄河中下游流域的河套、华北地区以及华南则降水偏少。

卫星测高沿轨海面高的精细结构及其应用技术初探

首先介绍了频域和多尺度域中的两种沿轨测高海面高精细结构 ,进而提出了利用沿轨测高海面高精细结构计算平均海面高与海平面距平的新方法 ,最后进一步讨论了沿轨平均海面高和海平面距平的频谱和多尺度分解 ,以及它们随时间的变化特性。