基于浮标实测数据的WindSat海洋反演产品精度分析

To evaluate the ocean surface wind vector and the sea surface temperature obtained from Wind Sat, we compare these quantities over the time period from January 2004 to December 2013 with moored buoy measurements. The mean bias between the Wind Sat wind speed and the buoy wind speed is low for the low frequency wind speed product(WSPD_LF), ranging from –0.07 to 0.08 m/s in different selected areas. The overall RMS error is 0.98 m/s for WSPD_LF, ranging from 0.82 to 1.16 m/s in different selected regions. The wind speed retrieval result in the tropical Ocean is better than that of the coastal and offshore waters of the United States. In addition, the wind speed retrieval accuracy of WSPD_LF is better than that of the medium frequency wind speed product. The crosstalk analysis indicates that the Wind Sat wind speed retrieval contains some cross influences from the other geophysical parameters, such as sea surface temperature, water vapor and cloud liquid water. The mean bias between the Wind Sat wind direction and the buoy wind direction ranges from –0.46° to 1.19° in different selected regions. The overall RMS error is 19.59° when the wind speed is greater than 6 m/s. Measurements of the tropical ocean region have a better accuracy than those of the US west and east coasts. Very good agreement is obtained between sea surface temperatures of Wind Sat and buoy measurements in the tropical Pacific Ocean; the overall RMS error is only 0.36°C, and the retrieval accuracy of the low latitudes is better than that of the middle and high latitudes.     

Performance of the CCIW wave direction buoy at ARSLOE

The performance at the Atlantic Remote Sensing Land Ocean Experiment (ARSLOE) of the Canada Centre for Inland Waters (CCIW) wave direction buoy is examined. The waveheight and period data show good agreement with data from neighboring buoys. Nondimensional energy and fetch for wind sea cases agree well with data collected from fixed sensors in Lake Ontario. Direction measurements for a particularly well-defined swell agree well with the Experimental Environmental Research Buoy (XERB) measurements. Meteorological data are compared with that collected at the XERB. Windspeed estimates are reasonably well-correlated and much of the scatter is due to the 24-kin separation between the buoys. There is some systematic bias in the wind direction estimates.     

Influence of the type of sea waves on the backscattered radar cross section at medium incidence angles

We consider the influence of the sea surface state on the backscattered radar cross section and the accuracy of the wind speed retrieval from the scatterometer data. We used a joint set of radars and buoys to determine the type of sea waves. Three types of sea waves were distinguished: developing wind waves, fully developed wind waves, and mixed sea. It is shown that the retrieval error of the near surface wind speed using a one-parameter algorithm is minimal in the case of fully developed wind waves. We compared these data with the results of radio-altimeter data analysis and showed that in both cases underestimation of the retrieval wind speed exists for developing wind waves and overestimation occurs for mixed sea. A variety of swell parameters (length of the dominating wave, swell height, swell age) significantly influence the backscattered radar cross section, leading to a growth in the mean square error of the retrieved wind speed during vertical sounding (radio-altimeter data), and only slightly influence the mean square error of the scatterometer data (medium incidence angles). It is necessary to include the information about the parameters of sea waves in the algorithms and take into account the regional wave properties to increase the accuracy of wind speed retrieval.     

A wavelet-based test for swell stationarity

The temporal behaviour of swell is examined using the wavelet transform, and a test of stationarity using the wavelet transform is described. The method is demonstrated on time series data from a Directional Waverider buoy deployed at Duck, North Carolina, and it is shown that non-stationary sea states are usually associated with local wind-sea growth rather than significant changes in the swell component, which can be considered stationary for at least as long as the 160-min records. This is close to the 3-h duration that is typically assumed for a stationary sea state. The stationary character of swell is an important result for offloading from an LNG barge to carrier.     

Coupling winds to ocean surface currents over the global ocean

A Wind stress–Current Coupled System (WCCS) consisting of the HYbrid Coordinate Ocean Model (HYCOM) and an improved wind stress algorithm based on Donelan et al. [Donelan, W.M., Drennan, Katsaros, K.B., 1997. The air–sea momentum flux in mixed wind sea and swell conditions. J. Phys. Oceanogr. 27, 2087–2099] is developed by using the Earth System Modeling Framework (ESMF). The WCCS is applied to the global ocean to study the interactions between the wind stress and the ocean surface currents. In this study, the ocean surface current velocity is taken into consideration in the wind stress calculation and air–sea heat flux calculation. The wind stress that contains the effect of ocean surface current velocity will be used to force the HYCOM. The results indicate that the ocean surface velocity exerts an important influence on the wind stress, which, in turn, significantly affects the global ocean surface currents, air–sea heat fluxes, and the thickness of ocean surface boundary layer. Comparison with the TOGA TAO buoy data, the sea surface temperature from the wind–current coupled simulation showed noticeable improvement over the stand-alone HYCOM simulation.     

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April.     

2016年苏北近海风场和波浪场多时间尺度变化的数值模拟研究

利用高分辨率的大气和波浪数值模式,模拟了2016年苏北近海的风场和波浪场,并与卫星高度计资料、散射计风场、再分析资料以及实测浮标资料进行了比较,验证了模式的准确性。基于这套模式结果,系统地分析了江苏近海的风场和波浪场的多时间尺度变化:季节变化、日变化以及季节内变化(台风、寒潮)。分析结果表明:苏北近海海域的风速、有效波高和涌浪在冬季和秋季较大、春季和夏季较小;冬季盛行西北风,常浪向为西北向,夏季盛行东南风,常浪向为东南向。风场和波浪场还具有显著的日变化特征,且日变化存在季节变化规律,离岸越近海域日变化特征越明显。同时,江苏近海还会经历季节内尺度的强天气过程的影响,比如台风和寒潮。     

Analysis of directional wave fields using X-band navigation radar

The aim of this work is to present an approach to describe complex sea states including the ones consisting of superpositions of swell and wind sea components, using a nautical radar in X-band as a remote sensing technique. In the present article, the inversion method to obtain the spectral representation of the wave fields is described. The method is applied to analyse data obtained from simulation techniques, as well as from measurements obtained during oceanographic campaigns in the Bay of Biscay and North Sea.     

Estimation of space-time characteristics of surface roughness based on video images

The technique of operative measurements of wind-induced wave characteristics based on video imaging of the sea surface and simultaneously measuring the current spectra of wind waves using an anchored buoy is presented. This technique makes it possible to obtain the data on frequency-angular and dispersion characteristics of surface roughness required for acoustic measurements. The results of processing the video data obtained from the Baltic Sea and the Gorky Reservoir are in agreement with corresponding theoretical dependences.     

两种海面风场的对比及对海浪模拟的影响

海面风场在海浪模拟研究和预报中起着关键性的作用,再分析风场数据可为海浪模式提供长时间的大范围、高时空分辨率海面风场。利用日本浮标站资料和卫星高度计资料对再分析风场QuickSCAT/NCEP(Q/N)混合风场和ERA风场进行验证分析,并利用WAVEWATCH-Ⅲ模式进行连续12个月的数值模拟试验。对比风场和计算得到的海浪场得出结论:在风速较小的时候,ERA和Q/N风场较实测风场大,在风速较大的时候,ERA和Q/N风场较实测风场小;ERA风场模拟浪高较浮标观测波高偏小;Q/N混合风场模拟的浪高更接近实测浪高。     

The acoustic transient recording buoy (ATRB): system descriptionand initial measurement results

An acoustic transient recording buoy (ATRB) developed to provide improved dynamic range and recording capacity in a reconfigurable manner is described. This digital system can acquire and record up to 16 h of broadband wide dynamic range (≈80 dB) acoustic data from eight hydrophones. A unique feature is the use of two inexpensive video cassette recorders to obtain up to 10 Gb of data storage capacity. The system is self-contained and capable of unattended bottom-moored operation. An experiment designed and conducted using a single ship and this system to obtain simultaneous measurements of sea surface forward scatter, propagation loss, and sea floor interaction is reported. Data obtained demonstrate the utility of this system for ocean acoustic experiments. Explosive charge source levels using direct path measurements agreed with previous measurements. Surface reflected data exhibited a frequency dependence attributed to sea surface swell and roughness     

Evaluation of ENVISAT ASAR data for sea surface wind retrieval in Hong Kong coastal waters of China

The C-band wind speed retrieval models, CMOD4, CMOD - IFR2, and CMOD5 were applied to retrieval of sea surface wind speeds from ENVISAT （European environmental satellite） ASAR （advanced synthetic aperture radar） data in the coastal waters near Hong Kong during a period from October 2005 to July 2007. The retrieved wind speeds are evaluated by comparing with buoy measurements and the QuikSCAT （quick scatterometer） wind products. The results show that the CMOD4 model gives the best performance at wind speeds lower than 15 m/s. The correlation coefficients with buoy and QuikSCAT winds are 0.781 and 0.896, respectively. The root mean square errors are the same 1.74 m/s. Namely, the CMOD4 model is the best one for sea surface wind speed retrieval from ASAR data in the coastal waters near Hong Kong.     

Air-Sea Interactions under the Existence of Opposing Swell

Data of a comprehensive laboratory study on the coexistent system of wind waves and opposing swell (Mitsuyasu and Yoshida, 1989) have been reanalyzed to clarify the air-sea interaction phenomena under the coexistence of wind waves and swell. It is shown that the magnitude of the decay rate of swell due to an opposing wind is almost the same as that of the growth rate of swell caused by a following wind, as measured by Mitsuyasu and Honda (1982). The decay rate is much smaller than that obtained recently by Peirson et al. (2003), but the reason for the disagreement is not clear at present. The effect of an opposing swell on wind waves is very different from that of a following swell; wind waves are intensified by an opposing swell while they are attenuated by a following one. The phenomenon contradicts the model of Phillips and Banner (1974), but the reason for this is not clear at this time. The high-frequency spectrum of wind waves shows a small increase of the spectral density. Wind shear stress increases a little due to the effect of opposing swell. The intensification of wind waves by opposing swell and the small increase of the spectral density in a high-frequency region can be attributed to the increase of wind shear stress. Such organized phenomena lead to the conclusion that the hypothesis of local equilibrium for pure wind waves (Toba, 1972) can also be satisfied for wind waves that coexist with opposing swell. The recent finding of Hanson and Phillips (1999) can be explained by this mechanism.     

The sheltering effect of the Balearic Islands in the hindcast wave field

The sheltering effect of the Balearic Islands in the hindcast wave field was studied for typical Mediterranean wave situations of Llevant, Tramuntana and Mestral and for mild conditions such as the Garbí and Ponent winds. For this purpose, a third generation wave model was applied to the Mediterranean Sea and different patterns of the sheltered areas were found for the various representative situations depending on the wind variability and on the magnitude of the wind speed. From the analysis it was concluded that the sheltered zones created during storms generally persist for short periods of time of the order of 6 h, possibly reaching a maximum of 12 h. In contrast with earlier results obtained for swell dominated ocean areas, it was observed that in this area, due to the short fetches the sea states are mainly local wind seas and thus the wave field behind the islands depends on the local wind.     

一种浅海锚泊测流浮标系统的实验

早在五十年代,海洋科技工作者已开始利用浮标布设海洋调查仪器,进行海上观测的试验工作。目前被采用的浮标系统,大体有三种类型:(1)锚泊浮标系统,利用各类自含式海洋调査仪器进行测量,定期收回资料;(2)遥测浮标系统,利用无线电遥控和收发各种海洋观测数据;(3)漂移浮标系统,利用浮标本身的漂移,进行海流和其他要素的观测。本文主要介绍浅海锚泊浮标系统的设计和使用情况。 对锚泊浮标系统的研究和实验,许多国家已做了大量有成效的工作。目前关于浮标的设计和锚泊方法尚无統一意见,但是可以看出,大多趋向于采用水下浮标张缆锚泊。这种方法使得浮标系统比起遥测浮标系统来,较为轻小、经济、方便,适合于进行多站同步观测。国外在海洋调查中经常利用这种系统作较长期的海流观测。 我所在六十年代初就已开始了锚泊浮标系统的研究、实验,1964年进行了新的研究设计工作,并在“全国海洋仪器会战”期间,完成了整套系统的计算设计与海上实验,经过鉴定,建议作小批量生产。 近年来,国家海洋局第一海洋研究所、中国科学院南海海洋研究所利用该浮标系统作过多次海上试用,取得了海流长期观测资料,初步考验了该系统的性能。我们最近又对某些部件作了一定的改进,并进行了海上实验。但是,实验也表明:此方法不宜在渔场区和台风盛行季节使用,因易被渔网拖损和丢失。现综合报告如下。     

ERA-Interim和NCEP/NCAR再分析资料在我国东南近海适用性分析

利用我国东南近海5个浮标站观测资料,对2012—2016年ERA-Interim和NCEP/NCAR再分析资料10 m风、2 m气温、海平面气压的适用性进行了评估。结果表明:NCEP/NCAR的再分析10 m风适用性更好,ERA-Interim的2 m气温适用性更好,海平面气压两者差异不大。风速再分析值与观测值具有较好的一致性,相关系数达0.8～0.9,但再分析风速总体上有偏小的趋势,平均偏差在-1.3～0 m/s之间,均方根误差在1.5～3 m/s。再分析资料的平均风向有顺时针偏差的趋势,温州浮标偏右达14°以上,均方根误差大多在40°～50°。不管风速还是风向,5个浮标站中均以舟山浮标的再分析值与观测值最为接近;分析还表明,再分析资料的冬季风代表性相对较差,这是造成风速和风向系统性偏差的主要原因。再分析资料与观测2 m气温相关系数均在0.95以上,且有偏高的趋势,NCEP偏高更为明显,有4个浮标站平均偏差达1～2℃,而ERA-I仅1个浮标站偏差1～2℃,4个在1℃以内。春季和冬季气温偏高最为明显,春季升温过程存在异常偏高的可能,秋季气温与观测值最为接近。海平面气压适用性较好,总体优于10 m风和2 m气温,且季节间差异也不大。     

On the application of HF ocean radar to the observation of temporal and spatial changes in wind direction

The application of a 30-MHz narrow-beam ground-wave ocean radar to the observation of wind directions is described. It is found that thecos^{s} (theta/2)model for wind-wave directions does not apply in a specific case of shallow water where swell waves are behaving nonlinearly. To experimentally extract unambiguous wind directions from this model requires sampling three different beam angles simultaneously. In practice some time and space stationarity is assumed. Detailed analysis in time and space reveals structure in the transition of the cold front from sea to land which, although unexpected, agrees with coastline observations where they are available. The nature of the structure is only briefly discussed. The response of thelambda = 5-m wind waves to the frontal change was two orders of magnitude faster than time constants for similar events previously modeled using pitch-and-roll buoy data. This discrepancy needs to be reconciled before lower frequency radars can be used without ground truth for wind-direction changes.     

A note on nearshore wave features: Implications for wave generation

This paper analyses 10 years of wave data from the Mediterranean Spanish (Catalan) coast considering the mean wave climate and storm events from the standpoint of wind-wave momentum transfer and wave prediction. The data, registered by a buoy at about 12 km from the coastline, revealed two main groups of wave storms, with NW and E directions. NW storms correspond to a fetch-limited situation since the intense wind blows from land. Low-pressure centres located over the Mediterranean Sea produce easterly storms. Near the coast the eastern winds from the sea are replaced by NW winds coming from meteorological patterns over northern Spain and south-western France. Wave storms are classified and studied to obtain their main features (including spectral width, wave length, wave age and bimodality) and discussed in terms of wind-wave momentum transfer for operational wave predictions. Observations show a complex coastal wave climate. Fetch-limited storms presented smaller spectral widths while varying wind situations presented larger widths due to the presence of bimodal spectra. These wave features are highly relevant for wind–ocean momentum transfer and, thus, for current and wave predictions. The spectral width proved to be a good indicator of sea complexity and is thus applicable for improved wind drag estimations. A new drag coefficient formulation is proposed, based on existing wind dependent drag expressions, but including also spectral wave properties (a spectral width parameter) that highlights the characteristics of wind-wave generation under pre-existing swell. Such a formulation, once properly validated with field observations, is expected to improve wind-wave predictions.     

降雨条件下全极化微波辐射计海面风场校正

为提高降雨条件下星载全极化微波辐射计海面风场精度,通过匹配WindSat海面风场和降雨率数据以及美国国家浮标中心浮标观测数据,得到18 996组匹配样本,深入分析了降雨对海面风场反演精度的严重影响,构建了风场校正模型。试验结果表明,降雨导致海面风速被严重高估,风向误差随着降雨率的增大而增大。校正后的风速精度在低风速段提升明显。无论降雨率多大,校正后风速精度均比校正前高。风速均方根误差由原来的2.9 m/s降低到了2.1 m/s,风向均方根误差由原来的26.9°降低到了26.3°。     

基于浮标站和ERA5 再分析资料的浙江沿海台风浪特征分析

为了分析台风影响下浙江沿海风和浪的演变特点，利用浙江省海洋浮标站监测数据和欧洲中期天气预报中心第五代全球气候大气再分析数据（European Centre for Medium-Range Weather Forecasts Reanalysis v5，ERA5），选取2010年以来严重影响浙江的7次台风个例，对台风作用下浙江沿海海面风和浪的演变特点进行分析。结果表明：在台风影响过程中，海浪波型多数呈现混合浪-风浪-混合浪的演变规律；涌浪波型的出现与台风强度及其与浮标站的距离和方位有关，也与海洋潮汐现象紧密相关。台风影响期间，浙江沿海浪高的变化受风速和风向共同作用影响。在风向不变的情况下，持续风速增大对浪高的增大有明显作用；风向的变化也会对浪高变化产生影响，向岸风和离岸风的转变会造成浪高出现剧烈变化。ERA5 再分析资料有效波高在台风浪较大时会呈现偏小的趋势，分析订正后的ERA5 有效波高发现，台风浪有效波高大值区与台风中心位置相关。研究结果可为严重影响浙江沿海的台风浪预报服务提供参考。