WAVEWATCHⅢ同化模块的建立和检验

将基于最优插值（OI）的同化并行模块植入全谱空间的第三代海浪模式 WAVEWATCH III ver-sion3.14,建立数据同化的海浪模式预报系统,并通过实际的预报个例对同化系统进行检验。个例实验是以5°S以北的印度洋海域为目标计算区域,海面风场强迫采用业务单位的中尺度天气预报模式WRF （weather research and forecast）提供的逐时海面风场预报产品。模式积分过程中连续同化2010年12月15日、16日和17日过境北印度洋的Jason-2卫星高度计沿轨有效波高（SWH）数据（需要指出的是,每次同化得到新的SWH分析场后需重构相应的二维海浪谱用于谱模式）。SWH同化分析值和无同化的对照组分别与高度计沿轨观测数据比较发现,就日平均统计来看,同化较无同化使SWH分析值的均方根误差减小约25%-50%。以 SWH同化分析场作为初始场的预报表明,同化对预报影响的时效性可延长至48-60 h。本研究目的是通过将高度计测量的SWH数据同化到海浪模式进一步提升海浪数值预报的准确度。

南海灾害性波浪基本特征研究

本文基于1991-2016年全球卫星高度计融合数据对南海灾害性波浪基本特征进行了分析,根据灾害性波浪诱发天气类型不同,将其分为"台风浪"和"非台风浪"。依此主线,对两类波浪在南海不同海域的特征进行了研究,并提出了用于定量研究两类波浪强度关系的台风浪权重系数(W),得到了两类波浪在南海相对强弱关系的分布规律,量化研究了南海灾害性波浪的特征。本文以卫星高度计波高数据为样本进行了极值分析,得到了南海重现期波浪要素整体分布规律,研究发现W值大小与广义极值曲线类型显著相关。

A background error covariance model of significant wave height employing Monte Carlo simulation

The quality of background error statistics is one of the key components for successful assimilation of observations in a numerical model.The background error covariance(BEC) of ocean waves is generally estimated under an assumption that it is stationary over a period of time and uniform over a domain.However,error statistics are in fact functions of the physical processes governing the meteorological situation and vary with the wave condition.In this paper,we simulated the BEC of the significant wave height(SWH) employing Monte Carlo methods.An interesting result is that the BEC varies consistently with the mean wave direction(MWD).In the model domain,the BEC of the SWH decreases significantly when the MWD changes abruptly.A new BEC model of the SWH based on the correlation between the BEC and MWD was then developed.A case study of regional data assimilation was performed,where the SWH observations of buoy 22001 were used to assess the SWH hindcast.The results show that the new BEC model benefits wave prediction and allows reasonable approximations of anisotropy and inhomogeneous errors.

Wave Height Distribution for Spilling Waves in and outside the Surf Zone

The wave characteristics affecting coastal sediment transport include wave height, wave period and breaking wave direction. Wave height is a critical factor in determining the amount of sediment transport in the coastal area. The force of sediment transport is much more intense under breaking waves than under non-breaking waves. Breaking waves exhibit various patterns, principal- ly depending on the incident wave steepness and the beach slope. Based on the equations of con- servation of mass, momentum and energy, a theoretical model for wave deformation in and outside the surf zone was obtained, which is used to calculate the wave shoaling, wave set-up and set- down and wave height distributions in and outside the surf zone. The analysis and comparison were made about the breaking point location and the wave height decay caused by the wave breaking and the bottom friction. Flume experiments relating to the spilling wave height distribution across the surf zone were conducted to verify the theoretical model. Advanced wave maker, data sampling de- vices and data processing system were utilized in the flume experiments with a slope covered by sands of different diameters to facilitate the observation and research on the wave transformation and breaking. The agreement between the theoretical and experimental results is good.

Research on a High-Precision Delay Circuit in Data Acquisition Systems

This paper presents a novel precision delay circuit design for high-speed data acquisition systems. Many studies have suggested that various advanced electronic measurement apparatuses require that the delay circuit should have a high precision and a short delay interval. Practically, however, such measurement apparatuses are low in preci- sion and long in delay interval at present. The structure and function of a data acquisition system is introduced first; then the principle of ramp-based precision delay circuits and the digitally programmable delay generator is studied and the precision delay circuit is designed. The authors also demonstrated 8-bit programmable delay circuits with a timing pre- cision of 10 ps. Therefore the programmable precision delay circuit here presented has a higher precision, shorter inter- val and more detectable function than any other precision delay circuit.

The improvement of cross-calibration of IIM data and band selection for FeO inversion

Chang’E-1(CE-1)Interference Imaging Spectrometer(IIM)dataset suffers from the weak response in the near infrared(NIR)bands,which are the important wavelength for retrieving the minerals and elements of the Moon.In this paper,the cross-calibration was implemented to the IIM hyperspectral data for improving the weak response in NIR bands.The results show that the cross-calibrated IIM spectra were consistent to the Earth-based telescopic spectra,which suggests that the cross-calibration yields acceptable results.For further validating the influence of the cross-calibration on the FeO inversion and searching the optimal bands to retrieve lunar FeO contents,four band selection schemes were designed to retrieve FeO using the original and cross-calibrated IIM spectra.By comparing the distribution patterns and histograms of the IIM derived FeO contents with the Clementine derived FeO,the IIM 891 nm band after cross-calibration showed a higher accuracy in the FeO inversion,hence most useful for lunar FeO inversion.

The role of cloud height and warming in the decadal weakening of atmospheric heat source over the Tibetan Plateau

The warming over the Tibetan Plateau(TP) is very significant during last 30 years,but the thermal forcing has been weakened.The thermal weakening is attributed mainly to the enhancement of the TOA(top of atmosphere) outgoing radiation.This enhancement is opposite to the greenhouse-gas-induced weakening of the global mean TOA outgoing radiation and is also unable to be explained by the observed decrease of total cloud cover.This study presents the importance of cloud height change and the warming over the TP in modulating the TOA radiation budget and thus the thermal forcing during spring and summer.On the basis of surface observations and satellite radiation data,we found that both the TOA outgoing shortwave radiation and longwave radiation were enhanced during this period.The former enhancement is due mainly to the increase of low-level cloud cover,which has a strong reflection to shortwave radiation,especially in summer.The latter enhancement is caused mainly by the planetary warming,and it is further enhanced by the decrease of total cloud cover in spring,as clouds extinguish outgoing longwave radiation emitted from the land surface.Therefore,the radiative cooling enhancement and thus the thermal weakening over the TP is a response of the earth-atmosphere system to the unique change of cloud cover configuration and the rapid warming of the land surface.However,these trends in cloud cover and TOA outgoing radiation are not well represented in four reanalyses.

Stepwise decomposition and relative radiometric normalization for small footprint LiDAR waveform

As an advanced generation instrument of earth observation,small footprint full waveform light detection and ranging(LiDAR) technology has been widely used in the past few years.Decomposition and radiative correction is an important step in waveform data processing,it influences the accuracy of both information extraction and further applications.Based on a stepwise strategy,this study adopts Gaussian mixture model to approximate the LiDAR waveform.In addition to waveform decomposition,a relative correction model is proposed in this paper,the model considers the transmit pulses as well as the different of the travel path for implementing LiDAR waveform relative correction.Validation of the stepwise decomposition and relative correction model are carried out on LiDAR waveform acquired over Zhangye,China.The results indicate that stepwise decomposition identified the number of peaks in LiDAR waveforms,center position and width of each peak well.The relative radiometric correction also improves the similarity of waveforms which acquired at the same target.

Understanding the Moon's internal structure through moonquake observations and remote sensing technologies

Explorations for the interior structure of the Moon mainly involve three technologies: the early gravitational observations via circumlunar satellites, the moonquake observations during the Apollo period, and the recent high-resolution remote sensing observations. Based on these technologies, we divided the development of the moon's interior structure into three stages. The first stage is the discovery of high-density anomalous masses(mascons) on the lunar surface with the low-order gravitational field models, which were obtained by observing perturbations of the early lunar orbital satellites. The second stage is the preliminary understanding of the layer structure with the help of moonquake observations during the Apollo period. The third stage is the deep understanding of the structure of the lunar crust, mantle, and core, with the use of high-resolution remote sensing data and the reassessment of moonquake data from the Apollo's mission. This paper gave detailed introduction and comments on different observation technologies, gathered data, and data processing techniques used at the three stages. In addition, this paper analyzed the current issues in the researches on the Moon's internal structure and discussed the prospects for future explorations.

Observed splitting eastbound propagation of subsurface warm water over the equatorial Pacific in early 2014

El Nino, as characterized by above average sea surface temperatures in the equatorial tropical Pacific, is the largest source of natural climate variability from sea- sonal to interannual scales and can profoundly reshape the global weather patterns. Currently, the tropical Pacific Ocean appears to be primed for a potentially significant El Nino event, and some similarities exist between the oce- anic and atmospheric states in early 2014 compared to the observations shortly before the onset of the 1997/1998 Super El Nino event. For example, as one of the most important early signs of El Nino, a splitting eastbound propagation of the subsurface warm water is evident over the equatorial Pacific since January 2014. In this study, the pulses of subsurface warm water are reflected by the Kel- vin waves over the equatorial Pacific estimated from the satellite altimetry data. Results show that the current （i.e., March 2014） Kelvin wave over the equatorial Pacific has achieved the largest amplitude compared to those in the corresponding period prior to the E1 Nifio events since the availability of satellite altimetry, and is even significantly larger than the one that preceded the 1997/1998 Super El Nifio event. As the Kelvin waves can help induce El Nino conditions within about 2--4 months, the current fastest/ strongest eastbound propagation of subsurface warm water indicates that the likelihood of an El Nino event will sig- nificantly increase during the next several months in 2014.