基于FY-3C星微波成像仪毫米波通道的海面大风算法研究

对基于FY-3C星微波成像仪(MWRI)毫米波通道的海面大风算法进行了研究。根据在中国海域观测到的海面后向热辐射数据,认为联合多个毫米波通道分析方法可利于海面大风反演。对中低风速(0~15m/s)下D-矩阵算法进行修正,给出了适于MWRI的海面风速反演新模型。与浮标数据拟合结果表明:FY-3B,C星MWRI均方差(RMS)分别为1.24,1.18m/s。用带泡沫散射层的双尺度随机粗糙面的复合模型计算后向热发射。考虑各通道频率、灵敏度和定标精度等因素,用回归分析法分析了各通道热辐射特性随海面风速变化的不同响应特性,建立了适于FY-3C星MWRI的大风风速反演模型。中低风速模型和大风速模型反演的全球海面风速分布结果表明:中低风速精度标准差1.2m/s;反演大风数据和海岛固定浮标数据有一致性,模型的实际应用效果较好,可为我国沿海的大风监测和预警提供保障。

烟台海域海岛自动站大风对比试验

烟台北部面临黄、渤海,海岛自动站分布众多。我们发现,在同一大风过程中,各海岛自动站的风速、风向因为海拔高度、周围地形影响、下垫面摩擦的不同造成明显差异。本文主要以长岛作为渤海海峡大风的代表站,以崆峒岛和芝罘岛作为烟台北部沿海海域大风的代表站,利用便携自动站的观测数据近似代表海面大风的实况,与代表站进行大风的对比试验,对比试验的数据均采用指数廓线公式订正到海面10 m高度。分析了三个海岛自动站的不同风向下的海面大风的实际代表性,并给出不同风向下的大风订正值。

Interannual Variability of SST,SLA and Wind Waves in the Hawaii Area and Their Responses to ENSO

Time series of sea surface temperature （SST）, wind speed and significant wave height （SWH） from meteorological buoys of the National Data Buoy Center （NDBC） are useful for studying the interannual variability and trend of these quantities at the buoy areas. The measurements from 4 buoys （B51001, B51002, B51003 and B51004） in the Hawaii area are used to study the responses of the quantities to El Nino and Southern Oscillation （ENSO）. Long-term averages of these data reflect precise seasonal and climatological characteristics of SST, wind speed and SWH around the Hawaii area. Buoy observations from B51001 suggest a significant warming trend which is, however, not very clear from the other three buoys. Compared with the variability of SST and SWH, the wind speeds from the buoy observations show an increasing trend. The impacts of EI Nifio on SST and wind waves are also shown. Sea level data observed by altimeter during October 1992 to September 2006 are analyzed to investigate the variability of sea level in the Hawaii area. The results also show an increasing trend in sea level anomaly （SLA）. The low-passed SLA in the Hawaii area is consistent with the inverse phase of the low-passed SOI （Southern Oscillation Index）. Compared with the low-passed SOl and PDO （Pacific Decadal Oscillation）, the low-passed PNA （Pacific-North America Index） has a better correlation with the low-passed SEA in the Hawaii area.

Comparison of nonlinear and linear PCA on surface wind,surface height,and SST in the South China Sea

We compared nonlinear principal component analysis(NLPCA) with linear principal component analysis(LPCA) with the data of sea surface wind anomalies(SWA),surface height anomalies(SSHA),and sea surface temperature anomalies(SSTA),taken in the South China Sea(SCS) between 1993 and 2003.The SCS monthly data for SWA,SSHA and SSTA(i.e.,the anomalies with climatological seasonal cycle removed) were pre-filtered by LPCA,with only three leading modes retained.The first three modes of SWA,SSHA,and SSTA of LPCA explained 86%,71%,and 94% of the total variance in the original data,respectively.Thus,the three associated time coefficient functions(TCFs) were used as the input data for NLPCA network.The NLPCA was made based on feed-forward neural network models.Compared with classical linear PCA,the first NLPCA mode could explain more variance than linear PCA for the above data.The nonlinearity of SWA and SSHA were stronger in most areas of the SCS.The first mode of the NLPCA on the SWA and SSHA accounted for 67.26% of the variance versus 54.7%,and 60.24% versus 50.43%,respectively for the first LPCA mode.Conversely,the nonlinear SSTA,localized in the northern SCS and southern continental shelf region,resulted in little improvement in the explanation of the variance for the first NLPCA.

Formation of the modern current system in the East China Sea since the early Holocene and its relationship with sea level and the monsoon system

The Okinawa Trough is a natural laboratory for the study of air-sea interaction and paleoenvironmental change. It has been demonstrated that present offshore export of particles in the bottom nepheloid layer occur primarily with downwelling from the northeast winter monsoon, which is inhibited by a transverse circulation pattern in summer. This current system was very different during the Last Glacial Maximum owing to low sea level （-120 m） and exposure of a large shelf area. We collected sediment core Oki01 from the middle Okinawa Trough during 2012 using R/V Kexue No. 1 to elucidate the timing and cause of the current system transition in the East China Sea. Clay mineral, dry density, and elemental （Ti, Ca） composition of core Oki01 was analyzed. The results indicate that clay minerals derived mainly from the Huanghe （Yellow） and the Changjiang （Yangtze） Rivers during 16.0-11.6 ka, and the modem current system in the East China Sea formed beginning in the early Holocene. Therefore, mixing of East China Sea continental shelf, Changjiang River and partially Taiwan Island sediment are the major contributors. The decrease of log（Ti/Ca） and alternating provenance since the early Holocene indicate less sediment from the East China in summer because of resistance of the modern current system, i.e., a ＂water barrier＂ and upwelling. Conversely, sediment delivery persists in winter and log（Ti/Ca） indicates the winter monsoon signal since the early Holocene. Our evidence also suggests that sediment from Taiwan Island could be transported by the Kuroshio Current to the middle Okinawa Trough, where it mingles with winter monsoon- induced export of sediment from the Changjiang River and East China Sea continental shelf. Although the present research advances understanding of the evolutionary history of paleoenvironmental change in the Okinawa Trough, more sediment cores should be retrieved over wide areas to construct a larger scenario.