Climate projections of spatial variations in coastal storm surges along the Gulf of Mexico and U.S. east coast

Using statistically downscaled atmospheric forcing, we performed a numerical investigation to evaluate future climate's impact on storm surges along the Gulf of Mexico and U.S. east coast. The focus is on the impact of climatic changes in wind pattern and surface pressure while neglecting sea level rise and other factors. We adapted the regional ocean model system(ROMS) to the study region with a mesh grid size of 7–10 km in horizontal and 18 vertical layers. The model was validated by a hindcast of the coastal sea levels in the winter of 2008. Model's robustness was confirmed by the good agreement between model-simulated and observed sea levels at 37 tidal gages. Two 10-year forecasts, one for the IPCC Pre-Industry(PI) and the other for the A1 FI scenario, were conducted. The differences in model-simulated surge heights under the two climate scenarios were analyzed. We identified three types of responses in extreme surge heights to future climate: a clear decrease in Middle Atlantic Bight, an increase in the western Gulf of Mexico, and non-significant response for the remaining area. Such spatial pattern is also consistent with previous projections of sea surface winds and ocean wave heights.     

Trends of sea surface wind energy over the South China Sea

Studies on climate change typically consider temperature and precipitation over extended periods but less so the wind.We used the Cross-Calibrated Multi-Platform(CCMP)24-year wind field data set to investigate the trends of wind energy over the South China Sea during 1988-2011.The results reveal a clear trend of increase in wind power density for each of three base statistics(i.e.,mean,90 th percentile and 99 th percentile)in all seasons and for annual means.The trends of wind power density showed obvious temporal and spatial variations.The magnitude of the trends was greatest in winter,intermediate in spring,and smallest in summer and autumn.A greater trend of increase was found in the northern areas of the South China Sea than in southern parts.The magnitude of the annual and seasonal trends over the South China Sea was larger in extreme high events(i.e.,90~(th) and 99~(th) percentiles)compared to the mean conditions.Sea surface temperature showed a negative correlation with the variability of wind power density over the majority of the South China Sea in all seasons and annual means,except for winter(41.7%).     

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.     

Interannual oscillation of meridional sea level wind and its impact on sea surface temperature in the South China Sea

Analysis of COADS data (1958–1987) showed that there is obviously interannual SST oscillation including QBO (Quasi-biennial oscillation) and quasi-3.5 year oscilation, etc., of the SCS (South China Sea), which is the response of the upper mixed layer of the sea to the impact of the East Asian Monsoon anomaly. Most SST anomalies appear in the central basin of the SCS. The phase-locked phenomena linking the SST annual cycle and interannual oscillation is an important characteristic of the SCS climate. There is not only SST response to atmospheric impact, but also feedback to the air. The authors put forward a scheme of regional air-sea interaction in winter time in the SCS. Project 49676276 supported by NSFC and also supported by FSEC.     

Co-variation of the surface wind speed and the sea surface temperature over mesoscale eddies in the Gulf Stream region:momentum vertical mixing aspect

The co-variation of surface wind speed and sea surface temperature(SST)over the Gulf Stream frontal region is investigated using high-resolution satellite measurements and atmospheric reanalysis data.Results show that the pattern of positive SST-surface wind speed correlations is anchored by strong SST gradient and marine atmospheric boundary layer(MABL)height front,with active warm and cold-ocean eddies around.The MABL has an obvious transitional structure along the strong SST front,with greater(lesser)heights over the north(south)side.The significant positive SST-surface wind-speed perturbation correlations are mostly found over both strong warm and cold eddies.The surface wind speed increases(decreases)about 0.32(0.41)m/s and the MABL elevates(drops)approximate 55(54)m per 1℃ of SST perturbation induced by warm(cold)eddies.The response of the surface wind speed to SST perturbations over the mesoscale eddies is mainly attributed to the momentum vertical mixing in the MABL,which is confirmed by the linear relationships between the downwind(cro sswind)SST gradient and wind divergence(curl).     

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.     

Linkages between Arctic sea ice cover,large-scale atmospheric circulation,and weather and ice conditions in the Gulf of Bothnia,Baltic Sea

During years 1980/1981–2012/2013, inter-annual variations in sea ice and snow thickness in Kemi, in the northern coast of the Gulf of Bothnia, Baltic Sea, depended on the air temperature, snow fall, and rain. Inter-annual variations in the November—April mean air temperature, accumulated total precipitation, snow fall, and rain, as well as ice and snow thickness in Kemi and ice concentration in the Gulf of Bothnia correlated with inter-annual variations of the Pacific Decadal Oscillation(PDO), Arctic Oscillation(AO), North Atlantic Oscillation(NAO), Scandinavian Pattern(SCA), and Polar / Eurasian Pattern(PEU). The strong role of PDO is a new finding. In general, the relationships with PDO were approximately equally strong as those with AO, but rain and sea ice concentration were better correlated with PDO. The correlations with PDO were, however, not persistent; for a study period since 1950 the correlations were much lower. During 1980/1981—2012/2013, also the Pacific / North American Pattern(PNA) and El Nino–Southern Oscillation(ENSO) had statistical connections with the conditions in the Gulf of Bothnia, revealed by analyzing their effects combined with those of PDO and AO. A reduced autumn sea ice area in the Arctic was related to increased rain and total precipitation in the following winter in Kemi. This correlation was significant for the Pan-Arctic sea ice area in September, October, and November, and for the November sea ice area in the Barents / Kara seas.     

Geochemical studies of U,Th, Ra,40K in seciments of the China Sea and adjacent sea area,and lower reaches of several Chinese Rivers

Geochemical studies of the U, Th, Ra, and⁴⁰K in surface sediments of the China Sea and adjacent sea areas, the lower reaches of the Huanghe and Changjiang Rivers and the estuaries of the Zhujiang and Rongjiang Rivers were carried out with a model 8180-4K multichannel Ge(Li)γ spectrometer in 1981–1985. The mean values of U, Ra, Th,⁴⁰K are about 2.11 ppm, 7.67×10⁻¹³g/g, 11.00 ppm, and 2.33 ppm respectively, in the China Sea, the Okinawa Trough, and the Changjiang and Huanghe River estuaries. The distribution of the four isotopes is uniform in the above zone. The contents of U and Th in the sediments of the Zhujiang and Rongjiang Rivers and the Fujian coast are 1–4 times higher than those of the above zone and are related to the granite and radioactive ore present in the upper reaches of these rivers or the adjacent mountains. The distributions of U, Th, Ra, and⁴⁰K are related to the physico-chemical property, redox state, geological type and grain size of the sediment, and biotic activity. Contribution No. 1408, Institute of Oceanology, Academia Sinica, Qingdao.     

Review of Global Ocean Intermediate Water Masses： 1. Part A, the Neutral Density Surface （the ＇McDougall Surface＇ ） as a Study Frame for Water-Mass Analysis

This review article commences with a comprehensive historical review of the evolution and application of various density surfaces in atmospheric and oceanic studies. The background provides a basis for the birth of the neutral density idea. Attention is paid to the development of the neutral density surface concept from the nonlinearity of the equation of state of seawater. The definition and properties of neutral density surface are described in detail as developed from the equations of state of seawater and the buoyancy frequency when the squared buoyancy frequency N2 is zero, a neutral state of stability. In order to apply the neutral density surface to intermediate water-mass analysis, this review also describes in detail its practical oceanographic application. The mapping technique is focused for the first time on applying regularly gridded data in this review. It is reviewed how a backbone and ribs framework was designed to flesh out from a reference cast and first mapped the global neutral surfaces in the world＇s oceans. Several mapped neutral density surfaces are presented as examples for each world ocean. The water-mass property is analyzed in each ocean at mid-depth. The characteristics of neutral density surfaces are compared with those of potential density surfaces.     

Absolute calibration of HY-2A and Jason-2 altimeters for sea surface height using GPS buoy in Qinglan,China

GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration.This study introduces the results of the Qinglan calibration campaign for the HY-2 A and Jason-2 altimeters.It took place in two time slices;one was from August to September 2014,and the other was in July 2015.One GPS buoy and two GPS reference stations were used in this campaign.The GPS data were processed using the real-time kinematic(RTK)technique.The final error budget estimate when measuring the sea surface height(SSH)with a GPS buoy was better than 3.5 cm.Using the GPS buoy,the altimeter bias estimate was about-2.3 cm for the Jason-2 Geophysical Data Record(GDR)Version 'D' and from-53.5 cm to-75.6 cm for the HY-2 A Interim Geophysical Data Record(IGDR).The bias estimates for Jason-2 GDR-D are similar to the estimates from dedicated calibration sites such as the Harvest Platform,the Crete Site and the Bass Strait site.The bias estimates for HY-2 A IGDR agree well with the results from the Crete calibration site.The results for the HY-2 A altimeter bias estimated by the GPS buoy were verified by cross-calibration,and they agreed well with the results from the global analysis method.