Expansion of the South China Sea basin:Constraints from magnetic anomaly stripes,sea floor topography,satellite gravity and submarine geothermics

The widely distributed E-W-trending magnetic anomaly stripes in the central basin and the N-Etrending magnetic anomaly stripes in the southwest sub-basin provide the most important evidence for Neogene expansion of the South China Sea.The expansion mechanism remains,however,controversial because of the lack of direct drilling data,non-systematic marine magnetic survey data,and irregular magnetic anomaly stripes with two obvious directions.For example,researchers have inferred different ages and episodes of expansion for the central basin and southwest sub-basin.Major controversy centers on the order of basinal expansion and the mechanism of expansion for the entire South China Sea basin.This study attempts to constrain these problems from a comprehensive analysis of the seafloor topography,magnetic anomaly stripes,regional aeromagnetic data,satellite gravity,and submarine geothermics.The mapped seafloor terrain shows that the central basin is a north-south rectangle that is relatively shallow with many seamounts,whereas the southwest sub-basin is wide in northeast,gradually narrows to the southwest,and is relatively deeper with fewer seamounts.Many magnetic anomaly stripes are present in the central basin with variable dimensions and directions that are dominantly EWtrending,followed by the NE-,NW- and NS-trending.Conversely such stripes are few in the southwest sub-basin and mainly NE-trending.Regional magnetic data suggest that the NW-trending Ailaoshan-Red River fault extends into the South China Sea,links with the central fault zone in the South China Sea,which extends further southward to Reed Tablemount.Satellite gravity data show that both the central basin and southwest sub-basin are composed of oceanic crust.The Changlong seamount is particularly visible in the southwest sub-basin and extends eastward to the Zhenbei seamount.Also a low gravity anomaly zone coincides with the central fault zone in the sub-basin.The submarine geothermic distribution demonstrates that the southwest sub-basin has a higher geothermal value than the central basin,and that the central fault zone is defined by a low thermal anomaly.This study suggests that NW-SE expansion of the southwest subbasin is later than the N-S expansion of the central basin with the sub-basin extending into the central basin and with both expansions ending at the same time.The expansion of southwestern sub-basin,similar to the Japanese Sea,is likely caused by left-lateral strike slip on the central fault zone in the South China Sea,which may have significance for finding oil and gas in this region.

Algorithm based on local breeding of growing modes for convection-allowing ensemble forecasting

We propose a method based on the local breeding of growing modes(LBGM) considering strong local weather characteristics for convection-allowing ensemble forecasting. The impact radius was introduced in the breeding of growing modes to develop the LBGM method. In the local breeding process, the ratio between the root mean square error(RMSE) of local space forecast at each grid point and that of the initial full-field forecast is computed to rescale perturbations. Preliminary evaluations of the method based on a nature run were performed in terms of three aspects: perturbation structure, spread,and the RMSE of the forecast. The experimental results confirm that the local adaptability of perturbation schemes improves after rescaling by the LBGM method. For perturbation physical variables and some near-surface meteorological elements, the LBGM method could increase the spread and reduce the RMSE of forecast,improving the performance of the ensemble forecast system.In addition, different from those existing methods of global orthogonalization approach, this new initial-condition perturbation method takes into full consideration the local characteristics of the convective-scale weather system, thus making convectionallowing ensemble forecast more accurate.