Using Moving North Pacific Index to Improve Rainy Season Rainfall Forecast over the Yangtze River Basin by Analog Error Correction

A new analog error correction （AEC） scheme based on the moving North Pacific index （MNPI） is designed in this study. This scheme shows obvious improvement in the prediction skill of the operational coupled general circulation model （CGCM） of the National Climate Center of China for the rainy season rainfall （RSR） anomaly pattern correlation coefficient （ACC） over the mid-to-lower reaches of the Yangtze River （MLRYR）. A comparative analysis indicates that the effectiveness of the new scheme using the MNPI is better than the system error correction scheme using the North Pacific index （NPI）. A Euclidean distance- weighted mean rather than a traditional arithmetic mean, is applied to the integration of the analog year＇s prediction error fields. By using the MNPI AEC scheme, independent sample hindcasts of RSR during the period 2003-2009 are then evaluated. The results show that the new scheme exhibited a higher forecast skill during 2003-2009, with an average ACC of 0.47; while the ACC for the NPI case was only 0.19. Furthermore, the forecast skill of the RSR over the MLRYR is examined. In the MNPI case, empirical orthogonal function （EOF） was used in the degree compression of the prediction error fields from the CCCM, whereas the AEC scheme was applied only to its first several EOF components for which the accumulative explained variance accounted for 80% of the total variance. This further improved the ACC of the independent sample hindcasts to 0.55 during the 7-yr period.

Differences in both the structure and interaction of the crust and mantle on the eastern and western sides of the Ordos Block

The Ordos Block,the western part of the North China Craton(NCC),has preserved most of its cratonic lithospheric roots during the destruction and modification of the NCC,and nowconnects two distinctly different tectonic units,i.e.,the Tibetan Plateau(TP)to the west and the North China Plain to the east.It is important to studythe detailed crust-mantle structure of the Ordos Block and surroundings to understand the interactions between the Ordos and adjacent regions and the dynamics of the NCC evolution.In this study,the S-wave velocity structure at depths of 0–100 km along an E-W profile at around 36.5°N from the Qilian orogen(QLO)to the Trans-North China Orogen(TNCO)within the NCC was investigated by joint inversion of the receiver functions(RFs)and surface wave dispersion data from 104 broadband seismic stations deployed in the region under the ChinArray project(PhaseⅡand PhaseⅢ).The image of discontinuity structures along the profile was further constructed by common conversion point stacking of RFs.The main results are as follows:(1)The depth of the Moho in the study region gradually decreases from west to east,being the deepest in the QLO,the second in the Ordos Block,and the shallowest in the TNCO.Local depression and uplift of the Moho are also identified beneath the Haiyuan fault zone and the Shanxi-Shaanxi rift system(SSR),respectively.(2)The crust-mantle structure displays obvious lateral heterogeneities among tectonic regions.A pronounced low-velocity anomaly is observed at depths of 20–40 km beneath the QLO and becomes weakened and thinned to the east,indicating that thickening of the mid-to-lower crust probably occurred in the QLO during the growth and lateral extrusion of the northeastern TP under the resistance of the NCC.The lithosphere-asthenosphere boundary beneath the TNCO is imaged at~90 km depth,which is significantly shallower than that beneath the Ordos Block.This observation suggests that the lithosphere of the TNCO may have experienced a notable thinning,possibly by thermal erosion and modification due to the mantle upwelling associated with the western Pacific subduction in the Mesozoic.(3)The uplifted Moho under the SSR and its neighboring areas is spatially coincident with the thinned lithosphere in the TNCO,indicating a close relationship between the development of the SSR and the lithospheric thinning and modification in this region.