Impacts of Land Process on the Onset and Evolution of Asian Summer Monsoon in the NCEP Climate Forecast System

Impacts of land models and initial land conditions （ICs） on the Asian summer monsoon, especially its onset, were investigated using the NCEP Climate Forecast System （CFS）. Two land models, the Oregon State University （OSU） land model and the NCEP, OSU, Air Force, and Hydrologic Research Laboratory （Noah） land model, were used to get parallel experiments NCEP/Department of Energy （DOE） Global Reanalysis 2 System （GLDAS）. The experiments also used land ICs from the （GR2） and the Global Land Data Assimilation Previous studies have demonstrated that, a systematic weak bias appears in the modeled monsoon, and this bias may be related to a cold bias over the Asian land mass. Results of the current study show that replacement of the OSU land model by the Noah land model improved the model＇s cold bias and produced improved monsoon precipitation and circulation patterns. The CFS predicted monsoon with greater proficiency in E1 Nifio years, compared to La Nifia years model in monsoon predictions for individual years. and the Noah model performed better than the OSU These improvements occurred not only in relation to monsoon onset in late spring but also to monsoon intensity in summer. Our analysis of the monsoon features over the India peninsula, the Indo-China peninsula, and the South Chinese Sea indicates different degrees of improvement. Furthermore, a change in the land models led to more remarkable improvement in monsoon prediction than did a change from the GR2 land ICs to the GLDAS land ICs.

Statistical Characteristics of Convective Initiation in the Beijing-Tianjin Region Revealed by Six-Year Radar Data

Characteristics of convective initiation（CI） in the Beijing-Tianjin region during the warm season of 2008-2013 are examined.A total of 38877 CI cases are identified by a thunderstorm identification,tracking,analysis,and nowcasting algorithm.CI cases are evaluated in the context of associated terrain,weather systems,and land cover properties.The spatial distribution of all CI cases shows that there are dense CI activities around the 200-m elevation,which means that convective storms are more easily triggered over foothills.From 1500-1800 to 0300-0600 BT（Beijing Time）,the high-occurrence CI region tends to propagate southeastward（i.e.,from mountains to plains,then to ocean）.Among the four local weather systems,the Mongolian cold vortex has the highest CI frequency while the after-trough system has the lowest CI frequency.For the land cover relationships with CI,the urban land cover has the highest CI density and the forest-type land cover has the second highest CI density;these two types of land cover are more conducive to CI formation.