Change Charactreristics Of Specific Humidity Over East China During Recent 50 Years

Based on the monthly mean surface dataset from 315 weather stations over East China (to the east of 110°E) during the period of 1963-2012, the spatial distribution characteristics of specific humidity (SH) over East China are analyzed and compared. Also, the contributions of geographical factors (including longitude, latitudes and elevation) to SH spatial distribution are discussed. Then we figured out the coupling association between precipitation and SH, surface air temperature and SH respectively and then focused on the rates of SH increase with surface air temperature. The results are as follows:(1) The mean values of SH show zonal spatial distribution decreasing with latitude over East China in winter months. The overall mean values of SH in summer months are higher than that in winter months and the mean values of SH decrease from the southeast coast to the northwest inland in summer months. The variations of SH are also discussed. In general, it turns out to be lower (higher) variation in the areas with higher (lower) mean values of SH.(2) SH shows consistently positive trends in winter months during recent 50 years over East China and the values of trends are higher to the north side of Qinling Mountains-Huai River than to the south side. The SH trends in summer months are weaker than that in winter months and present to be positive to the north side of Qinling Mountains-Huai River and negative to the south side.(3) The spatial distribution of SH is apparently affected by geographical locations. In details, the distribution of SH mean values (variations) in winter and summer are both mainly dependent on latitude over East China and its values decrease (increase) with latitude increase. Longitude and elevation also play a big part in the the distribution of SH after latitude. SH mean values (variations) increase (decrease) with longitude increase and elevation decrease. Besides, the influence of longitude on SH variations distribution is comparatively more significant than on SH mean values and the influence of elevation is relatively stronger in summer than in winter.(4) The changes of SH are also closely associated with both precipitation amount and surface air temperature whenever in winter or summer months. When precipitation amount is more (less) than normal years over East China, the corresponding SH over the same period is as well higher (lower). Comparatively, the relationship between SH and surface air temperature is more obvious than SH and precipitation. When surface air temperature is higher (lower) than normal years, the corresponding SH over the same period is as well higher (lower) than normal years.(5) SH remarkably increases with warming. The rates of SH increase with surface air temperature presents the feature of higher rate in central than in the north and south sides in winter months. In summer months, the overall rates of SH increase with air temperature are generally lower than that in winter months and present the feature of decreasing from east coast to inland to the north side of Qinling Mountains-Huai River and increasing with latitude to the south side with the higher values in Bohai Bay area.(6) The rates of SH increase with surface air temperature in winter months tend to be gradually falling since 1980s to the north side of Qinling Mountains-Huai River but are comparatively steady and show no significant trend to the south side. The rates of SH increase with surface air temperature in summer months tend to be gradually falling since 1990s.