Affected by multi-scale circulation systems and the topography, precipitation over the central North China (CNC) presents large variations in spatial and temporal aspects. Previous studies pointed out that the peak time of summer rainfall gradually delays southeastwardly from the afternoon (northwestern mountains) to the midnight and the early morning (the southeastern plain and coastal regions) over CNC, which are also observed along the Yangtze River Valley. However, whether the rainfall characteristics are consistent in the two areas needs further analysis.

Dr. YUAN Weihua and her colleagues from Institute of Atmospheric Physics found that the spatiotemporal features of rainfall events are highly correlated with the topography. The largest frequency of total and short-duration rainfall events locates in the southeastern inner periphery of Taihangshan and Yanshan mountains, which may be related with the distributions of the temperature and water vapor in the afternoon.

Further analysis showed that the delayed features are mainly contributed by the short-duration rainfall events rather than the long-duration ones (Fig. 1) and more obvious in the inactive monsoon period rather than the active one (Fig. 2), which are different from those along the Yangtze River Valley. Short-duration rainfall over the northwestern mountains often occurs in the afternoon. Influenced by the topography and low-level circulations, some of them propagate to the southeastern plain around the late evening, even later to coastal regions.

Their findings were recently published in Journal of Geophysical Research: Atmospheres recently.

Reference: 
Yuan, W., W. Sun, H. Chen, and R. Yu, 2014: Topographic effects on spatiotemporal variations of short-duration rainfall events in warm season of central North China, J. Geophys. Res. Atmos., 119, 11,223–11,234. 

Fig. 1 Most frequent starting (white vectors) and ending (black vectors) time (BJT) of (a) short- and (b) long-duration rainfall events averaged in the warm season and the topography (shaded, unit: m).