Statistics of Isolated Deep Convection Initiation and Its Relation to Topography in the North China Area

This study investigates the statistical characteristics of isolated deep convection initiation (DCI) and its relation to topography in the North China area during the summer season of 2017-2019. A total of 2,534 isolated DCI events are identified using the infrared brightness temperature data from Himawari-8 satellite with a resolution of 0.05 degrees x 0.05 degrees. The spatial distribution of DCI shows clustering over mountains and hills, indicating that the local topography may be critical for DCI. Topography is described with elevation and relief amplitude in this study. Results show that normalized DCI counts increase with elevation and relief amplitude. For the regime characterized by fewer morning clouds (regime one), DCI strongly depends on elevation and relief amplitude, while for the regime with more morning clouds (regime two), topography only moderately impacts DCI. Linear regression analyses suggest the existence of significant linear relationships between DCI and relief amplitude when elevation is relatively high. Topography is also categorized into four types: plain/sea areas, plateaus, hilly areas, and mountains. Normalized DCI counts show that mountains and hilly areas are more favorable for initiating isolated deep convection, especially for regime one. Moreover, DCI counts in regime one show a stronger diurnal variation and a peak occurring 2 hr earlier than that of regime two. We suggest that special attention should be paid to elevation and relief amplitude, as well as morning cloud cover condition when forecasting DCI in the North China area. Further study is necessary to understand this DCI occurrence preference on specific topography.