Precipitation Characteristics in Mid-Latitude East Asia as Observed by TRMM PR and TMI

抄録

Precipitation radar and microwave radiometer data from the Tropical Rainfall Measuring Mission (TRMM) satellite during the spring and summer months of 1998 are used to study the precipitation characteristics in the mid-latitude East Asia region (20°-40°N, 100°-140°E), with particular emphasis on comparing the differences between stratiform and convective rains, and between rains during spring and summer. The characteristics in the mid-latitude are also compared with those in the tropics. The two-season mean results for the mid-latitudes show that the mean rainfall rate for stratiform clouds is ∼2 mm h^-1, at least 6 times lower than its convective counterpart. The mean convective rainfall rate is higher over land than over ocean, and higher in the mid-latitude than in the tropics. Generally, convective clouds generate more rain total for both mid-latitudes and tropics although they cover less area than stratiform clouds. Comparing between mid-latitude and tropical regions, the contribution of stratiform rains is larger in the mid-latitudes than in the tropics.
There are distinct differences between stratiform and convective precipitation profiles, as well as noticeable seasonal variations of these profiles. The mean vertical profiles showed that stratiform rains have a quasi-constant rainfall rate below freezing level and a sharp drop-off above. Convective profiles, on the other hand, often have a maximum rainfall rate somewhere below the freezing level. Above the freezing level, precipitation layer for convective rains is thicker than for stratiform rains. For convective rains, significant differences are found between profiles over land and ocean, with a significant deeper layer for land convections given the same surface rainfall rate. Consistently, microwave scattering signature over land, expressed by polarization-corrected temperature at 85 GHz, is nearly twice as strong as that over ocean for the same surface rainfall rate. Precipitation profiles are similar in shape and depth between mid-latitude and tropical regions during summer when the freezing level heights are also similar between the two regions. However, compared to being no noticeable variation in the tropics during a year, there is a significant seasonal change for the precipitation profiles in mid-latitudes. The seasonal difference of precipitation profiles arises from the deeper precipitation layer in the summer than in the spring for a given surface rainfall rate, being in consistent with the seasonal variation of the freezing level height. This change in precipitation depth applies to both stratiform and convective rains, and to rains over both land and ocean. It should be mentioned that all the aforementioned results, except for the 85 GHz scattering signature, are derived from TRMM precipitation radar data.