Time‐Lag Correlation between Passive Microwave Measurements and Surface Precipitation and Its Impact on Precipitation Retrieval Evaluation

This study investigates the correlation between the upwelling microwave brightness temperature measured by satellite radiometer and surface precipitation rate from ground radar observations at different time lags. Results show that brightness temperatures correlate more strongly with the lagged surface precipitation rate than the simultaneous surface precipitation rate. The lag time for snowfall ranges from 30 to 60 min. This time lag effect has an important influence when evaluating the satellite retrieval results relative to ground observations. For example, the falsely identified pixels can decrease by as much as 23.88% when considering a 30‐min lag time. Furthermore, the satellite‐retrieved snowfall rate shows much stronger correlation with the time‐lagged surface snowfall rate than the simultaneous snowfall rate in cold environments and for tall storms. This work implies that the time of the level‐2 swath‐retrieved snowfall rate needs to shift forward when incorporated into the level‐3 gridded products.