We have developed a method to correct this bias by comparing model precipitation received each day by the soil against a daily precipitation analysis (the NCEP/CPC 1/8 deg gauge analysis), and accumulate this daily deficit/surplus into a long-term precipitation budget history array for the model domain. We then use this budget history array to modify the hourly input for precipitation assimilation, with the aim of balancing out the budget deficit/surplus within the next 24 hours. The maximum amount of adjustment to the hourly precipitation input is limited to +/-20% of the original analysis value. This long-term budget check/adjustment approach has proven to be beneficial to the quality of the model's water cycle components and helpful in fine-tuning the model's soil moisture field.
The bias-adjustment of the hourly precipitation input was implemented into the Eta model on 16 Mar 2004. Detailed discussion of the approach and its impact on the model will be presented at the time of the AMS meeting.