Precipitation Uncertainties at Climate Time Scales

The Global Precipitation Measurement (GPM) mission was launched in February 2014 as a joint mission between JAXA from Japan and NASA from the United States.  By applying the insight provided by the GPM radars, the program has contributed enormously to the quality of the passive microwave radiometer time series that now spans almost 40 years.  This talk will examine the long time series of precipitation from 3 approaches.  The first is an uncertainty analysis based upon first principles.  It shows that time series can be homogenized, but that potential changes in convective organization over annual time scale must be included as a source of uncertainty in order to homogenize the time series of different satellites.  This is verified with the second approach that focuses on closing the water budget on regional scales.  While not as direct, it also hints strongly at the fact that our current time series overestimate precipitation when convection is better organized into large Mesoscale Convective Complexes.  The final approach seeks to correlate biases with large scale meteorological conditions to also show that biases due to convective organization are predictable.  While not applied in any product yet, this insight may serve as a blueprint for gaining confidence in our time series of precipitation where even a 1% change/decade in global precipitation is more than currently expected from observed warming trends.