Impact of Gridding Scale on TRMM Microwave Imager Cloud Water Information

Satellite observation data are valuable for model evaluation, but to readily compare satellite-based data with model simulations, swath pixel data must first be gridded. In this study, data distortions caused by gridding (0.1°, 0.25°, 0.5°, 1.0°, and 2.5° gridding resolutions) are investigated using instantaneous and monthly pixel data from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) liquid water path (LWP) data. Results from this case study show that data gridded at grid scales of 0.1°, 0.25°, and 0.5° retain more local details in the instantaneous pixel data, while the details tend to be smoothed out at coarser grid resolutions. So data with grid scales no coarser than 0.5° are suitable for analyzing weather activities from the mesoscale to the synoptic scale. In terms of the monthly pixel LWP, data with gridding resolutions of 0.1°, 0.25°, and 0.5° also retain more detail. Although, probability density functions (PDF) of the LWP show similar patterns at all the gridding scales considered. So when analyzing monthly LWP data, the impact of gridding scales is not significant. Finally, this study compared the gridded TMI LWP data with the European Centre for Medium-range Weather Forecasts Interim reanalysis (ERA-Interim) and NCEP Climate Forecast System Reanalysis (CFSR), and found that both of these reanalyses overestimate the magnitudes of the LWP. Gridded TMI LWP data, the ERA-Interim, and the CFSR show reasonably similar regularities in the variance of the LWP.