Precipitation and Cloud Water Paths on Land Surface Temperature Investigation

It has been noticed that the operational forecasts of land surface temperature show some warm and cold trends in summer and winter respectively in the Navy’s Global Environmental Prediction System (NAVGEM). The modeled trends lead to temperature bias increasing with time gradually in 5 to 10-day forecasts. There are various reasons in a numerical weather model to cause land surface modeling biases, however, precipitation and cloud water paths of liquid and ice are well known to play important roles in modulating surface temperature through the changes of moisture and radiative fluxes at the ground. In this study, NAVGEM land surface temperature, precipitation, cloud water paths, and cloud coverage are compared with those produced by GFS physics that runs within NAVGEM framework. The comparisons reveal that the GFS produces little trend in the surface temperature forecasts, while NAVGEM generates much less liquid and ice cloud water with smaller cloudiness than GFS does over land surface, so is NAVGEM precipitation less than that of GFS averaging in both summer and winter periods. Moreover, NAVGEM predications of precipitation, liquid and ice water show a slight trend of declining in extended long forecasts. Verifying with NASA Integrated Multi-satellitE Retrievals for GPM (IMERG) of precipitation measurement data helps further to understand the impact of precipitation forecasts on land surface temperature and relative humidity. These are the major products of operational weather forecasts.