Balancing atmospheric moisture budgets over the tropical Indian and tropical West Pacific Oceans

Atmospheric moisture budgets over oceans are balanced through the relationship between freshwater fluxes (evaporation minus precipitation) and vertically integrated atmospheric water vapor transport (divQ). These components of atmospheric moisture budgets can be quantified using satellite-derived observations and reanalyses. The degree to which observation-based evaporation (SeaFlux), precipitation (GPCP) and reanalysis divQ (ERA-Interim) budgets balance varies, in tropical ocean regions (15°S, 15°N). Over the period 1998 – 2007, the average difference between the monthly freshwater flux and divQ in the tropical Indian Ocean is 3.8%, relative to the regions average evaporation and precipitation. Central Pacific, eastern Pacific and Atlantic Ocean moisture budgets show slightly larger differences at 4.2% and 8.2% of average evaporation and precipitation. The tropical West Pacific Ocean region has the largest imbalance, which increases from 8.5% in 1998 to 20.6% in 2007. ERA-Interim reanalysis data produces greater convergence of moisture in the west Pacific, compared to observed freshwater fluxes. Similar imbalances are found using MERRA reanalysis data. The differences between atmospheric moisture flux variables (e.g. total column water vapor, vertical velocity, wind speed) in the Indian and West Pacific Oceans are compared to determine what is creating the imbalance between observations and reanalysis products in the West Pacific. Both reanalysis and observational data sets are used in these comparisons.