Balancing the atmospheric water budget's annual cycle using satellite-based products and ERA5 reanalysis in tropical ocean regions

Regional atmospheric water budgets are challenging to balance using independent data products. Six tropical ocean regions are evaluated for an annual cycle in closure exhibited between SeaFlux evaporation – Global Precipitation Climatology Product (GPCP) precipitation and ERA5 atmospheric moisture divergence. The annual cycle in monthly average closure for 1998 – 2021 indicates that there are systematic regional differences in the products throughout the year. The eastern Indian Ocean region has the largest cycle in closure of ~2 mm d^-1, which largely relates to a lack of change in SeaFlux evaporation during the year. Comparisons with buoy and ship observations and show that SeaFlux underestimates higher wind speeds when they peak in the boreal summer, flattening evaporation at this time of year, and contributing to the cycle in the water balance residual. Three other regions, namely the western Indian, western Pacific and eastern Pacific ocean basins also all show an annual cycle in closure related to biases in near-surface humidity in SeaFlux evaporation, passive microwave sensor convective states in GPCP precipitation and atmospheric moisture divergence in ERA5, respectively. Central Pacific and Atlantic ocean regions are generally close to closure and show little monthly change. Regional biases exist in SeaFlux evaporation, GPCP precipitation and ERA5 atmospheric moisture divergence, and these biases influence the annual cycle of closure of monthly tropical atmospheric water budgets over the ocean.