Thermodynamic Scaling of Extreme Daily Precipitation over the Tropical Ocean from Satellite Observations

Abstract

 Extreme precipitation theory has been matured over the last decade and stipulates that the intensity of the extreme precipitation scales with the surface humidity. Surface humidity changes can further be approximated by the surface temperature changes. The analytically derived scaling coefficient based on the Clausius-Clapeyron derivative is ∼ 6 %K⁻¹ in the tropics. While frequently confronted with observations over land, the theory has so far only been marginally evaluated against precipitation data over the ocean. Using an ensemble of satellite-based precipitation products and a suite of satellite-based SST analysis all at the 1°-1day resolution, the extreme scaling is investigated for the tropical ocean (30°S-30°N). The focus is set on the robust features common to all precipitation and SST products. It is shown that microwave constellation-based precipitation products are characterized by a very robust positive scaling over the 300 to 302.5 K range of 2-day lagged SST. This SST range corresponds to roughly 60 % of the tropical precipitation amount. The ensemble mean scaling varies between 5.67 %K⁻¹ ± 0.89 %K⁻¹ to 6.33 %K⁻¹ ± 0.81 %K⁻¹ depending on the considered period and is found very close to the theoretical expectation. The robustness of the results confirms the fitness of the current generation of constellation-based precipitation products for extreme precipitation analysis. Our result further confirms the extreme theory for the whole tropical ocean. Yet, significant differences in the magnitude of the extreme intensity across the products prompts the urging necessity of dedicated validation efforts.