衛星観測に基づく熱帯海洋上の極端日降水における熱力学的スケーリング

抄録

The theory of extreme precipitation has matured over the last decade and stipulates that the intensity of the extreme precipitation is balanced with the surface humidity. The changes in surface humidity can further be approximated by the changes in surface temperature. 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 sea-surface temperature (SST) analyses at 1°-1day resolution, extreme scaling is investigated for the tropical ocean (30°S–30°N). The focus is on the robust features common to all precipitation and SST products. It is shown in this study that microwave constellation-based precipitation products are characterized by a very robust positive scaling over the 300–302.5-K range of 2-day-lagged SST. This SST range corresponds to roughly 60 % of the amount of tropical precipitation. The ensemble mean scaling varies between 5.67 ± 0.89 % K⁻¹ and 6.33 ± 0.81 % K⁻¹ depending on the considered period and is found to be very close to the theoretical expectation. The robustness of the results confirms the suitability of the current generation of constellation-based precipitation products for extreme precipitation analysis. Our result further confirms the extreme theory for the entire tropical ocean. Yet, the significant differences in the magnitude of the extreme intensity of the products require dedicated validation efforts.