Observed Evolution of the Tropical Atmospheric Water Cycle with Sea Surface Temperature

Erik Hojgard-Olsen (1, 2) , Hélène Brogniez (1) , Hélène Chepfer (2)

1 SPACE - LATMOS
2 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

Better understanding of how moisture, clouds and precipitation co-vary under climate warming lacks a comprehensive observational view. This paper analyzes the tropical atmospheric water cycle’s evolution with sea surface temperature (SST), using for the first time, the synergistic dataset of instantaneous observations of the relative humidity profile from the Megha-Tropiques satellite, clouds from CALIPSO satellite and near-surface precipitation from the CloudSat satellite, and quantifies their rates of change with SST warming. The dataset is partitioned into three vertical velocity regimes, with cloudy grid boxes categorized after phase (ice/liquid), opacity (opaque/thin) and the presence of near-surface precipitation. Opaque cloud cover is always larger in the presence of near-surface precipitation (high ice clouds especially). Low liquid water clouds in the descending regime dominate for SSTs < 299.25 K, where the free troposphere is dry (∼20 %), and opaque liquid water cloud cover decreases with SST warming (–8 % K-1) and thin liquid water cloud cover stays constant (∼20 %). High ice clouds dominate the ascending regime in which, for 299.25 < SST < 301.75 K, humidity increases with SST in the lower free troposphere and peaks around 302 K. Over the warm SST range (> 301.75 K), in the ascending regime, opaque high ice cloud cover decreases with SST (–13 % K-1), whilst thin ice cloud cover increases (+6 % K-1). Over the warm SST range, total cloudiness decreases with warming in all regimes. This paper characterizes fundamental relationships between aspects of the tropical atmospheric water cycle and SST.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Océan, Atmosphère

Erik Hojgard-Olsen, Hélène Brogniez, Hélène Chepfer. Observed Evolution of the Tropical Atmospheric Water Cycle with Sea Surface Temperature. Journal of Climate, 2020, 33 (9), pp.3449-3470. ⟨10.1175/JCLI-D-19-0468.1⟩. ⟨insu-02491146⟩