Abstract / Description of output
Variations of upper tropospheric humidity (UTH) and cold cloud in the tropics reveal coherent changes that propagate eastward from the Indian Ocean into the Pacific. The coherence of UTH is high at periods of 30–90 days along the equator. Near the tropical tropopause, UTH coherence is large over the equator in the Indian Ocean and over the subtropics in the central Pacific. A composite life cycle shows that enhanced UTH in the subtropics coincides with two anticyclonic gyres. They straddle anomalous cold cloud over the equator as it propagates eastward. The enhancement of UTH is consistent with anomalously-cold temperature, which mirrors the anticyclonic gyres. Those temperature anomalies cancel the height anomaly of the gyres overhead. The complex of anomalous UTH, cold cloud, and anticyclonic motion marches eastward across the western Pacific, until reaching the dateline. Anomalous convection over the equator then collapses, along with the subtropical gyres and enhanced UTH accompanying it.