The Mechanisms Governing the Evolution of Precipitation Over Tropical Land and Ocean During the Past 22,000 Years

Abstract:

Proxies of monsoons indicate a nearly synchronous fluctuation across northern monsoon domains on orbital timescales. Using a transient climate simulation, we have shown that precipitation evolves differently over tropical land and ocean. During the deglacial (22 ka to 11 ka) precipitation over land and ocean are in phase, whereas they are out of phase during the Holocene (11 ka to 0 ka). We have used the energetics framework of monsoon to diagnose these changes in precipitation over India and the Bay of Bengal (BoB). This diagnosis attributes the variations in moisture convergence to the net energy flux into the atmosphere and total column water vapor. During the deglacial, the effect of water vapor on precipitation is dominant. Since water vapor has similar variations over land and ocean, precipitation over India and the BoB are in phase. Across the Holocene, precipitation is driven by the net energy fluxes, which is out-of-phase between India and the BoB. This is due to the large contribution from surface energy fluxes over the BoB. Proxies from the BoB support our results. This study highlights that feedbacks internal to the climate system can amplify or counter the impact of solar forcing on precipitation.