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Why Record-Breaking Extreme Precipitation events tend to occur over Land than Ocean under Global Warming?

Presentation Date
Wednesday, January 31, 2024 at 1:45pm - Wednesday, January 31, 2024 at 2:00pm
Location
The Baltimore Convention Center - Ballroom III/ IV
Authors

Author

Abstract

In this study, we have investigated the changing characteristics of climatic scale (monthly) tropical extreme precipitation in warming climates using the DOE Energy Exascale Earth System Model (E3SM). From AMIP-type simulations, we found that as the surface warmed under a) uniform 4K rise in SST and b) 4xCO2 radiative and SSTA forcing from ensemble CMIP6 model simulations, there is an increasing fractional contribution of stratiform rain as a function of the precipitation intensity, with the most extreme but rare “record breaking” events occurring preferentially over land more than the ocean, and more so under 4xCO2 than P4K. Extreme precipitation is facilitated by increased precipitation efficiency, reflecting in accelerated rates of recycling of precipitation cloud water (both liquid and ice phases) in regions with colder anvil cloud tops. Changes in the vertical profiles of clouds, condensation heating, and vertical motions indicate increasing MCS-like precipitation–cloud–circulation organization from the control to P4K, to 4xCO2.

Analyses of the surface moist static energy (CpT+Lq) distribution show that increases in surface moisture (Lq) under P4K and 4xCO2 is the key driver leading to enhanced convective instability over tropical oceans. In contrast, over land, increased warming of the mid-to-lower troposphere from large-scale descending motions, and increased downward solar radiation due to cloud clearing, coupled to a lack of available local moisture supply lead to excessive land surface warming, and strong reduction in land surface relative humidity, reflecting severe drying and enhanced convective inhibition (CIN) near the land surface. It is argued that very extreme and rare “record-breaking” precipitation events found over land under P4K, and more so under 4xCO2, are likely due to the delayed onset of deep convection, i.e., the longer the suppression of deep convection by CIN, the more severe the extreme precipitation when it eventually occurs, due to the release of a large amount of stored surplus convective available potential energy (CAPE) in the lower troposphere during prolonged CIN.

Funding Program Area(s)
Additional Resources:
NERSC