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Convective-permitting ensemble simulations are used to understand the roles of thermodynamic and dynamic processes in changing intense storms over the West African Sahel due to increases in atmospheric greenhouse gas concentrations. Ensemble simulations with 16 members represent recent August conditions during the height of the boreal summer monsoon season over the Sahel. They are compared with 5 Future-Warming ensemble simulations with increased greenhouse gas concentrations under the late-21st-century high-emission SSP5-8.5 scenario and initial/boundary conditions from the Current-Climate data plus the multi-model mean anomalies derived from CMIP6 experiments. The Current-Climate simulations reproduce observed precipitation and environmental conditions over the Sahel well. The frequency of heavy rainfall events with 24-hr rainfall >77 mm (the 99.9th percentile) increases by ≥38.2% in the Future-Warming simulations. While the low- to mid-level vertical wind shear increases in the Future-Warming simulations, we find no significant correlations between the environmental shear strength and peak storm rain rates. In contrast, lower (middle) tropospheric moisture and temperature are correlated (anticorrelated) with peak rain rates and/or the maximum updraft velocity of intense events, consistent with significant correlations between the increased atmospheric instability and storm intensity. Thus, thermodynamic processes and not dynamical (shear-related) processes dominate the rainfall intensification over the Sahel in the simulations. Nevertheless, the enhanced shear strength is associated with larger rain-shield areas and propagation speeds of intense storms in Future-Warming. Wind shear strength is also correlated with pre-storm atmospheric instability, which grows less/more under strong/weak shear with greenhouse gas increases and is relevant for sub/super Clausius-Clapeyron scaling of precipitation.
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The Response of Tropical Cyclone Inner Core and Outer Rainband Precipitation to Warming in Idealized Convection‐Permitting WRF
Abstract Global mean and extreme tropical cyclone (TC) precipitation have been increasing over the past few decades and are expected to continue to increase into the future due to climate change. Most projections of future TC precipitation use climate models with grid spacings of 25–100 km, which are too coarse to resolve the convective structures and small‐scale precipitation processes within TCs. This work uses convection‐permitting Weather Research and Forecasting model simulations to investigate how precipitation and precipitation processes change in the inner core (IC) and outer rainbands (OR) of TCs in response to sea surface temperature (SST) warming. The simulations are idealized, with single TCs initialized from weak vortices over domain‐constant SSTs. In these simulations, TC intensity and IC precipitation greatly increase with SST warming while OR precipitation increases slightly. A greater area in the IC is occupied by deep convection more frequently in the warmer simulations, while the deep convective activity remains relatively constant with warming in the TC OR. Mixing ratios of hydrometeors and cloud ice increase with warming in both the IC and OR, while the TCs' vertical circulations deepen, melting levels rise, and mean upward velocities strengthen. This work demonstrates how analysis of three‐dimensional storm structures can provide insight into processes that change TC precipitation in different regions of the storm, and future work will include applying this analysis to more realistic convection‐permitting simulations.
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- Award ID(s):
- 2312317
- PAR ID:
- 10652562
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 130
- Issue:
- 4
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024JD042217
