Robust Relationship Between Mid-latitudes CAPE and Moist Static Energy in Present and Future Simulations

TL;DR

This paper demonstrates that the relationship between CAPE and moist static energy is robust across climate states, enabling better prediction of future CAPE distributions using a simple scaling approach.

Contribution

It introduces a new framework linking CAPE changes to MSE surplus, improving upon traditional theories for climate impact assessments.

Findings

CAPE increases with warming but distributional changes are not fully captured by simple theories.

CAPE correlates tightly with MSE surplus, which determines its development and magnitude.

Future CAPE distributions can be accurately scaled from present data using a three-parameter model.

Abstract

Convective available potential energy (CAPE), a metric associated with severe weather, is expected to increase with warming. Under the most widely-accepted theory, developed for strongly convective regimes, mean CAPE should rise following the Clausius-Clapeyron (C-C) relationship at 6-7%/K. We show here that although the magnitude of CAPE change in high-resolution model output is only slightly underestimated with simple theories, it is insufficient to describe the distributional changes, which has a down-sloping structure and is crucial for impact assessment. A more appropriate framework for understanding CAPE changes uses the tight correlation between CAPE and moist static energy (MSE) surplus. Atmospheric profiles develop appreciable CAPE only when MSE surplus becomes positive; beyond this point, CAPE increases as $\sim$25% of the rise in MSE surplus. Because this relationship is robust across climate states, changes in future CAPE distributions can be well-captured by a simple scaling of present-day data using only three parameters.