Abstract
Changes to the storm-scale physical processes of an eastern United States mesoscale convective system (MCS) on 14 May 2018 in response to global warming are quantified using the pseudo global warming (PGW) numerical method. Climate perturbations in temperature (ΔT) and specific humidity (ΔQ) of different magnitudes are imposed separately and simultaneously. The mid-twenty-first century environment become increasingly unstable with larger ΔT, promoting more favorable MCS conditions. By the late twenty-first century, however, this warming, which maximizes in the mid-troposphere, results in increased convective inhibition (CIN) and decreased convective available potential energy (CAPE). Mid-level warming also reduces cold pool generation through the downward advection of the relatively warm mid-level air. Consequently, the MCS of interest is weak in the mid-century, and propagates discretely over the Appalachian Mountains, while it fails to initiate in the late century. In contrast, projected increases in ΔQ support more intense MCSs both the mid- and late twenty-first centuries. Moisture increases are maximized in lower troposphere, increasing CAPE and decreasing CIN. Additionally, the stronger convections generate deeper and denser cold pools. Therefore, storms remain robust as they move over the Appalachian Mountains. However, leeside isolated convective cells, which form due to lee waves in the more unstable environment, and their widespread cold pools reduce the leeside instability. This, in conjunction with the more intense MCS cold pools, leads to rapid MCS weakening in the lee. Experiments with both ΔT and ΔQ illustrate that larger magnitude increases in one thermodynamic variable may supersede increases in the other.
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