1. Updraft Width Modulates Ambient Atmospheric Controls on Convective Cloud Depth.
- Author
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Varble, A. C., Feng, Z., Marquis, J. N., Zhang, Z., Geiss, A., Hardin, J. C., and Jo, E.
- Subjects
WEATHER ,STORMS ,CONVECTIVE clouds ,HUMIDITY ,ATMOSPHERIC transport - Abstract
The depth of convective clouds affects vertical transport of atmospheric constituents, influencing downstream weather and climate. Atmospheric controls on the maximum depth reached by moist convection are investigated with radar‐tracked convective cells tagged with sounding‐derived atmospheric parameters from a field campaign in central Argentina. Regression analyses show that narrow (<12‐km diameter) and wide (>16‐km diameter) cell depths respond to disparate factors, where cell areas are defined using composite reflectivity signatures. Undiluted lifted parcel indices including convective available potential energy (CAPE) and level of neutral buoyancy (LNB) are top predictors of wide cell maximum depth while mid‐tropospheric relative humidity is the top predictor of narrow cell maximum depth. Because narrow cells are more numerous than wide cells, the overall outcome of the full cell population does not strongly correlate with CAPE and LNB conditions. Tracked cells and atmospheric conditions in a simulation with 3‐km grid spacing covering the field campaign produce similar results to those observed. Narrow cells that are relatively deep have a cooler and moister mid‐troposphere with weaker free tropospheric subsidence, while relatively deep wide cells have much warmer and moister lower tropospheric conditions. These atmospheric differences are present 1 hr before cell initiation at both a fixed observing site and variable cell initiation locations. Simulated narrow cell maximum equivalent potential temperature decreases with height at a rate similar to the ambient vertical gradient, causing these cells to fall short of their LNB and supporting the view that entrainment‐driven dilution is a dominant control on their depth. Plain Language Summary: The depth that storms reach impacts where the heat, moisture, momentum, aerosols, and trace gases that they are transporting are deposited, but this depth is difficult to predict because most storms fall short of their theoretically maximum possible depth. The reason for this shortfall is that most storms are narrow, such that they are effectively diminished by mixing with surrounding drier air as the storm deepens. Thus, a dominant control on the depth of these clouds is the humidity of this surrounding air. However, wide storms are less vulnerable to destructive mixing with dry air. As a result, they more consistently reach depths that are well predicted by theory. These conclusions were reached via analysis of over a thousand storms over several months using field experiment measurements and a computer simulation. Key Points: Wide convective cell depth responds most to available instability, while narrow cell depth responds most to midlevel relative humidityEntrainment‐driven reduction of buoyancy decreases as cell width increases, causing disparate narrow and wide cell depth responsesA convection‐permitting simulation with 3‐km horizontal grid spacing generally reproduces observed relationships [ABSTRACT FROM AUTHOR]
- Published
- 2024
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