Identifying the Mechanism of Interaction Between Soil Moisture State and Summertime MCS Initiations in Weakly Forced
Rachel Gaal1, James L Kinter2, Paul A Dirmeyer2
1Department of Atmospheric Science Rosenstiel School of Marine and Atmospheric Science University of Miami Miami FL USA.
Journal of Geophysical Research. Atmospheres : JGR
|December 3, 2024
Summary
Soil moisture patterns influence the development of mesoscale convective systems (MCS). Drier soils to the southwest of initiation points can lead to earlier MCS events by altering atmospheric conditions.
Area of Science:
- Atmospheric Science
- Hydrology
- Meteorology
Background:
- Mesoscale Convective Systems (MCS) are significant weather phenomena, particularly during boreal summer.
- Understanding the factors influencing MCS initiation is crucial for improving weather forecasting.
- Soil moisture (SM) is a key land surface variable that can impact atmospheric processes.
Purpose of the Study:
- To identify the interaction mechanism between soil moisture (SM) state and the occurrence of weakly forced synoptic scale MCS events.
- To investigate how SM heterogeneity influences MCS initiation timing and location.
- To explore the role of near-surface atmospheric variables in SM-driven MCS development.
Main Methods:
- Utilized the Weather Research and Forecasting (WRF) model for sensitivity studies over the US Great Plains.
- Performed simulations with a uniformly dry SM patch (5° × 5°) centered on documented MCS initiation points.
- Conducted storm-centered composite analysis of SM, 2m-temperature, and 2m-humidity for 97 simulated MCS cases (2004-2017).
Main Results:
- A SW-to-NE gradient of drier to wetter SM was observed around simulated MCS initiation sites.
- This SM gradient influenced near-surface fluxes, creating aligned gradients in 2m-temperature and 2m-humidity.
- MCS initiation occurred earlier (∼1-2 hours) in simulations with dry SM perturbations, particularly on the drier side of SM transition zones.
Conclusions:
- Soil moisture heterogeneity, structured as SW-to-NE gradients, can drive MCS initiation in weakly forced synoptic environments.
- The primary mechanism involves SM influencing near-surface fluxes, altering temperature and humidity, and affecting planetary boundary layer growth.
- Alignment of low-level wind fields with organized SM gradients is critical for SM-driven MCS initiation.
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