Influence of Soil Moisture on Rainfall and Cloud Properties in the Houston Area during TRACER

Interactions between land surfaces and cloud processes are some of the most poorly understood topics in atmospheric science, and they represent a significant challenge for climate modeling. As important contributors to Earth’s atmospheric energy balance, clouds are crucial to understanding and forecasting weather and climate. Accordingly, investigation of environmental factors that influence cloud properties is necessary for advancing the atmospheric sciences. This observational study assesses the influence of soil moisture on cloud cover and surface rainfall in the Houston, Texas region during the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) facility’s recent TRacking Aerosol Convection Interactions ExpeRiment (TRACER). Cloud cover was characterized using retrievals from passive and active sensors at the main ARM Mobile Facility site in La Porte, TX. These were combined with in-situ soil moisture data from the Texas Soil Observation Network, as well as the Stage IV gridded precipitation data set produced by the National Centers for Environmental Prediction, in order to assess the influence of early morning soil moisture on cloud formation and rainfall extent during the subsequent 24 hours.

Initial positive correlations between daily soil moisture and daytime cloud cover, as well as between soil moisture and rainfall, are observed during the TRACER intensive operational period (June to September 2022). A self-organizing maps algorithm is used to classify daily synoptic conditions in southeastern Texas based on 500 hPa geopotential height anomalies in the ERA5 reanalysis data set . When field campaign days are grouped by synoptic classification, days associated with high pressure weather systems exhibit the most robust positive correlations. Additionally, early morning sounding data from the daily TRACER balloon launches were analyzed using the CTP-HIlow framework, which predicts whether a given environment will favor rainfall over wet soil or dry soil. The observed precipitation trends with respect to soil moisture are consistent with this framework. Soil moisture measurements at 5 cm and (especially) 10 cm depths generally exhibit the most significant relationships with cloud cover and precipitation, whereas the trends based on the deeper 20 cm soil moisture measurements are associated with less statistical significance. While this study is limited to the data collected during TRACER, these results justify further study of these relationships through more extensive investigation into soil type, local weather patterns, surface energy fluxes, and other environmental conditions to assist in understanding the physical processes involved. Additionally, comparison with other geographical regions would expose potential biases associated with the Houston region’s unique urban coastal environment.