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Soil moisture-precipitation feedbacks: interactions between MCS and non-MCS rainfall through the soil moisture pathway

Presentation Date
Monday, December 14, 2020 at 4:04pm



Land-atmosphere interactions play an important role in summer-time rainfall in the central US where mesoscale convective systems (MCSs) contribute to 30-70% of warm season precipitation. Here, using a unique combination of observed rainfall associated with MCS and non-MCS events in July and land surface simulations with numerical tracers to quantify soil moisture sourced from earlier-season MCS and non-MCS rainfall, we investigate the soil moisture-precipitation feedbacks, with a focus on the role of MCS and non-MCS rainfall events and their interactions through the soil moisture pathway. Characterized by higher intensity and larger area per storm, MCS rainfall can produce coherent spatial heterogeneity in soil moisture important for initiating afternoon rainfall dominated by non-MCS convection. Such soil moisture heterogeneity induced by MCS rainfall features a dry soil advantage or negative soil moisture-precipitation feedback. On the other hand, soil moisture sourced from both MCS and non-MCS rainfall contributes to lower level atmospheric moistening, providing favorable conditions for upscale growth of MCSs at night. Hence both precedent MCS and non-MCS rainfall play a role in the positive feedback between soil moisture and MCS rainfall. However, soil moisture from non-MCS rainfall contributes to subsequent MCS rainfall with shorter lead time, partly because with moderate intensity, non-MCS rainfall has shallower infiltration and thus faster turnover in the soil. In contrast, higher intensity MCS rainfall can percolate into the deeper soil and induce longer-term impact on subsequent MCS rainfall. These contrasting dynamics of soil moisture-precipitation feedback associated with MCS and non-MCS rainfall have important implications for predictability of summer rainfall in regions where MCSs contribute significantly to warm season rainfall.

Funding Program Area(s)