1.3 Mesoscale Convective Systems and Their Large-Scale Environment in a Hierarchy of Model Simulations (Invited Presentation)

Monday, 8 January 2018: 9:45 AM
Room 4ABC (ACC) (Austin, Texas)
L. Ruby Leung, PNNL, Richland, WA; and R. A. Houze Jr., Z. Feng, K. Sakaguchi, and Q. Yang

Mesoscale convective systems (MCSs) are important precipitation producers that account for 30-70% of warm season rainfall between the Rocky Mountains and Mississippi River and some 50-60% of tropical rainfall. Besides the tendency to produce floods, MCSs also carry with them a variety of attendant severe weather phenomena. Our analysis found that observed increases in springtime total and extreme rainfall in the central United States in the past 35 years are dominated by increased frequency and intensity of long-lasting MCSs. Understanding the environmental conditions producing long-lived MCSs is therefore a priority in determining how heavy precipitation events might change in character and location in a changing climate. MCSs and their large-scale environment from convection-permitting regional and global variable resolution seasonal simulations and global low- and high-resolution climate simulations are being compared and evaluated by applying novel MCS tracking methods to the observations and model simulations. The convection-permitting simulations generally reproduce realistic structure and frequency distribution of lifetime and event mean precipitation of MCSs over the central United States. The simulations show that MCSs systematically form over the central Great Plains ahead of a trough in the westerlies in combination with an enhanced low-level moist jet from the Gulf of Mexico. These environmental properties at the time of storm initiation are most prominent for the MCSs that persist for the longest times. MCSs reaching lifetimes of 9 h or more occur closer to the approaching trough than shorter-lived MCSs. These long-lived MCSs exhibit the strongest feedback to the environment through diabatic heating in the trailing regions of the MCSs that helps to maintain them over a long period of time. The identified large-scale and mesoscale ingredients provide a framework for understanding and modeling the potential changes in MCSs and associated hydrometeorological extremes in the future.
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