Greg Blumberg-March 9

Demystifying the 6 o’clock Magic Phenomenon: Observations and Simulations of Water Vapor Changes During Sunset in the Southern Great Plains

Each spring, the U.S. Southern Great Plains (SGP) hosts a wide variety of ingredients (e.g. moisture, shear, instability, and lift) critical to understanding the life-cycle of deep, moist convection.  Tracking the spatiotemporal evolution of these ingredients is critical to understanding the initiation, maintenance, and demise of deep, moist convection.  In the case of the afternoon to evening transition (AET), our current understanding focuses primarily on shear and instability.  While increases in low-level static stability during the AET may act to destroy deep convection, increases in low-level shear (e.g., the nocturnal low-level jet stream) may promote the maintenance of convective updrafts.  Consideration of only these two ingredients presents an incomplete and conflicting conceptual model of how the AET can impact the life-cycle of deep convection.

To improve this conceptual model, a new line of research aims to understand the evolution of water vapor during the SGP AETs.  Recent research has uncovered observations showing rapid increases in surface moisture (1-4 g/kg) that can reverse the loss of conditional instability caused by the setting sun.  In the SGP, these jumps show a dependence on land surface characteristics and are often concentrated near the SGP Winter Wheat Belt.  In this seminar, instruments and simulations of the AET at the Atmospheric Radiation Measurement site in northern Oklahoma are used to expand our understanding of these moisture jumps into the vertical dimension.  This combined observation and modeling strategy aims to clarify the interplay between decaying turbulence and moisture advection on moisture and conditional instability during the AET.  The results from this study lends support to a conceptual model that the AET “opens the floodgates” to enable a more efficient and rapid transport of moisture that may initiate or intensify deep, moist convection.