*Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, MD
*Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD
Diurnal cycles of summertime rainfall rates are re-examined over the conterminous United States, using 1/8degree NLDAS radar-gauge assimilated hourly rainfall data [Matsui et al. 2010]. As in earlier studies, the 10-year climatology of rainfall diurnal composites shows a well-defined region of rainfall propagation over the Great Plains and an afternoon maximum area over the south and eastern portion of the United States. Using Hovmöller diagrams, zonal phase speeds of diurnal composite rainfall are estimated in three different small domains over Great Plains and Maryland, and are evaluated with background meteorological conditions such as background wind profiles and thermodynamics profiles using the MERRA data. Results qualitatively indicate that the latent heat release (as a function of CAPE) together with background steering wind speed are a more robust theory that explains the unique rainfall propagation speeds in the three different geographic domains, rather than the effect of boundary-layer gust front disturbance (as a function of boundary-layer dryness).
For more detailed study in the propagating Mesoscale Convective System, a high-resolution regional cloud-resolving model, NASA-Unified Weather Research and Forecasting (NU-WRF) model, has been applied over the Southern Great Plains during the Midlatitude Continental Convective Clouds Experiment (MC3E) in 2011. When all forecast days are composited, the mean forecast depicts accurate, propagating precipitation features and thus the overall diurnal variation. The sensitivity study suggests the importance of cold-pool dynamics and height of terrain, while surface turbulent flux has secondary impact [Tao et al. 2013]. This suggests the severe limitation of representing soil moisture feedback using coarse-resolution climate models.
Matsui, T., D. Mocko, M.-I. Lee, W.-K. Tao, M. J. Suarez, and R.A. Pielke Sr. (2010), Ten-year climatology of summertime diurnal rainfall rate over the conterminous U.S., Geophysical Research Letters, 37, L13807, doi:10.1029/2010GL044139.
Tao W.-K., D. Wu, T. Matsui, C. Peters-Lidard, S. Lang, A. Hou, and M. Rienecker, 2012: The Diurnal Variation of Precipitation during MC3E: A Numerical Modeling Study, Journal of Geophysical Research (revised).
Dr. Toshi Matsui received his Ph.D in Atmospheric Science at Colorado State University in 2007. After graduating, he joined the NASA GSFC, Mesoscale Lab. His primary work is development and application of multi-satellite simulators to support various satellite missions and mesoscale model development at GSFC. Dr. Matsui’s scientific research ranges from modeling and analysis of land-surface interaction, aersosol-cloud-precipitation processes using the high-resolution mesoscale models, satellite / in-situ measurement, and satellite simulator. He is currently Co-PI of the NASA-Unified WRF Project and Head of the NASA GSFC AeroCenter Committee.