Observing and Understanding the Variability of Water in Weather and Climate


Mesoscale variability in CBL structure observed during IHOP: causes and implications for convective initiation

Kenneth J. Davis, Penn State Univ., University Park, PA; and K. J. Craig, A. R. Desai, S. Kang, N. L. Seaman, D. R. Stauffer, B. P. Reen, and S. J. Richardson

The International H2O Project (IHOP) was conducted during May and June of 2002 encompassing a large region (~ 300km x 400km) within the southern Great Plains. Extensive observations of the structure of the convective atmospheric boundary layer (CBL) and forcing boundary conditions, particularly surface fluxes, were collected. Of particular interest are data needed to produce areal maps of the surface energy balance over the region as well as direct observations of regional CBL depth and water vapor content obtained via airborne water vapor differential absorption lidar (DIAL). These data were collected on ~10 days spanning several frontal passages. Ground-based CBL remote sensors added point data that were continuous in time, complementing the airborne observations. The observations document the interactions between the CBL and the land surface from micro- to meso-scales. These interactions may lead to favored locations for convective initiation.

Ongoing analyses will lead to a database of surface flux fields and CBL characteristics that will enable quantitative and rigorous tests of surface-CBL coupling, and provide validation for high resolution numerical simulations with MM5. These databases, which will be made available to the IHOP and broader atmospheric sciences community, will be described.

The cases captured by IHOP observations, as well as preliminary results and hypotheses will be reviewed. Phenomena that are captured include highly heterogeneous land surface forcing at a variety of scales, and varying response by the CBL, wave structures, and detailed characterization of the CBL entrainment zone. At the largest scales, CBL depths and moisture content varied by as much as a factor of two, but in other cases strong potential temperature inversions limited the heterogeneity in CBL depth. Many cases showed evidence of widespread wave structure within and above the CBL. These waves may be a significant source of CBL modulation that is independent of heterogeneous land surface forcing. Cases where surface flux heterogeneity led to favored locations for convective initiation were not immediately apparent, but the pre-conditioning of the CBL was clearly heavily dependent on the surface energy budget.

Session 1, International H2O Project (IHOP)
Monday, 10 February 2003, 10:45 AM-2:30 PM

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