89th American Meteorological Society Annual Meeting

Monday, 12 January 2009
Preliminary Results for the Retrieval of Convective Momentum Fluxes Using TRMM and CloudSat
Hall 5 (Phoenix Convention Center)
Christopher P. Jewett, Univ. of Alabama, Huntsville, AL; and J. R. Mecikalski
Research and case studies have shown that convection plays a significant role in large-scale environmental circulations. Convective momentum fluxes (CMFs) have been studied for many years using in-situ and aircraft measurements, along with numerical simulations. However, despite these successes, little work has been conducted on methods that use satellite remote sensing as a tool to diagnose these fluxes. Uses of satellite data have the capability to provide continuous analysis across regions void of ground-based remote sensing. Therefore, the project's overall goal is to develop a synergistic approach for retrieving CMFs using a collection of instruments including GOES, TRMM, CloudSat, MODIS, and QuikScat. However, this particular study will focus on the work using TRMM and CloudSat.

Sound research has already been conducted for computing CMFs using the GOES instruments (Jewett 2007). Using satellite-derived winds, namely mesoscale atmospheric motion vectors (MAMVs) as described by Bedka and Mecikalski (2005), one can obtain the actual winds occurring within a convective environment as perturbed by convection. Surface outflow boundaries and upper-tropospheric anvil outflow will produce “perturbation” winds on smaller, convective scales. Combined with estimated vertical motion retrieved using geostationary infrared imagery, CMFs were estimated using MAMVs, with an average profile being calculated across a convective regime or a domain covered by active storms.

Current work involves estimating draft-tilt from CloudSat and TRMM PR radar reflectivity. Computing draft-tilts enables for estimates of u' and v', as seen in 915 MHz profiler data by Mecikalski (2004). However, with CloudSat located in space and pointing only at nadir, it is limited in its abilities to compute a three-dimensional draft-tilt. However, this instrument can provide critical information toward estimating CMFs. Determining storm motion from a cloud-resolving model could supply the needed information to compute the updraft tilt. In the beginning, research will primarily be focused on the Huntsville area where substantial ground-based instrumentation (dual-polarimetric radar, WSR-88D, X-band radar, 915 MHZ profiler) already exist towards validating and developing a satellite-based methodology of estimating CMFs. The preliminary case involves the squall line associated with the 5-6 February 2008 severe weather outbreak as both TRMM and CloudSat passed over the convective line within hours of each other.

Other work involves determining several ways to improve our estimates of perturbation vertical velocities (w'). Level 2 products of CloudSat provide droplet size profiles and number concentrations of hydrometeors. Therefore, it would be reasonable that a determination of the mass condensate could be made, which can be related to vertical mass transport similar to the algorithm used in TRMM (i.e. in which w' was estimated via a measure of updraft strength and drop size). Also, with the mass condensate and entrainment rates known, it is possible then to estimate vertical motion within the cloud (Austin and Houze 1973).

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