A Multi-Sensor Satellite-Based Approach to Retrieving Convective Momentum Fluxes

Research and case studies have shown that convection plays a large 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 goal is to develop a synergistic approach to retrieving CMFs using a collection of instruments including GOES, TRMM, CloudSat, MODIS, and QuikScat.

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. Calculating draft-tilts will enable for estimates of u' and v', as seen in 915 MHz profiler data by Mecikalski (2004). CloudSat is an important instrument to consider, being similar to the 915 MHz profiler, only space based. However, with CloudSat being in space, only pointing at nadir, it is limited in its abilities to compute a three-dimensional draft-tilt, albeit this instrument provides critical information toward estimating CMFs.. Therefore, we will take an integrated approach using several instruments together, including TRMM PR (as noted above) and MODIS cloud properties (such as optical thickness, effective radius, and liquid water path). Results from these data will then be correlated to CloudSat radar reflectivities to compose CMF profiles over varying convective regimes. As a beginning, research will focus 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. Cloud-resolving modeling will also be used.

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). Further work will also include refining the study using TRMM (Mecikalski 2004) and evaluating QuikScat data to determine fluxes occurring below cloud base.