Retrieval of convective momentum fluxes through satellite-based methods

Research and case studies have shown that convection plays a significant role in large-scale environmental circulations. Despite being studied extensively by in-situ and aircraft measurements, little work has been conducted using satellite measurements until now. Uses of satellite data have the capability to provide continuous analysis across regions void of ground-based remote sensing. Therefore, this study's overall goal is developing a synergistic approach for 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 and Mecikalski 2009, J. Geophys. Res. In press). 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.

This study involves estimating the draft-tilt of convection from TRMM PR radar reflectivity. This technique, developed initially for a 915 MHz profiler (Mecikalski 2003), correlates the first-order signals of updraft tilt and precipitation fall angle relative to Earth with the gross momentum transport character of the radar-observed convection. Vertical motion estimates are made using model climatology results for deep convection as defined by Austin and Houze (1973).

Despite QuikScat's recent failure, QuikScat provided 10 years of data that can be used to show the future use of scatterometer data in convective momentum flux diagnosis. Using BYU's 2 km wind algorithm, a method has been derived to estimate convective momentum fluxes using the divergence (convergence) along the surface along with continuity equation to estimate sub-cloud base downward (upward) vertical motion. These estimates of CMFs can then be combined with TRMM's estimates of CMFs above cloud base.

This project also incorporates the unique dataset provided by the space cloud radar, CloudSat. However, with CloudSat pointing only at nadir, it is limited in its abilities to compute a three-dimensional draft-tilt. Nevertheless, this instrument can provide critical information toward estimating CMFs. Efforts are currently being made to correlate the Ice Water Content and Liquid Water Content (IWC/LWC; from product 2B-CWC-RO) of convective storms to vertical velocities. It is hypothesized that a positive correlation exists between IWC/LWC and vertical velocity (Li 2006). With a positive correlation, vertical velocity estimates can be applied to CloudSat data. These vertical velocity estimates will be included in the TRMM algorithm to create a synergistic approach to estimating convective momentum fluxes.