Divergence structures associated with the spectrum of precipitating systems in
the subtropics and midlatitudes are not well documented. A mesoscale model (MM5) is
employed to quantify the relative importance different baroclinic environments have on
divergence profiles for common storm types in southeast Texas, a subtropical region.
Divergence profiles averaged over a 100 x 100 nested grid with 3-km grid spacing are
calculated from the model-derived wind fields for each storm. The divergence profiles
simulated for selected storms are consistent with those calculated from an S-band radar
using the velocity-azimuth display (VAD) technique.
Divergence profiles from well-modeled storms vary in magnitude and structure
across the spectrum of baroclinicities and storm types common in southeast Texas.
Barotropic storms more characteristic of the Tropics generate the most elevated
divergence (and thus diabatic heating) structures with the largest magnitudes. As the
degree of baroclinicity increases, stratiform area fractions increase while the levels of
non-divergence (LNDs) decrease. However, some weakly baroclinic storms contain
stratiform area fractions and divergence profiles with magnitudes and LNDs that are similar to barotropic storms, despite having lower tropopause heights and less deep
convection. Additional convection forms after the passage of some of the modeled
barotropic and weakly baroclinic storms that contain elevated divergence signatures,
circumstantially suggesting that heating at upper-levels may cause diabatic feedbacks
that help drive regions of persistent convection in the subtropics.
Applying a two-dimensional stratiform-convective separation algorithm to MM5
reflectivity data generates realistic stratiform and convective divergence signals.
Stratiform regions in barotropic storms contain thicker, more elevated mid-level
convergence structures with larger magnitudes than strongly baroclinic storms, while
weakly baroclinic storms have LNDs that fall somewhere in between with magnitudes
similar to barotropic storms. Divergence profiles within convective regions typically
become more elevated as baroclinicity decreases, although variations in magnitude are
less coherent. These simulations suggest that MM5 adequately captures mass field
perturbations within convective and stratiform regions, the latter of which produces
diabatic feedbacks capable of generating additional convection. As a result, future
research determining the climatological dynamic response caused by divergence profiles
in MM5 may be feasible.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3277 |
| Date | 15 May 2009 |
| Creators | Hopper, Jr., Larry John |
| Contributors | Schumacher, Courtney |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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