Hopper, Jr., Larry John (2008-05). Effects of baroclinicity on storm divergence and stratiform rain in a precipitating subtropical region. Master's Thesis. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • May 2008