A study of the development of extratropical cyclones with an analytic model. Part II: Sensitivity to tropospheric structure and analysis of height tendency dynamics
Hirschberg, Paul A.
Fritsch, J. Michael
MetadataShow full item record
An analytic quasigeostrophic model is used to examine the sensitivity of type B cyclogenesis to the vertical structure of the troposphere given a particular stratospheric temperature configuration. It is found that there is an optimal tropospheric configuration that produces the largest negative height tendency at the center of the 1000-mb model cyclone. Based on the response of the 1000-mb height tendencies, altering the baroclinicity in the model planetary boundary layer (PBL) does not significantly affect the instantaneous quasigeostrophic dynamics of the deep atmosphere. Rather, the PBL temperature anomalies affect the development of lowertropospheric model lows by hydrostatically shifting or steering the cyclone centers to locations beneath more (or less) favorable deep atmospheric quasigeostrophic conditions for development. Diagnostic analyses of three individual stratospheric-tropospheric model configurations are also performed to examine the dynamics that drive the height (pressure) tendency field. Generally, the analytic model findings confirm previous observational and numerical investigations of height tendency mechanisms and support the notion of a stratospheric level of insignificant dynamics. In the optimal development case, the 1000-mb low is located almost directly underneath the region of strongest 200-mb temperature advection associated with a tropopause undulation (potential vorticity anomaly). This strong lower-stratospheric warm advection instantaneously overwhelms adiabatic cooling in the stratosphere and troposphere so that there are height falls over and downstream of the 1000-mb low. When the static stability is lowered in the troposphere and raised in the stratosphere to realistic "warm-sector" values, the vertical motion increases, and the local warming in the stratosphere and cooling in the troposphere decrease. The reduced tropospheric cooling results in larger net local column warming that intensifies the 1000-mb height falls. The intensified vertical circulation also acts to amplify the tropopause undulation. As the amplitude of the undulation increases, characteristics of the occlusion process can be identified.
Showing items related by title, author, creator and subject.
Danard, Maurice B. (1969-01);A simple method of compqting longwave radiative cooling in the troposphere associated with water vapor is described. The procedure may readily be incorporated into a tropospheric numerical prediction model. Radiation from ...
Danard, Maurice B. (Monterey, California. Naval Postgraduate School, 1968-01); NPS-51DD8011AA simple method of computing long-wave radiative cooling in the troposphere associated with water vapor is described. Radiation from ozone and carbon dioxide is not considered. However, Influences of arbitrary vertical ...
Twigg, Katherine L. (Monterey, California. Naval Postgraduate School, 2007-09);Surface electromagnetic propagation over the ocean is highly sensitive to near-surface atmospheric variability, particularly the height of the evaporation duct. Seasonal variation in near-surface meterological factors and ...