| Autor: |
Kaplan, Michael I., Koch, Steven E., Yuh-Lang Lin, Weglarz, Ronald P., Rozumalski, Robert A. |
| Předmět: |
|
| Zdroj: |
Monthly Weather Review; Jun97, Vol. 125 Issue 6, p1185, 27p |
| Abstrakt: |
Mesoscale model simulations are performed in order to provide insight into the complex role of jet streak adjustments in establishing an environment favorable to the generation of gravity waves on 11--12 July 1981. This wave event was observed in unprecedented detail downstream of the Rocky Mountains in Montana during the Cooperative Convective Precipitation Experiment. The high-resolution model simulations employ a variety of terrain treatments in the absence of the complicating effects of precipitation physics in order to examine the complex interactions between orography and adiabatic geostrophic adjustment processes. Results indicate that prior to gravity wave formation, a four-stage geostrophic adjustment process modified the structure of the mid- to upper-tropospheric jet streak by creating secondary mesoscale jet streaks (jetlets) to the southeast of the polar jet streak in proximity to the gravity wave generation region (WGR). During stage I, a strong rightward-directed ageostrophic flow in the right exit region of the polar jet streak (J1 ) developed over west-central Montana. This thermally indirect transverse secondary circulation resulted from inertial-ad-vective adjustments wherein momentum was transported downstream and to the right of J1 as air parcels de-celerated through the exit region. During stage II, a highly unbalanced jetlet (J2 ) formed just northwest of the WGR in response to the inertial-advective forcing accompanying the ageostrophic circulation associated with J1 . The mass field adjusted to this ageostrophic wind field. An adiabatic cooling and warming dipole resulting from this thermally indirect secondary circulation was the cause for frontogenesis and a rightward shift in the midtropospheric pressure gradients. Since this secondary circulation associated with J2 occurred above a dramatic vertical variation in the thermal wind, the vertical transport of potentially colder air from below was larger ahead of... [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
