HR: 16:15h
AN: A12E-02    [PDF]
TI: Key Issues and Strategies for Measurements in the Tropical, Subtropical and Midlatitude UT/LS
AU: * Dunkerton, T
EM: tim@nwra.com
AF: NorthWest Research Associates, PO Box 3027, Bellevue, WA 98009 United States
AU: Gettelman, A
EM: andrew@ucar.edu
AF: National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 United States
AB: The tropical upper troposphere and lower stratosphere (UT/LS) contain critical questions for atmospheric chemistry and climate. This region also represents the gateway for constituents entering the middle atmosphere, and contains the Tropical Tropopause Layer (TTL). The concept of a tropopause layer, as opposed to level, recognizes that the composition and motion of air in this region are influenced by a combination of tropospheric and stratospheric processes. The TTL extends vertically from the level of maximum convective outflow (200-250 hPa) to the cold point tropopause or, alternatively, to the highest altitude of convective clouds, which sometimes overshoot the tropopause. The TTL extends meridionally to the subtropical jets and tropopause break. During boreal summer, the jet stream and tropopause break are displaced well to the north, near 45$\deg$ N, and the thermodynamic characteristics of tropical air extend into midlatitudes. During boreal winter, equatorial tropopause temperatures attain their lowest values. These seasonal variations are climatological features of the TTL that recur from year to year. Interannual variations are of secondary importance compared to climatology. More important are the enormous spatial variations, due to monsoon circulations, that accompany the seasonal evolution of the UT/LS. In order to understand the role of the UT/LS and TTL in Earth's climate system it is essential to understand the climatological behavior of this region and spatial variations of the climatology. Observational sampling of the UT/LS is currently a priority in the US, Europe and Japan. Measurement strategies require guidance on the nature of the UT/LS and the identification of key unanswered questions. Certain questions are particularly amenable to ground-based observations. Such observations serve a two-fold purpose: (i) direct measurement of the UT/LS, and (ii) validation of satellite data in this critical, but difficult to observe, altitude range. Our talk presents a brief overview of UT/LS climatology, some comments on aspects of the climatology that require further study, and a focus on the extremes of the climatology for the purpose of satellite validation. The implications of UT/LS behavior for validation of EOS satellite datasets are discussed, along with possible strategies to augment the planned or proposed field missions with one or more balloon campaigns in order to extend the spatial coverage of satellite validation.
DE: 0341 Middle atmosphere--constituent transport and chemistry (3334)
DE: 0368 Troposphere--constituent transport and chemistry
DE: 3319 General circulation
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting