Mesoscale temperature fluctuations in the stratosphere

[摘要] An airborne instrument that measures altitude temperature profiles isideally suited for the task of characterizing statistical properties of thevertical displacement of isentrope surfaces. Prior measurements oftemperature fluctuations during level flight could not be used to inferisentrope altitude variations because lapse rate information was missing.The Microwave Temperature Profiler instrument, which includes lapse ratemeasurements at flight level as a part of temperature profiles, has beenused on hundreds of flights to produce altitude versus ground trackcross-sections of potential temperature. These cross-sections show isentropealtitude variations with a horizontal resolution of ~3 km for a >6 kmaltitude region. An airborne isentrope-altitude cross-section (IAC) canbe compared with a counterpart IAC generated from synoptic scale data, basedon radiosondes and satellite instruments, in order to assess differencesbetween the altitudes of isentrope surfaces sampled at mesoscale versussynoptic scale. It has been found that the synoptic scale isentropes fail tocapture a significant component of vertical displacement of isentropesurfaces, especially in the vicinity of jet streams. Under the assumptionsthat air parcels flow along isentrope surfaces, and change temperatureadiabatically while undergoing altitude displacements, it is possible tocompute mesoscale temperature fluctuations that are not present in synopticscale back trajectory parcel temperature histories. It has been found thatthe magnitude of the mesoscale component of temperature fluctuations varieswith altitude, season, latitude and underlying topography. A model for thesedependences is presented, which shows, for example, that mesoscaletemperature fluctuations increase with altitude in a systematic way, aregreatest over mountainous terrain, and are greater at polar latitudes duringwinter.

[学科分类] 大气科学