The MTP aboard the DC-8 measured vertical movements of two types during this mission: 1) mountain wave uplift, causing the tropopause to be displaced upward where lenticular clouds form, and 2) non-orographic generated thickening and thinning of a shallow layer immediately above the tropopause. The tropopause and isentrope surface uplift is the more dramatic of the two, especially considering that the tropopause above lenticular clouds was observed to fall 600 feet before rising to 2000 feet above the undisturbed level near the lenticular cloud, and finally fall to 600 feet below the undisturbed altitude on the downwind side before returning to the normal altitude.
Cooling rates of 10,000 K/day were measured. we believe these are the
first mesoscale measurements of the two-dimensional topography of the tropopause!
Isentrope surface cross-sections verify that the tropopause displacements
are correlated with isentrope displacements, which is an expected result.
However, if lenticulars are formed from air that has first been heated,
as the present measurements indicate, then it is natural to ask if this
pre-heating in any way pre-conditions the aerosols to favor only a few
for subsequent condensation, thus accounting for the significant number
of large particles found in lenticulars. Possibly of greater significance,
we believe, are the measurements of a subtle oscillation of the thickness
of a layer of stratospheric air bordering the tropopause. During a 40-minute
period of flight in air that was remote from convective storm systems,
isentrope surfaces within a 1-km thick region immediately above the tropopause
were observed to separate and come together quasi-periodically for two
cycles. The associated adiabatic heating and cooling caused the "temperature
field tropopause" to briefly jump into the stratosphere, to the top of
the dynamic layer. Meanwhile, the main tropopause moved upward and downward,
crossing isentropic surfaces in phase with the overlying layer's changes.
Such behavior might possibly lead to the exchange of air between the stratosphere
and troposphere, and warrants further study in the context of understanding
mechanisms for the redistribution of aircraft exhaust throughout the atmosphere.