GRAVITY-WAVE AND EQUATORIAL WAVE MORPHOLOGY OF THE STRATOSPHERE DERIVED FROM LONG-TERM ROCKET SOUNDINGS

Fluctuations in vertical profiles of atmospheric temperature and horiz ontal wind in the 20-60 km altitude range have been isolated from mete orological rocket measurements during 1977-87 at 15 widely separated s ites. The seasonal, geographical, and vertical variability of the vari ance of horizontal velocities, u'(2) + v'(2), and relative-temperature perturbations, T'(2), were studied. The bulk of the variance of both quantities in the 2-10 km and 2-20 km vertical-wavelength bands was a ssociated with gravity-wave motions, although in-depth study of the wa ve polarization shows that planetary-scale equatorial wave modes contr ibute to the variance at equatorial sites. Annual mean variances varie d widely among the 15 stations, suggesting appreciable geographical va riability in stratospheric wave activity. Whereas u'(2) + v'(2) values generally increased significantly with altitude throughout the strato sphere, T'(2) values grew less substantially and often decreased with altitude at upper heights. Rotations of wave-velocity phasors with he ight were always more frequently clockwise than anticlockwise in the n orthern hemisphere, consistent with upward-propagating wave energy, ye t these percentages (>50%) showed a marked semi-annual variation, with equinoctial maxima and minima at the solstices. At high latitudes (si milar to 50 degrees N-80 degrees N) variances exhibited a strong annua l variation, with the minimum in summer and a strong peak during winte r at both lower (20-40 km) and upper (40-60 km) heights. The annual va riance cycle attenuated somewhat at mid-latitudes (similar to 25 degre es N-40 degrees N), and a strong peak in August dominated the u'(2) v'(2) variations at 40-60 km. The peak was also evident in T'(2), but was smaller relative to the winter peak. At low latitudes (similar to 15 degrees N-25 degrees N) the wave morphology was broadly similar to that at mid-latitudes, apart from an additional upper-level peak in t he variance in May. This peak in May occurred in some years but not in others at mid-latitude stations. At the equatorial stations (similar to 10 degrees N-10 degrees S) the low-level variance showed little sys tematic seasonal variability, but exhibited clear modulation over a qu asi-two-year period. Much of this variance was consistent with the Kel vin modes thought to drive the eastward phase of the stratospheric qua sibiennial oscillation (QBO). However, the uniform east-west alignment of waves was inconsistent with the expected polarization of the mixed Rossby-gravity wave mode which is believed to drive the westward phas e bf the QBO. At 40-60 km, the variance was strongly attenuated around April-May and November, when both u'(2) + v'(2) and T'(2) decreased with height around the 40-45 km range, indicating that wave dissipatio n occurs here. This produced a semi-annual variation at upper heights, with maxima around January and July, which may contribute significant ly to the semi-annual wave driving of the equatorial upper stratospher e. Polarization studies showed that this variance in the 2-10 km band was mostly due to gravity waves, although equatorial modes contributed during December-February.