| Falling sphere and balloon wind and temperature data from the MaCWAVE winter
campaign, which was conducted in northern Scandinavia during January 2003,
are analyzed to investigate gravity wave characteristics in the stratosphere
and mesosphere. There were two stratospheric warming events occurring during
the campaign, one having a maximum temperature perturbation at ~45 km
during 17–19 January, and the other having a maximum perturbation at ~30 km
during 24–27 January. The former was a major event, whereas the latter
was a minor one. Both warmings were accompanied by upper mesospheric
coolings, and during the second warming, the upper mesospheric cooling
propagated downward. Falling sphere data from the two salvos on 24–25 January
and 28 January were analyzed for gravity wave characteristics. Gravity wave
perturbations maximized at ~45–50 km, with a secondary maximum at
~60 km during Salvo 1; for Salvo 2, wave activity was most pronounced
at ~60 km and above.
Gravity wave horizontal propagation directions are estimated using the
conventional hodographic analysis combined with the S-transform (a Gaussian
wavelet analysis method). The results are compared with those from a Stokes
analysis. They agree in general, though the former appears to provide better
estimates for some cases, likely due to the capability of the S-transform to
obtain robust estimates of wave amplitudes and phase differences between
different fields.
For Salvo 1 at ~60 km and above, gravity waves propagated towards the
southeast, whereas for Salvo 2 at similar altitudes, waves propagated
predominantly towards the northwest or west. These waves were found not to be
topographic waves. Gravity wave motions at ~45–50 km in Salvo 1 were
more complicated, but they generally had large amplitudes, short vertical
scales, and their hodographs revealed a northwest-southeast orientation. In
addition, the ratios between wave amplitudes and intrinsic phase speeds
generally displayed a marked peak at ~45–50 km and decreased sharply at
~50 km, where the background winds were very weak. These results
suggest that these wave motions were most likely topographic waves
approaching their critical levels. Waves were more nearly isotropic in the
lower stratosphere. |