Horizontal wavenumber spectra of winds, temperature, and trace
gases during the Pacific Exploratory Missions: 2. Gravity waves,
quasi-two-dimensional turbulence, and vortical modes
We examine the horizontal wavenumber spectra of horizontal velocity
and potential temperature collected by aircraft above the Pacific
Ocean to determine whether gravity waves, quasi-two-dimensional (Q2D)
turbulence, or vortical modes dominate atmospheric fluctuations at
scale sizes of 1-100 km and altitudes of 2-12 km. We conclude from
the study of Doppler-shifting effects that Q2D turbulence and/or
vortical modes are more prevalent than gravity waves over the ocean,
except in the equatorial zone. The results are consistent with recent
numerical simulations of Q2D turbulence that show the characteristic
inverse cascade of energy greatly facilitated by the presence of
background rotation. Furthermore, a Stokes-parameter analysis reveals
the general paucity of coherent wavelike motions, although specific
cases of gravity-wave propagation are observed. Finally, a case study
of a long flight segment displays a k-3 horizontal
velocity variance spectrum at scales longer than about 100 km.
Doppler-shift and Stokes-parameter analyses reveal that these
large-scale fluctuations are due to vortical modes rather than
inertio-gravity waves.
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