Horizontal wavenumber spectra of winds, temperature, and trace gases during the Pacific Exploratory Missions: 2. Gravity waves, quasi-two-dimensionalturbulence, and vortical modes

We examine the horizontal wavenumber spectra of horizontal velocity and pot ential temperature collected by aircraft above the Pacific Ocean to determi ne whether gravity waves, quasi-two-dimensional (Q-2-D) turbulence, or vort ical 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 effec ts that Q-2-D turbulence and/or vortical modes are more prevalent than grav ity waves over the ocean, except. in the equatorial zone. The results are c onsistent with recent numerical simulations of Q-2-D turbulence, which show that the characteristic inverse cascade of energy is greatly facilitated b y the presence of background rotation. Furthermore, a Stokes-parameter anal ysis reveals the general paucity of coherent wavelike motions, although spe cific cases of gravity-wave propagation are observed. Finally, a case study of a long flight segment displays a k(-3) horizontal velocity variance spe ctrum at scales longer than about 100 km. A Stokes-parameter analysis indic ates that these large-scale fluctuations were likely due to vortical modes rather than inertio-gravity waves.