Studies of relative contributions of internal gravity waves and 2-D turbulence to tropospheric and lower-stratospheric temporal wind spectra measured by a network of VHF windprofiler radars using a decade-long data set in Canada

Tropospheric and lower-stratospheric motions at mesoscales and larger are a mixture of waves and two-dimensional (2-D) turbulence. Determining their relative importance is necessary, since waves are capable of coordinated systematic momentum transport accompanying the wave propagation, and associated wind forcing, in ways that 2-D turbulence is not. This can impact weather forecasting. Using a network of ten windprofiler radars in eastern Ontario and western Quebec in Canada, plus an additional one in the Arctic, the relative roles of internal gravity (buoyancy) waves and two-dimensional turbulence are examined at temporal scales from about 3-4 hrs to several tens of hours (horizontal spatial scales of typically one or two hundred kilometres to a few thousand kilometres), with the purpose of investigating the respective roles of these two distinct characteristic fluid motions as functions of location, season and year. The emphasis is on studies of spectral slope variability, rather than absolute spectral magnitudes, giving a perspective not previously substantially presented. In particular, we have found a frequency band in which gravity-wave Doppler shifting produces distinctly different spectral slopes than those predicted for 2-D turbulence, and these differences are employed to distinguish the flow fields. The network used (excluding the Arctic site) covers an area of similar to 10(6) km(2) and includes a variety of different terrains. Radial velocities have been recorded on time scales of minutes for data lengths covering durations of up to 12 years. Altitude coverage is from 1 km to typically 14 km, at 500 m resolution. Results suggest a region from similar to 2 to similar to 5 km altitude (deeper for some radars) where waves are weaker and 2-D turbulence appears to be generally more significant, but where occasional bursts of gravity-wave activity can occur, while above typically 6-8 km, gravity waves increase in significance. There are distinct site-to-site variations.