A wave packet analysis method for vertical energy flux measured by VHF radar

A wave packet analysis method, which can be used to analyze the data taken by VHF radars in the study of the energy transport by gravity waves in the vertical direction, is presented. It consists of two parts. The first is to analyze the height profiles of the horizontal atmospheric motion, in order to obtain the vertical phase and group velocities of the atmospheric gravity wave motion by the technique of phase and group velocity tracing. The second is to separately calculate the height profiles of the time average of the energy densities and vertical group velocities for the phase-upward waves and phase-downward waves. Then the height profiles of the mean energy flux can be obtained by multiplying the energy density with the group velocity. As an example we present here the application of this method to the data taken by the SOUSY-Svalbard Radar. In the event shown here, most of the wave packets (about three quarters) in the Range-Time-Intensity (RTI) plots of velocity show that the vertical phase and group velocities are in the opposite direction (Type 1 wave packets). The rest (about one quarter) are shorter lasting wave packets showing that the vertical phase and group velocities are in the same direction (Type 2 wave packets). The horizontal wind data during this selected period shows strong wind peaking below the tropopause and a large vertical shear just below and above this height. This jet-like wind field reversed its direction around this time period, and the energy flux calculation indicates that such a direction reversal might have triggered a large gravity wave transporting energy upward.