The vertical structure and source regions of large and small scale waves in the middle atmosphere

Abstract

Atmospheric waves are periodic oscillations of the atmospheric variables such as density and temperature, which can have spatial sizes from a few kilometer to thousands of kilometers, and temporal variations from days to minutes. Given the role of atmospheric waves in determining global circulation and thermal balance of the middle atmosphere, the origin, structure, propagation and dissipation of these waves have been a subject of active international research in the past few years.

The primary objective of this study is to investigate the vertical phase structure of atmospheric waves of various scales in the middle atmosphere (30‐90 km) so as to identify their source regions and where they deposit their energy and momentum.

The study used four different datasets of high temporal resolution ozone mixing ratio obtained ground‐based microwave radiometer, nightly averaged mesospheric temperature derived from the hydroxyl nightglow, polar mesospheric summer echoes (PMSE) extracted from Super Dual Auroral Radar (SuperDARN) and a high resolution noctilucent cloud (NLC) images from digital camera in Trondheim. Output from Gravity Wave Regional or Global Ray Tracer (GROGRAT) is also used in an attempt to identify the characteristics and source regions of gravity waves. Many methods of data processing are involved in this study, such as a digital filtering, fast Fourier transform (FFT), cross‐spectral analysis, image projection and analysis.

The results of the investigations show that wave motions observed near the mesopause region have their origin in the lower atmosphere. The 16‐day oscillation is found to have vertical phase fronts consistent with a normal‐mode structure, but undergoes a large phase shift and diminished amplitude around 55km, where it deposits some of its energy. The 5‐and 6.5‐days planetary waves, which have similar zonal structure but different vertical phase structure, are responsible for the modulation of the PMSE ocurrence frequency. Similarily, the short period gravity waves propagating from the tropopause are more likely to be the sources of the prominent wave structures observed in the NLC.