Experimental investigation of the dynamics near the winter northern polar mesopause.

Abstract

An investigation of the dynamics near the winter northern polar mesopause has been carried out at the Early Polar Cap Observatory at Resolute Bay, Canada (74.9&deg;N, 94.9&deg;W). Tidal and planetary wave characteristics were studied using experimental and theoretical tools. The daily, monthly, and annual variations of the tidal field were studied using the 1995/1996 and 1996/1997 data. Ground-based measurements were obtained using a Fabry-Perot Interferometer with a Circle-to-Line Interferometric Optical system (FPI/CLIO) and an E-Region Wind Interferometer (ERWIN). The FPI/CLIO observed the Doppler winds of the OH emission near 86 km. The ERWIN provided simultaneous OH (86 km) and O<super>1</super>S (97 km) wind measurements. Monthly data were compared to the Global Scale Wave Model (GSWM) and the Forbes/Vial Solar Semidiurnal Tidal Model predictions. Additionally, a Global Empirical Vector Spherical Harmonics (VSH) Model was used to investigate the seasonal upper mesosphere and lower thermosphere tides. Classical tidal theory predicts that the winter polar region is relatively undisturbed by tides---oscillations of integral sub-harmonics of one day. Contrary to this theory, the semidiurnal (12 h) oscillation has been detected at Resolute. Analysis of this oscillation at 86 and 97 km, indicates that it is persistent and characteristic of a semidiurnal propagating tide. The research presented constitutes the first long-term study (&sim;3 months of data over 2 years) of the dynamical structure of the winter northern polar mesopause using optical instruments. Significant and new contributions include that the semidiurnal tide has been found to be highly variable in amplitude and phase from day to day. Planetary waves with periods near 5, 8, and 16 d are shown to modulate the semidiurnal amplitudes and background winds. In addition, non-linear interactions between planetary waves and the semidiurnal tide are detected near the polar mesopause. Spectral analysis reveal a variety of waves---tidal waves, planetary waves, and secondary waves as a result of non-linear wave interactions---which are geophysical and not attributed to spectral leakage.