Semidiurnal Hough Mode Extensions in the Thermosphere and Their Application

Semidiurnal tidal modes propagate vertically without change of meridional structure in the lower atmosphere. However, in the thermosphere where viscosity, ion drag, and other processes assume importance, individual tidal modes, propagating into the thermosphere from below, begin to change meridional structure as they propagate vertically. In addition, the modes are subject to attenuation. The extent of meridional alteration and vertical attenuation depends on the mean thermal structure of the thermosphere and the degree of ionization, both of which vary during the solar cycle. This note gives the results of numerical calculations of the explicit behaviour of the 2,2, 2,3, 2, 4, and 2,5 Hough modes within the thermosphere under conditions typical of sunspot maximum and minimum. In addition we present a numerical description of semidiurnal tides excited within the thermosphere. For the convenience of the reader a copy of a paper by Hong and Lindzen giving details of the numerical program is included. The present report can be considered an extensive addendum to this paper.