Diurnal atmospheric oscillation: 1. Eigenvalues and Hough functions

The diurnal oscillation in the earth's atmosphere is investigated, and allowed modes of that oscillation are determined. Some of these modes are analogous to the oscillation of an ocean with negative depths. However, these oscillations should be allowed not in the ocean but in the atmosphere, because we find no specific reason to discard them. We find a good resemblance of the pressure variation of the first negative mode to that deduced from the geomagnetic Sq variations. In Part 2 we shall discuss the vertical structure of this negative mode under thermal excitation in the upper atmosphere and find conspicuous differences from positive mode.