Diurnal Tidal Motions between 30 and 60 Kilometers in Summer

Abstract

Routine wind observations for nine Meteorological Rocket Network stations located between 88 and 64N are examined for evidence of diurnal tidal motions. Only the behavior of the meridional component in summer is considered. The amplitude of this component is found to be small (about 1 m sec?1) below 40 km, to increase rapidly near 45 km, and to achieve a maximum value of 5?8 m sec?1 or somewhat above, 50 km. Between 55 and 60 km the amplitude diminishes slightly, while higher up it appears, from the meager data available, that a further increase takes place. At the Northern Hemisphere stations the maximum south wind occurs at about noon near 50 km and two or three hours later several kilometers below. There is evidence of a pronounced semidiurnal oscillation above 55 km at Ascension Island (8S). A global model of the diurnal tidal motions, based in part on observation and in part on theory, is presented. The proposed instantaneous motions are tangential to great circle arcs which connect the point on the equator, where it is local noon, to its conjugate point, The vertical motion is upward in the vicinity of the former point, giving adiabatic cooling around noon. Subsidence and adiabatic warming occur about the conjugate point on the dark side of the earth.