GRAVITY-WAVES NEAR 300 KM OVER THE POLAR CAPS

Distinctive wave forms in the distributions of vertical velocity and t emperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 bm over the polar caps . These are interpreted as being due to internal gravity waves propaga ting in the neutral atmosphere. The disturbances are characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 lan. They often ex tend across the entire polar cap. The associated temperature perturbat ions indicate that the horizontal phase progression is from the nights ide to the dayside. Vertical displacements are inferred to be of the o rder of 10 bm and the periods to be of the order of 10(3) s. The waves must propagate in the neutral atmosphere, but they usually are most c learly recognizable in the observations of ion vertical velocity and i on temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical compo nent of the neutral velocity, an upward energy flux of the order of 0. 04 erg/cm(2)-s at 250 lan has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. U pward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 lan indicate relatively little attenuation w ith altitude.