Longitudinal modulation of the O/N_2 column density retrieved from TIMED/GUVI measurement

【摘要】：正[1]The longitudinal variation of thermospheric O/N_2 column density ratio is studied,based on the TIMED/GUVI measurements collected during 2002-2007.In October,a four-peaked longitudinal fluctuation in O/N_2 is found.The wavenumber-4 fluctuation in equatorial O/N_2 is generally stronger at lower solar activity,and maximizes in the morning of boreal summer and autumn.In boreal winter,the wavenumber-4 component gives way to the wavenumber-3. Such seasonal variation and solar activity dependence are consistent with those of the diurnal eastward-propagating mode with wavenumber-3,but the local time dependence is not.The daytime wavenumber-4 pattern in O/N_2 does not shift eastward in local time as expected if it is directly connected to the DE3.No definite explanation is found for this structure,but a consideration of various mechanisms suggests that the vertical wind effect may be the most potential candidate.