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Thermospheric composition variations due to nonmigrating tides and their effect on ionosphere

The TIMED/GUVI thermospheric composition (O/N2 ratio) over 2009 reveals clear wave‐3 (summer season) and wave‐4 (Fall season) longitudinal dependence. The wave peak to valley varies from 7 to 11% of the background O/N2. The low Kp (yearly mean of 0.9) and low solar EUV flux indicates that the wave features were not caused by geomagnetic activity or solar EUV variation. A more likely explanation is nonmigrating diurnal eastward propagating DE2 and DE3 tides. Model calculations indicate that a 10% variation in O/N2 makes 1/3 contribution to the nightside equatorial 135.6 nm intensities compared to the variation due to the E‐region dynamo electric field. This study confirms that nonmigrating tides can penetrate toward the upper thermosphere, both O/N2 and the E‐region dynamo should be considered in analyzing ionospheric density variations due to nonmigrating tides. Comparison with MSIS results indicates that the nonmigrating tides have stronger effect on O/N2 than the migrating tides.