Quasi Two-, Three-, and Six-Day Planetary-Scale Wave Oscillations in the Upper Atmosphere Observed by TIMED/SABER Over ∼17 Years During 2002-2018

We present for the first time the global climatology of two-, three-, and six-day planetary waves in the upper atmosphere using nearly 17 years of temperature observations by Thermosphere Ionosphere and Mesosphere Electric Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) during January 2002-December 2018. The observations span the altitude range similar to 30-110 km and are continuously available over 50 degrees S-50 degrees N latitudes throughout the time interval. The amplitudes and phases of the oscillations with periods in the ranges of 1.5-2.5, 2.5-3.5, and 5.5-6.5 days, and longitudinal zonal wave numbers of W3 (westward propagating wave number-3) and E1 (eastward propagating wave number-1) are determined from the two-dimensional (2-D) least squares analysis of the data. The study finds that the two-day W3 waves can penetrate into the equatorial region, although they are mostly observed at higher latitudes. The three- and six-day E1 waves are trapped at low latitudes, and their amplitudes vary with latitude following a Gaussian function with the maximum centered at the equator and the e-folding width of 27 degrees and 24 degrees latitudes. In the equatorial region, the monthly mean amplitudes are similar to 3.8-4.8 K for the three-day waves, and the two- and six-day waves have relatively smaller amplitudes. The waves have the amplitude maximums around solstices and the minimums close to equinoxes. The peak amplitudes are larger during the solar maximum than during the solar minimum, and superimposed with the quasi two-year cycle. The vertical wavelengths are approximately 30-40 km, suggesting the propagations to the equatorial upper atmosphere. The climatology revealed could be useful for general circulation models.