Annual and interannual variations in global 6.5DWs from 20 to 110 km during 2002–2016 observed by TIMED/SABER

Abstract

Using version 2.0 of the TIMED/SABER kinetic temperature data, we have conducted a study on the annual and interannual variations of 6.5DWs at 20–110 km, from 52°S to 52°N for 2002–2016. First, we obtained global annual variations in the spectral power and amplitudes of 6.5DWs. We found that strong wave amplitudes emerged from 25°S/N to 52°S/N and peaked in the altitudes of the stratosphere, mesosphere, and the lower thermosphere. The annual variations in the 6.5DWs are similar in both hemispheres but different at various altitudes. At 40–50 km, the annual maxima emerge mostly in winters. In the MLT, annual peaks occurred twice every half year. At 80–90 km, 6.5DWs appeared mainly in equinoctial seasons and winters. At 100–110 km, 6.5DWs emerged mainly in equinoctial seasons. Second, we continued the study of the interannual variations in 6.5DW amplitudes from 2002 to 2016. Frequency spectra of the monthly mean amplitudes showed that main dynamics in the long‐term variations of 6.5DWs were AO and SAO in both hemispheres. In addition, 4 month period signals were noticed in the MLT of the NH. The amplitudes of SAO and AO were obtained using a band‐pass filter and were found to increase with altitude, as do the 6.5DW amplitudes. In both hemispheres, the relative importance of SAO and AO changes with altitude. At 40–50 and 100–110 km, AO play a dominant role, while at 80–90 km, they are weaker than SAO. Our results show that both the annual and interannual variations in 6.5DWs are mainly caused by the combined action of SAO and AO.

Climatology of the Quasi‐6‐Day Wave in the Mesopause Region and Its Modulations on Total Electron Content During 2003–2017

“…The occurrence date and the period of all the Q6DWs during 2003–2017 are recorded, and their statistical results are shown in Figures and . Figure indicates that this planetary wave usually appears in April–May and August–October, exhibiting a quasi‐semiannual oscillation, which is consistent with previous study (Huang et al, ; Jiang et al, ; Lieberman et al, ; Liu et al, ; Talaat et al, ; Wu et al, ). Besides, we noticed that there are three Q6DW events during February, which are slightly more than those that occur in January (one event) and March (two events).…”

“…Our statistical results also show the Q6DW peaks during April/May and September/October, which exhibit a quasi‐semiannual oscillation with a period of not exactly 6 months as shown by Huang et al (). Additionally, we found that the Q6DW also shows a relatively high occurrence rate during February, the reason of which is still unclear.…”

Study of the Quasi‐5‐Day Wave in the MLT Region by a Meteor Radar Chain

“…It is surprising to see that TAO in the 5DW amplitudes is as important as the commonly recognized AO and SAO at MLT region. Using the SABER temperature measurements averaged in the altitude range from 80 to 90 km, Huang et al () found that the 6.5‐day wave has a strong TAO in the latitudinal range from 40°N to 52°N, which is consistent with our results. They stated that SAO is stronger than AO at 80 to 90 km in the latitudinal range from 30°N to 52°N.…”

“…Note that oscillations with periods between 4 and 7 days are considered as the 5DWs in this study. For satellite observations, the two‐dimensional fast Fourier transform is an effective way to obtain spectral analysis (e.g., Huang et al, ; Merzlyakov & Pancheva, ) and is adopted in this study. Figure a presents a moving periodogram of the zonal wind at 90 km in the period of 20 April to 20 May 2012 over MH.…”

“…In high‐latitude and polar regions, 5DWs are found to be associated with the polar mesospheric clouds and polar mesospheric summer echoes (e.g., Kirkwood et al, ; Merkel et al, ; von Savigny et al, ). In the middle and low latitudes, satellite observations show that 5DWs are enhanced around the equinoxes and minima at solstices (e.g., Huang et al, ; Talaat et al, , ; Wu et al, ). Based on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED)/Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) measurements, Forbes and Zhang () reported that the maximum amplitude of quasi‐6‐day wave usually occurs during the day of year 60–120 and 180–300.…”