Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Observation of semiannual and annual oscillation in equatorial middle atmospheric long term temperature pattern

“…This discrepancy of the observed results is possibly due to the effect of tidal aliasing in the case of earlier observations carried out from the extra-tropical latitude regions. Also Taylor et al (2005) found the SAO amplitude of ∼5-6 K over 25 month period of observation from an extra tropical latitude (20.8 • N) station, using mesospheric airglow emissions, which is higher in magnitude than ours.…”

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

“…This is quite surprising, as we would normally expect the maxima of a SAO-driven forcing to occur around equinox (e.g. Opio et al, 2015;Taylor et al, 2005;Williams, 1994). The fitted curve for MH-NSY GCP data shows the SAO maxima dur-ing mid-November and mid-May, while the oscillation maximizes at the beginning of December and June in the DN-NWC GCP data.…”

“…However, the phase of the measured SAO may be determined by a number of effects. The observed difference between the SAO phase in DN-NWC and MH-NSY might originate in the phase differences between the phenomena as a function of latitude, or be due to the changes of the phenomena's phases as a function of latitude and altitude (e.g., Groves, 1972;Lysenko et al, 1994;Russell et al, 2004;Taylor et al, 2005). In order to test our hypothesis, we decided to compare the phase of the SAO in the VLF measurements to the SAO phase detected in peak emission values of the OH * 2.0 µm emission band, using the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite (Mlynczak, 1997;Russell III et al, 1999).…”

“…One of these oscillations is the semi-annual oscillation (SAO). Among different parameters, the SAO can be detected in neutral atmospheric measures, e.g., the wind regime in the mesosphere-lower thermosphere (MLT) (e.g., Groves, 1972;Gregory and Manson, 1975;Lysenko et al, 1994); MLT temperatures (e.g., Groves, 1972;Takahashi et al, 1995;Taylor et al, 2005;Huang et al, 2006;Shepherd et al, 2006); and concentrations of atmospheric species, such as atomic oxygen at 80-115 km altitudes (e.g, Russell et al, 2004) and excited hydroxyl (OH * ) molecules around 87 km (e.g., Takahashi et al, 1995;Marsh et al, 2006;Shepherd et al, 2006;Gao et al, 2010). In addition, the charged part of the atmosphere (i.e., the ionosphere), experiences the SAO, which was observed and derived in and from measurements of several parameters, e.g., the ionospheric lower transition height at ∼ 180-260 km (a level where atomic and molecular ion concentrations become equal) (e.g., Lei et al, 2004); the electron and plasma density within the daytime D, E, and F regions of the ionosphere (e.g., Lauter and Nitzsche, 1967;Bremer and Singer, 1977;Forbes et al, 2000;Peters and Entzian, 2015); and also ionospheric total electron content (TEC) (e.g., Zhao et al, 2007;Opio et al, 2015).…”

On the use of simultaneous measurements of OH and O<sub>2</sub> emissions to investigate wave growth and dissipation

“…The wave packet would include a spectrum of waves consisting of a long period as well as shorter period perturbations present in the data on that night. One can notice that temperature data broadly ranged from 185 to 215 K (mean value 199.6 K) for O 2 while the OH temperature was around 175 K to 220 K, with a mean value of 196.9 K. In their report, Taylor et al (2005) concluded the periodicity of the dominant variation to be near 180 days, exhibiting a semiannual-type oscillation in the mesospheric temperatures. Further, a 15-day averaging of the mean temperatures was carried out to clearly bring out the seasonal pattern and the results are shown in plots as connecting solid lines.…”