Seasonal Variation of O/N₂ on Different Pressure Levels From GUVI Limb Measurements

Abstract

The ratio of O number density to N2 number density (O/N2) is an important parameter to describe thermospheric composition changes and its effects on the ionosphere. Based on Global Ultraviolet Imager (GUVI) limb measurements, we investigate the seasonal behaviors of O/N2 volume density ratio on different constant pressure levels during geomagnetically quiet periods. The global O/N2 shows the prominent annual and semiannual variations with solar activity dependence. An empirical model considering the solar activity and annual/semiannual variations can reasonably reproduce the original O/N2. The modeled O/N2 captures the hemispheric asymmetry of the annual variations in both length and magnitude. Global maps of the seasonal harmonic components of the modeled O/N2 indicate the latitudinal and altitudinal dependence of O/N2 seasonal variations. The annual component dominates over the semiannual component at mid‐latitudes, but it is smaller than the semiannual component at low latitudes. In the Northern Hemisphere, and at low geomagnetic latitudes of the Southern Hemisphere, the annual component peaks around December solstice at all altitudes, whereas at middle geomagnetic latitudes of the Southern Hemisphere, it peaks around June solstice. The semiannual component peaks at the equinoxes in almost all regions over the globe at all altitudes. The annual and semiannual amplitudes both increase with altitude. In addition, O/N2 annual variations and solar activity dependence are more influenced by the thermal expansion and contraction.

Seasonal Variation of Thermospheric Composition Observed by NASA GOLD

“…( 2019 ) and Yu et al. ( 2020 ) found that the annual and semiannual variations in composition have a constant phase with altitude throughout the thermosphere. Figure 7a shows GOLD 3‐year average ∑ O/N 2 (2019, 2020, and 2021) for 42.5°N and 22.5°N from Figure 6 of this paper, and GUVI 3‐year average O/N 2 (2004, 2005, and 2006) at 8.4 × 10 −4 Pa (∼130 km) in the latitude bins of 50°N–30°N and 30°N–10°N based on Figure 6 of Yue et al.…”

Investigation of a Neutral “Tongue” Observed by GOLD During the Geomagnetic Storm on May 11, 2019

“…∑O/N 2 is obtained by integrating densities of O and N 2 from infinity down to an altitude where the column number density of N 2 is 1 × 10 17 /cm 2 and thus it is actually defined on a constant pressure surface with no altitude information (Correira et al., 2020). O and N 2 number densities decrease exponentially with altitude, so the column number densities of O and N 2 at the altitude where the N 2 column number density is 1 × 10 17 /cm 2 is mainly from altitudes immediately above this level (∼140–180 km) (Yu, Ren, Le, et al., 2020; Yu, Ren, Yu, et al., 2020). This altitude region encompasses most of LBH radiance and minimizing the uncertainty in ∑O/N 2 as a function of 135.6 nm/LBH.…”

An Unusually Large Electron Temperature Increase Over Arecibo Associated With an Intense Geomagnetic Storm

“…Based on GUVI limb measurements, Yu et al. (2020) suggested that $$[O]/[{N}_{2}]$$ volume density ratio presents prominent annual and semiannual variations with solar activity dependence. The upwelling of the oxygen‐depleted or nitrogen‐rich air from much lower altitude in the thermosphere into the F‐region during the geomagnetic storm is reported in previous studies (e.g., Buonsanto, 1999; Mayr & Volland, 1972; Prölss, 1980).…”

“…𝑁𝑁2] is affected by the horizontal and vertical motion of neutral particles, molecular diffusion, and other effects in the thermosphere, which are relevant to the solar activity and geomagnetic disturbance. Based on GUVI limb measurements, Yu et al (2020) 𝑁𝑁2] volume density ratio presents prominent annual and semiannual variations with solar activity dependence. The upwelling of the oxygen-depleted or nitrogen-rich air from much lower altitude in the thermosphere into the F-region during the geomagnetic storm is reported in previous studies (e.g., Buonsanto, 1999;Mayr & Volland, 1972;Prölss, 1980).…”