Variations of the 630.0 nm airglow emission with meridional neutral wind and neutral temperature around midnight

Abstract

Abstract. The ISUAL payload onboard the FORMOSAT-2 satellite has often observed airglow bright spots around midnight at equatorial latitudes. Such features had been suggested as the signature of the thermospheric midnight temperature maximum (MTM) effect, which was associated with temperature and meridional neutral winds. This study investigates the influence of neutral temperature and meridional neutral wind on the volume emission rates of the 630.0 nm nightglow. We utilize the SAMI2 model to simulate the charged and neutral species at the 630.0 nm nightglow emission layer under different temperatures with and without the effect of neutral wind. The results show that the neutral wind is more efficient than temperature variation in affecting the nightglow emission rates. For example, based on our estimation, it would require a temperature change of 145 K to produce a change in the integrated emission rate by 9.8 km-photons cm−3 s−1, while it only needs the neutral wind velocity to change by 1.85 m−1 s−1 to cause the same change in the integrated emission rate. However, the emission rate features a local maximum in its variation with the temperature. Two kinds of tendencies can be seen regarding the temperature that corresponds to the turning point, which is named the turning temperature (Tt) in this study: firstly, Tt decreases with the emission rate for the same altitude; secondly, for approximately the same emission rate, Tt increases with the altitude.

Retrieval of Airglow Emission Rates in Analytical Form for Limb‐Viewing Satellite Observations at Low Latitudes

“…Thus, it is important for data to correctly indicate the locations with the largest emission rates, so as not to misguide the development of theories. For the 630.0-nm airglow, calculations of the volume emission rates by Chiang et al (2018) have shown that the presence of neutral wind could significantly shift the latitudes and heights of airglow occurrence. Unfortunately, as we have discussed, radiance data-with the line-of-sight measurements projected to the tangent point as in the case of ISUAL-could underestimate the height of the brightest region in a 630.0-nm airglow event by 15 km or more.…”

“…Based on these reactions, the volume emission rate of the OI 630.0-nm airglow, according to Chiang et al (2018), is…”

“…Based on these reactions, the volume emission rate of the OI 630.0‐nm airglow, according to Chiang et al. (2018), is where [ ] denotes the density of the species inside the square bracket, is the rate coefficient of Reaction (), A 1D is the transition coefficient of Process (), is the transition coefficient for producing the OI emission at 636.4 nm, , , and are the rate coefficients for the quenching of O( 1 D) by N 2 , O 2 , and O, respectively, and is the quantum yield of O( 1 D) in Reaction (), which is 0.9–1.3 according to the review study by Torr and Torr (1982). In this study, is taken to be 1.0.…”

Signature of gravity wave propagations from the troposphere to ionosphere

“…where O( 1 D) is an excited state of atomic oxygen responsible to emit a photon of 630.0 nm. The emission rate, therefore, depends on the concentration of the electron density [e] and its height profile (Chiang et al, 2018). The electron density profile, especially its bottom side profile, could be estimated by ionograms.…”

“…On the other hand, the ionosonde at Cachoeira Paulista observed the peak altitude at 260 ± 10 km. From the estimated electron density profiles, we calculated the OI 630 nm volume emission rates based on the equation presented by Chiang et al (2018). The peak emission altitude at Fortaleza was at 200 km.…”