Low‐latitude midnight brightness in 630.0 nm limb observations by FORMOSAT‐2/ISUAL

Abstract

This paper investigates the intense airglow brightness often observed in the 630.0 nm limb images taken using Imager of Sprites and Upper Atmospheric Lightnings (ISUAL), onboard FORMOSAT-2 satellite, where the tangent plane of the measurement falls in the local midnight sector. Most of the images show only single brightness, but in some cases there could be multiple peaks, which sometimes appears to be centered on geographic equator and in some cases falls on either sides of the magnetic equator. In order to understand such intense emission in the near-midnight hours, the observations are simulated using SAMI2 (SAMI2 is Another Model of the Ionosphere) model parameters based on the ISUAL viewing geometry. The simulations reproduced the measured airglow intensity pattern quite remarkably and suggested that the meridional neutral wind and the resulting plasma distribution are closely related with the observed brightness. The intensity and locations of the airglow brightness peaks could potentially be utilized to infer the strength of meridional neutral wind.

Space‐based imaging of nighttime medium‐scale traveling ionospheric disturbances using FORMOSAT‐2/ISUAL 630.0 nm airglow observations

“…Second in the series of “FORMOSATs” developed by Taiwan, the FORMOSAT‐2 homes the set of optical instruments acronymed ISUAL, which includes a CCD imager that images the Earth's limb at 630.0 nm wavelength in high spatial and temporal resolutions [ Chern et al ., ]. The limb‐viewing geometry of ISUAL provides a unique opportunity to examine the characteristics of 630.0 nm emission in great detail and to infer the electrodynamical processes involved in the intensity variations during the midnight period [ Rajesh et al ., , ; Adachi et al ., ]. In addition, many of the images also reveal wavelike patterns of intensity modulation or regularly spaced distinct bands of enhancement, suggesting that they could be the optical signatures of MSTIDs in airglow images when viewed from space [for example, see, Adachi et al ., ].…”

“…A similar procedure described by Rajesh et al . [] has been used for the simulations, where plasma and neutral parameters derived from Sami2 is Another Model of the Ionosphere (SAMI2) [ Huba et al ., ] are projected to the ISUAL line‐of‐sight geometry. The 630.0 nm volume emission [ Link and Cogger , ; Vlasov et al ., ] is calculated along the line of sights corresponding to each pixel and is integrated to reproduce the ISUAL observation.…”

Equatorial aurora: the aurora-like airglow in the negative magnetic anomaly

“…The red auroras only occur during geomagnetic disturbances in the southern sky of Hawaii and are visible to the unaided eye. Considering that the typical angular distance between the equatorial ionospheric anomaly (EIA, which also lies southward of Hawaii and has considerable red line emissions) and Hawaii is about 5°, and the angular scope of the EIA emissions is ∼5° [ 64 ], it is inferred from Fig. 3 e (α = 5° and β = 5°) that the EIA emissions may have little contribution to the slant intensity.…”

Case study of an Equatorial Plasma Bubble Event investigated by multiple ground-based instruments at low latitudes over China

“…Using observations from the Imager for Sprites and Upper Atmospheric Lightning (ISUAL) payload onboard the FORMOSAT-2 satellite data, Adachi et al (2010) found that an airglow-type of blob in their study was caused by a brightness wave that passed by (BW; e.g., Herrero et al, 1993;Colerico et al, 1996;Colerico and Mendillo, 2002). Using the same database, Rajesh et al (2014) revealed that a convergence of a strong transequatorial wind and a relatively weaker equatorward wind could also generate similar airglow brightness. Our recent investigation has noticed that an LSWS on the bottomside of EPB depletions could also induce plasma blobs at low-latitudes over China.…”