Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences

Abstract

Abstract. Measurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6 • N, 73.7 • E, dip lat 19.09 • N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00-15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind.

Electrodynamic influence on the diurnal behaviour of neutral daytime airglow emissions

“…This result indicated the imprint of electrodynamic effect on the 630.0 nm dayglow emission intensities, both of which were obtained from the same location. Observations from an EIA crest region, Mt Abu (24.6 • N, 72.8 • E) in India, during high solar activity showed different behaviour in the OI 630.0 nm emission intensities on the equatorial electrojet and counter electrojet days (Chakrabarty et al, 2002). All these results corroborate our conclusion that the asymmetric diurnal behaviour of the optical dayglow emission intensities seen in the low latitudes is mainly due to the equatorial electrodynamic variations.…”

Thermospheric gravity wave modes over low and equatorial latitudes during daytime

“…However, it is well known that, during quiet periods, the variation in the S q electric field over low equatorial latitudes (with the exception of prereversal enhancement) is essentially due to tidal modes (diurnal(1,−2) and semidiurnal(2,4) modes) (e.g., see the review by Fejer [1981]). In fact, the width of the daytime 630.0 nm emission intensity variation over Mount Abu was shown [ Chakrabarty et al , 2002] to be correlated with the equatorial zonal electric field and hence detrending the secular variation over a day to filter out the residual intensity fluctuations eliminate, to the first order, the effect of zonal electric field. The effect due to the prereversal enhancement in the zonal electric field is also avoided by restricting the data, on a given day, well before the local sunset.…”

“…Mount Abu was shown [Chakrabarty et al, 2002] to be correlated with the equatorial zonal electric field and hence detrending the secular variation over a day to filter out the residual intensity fluctuations eliminate, to the first order, the effect of zonal electric field. The effect due to the prereversal enhancement in the zonal electric field is also avoided by restricting the data, on a given day, well before the local sunset.…”

Evidence for OI 630.0 nm dayglow variations over low latitudes during onset of a substorm

“…Although measurements of 630.0 nm dayglow emission were carried out from satellite platform a long time ago [e.g., Hays et al , 1978], systematic ground‐based observations of 630.0 nm dayglow are sparse mainly due to the difficulty of detecting the faint emission buried in bright background continuum [e.g., Chakrabarti , 1998 and references cited therein]. In the past couple of decades, remarkable progress has been made in this regard to address the coupling aspects of ITS using 630.0 nm dayglow emission as tracer [e.g., Sridharan et al , 1991, 1992a, 1992b, 1994; Chakrabarty et al , 2002; Pallamraju et al , 2002]. Many of those results highlighted the importance of zonal electric field over the dip equator in the plasma distribution throughout the low‐latitude ionosphere.…”