An analysis of the spatial distribution of dayside cleft optical emissions

Abstract

An analysis of measurements of the 4278-A, 5200-A, 5577-A, and 6300-A emissions obtained from a rocket launch through the postnoon dayside cleft into the polar cap ionosphere is reported. The 4278-A and 5577-• emissions show a clearly defined decrease in intensity at the poleward.edge of the dayside particle precipitation, while the 5200-A emission extends well into the polar cap with only a slight decrease in intensity. The 6300-A emission displays a behavior intermediate between these extremes. The optical data are analysed by using a dynamical model of dayside cleft auroral processes incorporating transport by ion and neutral winds. It is concluded that neutral winds are responsible for modifying the spatial distribution of the 5200-A and 6300-A emission, while the ion drift component is negligible. In addition, it is found that (1) 80% of the 4278-A emission intensity is due to resonance fluorescence in the sunlit cleft ionosphere, (2) the reaction O2(c•Y',., -) + O• O 2 + O(•S) is consistent with the 5577-• data if the yield of O(•S) from the dissociative recombination of 02 + is about 2%, and (3) the rate of the reaction N2 + + O• NO + + N is apparently higher in the ionosphere than indicated by the laboratory measurements. examination of both ion drift and neutral wind effects and is based on the study of Link [1982]. Preliminary results from this study have been presented by Link et al. [1976, 1978]. Recently, G•rard and Roble [1982] have presented an independent analysis of the AMF-VB-41 5200-J• data, based on a neutral wind transport model. More recently, Link [1983] has discussed the implications of the spatial distribution of the 5200-J• emission for the mechanisms of O(XD) production. CLEFT CAMPAIGN MEASUREMENTSThe following section presents optical and other supporting measurements obtained from the Black Brant AMF-VB-41

Dayside red auroras at very high latitudes: The importance of thermal excitation

“…But Te could increase and thermal excita- tion could become important if there were a significant downward heat flux. In contrast, our results do not agree with previous combinations of observations and theory [Gault et al, 1981;Link et al, 1983] which dismiss the importance of thermal excitation. While we do not have correlative 6300-A intensities, they did not have correlative electron temperatures.…”

“…Although on the dayside, these observations have been in the winter hemisphere at such locations that the sun was well below the horizon. The high intensity regions, which are limited in latitude (1 to 5 ø) and extended in longitude (1 to 10 hrs), have been associated with either magnetospheric features, the cusp and cleft [Shepherd, 1979, and references therein], or ionospheric features, the morning and afternoon convection cells [Reiff et al, 1978]. The source of excitation for the atomic oxygen has been attributed to low energy electrons [Shepherd, 1979, and references therein].…”

“…The source of excitation for the atomic oxygen has been attributed to low energy electrons [Shepherd, 1979, and references therein]. Possible mechanisms for the excitation have been examined by combining theoretical models and observations [Gault et al, 1981;Link et al, 1983], with the conclusion that direct electron impact and dissociative recombination dominate.…”

Deducing composition and incident electron spectra from ground‐based auroral optical measurements: A study of auroral red line processes

“…Duboin et al [1984] also found that on the basis of temporal variability of ground-based observations of N I 5200 ]k and O I 6300 ]k, the N(2D) source is not the major source mechanism for O(1D). Link et al [1983] further argue against this process and point out that the need for this source in the dayglow is inconclusive. Also, the empirical relationship between O I 6300 ]k and the energetic electron flux found by Shepherd et al [1980] suggests that electron impact excitation is the main source of the red line.…”

Modeled F region response to auroral dynamics based upon Dynamics Explorer auroral observations

“…On the gross scale shown in Plate 1, the 557 nm images identify regions of auroral electron precipitation for which typical electron energies are several to many keV. In contrast, the 630 nm images identify regions of low-energy (E • 500 eV) electron precipitation [Shepherd et al, 1980;Murphree et al, 1983;Link et al, 1983]. Hence, the different wavelength bands lead to general information about the precipitating electrons spectral softness or hardness as well as the energy fluxes [Rees and Luckey, 1974].…”