Auroral O(¹S) production and loss processes: Ground‐based measurements of the artificial auroral experiment precede

Abstract

An artificial auroral experiment, Precede, was performed in the 80‐ to 120‐km altitude range above the White Sands Missile Range, New Mexico, in October 1974. A 2‐kW rocket‐borne electron accelerator, square wave modulated at 0.5 Hz, was activated at 95 km on payload ascent, was pulsed continuously through apogee (120 km) to a descent altitude of approximately 80 km, and provided a total of 90 pulses of a 2.5‐kV 0.8‐A electron beam over a period of 180 s. A ground‐based dual channel telephotometer recorded the time‐dependent photon emission rate of the N2+(B²Σu+→X²Σg+) first negative (0–0) band at 3914 Å and the O(¹S → ¹D) transition at 5577 Å induced in the night atmosphere by the pulsed electron source. An electron‐induced luminous efficiency of (4.5±0.4) × 10−3 was determined for the N2+ 1N (0–0) transition at 3914 Å in the 80‐ to 100‐km altitude range. The photon emission rates of several bright stars were measured to calibrate the telephotometer and to correct for the effects of atmospheric extinction. The time‐dependent O(¹S) 5577‐Å photon emission rate has been fitted with a model calculation providing insight into O(¹S) production and loss processes resulting from the deposition of energetic electrons in the 90‐ to 116‐km altitude range. At altitudes in excess of approximately 110 km the O(¹S) time‐dependent photon emission profiles indicate that consecutive reactions involving energy transfer from N2(A³Σu+) to O(³P) is the dominant O(¹S) production process. A rate coefficient of 5.7 × 10−12 cm³ s−1 representing an O(¹S) yield of 0.29 has been inferred from the data for the reaction of N2(A³Σu+) and O(³P). The dissociative recombination of O2+ has been established as the dominant O(¹S) production process at altitudes less than 96 km with an O(¹S) yield of 4.5–6.0% per dissociation. Other processes account for approximately 20% or less of the total O(¹S) production at 90 km with smaller contributions indicated at higher altitudes. Collisional deactivation by O(³P) accounts for approximately 50% of the total O(¹S) depopulation rate in the 95‐ to 116‐km altitude range with a rate coefficient of 6.0 × 10−11 e−305/T cm³ s−1. Quenching by O2 dominates as an O(¹S) loss mechanism at altitudes less than 94 km with an estimated rate coefficient of 1.2 × 10−11 e−850/T cm³ s−1. The rate coefficients determined for O(¹S) produced by the reaction of N2(A³Σu+) and O and the collisional deactivation processes have a probable error of approximately 25% if it is assumed that the model atmosphere used in the analysis contributes no significant uncertainty.