The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6-12 April 1990

Abstract

Abstract. We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6±12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earth's ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O 4 S ions as a result of new high-temperature¯owing afterglow measurements of the rate coe cients u 1 and u 2 for the reactions of O 4 S with N 2 and O 2 . The deviations from the Boltzmann distribution for the ®rst ®ve vibrational levels of O 2 v were calculated, and the present study suggests that these deviations are not signi®cant. It was found that the di erence between the non-Boltzmann and Boltzmann distribution assumptions of O 2 v and the di erence between ion and neutral temperature can lead to an increase of up to about 3% or a decrease of up to about 4% of the calculated NmF2 as a result of a respective increase or a decrease in u 2 . The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N 2 v b 0 and O 2 v b 0 in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N 2 v b 0 and O 2 v b 0 . This could be due to possible uncertainties in model neutral temperature and densities, EUV¯uxes, rate coe cients, and the¯ow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the¯ux of ionization above the station. Our calculations show that the increase in the O N 2 rate factor due to N 2 v b 0 produces a 5± 36% decrease in the calculated daytime peak density. The increase in the O O 2 loss rate due to vibrationally excited O 2 produces 8±46% reductions in NmF2. The e ects of vibrationally excited O 2 and N 2 on x e and e are most pronounced during the daytime.

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion

“…However, the reaction rates for both O 2 and N 2 may be a ected by vibrational excitation (e.g. Pavlov, 1998), though not necessarily in the same way.…”

New electron energy transfer and cooling rates by excitation of O2

“…(4). Pavlov (1998) found that during the undisturbed and geomagnetic storm periods at middle latitudes at moderate solar-activity conditions deviation from a Boltzmann distribution of O 2 v was large at the vibrational energy levels v b 3 and close to a Boltzmann distribution of O 2 v for v 1Y 2Y and 3. The main contribution to vv 0 arising from the deexcitation of O 2 v is brought by the deexcitation of O 2 1 and O 2 2X As a result, it is possible to use a Boltzmann distribution of O 2 v in calculations of vv 0 as…”

“…The number density of vibrationally unexcited O 2 is much larger than the number density of vibrationally excited O 2 during the undisturbed and geomagnetic storm periods at middle latitudes (Pavlov, 1989(Pavlov, , 1994(Pavlov, , 1998. As a result, the collisions of thermal electrons with vibrationally unexcited O 2 yield the main contribution to v vib O 2 and the possible error of Eq.…”

“…Lane and Dalgarno (1969) have shown that the electron cooling by excitation of O 2 should be important in the E-region of the ionosphere (we shall use the symbol O 2 for the ground electronic state X 3 À g of O 2 ). Hierl et al (1997) found that the big dierence between the high temperature¯owing afterglow and drift tube measurements (McFarland et al, 1973;Albritton et al, 1977) of the eective rate coecient for the reaction of O 4 S with O 2 results from the input of the reactions between the vibrationally excited O 2 and O 4 S. Pavlov et al (1998) and Pavlov (1998) found that at solar maximum and moderate solar-activity conditions the increase in the O 4 S O 2 loss rate due to vibrationally excited O 2 produces up to 40% reductions in the calculated daytime F2 peak electron density if the vibrational temperature of O 2 is the same as the neutral translation temperature. To calculate real values of the O 2 vibrational temperatures and the eects of vibrationally excited O 2 on the calculated electron density the knowledge of the energy transfer rates from thermal electrons to vibrationally excited O 2 is required.…”

“…To calculate O 2 v it is necessary to solve the vibrational quanta continuity equation [a Boltzmann distribution of O 2 v] or the full continuity equations for densities of O 2 v [a non-Boltzmann distribution of O 2 v]. The system of full continuity equations and the vibrational quanta continuity equation are described by Pavlov (1989Pavlov ( , 1994Pavlov ( , 1998 (1) can be calculated as…”