Ionospheric effects of the March 1990 Magnetic Storm: Comparison of theory and measurement

Abstract

This paper presents a comparison of the measured and modeled ionospheric response to magnetic storms at Millstone Hill and Arecibo during March 16-23, 1990. Magnetic activity was low until midday UT on day 18 when Kp reached 6, days 19 and 20 were quiet, but a large storm occurred around midnight UT on day 20 (Kp=7) and it was moderately disturbed (Kp=4) for the remainder of the study period. At Millstone Hill, the daytime peak electron density (NmFz) showed only a modest 30% decrease in response to the first storm and recovered to prestorm values before the onset of the second storm. The model reproduces the daytime peak electron density well for this period. However, the severe storm on March 20 caused a factor of 4 depletion in electron density, while the model densities were not greatly affected. The inclusion of vibrationally excited nitrogen (N2') in the model was unable to account for the observed large electron density depletions afterward March 20. The storm did not appear to affect the overall magnitude of the electron density at Arecibo very much, but did cause unusual wavelike structure in the peak density and peak height following the storm. The model reproduces the daytime NmF 2 very well for Arecibo, but after sunset the model densities decay too rapidly. This study indicates that successful modeling of severe ionospheric storms will require better definition of the storm time inputs, especially of the neutral atmosphere. Furthermore, the effects of electric fields and neutral winds on the low-middle ionosphere during the March 90 storm were discussed by Buonsanto and Foster [1993], who compared the observed ionospheric behavior at Millstone Hill and Arecibo. A brief review of ionospheric storm behavior has been published by Rishbeth [1991] and further discussion of magnetic storm behavior is provided in the paper by Buonsanto et al. [1992]. The present paper is primarily concerned with comparing the modeled and observed ionospheric behavior at Millstone Hill and Arecibo during March 16-23, 1990. The possible role of vibrationally excited N 2 in producing the negative phase of ionospheric storms has been investigated by Richards et al. [1989] and by Pavlov [1994]. It affects the electron density in the F region because it reacts more quickly with O + than ground state N2. Richards et al. [ 1989] found little effect during the September 1984 storm, and this result was confirmed by Pavlov [ 1994]. However, Pavlov did find N2' to be important in some other storms, particularly at solar maximum. Model The field line interhemispheric plasma (FLIP) model has been developed over a period of more than 10 years and has been described previously by Richards and Torr [1988], by Torr et al. [1990], and by Richards et al. [1994a, b]. The main component of this one-dimensional model calculates the plasma densities and temperatures along entire magnetic flux tubes from 80 km in the northern hemisphere through the plasmasphere to 80 km in the southern hemisphere. The model uses a tilted dipole approximation to the...

A comparative study of global ionospheric responses to intense magnetic storm conditions

“…By way of contrast, our observations show an instantaneous or near-instantaneous response (i.e., At=0-2 hours) of haF 2, suggesting that faster mechanisms are in effect (e.g., penetrating electric fields) at least in the first several hours of storm development. Such an instantaneous response in haF,_ was also reported by Richards et al [ 1994]; and studies of the same storm period by Buonsanto et al [1993], using observations at Millstone Hill and Arecibo Observatories, pointed to the importance of penetrating magnetospheric electric fields and disturbance dynamo fields. phase.…”

On the mechanism of seasonal and solar cycleNmF2variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

“…It should be kept in mind that the thermosphere density at satellite heights is mainly presented by [O], and therefore the observed discrepancies with empirical models tell us about the problems with model description of [O] variations. It is known that negative F 2 layer storm effects cannot be satisfactory modeled without special fitting of thermospheric parameters for each particular ionospheric storm, and it has been demonstrated repeatedly [e.g., Richards et al, 1989Richards et al, , 1994bRichards et al, , 1998]. …”

Seasonal and solar cycle variations of the ionospheric peak electron density: Comparison of measurement and models

“…In fact, detailed quantitative studies of ionospheric NmF2 behavior have only recently become meaningful as a result of our development of an algorithm to determine neutral winds that reproduce the observed peak height (hmF2) of the ionosphere [Richards, 1991] [ 1995] all indicated that it may reduce the peak electron density by as much as a factor of 2 in summer at solar maximum. It may also contribute to the negative phase of ionospheric storms [Richards et al, 1989[Richards et al, , 1994bPavlov, 1994]. This paper also presents model results that include the effects of vibrationally excited N2.…”