The solar flare of 18 August 1979: Incoherent scatter radar data and photochemical model comparisons

Abstract

Measurements of electron density at seven D-region altitudes were made with the Arecibo radar during a Class-X solar flare on 18 August 1979. Measurements of solar x-ray fluxes during the same period were available from the GOES-2 satellite (0.5-4 A and 1-8 A) and from ISEE-3 (in four bands between 26 and 400 keV). From the x-ray flux data we computed ionization rates in the D-region and the associated chemical changes, using a coupled atmospheric chemistry and diffusion model (with 836 chemical reactions and 19 vertical levels). The computed electron densities matched the data fairly well after we had adjusted the rate coefficients of two reactions, viz: o}+o-~ot + o 3 and We discuss the hierarchies among the many flare-induced chemical reactions in two altitude ranges within the D-region and the effects of adjusting several other rate coefficients.

Large solar flares and their ionospheric D region enhancements

“…The (angular) plasma frequency is related to the electron density by ω o 2 ( z ) = N ( z ) e 2 /(ɛ o m ) ≈ 3180 N ( z ). Hence the electron density increases exponentially with height in the D region as In Figure 10 are plotted the electron densities for (1) a typical unperturbed midsolar cycle day (β = 0.39 km −1 , H ′ = 71 km [ McRae and Thomson , 2004]), (2) an X6 flare as determined by Zinn et al [1990] from a set of incoherent scatter observations, (3) an X6 flare from the H ′ and β values determined from VLF measurements as in Figure 9 [ McRae and Thomson , 2004], and (4) the great X45 flare of 4 November 2003.…”

“…The ( In Figure 10 are plotted the electron densities for (1) a typical unperturbed midsolar cycle day (b = 0.39 km À1 , H 0 = 71 km [McRae and ), (2) an X6 flare as determined by Zinn et al [1990] from a set of incoherent scatter observations, (3) an X6 flare from the H 0 and b values determined from VLF measurements as in Figure 9 [McRae and , and (4) the great X45 flare of 4 November 2003.…”

Possible persistent ionization caused by giant blue jets

“…We consider reaction proceeding with the rate of ∼10 −11 cm 3 s −1 [ Fehsenfeld and Ferguson , 1974]. We estimate N [NO] from Zinn et al [1990, Figure B1] and obtain A ≃ 3 × 10 −20 N s −1 –10 −18 N s −1 (see Figure 1). In the work of Mitra [1975], an analogous rate was denoted as but the products of the relevant reaction were intermediate ions (denoted X − in the same paper), such as CO 3 − .…”

“…To describe the effect of GBJ on ionosphere and the perturbation of a VLF signal, we must model the time‐dependent relaxation of ionization. There is a plethora of dynamic ionization models, which include, e.g., Glukhov‐Pasko‐Inan (GPI) model with 3 kinds of ions [ Glukhov et al , 1992], Zinn‐Sutherland model with 9 species of negative and 23 species of positive ions, with 997 chemical reactions [ Zinn et al , 1990], Mitra‐Rowe model with 6 kinds of ions [ Mitra , 1975]. However, most of these models, even the most elaborate ones [ Zinn et al , 1990], have only been used above 50 km, and might not describe accurately the relaxation of ionization in the stratosphere ( h < 50 km).…”

Plasma chemistry of sprite streamers

“…The characteristic timescale for electrical breakdown in the upper atmosphere ranges from submillisecond in the case of sprites and ELVES to a few tens to hundreds of ms for blue jets and gigantic jets. This is much shorter than other kinds of external forcing processes that induce time varying chemical effects in the terrestrial system, such as day‐night variations in solar photoionization [ Roble , 1995] and X‐ray flares [ Zinn et al , 1990], precipitating particles, as for example in the aurora [ Rees , 1989] or in relativistic electron precipitation [ Callis et al , 1996], or by solar proton events or Forbush decreases associated with modulation of galactic cosmic ray flux by solar activity [e.g., Thorne , 1980].…”