"Evidence for the equatorward penetration of electric fields, winds, and compositional effects in the Asian/Pacific sector during the September 17–24, 1984, ETS interval""

Abstract

Data from a chain of eight ionosondes between 15° and 51° magnetic latitude near the −165° east magnetic meridian (Asian/Pacific sector) are analyzed to illustrate the equatorward penetration of ionospheric storm effects during the September 17–24, 1984, Equinox Transition Study (ETS) interval. Hourly values of measured f0F2, M(3000)F2, and f0E are used to infer the storm time deviations of f0F2, hmax, and an effective meridional wind speed from their average magnetically quiet values at the beginning of the interval. The latter parameters are subjected to a 5‐hour running average and are fit with Legendre polynomials in latitude to clarify the large‐scale dynamical features in a color‐coded display. The method illustrates the equatorward penetration of several phenomena in response to changing magnetic conditions, interpreted as follows: (1) Elevations in hmax of the order of 40 km occur down to 35°–45° magnetic latitude during the first, less intense, magnetic storm occurring on September 19; and elevations of the order of 50–70 km penetrate to at least 15° magnetic latitude during the more intense storm at the end of the interval. These effects are interpreted as primarily due to meridional winds driven by high‐latitude heating. (2) Daytime depressions in f0F2 occur on the following day (“storm negative phase”) of the order of 1.0–1.5 MHz (∼30% change) between 30° and 40° magnetic latitude after the first storm, and of the order of 2.0–2.5 MHz (∼45% change) down to 15°–20° magnetic latitude after the second storm, due to decreased [O]/[N2] ratios connected with the global heating and dynamical transport. (3) Enhancements in f0F2 of the order of 2.0–3.0 MHz (∼30–40% change) near 15°–20° magnetic latitude are interpreted as originating from a “pumping up” of the fountain effect by eastward electric fields penetrating to low latitudes during the early phases of the storms, and a secondary enhancement several hours later is consistent with the existence of an ionospheric disturbance dynamo. (4) Diurnal‐average meridional winds, inferred from the changes in hmax, illustrate disturbance mean meridional circulations of the order of 20–25 m s−1 and 30–50 m s−1 for the two disturbances, whose equatorward penetration is sensitive to the energetic input at high latitudes. This information forms one data set which numerical simulations of the ETS interval should strive to reproduce.