Simultaneous satellite and radar studies of theDregion ionosphere during the intense solar particle events of August 1972

Abstract

During the intense solar particle events of August 3–11, 1972, 28 cases of simultaneous data were obtained between the polar‐orbiting satellite 1971‐089A and the incoherent scatter radar at Chatanika, Alaska. Effective electron loss rates (ψ) in the D region ionosphere have been derived as a function of altitude, solar zenith angle (χ), and the magnitude of the production rate (Q). Production rate profiles extending from 3 × 10² to 3 × 104 ion pairs/cm³ s were calculated for the 40‐ to 90‐km region. Electron density profiles extending from 5 × 10³ to 105 el/cm³ were measured, useful data being obtained down to altitudes as low as 50 km. Values of ψ were obtained for daytime and sunrise/sunset conditions over a range of solar zenith angles from 50.4° to 98.6°. A strong diurnal dependence in ψ was observed only at altitudes below 80 km. Twilight values of ψ at the lower altitudes were over an order of magnitude larger than the daytime values. Between 70‐ and 90‐km altitude the present polar summer daytime values of ψ are significantly larger than those obtained in the winter daytime event of November 2, 1969. Near 80‐km altitude the present results are consistent with the dominant ions being the hydrated ions H3O+ (amu = 19) and H3O+·H2O (amu = 37). A strong seasonal dependence in the effective loss rates has therefore been established. A pronounced asymmetry in ψ and Ne between the sunrise and sunset twilights was measured at altitudes <80 km, the electron density at sunset being larger than at sunrise at the same solar zenith angle. The altitude behavior of ψ and the temporal leads and lags measured in the transitions between twilight and day were found to be consistent with the interaction of the solar visible and ultraviolet wavelengths with the ozone layers above the earth, leading to the sunrise increase and sunset decay of O and O2(¹Δ). The dependence of ψ on the magnitude of the production rate during the day was found to be weak, a slight positive dependence being measured at altitudes <63 km.

A new method of studying the relation between ionization rates and radio-wave absorption in polar-cap absorption events

“…In fact, there is some evidence from radar data that the effective recombination coefficient may vary slowly with time (Reagan and Watt, 1976;Hargreaves et al, 1993), and such a variation would plainly reduce the accuracy of the prediction. Further, no seasonal variations have been taken into account in the present study.…”

“…(1) Daytime, summer, the range of values over several days (Reagan and Watt, 1976). (2) Daytime, winter, the range of values over three hours near local noon (Hargreaves et al, 1987).…”

Ionospheric Radiowave Absorption Processes in the Dayside Polar Cap Boundary Regions

“…One should thus expect a steep change in absorption intensities as the absorbing region enters or leaves the sunlight. One of the relatively few published reports referring to riometer data is the study by Reagan and Watt [34] where they find a large asymmetry between sunrise and sunset with ionization lag times of the order of 45 min from sunset (x=90 0 ) at 70 km altitude and lead times of the order of 10 min from sunrise.…”

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

“…Roble et al (1987) found significant Joule heating of the mesosphere and lower thermosphere during solar proton events. Reagan and Watt (1976) and Reagan et al (1981) analyze satellite and radar measurements made during solar particle events and investigate direct effects in stratospheric ozone production. Solar proton events induce particle ionization in the mesosphere and upper stratosphere, enhancing the concentrations of short-lived HO x (H, OH, HO 2 ) and long-lived NO x (N, NO, NO 2 ) constituents.…”