Distribution of radar auroras over Alaska

Abstract

Analysis of data collected by five auroral radars in Alaska shows the distribution of of ionospheric disturbances as a function of time and location. The radars, operated during the IGY, were in a nearly straight line running magnetically north‐south across Alaska; these locations made it possible to observe disturbances continuously in the range from 60° to 80° geomagnetic latitude, which includes the visual auroral zone. An apparent radar auroral zone with a maximum at 67° geomagnetic latitude is shown. The decrease in occurrence to the south of this maximum is verified, but the decrease to the north cannot be accurately defined, as the role of aspect sensitivity is not fully understood. The radar auroral zone spreads to the south during increased magnetic disturbance, and some indication is found of a lessening of activity well north of the visual auroral zone. Further evidence is given to support the observation that the layer causing radio wave absorption during auroras is not uniform but contains ‘holes’ or regions of low absorption. The diurnal occurrence curves indicate two principal maxima. One is observed at all stations at times near local midnight. The time of the other maximum depends on the latitude of observations; it is later in the morning at the more northern locations. These two echoes exhibit different degrees of aspect sensitivity, the morning echoes having a narrower scattering polar diagram.

Radar auroral echo characteristics as seen by a 398-MHz phased array radar operated at Homer, Alaska

“…These maps are classified into types that are extensions of the 'diffuse' and 'discrete' echo types introduced by Leadabrand et al (1959) and Presnell et al (1959) for narrow beam radars. Many useful statistical studies have been made showing the diurnal and seasonal dependence of auroral echo characteristics [e.g., Unwin, 1959Unwin, , 1966Leonard, 1962; Blevis et al, 1963;Shipstone, 1969]. We show that interpretation of the occurrence of auroral echoes in terms of control by an electric field and by electron density in the radar scattering volume produces a consistent morphology of the radar aurora in relation to the other observed auroral processes.…”

“…Leonard [1962] and Unwin [1966] have shown statistically that the 50-MHz radar auroral zone extends from subauroral altitudes to polar cap latitudes. Some presunset examples are presented first together with a discussion of their characteristics especially in relation to the radar auroral echo characteristics found by previous investigators.…”

“…If this is the case, a driving force, such as an electric field, would be required in addition to the presence of significant ionization. Many useful statistical studies have been made showing the diurnal and seasonal dependence of auroral echo characteristics [e.g., Unwin, 1959Unwin, , 1966Leonard, 1962; Blevis et al, 1963;Shipstone, 1969]. Many useful statistical studies have been made showing the diurnal and seasonal dependence of auroral echo characteristics [e.g., Unwin, 1959Unwin, , 1966Leonard, 1962; Blevis et al, 1963;Shipstone, 1969].…”

Auroral orientation curves and the auroral oval I

“…The radio aurora and the visible aurora seem to be closely connected (cf. Leonard, 1962). Leonard used five auroral radars in Alaska and gave a diagram of the occurrence of radio aurora as a function of time and latitude.…”

URSI National Committee Report, XIV General Assembly, Tokyo, September 1963: Commission 3. Ionospheric Radio (7 Sections)

“…Two types of auroral sporadic E were attributed by Bates [1961 ] to least-time and aspect focusing by the same set of irregularities, in a similar way to the equatorial scatter. Leonard [1962] discussed the geographic distribution of radar auroras; Hook and Owren [1962] gave measurements of heights of E -region irregularities causing satellite scintillation in the auroral zone.…”