D- and E-region effects in the auroral zone during a moderately active 24-h period in July 2005

Abstract. The effects of energetic electron precipitation into the auroral region at a time of enhanced solar wind have been investigated during a continuous period of 24 h, using the European Incoherent Scatter (EISCAT) radar, an imaging riometer, and particle measurements on an orbiting satellite. The relative effects in the E region (120 km) and D region (90 km) are found to vary during the day, consistent with a gradual hardening of the incoming electron spectrum from pre-midnight to morning. Whereas the night spectra are single peaked, the daytime spectra are found to be double peaked, suggesting the presence of two distinct populations. A comparison between the radiowave absorption observed with the riometer and values estimated from the radar data shows generally good agreement, but with some discrepancies suggesting the occurrence of some small-scale features. The height and thickness of the absorbing region are estimated. Two periods of enhanced precipitation and the related radio absorption, one near magnetic midnight and one in the early morning, are studied in detail, including their horizontal structure and movement of the absorption patches. A sharp reduction of electron flux recorded on a POES satellite is related to the edge of an absorption region delineated by the imaging riometer. The observed particle flux is compared with a value deduced from the radar data during the overpass, and found to be in general agreement.

[1]  M. J. Birch,et al.  On the relations between proton influx and D-region electron densities during the polar-cap absorption event of 28-29 October 2003 , 2005 .

[2]  J. Hargreaves.  A new method of studying the relation between ionization rates and radio-wave absorption in polar-cap absorption events , 2005 .

[3]  I. McCrea,et al.  The statistical dependence of auroral absorption on geomagnetic and solar wind parameters , 2004 .

[4]  S. Kirkwood,et al.  Quantitative description of electron precipitation during auroral absorption events in the morning/noon local-time sector , 2001 .

[5]  J. Hargreaves,et al.  Co-ordinated studies using imaging riometer and incoherent scatter radar , 1997 .

[6]  J. Hargreaves,et al.  A study of substorm-associated nightside spike events in auroral absorption using imaging riometers at South Pole and Kilpisjärvi , 1997 .

[7]  J. Hargreaves,et al.  A localised co-rotating auroral absorption event observed near noon using imaging riometer and EISCAT , 1996 .

[8]  Bahram Honary,et al.  An imaging riometer for ionospheric studies , 1995 .

[9]  R. Heelis,et al.  Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF. Scientific report No. 1 , 1995 .

[10]  T. J. Rosenberg,et al.  A phased-array radiowave imager for studies of cosmic noise absorption , 1990 .

[11]  C. J. Burns,et al.  High-resolution incoherent scatter radar measurements during electron precipitation events , 1990 .

[12]  J. Hargreaves,et al.  Morning sector electron precipitation events observed by incoherent scatter radar , 1990 .

[13]  J. Hargreaves,et al.  EISCAT observations of the ionospheric D-region during auroral radio absorption events , 1986 .

[14]  J. Gledhill.  The effective recombination coefficient of electrons in the ionosphere between 50 and 150 km , 1986 .

[15]  T. Turunen,et al.  High resolution observations of D-region by EISCAT and their comparison to riometer measurements , 1985 .

[16]  J. Hargreaves.  D-region electron densities observed by incoherent-scatter radar during auroral-absorption spike events , 1980 .

[17]  J. Hargreaves.  Dynamics of auroral absorption in the midnight sector—The movement of absorption peaks in relation to the substorm onset , 1974 .

[18]  F. Mozer,et al.  Drifting energetic particle bunches observed on ATS 5 , 1974 .

[19]  J. Hargreaves,et al.  Studies of auroral radio absorption events at three magnetic latitudes—I: Occurrence and statistical properties of the events , 1967 .

[20]  J. Hargreaves.  On the variation of auroral radio absorption with geomagnetic activity , 1966 .

[21]  J. Burrows,et al.  CORRELATION BETWEEN INTENSITIES OF AURORAL ABSORPTION AND PRECIPITATED ELECTRONS , 1964 .

[22]  Syun-Ichi Akasofu,et al.  The development of the auroral substorm. , 1964 .