Earth Planets Space, Vol. 59 (No. 8), pp. e29-e32, 2007E-LETTER
P. T. Jayachandran1 and J. W. MacDougall2
1Physics Department, University of New Brunswick, Fredericton, New Brunswick, Canada
2Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
(Received December 20, 2006; Revised June 13, 2007; Accepted June 18, 2007; Online published August 8, 2007)
A recent study by Jayachandran et al. (Geophys. Res. Lett., 30, 2064, 2003) reported repeated and detectable changes in the polar cap convection associated with substorms. We report here our use of ionospheric convection measurements to determine the time scales of growth, expansion, and recovery/reconfiguration associated with the substorms. The average time scales, determined from polar cap convection, associated with growth, expansion, and recovery are 31.6, 22.4, and 38.8 min, respectively. A comparison of the growth and expansion time scales determined from the convection measurements with those determined from the geosynchronous satellite measurements revealed interesting differences. The growth time scale determined from the ionospheric convection measurement is smaller than that of the time scale determined from geosynchronous measurements, whereas the expansion time scale determined using the ionospheric convection is much larger than that of the time scale determined using the geosynchronous measurements. The implications of the results in the Magnetosphere- Ionosphere (M-I) coupling are discussed.
Key words: Magnetosphere-ionosphere interactions, plasma convection, polar cap phenomena, storms and substorms, polar ionosphere.