Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998-99

Abstract

The temporal and spatial behaviour of the ionospheric parameters foF2 and h'F during isolated substorms are examined using data from ionospheric stations distributed across Europe and western Asia. The main purpose is finding the forerunners of the substorm disturbances and a possible prediction of these disturbances. During the period from March 1998 to March 1999, 41 isolated substorms with intensities I = 60 - 400 nT were identified and studied. The study separated occasions when the local magnetometers were affected by the eastward electrojet (positive substorms) from those influenced by the westward electrojet (negative substorms). The deviations of the ionospheric parameters from their monthly medians (ΔfoF2 and Δh'F) have been used to determine the variations through the substorm. Substorm effects occurred simultaneously (< 1 h) across the entire observatory network. For negative substorms, ΔfoF2-values increase > 6 h before substorm onset, T0, reaching a maximum 2-3 h before T0. A second maximum occurs 1-2 h after the end of the substorm. The Δh'F values 3-4 h before T0 have a small minimum but then increase to a maximum at T0. There is a second maximum at the end of the expansion phase before δh'F drops to a minimum 2-3 h after ending the expansion phase. For positive substorms, the timing of the first maximum of the δfoF2 and δh'F values depends on the substorm length - if it is longer, the position is closer to T0. The effects on the ionosphere are significant: ΔfoF2 and Δh'F reach 2-3 MHz (δfoF2 = 50-70% from median value) and 50-70 km (δ h'F = 20-30% from median value), respectively. Regular patterns of occurence ahead of the first substorm signature on the magnetometer offer an excellent possibility to improve short-term forecasting of radio wave propagation conditions.