Recovery Phase Of Geomagnetic Storm Research Articles

Precipitation of > 115 kev protons in the evening and forenoon sectors in relation to the magnetic activity

Data from a low altitude polar orbiting satellite, on auroral protons >115 keV in the evening and forenoon sectors, are presented. In the forenoon sector there is a weak but fairly steady precipitation at Λ ≈ 75° during quiet conditions. This precipitation is situated at higher invariant latitudes at local noon than at local dawn and can probably be ascribed to the high energy tail of the polar cleft protons. During moderately disturbed conditions, especially during the recovery phase of geomagnetic storms, there are some seemingly more “impulsive” precipitation events at Λ ≈ 65°. During very disturbed conditions these two precipitation zones in the forenoon sector seem to merge. In the evening sector a rather sharp equatorward boundary of the main precipitation, at Λ ≈ 69° during quiet conditions, varies fairly smoothly from pass to pass. South of this boundary, at invariant latitudes around 62°, there is a steady weak drizzle from the radiation belt. Due to a longitudinal effect this drizzle, as recorded by the satellite, shows a diurnal variation. The equatorward boundaries of the main precipitation at both local times move equatorward with increasing ring current strength. When D st gets less than about — 100 nT, the poleward boundaries are found to move equatorward too. From an attempt to reveal some of the substorm-dependent changes of the precipitation it is found that an equatorward shift of the precipitation areas takes place during, or just prior to, the substorm expansive phase, accompanied by a large intensity increase in the evening sector, whereas the recovery phase is linked with a poleward expansion of the precipitation at both local times.

Periodically structured Pc 1 micropulsations during the recovery phase of intense magnetic storms

The occurrence of periodically stractured Pc 1 (pPc 1) during several intense geomagnetic storms is examined in detail. Unlike unstructured or quasi- structured Pc 1, pPc 1 strongly tend to occur only during a later epoch of the recovery phase of geomagnetic storms. The available pPc 1 data, together with satellite and ionospheric data, are consistent with the idea that pPc 1 activity originates in the proton electromagnetic cyclotron instability that occurs when the high-energy tail of the ring current is brought to the stable trapping limit. This occurs in the late recovery phase when the plasmasphere has filled sufficiently from the ionosphere. Some characteristics of the observed pPc 1 activity are found to be dependent on the character of minor substorm activity occurring on the ring current recovery phase. (auth)

Decay rate of recovery phase of Geomagnetic Storms And dissipation of associated Ring Currents

Decay rates of the recovery phases of some 130 geomagnetic storms recorded at Alibag during the period 1924 to 1959, classified as great, are investigated with a view to ascertain (1) the precise relation between amplitude of depression of the main phase and the rate of decay of the recovery, phase of storm, (2) the possibility of more than one ring current being associated with each storm and (3) the solar-cycle variation in the decay rate of the recovery phase. Decay times are determined for the first 36 hours of the recovery phase by fitting an exponential curve and finding the time constant for the amplitude of the fitted curve to decay to l/e of the initial amplitude. As a second method, free-hand smooth curves are drawn best fitting the 36-hourly depressions and picking up the time for the initial amplitudes, given by the fitted curve, to decay to 1/2 its initial value. The recovery phase appears to have two distinct portions, an initial portion of less than 12 hours with a rapid decay rate and a later portion with a slower decay rate, suggesting the possibility of two ring currents being associated with each storm. Decay rates for the two portions of the recovery phase are separately investigated by the method of free-hand smooth curves. The generally known characteristic that decay rates are faster for the larger intensity storms is seen, but considerable scatter in decay rates is observed for any storm-intensity group. The scatter is less for decay rates of the initial portion 01 the recovery phase. There is a clear tendency, especially for storms of more than 200y (main-phase depression, for decay rates to be faster for the solar minimum epoch than for the maximum epoch. But the relative rates are far from the factor 3 expected by Dessler et al. This factor is, however, approached if extreme values of recovery rates of the initial portion of the recovery phase only are considered. For the later portions of the recovery phase no significant differences in decay rates are observed for the two solar epochs. Currents of the order of 101 amperes are associated with the inner ring current, which is considered large enough to produce shielding effects on the outer ring current field. The main phase depression appears, therefore, to be largely the effect of the inner ring current, especially for the large intensity storms.

On recovery phase of geomagnetic storms and dissipation of ring currents

On recovery phase of geomagnetic storms and dissipation of ring currents