The Ground-level Enhancements of 1989 September 29 and October 22

Abstract

During the solar maximum of 1989-91 an un-recedented sequence of 13 cosmic ray ground-level ELECT E I--enhancements (GLEs) was observed by the world-wide MAR 3 01994 neutron monitor network. Of particular interest Were two OLEs observed by the Australian network. The 1989 , September 29 event was the largest GLE in the space era F while the October 22 GLE included an highly anisotropic precursor peak. Analysis of both these OLEs. calking into account disturbed geomaeonetic conditions, shows that the oarTicle arrivals at the earth were unusual. The September 29 GLE had significant particle propagation in the reverse direction and as the particle flux decreased following the peak the spectrum also softened. In contrst. the 1989 October 22) precursor exhibited extreme anisotropy while the particles involved in the main OLE showed a complex temporal structure possibly indicating multiple particle injection at the solar acceleration region.

Possible effect of extreme solar energetic particle events of September–October 1989 on polar stratospheric aerosols: a case study

“…These SEP events were among the strongest ones in the 22nd solar cycle (Duldig et al, 1993;Lovell et al, 1998). On the other hand, the atmospheric conditions were monitored by several spaceborne instruments during that period, making a detailed case study possible.…”

Modeling ground level enhancements: Event of 20 January 2005

“…The functions that are being used have been chosen as to represent the physical processes involved in the particle rigidity distribution and propagation as well as the responses of the atmosphere to energetic solar particle fluxes. A special method for calculating the NM response during a solar proton event has been developed over many years [ Shea and Smart , 1992; Humble et al , 1991; Duldig et al , 1993] and it is described by Cramp et al [1997]. During the 1990s, significant improvements of the modeling have included more accurate calculations of the effect of the Earth's magnetic field on the particle arrival [ Flückiger and Kobel , 1990] using better and more complex representations of the field [ Tsyganenko , 1989].…”

Intense Ground-Level Enhancements of Solar Cosmic Rays During the Last Solar Cycles

“…they appeared less impulsive). An interesting remark arising from this analysis is that if we compare the flare coordinates with the time profiles of GLE45 and GLE70 we should expect the opposite picture, with the time profile of GLE45 being the sharpest one since its related flare is located near the foot point of the garden hose (Parker spiral) field line (Duldig et al, 1993). The fact that the event GLE45 took place during a medium disturbed condition, K p = 4, should also be taken into consideration for this difference in the profiles, since the direction of the garden hose field line and the foot point at the Sun may vary considerably when the interplanetary conditions deviate from the quiet case (Duldig et al, 1993).…”

“…An interesting remark arising from this analysis is that if we compare the flare coordinates with the time profiles of GLE45 and GLE70 we should expect the opposite picture, with the time profile of GLE45 being the sharpest one since its related flare is located near the foot point of the garden hose (Parker spiral) field line (Duldig et al, 1993). The fact that the event GLE45 took place during a medium disturbed condition, K p = 4, should also be taken into consideration for this difference in the profiles, since the direction of the garden hose field line and the foot point at the Sun may vary considerably when the interplanetary conditions deviate from the quiet case (Duldig et al, 1993). More information about the acceleration mechanisms of these events could be deduced after a comparison of the ground-based time profiles of the neutron monitors with observations of electromagnetic radiations from the Sun at different wavelengths Masson et al, 2009) but this could be a difficult procedure, especially when the interplanetary conditions are not quiet, as for example in the case of GLE45.…”

“…The event started approximately at 11:40 UT on the ground and some evidence revealed the possibility of the two-peak structure that was reported by Mathews and Venkatesan (1990) and . An analysis of this event together with the event of 22 October 1989, which recorded an increase in cosmic ray intensity higher than 150%, can be found in Duldig et al (1993).…”