- Open Access
Forbush decrease of June 8, 1969: Causes of the unusually long recovery
Earth, Planets and Space volume 53, pages993–999(2001)
The cosmic-ray decreases and interplanetary disturbances, that occurred at 1 AU during the period, June 8–July 21, 1969, have been investigated by using the cosmic-ray intensity data recorded with ground-based monitors at Mt. Washington and Deep River, as well as the Interplanetary Magnetic Field (magnitude and direction) and the Solar Wind Plasma bulk speed, density and temperature at 1 AU. We observed a two-step Forbush decrease on June 8–9, 1969, which was due to the structure within the shock and sheath preceding the interplanetary coronal mass ejection. We also observed two cosmic-ray depressions on June 16–20 and July 13–15, 1969, which were attributed to a long-lived corotating high-speed solar wind stream. The outward propagating interplanetary shock waves that occurred at about 0700 UT on June 16, 1969, and at about 1400 UT on July 13, 1969 and which were associated with the long-lived corotating high-speed solar wind stream, most probably swept away the galactic cosmic rays, causing the delay in the Forbush decrease recovery at 1 AU, and, hence, the unusually long recovery of the two-step Forbush decrease at 1 AU with onset on June 8, 1969. The additional depressions by the interplanetary shocks associated with the long-lived corotating high-speed solar wind streams which were superposed on the recovery phase of the Forbush decrease of June 8, 1969, were shown to be larger on the lower energy galactic cosmic-ray particles, and therefore the duration of the recovery phase would be much longer in the lower energy region, an expectation which is consistent with the observations.
Barnden, L. R., The Large-scale magnetic field configuration associated with Forbush decreases, Proc. 13th Int. Cosmic-Ray Conf. 2, 1277, 1973.
Burlaga, L. F., E. Sittler, F. Mariani, and R. Schwenn, Magnetic loop behind an interplanetary shock; Voyager, Helios, and IMP 8 observations, J. Geophys. Res., 86, 6673–6684, 1981.
Cane, H. V. and I. G. Richardson, Cosmic-Ray decreases and solar wind disturbances during late October 1989, J. Geophys. Res., 100, 1755, 1995.
Cane, H. V., I. G. Richardson, T. T. Von Rosenvinge, and G. Wibberenz, Cosmic-Ray decreases and shock structures: A multispacecraft study, J. Geophys. Res., 49, 21429, 1994.
Fluckiger, E. O., Solar and terrestrial modulation, Proc. 22nd Intern. Cosmic-Ray Conf., 5, 273–291, 1991.
Gold, T., Energetic particle fluxes in the solar system near the earth, Astrophys. J. Suppl. Ser., 4, 406, 1960.
Ifedili, S. O., Solar modulation of cosmic-ray albedo neutrons, Astrophys. Lett., 15, 49–54, 1973.
Ifedili, S. O., Spacecraft measurement of Forbush decreases in the cosmic radiation, Solar Phys., 168, 195–203, 1996a.
Ifedili, S. O., Forbush decreases in the cosmic-ray albedo neutron flux, J. Geomag. Geoelectr., 48, 1025–1031, 1996b.
Ifedili, S. O., Forbush decreases in the cosmic radiation: Measurement of the extent of the modulating region, Planet. Space Sci., 45, 511–514, 1997.
Ifedili, S. O., Cosmic ray decreases and interplanetary disturbances during early November 1969, Planet. Space Sci., 47, 267–272, 1999.
Iucci, N., M. Parisi, and G. Villoresi. The change in the long-term modulation function of cosmic-rays in 1969, J. Geophys. Res., 79, 659–660, 1974.
Kadokura, A. and A. Nishida, Two dimensional modeling of the cosmic-ray storm, J. Geophys. Res., 91, 13–29, 1986.
King, J. H., Interplanetary medium Data Book-Appendix, NSSDC/WDC-A-R & S 77–04a, September, 1977a.
King, J. H., Interplanetary medium Data Book, NSSDC/WDC-A-R & S77-04, September, 1977b.
Lockwood, J. A., Forbush decreases in the cosmic radiation, Space Science Reviews, 12, 688–715, 1971.
Lockwood, J. A., J. A. Lezniak, and W. R. Webber, Change in the 11-year modulation at the time of the June 8, 1969. Forbush decrease, J. Geophys. Res., 77, 4839–4844, 1972.
Lockwood, J. A., W. R. Webber, and H. Debrunner, The rigidity dependence of Forbush decreases observed at the earth, J. Geophys. Res., 96, 5447–5455, 1991.
Nishida, A., Numerical modeling of the energy spectrum of the cosmic ray Forbush decrease, J. Geophys. Res., 88, 785–791, 1983.
Parker, E. N., Interplanetary Dynamical Processes, Intersciences, John Wiley & Sons, New York, 1963.
Richardson, I. G., G. Wibberenz, and H. V. Cane, The relationship between recurring cosmic ray depressions and corotating solar wind streams at 1 AU: IMP 8 and Helios 1 and 2 anticoincidence guard rate observations, J. Geophys. Res., 101, 13483, 1996.
Zhang, G. and L. F. Burlaga, Magnetic clouds, Geomagnetic disturbances, and cosmic ray decreases, J. Geophys. Res., 93, 2511–2518, 1988.
About this article
Cite this article
Ifedili, S.O. Forbush decrease of June 8, 1969: Causes of the unusually long recovery. Earth Planet Sp 53, 993–999 (2001) doi:10.1186/BF03351696
- Interplanetary Magnetic Field
- Magnetic Cloud
- Neutron Monitor
- Solar Wind Plasma
- Forbush Decrease