Relative Timing on Magnetospheric Substorm Onset Signatures
A unified time reference frame, T = 0, is critical in determining the correct morphology of magnetospheric dynamics associated with substorm observations, and the relative timing of onset between different substorm signatures at various locations in space is essential to the understanding of the physical mechanisms of substorm onset. In this paper we will emphasize the importance of this issue by demonstrating inconsistency among several widely used onset signatures as a substorm onset indicator. Proxies for substorm onsets used for this study include auroral breakups, sharp decreases in negative bays at high latitudes, low-latitude Pi 2 pulsations, dispersionless injections at geostationary orbits, and auroral kilometric radiation. We use the auroral breakup as the common reference frame to calibrate other substorm onset indicators. The auroral breakup is identified with ultraviolet images acquired by the ultraviolet imager aboard the Polar spacecraft. Our results, based on a typical substorm event, indicate that a sharp decrease in negative bays is associated with the overhead crossing of the auroral surge. In addition, the onset-associated Pi 2 pulsations lag behind auroral breakups by 1 min. The dispersionless plasma injection seen at the geostationary orbit, within 2 MLT from the auroral breakups, is also found to be delayed by 3 min. The auroral kilometric radiation can time the onset of an isolated auroral substorm best among others when the observational location is favorable. On the basis of the results of this study, we recommend that the auroral breakup can be best suited for the T = 0 reference time frame for magnetospheric substorm.
KeywordsInterplanetary Magnetic Field Geostationary Orbit Substorm Onset Ultraviolet Imager Magnetospheric Substorm
Unable to display preview. Download preview PDF.
- 7.Reeves, G. D., Belian, R. D., Cayton, T. C., Christensen, R. A., Henderson, and M. G., McLachlan, P. S. (1996) Los Alamos space weather data products: On line and on time, in Proc. Third International Conference on Sub.storms (ICS-3), p. 689, ESA SP-389, Noordwijk, Holland.Google Scholar
- 8.Slavin, J. A., Smith, M. F., Mazur, E. L., Baker, D. N., Hones, E. W., Jr., Iyemori, T., and Greenstadt, E. W. (1993) ISEE 3 observations of Traveling Compression regions in the Earth’s magnetotail, J. Geophys. Res., 98, 15,425.Google Scholar
- 16.Green, J. L., Gurnett, D. A., and Hoffinan, R. A. (1979) A correlation between auroral kilometric radiation and inverted V electron precipitation, J. Geophys. Res., 84, 5216.Google Scholar
- 21.Meng, C.-I. (May 1965) Polar magnetic and auroral substorms, M. S. thesis, University of Alaska.Google Scholar
- 23.Liou, K., Meng, C.-I., Lui, A. T. Y., Newell, P. T., Brittnacher, M., Parks, G., and Nosé, M. (1998) A fresh look at substorm onset identifiers, in Substorms-4, edited by S. Kokubun and Y. Kamide, Dordrecht, The Netherlands, Kluwer Academic Publishers, p. 249.Google Scholar
- 25.Reeves, G. D., Belian, R. D., and Fritz, T. A. (1991) Numerical tracing of energetic particle drifts in a model magnetosphere, J. Geophys. Res., 96, 13,997.Google Scholar