Browsing by Author "Cai, Xia"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Magnetotail total pressure and lobe magnetic field at onsets of sawtooth events and their relation to the solar windHuang, Chao-Song; Cai, Xia (American Geophysical Union, 2009-04-01)Sawtooth events in the Earth's magnetosphere are global, large-amplitude oscillations of energetic plasma particle fluxes at geosynchronous orbit and represent periodic magnetospheric substorms with a typical period of similar to 3 hours. Sawtooth events generally occur during magnetic storms, when the magnetosphere is continuously driven by southward interplanetary magnetic field and high-speed solar wind stream. However, it has not been well understood how the magnetotail parameters (the total pressure, the lobe magnetic field, and the tail lobe total magnetic flux) at the onset of sawtooth events are related to the solar wind driver. In this study, we conduct a statistical analysis of the magnetotail parameters measured by the Geotail satellite during sawtooth events over 1998-2006. At the onset of sawtooth events (storm-time substorms), the magnetotail total pressure and the lobe magnetic field increase with the solar wind pressure and merging electric field, and the total magnetic flux in the tail lobe increases with the merging electric field. Empirical formulas of the relationship of the magnetotail parameters at the sawtooth onset and the solar wind are derived for the first time. We have made a superposed epoch analysis. The magnetotail total pressure and lobe magnetic field take 52 min for gradual buildup and then 26 min for rapid increase before the sawtooth onset, and they decrease for 77 min after the onset. We have also compared our results with previous studies on quiet time tail behavior and isolated substorms. The magnetotail total pressure at the sawtooth onset is about three times that of the quiet time magnetotail, and the lobe magnetic field at the sawtooth onset is 8-10 nT higher than the quiet time value. The results imply that the sawtooth onset occurs when the magnetotail reaches a critical state and that the critical state depends on the solar wind parameters. Our findings provide new insights into the storm-time magnetospheric dynamics and important guidance for model simulations.
- Relationship between sawtooth events and magnetic stormsCai, Xia; Zhang, J. C.; Clauer, C. Robert; Liemohn, Michael W. (American Geophysical Union, 2011-07-01)The relationship between sawtooth events and magnetospheric substorms has been discussed extensively. However, the relationship between sawtooth events and magnetic storms has not been systematically examined. Using the sawtooth event list and magnetic storm list from January 1998 to December 2007, we investigate whether sawtooth events are storm time phenomena and whether there is a dependence on the strength and phase of storms. We have found that most of sawtooth events occur during storm time. Nevertheless, there are still 6 sawtooth events (5.4% of total events) that occur during nonstorm intervals. Sawtooth events also tend to occur during intense storms, with an occurrence rate of 63.5%. Sawtooth events can initiate during any stage of storms, however 55.9% of sawtooth events occur during the storm main phase through the time the ring current reaches its maximum strength. Therefore we conclude that sawtooth events are very often but not necessarily storm time phenomena. And not all storms contain sawtooth events. We suggest most sawtooth events occur during a special subset of storms that have just the right driving conditions to set intense, periodic, near-tail magnetic reconnection bursts.