Physics
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010jgra..11501213i&link_type=abstract
Journal of Geophysical Research, Volume 115, Issue A1, CiteID A01213
Physics
4
Magnetospheric Physics: Magnetosphere: Inner, Magnetospheric Physics: Ring Current, Magnetospheric Physics: Plasma Sheet, Magnetospheric Physics: Magnetic Storms And Substorms (7954), Magnetospheric Physics: Numerical Modeling
Scientific paper
This study investigates the role of fluctuations in the solar wind parameters in triggering a magnetic storm and assesses the storm simulation ability of the Space Weather Modeling Framework (SWMF) through a model-data comparison. The event of 22 September 1999 is examined through global magnetosphere simulations, using as input Advanced Composition Explorer (ACE) observations (4 min temporal resolution) along with running averages of this data with windows of 60, 120, and 180 min. It is noted that for this storm the model produces a two phase, fast then slow recovery phase due to a sudden drop in plasma sheet density during the interval of southward interplanetary magnetic field (IMF). Also, smoothing the input with a window larger than 60 min changes the entire magnetosphere and reduces the plasma sheet density and pressure, therefore a less intense storm develops. It is worth mentioning that the main phase (measured from Storm Sudden Commencement to minimum Dst) for this magnetic storm lasted about 3 h. This explains the change in the Dst profile for the 120 and 180 min averaged input. Averaging only IMF Bz or solar wind density reveals that all input parameters are important for the development of the storm, but Bz is the most significant. Also, comparison with Dst predictions (using the formula of O'Brien and McPherron (2000)) are presented and discussed. For all cases studied, there are no significant differences for Cross Polar Cap Potential (CPCP) in both hemispheres, while the nightside plasma sheet density shows a sharp drop when the input is averaged over 60 min or more. Our results indicate that the magnetosphere responds nonlinearly to the changes in the energy input, suggesting the need for a threshold in the amount of energy transferred to the system in order for the ring current to develop. Further increase of the energy input leads to a saturation limit where the inner magnetosphere response is no longer affected by any additional amount of energy contained within high-frequency oscillations, because the magnetospheric system acts as a low-pass filter on the interplanetary magnetic field.
Ilie Raluca
Liemohn Michael W.
Ridley A. A.
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