New insights on geomagnetic storms from observations and modeling Page: 4 of 7
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primarily one long-term enhancement on 22 April (Figure 1c) during the main phase of the CME-driven storm. This
enhancement peaks at hour -34.5 using UNH-IMEF model, and at hour ~40.5 using V-S or VS-SAPS models. In
contrast, several short-term intensifications occur during 24 October (Figure Ig) corresponding to the increase of the
convection strength and plasma sheet density during the main phase of this HSS-driven storm. The convection
potential predicted with UNH-IMEF model is smaller and leads to a smaller injection rate than using VS or VS-
SAPS model during both storms.
VS Model vs' (a M __V odel r (e
ad- _ VS SAPS --- __ VS d-SAe n I VS-SAPS
2_ 3 - U H -----UNH E - 2 30 UNH-IM F
* (c). ()
C I j
-50 - ..VS ModeI -4 - -50- ...VSModoI -
- 02 - UNH-IMEF - -TOO - .......UNII-IMEF-
Dxl in dex ....-Moos jred Dsi .- ---.. Dxt indo x ___ joosurod DsI
-0 . . .. .. . . . . . ... -150
0 24 48 72 " 24 48 72
Hours after 00 UT. April 21. 2001 ItourS .1kr 00 UT. Oxlobor 23. 2002
FIGURE 1. (a, e) Polar cap potential drop obtained with the Volland-Ste _ model (dashed line), Volland-Ste model including
SAPS (dash-dotted blue line), and the UNH-IMEF model (solid red line). (b, t) Nightside plasma sheet ion density at
geosynchronous orbit. (c, g) Calculated ring current injection rate using V-S model (dashed), VS-SAPS model (dash-dotted), and
UNH-IMEF model (solid). (d, h) Computed Dst index using the three model formulations compared with measured Dsz (starred
line) and Dxi (dash-dot-dotted green line) indices. The left panels (a), (b), (c), and (d) refer to the April 2001 storm, while the
right panels (e), (0, (g), and (h) refer to the October 2002 storm.
STORM RECOVERY PHASE
The ring current decay during the recovery phase of the magnetic storm leads to the restoration of the surface
magnetic field of the Earth to its pre-storm values. Ring current particles are lost due to collisions with neutral
atoms from the upper atmosphere as well as with low-energy plasmaspheric particles, and are subject to interactions
with plasma waves. In addition, particles are lost at the dayside magnetopause when they flow out of the trapping
region [e.g., 19]. Ring current energy is deposited into the thermosphere-plasmasphere system through particle and
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Jordanova, Vania K. New insights on geomagnetic storms from observations and modeling, article, January 1, 2009; [New Mexico]. (digital.library.unt.edu/ark:/67531/metadc933491/m1/4/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.