Substorm Electric And Magnetic Fields In The Earth's Magnetotail: Observations Compared To The WINDMI Model Pavithra Ganesh Srinivas1, Edmund A Spencer1, Sai Krishna Vadepu1 and Wendell Horton Jr2 (1)University of South Alabama, Mobile, AL, United States, (2)University of Texas at Austin, IFS and Applied Research Laboratory, Austin, TX, United States ABSTRACT INTRODUCTION Substorm 1: 9th March 2008 Substorms 2 and 3: 26th February 2008 DISCUSSION

We compare satellite observations Using ACE solar wind data and IMF data, identification of Substorm Event At 05:24:00 UT Substorm Event at 04:00:00 and 04:55:00 UT 1. For the March 9 2008 event, measurement from two different satellites, electric field from THEMIS B, and of substorm electric fields and substorm onset times from previous papers, the AL index magnetic field from THEMIS D, were used to infer onset magnetic fields to the output of a from WDC Kyoto and the SML index fom SuperMAG, we constrain the WINDMI model to trigger substorm events, times.

low dimensional nonlinear physics Volts and compare the model intermediate variables to THEMIS 2. WINDMI model electric fields and geotail currents vary over a model of the nightside longer period than the measurements. and GEOTAIL satellite data in the magnetotail. By forcing the magnetosphere called WINDMI. The 3. An extra shift of solar wind input by about 10 minutes for the electric and magnetic field satellite model to be consistent with satellite electric and magnetic mV/m March 9 2008 event and by about 5 minutes for the 26 field observations, we are able to track the magnetotail data can be used to calculate the E X THB THE February events is needed for the model prediction to B drift, which is related to energy dynamics, the field aligned current contributions, coincide with the data. intermediate variables of the energy injections into the ring current, and ensure that they nT 4. A third substorm is predicted by the WINDMI model between are within allowable limits. In addition we are able to THD WINDMI model. THE the 2 substorms on 26 February 2008. constrain the physical parameters of the model, in particular 5. Solar wind input energy is different for both substorms, in the the lobe inductance, the plasma sheet capacitance, and the 300kV range for March 9 2008, but in the 50 kV range for

The WINDMI model uses solar wind km/s

resistive and conductive parameters in the plasma sheet and THE February 26 2008. and IMF measurements from the THB ionosphere. mins mins ACE spacecraft as input into a Figure 4. Above. Panel 1 shows solar wind input (rectified VBs) calculated from ACE measurements and shifted by propagation Figure 1. Above. Panel 1 shows solar wind input (rectified VBs) calculated from ACE measurements and shifted by from L1 to the nose of the magnetosphere (69 mins.). Panel 2 and 4 show E field and ion velocity from THEMIS E located at (-9.8 propagation from L1 to the nose of the magnetosphere (49 mins.). Panel 2 and 4 show E field and Ion velocity from THEMIS RE, 4.9 RE, -5 RE). Onset is at 04:05 UT and 04:55 UT. system of 8 nonlinear ordinary B located at (-18 RE, 5 RE, -4 RE). Panel 3 shows B field from THEMIS D located at (-10 RE, 4 RE, -3 RE). Onset is at 05:24 UT. CONCLUSIONS differential equations. The state WINDMI Model variables of the differential • The WINDMI model is able to capture isolated substorm equations represent the energy ➢ An 8-dimensional state space model of the nightside activity under solar wind forcing and appropriate trigger stored in the geomagnetic tail, Magnetosphere-Ionosphere parameters associated with plasma sheet conditions. • Substorm onset time from the model depends crucially on central plasma sheet, ring current ➢ Nonlinear ODE’s result from the application of propagation delay of solar wind parameters from L1 to the and field aligned currents. The conservation laws to global energy components of the system. magnetospehere. output from the model is the ground • Substorms can be triggered under very different based geomagnetic westward ➢ Lumped nonlinear representation of magnetosphere. ➢ Kinetic effects are included in a simplified manner. magnetospheric conditions (Input energy, magnetosphere auroral electrojet (AL) index, and the dimensions, plasma parameters). Trigger conditions may The largest energy reservoirs in the magnetosphere- Dst index. depend on pre-conditioning. ionosphere system are: • A more comprehensive study of electric fields, magnetic ➢ Plasma ring current energy Wrc. fields, and particle velocities is left to future work. ➢ Geotail lobe magnetic energy Wm. ➢ The R1 FAC associated with the westward auroral mins mins Figure 2: WINDMI Model predictions compared to AL index (Kyoto WDC) and SML index (SuperMAG). Model AL peak occurs 10 Figure 5. WINDMI Model predictions compared to AL index (Kyoto WDC) and SML index (SuperMAG). Model onset occurs 5 ACKNOWLEDGEMENTS electrojet. minutes before actual AL and SML peak. minutes before onset determined from THEMIS measurements. ➢ The FAC at the lower latitude closing on the partial ring 1. Satellite data from ACE and THEMIS was obtained from NASA current. SPDF. CONTACT ➢ Kinetic energy proportional to E × B perpendicular 2. AL index was obtained from WDC Kyoto, SML index was obtained from SuperMAG. plasma flows. Pavithra Ganesh Srinivas 3. THEMIS data was analyzed using SSC BERKELY and SPEDAS ➢ Kinetic energy K parallel due to mass flows along University of South Alabama 4. NSF EPSCOR magnetic field lines. Email: [email protected] ➢ Plasma Sheet thermal energy component. Phone: +1 251-767-5833 REFERENCES 1. A.T.Y. Lui, Revisiting Time History of Events and Macroscale Interactions during The character (growth, expansion, recovery phases) is Substorms (THEMIS) substorm events implying magnetic reconnection as the strongly controlled by three equations of the model: substorm trigger, JGR, 9 March 2011, 10.1029/2010JA016078. 2. Z. Y. Pu et. al., THEMIS observations of substorms on 26 February 2008 initiated by magnetotail reconnection, JGR, 26 February 2010, 10.1029/2009JA014217.

mins 3. X. Xing et. al., Substorm onset by new plasma intrusion: THEMIS spacecraft mins Figure 3. The large scale cross-tail electric field and geotail current obtained from the WINDMI model for 9 March 2008. Figure 6. The large scale cross-tail electric field and geotail current obtained from the WINDMI model for 26 observations, JGR, 27 October 2010, 10.1029/2010JA015528. ퟑ February 2008. Model Parameters: L = 50 H, Ic = 2.1 MA, C = 8000 F, ∑ = 8 S, Ω = 4000 (푹푬)ퟑ - (1) Model Parameters: L = 50 H, Ic = 6.2 MA, C = 3000 F, ∑ = 8.8 S, Ω풄풑풔 = 4000 (푹푬) 풄풑풔 4. E. Spencer et. al., Analysis of the 3–7 October 2000 and 15–24 April 2002 geomagnetic storms with an optimized nonlinear dynamical model, 28 April - (2) WINDMI model triggers substorm about 10 minutes WINDMI model triggers first substorm about 5 minutes 2007, 10.1029/2006JA012019. before actual onset time. Solar wind input is around before actual onset time. 3 substorms occur in the 5. W. Horton et. al., A dynamical model for the coupled inner magnetosphere SM31A-2616 300 kV. model. Solar wind Input is around 50 kV. and tail, IEEE Trans. Plasma Sc. DOI 10.1109/TPS.2004.833388Volume: 32, - (3) August 2004.