1 Geomagnetic/Ionospheric Models NASA/GSFC, Code 692 During the early part of April 6, 2000 a large coronal “ejecta” event compressed and interacted with the magnetosphere to produce a geomagnetic storm. In the course of the storm geomagnetic models were driven by solar wind input from the ACE spacecraft in near real time. In the following we present ongoing modeling work for mid- and high-latitude geomagnetic models during this interval. D. Vassiliadis A. J. Klimas April 6-7, 2000: Predicted Dst Index “+”: Kyoto Quicklook Dst

2 Method and Database Database: 35 high-latitude ground magnetometers; magnetic indices, WIND measurements. Duration/Epoch: January-February 1995 Resolution: 1 min Model URL: Method: a) To predict an event, we identify the geomagnetic state of the high-latitude (polar and auroral) region. The state is further divided in local time bins. b) We search a geomagnetic/solar wind database for similar historical states. Use nonlinear dynamics theory to construct a local model, and obtain the future state and its stability properties. t t+  t a) b)

3 Model Output Polar view of ground field, B x comp. (Main Output) Highest latitude: 80º Lowest: 60º Derived AL, AU indices from IMAGE, MM210 chains Input to model (here: PC index used in “nowcasting” mode) Location of Min and Max disturbance in latitude and local time Electrojet currents + - Current time

4 Geomagnetic Field Prediction with a Nonlinear Dynamical Model First 10 hours of storm, April 6, 2000 Model auroral geomagnetic indices Kyoto Quicklook Indices Auroral geomagnetic field pattern Derived max, min indices from 2 magnetometer arrays Predicted AL saturates at ~-600 nT (limited by size of largest substorm currently in database.) PC index (model input)

5 Noon meridian To Sun Midnight meridian Magnetic Field (B x ) Predictions at Meridional Cross-Sections The positions of the ground magnetometers define a longitude-local-time grid. We take cross-sections at 2 meridional cross-sections of the predicted field to estimate the local equivalent currents. Negative B x due to westward electrojet and substorm current wedge Model Predictions at Midnight Time Model Predictions at Noon Positive B x due to eastward electrojet Time

6 * The April 6-7, 2000, solar wind ejecta and accompanying magnetic storm was studied as part of our developing mid- and high-latitude geomagnetic and ionospheric models. * The mid-latitude Dst index captured both the main and recovery phase of the storm rather well and thus modeled the dynamics of the magnetospheric ring current. It failed close to the peak of the storm; that may have been due to a temporary solar wind data gap, or a problem of the model. The model reproduced oscillations during the main phase which are linked to injections of particle into the ring current. * The high-latitude spatiotemporal model captured the qualitative aspects of polar cap expansion. The model database is still limited to small and moderate events, and so the model amplitude saturated quickly to -600 nT while the actual AL activity went further down to nT. We plan to increase the scope of the database. Summary