SA42A-01 10:20h
Testing the Hill-Siscoe Model of Polar Cap Potential Saturation Using Observations From the October/November 2003 Superstorms
Under extreme conditions of the solar wind the induced cross polar cap potential in the ionosphere saturates, and this has been definitely demonstrated in recent studies. The Hill-Siscoe model (Siscoe et al., JGR-Space Physics, 2002) is the leading candidate to explain and predict the magnitude of the saturated potential as a function of the solar wind parameters and ionospheric conductivity. All the parameters in the Hill-Siscoe formula can be directly measured except for the average Pedersen conductivity, so this leaves a free parameter that may be adjusted to fit any set of observed data. In the absence of direct measurements of the Pedersen conductivity, we can use the conductivity from the AMIE procedure to test the Hill-Siscoe model. In this talk we compare the conductivity values from the AMIE runs for the October and November 2003 superstorms with the predicted conductivity values from the Hill-Siscoe model based on the observed data from the DMSP, ACE, and GEOTAIL spacecraft.
SA42A-02 10:35h
Numerical Simulations of the October-November 2003 Super Storms
We present here the results of our latest simulations of the magnetosphere and ionosphere during the period from October 29 to November 1, 2003. These results supersede our initial attempt to simulate the events of this period at the Spring Joint Assembly. We found then the extreme solar wind conditions during this period challenged not only our simulation, but also the solar wind observations. Our initial simulation, which showed many interesting features, was driven using the best solar wind values available from ACE at that time Since then, comparison of solar wind observations from ACE, GEOTAIL, and WIND, have led to a better understanding of the solar wind parameters. Using a synthesis of the ACE and GEOTAIL plasma data, we have using the Lyon-Fedder-Mobarry (LFM) global MHD code to simulate both the magnetosphere and ionosphere, with progressively larger grid resolutions. We present as well results from the CMIT model, in which the ionosphere of the LFM is replaced by the NCAR Thermosphere Ionosphere Nested Grid (TING). [This work is supported by NSF grant ATM-0120950].
SA42A-03 10:50h
Global Energy Partition During Superstorms
The geomagnetic storms of October and November 2003 as well as July 2000 were among the most significant of the past decade. The solar disturbances associated with these superstorms included strong solar flares, solar energetic particles, and coronal mass ejections. All three storms reached minimum Dst values less than -400 nT and maximum AE values greater than 3000 nT. The purpose of this presentation is to provide a quantitative examination of global energy deposition during these three superstorms in terms of ionospheric Joule heating, auroral particle precipitation, and magnetospheric ring current injection. We will compare the magnetospheric and ionospheric energy deposition with the available solar wind energy inputs to shed new light on the relative geoeffectiveness of magnetic clouds versus fast solar wind streams during superstorms. Finally, we compare the various solar energetic outputs arriving at the Earth's geospace environment in the forms of solar radiation, solar energetic particles, and solar wind kinetic and magnetic energies, and we discuss their respective impacts on the upper atmosphere.
SA42A-04 11:05h
Effect of The October-November 2003 Super-storms On Thermospheric Density and Composition
Changes in the density and composition of the neutral atmosphere create variable satellite drag, adversely affecting our ability to identify and track objects in space and to predict their re-entry into the atmosphere. There is currently limited insight into their causes, or ability to predict these density changes. In recent years, models of the coupled thermosphere-ionosphere system have been developed that identify the major contributors to the aeronomy of the upper atmosphere, and offer the potential for space-weather specification and prediction. Very little work has been done to validate the global models with large ionosphere-thermosphere data sets. Some of the uncertainty in the global first-principles models results from difficulty in accurately specifying the inputs of solar fluxes at a range of wavelengths, high-latitude particle precipitation and electric fields, and upward propagating waves and tides. Another difficulty is finding adequate data for a meaningful validation. The October-November 2003 Super-storms provide an opportunity to validate the models for extreme conditions. There are a large number of observations to help specify both the inputs to the model, and to validate the model predictions. We present accelerometer data from the GRACE mission to test our understanding and modeling of the effects of solar EUV, Joule heating and momentum forcing on thermospheric densities in the 300 - 500 km region for these storms. We also use observations from the TIMED-GUVI instrument to validate the model predictions of thermospheric composition.
SA42A-05 11:20h
Composition Change in the Lower Thermosphere during the Great Magnetic Storm of November 20 2003 from TIMED Ground-Based and GUVI Observations
While much attention has been given to the 2003 Halloween period geomagnetic storms, during the a following solar rotation a very large geomagnetic storm occurred on November 20th 2003. This storm was isolated rather than the muliple storm events which occurred during the previous month. The Ap on 11/20/03 was 150 with the Kp index reaching 9-. In contrast on the day before, 11/19/03, the Ap was 12, one of the quietest days of the month. Auroral activity continued after 11/20/03 although by 11/24/03 the Ap returned to a quiet level of 13. Here we will use dayglow and auroral measurements derived from the GUVI instrument on TIMED to study the evolution of the thermospheric [O]/[N$_2$] ratio before (Nov 19), during (Nov 20), and after (Nov 21-24) this storm.While the GUVI data will provide the global response (at similar local times) we will also use ground-based photometer and Fabry-Perot OI(5577) temperature data from instruments located at Poker Flat and Fort Yukon, Alaska to study the evolution of the composition changes as a function of local time at fixed geographic locations. This will allow a comparison of the local and global responses to a large isolated auroral event.
SA42A-06 INVITED 11:35h
Impacts of Solar Superstorms on the Earth's Middle Atmosphere
This presentation focuses on the effects of solar superstorms on the middle atmosphere, with an emphasis on the penetration depth and duration of these effects. The primary mechanism by which extreme solar events affect the middle atmosphere is via production of nitrogen oxides (NOx) after energetic particle impacts on molecular nitrogen and oxygen. The NOx catalytic cycle is the primary loss mechanism for ozone in the middle stratosphere, so solar storm effects that penetrate into the stratosphere play a critical role in controlling ozone distributions. Highly energetic solar protons can result in immediate NOx enhancements directly in the stratosphere, although this happens only rarely. More frequently, energetic protons and electrons lead to delayed enhancements of stratospheric NOx. That is, production of NOx first occurs in the mesosphere and thermosphere; under appropriate conditions, the NOx so produced will then descend into the stratosphere. The current status of our understanding of this type of coupling between solar storms and stratospheric composition will be reviewed. Evidence will be presented for both immediate and delayed enhancements of NOx in the stratosphere following the solar storms of October 2003. Stratospheric NOx enhancements in the northern hemisphere springtime of 2004 were unprecedented in the available satellite data sets going back to 1979, and persisted into the summer. These NOx enhancements were accompanied by unprecedented reductions in ozone. The observations of 2003-2004 will be compared to those in other years where more subtle, but often analogous, effects pertained. Areas of largest uncertainty in our understanding of the coupling between superstorms and lower altitudes will be highlighted, and needs for future measurements and modeling will be discussed.
SA42A-07 11:50h
October 29-31, 2003 geomagnetic storm: geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system
In October 30, 2003, an ongoing geomagnetic superstorm knocked down a part of the high-voltage power transmission system in southern Sweden operated by the Sydkraft company. The blackout lasted for an hour and left about 50000 people without electricity. The incident was probably the most severe GIC failure observed since the well-known March 1989 Qu\'ebec blackout and thus the problems in a Swedish system deserve a closer look. The geophysical background and the impacts on the Swedish high-voltage power transmission system of the October 29-31, 2003 geomagnetic storm are described in the study at hand. It was seen that athough no serious problems in North-America have been reported, the "three-phase" storm produced exceptionally large geomagnetic activity at the Fennoscandian auroral region. It was also seen that GIC modeled for southern Sweden region using very simplistic methods were able to explain the times of the failures in the Swedish system thus confirming the sources of experienced problems and adding also GIC to the long list of causes of technological impacts of the storm. Though the great diversity of the GIC drivers are addresses in the study, the problems in operating the Swedish system during the exceptionally intense storm of October 29-31, 2003 are attributed geophysically to substorms, SSCs and enhanced ionospheric convection all of which were creating large and complex geoelectric fields capable of driving large GIC. Based on the basic two-fold nature of the failure-related geoelectric field characteristics, a semi-deterministic approach for forecasting GIC-related geomagnetic activity in which average overall activity is supplemented with statistical estimations of the amplitudes of GIC fluctuations is suggested.
SA42A-08 12:05h
Evolution of the Aurora during the Great Geomagnetic Storm of 1859
The great geomagnetic storm of 1859 extended over a period from August 28 through to September 3 and was, arguably, the first space weather event of the modern age. The storm clearly demonstrated that the sun and aurora were connected and that auroras generated strong currents. A significant portion of the world's 140,000 miles of telegaph lines were adversely effected, many of which were unusable for a number of hours. In addition to the scientific measurements that where published, primarily in the American Journal of Science, newspapers of that era provided an untapped wealth of first hand observations giving time and location along with reports of the auroral forms and colors. Low latitude auroral events where big news for both small local and metropolitan newspapers. If the weather was clear during an auroral display, you could almost guarantee a story in the local news the next day or even a few days later. The evolution of the aurora over the great storm period will be shown and is accomplished by combining the observations from many available sources (ie: scientific observations, newspaper accounts, ship logs, and national weather services reports) in two-hour intervals. At its height, the aurora was described as a blood or deep crimson red that was so bright that one could read a newspaper by. The precipitation extended over L shells from 4 to 1.3. The implications of the configuration of the magnetosphere during the great storm will also be discussed.