SM32A-01 

The Annual Variation in Plasmaspheric Mass Density

* Menk, F W (fred.menk@newcastle.edu.au), The University of Newcastle, School of Mathematical and Physical Science, Callaghan, NSW 2308, Australia Clilverd, M A (macl@bas.ac.uk), British Antarctic Survey, Madingley Road, Cambridge, CB3 0ET, United Kingdom Grew, R S (russell.grew@newcastle.edu.au), The University of Newcastle, School of Mathematical and Physical Science, Callaghan, NSW 2308, Australia

Due to the tilt of the geomagnetic field, there is a longitude-dependent asymmetry in ionospheric solar illumination at conjugate points in winter and summer months. This difference is greatest at American longitudes, where, for example, the L=2.5 field line with footprint in Antarctica near 65^o geographic latitude and 300^o longitude, has its conjugate point at 42^o geographic latitude in the northern hemisphere. Previous VLF whistler-based and CRRES spacecraft observations have shown that plasmaspheric electron density is larger by a factor of 2.7 (at solar maximum) in December than in June at L=3.0 at American longitudes. There is a corresponding minimum in electron density at American longitudes in June. Using ground magnetometer data, we determined seasonal average ion mass densities in the equatorial plane at L=2.5 for a range of longitudes. These were compared with the annual variation in electron density and in IMAGE EUV He+ densities. This provides new insight on the seasonal/longitudinal variation in mass density, and also furnishes an estimate of the seasonal variation in plasmaspheric mass loading.

SM32A-02 

Injection of solar wind and ionospheric ions into the inner magnetosphere during storm-time substorms

* Peroomian, V (vahe@igpp.ucla.edu), UCLA-IGPP, Box 951567, Los Angeles, CA 90095-1567, United States El-Alaoui, M (mostafa@igpp.ucla.edu), UCLA-IGPP, Box 951567, Los Angeles, CA 90095-1567, United States Brandt, P C (brandpc1@jhuapl.edu), Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd., Laurel, MD 20723-6099, United States

The October 28, 2001 geomagnetic storm (minimum Dst ~-157 nT) was characterized by a number of substorms, most notably at the peak of the main phase, at ~1200 UT. We have investigated ion access to the plasma sheet and inner magnetosphere during this storm by using the large-scale kinetic (LSK) particle tracing technique and ion sources in the solar wind and in the ionosphere. The three-dimensional, time- dependent magnetic and electric fields for this calculation were obtained from a global magnetohydrodynamic (MHD) simulation that used solar wind and interplanetary magnetic field data from the GEOTAIL spacecraft. To study solar wind entry, we launched ions upstream of the bowshock beginning two hours prior to the shock arrival and continuing for twelve hours during the sudden storm commencement and the main phase of the storm, as well as the substorm that occurred at ~1200 UT. Ions were launched with the solar wind streaming velocity and thermal speed measured at that time. The outflow rates and locations of ionospheric H⁺ and O⁺ ions were specified by empirical models. H⁺ and O⁺ densities in the near-Earth plasma sheet obtained from the LSK calculations were compared with densities obtained by inverting IMAGE/HENA data, with special emphasis on the effect of the substorm on ion distributions in the inner magnetosphere.

SM32A-03 

Observations and Simulation of Drift Resonant Interactions of Energetic Particles with Pc5 pulsations

* Sarris, T E (tsarris@ee.duth.gr), LASP/University of Colorado, 1234 Innovation Drive, Boulder, CO 8030, United States * Sarris, T E (tsarris@ee.duth.gr), Demokritus University of Thrace, Vasilisis Sofias 1, Xanthi, 67100, Greece Li, X (lix@paracel.colorado.edu), Demokritus University of Thrace, Vasilisis Sofias 1, Xanthi, 67100, Greece

Both proposed acceleration mechanisms, radial diffusion and in-situ acceleration, can lead to electron flux enhancements in the outer radiation belt. In this presentation, we show evidence of flux increases during a narrow-band magnetospheric pulsation event, during which the energetic electron fluxes enhance more rapidly for those with drift frequencies close to the narrow-band pulsations. A simulation was performed to quantify and further investigate the drift resonant interaction: in the simulation an analytic model of magnetospheric fluctuations was parameterized to have characteristics similar to the observations on that day and 500.000 electrons were traced in the modeled fields. We found that the simulation results confirm a drift resonant interaction.

SM32A-04 

Observations of Magnetospherically Reflected (MR), Specularly Reflected (SR), and Back Scattered (BS) Whistler Mode (WM) Echoes Observed by Radio Plasma Imager (RPI) on IMAGE: Diagnostics of Electron Density, Density Structure, and Ion Composition

* Sonwalkar, V S (ffvss@uaf.edu), University of Alaska Fairbanks, POB 755915, Electrical and Computer Engineering Department, University of Alaska Fairbanks, Fairbanks, AK 99775, United States Reddy, A (ftar1@uaf.edu), University of Alaska Fairbanks, POB 755915, Electrical and Computer Engineering Department, University of Alaska Fairbanks, Fairbanks, AK 99775, United States Carpenter, D L (dlc@nova.stanford.edu), Stanford University, Electrical Engineering Department, STAR Laboratory, Stanford University, Stanford, CA 94305, United States Reinisch, B (bodo_reinisch@uml.edu), University of Massachusetts Lowell, Department of Environmental, Earth & Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA 01845, United States

At low altitude (<5,000-10,000 km) RPI on IMAGE has observed a variety whistler mode (WM) echoes at all latitudes at frequencies up to 300 kHz. A survey of WM echoes observed in 2004-2005 during 3.2 ms pulse transmissions in the 6-63 kHz frequency range, with a step frequency of 0.3 kHz, has revealed several new features of WM echoes and helped in their interpretation. Based on the reflection mechanism WM echoes can be classified as: magnetospherically reflected (MR), or specularly (SR) reflected, or back scattered (BS). Furthermore, based on the characteristic spectral form WM echoes can be classified as discrete, or multipath, or diffuse echoes. The MR echoes are reflected at the altitude (>1,000 km) where the local lower hybrid frequency (f_lh) is equal to the transmitted pulse frequency f. The SR echoes are reflected at the Earth-ionosphere boundary (altitude ~90 km). The BS echoes are the result of diffuse reflections from small scale plasma density irregularities close to IMAGE. The discrete WM echoes with relatively small spreading in time delays (<5-10 ms) at each frequency occur under relatively smooth plasma density variation along the geomagnetic field (B₀) passing through IMAGE. The multipath echoes with medium spreading in time delays (~ 10-30 ms) at each frequency occur when large scale (~1-10 km) field aligned irregularities (FAI) are present near (B₀). The diffuse echoes with large spreading in time delays (>30-40 ms) occur when small scale (~10 m - 100 m) field aligned irregularities (FAI) are present near (B₀). We distinguish diffuse SR and MR echoes from BS echoes. The first two undergo reflections at the Earth-ionosphere boundary and MR reflection, respectively, whereas the third one does not. Though most of the WM echoes observed in a typical RPI plasmagram can be classified as above, a significant number of echoes display characteristics of one type of echo at certain frequencies and that of other type at certain other frequencies. We provide examples of the variety of echoes (discrete, multipath, and diffuse SRWM; discrete, multipath, and diffuse MRWM; BS) observed and explain their generation mechanisms. With the help of two case studies we illustrate how observed dispersion of MRWM and SRWM echoes combined with ray tracing simulations leads to the determination of electron density, density irregularities, and ion composition along the field line passing through IMAGE.

SM32A-05 

When is it alright to use SYM-H as a storm index?

* Wanliss, J A (wanliss@hotmail.com), Space Sciences LAb, ERAU, 600 S. Clyde Morris Blvd, Daytona Beach, FL 32114, United States

Recently many scientists have begun to use the SYM-H geomagnetic index as if it is a replacement for the classic storm index, viz. Dst. However, the indices are not only different in time resolution, but also in the number and location of magnetometer stations used, and especially in the method used to convolve station data into a final index. It is certainly not an a priori given that these two indices may be used interchangeably in any operational sense. Since SYM-H has the distinct advantage of having 1-min time resolution compared to the 1- hour time resolution of Dst, it is worth determining if the differences introduced by using different ground stations and different convolution methods produce statistically significant differences in the values of the indices. We have examined data from these indices collected over more than 20 years to determine the extent to which Dst and SYM-H are equivalent or different, and discuss sources of differences. We found that a simple combination of linear trends with a break at SYM-H = -300 nT provides an excellent comparison with the Dst index. For quiet times and for small storms the deviations are typically no more than 10 nT. Moderate storms feature deviations typically only slightly more than 10 nT, and intense storms have deviations that are usually less than 20 nT. We conclude that the classic view is accurate and recommend that in future studies the SYM-H index be used as a de facto high-resolution Dst index. http://faculty.erau.edu/wanlib01/writing.html

SM32A-06 

Investigating the periodicity of sawtooth events using the Space Weather Modeling Framework (SWMF) - preliminary results

* Cai, X (xcai@umich.edu), Bradley Department of Electrical and Computer Engineering Virginia Tech, 302 Whittemore Hall, Blacksburg, VA 24061, United States * Cai, X (xcai@umich.edu), Department of Atmospheric, Oceanic and Space Science University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Clauer, C R (rclauer@vt.edu), Bradley Department of Electrical and Computer Engineering Virginia Tech, 302 Whittemore Hall, Blacksburg, VA 24061, United States Ridley, A J (ridley@umich.edu), Department of Atmospheric, Oceanic and Space Science University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Toth, G (gtoth@umich.edu), Department of Atmospheric, Oceanic and Space Science University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Liemohn, M W (liemohn@umich.edu), Department of Atmospheric, Oceanic and Space Science University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Gombosi, T I (tamas@umich.edu), Department of Atmospheric, Oceanic and Space Science University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States Kuznetsova, M M (Maria.M.Kuznetsova.1@gsfc.nasa.gov), NASA Goddard Space Flight Center, Code 674, Greenbelt, MD 20771, United States

By introducing a non-gyrotropic correction to the induction equation in a BATS-R-US simulation, it has been reported that periodic dipolarizations similar to sawtooth oscillations are seen at geosynchronous orbit in the magnetosphere. However the simulated periodicity reported is around 60 minutes, while the observed periodicity, obtained from a analysis of around 400 individual teeth, is about 180 minutes. We report here preliminary results from an investigation that examines how solar wind parameters may affect the periodicity using a series of Space Weather Modeling Framework (SWMF) simulations which includes the non-gyrotropic BATS-R-US model. We examine the effects of the external driving conditions by systematically changing the magnitude of solar wind dynamic pressure and interplanetary magnetic field (IMF) southward component (B_z) in the simulations.

SM32A-07 

How Good Are They? Comparing Commonly Used External Magnetic Field Models

* McCollough, J P (mccollou@colorado.edu), University of Colorado, Laboratory for Atmospheric and Space Physics 1234 Innovation Drive, Boulder, CO 80303-7814, United States Gannon, J L), NOAA Space Environment Center, 325 Broadway, Boulder, CO 80305, United States Baker, D N), University of Colorado, Laboratory for Atmospheric and Space Physics 1234 Innovation Drive, Boulder, CO 80303-7814, United States Gehmeyr, M), University of Colorado, Laboratory for Atmospheric and Space Physics 1234 Innovation Drive, Boulder, CO 80303-7814, United States Gehmeyr, M), NOAA Space Environment Center, 325 Broadway, Boulder, CO 80305, United States

Accurate geomagnetic field models are crucial to the study of radiation belt phenomena. We quantitatively examine the prediction capability of many external models widely in use. We study two years characterized by very different space weather conditions: 1995 and 2003. The year 1995 exhibited many high-speed streams and co- rotating interaction regions (CIRs), while 2003 included the "Hallowe"en storm," one of the most intense geomagnetic storms recently on record, caused by a coronal mass ejection (CME). The performance of each model, as measured by prediction efficiency and skill score, is evaluated as a function of magnetospheric conditions (reflected by Kp and Dst) and local time. We look in detail at when the models fail and discuss the possible reasons. Not surprisingly, the newer models tend to perform better, and interesting comparisons arise between the performances of the models during CIR- and CME-driven geomagnetic events.

SM32A-08 

Magnetospheric Energy Coupling During CIR-Driven Storms

* Turner, N E (neturner@fit.edu), Physics and Space Sciences Florida Institute of Technology, 150 W Univ. Blvd, Melbourne, FL 32901, Cramer, W D (wcramer@fit.edu), Physics and Space Sciences Florida Institute of Technology, 150 W Univ. Blvd, Melbourne, FL 32901, Laughlin, L (llaughl@clemson.edu), Clemson University, Physics Dept., Clemson, SC 29634, Mitchell, E J (mitchele@fit.edu AF:

Magnetic storms due to Corotating Interaction Regions (CIRs) have been shown to elicit different responses in the magnetosphere than those prompted by other types of solar wind conditions. In particular, recent work has shown that magnetic storms driven by CIRs deposit more energy in the ionosphere and ring current than would be expected from the electromagnetic energy input from the CIR. They appear to be more geoefficient, in the sense that the ratio of the measured energy deposited (ring current, Joule heating, and auroral precipitation) to energy input is greater than that for Coronal Mass Ejections (CMEs). In this study, we investigate this enhanced geoefficiency and also its source. We will present analysis of the differences in the solar wind during CIRs (e.g., Bz variation, solar wind speed, Mach numbers, etc.) and their possible influence on energy coupling and magnetospheric energy deposition.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.