SM33C-01
Sounding rocket wave electric field measurements with a new all-digital, ultra-low noise receiver
In February/March of 2007 the sounding rocket CHARM (Correlations of High-frequencies and Auroral Roar Measurements) will be launched from Poker Flat, Alaska. This rocket will carry the standard Dartmouth High- Frequency wave Electric field receiver (HFE), a wave-particle correlator to correlate the Langmuir waves with the auroral electrons and a new all-digital, ultra-low noise, precise-bandwidth wave electric field receiver (RX-DSP) which will attempt the first modern rocket-borne measurements of auroral roar. The RX-DSP will feature a high speed 66 MHz, 16-bit analog to digital conversion at the input and flexible programmable all-digital processing. For CHARM, two of these receivers will be flown, using mutually perpendicular double probe antennas which are both perpendicular to the rocket's spin axis, which is aligned with the earth's magnetic field. Each receiver will be tuned with an extremely sharp band pass filter to the typical frequency range of auroral roar observed at ground level in northern alaska, 2.6-2.9 MHz. These instruments will measure two components of both the wave electric and magnetic field, allowing estimation of the polarization and direction of arrival of the roar, as well as its amplitude along all points of the rocket's trajectory. Using these measurements, together with electron distribution functions and wave measurements from a ground station, this rocket experiment will serve to answer several outstanding questions about auroral HF emissions. Among these is the question of whether the intermittent nature of auroral roar observed on the ground is due to ionospheric effects or to actual temporal or spatial variations of the auroral roar source. Because ionospheric absorption of these waves is significant, accurate direct measurements with rockets are required to estimate the global power level of these emissions. The direction-finding capability of the CHARM measurements will allow ray tracing to determine the source location, which together with the amplitude data will reveal the source of the intermittency of the ground based observations. Another question CHARM measurements, specifically the direction finding, will allow us to answer concerns the source sizes of the roar emissions and their temporal variation. Furthermore, using the measurements of the electron distribution function in conjunction with the auroral roar measurements, we also hope to determine whether auroral roar is associated with auroral precipitation events such as suprathermal electron bursts or certain segments of inverted-V events or whether the roar is more favorable emitted in the upward current region or downward current region. Lastly, if the rocket penetrates the source region of the roar, the RX-DSP would give us information about the electric fields of the causative upper hybrid waves. Answers to these questions would significantly improve our understanding of auroral roar emissions, as well as highlight the capabilities and possible future uses for the RX-DSP.
SM33C-02
Magnetic Pulsation and Riometer Absorption Signatures During Two Geomagnetic Storms in Late 2006
Late in 2006 two geomagnetic storms occurred with minimum Dst of -96 nT and -187 nT on November 30 at 14 UT and December 15 at 8 UT, respectively. The occurrences and latitudinal patterns of broadband and narrowband magnetic pulsations in the Pc1-2 frequency band (0.1-5 Hz) at various latitudes in both hemispheres were compared to the signatures of riometer absorption at the same locations for these two storm intervals. We used data from Antarctic search coil magnetometers and riometers located at Halley (-62° MLAT), AGO P2 (-70° MLAT), South Pole (-74° MLAT), and McMurdo (-80° MLAT) and from Northern hemisphere sites Sondrestrom, Greenland (74° MLAT) and the seven-station Finnish chain (57° - 72° MLAT). During the main phase of the December 2006 storm and continuing into the local morning sector of the following day, Pi1-2 broadband noise was the dominant feature at all latitudes in both hemispheres and was accompanied by increased riometer absorption. Narrowband Pc1-2 waves began to occur 5 hours after minimum Dst at the lowest latitude Finnish station and 6 hours after at the higher latitude Finnish stations. The Antarctic stations, located ~5 hours MLT farther west, detected similar Pc1-2 activity 8 hours after minimum Dst. In contrast, during the November 2006 storm Pc1-2 activity occurred 3 hours after minimum Dst at Halley and not until the following day at the Finnish stations and other Antarctic stations. We believe this is a local time effect; during both storms the Pc1-2 activity occurred first at sites which were in the noon-afternoon sector. Both arrays showed continued Pc1-2 activity for 2-3 days after each storm, while broadband ULF noise and riometer absorption diminished.
SM33C-03
AKR Emissions During Magnetic Storms
It is well known that the Auroral Kilometric Radiation (AKR) is amplified during magnetic substorms, presenting a good correlation with the AE index. However, recent studies have shown that AKR disappears during the initial and main phases of some magnetic storms (MS), in spite of the large enhancements of AE index and field- aligned currents. In such cases, radiation activates strongly in the recovery phase of these MS. Observations suggest that the field-aligned electric field, which accelerates precipitating electrons and drives field-aligned currents, is not formed in the initial and main phases of MS when AKR disappears. Our objective here is to quantify AKR emissions, starting from the AKR spectrograms, and to investigate how solar wind parameters could influence these emissions during magnetic storms. In order to get such results, it was developed a numerical index based on the intensity of the auroral radiation exhibited by the dynamical spectrograms. This numerical index represents the intensity of the radiation and was called AKR index. Events for those it was possible to obtain the AKR spectrograms, space plasma parameters and the geomagnetic indices AE and Dst were selected. Among the chosen events, in some of them AKR is emitted during all the period of the storm, whereas in others AKR is not present during the initial and main phases. By analyzing these events, we found that the disappearance of AKR is related to a high density in the plasma sheet, while the space plasma parameter that better correlates with AKR is the solar wind speed.
SM33C-04
Global Hybrid Modeling of Magnetic and Energetic Particle Storms on Magnetosphere
A 2.5 dimensional hybrid model of massless fluid electrons and kinetic ions which also includes a simple ionosphere-magnetosphere coupling is used to investigate the impacts of interplanetary shocks and high energy particles presumably resulting from magnetic storms on the magnetosphere. The code is structured to model the magnetosphere dynamics of the arth-Solar wind system by utilizing a finite element mesh specifically tailored to magnetosphere's regions. It spans many hundred Earth radii in each direction (upstream, downstream, dawn and dusk). Realistic parameters characteristic of solar wind, its IMF and geomagnetic field are used. The code has been tested by its ability to predicting a magnetosphere by nitializing a dipole at equilibrium with a flow subjected to an incoming solar wind with an IMF. The tests revealed generation of a steady state bow shock, as well as dayside reconnection (for southward IMF) as well as a tail sheet formation. The interplanetary shock is generated by a sudden enhancement of the incoming IMF by an order of magnitude. This act introduced a fast MHD shock which propagated downstream and collided with the bow shock. This collision resulted not only in a steep rise in density and temperature of the bow shock, but also in the tail sheet region as the shock propagated downstream. The densities and temperatures, though, eventually relaxed to what are normal bow shock and tail values as he fast shock left the simulation domain. The sharp rise in the tail density which is insulated by geomagnetic field lines, can only be a result of kinetic effects. The results are analyzed and the role of different kinetic effects along with diagnostics discussed. The high energy flux of particles are simulated by injecting Kev to Mev range particles. These particles are raced as their trajectories are stored. The deflection angle of the incoming particles versus their incident energies and their incident latitudes are obtained for the cases in which the incident IMF points north versus southward. Both these investigations are aimed at better understanding of the transport of energy and momentum by geomagnetic storms through their resulting interplanetary shock waves and high energy particles into the inner magnetosphere. This work is supported by the NSF-ATM-0651690.