Substorms, Aurorae, and Ion Outflows I Posters
Presiding: C Kletzing, University of Iowa; J LaBelle, Dartmouth College
SM43C-01 1330h
Survey of Substorm Activity From Polar Patrol Balloons &35;8 and &35;10
The first campaign of the Polar Patrol Balloon (PPB) experiment (1st-PPB) was carried out at Syowa Station in Antarctica during 1990-1991 and 1992-1993. Based on the results of the 1st-PPB experiment, the next campaign (2nd-PPB) was carried out in the austral summer of 2002-2003. This paper will present an overview of ULF wave activity during the 2nd-PPB experiment. In that experiment, two balloons were launched for the purpose of upper atmosphere physics observation. Payloads of these 2 flights were identical with each other, and were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. Such a "Balloon Cluster" is suitable to observe temporal evolution and spatial distribution of phenomena in the ionospheric regions and boundaries that the balloons traversed during their circumpolar trajectory. Balloon separation varied from ~60 to ~500 km. More than 20 days of simultaneous fair weather 3-axis electric field data were obtained at geomagnetic latitudes ranging from sub-auroral to the polar cap. This paper will present the observations of substorms that occurred on January 25th, 2003, with emphasis on the temporal and spatial variations.
SM43C-02 1330h
Modeling of Oxygen ions in inner plasma sheet during substorms
The HENA instrument on IMAGE has observed that during substorm onset significant increases in the Oxygen energetic neutral atom (ENA) signature, while relatively small change in the Hydrogen signature. To study this phenomenon, we use a particle trajectory simulation developed by Delcourt to study the response of magnetospheric Oxygen ions to dipolarization of the geomagnetic field. Geomagnetic dipolarization is represented by temporal interpolation of the Tsyganenko 89 model between high and low levels of magnetic activity. We compare analysis of HENA measurements and simulation results.
SM43C-03 1330h
Cluster/Rapid Electron Pitch Angle Transitions During a Storm Time Substorm Event on October 07, 2002 in the Context of Global Multi-Spacecraft Observations
Electrons traveling along and perpendicular to magnetic field lines have been observed in the magnetotail at L~17 and 22MLT during the recovery phase of a storm time substorm event on October 07, 2002. Our analysis is based on data obtained from geosynchronous and Cluster satellites. According to geosynchronous measurements an electron dispersionless injection is very well correlated with a dipolar re-configuration of the magnetic field something that has been previously observed in the case of the 27 August 2001 substorm for the case of protons. The later supports the idea that electrons and in general particle injections at geosynchronous altitude are directly related to electric fields that arise from field dipolarization/current disruption. By calculating the 90 degree electron spectrum at Cluster location we find that is shifted relatively to the bidirectional one. This could either mean a) that we have a net supply of 90 degree electrons from a remote location which are drifting perpendicular to the ambient magnetic field (vertical shift of the spectrum) b) that we have a local energization and most of the gained energy is transformed to perpendicular energy (betatron acceleration, horizontal shift of the spectrum) and c) that both mechanisms are active. However, by examining the relative ratios of the bi-directional and 90 degree electrons for the selected time intervals we observed that the two populations act independently with the bi-directional electrons preserving their count rate. The later supports the idea that the spectrum shifting is due to an electron transportation perpendicular to the magnetic field by means of gradient/curvature drift from a remote location while the bi-directional electrons are most likely related with a neutral line formation.
SM43C-04 1330h
Comparisons of Thermal Electron Measurements on two Sounding Rocket Experiments
Thermal electron instruments built by the University of New Hampshire have accompanied standard instrumentation flown on a series of two sounding rocket flights, SIERRA and SERSIO. In 2002, SIERRA was launched from Poker Flat Research Range, Alaska, to 735 km into a modest substorm. The instrument response of the thermal electron detector (TED) has been studied extensively (MacDonald et al., 2004). The TED design featured a pinhole electrostatic analyzer designed to detect the flux and energy distribution of the coldest ambient ionospheric electrons. Despite positive biasing the instrument exhibited formation of a potential barrier restricting access to the thermal core. Using coincident data from other instruments information about the thermal plasma temperature, density, and spacecraft potential can be reconstructed. These data and the theories developed to examine them can be examined in conjunction with the next flight. In 2004, SERSIO was launched from Svalbard, Norway to 780 km in intense pre-storm cusp ion outflow. This payload contained two different designs for measuring thermal electrons and two identical but orthogonal top-hat thermal ion analyzers. In addition to the TED, another new instrument, the ERPA, was developed for detecting thermal electrons via an omni-directional retarding potential current collector. On the TED, the bias sweep and coating were altered to improve performance. Additionally the payload flew into sunlight whereas the previous flight was into total darkness which greatly changes the nature of the payload current balance situation. Unfortunately SERSIO data was severely limited by mechanical problems which affected instrument deployment and orientation but is still useful for this purpose. Extensive ground-based radar observations should prove useful for facilitating quantitative comparisons. The performances of the two TEDs are contrasted with the aim of identifying differences due to changes in internal instrumental parameters versus external environment parameters. Also, the two different thermal electron designs on SERSIO, the TED and the ERPA can be compared. Finally, this payload allows a complete comparison between ground-based thermal parameters and their in-situ electron and ion counterparts. This work should help us to understand more about the true nature of the potential sheath around a rocket, necessary for successful direct measurement of ionospheric thermal electrons.
SM43C-05 1330h
Ionospheric Kappa Electron Distributions
In the Earth's auroral zone at low to intermediate altitudes (2000-8000 km), plasma sheet electrons mix with colder ionospheric electrons producing a two-temperature plasma. The plasma sheet component has been shown by several researchers to have kappa distribution character rather than Manxwellian. The kappa distribution function is characterized by a Maxwellian-like core distribution with a hotter tail. We show theory and observations of the interpretation of Langmuir sweep data for the case of a kappa distribution background that suggest that the cold ionospheric plasma is also better characterized by a kappa distribution at these altitudes. We also examine the effects of these distributions on the acceleration of electrons by propagating Alfven waves.
SM43C-06 1330h
Rocket observations of auroral Z-mode emissions above and below fpe
The SIERRA sounding rocket was launched into an active substorm aurora north of Poker Flat, Alaska, on Jan 14, 2002, achieving an apogee of 735 km. Instrumentation included continuous waveform measurements of 100 kHz--5 MHz electric fields detected with a single 6-m double probe antenna which rotated in a plane containing the ambient magnetic field. A host of high frequency plasma waves occurred along the trajectory, including structured whistler mode waves at 250--500 kHz, Langmuir waves, and Z-mode waves both above and below fpe. A particularly striking example of Z-mode waves extending well below fpe occurred during the downleg, 640-690 s into the flight, at altitudes 651-584 km. In this paper, we report the amplitude, frequency range, and polarization (Δ E||/ Δ E⊥) of these waves inferred from the measurements of electric field using the spinning antenna and investigate the The relation of the signals to the local electron distribution function measured by particle instruments on the payload. Measurements of Z-mode signals well below fpe are somewhat rare at rocket altitudes. We interpret this observation in context of previous low-altitude in-situ wave measurements as well as the possible relation of these Z-mode emissions to MF-burst, a broadband radio emissions observed at ground level at 1-4 MHz.
SM43C-07 1330h
High Resolution Measurement of LF Auroral Hiss at South Pole
In December 2002, a Versatile Electromagnetic Wave Receiver (VIEW) and a new digitization system were deployed at South Pole station(-74° magnetic latitude). The motivation was to measure three types of auroral radio emissions: Auroral Roar, a relatively narrowband (Δf/f<0.1) emission near 2 and 3 times the F region ionospheric electron cyclotron frequency (fce); Auroral Hiss, a whistler mode wave emission with frequencies lower than 1MHz; and Auroral medium frequency (MF) burst, broadband impulsive radio emissions observed at ground level during the breakup phase of auroral substorms. High resolution broad band structure of those three emissions are recorded automatically at South Pole, and are crucial to our understanding the mechanism and relations of auroral radio emissions. This experiment uses a 3×3 meter square magnetic dipole antenna, located 1.7 km away from the South Pole station. A pre-amplifier is buried right below the eastern pylon of the antenna, connected by a 1.7 km long co-axial cable to a LF-HF receiver in the station. The output of the receiver is fed into the Versatile Electromagnetic Wave Receiver (VIEW) and Windows system equipped with a digitization board. Customed software was used to digitize the selected signals at 1-2 MHz. This data acquisition system was designed so that researchers at Dartmouth College can review the data from South Pole weekly and save interesting parts according to instructions sent from Dartmouth. In the year of 2004(from Jan through September), the experiment concentrated on the auroral hiss frequency band, covering either 0-500 kHz or 0-1000 kHz. With 3-6 hours window per day, VIEW captured more than 30 GBytes data of auroral hiss waveforms. Many experiments report wave forms of VLF auroral hiss at f < 30 kHz. We focused on waveforms of LF auroral hiss, typically at 100-300 kHz. At these frequencies, the hiss shows striking fine structure. We classified our LF hiss events into three different types: standard wide band feature, seen on the spectrogram as vertical straight lines several hundreds of kHz wide in frequency; patchy feature, which apprears on the spectrogram as a smeared area a couple of hundreds kHz wide and several seconds long; and discrete features, small sparse regions of emission, shown as dark spots of a few tens of kHz wide and a few tenths of a seconds long on spectrograms. We also find some cases showing that the intensity of LF auroral hiss is modulated by a frequency in the ~30 Hz range; in other words, the hiss is flickering. Auroral hiss has sometimes been considered a featureless impulsive emission; however, VLF observations have long shown structure in auroral hiss, such as hisslers for example, and our observations show that LF hiss is likewise characterized by complex structure.
SM43C-08 1330h
Numerical Simulation of Wave Energy Transport in Auroral Flux Tubes
A pseudospectral method is used to solve the three-dimensional, nonlinear reduced magnetohydrodynamic equations. The model is applied to auroral flux tubes and we investigate the development of fine scale structure through nonlinear wave coupling. Further refinements and applications, such as the inclusion of compressibility and the study of density cavity formation, are discussed.