SA51B-0516
Probing the auroral acceleration region through ISR inversion
The power source for the aurora is known to be a Poynting flux carried by Earthward directed Alfven waves originating in the distant equatorial magnetosphere. The attenuation of this electromagnetic (EM) power in the ionosphere produces elevated ion temperatures in ionospheric E-region, which can be directly sensed by incoherent scatter radar (ISR). At altitudes of 2-3 Re above the discrete aurora, some of this EM flux is converted to electron kinetic energy (KE) flux through plasma processes that remain poorly understood. The attenuation of this KE flux in the ionosphere produces plasma density enhancements over an altitude range of ~80-300 km, which are also directly sensed by ISR. Using an appropriate forward model for the ionospheric response, ISR measurements of plasma temperature and density may be inverted to provide estimates of the causative magnetospheric power source (KE or EM) on a given flux tube. When this procedure is applied to time- dependent ISR measurements across an active auroral boundary, a unique tool emerges for investigating time- dependent energy conversion in the near-Earth magnetosphere. This paper describes a formalism for applying ISR inversion in the study of the auroral acceleration. Examples from both the Sondrestrom and the Poker Flat ISR (PFISR) facilities are presented. http://people.bu.edu/jls
SA51B-0517
Mesospheric Joule Heating During the 2003 Halloween Superstorm
A large solar flare and coronal mass ejection produced an intense geomagnetic storm on 28-30 Oct 2003, referred to as the Halloween Storm. From 6 to 10 UT on 29 Oct 2003, the Sondrestrom incoherent scatter radar (ISR) observed enhanced high-latitude D-region electron densities and electric fields between 65 and 95 km. The observations indicate discrete enhancements of electron density associated with relativistic electron precipitation and diffuse enhancements, measuring 10x1011 m-3, due to proton precipitation. Diffuse enhancements were sustained for the four hour observing period. The large electron density, in combination with co-located electric fields observed to be in excess of 70 mV/m, leads to significant electron frictional heating. Using the TIME-GCM, it is shown that Joule heating rivals chemical and solar heating in the mesosphere during the observing period. We also demonstrate a sensitivity of mesospheric Joule heating to electron temperature, requiring the re- examination of the electron energy balance in the mesosphere.
SA51B-0518
Polar E-Region Thermospheric Properties from Ion Motion Characteristics
The ion motion in the polar ionosphere deviates from the E × B plasma drift motion with descending altitude as the neutral gas density and wind exert a greater influence. The neutral gas density imposes a drag force on the ions resulting in a decrease in the ion velocity magnitude and a rotation of the ion velocity vector towards the local electric field direction. The neutral wind also affects the ion velocity in the E-region but in a less predictable manner. High-latitude incoherent scatter radar observations of ion motion indicate, at times, that the E-region ion speed can exceed the F-region E × B drift speed. This can be attributed to neutral winds. The accompanied observation of ion temperature profiles, when used with the observed ion velocity, also show vertical structure that can be attributed to neutral winds. Data from the incoherent scatter radars of Sondrestrom, Poker Flat, and EISCAT Svalbard are used to isolate contributions from the neutral gas density and winds and, in particular, to investigate the ionospheric conditions surrounding enhanced ion speed in the E-region. A global ionosphere thermosphere model (GITM) will demonstrate the impact of the thermospheric gas on the ion motion and separate the effects due to neutral gas density and wind.
SA51B-0519
Variation of TMA Optical Spectra With Altitude as Observed During the JOULE-2 and HEX-2 Rocket Experiments
During the JOULE-2 and HEX-2 rocket experiments a total of 7 rockets releasing tri-methyl aluminum (TMA) were launched from the Poker Flat Research Range. Four of the TMA trails were observed with a video imaging spectrograph located at Poker Flat: two during the JOULE-2 experiment in the 400 to 650 nm wavelength range, and two during the HEX-2 experiment in the 615 nm to 890 nm wavelength range. The spectrograph has an angular extent of about 10 degrees along the slit and a spectral resolution of 8 nm. The spectra show that the TMA emissions comprise a broadband continuum, with no significant narrowband emission or molecular band structure apparent. When spectra are compared for TMA released at different altitudes, the continuum shows no difference between 400 nm and 600 nm. However, at wavelengths longer than 650 nm, spectra from 100 km altitude show 20 to 40% greater intensity than spectra from 90 km, when normalized at 615 nm. Proposed mechanisms for photon production in TMA generally invoke a catalytic cycle of chemiluminescence reactions between AlO and O, O2, and in some cases OH and H2O. We report the quantitative variation in spectrum with altitude for TMA in these two releases, ongoing work to use (rarely calibrated) literature data on AlO chemiluminescent reactions to determine the most likely mechanism for photon production in TMA releases, and speculate on whether the spectrum of a TMA release can help reveal geophysical information in the upper atmosphere.
SA51B-0520
Neutral Wind Dynamics Measured Near the Poker Flat ISR Facility
We present a comparison between a new Fabry-Perot Interferometer at Poker Flat, AK (65.1 N, 147.5 W) and the Global Ionosphere Thermosphere Model (GITM) for 19 January 2007. An additional FPI was installed at Fort Yukon, AK (66.6 N, 145.3 W). Both the Poker Flat FPI and Fort Yukon FPI operated continuously for the winter season of 2006-2007 collecting measurements of the thermospheric winds and temperatures from the OI 630- nm emission line. The Poker FPI measurements have errors of 5-10 ms-1 and 30-35 K for quiet times and 2-4 ms-1 and 6-12 K for periods of significant 630-nm emission. GITM is a relatively new, self-consistent, first-principles model of the coupled ionosphere-thermosphere system from 100 km to 500 km. The model run for 19 January 2007 was driven by the assimilative mapping of ionospheric electrodynamics (AMIE) techniques with input data including the Poker Flat ISR, GUVI data, and magnetometers. The horizontal neutral wind flows and the temperature are compared, and both are well modeled. The two dimensional flow patterns produced by the model at 240 km altitude are consistent with the measurements made by the FPIs.
SA51B-0521
Modeling Ionospheric Outflow During a Geomagnetic Storm
Ionosheric outflow can be a significant contributor to the plasma population of the magnetosphere during active geomagnetic conditions. Most Magnetosphere-Ionosphere Coupling (MIC) models do not include this outflow in a physical manner; instead they rely on pressure gradient terms to draw plasma off the inner boundary of the magnetosphere. We present preliminary results of new efforts to model the source and effects of out-flowing plasma in the Space Weather Modeling Framework (SWMF). In particular, we use the Polar Wind Outflow Model (PWOM), a field-aligned multi-fluid polar wind code, coupled to the Ionosphere Electrodynamics (IE), and Global Magnetosphere (GM) components of the SWMF. We present our methodology for the MIC, as well as the evolution of the outflow during a geomagnetic storm.
SA51B-0522
Monte Carlo vs. Transport Equations' Description of Outflowing Fully-Ionized Ionospheric Plasma
At terrestrial high latitudes, the plasma flows along "open" field lines from the high-pressure ionosphere into the low-pressure magnetosphere. At relatively high altitudes, the plasma is fully ionized and the dominant collision mechanism corresponds to the Coulomb interaction. As the plasma flows upward, it gradually goes from a collision-dominated region into a collisionless region. Over several decades, the (fluid-like) generalized transport equations, and the (particle-based) Monte Carlo approaches evolved as two of the most powerful simulation techniques that address this problem. Each approach has its intrinsic advantages and drawbacks. For example, the transport equations' approach is relatively much more computationally efficient but its validity is questionable in the collisional-to-collisionless transition region where double-peaked velocity distribution functions can form. On the other hand, the Monte Carlo's approach can handle a wide variety of velocity distributions, but it is computationally intensive, especially deep into the collision-dominated regions. In this study, we discuss the inherent strengths and weaknesses of these two approaches as they are applied to the problem of plasma outflow at high latitudes. Special attention is given to the different techniques of improving the performance of each approach. We also discuss how these two approaches can be combined and the corresponding potential pitfalls.
SA51B-0523
Residence time of flux tubes in the auroral oval
Ion outflow helps to maintain the density of the magnetosphere by moving ions up from the ionosphere. There are two sets of mechanisms involved in producing the outflow that has been observed by satellites such as FAST. The first involves moving ions up into the energization region and the second involves the energization processes themselves. These processes, and particularly the former ones, take time to act on the flux tube to allow outflow to occur. Such a time delay raises the question: do flux tubes remain in the auroral oval long enough for these energization processes to occur? In this presentation we address this issue by presenting auroral residence times calculated by a simple flux tube trajectory model. This model uses known ion drifts (in this case from the LFM model) and a known auroral oval (in this presentation it is calculated from electron densities at the z=-2.5 pressure surface of TING) to determine how long flux tubes have been in the auroral oval. The results are presented as a contour map of residence times that can later be compared with ion outflow simulations to see if the flux tubes spend enough time in the auroral oval to produce the required ion outflows.
SA51B-0524
Enhanced Aurora and Thin, Dense, Heavy Ion Ionization Layers
Thin layers of enhanced luminosity are commonly observed during auroral displays. The enhanced luminosity occurs at altitudes where thin, dense, heavy ion layers are often observed in the E-region. Based on the spectral characteristics of the enhanced layers, it is believed that the enhanced emissions result when wave-particle interactions heat ambient electrons to energies at or above the 17 eV ionization energy of N2. We investigate instabilities that could occur in dense, heavy ion layers in the presence of strong cross-field currents that accompany electron precipitation. We present analytical studies of the cross-field current driven instability including kinetic effects, ion-neutral, and electron-neutral collisions. Electrostatic simulations have shown that the instability heats ambient electrons into a suprathermal tail that could produce enhanced emissions. We discuss the nonlinear development of the instability and compare the expected electron energy flux with typical auroral observations. http://w3.pppl.gov/~jrj/ionization.html
SA51B-0525
Seasonal study of the micrometeor input function at high latitudes using PFISR
We present a seasonal study of the micrometeor input function (MIF) at high latitudes using meteor head-echo radar observations performed with the new Poker Flat Incoherent Scatter Radar (PFISR). This flux is responsible for a number of atmospheric phenomena, one of which, may be the production of meteoric smoke which would act as a condensation nuclei in the formation of ice particles in the polar mesosphere. The observations were performed during 24 hrs periods near the summer and winter solstices and spring and autumn equinoxes, times at which the seasonal variability of the MIF is predicted to be large at high latitudes. Precise altitude and radar instantaneous line-of-sight (radial) Doppler velocity information are obtained for each of the hundreds of events detected ever day. The results to be discussed include, diurnal meteor rate curves and altitude and radial meteoroid velocity distributions. We compared observed and modeled results and find them to be in good agreement. A surprising result is that the peak of the detected meteor altitude distribution varies up to an atmospheric scale height depending on season. We will discuss if these changes are due to seasonal variability of the atmospheric temperature in the mesosphere or in the directionality of the meteoric influx.
SA51B-0526
PFISR Observations of UHF Polar Mesospheric Summer Echoes During the Summer of 2007
The Poker Flat Incoherent Scatter Radar (PFISR) has been running nearly continuously throughout the summer of 2007, which permits an unprecedented, long-term study of polar mesospheric summer echoes (PMSE) at UHF. When not being run for specific user experiments, PFISR runs in its low-duty cycle International Polar Year (IPY) mode, which, through August of 2007, consisted of a single beam looking up the local magnetic field line. IPY data were examined from May through September, and tens of instances of PMSE were identified. The first event was observed on May 24, with the occurrence of PMSE becoming more common as the summer progressed. The rates of occurrence of PMSE are compared to space shuttle launch times to investigate a possible connection. Additionally, PMSE shows a strong dependence on the level of background ionization. PMSE was observed most frequently around noon when the solar zenith angle was largest. The PMSE that was observed at night was almost always accompanied by auroral ionization. A typical event persists for twenty minutes, but events as long as eighty-five minutes were observed. Spectral widths were estimated by assuming a Lorentzian spectrum and fitting an exponential to the measured autocorrelation functions. A half power half width of 20 Hz was typical. In addition, preliminary results will be presented from a lidar/radar/AIM satellite campaign held in August.