SA51B-1129
Coherent Scatter Imaging Radar Observations: Insights Provided By a New Tool for Studies of Midlatitude Sporadic E and Quasi-Periodic Echo Structures
The development of the coherent scatter radar imaging technique has provided a unique new tool for studying the structure of plasma irregularities in the ionosphere. This in-beam or aperture synthesis technique was applied extensively in an experiment carried out in June and July 2002 on the island of St. Croix in the Caribbean in which the coherent scatter looked westward toward the island of Puerto Rico. In particular, the imaging radar instrumentation was used in conjunction with the Arecibo Observatory incoherent scatter radar to study the horizontal and vertical spatial structure in quasi-periodic echoes associated with sporadic E layers located over Puerto Rico. The imaging technique has provided new measurements with unprecedented resolution that show both the spatial structure and movement of the irregularities. The St. Croix observations show that the quasi-periodic structures are localized in the vertical and horizontal directions. Although there is a slight preference for propagation along the northeast to southwest direction, other propagation directions also occur. Especially when viewed in the context of recent rocket and radar experiments, such as the SEEK 2 experiment that was carried out in Japan, the St. Croix data provide an important new perspective on the dynamics associated with the quasi-periodic echo structures. The types of measurements that can be provided by the imaging technique will be presented, and the observations of quasi-periodic echo structures will be analyzed in the context of other recent rocket and radar experiments.
SA51B-1130
Predicting Equatorial Ionospheric Densities and Scintillation -- a Challenging Aeronomy Frontier
There is a strong space weather need to forecast ionospheric density and irregularities. The Communication / Navigation Outage Forecasting System (C/NOFS) Mission of the Air Force Research Laboratory has been designed for that purpose. The C/NOFS satellite, scheduled for launch in February 2006 into a low inclination (13°), elliptical (~ 375 x 710 km) orbit, is the main component of the C/NOFS Mission. Complementary ground-based measurements are also part of the Mission. C/NOFS sensors will measure the following parameters: ambient and fluctuating electron densities; ion and electron temperatures; neutral winds, AC and DC electric and magnetic fields. C/NOFS will also be equipped with a GPS occultation receiver, and a radio beacon. Models have been developed that ingest C/NOFS satellite and ground based data in order to forecast the ambient ionosphere and scintillation regions. This talk will present pre-C/NOFS validation efforts, as well as validation plans for the C/NOFS era. Ion drift measurements at the magnetic equator (Jicamarca, Peru) are used as input for some of the pre-C/NOFS validation runs. Close to Jicamarca, the density model can provide a reasonable agreement with the ground truth data, at least during geomagnetically quiet times. Specifying density at other latitudes, however, is not always easy. Forecasting these densities is even more difficult. Several factors contribute to this problem. In particular, the difficulty in specifying and predicting drivers such as electric field, neutral wind, and neutral composition hampers the model accuracy. These studies clearly demonstrate the need for improved measurements of ionospheric and thermospheric parameters in the equatorial regions, and improved ability to forecast the ionospheric drivers. Collaborative C/NOFS observations using ground and space-based observations will provide tools to improve our predictive capability.
SA51B-1131
Modeling shear flow and postsunset stability in the equatorial {\em F} region ionosphere
Sounding rocket and Altair radar data taken during the NASA EQUIS-II campaign on Kwajalein in August, 2004, are incorporated into a computational model of the electrodynamics of the low-latitude ionosphere. The purpose is to understand and quantify sources of the strong shear flow observed in the bottomside {\em F} region around and after sunset and to assess its influence on postsunset stability and the production of equatorial spread {\em F}. Possible sources of shear include 1) zonal electric fields on flux tubes with significant Hall conductivity, as are responsible for driving the equatorial electrojet, 2) zonal winds on flux tubes with significant Pedersen conductivity, as drive the {\em E} and {\em F} region dynamos, 3) vertical winds, a largely unknown quantity, and 4) vertical boundary currents forced from above or below the flux tube in question. The model solves for the electrostatic potential in three dimensions as a function of the background conductivity, background electric field, and the winds. We do not assume equipotential field lines but instead solve for the potential exactly using a multigridded solver. Shear flow may destabilize the postsunset ionosphere through a collisional shear instability related to electrostatic Kelvin Helmholtz [{\it Hysell and Kudeki}, 2004]. Assessing the viability of the instability requires us to identify and rank in importance the sources of the shear.
SA51B-1132
Mid-Latitude Thermosphere-Ionosphere Storm Response: An Aeronomy Frontier
The primary descriptions of the large scale thermosphere and ionosphere system have been based on micro-scale aeronomy processes, i.e., atomic and molecular chemistry and physical interactions, whose outcomes are then redistributed by macro-scale processes to describe regional morphologies as well as vertical stratification of the plasma environment. To a large extent the redistribution processes are understood but almost always represented by climatological drivers, i.e., neutral atmosphere -"MSIS"; neutral winds -"Hedin HWM"; auroral ionization and energy deposit ion - "Hardy"; convection and joule heating - "Weimer". Even when first principles physics models represent these drivers the models inherent space-time resolution reduces their descriptions to smoothed morphologies. A consequence of these shortcomings is that when the FAA studied mid-latitude ionospheric knowledge to design their WAAS system a major piece of ionosphere extreme weather was missed, with eventual adverse effects. This identifies a significant aeronomy frontier. This presentation emphasizes the mid-latitude regions aeronomy drivers that probably have a significant role to play in resolving our lack of knowledge. Both observations and model results will be presented to highlight why these suggested drivers are geo-effective. The consequence and hence observational requirements will be outlined. Since these conclusions depart significantly from the prevailing explanations of how mid-latitude storm aeronomy operates, specific contrasts will be made between these explanations again using observations and model results.
SA51B-1133
Dippers, Constellations, and Mappers -- Satellite Orbits and Multiple Satellite Configurations to Significantly Advance our Knowledge of the Earth's Ionosphere and Thermosphere
Direct measurements using in situ probes have been at the forefront of aeronomy research since the earliest satellite and rocket-borne measurements of the upper atmosphere. The most effective in situ measurement packages are those that gather simultaneous measurements of comprehensive gas properties (density, composition, temperature, and velocity of both the neutral and ionized species), electrodynamic parameters (DC and AC electric fields and magnetic fields), and energetic charged particle populations including both electrons and ions from suprathermal to higher energies. Although satellite measurements are essential for revealing the numerous physical plasma and neutral gas processes at work in the upper atmosphere and how they are related to the magnetosphere above and the troposphere below, there remain many critical regions of the earth's upper atmosphere that have not yet been sampled, or have been sampled very poorly. Chief among these is the lower ionosphere/thermosphere (below 200 km), where our direct knowledge of the energy transfer and dissipation, winds, electrodynamics, and chemistry are practically non-existent. The lower ionosphere remains very much a 'frontier' within geospace for which our knowledge base is poor and for which critical measurement inputs for models of the ionosphere/thermosphere system are not available. Multiple satellite missions in the ionosphere/thermosphere region are expected to revolutionize our knowledge of aeronomy in the earth's ionosphere/thermosphere system. Examples of new missions concepts, including some that are already far advanced in the NASA formulation stage, include: (1) constellations of identical satellites (e.g., GEC) that will be flown in a variety of configurations to provide information on the neutral and plasma scales and how they interact, couple, and dissipate energy; (2) missions with simultaneous orbits along different longitudes (e.g., I-TSP, Ionospheric Mappers) that promise to provide critical information at different local times which are essential to understand the large scale/global extent of key physical processes; and (3) multiple satellites in elliptical orbits within the same orbit plane but with diametrically opposed major axes (e.g., Tropical Coupler) which will provide the simultaneous measurements at different altitudes needed for understanding the chemistry, gravity wave, and electrodynamic structuring within the I-T system with respect to altitude. This talk will present a variety of new mission concepts involving in situ probes and discuss the most critical areas in aeronomy for which such measurements promise to significantly advance our knowledge and understanding. We discuss the trade space and challenges of optimizing orbit and platform selection given the restrictions imposed by both finite resources as well as the physical laws of motion which govern satellite orbits.
SA51B-1134
Non-linear Response of foF2 to solar activity and the Resulting Impacts on Derived Trends.
Trends in the foF2 layer may offer clear indications of climate change or give insight into the impact of the solar cycle on the lower atmosphere. For both inquiries, the influence of the solar cycle on the foF2 data needs to be characterized appropriately. Years with higher solar activity result in higher foF2. However, detailed investigation shows that the response of foF2 can be notably non-linear with both positive and negative second derivatives observed in data. These results are qualitatively independent of solar proxy used. The implications of these results are large for the trends derived using the data with possible false trends and false uncertainties on the trends if the non-linearity is not appropriately included in the trend detection techniques.
SA51B-1135
IMF Control of High Latitude Electromagnetic Energy Flux
Electromagnetic energy flux is the dominant magnetospheric energy input to the dayside high latitude ionosphere-thermosphere system but it is difficult to evaluate its distribution. We use electric field estimates from SuperDARN observations and magnetic field observations from Iridium to obtain distributions of electromagnetic energy flux for a range of solar wind/IMF to characterize the variation in the distribution of energy input with driving conditions. Comparisons with DMSP derived estimates of Poynting flux along the DMSP track are used to quantify the uncertainties in the results. The distributions vary dramatically with the IMF in concert with variations in the large scale current distributions. The largest energy flux occurs between the dayside large scale currents. For strongly southward IMF, the energy flux generally has two maxima pre and post noon with a moderate flux around the auroral oval and over the polar cap. In the northern hemisphere for southward IMF but with a strong Y component, the energy flux increases in intensity and develops an arc corresponding to the convection driven by magnetopause reconnection. For positive IMF BY, this arc of energy flux extends from dusk to noon and crosses the nominal cusp region and extends into the polar cap. For negative IMF BY the arc extends from dawn to noon. The results suggest that the strongest energy flux in the cusp region occurs not for purely southward IMF but when the IMF BY component is strong. Also, since the convection associated with this energy flux has approximate mirror symmetry in the opposite hemisphere this IMF dependence will lead to asymmetric hemispherical distributions in the input energy flux.
SA51B-1136
SuperDARN-Storms: A Proposed Expansion of the SuperDARN Network to Allow Global-Scale Observations of Storm-Time Electric Fields and Plasma Convection in the Ionosphere
Recently, the Johns Hopkins University Applied Physics Laboratory in collaboration with the Goddard Space Flight Center Wallops Flight Facility began operation of a new SuperDARN radar located near the Wallops Island sounding rocket launch site. This is the prototype of a proposed expansion of the current high-latitude SuperDARN radar network to allow improved determination of the spatial and temporal evolution of storm-time convection and electric fields in the subauroral and mid-latitude ionospheres. In this paper, we present some of the exciting initial observations with the new radar and discuss how it might be extended into a global network. The global network will require international participation that has already begun. The North-American component of SuperDARN-Storms will eventually require the construction of 6 radars sited at 3 locations across the U.S.
SA51B-1137
Effects of Auroral Precipitation on Ionosphere and Thermosphere
Auroral precipitation is one important form of magnetospheric energy input to the high-latitude ionosphere and thermosphere. It has a significant impact on thermospheric chemistry, eneregics, and dynamics, as well as ionospheric electrodynamics. To illustrate the need for an accurate specification of auroral precipitation, we show how global ionospheric conductivity, plasma convection, electric currents, and Joule heating are affected by the spatial and temporal variations in auroral precipitation. Effects of auroral precipitation on the thermospheric composition and heating and on the electron density are also discusse
SA51B-1138
Toward Absolute Thermospheric Densities
New spectroscopic methods are being developed to monitor the density and composition of the thermosphere. These new measurements on GUVI and DMSP require validation by comparison with other kinds of absolute density measurements. Recent advances in our understanding of gas-surface interactions on satellite surfaces has led to the determination of improved physical drag coefficients of satellites, placing us on the threshold of deriving absolute densities. This progress provides two avenues of validation: The densities derived from the spectrometers can be compared with absolute densities inferred from (1) the drag on a satellite near the same time and place as the spectrometric measurements, or (2) the density of a model atmosphere corrected to remove the bias introduced by using inappropriate drag coefficients in the original development of the model. The advances in satellite drag coefficients have proceeded from improved knowledge of the parameters which determine the momentum transfer to the satellite: the energy accommodation coefficients and angular distributions of molecules reemitted from satellite surfaces. These parameters depend on the amount of atomic oxygen adsorbed on the satellite surface as well as on the altitude and local atmospheric temperature. We present the parameters as a function of satellite altitude and time in the sunspot cycle. An example of the removal of a bias in a thermospheric model is given in the case of the Jacchia model.
SA51B-1139
A new approach for daytime auroral observations
The brightness of the sunlit atmosphere makes auroral observation very difficult. In the past, aurora in the sunlit atmosphere has been observed from space in the EUV and FUV wavelength range, and from the ground using high spectral resolution observations of the OI(630nm) line. We propose a new technique of auroral imaging in the near IR from high altitude balloons. The sky brightness diminishes as altitude and wavelength increases. Model calculations show that the bright auroral N$_2^+$ Meinel emissions are comparable to the sunlit sky brightness above 45~km altitude. We will discuss the possibilities of daylight auroral observations and present examples of ground based nighttime and twilight auroral images that were obtained in the near IR wavelength range.
SA51B-1140
Using the Far-Infrared to Understand the Thermosphere
Atomic oxygen is the dominant constituent of the thermospheres of the Earth, Venus, and Mars. It is formed by photodissociation of a major molecular species from the lower atmosphere of each planet. Remote sensing of O greatly increases the amount of data available from each atmosphere. Several parts of the electromagnetic spectrum can be used to sense O, but the far-infrared line at 63~μm has several advantages, which we will discuss. The greatest advantage to using this line is the ability to resolve the tidal structure of the thermosphere. Using broadband radiometry to measure the limb radiance of this spectral feature will be discussed in the context of the OPIE (Oxygen Profiling Infrared Experiment) instrument. Some thoughts on the optimal orbit for these instruments with be presented.
SA51B-1141
Future directions for ITM imaging
Remote sensing of the Earth's ionosphere-thermosphere-mesosphere photon emissions has been one of the workhorse tools for Aeronomic research. With the access of space in the 1960s, the window of wavelengths opened wider. As a consequence new insights have been gained of the relationship and coupling of the space above and the atmosphere below this region. Even as this area of research has matured, significant and compelling questions remain unresolved. This talk will address significant and compelling questions that remain open and what role remote sensing plays in helping resolve them. Possible directions for future technology and implementation strategy will be explored.
SA51B-1142
Calculating Martian Auroral Emission including Strong Field Gradients and Accelerated Electron Spectra
Auroral emission has been detected at every planet in the solar system which has a known global magnetic field and a substantial atmosphere. Recent Mars Express observations have shown that auroral emission also exists on Mars, which lacks a global magnetic field but does have localized regions of strong magnetic crustal sources. Additionally, accelerated electron spectra, reminiscent of those observed in Earth's auroral region, have recently been found in data from Mars Global Surveyor. These recent developments have prompted us to revisit the question of auroral emission on Mars. Previous calculations of auroral emission on Mars have neglected the effects of strong magnetic field gradients associated with converging fields near localized crustal sources. Also, previous calculations used typical sheath or tail electron spectra rather than the newly discovered accelerated spectra. We use observed MGS electron spectra as input into a new coupled electron transport and emission model which includes realistic magnetic field gradients. We analyze the effect the strong gradients have on the electron intensity in the upper atmosphere and the resulting excitation and ionization rates and emissions. In addition, we explore the range of excitation and ionization rates and emissions due to the different classes of observed electron spectra from sheath-like, to highly accelerated, to those observed during solar energetic particle events.
SA51B-1143
Continuous, Global Ultraviolet Observations of Earth: The Future for Space Weather Observations
Developing the scientific understanding necessary to effectively address those aspects of the Connected Sun-Earth system that directly affect life and society is an important and challenging goal for the scientific community in general, and the Living With a Star (LWS) program in particular. While the Far Ultraviolet (FUV) sensors flown on satellites have made tremendous contributions to our understanding of the Earth's Space Weather, the spatial and spectral resolution of the sensors used have limited the usefulness of these observations although they have suggested the tremendous potential of global remote sensing of the Earth's upper atmosphere. Recent advances in instrument designs and fabrication techniques now allow us to overcome many of the limitations of previous FUV sensors. It is now feasible to build an FUV imager capable of providing vital measurements for understanding neutral composition, ionospheric conductivities, and electron density variations on a global scale. Combined with recent advances in modeling and analyzing FUV observations, these new measurements can be used to determine the effects of long and short term variability of the Sun on the global-scale behavior of the ionospheric electron density. These observations are especially important for understanding how the mid and low-latitude Ionosphere-Thermosphere system responds to geomagnetic storms. They are especially important for providing at least a limited context and connection between the Solar and radiation belt measurements that will come from the LWS program.