Preparing for the Living With a Star Ionosphere-Thermosphere Storm Probe III Posters Mission III Posters
Presiding: D Bilitza, Raytheon Company; f A herrero, NASA Goddard Space Flight Center
SA23A-01 1330h
Changes in EUV created conductivity as a result of geomagnetic storms
Although much of the current flowing between the magnetosphere and the ionosphere is conducted horizontally through ionization produced by auroral precipitation, a significant amount may be conducted through ionization produced by solar UV and EUV ionization. The latter effect should be more important in the summer hemisphere where solar UV and EUV radiation can produce ionization across the polar cap. However, the importance of this solar EUV induced ionization depends on its not being changed significantly by the effects of auroral precipitation. In this talk, we use the Coupled Magnetosphere-Ionosphere-Thermosphere model to show that the conductivity associated with solar UV and EUV radiation is in fact considerably reduced during geomagnetic storms to the point where the changes produced in the system are of the same order of magnitude as the seasonal differences. Furthermore, we show that the causes of these changes occurs both as a result of a change in ion density near 120 km, and as a result of changes in ion composition from the collisionally effective O2+ to the less collisionally effective NO+. Both this change in composition and the reduction in ion densities are the result of the build up of NO during the geomagnetic storm.
SA23A-02 1330h
GPS Occultation Measurements the Post-Sunset E-Region
It has been conclusively shown that E-region conductivity is a key factor in the development of low-latitude dynamo electric fields and their effects on the ionosphere. One of the most striking features of the low latitude ionosphere is the pre-reversal enhancement of the vertical ion drifts. The associated uplift of the F-layer is connected with plasma instabilities that generate ionospheric irregularies that cause scintillation of radio signals. GPS occultation observations, which provide highly precise measures of limb total electron content, can be analyzed to provide a means of remotely sensing the E-region at the relatively low nightside densities that can be difficult to measure using traditional ground-based ionosondes. We report the results of initial statistical studies of E-region retrievals in the post-sunset time period using data from the Ionospheric Occultation Experiment (IOX) and the CHAMP GPS occultation sensor.
SA23A-03 1330h
Correlative Study of Ionopsheric Low-Latitude Electric Fields with EUV Images of the Plasmasphere
ROCSAT-1 ion drift meter and retarding potential analyzer measurements have been used to deduce low-latitude (< 35°) convective electric fields in the ionosphere. In this paper signatures of convective electric fields are compared with simultaneous EUV images of the plasmasphere from the IMAGE satellite during the recovery phase of the magnetic superstorm from 0200 - 0700 UT on July 16, 2000. The nightside profile of electric fields contains features of localized enhancement in both zonal and radial electric fields in association with density depletion and enhancement structures. EUV images have indicated the presence of plasmasphere plumes in the dusk sector from 0200 till 0530 UT and absence of plumes afterward. Through the recovery phase the radial electric field was greatly enhanced in the dayside sector and dropped off rapidly with local time in the dusk sector. The magnitude of electric fields also decreased with time, more noticeably for the radial component. For comparison with EUV images of the plasmasphere, signatures of electric fields are mapped to the equatorial plane in the inner magnetosphere. Based on the comparison, we suggest that creation of plasmaspheric plumes may depend on the ratio of zonal to radial electric fields.
SA23A-04 1330h
Formation of the large equatorial plasma depletions during superstorms by the ionosphere-thermosphere coupling effect
We investigate the formation mechanism of the severe equatorial plasma depletions during the the large geomagnetic storms of July 15, 2000, March 31, 2001, October 29, 2003, and November 20, 2003. These phenomenon has been understood as produced by the perturbation electric fields. The characteristics of the large plasma depletions observed from DMSP F15 and ROCSAT-1 show the formation of steep walls and flat bottom, deepening and widening during the night, and co-locations with plasma bubbles. These observations demonstrate that the large equatorial plasma depletions are origined at the equatorial plasma bubbles. As a widening and deepening mechanism of the bubbles, we suggest the thermospheric compositon change. That is, the molecule-rich air produced by the heating of the polar atmosphere flows along plasma bubbles and additional plasma depletion inside bubbles can create the large depletions. This idea will be validated by presenting the observations and model simulations.
SA23A-05 1330h
LWS Investigation of Middle-Latitude Topside Ionospheric Vertical Electron-Density Profiles
A Living With a Star (LWS) Targeted Research and Technology (TR&T) proposal has been selected to determine the dependence of the mid-latitude topside ionospheric electron-density (Ne) altitude distributions on long-term solar-cycle variations and short-term solar-wind and magnetic disturbances. The main focus is on Ne profiles from the height of the ionospheric Ne maximum to ~3,000 km as deduced from ISIS (International Satellites for Ionospheric Studies) topside-sounder data. These data, obtained over an 18-year time interval, can be used to investigate secular changes in the topside Ne profiles, which reflect altitude changes in plasma temperature and ion composition, over more than a solar cycle. In addition to providing average distributions the data, which extend from the O+ dominated high-altitude F region to the H+ dominated plasmasphere, provide a unique framework for delineating the altitude dependence of mid-latitude ionospheric structures associated with the plasmapause, plasmaspheric tails and Storm Enhanced Densities (SEDs). The approach used is to determine the locations of mid-latitude O+/H+ transition altitudes by fitting the topside Ne profiles with modeled H+ and O+ profiles that have the base electron temperature and temperature gradient at 400 km as variables. The investigation makes use of existing topside Ne profiles obtained from 1960's manual scaling of 35-mm film-format ionograms, available from ftp://nssdcftp.gsfc.nasa.gov/, and profiles deduced from digital topside ionograms available from http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html.
SA23A-06 1330h
Solar Activity Variations of Electron Temperature in the Topside Ionosphere
Over the past three decades a large volume of electron temperature (Te) and density (Ne) measurements has been accumulated by satellite insitu instruments as well as ground-based incoherent scatter radars. We have established a data base with the most important of the satellite measurements reaching from the early Explorers to the recent KOMPSAT and DMSP satellites and including close to 7 million data points. Using this database we have studied the variation of Te with solar activity at different altitudes, latitudes, and seasons. Whereas the electron density generally increases with solar activity at all studied altitudes, latitudes and seasons, the electron temperature can either increase, decrease or stay constant depending on the specific altitude, latitude, and season. We have compared these variations patterns with those found with incoherent scatter radar data and with those predicted by the FLIP model. Our comparisons show overall good agreement thus (i) confirming the variation patterns established by this study, (ii) showing the compatibility of the two measurement techniques, and (iii) validating the solar cycle Te predictions of the FLIP model. An important goal of this work is the inclusion of an accurate representation of Te solar cycle variations in the International Reference Ionosphere (IRI) model.
http://nssdc.gsfc.nasa.gov/space/model/ionos/iri.html
SA23A-07 1330h
How well Does the IRI/STORM Model Represent the Ionospheric Effects of the 2002-2004 Storms?
The empirical International Reference Ionosphere (IRI) model is a widely used standard for ionospheric parameters. It's most recent version includes a storm-time foF2 correction model (STORM) driven by the time-history (previous 33 hours) of magnetic activity as represented by the ap magnetic indices. The model was developed with ionosonde data from the time period prior to 2001 and reproduces the most consistent ionospheric effects of magnetic storms. An evaluation of the model with ionosonde data for the 2001 storm-time periods showed an overall improvement of IRI predictions by 50%. With the present study we are continuing this validation effort now looking at the storms during the 2002 to 2004 time period. This period includes 23 magnetic disturbance events with ap greater than 100 and 6 events with ap greater than 230. We have compared the IRI predictions against the observations from several stations distributed along different latitudes. A statistic summary of this comparison will summarize this study.
http://nssdc.gsfc.nasa.gov/space/model/ionos/iri.html
SA23A-08 1330h
Atmospheric Neutral Density Response to Geomagnetic Heating
Determination of how the Ionosphere-Thermosphere (I-T) system responds to the development and subsidence of geomagnetic storms is an ongoing area of interest in predicting the effect of atmospheric drag on satellites. We use daily estimates of neutral atmospheric density from the period 1988 to 2003, derived from observations of satellite orbital elements to investigate the effects of geomagnetic heating on the neutral density portion of the I-T system. Geomagnetic heating is estimated with a Joule heating proxy developed for the polar cap regions. We investigate changes in the atmospheric neutral density during periods of intense Joule heating to develop a simple linear relationship between the two. This relationship would be suitable for use in a short term forecast of neutral density changes during geomagnetic storms.
SA23A-09 1330h
Optimizing the Operational Use of GAIM by Varying Input Data Sets
The Global Assimilative Ionospheric Model (GAIM) has been developed since 1999 under the Multidisciplinary University Research Initiatives (MURI) program sponsored by the U.S. Department of Defense. For more than a year, the Naval Research Laboratory has been evaluating GAIM for potential application to a number of ionospheric mitigation needs. Data sets that may be ingested by GAIM include slant path (TEC) measurements from GPS ground-based receivers, bottomside electron density profiles from ground-based ionosondes, line-of-sight ultraviolet emissions and in situ electron density measurements from DoD satellites. A particular concern for the implementation of GAIM for routine density specification is the amount of data required to specify the ionosphere and the increase in processing time. This work focuses on using GAIM to estimate the point of diminishing returns for improving the density specification by increasing the amount of available data verses processing time. The quality of the GAIM specification will be evaluated against ground-truth data that was not assimilated. The results of this work will be used to determine how to maximize the use data sources available to GAIM in an operational environment. Conditions of high and low geomagnetic scenarios are considered.
SA23A-10 1330h
GAIM Derived Variations in Electron Density during Active Geomagnetic Conditions
For more than a year, the Naval Research Laboratory has been evaluating the Global Assimilation of Ionospheric Measurements (GAIM), developed by Utah State University, for potential application to a number of Navy ionospheric mitigation needs. Of particular interest is the capability of any ionospheric model to capture the variations in electron density during disturbed period of high geomagnetic activity. Within the past 18 months several significant geomagnetic storms have occurred where GPS monitoring stations have indicated large fluctuations in total electron content. The density of GPS monitoring stations over the continental United States (CONUS) provides an excellent laboratory for testing the capability of GAIM to recreate the observed ionospheric structure. This presentation focuses on the ability of GAIM to recreate the ionospheric variability observed by the GPS ground stations for several significant storms such at the October 31 2003 and the July 17 2004. For these tests, GAIM was used to assimilate a subset of the available CONUS GPS stations, in situ electron density measurements from the DMSP, and ionosondes. The output of GAIM was compared to GPS measurements that were not assimilated to verify accuracy. Further examination is given to the density of measurements required to reproduce the ionospheric variability observed during storm conditions in comparison to quiet geomagnetic conditions.
SA23A-11 1330h
Comparison of the USU GAIM ionospheric plasma densities with Arecibo ISR observations
Physics-based data assimilation models of the ionosphere were developed at Utah State University as the central part of a DoD MURI funded program called GAIM (Global Assimilation of Ionospheric Measurements). Recently, the Air Force Weather Agency (AFWA) has selected one of the USU GAIM models for its operational use and the same model will also be implemented at the Community Coordinated Modeling Center (CCMC) for scientific studies. The selected model is based on a physics-based model of the ionosphere and a Gauss-Markov Kalman Filter (GMKF) as a basis for assimilating a diverse set of real-time (or near real-time) observations. The physics-based model is the Ionospheric Forecast Model (IFM), which accounts of five ion species and covers the E-region, F-region and the topside from 90 to 1400 km altitude. Within the GMKF, the IFM derived ionospheric densities constitute a background density field on which perturbations are superimposed based on the available data and their errors. In the current configuration the GMKF assimilates slant TEC from a variable number of ground GPS sites, bottom-side Ne profiles from a variable number of ionosondes, in situ Ne from four DMSP satellites, and nighttime line-of-sight UV radiances measured by satellites. In the current application of the model the ionospheric plasma densities at F region heights obtained from our GAIM model will be compared with observed plasma densities from the Arecibo incoherent scatter radar. The emphasis of this comparison is on the observed and modeled day-to-day variability over Arecibo and its spatial extend as specified by the global and regional GAIM model. The comparison will cover several periods of Arecibo observations with both small and large day-to-day variability.
SA23A-12 1330h
First Results from the Flare Irradiance Spectral Model (FISM): a Model of Solar Vacuum Ultraviolet Irradiance Over Time Scales from Flares to Solar Cycles
The Flare Irradiance Spectral Model (FISM) is an empirical model of the solar irradiance spectrum from 0.1 to 195 nm at 1nm resolution and on a 1-minute time cadence. The goal of FISM is to provide accurate solar spectral irradiances over the vacuum ultraviolet (VUV: 0-200 nm) range as input for ionospheric and thermospheric models that are used for space weather research and operations. The FISM is based on the solar VUV irradiance measurements by the TIMED Solar EUV Experiment (SEE) and uses as proxies the solar EUV images from the SOHO EUV Imaging Telescope (EIT) and the solar X-ray irradiances from the GOES X-Ray Sensor (XRS). The FISM accounts for the significant irradiance changes due to solar flares, which includes orders of magnitude increases in the X-rays to factors of two increases in the EUV, as well as the solar cycle and solar rotational variations. The first results from FISM will be discussed, as well as the future improvements that are planned for the model.
SA23A-13 1330h
SDO-EVE: Providing Solar EUV Irradiance Measurements for LWS
The solar extreme ultraviolet (EUV: 0-125 nm) irradiance is a primary energy input for the thermosphere and ionosphere. The variability of the solar EUV irradiance ranges from several percent at some wavelengths to orders of magnitude at others, on timescales from minutes to years. This solar spectral irradiance variability can cause profound variability in the terrestrial upper atmosphere, which is why knowledge of the solar EUV irradiance is of great importance to the Living With a Star (LWS) Geospace Program. The EUV Variability Experiment (EVE) on the upcoming Solar Dynamics Observatory (SDO) mission will provide measurements of the solar EUV irradiance starting in 2008 and extending through its nominal five year mission. EVE will measure from 0.1 to 105 nm, plus the hydrogen Lyman-alpha at 121.6 nm at a time cadence of 10 seconds, with a resolution of 0.1 nm for 5-105 nm and 1 nm elsewhere, and with an accuracy of better than 25% throughout the mission. SDO will be in a geosynchronous orbit, allowing for nearly continuous measurements of the Sun. This presentation will provide an overview of solar EUV variability and will detail the EVE measurements and data products that will be made publicly available to the geospace community.
SA23A-14 1330h
The Magnesium II Index at High Spectral and Temporal Resolution
The Magnesium II core-to-wing ratio is a useful proxy for solar EUV irradiance variability. The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOLar Radiation and Climate Experiment (SORCE) has a much higher resolving power than the SBUV instruments that produce the standard NOAA Mg II index. It also has the capability of measuring the index on timescales of minutes rather than once per day. The spectral resolution affects the precision of the Mg II index and we will show how this impacts our ability to measure short-timescale changes in the solar irradiance. We will also discuss the role of higher time cadence observations on the accuracy of the index as a measure of solar irradiance variability.
SA23A-15 1330h
Comparison of Observed Lyman-Birge-Hopfield Band Emissions with Model Calculations
Comparisons of N2 Lyman-Birge-Hopfield (LBH) band observations from the Advanced Research and Global Observation Satellite (ARGOS) with model calculations provide reasonable agreement with model calculations. These comparisons also provide independently verifiable test of assumptions and rates used in the model. Fits to these high spectral resolution (~0.2 nm) observations give a v=1 to v=5 band ratio of 1.0:0.88± 0.03 at 200 km, the tangent altitude of the best measurements previously reported. This ratio agrees with the earlier observations, and it is higher than the calculated ratio. Improvements in the LBH model calculations (e.g., inclusion of more recent data for transition rates during collisions) and in the calculation of model fits to the data give significantly more accurate results than were previously available. In order for calculations to match the observations, contributions from a' and w state vibrational energy levels above the a state predissociation limit of v=6 are required. While it is well known that the a state predissociates above v=6, the amount of predissociation in the a' and w states is uncertain. These results suggest that the predissociation threshold for the a' and w states is higher than the a state.
SA23A-16 1330h
FUV Imaging for the Living With a Star Program.
Decades of global-scale terrestrial imaging from space at far-ultraviolet wavelengths have provided many examples of solar- and geomagnetic storm-driven disturbances of the ionosphere/thermosphere system. However, in most cases the monitoring of ionospheric and thermospheric emissions has been a secondary mission goal, with auroral imaging taking precedence. Only recently have routine measurements of the state of the ionosphere and thermosphere through remote FUV imaging become a top science focus of missions such as TIMED. Measurements like these, along with years of dayside and nightside measurements of the FUV emissions of atomic oxygen by IMAGE/FUV have provided the best global picture of solar flare, substorm, and magnetic storm effects on the I-T system to date. The great utility of a high-altitude global imager is to provide continuous measurements for comparisons with data from satellites in low-earth orbit making periodic in-situ measurements. This was demonstrated during the Dynamics Explorer mission of the 1980s, and more recently in coordinated studies of space weather effects in the ionosphere and thermosphere, using data from the ROCSAT 1 and CHAMP satellite missions, respectively. Examples from these and other recent studies relevant to multiple sub-disciplines of I-T science will be discussed. These examples demonstrate the relevance and value of the LWS FUV imager to the proposed LWS I-T Storm Probes mission.
http://sprg.ssl.berkeley.edu/~immel
SA23A-17 1330h
Development of a Fast Wideband Self-Impedance Probe for Ionospheric Research
In situ measurements of the local plasma impedance provide highly accurate measurements of the absolute electron density as well as information concerning the plasma temperature, neutral densities, and collision frequencies. When immersed in a plasma, a probe will source or sink a current to or from the plasma when driven with a voltage signal, depending on its excitation frequency. Theoretical models predict that at low frequencies the probe couples capacitively to the plasma. At very high frequencies (above the upper hybrid frequency) the probe again couples capacitively. In between, the probe couples inductively. By measuring the impedance as a function of frequency, it is possible to determine the resonances where the imaginary part of the impedance changes sign. From the shape of the impedance curve as a function of frequency, and from the location of these resonances, it is possible to determine the electron density, and in principle, the electron temperature and collision frequency. We present a new design for a self-impedance probe that uses a pseudo-white-noise generator to measure the impedance at all frequencies simultaneously, allowing for high spatial resolution (40 m) on typical sounding rocket flights. This impedance probe measures the complex impedance between 7 kHz and 4 MHz, corresponding to plasma densities up to 1.8 × 105 cm-3. We present diagnostic measurements, theory of operation, and results from the first flights of this instrument on two sounding rockets launched during the NASA EQUIS-II campaign from Kwajalein Atoll. During these flights, the electron density profile was determined for densities greater than about 1 × 103 cm-3. The low-frequency "series" resonance, which contains information about the electron temperature and collision frequencies, was also identified. We will also discuss instrument developments that promise to improve the instrument's performance in the future.
SA23A-18 1330h
Laboratory Validation of the Ram Wind Sensor for the CINDI Mission of Opportunity
The ram wind sensor (RWS) is one of two components of the neutral wind meter instrument that is a key element in the Coupled Ion-Neutral Dynamics Investigation (CINDI). CINDI is a mission of opportunity that will fly on the Air Force's Communications/Navigation Outage Forecast System (C/NOFS) satellite, which is slated to launch in the fall of 2005. An engineering development model of the RWS instrument has been tested in a neutral beam facility at the Goddard Space Flight Center. We present the results of these tests using both argon and xenon neutral beams with velocities on the order of 3 kilometers/second. The test results illustrate the general form of the current-voltage characteristics expected from the flight instrument, and illustrate the basic validity of the measurement technique.
SA23A-19 1330h
Thermospheric Neutral Density, Composition and Winds from the AFRL ADS Experiment
Accurate measurements of the atmospheric composition and winds are critical to development of physical models for satellite drag forecasts. However, these measurements have been extremely sparse. The AFRL ADS (Atmospheric Density Specification) experiment provides the first set of accurate, high-resolution composition, neutral density and winds measurements as well as ion composition to address critical science questions needed to forecast geomagnetic storm variations using physical models. Two flight proven, uniquely complementary in-situ sensors measure a complete high-resolution, high-accuracy parameter set to drive and validate atmospheric models. The AFRL ADMS (Atmospheric Density Mass Spectrometer) instrument provides accurate density and neutral composition data as well as ionosphere measurements. A neutral winds sensor, ACME (Anemometer Crosstrack Measurement Experiment) will be supplied by the University of Texas at Dallas. The ADS data will be critical to physical model studies since they provide the quantities of prime interest with high accuracy and high temporal and spatial resolution. ADS will permit separation of the wind and density effects on drag; particularly important during geomagnetic storms when wind surges propagate equatorward. The full complement of data will support improved assimilation models and greatly improve constraints on the thermospheric driver estimation processes. ADS is planned for launch on board an Air Force satellite in summer 2005.
SA23A-20 1330h
Multi-point Measurements in the Ionosphere-Thermosphere System Enabled by the NASA Goddard Small Deflection Energy Analyzers (SDEA)
Based on laboratory tests and simulations of our small deflection energy analyzer (SDEA), it is now possible to obtain the neutral and ion parameters in the ionosphere-thermosphere system with a 500 gram instrument suite that uses less than 1 W of power. This suite will provide the neutral wind vector and neutral temperature, the ion-drift vector and ion temperature, and the neutral composition and ion composition with sensitivity from 120 to 600 km altitude and time resolution of about 0.1 to 5 seconds (spatial resolution 1 to 40 km). An additional instrument, a magnetometer, will require an additional 100 grams with 100 mW power. With these figures it is possible to formulate a realistic approach to a nanosat having roughly 10 times the mass of the instrument payload, That is, a nanosat with total mass about 10 kg or less, with an average power about 5 W. We will present the results of our formulation for a mission of 5 nanosats whose goal is to demonstrate that a) scientific measurements are possible with the new technology, and b) the cost level and fabricability would support a future mission of 100 or more nanosats at or below current mission cost levels. The 5 nanosats in the first mission will provide simultaneous coverage of all the Ionosphere-Thermosphere parameters measured by the instrument suite and magnetometer at 5 different altitudes from 120 to about 500 km and many latitude-longitude-local time combinations.