SPA-Aeronomy [SA]

SA11A
 MC:Hall D  Monday  0800h

The Equatorial Ionosphere I: Initial Results From the C/NOFS Mission, New Satellite and Ground-Based Observations, Progress in Forecast and Modeling Posters


Presiding:  V Eccles, Space Environment Corporation; N Maruyama, University of Colorado, CIRES

SA11A-1482

Community Access to the C/NOFS Satellite Data -- Facilitating New Opportunities for Space Weather Research

* Martin, S , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
de la Beaujardiere, O , Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
Hunton, D , Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
Wilson, G , Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
Roddy, P , Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
Coley, R , University of Texas, W. B. Hanson Center for Space Science, Richardson, TX 75083, United States
Heelis, R , University of Texas, W. B. Hanson Center for Space Science, Richardson, TX 75083, United States
Earle, G , University of Texas, W. B. Hanson Center for Space Science, Richardson, TX 75083, United States
Straus, P , Aerospace Corp., El Segundo Blvd., El Segundo, CA 90245, United States
Bernhardt, P , Naval Research Laboratory, Code 4780, Washington, DC 20375, United States
Bromund, K , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Candey, R , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Pfaff, R Robert.F.Pfaff@nasa.gov, NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Rowland, D , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Holzworth, R , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Holzworth, R , University of Washington, 070 Johnson Hall, Seattle, WA 98195, United States
Kessel, M , NASA Headquarters, SMD, Heliophysics Division, Washington, DC 20546, United States

The Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite was launched on April 17, 2008 into a low latitude orbit (401 by 867 km, 13 deg inclination) and is designed to understand, model, and forecast the presence of ionospheric irregularities that cause scintillations and other radiowave disruptions. Its instruments include those that sample the plasma density and temperature, DC/AC electric fields, DC magnetic fields, ion drift velocity, neutral density, and GPS occultations. A radiowave tomography experiment and a lightning detector are also included on the satellite. C/NOFS provides a tremendous opportunity to merge space-based and ground-based observations and research, while engendering comparisons with, and data input to, the latest ionospheric models and theoretical calculations and simulations. To help coordinate this research and exchange of data products, the C/NOFS satellite data will be made available to the community through the Coordinated Data Analysis web site (http://cdaweb.gsfc.nasa.gov/) that resides at the NASA/Goddard Space Flight Center. The data will be distributed via FTP, OPENDAP (data streaming), HTTP, and web services with output in CDF, ASCII listings, PDF, and PS formats. This activity is sponsored by the NASA/Living With a Star program. This data distribution web site is in addition to the main Air Force Research Laboratory web site for the C/NOFS program that is located at http://www.kirtland.af.mil/library/factsheets/factsheet.asp?id=12776 and includes links to the C/NOFS instrument web sites, ground-based research, and satellite updates. A description of the C/NOFS satellite instruments and their standard data products available to the community via the CDA web site will be provided.

SA11A-1483

The Vector Electric Field Investigation on the C/NOFS Satellite

* Pfaff, R Robert.F.Pfaff@nasa.gov, NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Acuna, M , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Kujawski, J , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Fourre, R , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Uribe, P , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Bromund, K , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Hunsaker, F , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Rowland, D , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Farrell, W , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Maynard, N , University of New Hampshire, Morse Hall, Durham, Ma 03824, United States
Holzworth, R , University of Washington, 070 Johnson Hall, Seattle, WA 98195, United States
Wilson, G , Air Force Research Laboratory, Hanscom AFB, Bedford, MA 01731, United States
Berthelier, J , CETP/IPSL, 4, Av. de Neptune, Sa, 94100, France
Steigies, C , Christian-Albrechts-Universitat, Olshausenstrae 40, Kiel, D-24098, Germany
Le, G , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Freudenreich, H , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
McCarthy, M , University of Washington, 070 Johnson Hall, Seattle, WA 98195, United States
Martin, S , CETP/IPSL, 4, Av. de Neptune, Sa, 94100, France
Martin, S , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Liebrecht, C , NASA/Goddard Space Flight Center, Mail Code 674, Greenbelt, MD 20771, United States
Liebrecht, C , Christian-Albrechts-Universitat, Olshausenstrae 40, Kiel, D-24098, Germany

We provide an overview of the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. VEFI is a NASA/GSFC instrument funded by the Air Force Research Laboratory whose main objectives are to: 1) investigate the role of the ambient electric fields in initiating nighttime ionospheric density depletions and turbulence; 2) determine the quasi-DC electric fields associated with abrupt, large amplitude, density depletions, and 3) quantify the spectrum of the wave electric fields and plasma densities (irregularities) associated with density depletions typically referred to as equatorial spread-F. The VEFI instrument includes a vector electric field double probe detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux-gate magnetometer, an optical lightning detector, and associated electronics. The heart of the instrument is the set of detectors designed to measure DC and AC electric fields that use 6 identical booms to form three orthogonal 20-m tip-to-tip double probes. Each probe extends a 12-cm diameter sphere containing an embedded preamplifier and short (30 cm) boom extensions outboard of the spheres to minimize photoelectron shadow effects. VEFI also includes a burst memory that enables snapshots of data from 1-8 channels of selected sensors to be sampled at rates of up to 32 kHz each. The bursts may be triggered by the detection of density depletions, intense electric field wave activity in a given frequency band, lightning detector pulses, or an event at a pre-determined time or location. All VEFI instrument components are working exceptionally well. A description of the instrument, its sensors, and their sampling frequencies and sensitivities will be presented. Representative measurements will be shown.

SA11A-1484

An Investigation of the Influence on Daytime and Evening Vertical ExB Drifts on the Evolution of the Nighttime Equatorial Ionization Anomaly using SAMI3

* McDonald, S E sarah.mcdonald@nrl.navy.mil, Naval Research Laboratory, Space Science Division 4555 Overlook Ave., S.W., Washington, DC 20375, United States
Coker, C clayton.coker@nrl.navy.mil, Naval Research Laboratory, Space Science Division 4555 Overlook Ave., S.W., Washington, DC 20375, United States
Dymond, K F kenneth.dymond@nrl.navy.mil, Naval Research Laboratory, Space Science Division 4555 Overlook Ave., S.W., Washington, DC 20375, United States

It has recently been suggested that E region dynamo winds that enhance daytime vertical ExB plasma drifts are the mechanism by which tides generated in the lower atmosphere couple with the F region ionosphere. But it is well known that nighttime ionospheric densities are significantly affected by the pre-reversal enhancement of the ExB drifts, which is primarily driven by the F region dynamo. In this work we investigate the relative contributions of the daytime and evening vertical ExB drifts to the nighttime plasma distributions in the low-latitude F region ionosphere under both solar minimum and maximum conditions. We perform simulation runs using the NRL SAMI3 (Sami3 is Also a Model of the Ionosphere), a three-dimensional physics-based model of the ionosphere, and modulate the vertical velocities of the daytime and prereversal enhancement of the plasma drifts to investigate the effects on the density and separation of the Equatorial Ionization Anomaly (EIA) crests. The role of F region neutral winds is also explored. We discuss our results in light of recent observations of longitudinal variations in the EIA attributed to non-migrating tides generated in the troposphere.

SA11A-1485

The Ionosphere and Atmosphere Between 400 km and 800 km : Initial Observations from the CINDI - C/NOFS During Solar Minimum.

* Heelis, R A heelis@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Earle, G A earle@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Coley, R R coley@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Power, B R power@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Perdue, M R perdue@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Hairston, M R hairston@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Lippincott, R R lippinco@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Harmon, L R harmon@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Holt, B R bjholt@texas-skies.com, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States
Haaser, B rah054000@utdallas.edu, University of Texas at Dallas, PO Box 830688, Richardson, TX 75025, United States

The CINDI project is being conducted as part of the payload for the C/NOFS satellite. Ion and neutral sensors on the C/NOFS satellite will make measurements of the variations in neutral and ion densities and drifts between 400 km and 800 km altitude and between -13 and 13 degrees latitude. This presentation will contain a brief description of the instrumentation and the measurement capabilities. During the initial period of CINDI operations the solar activity is very low with the F10.7 cm flux being below 68 W/cm2/s. Under these conditions the neutral atmosphere is contracted below the satellite perigee, thus limiting the diagnostic capability of the measurements. However, this presentation will illustrate what we can learn from the initial data. In the ionosphere examination of the data between 400 km and 800 km altitude allow the relationships between ion composition and dynamics to be investigated. This presentation will describe our initial findings in this area.

SA11A-1486

C/NOFS Validation Study: Comparison of In-Situ CORISS and PLP Electron Density Measurements

* Bishop, R L Rebecca.L.Bishop@aero.org, The Aerospace Corporation, 2350 E. El Segundo Blvd. M2/260, El Segundo, CA 90245,
Straus, P R, The Aerospace Corporation, 2350 E. El Segundo Blvd. M2/260, El Segundo, CA 90245,
Roddy, P , Air Force Research Laboratory, 29 Randolph Rd, Hanscom AFB, MA 01731-301,
Hunton, D E, Air Force Research Laboratory, 29 Randolph Rd, Hanscom AFB, MA 01731-301,

The C/NOFS satellite, launched April 16, 2008, contains a GPS receiver that performs routine occultation measurements. The C/NOFS Occultation Receiver for Ionospheric Sensing and Specification, CORISS, measures total electron content (TEC) along the line-of-sight between C/NOFS and occulting GPS satellites. Vertical density profiles are typically obtained from the TEC values by applying several assumptions and the Abel Transform. One of the assumptions, setting the electron density to zero at the topside of the profile precludes measuring the density values at the satellite. In this paper we describe a modified technique first developed by Synderdaard et al. [2004] to extract electron density values at the satellite. The extracted values are then validated against the on-board Plasma Langmuir Probe measurements. Reference: Syndergaard, S., D. C. Hunt, W. S. Schreiner, C. Rocken, In Situ Electron Density in Low Earth Orbit From Radio Occultation Data, presentation, American Geophysical Union Conference, 2004.

SA11A-1487

Post-Midnight Density Irregularities Observed by the Planar Langmuir Probe on C/NOFS

* Roddy, P A patrick.roddy@hanscom.af.mil, Air Force Research Laboratory, 29 Randolph rd, Hanscom AFB, MA 01731, United States
Hunton, D donald.hunton@hanscom.af.mil, Air Force Research Laboratory, 29 Randolph rd, Hanscom AFB, MA 01731, United States

The Planar Langmuir Probe (PLP) on C/NOFS measures in-situ ion number densities. PLP has routinely observed highly structured plasma densities in the post-midnight equatorial ionosphere since it began making measurements in early May, 2008. Relatively few disturbed regions have been observed directly following sunset. These disturbed regions are not uniformly distributed in longitude, with African and Australian sectors seeing the most activity. We will discuss the nature of these disturbances and possible mechanisms for their production.

SA11A-1488

COSMIC Observations of the Diurnal Variation of Longitudinal Structure in the Equatorial Ionization Anomaly

* Dymond, K F kenneth.dymond@nrl.navy.mil, Space Science Division, 4555 Overlook Ave., SW Naval Research Laboratory, Washington, DC 20375, United States
Budzien, S A scott.budzien@nrl.navy.mil, Space Science Division, 4555 Overlook Ave., SW Naval Research Laboratory, Washington, DC 20375, United States
McDonald, S E sarah.mcdonald@nrl.navy.mil, Space Science Division, 4555 Overlook Ave., SW Naval Research Laboratory, Washington, DC 20375, United States
Coker, C clayton.coker@nrl.navy.mil, Space Science Division, 4555 Overlook Ave., SW Naval Research Laboratory, Washington, DC 20375, United States
Chua, D H damien.chua@nrl.navy.mil, Space Science Division, 4555 Overlook Ave., SW Naval Research Laboratory, Washington, DC 20375, United States

We report observations of the average diurnal variability of longitudinal structure in the Equatorial Ionization Anomaly (EIA) based on electron density measurements made by the GPS Occultation Experiment (GOX) instrument aboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC/FORMOSAT-3) satellites during March 2007. We find that the longitudinal modulation of the EIA varies strongly throughout the day and that the modulation is hemispherically asymmetric, producing different longitudinal structure of the northern and southern EIA crests. Furthermore, in addition to the 4-cell pattern that has been previously observed and studied, we provide evidence of longitudinal modulations having from 1-cell through 6-cell patterns. The longitudinal modulation of the EIA is observed to continue varying post- dusk through dawn indicating that physical mechanisms other than tidal modulation of the E-region dynamo or tidal modulation of the pre-reversal enhancement of the zonal electric field may be important contributors to the modulation of the EIA.

SA11A-1489

Ion Temperature and Density Relationships Measured by CINDI from the C/NOFS Spacecraft During Solar Minimum

* Coley, W R coley@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Heelis, R A heelis@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Hairston, M R hairston@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Earle, G D earle@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Perdue, M D perdue@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Power, R A power@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Harmon, L L harmon@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Holt, B J holt1@airmail.net, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States
Lippincott, C R lippinco@utdallas.edu, W. B. Hanson Center for Space Sciences, University of Texas at Dallas, P.O. Box 830688 MS WT15, Richardson, TX 75083, United States

The Ion Velocity Meter (IVM) which is part of the CINDI instrument package on-board the C/NOFS spacecraft makes in-situ measurements of plasma temperature, composition, density, and velocity. The April 16, 2008 launch of C/NOFS coincided with the deepest solar minimum since the space age began with F10.7 cm radio fluxes in the 60-70 sfu range. Measurements taken near the spacecraftís 402 km perigee altitude indicate an unusually cold low-density ionosphere with nighttime ion temperatures at the magnetic equator reaching as low as 700 K with an [O+]/[H+] ratio of 3 and maximum daytime temperatures of 1400 K. Due to the 13° inclination of the orbit the location of the perigee advances through all local times in about 60 days. This allows seasonal sampling of ionospheric temperature, density, and composition as a function of local time, magnetic latitude, and altitude. We will present the average values of these parameters and discuss their differences from those seen under more typical conditions of solar activity.

SA11A-1490

Mapping the Topside Ion Temperature and Density Distribution with CINDI and DMSP

* Hairston, M R hairston@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Coley, W R EM: , Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Heelis, R A heelis@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Earle, G D earle@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Power, R power@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Perdue, M perdue@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Lippincott, R lippinco@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Harmon, L harmon@utdallas.edu, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States
Holt, B holt1@airmail.net, Center for Space Sciences, University of Texas at Dallas, WT15 800 West Campbell Road, Richardson, TX 75080-3021, United States

The CINDI plasma instrument package on board the C/NOFS spacecraft measures the velocity, temperature, composition, and density of the ionospheric ions. The equatorial orbit of C/NOFS is 402 by 850 km, so its apogee reaches the topside ionosphere at the same altitude as the polar-orbiting DMSP satellites which carry a similar plasma measurement package. Over the course of about 60 days the apogee of C/NOFS's orbit passes through all local times. This talk will present the apogee observations from the CINDI instruments showing the distribution of ion temperatures and densities at the local times which coincide with the four local times of the DMSP satellites' equatorial crossings (0630, 0915, 1830, and 2115 LT). Comparisons of the observations from CINDI and simultaneous DMSP observations will be used to establish the spatial and temporal gradients of the temperatures and densities at this altitude.

SA11A-1491

Equatorial Electrojet Observations in the African Continent

* Yizengaw, E ekassie@igpp.ucla.edu, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
Moldwin, M B mmoldwin@igpp.ucla.edu, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095, United States
Mebrahtu, A alemmeb@yahoo.com, Department of Physics, Mekelle University, Mekelle, 231, Ethiopia
Damtie, B bayliedamtie@yahoo.com, Washera Geospace and Radar Science Laboratory, Bahir Dar University, Bahir Dar, 079, Ethiopia
Pfaff, R Robert.F.Pfaff@nasa.gov, NASA Goddard Space Flight Center, 10208 Greenbelt Rd, Lanham, MD 20771, United States
Zesta, E Eftyhia.Zesta@hanscom.af.mil, Air Force Research Laboratory, AFRL/VSBXP, 29 Randolph Rd, Hanscom AFB, MA 01731, United States

Although Satellite observations in the African sector show unique equatorial ionospheric structures that can severely impact navigation and communication systems, the study of ionospheric disturbances in this region is difficult due to the lack of ground-based instruments. This has created a gap in global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes limitations on ionospheric density modeling efforts. Therefore, in order to have a more complete global understanding of equatorial ionosphere motion, the international space science community has begun to develop an observational infrastructure in the African sector. This includes the deployment of a number of arrays of small instruments, including the AMBER magnetometer array, through the International Heliophysical Year (IHY) cooperative program with the United Nations Basic Space Science (UNBSS) program. Two AMBER magnetometers have been deployed successfully at Adigrat (~6°N magnetic) in Ethiopia and at Medea in Algeria (28°N magnetic), and became fully operational on 03 August 2008. The remaining two AMBER magnetometers will be deployed soon in Cameroon and Namibia. One of the prime scientific objectives of AMBER is to understand the processes governing electrodynamics of the equatorial ionosphere as a function of latitude, local time, magnetic activity, and season in the African region. The most credible driving mechanism of ionospheric plasma (E × B drift) can be estimated using two magnetometers, one right at the equator and the other about 6 off the equator. Therefore, using the AMBER magnetometer at Adigrat and the INTERMAGNET magnetometer located at Addis Ababa (0.9°N magnetic) in Ethiopia, the equatorial electrojet (E × B drift) activities in that longitudinal sector of the African continent is estimated. The paper also presents the comparison between the estimated vertical drift and the drift values obtained from the vector electric field instrument observation onboard the C/NOFS satellite. The evolution of equatorial ionospheric irregularities will also be presented using data from the growing number of ground- and space-based (on Low-Earth-Orbit (LEO) satellites) GPS receivers in the African region.

SA11A-1492

C/NOFS Daytime ExB Drift Velocity Measurements Compared With Ground-based Magnetometer-inferred ExB Drift Velocity Observations in the Peruvian Sector

* Anderson, D N david.anderson@noaa.gov, NOAA/SWPC, 325 Broadway, Boulder, CO 80303, United States
Heelis, R heelis@utdallas.edu, Univ. of Texas Dallas, MS WT15, P.O. Box 830688, Richardson, TX 75083, United States
Pfaff, R F robert.f.pfaff@nasa.gov, NASA/GFSC, Code 696, Greenbelt, MD 20771, United States

A technique to determine realistic, daytime, vertical ExB drift velocities in the equatorial, ionospheric F-region has recently been developed. It has been established that taking the difference in the horizontal components (ÄH) between a ground-based magnetometer on the magnetic equator and one 6-9o away in magnetic latitude, provides these realistic velocities. Relationships between the ÄH values from the magnetometers at Jicamarca, Peru (1o N. mag. lat.) and Piura, Peru (6.5o N. mag. lat.) and the observed daytime ExB drift velocities from the JULIA (Jicamarca Unattended Long-term Ionosphere Atmosphere) coherent scatter radar have been developed and then applied, on a day-to-day basis, to obtain daytime, vertical ExB drift velocities between 0700 and 1700 LT in the Peruvian longitude sector. We briefly describe the ÄH-inferred ExB drift technique and demonstrate that the ÄH vs ExB drift relationship obtained in the Peruvian sector can be applied in other longitude sectors where appropriately-placed magnetometers exist. We then describe a study where we compare the ÄH-inferred ExB drift velocities obtained in the Peruvian sector with the CINDI/IVM (Ion Velocity Meter) and the DC VEFI (Vector Electric Field Experiment) observations in the Peruvian sector during the months of August, September and October, 2008. The local time of the observations range between 0900 and 1600 LT. The IVM velocity component and the VEFI electric fields perpendicular to B in the magnetic meridional plane are calculated and transformed to the apex altitude at the magnetic equator. The fact that daytime, vertical ExB drift velocities at the magnetic equator are essentially independent of altitude between 150 km and 800 km simplifies the comparisons with the ÄH- inferred ExB drift observations. It is important to validate the IVM and VEFI observations with a number of different ground-based ExB drift measurements and, while the Jicamarca ISR and JULIA are available, they are sporadic and all in one longitude sector. In contrast, the magnetometer-inferred ExB drift technique is available, continuously, day-to-day. In addition, the same technique can be used to validate VEFI and IVM daytime observations at other longitude sectors such as the Brazilian, African, Indian, Philippine and Indonesian sectors where appropriately-placed magnetometers already exist.

SA11A-1493

Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) of the November 2004 Geomagnetic Storm

* Datta-Barua, S seebany@astraspace.net, ASTRA, 12703 Spectrum Drive Suite 101, San Antonio, TX 78249, United States
Bust, G gbust@astraspace.net, ASTRA, 12703 Spectrum Drive Suite 101, San Antonio, TX 78249, United States
Crowley, G gcrowley@astraspace.net, ASTRA, 12703 Spectrum Drive Suite 101, San Antonio, TX 78249, United States
Curtis, N ncurtis@astraspace.net, ASTRA, 12703 Spectrum Drive Suite 101, San Antonio, TX 78249, United States
Reynolds, A areynolds@astraspace.net, ASTRA, 12703 Spectrum Drive Suite 101, San Antonio, TX 78249, United States

One of the current limitations to the community's understanding of ionospheric processes is knowledge of the local physical drivers responsible for the distribution of ionospheric electron density. Direct measurement of these drivers is infrequent and spatially scarce. Our ongoing goal has been to use measurements that are plentiful, such as TEC-based density specification, to infer the drivers. This technique we call Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE). The EMPIRE algorithm and validation methods, using simulated ionospheric data from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM-ASPEN) physics-based model [Crowley et al., 1999], were described by Bust et al. [2008]. The EMPIRE weighted least squares estimates of the field-aligned neutral winds in the equatorial region were in reasonable agreement with the TIMEGCM background model "true" winds. The other drivers, such as production, loss, diffusion, gravity, and drifts, were modeled as known quantities. Here we present results, based upon an improved algorithm, that estimate corrections to other physical drivers, such as diffusion, ExB drifts, production and loss, simultaneously with estimating the neutral winds. In addition, we apply the new algorithm to actual estimates of the 4D electron density field, obtained from the ionospheric data assimilation algorithm IDA4D, for a quiet day and for the November 2004 magnetic storm. The EMPIRE estimates of the field-aligned velocity terms in the continuity equation are compared to Arecibo incoherent scatter radar measurements, when available, for validation. Bust, G. S., S. Datta-Barua, G. Crowley, and N. Curtis [2008], "Estimation of neutral winds from 4D ionospheric imaging," presented at the XXIX General Assembly of the International Union of Radio Science (URSI), Chicago, IL, 7-16 Aug 2008. Crowley, G., C. Freitas, A. Ridley, D. Winningham, R. G. Roble, and A. D. Richmond, "Next Generation Space Weather Specification and Forecasting Model," Proceedings of the Ionospheric Effects Symposium, Alexandria, VA, pp 34-41, October 1999.

SA11A-1494

Global/Seasonal/Local-Time Variations of Ion Density Structure at Low-Latitude Ionosphere and Their Relationship to the Post-Sunset Irregularity Occurrences

* Su, S sysu@jupiter.ss.ncu.edu.tw, Institute of Space Science National Central University, 300 Chung-Da Road, Chung-Li, 320, Taiwan
Chen, M cmq@jupiter.ss.ncu.edu.tw, Institute of Space Science National Central University, 300 Chung-Da Road, Chung-Li, 320, Taiwan
Chao, C chchao@jupiter.ss.ncu.edu.tw, Institute of Space Science National Central University, 300 Chung-Da Road, Chung-Li, 320, Taiwan
Liu, C chliu2@gate.sinica.edu.tw, Academia Sinica, 128, Sec. 2, Academia Road, Nankang, Taipei, 115, Taiwan

Seasonal and longitudinal (s/l) variations of ion density structure at the 600-km low-latitude ionosphere observed by ROCSAT-1 between two similar solar activity years of 2000 and 2002 are examined at five different local-time (LT) sectors. The gross feature in the s/l variations of density structure is very similar to each other for these two years. A reproducibility of density structure can thus be assumed, including the shape of equatorial ionization anomaly (EIA) structure, for similar solar flux input. It is further noted that model result from either the 2006 International Reference Ionosphere (IRI) model or the thermosphere ionosphere electrodynamics general circulation model (TIEGCM) cannot reproduce the ROCSAT observed global/seasonal/local-time variations of ionospheric structure. Furthermore, the ROCSAT observed s/l variations of crest-to-trough ratio in the EIA structure fail to correlate with the s/l variations of the post-sunset irregularity occurrence rates because the magnetic declination effect that determines the post-sunset ionospheric conductivity for the ionospheric electrodynamics are not included in such s/l variations of ionospheric background density structure.

SA11A-1495

On the estimation of E-region density profiles using IDA4D and COSMIC occultations

* Nicolls, M J michael.nicolls@sri.com, SRI International, 333 Ravesnwood Avenue, Menlo Park, CA 94025,
Rodrigues, F S frodrigues@astraspace.net, Atmospheric and Space Technology Research Associates (ASTRA), 12703 Spectrum Drive Suite 101, San Antonio, TX 78249,
Bust, G S gbust@astraspace.net, Atmospheric and Space Technology Research Associates (ASTRA), 12703 Spectrum Drive Suite 101, San Antonio, TX 78249,
Crowley, G gcrowley@astraspace.net, Atmospheric and Space Technology Research Associates (ASTRA), 12703 Spectrum Drive Suite 101, San Antonio, TX 78249,

The E-region density is one of the key elements in the development of equatorial spread F. The linear growth rate of the generalized Rayleigh-Taylor instability depends heavily on the flux-tube integrated E-region Pedersen conductivity (e.g. Sultan,1996). Therefore, good estimates of E-region densities are necessary for a better understanding of ESF phenomenology. In this study, we investigate the estimation of E-region density profiles obtained with the Ionospheric Data Assimilation Four Dimensional (IDA4D). The profiles will be obtained by a) direct assimilation of radio occultation data into IDA4D and b) by using IDA4D F-region density results to assist the inversion of E-region profiles from occultation measurements. The results are compared with independent measurements of E-region density profiles made by the bistatic coherent scatter radar experiment in Peru (e.g. Hysell and Chau, 2001). Additionally, we present an analysis of the accuracy and variability of the E-region density predictions of the numerical models used to generate the background (initial state) ionosphere for IDA4D inversions (TIMEGCM and IRI).

SA11A-1496

The Low-latitude Ionospheric Sensor Network (LISN): Initial Measurements

* Valladares, C E valladar@bc.edu, Boston College, Institute for Scientific Research 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States

This paper describes the characteristics and illustrates the early measurements of the first distributed observatory that is being installed in the South American region to study the low-latitude ionosphere and upper atmosphere. The LISN distributed observatory will be comprised of nearly 70 GPS receivers with the capability to measure Total Electron Content (TEC), amplitude and phase scintillation and Traveling Ionospheric Disturbances (TIDs). The network will include 5 ionosondes able to measure nighttime E-region densities and 5 collocated magnetometers that will be placed along the same magnetic meridian. This network of GPS receivers and ionospheric sensors span from north to south in the South American continent west of the 55o West meridian. In addition to introducing the present capabilities of the LISN network, this paper will present the results of the first LISN campaign dedicated to detect medium-scale (~100 km) TIDs that was conducted at Huancayo using 3 closely-spaced GPS receivers. This paper also presents initial calculations of the vertical drift velocity using 3 magnetometers, two of them placed off the equator in opposite hemispheres and a detailed description of the measurements of the first LISN ionosonde that is presently operating near the magnetic equator.

SA11A-1497

Consistency of LISN Modeling Results with C/NOFS Observations of Low-Latitude Electrodynamics

* Eccles, V vince.eccles@spacenv.com, Space Environment Corporation, 221 N. Spring Creek Pkwy, Suite A, Providence, UT 84332-9791, United States
Valladares, C E valladar@bc.edu, Boston College, Institute of Space Research, 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States
Sheehan, R E sheehanp@bc.edu, Boston College, Institute of Space Research, 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States

The Low-Latitude Ionospheric Sensor Network (LISN) offers an unprecedented science opportunity by providing a distributed and dense set of observations of the low-latitude ionosphere in the South American longitude sector. LISN is currently collected data from GPS-TEC monitors, VIPIR ionosondes, and magnetometers to provide new insights into ionospheric electrodynamics and instabilities at low latitudes between the northern and southern Appleton anomaly regions. We present the early results of a detailed physics-based analysis of the data to draw out physical understanding of the ionosphere, the neutral winds, and the electrodynamics of the South American sector. The diverse data sets from LISN are used in combination with a Monte Carlo exploration of ionosphere representations generated by physics-based models of the ionosphere and its electrodynamics. This physics-based 'data-processing' methodology generates a consistent representation of the ionosphere and its drivers within the LISN region. The self-consistent drivers and ionosphere will permit investigations into underlying causes to ionospheric variability and instability. The first effort being performed on the data-model merging is the comparison of the representations of the ionosphere, neutral winds, and electrodynamics with independent data sets. Simulated C/NOFS observations of electric fields, neutral winds, and electron densities will be generated from the LISN data-model representations for comparison with C/NOFS results. Acknowledgment: We wish to acknowledge the support of NSF Funding support through grant ATM- 0745714.

SA11A-1498

Spatial Variation of the Pre-reversal Enhancement ¡V Model Results

* Fang, T twfang@ucar.edu, Institute of Space Science, National Central University, No. 300, Joongda Rd., Jhongli City, 32001, Taiwan
* Fang, T twfang@ucar.edu, High Altitude Observatory, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80302, United States
Richmond, A richmond@ucar.edu, High Altitude Observatory, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80302, United States
Liu, J jyliu@jupiter.ss.ncu.edu.tw, Institute of Space Science, National Central University, No. 300, Joongda Rd., Jhongli City, 32001, Taiwan
Maute, A maute@ucar.edu, High Altitude Observatory, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80302, United States

The pre-reversal enhancement (PRE) is one of the most important phenomena controlling the nighttime ionosphere and the generation of equatorial spread F (ESF), but its causal mechanism is still not fully understood. Radar and satellite observations provide us important but incomplete information about it: radars can only observe local time variations at a specific location, while satellites provide data mainly at a single altitude. The NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is capable of simulating ionospheric phenomena and the pre-reversal enhancement. In this research, we run the model under moderate solar activity (F10.7=150) and geomagnetic quiet conditions to monitor the variation of ionospheric parameters when the maximum upward drift of the PRE is occurring in the Peruvian longitude (75¢XW). Since it is a three dimensional model, it can provide us current flows, electric field changes and conductivity variations in Peruvian longitude and also longitudes to the east (after PRE) and west (before PRE). From the results, we are able to picture the spatial variations of the ionosphere surrounding the PRE and to evaluate effects due to wind driven current, the equatorial electrojet, and conductivity gradients. In addition, we evaluate the effects of winds and conductivities separately in the ionospheric E and F regions on the PRE, to understand and diagnose the complex electrodynamic processes.

SA11A-1499

The one-to-one relationship between the pre-reversal enhancement and equatorial plasma bubbles observed from ROCSAT and CNOFS/CINDI

* Kil, H hyosub.kil@jhuapl.edu, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, United States
Paxton, L J larry.paxton@jhuapl.edu, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, United States
Heelis, R A heelis@utdallas.edu, The University of Texas at Dallas, 800 W. Campbell Road Mail Station WT-15, Richardson, TX 75080, United States

The pre-reversal enhancement (PRE) is known to be the most important single parameter in the generation of equatorial plasma bubbles (EPBs). Observations in the Peruvian sector have shown that a threshold PRE velocity is required to generate EPBs. This connection was established through the correlation of observations of the PRE velocity and occurrence of spread F: the question is whether this cause-and-effect relationship holds on a global basis. The problem in establishing a causal link between a PRE velocity threshold and the occurrence of EPBs from satellite data is that the satellite with high inclination is not able to provide the PRE and EPB data at the same location in the consecutive orbits unlike a ground site in the equatorial region that can measure the PRE and then observe whether or not EPBs form at a later time. A low-inclination orbit, such as that of C/NOFS, enables one to observe the magnitude of the PRE on one pass and then detect EPBs on the next pass at or near the same location. We will analyze the observations of vertical ion velocity and ion density from ROCSAT and CNOFS/CINDI. The PRE characteristics (peak velocity and its occurrence local time) will be determined for each orbit and the occurrence of EPBs in association of the PRE characteristics will be investigated by monitoring the occurrence of EPBs in the following orbits. This study is the first attempt to demonstrate the capability to establish the one-to-one relationship between PRE and EPB using data from a single satellite.

SA11A-1500

Excitation of Equatorial Ionospheric Bubbles from Tropospheric Convection-Driven Gravity Waves

* Keskinen, M J keskinen@ppd.nrl.navy.mil, Naval Research Laboratory, Plasma Physics Division, Washington, DC 20375, United States
Vadas, S vasha@cora.nwra.com, Northwest Research Associates, 3380 Mitchell Lane, Boulder, CO 80301, United States

Using numerical simulation techniques, the triggering of equatorial ionospheric bubbles from tropospheric convection-driven gravity waves is studied. The evolution of the ionospheric bubbles is achieved using a 3D time-dependent nonlinear plasma fluid model. This model solves the 3D equations for ionospheric plasma continuity, momentum, and current continuity and incorporates inertial effects, off-equatorial Pedersen conductivity effects, vertical drifts from zonal electric fields, large scale background thermospheric winds, and gravity-wave (GW) wind effects. The gravity wave winds, wavelengths, and periods are derived from a recent model of tropospheric convection-driven gravity wave generation. The thermospheric GW model is developed using a ray tracing methodology and includes both viscosity and thermal conduction damping. In order to compute the time-dependent ionospheric bubble evolution we incorporate a spectrum of GWs with vertical and horizontal wavelengths and wave periods derived from the thermospheric GW model. Initial studies show that equatorial ionospheric bubbles can be triggered using the thermospheric GW model for a range of GW amplitudes and scale sizes. Comparison with satellite and radar observations are made.

SA11A-1501

Ionospheric Dynamics at Low Latitudes Obtained From the USU Physics-Based Data Assimilation Model (GAIM-FP)

* Scherliess, L ludger@gaim.cass.usu.edu, Center for Atmospheric and Space Sciences, Utah State University 4405 Old Main Hill, Logan, UT 84322-4405, United States
Thompson, D C don.thompson@usu.edu, Center for Atmospheric and Space Sciences, Utah State University 4405 Old Main Hill, Logan, UT 84322-4405, United States
Schunk, R W schunk@cc.usu.edu, Center for Atmospheric and Space Sciences, Utah State University 4405 Old Main Hill, Logan, UT 84322-4405, United States

The ionosphere-thermosphere system at equatorial and low latitudes is strongly coupled, and therefore, a study of ionospheric dynamics must take into account the interaction between the different domains. Over the past decades meteorologists and oceanographers have used data assimilation models to study complex systems. We have developed two data assimilation models with different complexity and both provide global and regional specifications of the 3-dimensional ionosphere-plasmasphere plasma densities. One of these models is a Full Physics-Based Kalman filter data assimilation model (GAIM-FP), which is based on a physics- based model for the ionosphere-plasmasphere system, a diverse array of data sources, and an ensemble Kalman filter data assimilation technique. This model covers the ionosphere-plasmasphere system from 90 to 30,000 km altitude and includes 6 ion species (NO+, N2+, O2+, O+, He+, H+). An important strength of this model is that in addition to the global and regional 3-D ionosphere electron density distribution it also determines the corresponding ionospheric drivers, including the thermospheric neutral winds and the low-latitude electric fields. The model can assimilate a variety of different data types, including GPS/TEC from hundreds of ground receivers, in situ Ne from several DMSP satellites, bottomside Ne profiles from tens of ionosondes, and occultation data from the six COSMIC satellites. With the recent launch of the C/NOFS satellite the possibility has opened to also assimilate data from the various instruments onboard this satellite. In the present study, we have used the model to study the dynamics of the equatorial and low latitude ionosphere over the American sector, where ground-based ionospheric observations are abundant. The model was used to determine the various driving forces and to study their temporal and spatial variability. We will present examples of the ionospheric and driver specifications obtained from our model runs and the results will be compared with independent data. If C/NOFS observations will become available before the presentation of this paper initial comparisons of our model results with C/NOFS observations will also be shown.