SA13A-1061
GPS Ionospheric Tomography over Japan with Constrained Least-squares Method
An ionospheric tomography method was developed for the GPS total electron data observed by a dense GPS receiver network in Japan. GEONET is a GPS network operated by Geographical Survey Institute, Japan, and consists of about 1,200 receivers. Its high-density distribution of the receivers, and wide coverage provide a suitable data set to reconstruct the electron density distribution in the ionosphere with high spatial resolution. The newly developed GPS ionospheric tomography (GPS-IT) model is based on the constrained least-squares method (CLM). The three dimensional distribution of the ionospheric electron is derived at every data sampling time, 30 seconds. A priori information requested for the GPS-IT is the intensity of restriction for the spatial gradient of the electron density. The vertical gradient of the electron density is restricted to be low above 800km altitude. The vertical boundary condition at bottom-side is based on the IRI model and at topside is based on the plasmaspheric model. The horizontal boundary condition is that the gradient of the electron density is nearly zero. The derived electron density distribution shows a good agreement with the electron density measured by the IS observation of the MU radar, and ionosondes. This GPS-IT can also include the data from the MU radar, ionosondes, and in-situ density measurements. This flexibility and robustness is an advantage of this GPS-IT model with CLM. The introduction of the algorithm, and the electron density distribution obtained in the quiet and disturbed days will be presented.
SA13A-1062
Ionospheric Structure from GPS and Radar Observations for Radio Array Calibration.
As part of the development of the Murchison Widefield Array (MWA) for solar, heliospheric and ionospheric observations, GPS receivers will be deployed at the site in Western Australia to assist in the calibration of the array. The MWA will operate in the frequency range of 80 to 300 MHz where ionospheric effects are the primary limiting factor for the array's measurement accuracy of Faraday rotation and other remote sensing techniques that will be applied. In preparation for the deployment, three GPS receivers (Model GSV4004B) were operated at Haystack Observatory during the month of December 2006 in conjunction with the Millstone Hill Incoherent Scatter Radar (ISR). High resolution time variations of total electron content (TEC) from GPS and ISR for a geomagnetically-quiet period (Dec 7, 2006) and during storm conditions (Dec 14, 2006) have been compared revealing excellent agreement between the instruments as well as providing estimates of plasmaspheric content and small scale structure induced by gravity wave and auroral disturbance effects. In the analysis of the GPS data, initial estimates were made of the effects of temperature on GPS receiver calibration and will be reported in this paper. This research was supported by NSF; the GPS receivers were provided courtesy of AFRL/AFOSR. http://www.haystack.mit.edu/ast/arrays/mwa/LFD
SA13A-1063
Seasonal and temporal variability of the equatorial ionosphere with radio occultation electron density profiles from CHAMP
This work summarizes a portion of the more than two hundred thousand electron density profiles captured by the Challenging Mini-Satellite Payload for Geophysical Research (CHAMP, GFZ) from 2002-2006. The electron density profiles used in this work were processed by the Cosmic Data Analysis and Archival Center (CDAAC, UCAR) and released in July 2007. This recent release includes data not previously distributed by CDAAC, and nearly doubles the number of electron density profiles available through CDAAC. The local time of the electron density profiles varies throughout the solar day due to the geometry of the experiment (one ~400 km altitude near-polar orbiter with a ~90 minute period receives GPS signals until occulted by Earth). For a majority of the profiles, sampling occurs at two local times each day, separated by 12 hours, such that roughly every 120 days, the sampling local time repeats. The progression of local time with day of year for the CHAMP electron density profiles drives the selection of data subsets used in this multi-year study of electron density. The data are divided into local time windows from 06:00-10:00 (four hours before noon) and 22:00-02:00 (four hours near midnight). For the years 2002-2006, this yields twelve 60-day before-noon data subsets, and thirteen 60-day near-midnight data subsets. Each subset consists of roughly two thousand profiles. For each of these 25 data subsets, the electron density profiles are interpolated onto a global map with latitude and longitude, from 150-400 km altitude. The data are summarized both in terms of bulk trends as well as with focus on zonal structure. For example, the seasonal and interannual variability of the zonal mean equatorial electron density are presented, as well as a wave decomposition of the observed equatorial zonal structure at fixed altitudes, such that the possible effects of non-migrating tides on the ionosphere can be considered. The retrieved electron density profiles are sometimes also biased by steep horizontal electron density gradients in the ionosphere, and negative biases can be detected at lower altitudes in these data. The magnitude and geographical distribution of these biases at lower ionospheric altitudes is also assessed.
SA13A-1064
Satellite Conjunction Study for Polar Cusp Neutral Upwelling
Recent observations have confirmed neutral particle upwelling at high latitudes which are localized to the polar cusp region and seem to be correlated to high auroral activity. For decades, thermospheric upwelling has been recognized as an important topic and has been studied observationally and theoretically, with efforts largely focused on Joule heating being the basic driver. As data and models have improved over the years, Joule heating has indeed proven to be fundamental to upwelling, at least at lower latitudes. At higher latitudes, however, the situation appears to be more complex and recent results indicate that Joule heating alone is not adequate. We address this issue using data acquired by FAST and CHAMP satellites during a number of favorable conjunction alignments. Specifically we compare FAST field and particle data to CHAMP accelerometer data, both analytically and numerically. We present early data from this study from a single 2-week conjunction window in 2002.
SA13A-1065
Comparison of the ionospheric profiles derived with radio occultation technique to the Digisonde data
COSMIC/FORMOSAT-3 is a joint Taiwan-U.S. multi satellite project that started in December of 2005, and is expected to last for five years. GPS radio occultation receivers onboard the satellites make it possible to measure ionospheric electron density profiles on a global scale using radio occultation (RO) technique. Such observations will provide data for studying ionospheric plasma structures and improving large-scale theoretical models. However, the RO measurements first need to be verified with other established ionospheric techniques. We present results of the comparison of the COSMIC RO profiles and simultaneous measurements made with ground based digisonde sounders using the data collected in December 2006. Results generally demonstrate a good agreement between the two techniques, at least in terms of the critical frequency, foF2, with the typical absolute error in RO measurements smaller than 1 MHz. A few cases of significant deviations of the RO profiles from the digisonde data have been observed, however. Having analyzed the erroneous RO measurements we make recommendations for future development of the RO technique and satellite observations on a global scale.
SA13A-1066
Meridional Winds Derived from COSMIC Radio Occultation Measurements
Meridional winds derived from F2 layer peak parameters (NmF2 and hmF2) measured by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) using the servo method, are compared at multiple locations with winds derived from incoherent scatter radar (ISR) and Fabry-Perot interferometer (FPI) measurements. The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR-TIEGCM) is then employed to simulate the longitudinal variations of meridional winds. Comparisons show that there is generally good agreement between COSMIC winds and ISR, FPI and TIEGCM winds, although COSMIC winds are more equatorward near sunset hours. The COSMIC winds show significant longitudinal variations at latitude 40N (local winter) and 40S (local summer). At 40N, the COSMIC winds exhibit distinct and long duration higher velocity near the midnight hours and during late morning hours within the longitude range 110W to 20W, near the negative declination sector. Similarly, at 40S, the winds are characterized by distinct larger velocity for poleward winds from sunrise to afternoon hours within the longitude range of 120°E to 110°W, near the positive declination sector. At 40°S, another notable feature for the nighttime maximum equatorward winds is seen: there is a local time shift by about 2h from longitude range of 60W to 90E within the negative declination sector to other longitudes within positive declination sector. The NCAR TIEGCM reproduces these longitudinal configurations well, except during the daytime at 40N, and there are some discrepancies in wind magnitude. Analysis of NCAR TIEGCM simulations suggests that the longitudinal variation of meridional winds is mainly controlled by the magnetic declination.
SA13A-1067
Horizontal Electron Density Gradients and Wave Propagation at Mid-latitudes
We investigate the spatial variability in the large-scale electron density gradients associated with the Appleton anomalies in the low-latitude, nightside ionosphere using a suite of instruments from the Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) spacecraft. We use measurements from the Tiny Ionospheric Photometer (TIP) instruments to infer the horizontal electron density gradients along each satellite track. We demonstrate that the OI 135.6 nm emission intensities measured by the TIP instruments track the horizontal electron density structure well with high spatial resolution and unprecedented sensitivity. Accurate measurements of the horizontal electron density gradients are important for improving retrieved electron density profiles from GPS occultation and other tomographic remote sensing techniques. The processes underlying the variability in the large-scale, nightside electron density gradients are the main drivers of ionospheric weather. TIP observations reveal significant variability in both the small and large scale structure of the nightside ionosphere. The relative intensities, relative widths, and latitudinal separation of the northern and southern ionization crests of the Appleton anomalies show a high degree of longitudinal variation. We demonstrate how the TIP measurements can be used to understand how the propagation of VLF whistler-mode waves is affected by gradients in electron density associated with equatorial ionospheric structure such as depletions and the Appleton anomalies.
SA13A-1068
Ionospheric Measurements for the Long Wavelength Array
The Long Wavelength Array (LWA) is a new telescope/interferometer facility being established to do astrophysical observations in the frequency range 10 MHz to 80 MHz. As such, measurements will be strongly affected by the ionosphere. In fact, part of the LWA mandate is to make highly precise measurements of the ionosphere. The work will require a combination of active and passive measurements, detailed modeling and improvement of existing "self-calibration" techniques. These techniques solve empirically for small differential ionospheric delays between interferometer elements and can be improved upon with knowledge of the real physical behavior of the ionosphere. This presentation will give an overview of the requirements, with the aim of stimulating discussion in the ionospheric community on how to address these issues. We will also present measurements and 3D reconstructions of the ionosphere over the LWA core site obtained from a recent experiment using the COSMIC satellite constellation, the Very Large Array 74 MHz system and GPS measurements.
SA13A-1069
Global assimilative ionospheric modeling and the Tiny Ionospheric Photometer on the COSMIC constellation
The FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) uses the Tiny Ionospheric Photometer (TIP) to characterize the nighttime ionosphere. TIP is a compact, nadir directed, narrow-band, ultraviolet photometer operating at the 135.6 nm wavelength. This emission is produced by recombination of O+ ions and electrons, which is the natural decay process for the ionosphere. At night, the strength of the emission is proportional to the square of the peak electron density. TIP measures the horizontal structure of the ionosphere with 15-30 km resolution and high sensitivity, providing remarkable detail even during solar minimum conditions. With six sensors on COSMIC providing global coverage, TIP is a valuable resource for evaluating ionospheric models. We present a comparison of TIP data with models which employ global assimilation of ionospheric measurements. Ground-based GPS observations are routinely ingested and serve as the primary data source for assimilative models. With the launch of the COSMIC constellation in 2006, research has begun on assimilating GPS radio occultations. These space-based observations provide global coverage and promise to improve ionospheric specification in both a vertical and horizontal sense. Comparison with TIP reveals the horizontal performance of these models and demonstrates the improvement obtained from ingesting radio occultation data.
SA13A-1070
Observing the auroral ionosphere with FORMOSAT-3/COSMIC
The auroral ionosphere were usually observed with incoherent scatter radar (ISR) or in situ measurement along the path of a spacecraft, which provided ionospheric information in a partial region. Due to the success of the FORMOSAT-3/COSMIC satellites mission since April 2006, global ionospheric structure can be monitored with the GPS radio occultation technique, especially in high latitude due to denser data distribution, and ionospheric radiance can be also observed with the space-borne tiny ionospheric photometer (TIP). We use the electron density profiles retrieved from COSMIC GPS occultation experiment and ionospheric radiance from COSMIC TIP, to display variations of the ionospheric auroral oval in the northern hemisphere, January 2007. The boundaries of the auroral oval are also discussed.
SA13A-1071
Numerical Simulation for Generalized Aurora Computed Tomography
The conventional method of aurora tomographic inversion is extended to a more generalized aurora computed tomography (CT). The generalized aurora CT is the method to reconstruct energy distribution of auroral precipitating electrons from multimodal data, such as electron density enhancement from the EISCAT radar and cosmic noise absorption (CNA) from imaging riometer, as well as auroral images. In this study, we evaluate the feasibility of the generalized aurora CT by numerical simulation. The forward problem is based on model calculation of auroral emission and electron density enhancement for incident electrons and the mapping of the results to the instruments. Assuming the energy and spatial distributions of the incident electrons, the three-dimensional (3D) distributions of volume emission rate and electron density are calculated. The data observed with the ALIS (Auroral Large Imaging System) cameras, the EISCAT radar, and the imaging riometer are obtained by mapping the volume emission rate and electron density to each instrument. We attempt to retrieve the initial distribution of precipitating electrons from the simulated observational data. The inversion analysis is based on the Bayesian inference, in which the problem is formulated as the maximization problem of posterior probability. The results are compared between the reconstruction from only auroral images and that from multimodal data.
SA13A-1072
Azimuthal structure of auroral arcs associated with various disturbed magnetic conditions
We investigated the mode numbers of azimuthally spaced auroral forms in various disturbed magnetic conditions using limb-view images of ISUAL (The Imager of Sprites and Upper Atmospheric Lightnings ) on board FORMOSAT-2 satellite. We choose 557.7nm and 630.0nm as our filter wavelengths. The 557.7nm green transition line of OI(1S→1D) is mainly produced by energetic electrons with energy ≥ 1keV and the 630.0nm red-line emission of OI(1D→3P) (triplet) is mainly produced by electrons with energy ~O(100eV). The auroral arcs have bright spots with approximately equal-spaced separation, in the azimuthal direction, which allows estimate of the azimuthal mode number. The azimuthal mode number of quiet time arcs is higher (m~720) and becomes lower at moderately disturbed times (m~360). For the breakup arcs at onset, the azimuthal mode number is lower with m~220. After onset, the observed breakup arcs move explosively in poleward direction from 64° to 70° latitude in about 2 minutes. The observed azimuthal structure of the substorm breakup arc at onset is similar to the events observed by THEMIS All Sky Imagers at Fort Yukon (m~250) and is consistent with the kinetic theory of ballooning modes [Cheng, Zaharia and Gorelenkov, 2004], which showed the most unstable mode at about -8RE with azimuthal mode number m~300.
SA13A-1073
Ionospheric Response to Flickering Aurora
Flickering aurora is characterized by optical emissions varying in intensity with frequencies typically between 5 and 20 Hz. Here we use high-speed narrow field-of-view imaging in white light to determine the intensity variation in the field aligned direction, which is also the direction of the beam of the EISCAT Svalbard Radar (ESR). Incoherent scatter radar data is noise-like, and must be integrated over multiple pulses to reduce the variance to useful levels, even for high signal to noise ratios. Usually, this means integrating over several seconds to some tens of seconds of observation, which is not very useful with respect to flickering aurora. In the experiment presented here, we have taken data at the voltage level, before any integration. By integrating pulses with the same relative phase with respect to the optical intensity we can determine the variation in radar back-scatter on time-scales of 0.02 s.
SA13A-1074
Vertical transport in the ionosphere derived from near-infrared spectroscopy of the aurora
This work presents a new technique for estimating vertical ion transport from photometric measurements of the aurora. The procedure involves (1) estimating the incident precipitating particle spectrum by inversion of multi- wavelength optical measurements in the magnetic zenith, (2) applying this incident spectrum to a theoretical fluid- kinetic model to estimate the ionospheric response. The forward model used in our procedure is a variant of the TRANSCAR model, originally developed to study high-latitude flux-tube dynamics. Our technique uses near infrared (NIR) brightness measurements of N2 1P, N2+ Meinel, O+ 732-733 nm, and O 844.6 nm. These emissions provide optimal access to the critical soft (< 300 eV) portion of the primary electron spectrum as well as adequately characterizing the keV component associated with visible aurora. The technique is validated using coordinated optical and incoherent scatter radar measurements from the Sondrestrom, Greenland research facility. Our technique represents a new use for NIR spectrograph data and a new tool for remotely sensing ionospheric dynamics and associated mass-coupling with the magnetosphere. ISR is currently the only remote sensing diagnostic for thermal ion upflows. Our approach constitutes an alternative that is less complex and less costly than ISR. Furthermore, a dense network of optical sensors can possibly be deployed en masse to provide global coverage of bulk ion motion. This research is also cast in the broader context of estimation of ionospheric state parameters via remote sensing. Preliminary work on estimation of ionospheric variables, other than upward flux, through optical measurements is discussed.
SA13A-1075
Seasonal dependence of SC amplitude on magnetic local time
In order to clarify a seasonal dependence of sudden commencement (SC) amplitude on magnetic local time in the low-latitude region, we analyzed geomagnetic field data obtained at Kakioka Magnetic Observatory for 12138 SC events which were identified in term of the SYM-H index and SC list provided from NGDC within a period from January 1976 to June 2007. In this analysis, we defined these SC events as a rapid increase of the SYM-H value with more than 5 nT within ten minutes. Moreover, we also used solar wind data obtained from the IMP-8, Geotail, Wind and ACE satellites within the data analysis periods from 1976 to 2007, from 1993 to 2007, from 1994 to 2007 and from 1998 to 2007, respectively. The SC events including the solar wind data were 8343 events. The diurnal variation of the normalized SC amplitude by the SYM-H value showed a remarkable dependence on magnetic local time, which indicates that the two peak values appear in the dayside sector of 11-14 h (MLT) and in the midnight sector of 22-02 h (MLT), respectively. The diurnal variation curve also showed the two minimum values in the morning sector of 5-7 h (MLT) and in the evening sector of 16-18 h (MLT), respectively, with a clear morning-evening asymmetry in their values. This trend indicates the magnetic field variations created by the dayside magnetopause, region-1 field-aligned currents (FAC) and the associated ionospheric Hall and Pedersen currents. Especially, the enhancement of the nightside SC amplitude can be considered as the FAC effect due to a weak intensity of the ionospheric current. Moreover, in this study, it is shown that the diurnal variation of SC amplitude in the low-latitude region has a seasonal dependence on MLT, which represents that the amplitude of the diurnal variation both the daytime and nighttime sectors tends to be larger in summer than in winter. This seasonal variation implies that the intensities of the FAC and reactant ionospheric current may be stronger in summer due to the enhancement of the ionospheric conductivity. Therefore, from the above result, it can be concluded that the dynamo of the FAC during SCs is a voltage generator rather than a current generator. In future, we need to investigate the variations of SC amplitude for solar activity and the direction of IMF around the solar wind shock and discontinuity.
SA13A-1076
Assimilative Modeling of Mid-Latitude Ionospheric Plasma Plumes during the October 2003 Storm
A significant daytime ionospheric total electron content (TEC) enhancement was observed at middle latitudes by the ground-based and space-borne GPS receivers during the geomagnetic storm on October 30, 2003. This TEC enhancement has been identified as the storm enhanced density (SED). To investigate ionospheric disturbances associated with the SED, GPS data collected from 200 ground stations and two low-Earth-orbiters (CHAMP and IOX) are assimilated into Global Assimilative Ionospheric model (GAIM). For the first time, the assimilative modeling with GPS data reveals 3D ionospheric plasma plumes, i.e., enhanced electron densities showing a plume feature towards higher altitude and latitude. Compared with the quiet-time ionospheric state also obtained by assimilative modeling, the model results show that F-layer densities increase by many hundreds of percent and the layer peak rises more than 200 km at middle latitudes. The plume feature indicates a strong zonal electric field penetration during the storm is likely the cause, which also drives a very significant equatorial- anomaly-like disturbance at middle latitudes seen in the GPS data collected from the CHAMP satellite.
SA13A-1077
Storm-time ionospheric electron density structures simulated by coupled model runs at mid- and low-latitudes
This study presents theoretical simulations of mid- and low-latitude ionospheric electron density structures produced by a storm-generated electric field. Various storm-time ionosphere electron density structures, such as mid- and low-latitude storm enhanced electron density, ionospheric electron density hole, electron density trough, electron density arches, and storm-generated additional layer (F3 layer), are predicted by coupled NCAR Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and Sheffield University Plasmasphere Ionosphere Model (SUPIM) runs. Possible physical processes and important drivers responsible for these storm-produced mid- and low-latitude ionospheric structures are discussed under various simulation conditions. A storm-time electron density hole may result from uplift of the original F-layer to much higher altitudes, while a new F-layer is formed at the original F-layer altitude when the photo-ionization process still operates. If the F-layer uplift occurred during evening hours, when the photo-ionization process becomes much weaker, an equatorial density trough is then formed. Meanwhile, a super-high F2 layer and/or F3 layer is also predicted to occur at the magnetic equator by the model runs when the electron density hole formed. After the significant F-layer uplift, the uplifted F-layer plasma diffuses downward along magnetic field lines to the adjacent higher latitudes, resulting in electron density arches. Our results also suggest that the storm-generated equatorward neutral winds can affect the latitudinal extent of the density arches as well as the formation of the additional F-layer at low-latitudes. The model predicted results are also compared with satellite and radar observations, showing good qualitative agreements.
SA13A-1078
Ionospheric Traveling Ionospheric Disturbance Measurements at Northern Mid- latitudes
Three low power coded transmitters have been used for measurement of gravity waves at London, Canada (43 geog. lat., 54 mag. lat). The transmitters are at apexes of an approximately equilateral triangle with 72 km sides. The signals reflected from the ionosphere are received at our university campus which is located within the triangle. TID measurements on 4 MHz during August show systematic motions: northeastward during daytime and northward during early nighttime. We compare our measurements with other measurements of midlatitude TIDs. The best comparison is with Munro's extensive TID measurements for Australia which showed daytime southeast directions in summer. This therefore is the same as we find: eastward and poleward in summer.
SA13A-1079
Characterizing the Relationship Between Ionospheric Effects and Forcing due to Hurricanes/Typhoons
Evidence of coupling between lower atmospheric regions and the ionosphere/thermosphere has steadily increased with the utilization of various instrument suites and sophisticated modeling efforts. In this presentation we utilize satellite-based GPS sensors to determine the extent of ionospheric disturbances in the vicinity of hurricanes/typhoons. Using GPS occultation data from the PicoSat and COSMIC satellites we investigate TEC levels and ionospheric scintillation near tropical storms. We characterize the relationship between any ionospheric effects and a storm's horizontal size, strength, and relative position. After examining over 150 tropical storms between 2001 and 2004, we find that scintillation occurs over 50% of the time within 1000 km of a storm center. The occurrence of scintillation seems to favor the area east and northeast of the storms" center.
SA13A-1080
Observations of tri-band beacon signal scintillation in the Taiwan zone
By applying the differential Doppler technique on three quadrature components of tri-band beacon signals, we were able to obtain total electric contents (TEC) values and scintillation along the radio path through the ionosphere. Such measurements can be used to derive the regional ionospheric irregularity and tomography (P. A. Bernhardt et. al, 2000). There are 83 scintillation days from April 2006 to April 2007 (395 days) and occurred usually at 18~05 LT in the night time, especially at pre-midnight or post-midnight. Scintillations at low-latitude have high correlation with months when Kp less than 3. They are usually happened at May-June and December- February less than the other months. On the contrary, scintillations are normally more frequent during the equinoctial months of August¡VOctober and March¡VApril. Meanwhile there are 16 scintillation days happened when Kp large than 3. During the equinoctial months of August¡VOctober and Mar¡VApril, when scintillations are normally more frequent, the generation of equatorial irregularities is in general absent during magnetic disturbances. Meanwhile, we show a typical blob event at 150N MLAT near the midnight, and approach the correctly location of the F region step by step by a simple optical model when the radio signals traveled through them, where they were subsequently compared the irregularity structure with the results of the Chung-Li Dynasonde (MF/HF radar) and the ionospheric tomography reconstruction.
SA13A-1081
Scintillation and TEC Receiver in Space (CITRIS)Instrument for Ionospheric Research*
Global ionospheric measurements of total electron content and radio scintillations provide direct inputs for space-weather models and for tracking of ionospheric disturbances. These measurements require propagation from transmitter beacons and receivers through large portions of the F- and E-region plasma. The Naval Research Laboratory (NRL) CITRIS receiver is currently in orbit at 560 km altitude on the STPSat1 satellite in a 35 degree inclination. CITRIS records TEC and radio scintillations from the global network of French DORIS beacons and from 150/400 MHz beacon transmitters on the Taiwan ROCSAT3, DMSP/F15, RADCAL, GFO and other satellites in low earth orbit. CITRIS also provides ionospheric TEC and radio scintillations in remote regions of the Earth because of the distribution of the 56 DORIS beacons around the globe. The CITRIS satellite- to-satellite measurement capability is new and exciting. A pass can go through three stages: 1) an ionospheric occultation geometry (at large distances), then 2) a nearly vertical sounding as the radio beacon passes directly over the receiver and 3) a second occultation. In such cases, it is possible to retrieve absolute TEC with less than 0.1 TECU errors. Another new capability for CITRIS is the ability to use three frequencies (150, 400, and 1067 MHz) for TEC measurements, which can also help resolve 2π ambiguities. We will report on the first six months of measurements for the CITRIS receiver. Future missions in space would benefit from flying CITRIS receivers to give global radio measurements of the ionosphere at 150, 400, 1067, and 2036 MHz. *The research was supported at NRL by ONR
SA13A-1082
A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations: initial results
The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this allows the drift velocities of each depletion to be determined as a function of magnetic latitude as well as local time. Previous ground-based airglow observations from a small number of locations have indicated that the drift velocities of depletions may vary rapidly with magnetic latitude. Here we shall present the first results from TOAD of this shear in drift velocities from our global sample of depletion drift velocities.
SA13A-1083
Modeling Study of the Field-Aligned, Ground-Based Imaging Technique
The field-aligned, ground-based imaging technique, in which a narrow-field imaging system is located approximately 17-23 degrees off the magnetic equator to observe equatorial ionospheric structure, has now been employed in two different longitude sectors. The images obtained using this technique provide detailed information on the development and dynamics of equatorial plasma bubbles associated with equatorial spread- F. The information provided by these imagers can be used to better specify the state of the ionosphere during the occurrence of equatorial plasma bubbles. However, there are several practical limitations and assumptions that are made in the analysis of these images, which we examine in detail in this study. These include the spatial resolution of the imaging system, the alignment of the imaging field-of-view with the magnetic field, and the assumed layer height of the emission being observed. We present results from a full three-dimensional simulation of the viewing geometry in which the 630.0-nm and 777.4-nm emissions are modeled using IRI2007 and NRLMSISE-2000. Field-aligned equatorial plasma bubbles with known parameters (scale size, location, and velocities) are imposed on the system. Images of the emissions are simulated by integrating through the models. We examine the effects of the assumed emission height layer on the derived spatial characteristics (scale size and location) and dynamics (velocities). We further examine the limitations imposed by the viewing geometry on resolving small-scale structure. This study highlights the strengths and practical limitations of the narrow-field viewing geometry in studying the properties of equatorial plasma bubbles.
SA13A-1084
Side-viewing observations of OI(1D) and OH night airglows by ISUAL
Optical and side-viewing images obtained from airglow surveys by ISUAL/FORMOSAT-2 often showed local enhancements in the F region and in the 90 km OH-layer. Detailed inspection of the latitudinal distributions of airglows in these two layers indicates the enhancements may be correlated. In some cases, the enhancements fell on two sides of the magnetic equator and could have been invoked by the Equatorial Ionization Anomaly (EIA) effect with an additional displacement contributed by the wind field. However in most cases, the cause(s) are far from clear. In addition, nonuniform luminescence, called spread F, was often observed in the pre-midnight regions and appears to exhibit longitudinal and seasonal variations. In the paper, the possible mechanisms of the enhancements will be discussed systematically.
SA13A-1085
Global-scale Observations of the Limb and Disk (GOLD) - New Observing Capabilities for Space Weather Specification and Forecasting
The Global-scale Observations of the Limb and Disk (GOLD) mission of opportunity will fly an ultraviolet imaging spectrograph on a geostationary satellite to measure neutral densities and temperatures in the thermosphere and ionosphere. GOLD will provide the first global-scale observations of temperatures in the lower thermosphere, in addition to more familiar measurements such as aurora location and energy input; peak electron densities in the nighttime ionosphere; and atomic oxygen to molecular nitrogen (O/N2) ratios. GOLD can provide nearly continuous real-time observations of one hemisphere. In addition to measurements on the disk of the Earth, GOLD will also provide measurements of molecular oxygen densities and the temperature profile in the lower thermosphere on the limb of the Earth from stellar occultations. Combined with the advanced models now available, measurements from GOLD will revolutionize our understanding of the global-scale response of the thermosphere and ionosphere to geomagnetic and solar forcing. GOLD is being proposed as a mission of opportunity in response to the Small Explorer (SMEX) and Missions of Opportunity from NASA's Science Mission Directorate, and it would leverage the scheduled solar (Solar Dynamics Observatory) and radiation belt (Radiation Belt Storm Probes) measurements. The data and knowledge gained from GOLD will enhance space weather specification and forecasting capabilities.
SA13A-1086
Ionospheric Electric Fields from Ion Distribution Images on Swarm
The dynamical behavior of the ionosphere is dominated at high latitudes by coupling to the magnetosphere, and at low latitudes by coupling to neutral winds. Magnetospheric forcing leads to highly structured plasma flows on spatial scales of one kilometer or less, particularly in the vicinity of auroral arcs; intrinsic plasma instabilities impose further plasma structure at all latitudes. All of these phenomena can be clarified through direct observations of the electric fields that mediate them. The European Space Agency's Swarm mission will make continuous global measurements of geo-electromagnetic fields during a four-year mission to begin in 2010. Electric Field Instruments (EFIs) on each of Swarm's three satellites will measure electric fields through vector ion drift measurements having a precision of 5 m/s and at rates of up to 16 vectors/second, or every 500 m along the orbit. The combination of precision electric and magnetic fields can be used to estimate low-frequency Poynting flux with a resolution of 1 μW/m2, sufficient to detect outward-propagating electromagnetic disturbances generated by gravity waves in the neutral atmosphere, for example, or to clarify the subtle interplay between electric and magnetic fields that leads to auroral arcs. This talk will overview the scientific potential of Swarm's electric field measurements along with the technical developments that underlie them.
SA13A-1087
An Innovative Low-Cost Program for Neutral Density and Wind Research With Small Satellites
The Drag and Atmospheric Neutral Density Explorer (DANDE) is a 50 kg, spherical spacecraft being developed at the University of Colorado, Boulder. The goal of the DANDE mission is to provide an improved understanding of the satellite drag environment in the lower-thermosphere. To achieve this goal DANDE will measure in-situ neutral density, composition, and horizontal winds between 200 and 350 km. The relationship between composition, density and winds during disturbed atmospheric conditions and the relative effect on satellite drag will be addressed using DANDE measurements. DANDE is an extremely low-cost mission supported in part through the AFRL University Nanosatellite program. A low-cost design is achieved by using commercial technology and accelerometers as well as innovative miniaturized wind and atmospheric temperature spectrometer (WATS) developed at the Goddard Space Flight Center. As a secondary payload, this low-cost mission-model will provide a reproducible and reliable method for obtaining global space weather data on launches of opportunity. The result of commissioning such spacecraft into various orbits is continuity of space weather information related to the neutral thermosphere for both scientific analysis and now-casting purposes. Finally, DANDE will provide a way for empirical atmospheric models to be calibrated in near real-time while validating first-principles models through in-situ data. University of Colorado graduate and undergraduate students are designing and integrating the spacecraft to be delivered for environmental testing by summer of 2009. http://spacegrant.colorado.edu/dande/index.htm
SA13A-1088
OH and O(1D) Airglow measurements at 630 nm from FORMOSAT 2 satellite
By using a 630 nm filter, airglow emissions in 60-250 km range were measured by the FORMOSAT-2 satellite using the ISUAL instrument (Imager of Sprites and Upper Atmospheric Lightning ). Measurements in Oct 2004 and March-April 2007 revealed two layers of airglow produced by OH and O(1D). The emissions of O(1D) and OH had maximum intensity in the equatorial regions, but with maximum latitude varied from day to day. The OH intensity showed an oscillation of two day period, but O(1D) varied by many factors. By comparing the relative intensity and height separation of these two airglow layers, we found the intensity of O(1D) was generally stronger than OH in the southern hemisphere but weaker or comparable with OH in the northern hemisphere.
SA13A-1089
Remote Sensing of the Lower Thermosphere by Solar X-ray Imaging During Occultations
Occultations of the Sun by Earth as viewed by a soft X-ray imager offer unique insight into the structure of the lower thermosphere (100-400 km). An initial analysis of GOES-12 Solar X-ray Imager (SXI) data demonstrated the utility of this technique, particularly the ability to instantaneously gain spatially resolved (better than 10km resolution) transmission measurements both in altitude and latitude. The GOES-13 SXI was launched in May 2007 and marks a significant improvement over the previous instrument in terms of spatial resolution, sensitivity, and reduced wide-angle scattering. We analyze GOES-13 observations from September 2006 and compare them to GOES-12 observations in terms of signal-to-noise, background levels, and apparent small-scale spatial structure. The transmission observations are modeled using the NRLEUV solar spectral model and the MSIS neutral atmosphere, both driven by the F10.7 solar activity proxy, and then convolved with the SXI response function. Discrepancies between the model and observations are investigated with regard to thermospheric cooling models and other observations of thermospheric density by independent means. The SXI thermospheric data are highly accurate because they are "self-calibrating" relative measurements. Sustained, long-term SXI observations are assured since the SXI program and the Solar Ultraviolet Imager (SUVI) follow-on are planned to operate through 2030. Thus, these observations will offer a valuable measure of cyclic and secular changes in the thermosphere over multi-year to decadal time-scales.
SA13A-1090
Daytime Observations of Mid-latitude Sporadic-E and QP Radar Echoes
Although sporadic-E layers and quasi-periodic (QP) radars are typically detected during nighttime conditions at mid-latitudes, they also may exist in the daytime lower ionosphere as well. We present observations of ionosonde observations of daytime sporadic-E layers gathered at the Wallops Flight Facility, Virginia, in the late morning to noon local times. The data reveal sporadic-E characteristics similar to nighttime observations including considerable variations in frequency and altitude. For one event, observed on 23 July 1999 near 14 U.T. (10 L.T.), we present coincident strong Wallops ionosonde sporadic-E observations and 50MHz backscatter radar observations of quasi-periodic echoes gathered with the University of Illinois radar situated at Ft. Macon, N.C., whose beam was perpendicular to the magnetic field in the lower E-region over Wallops. The radar data show daytime QP structuring that is very similar to the nighttime observations, suggesting a similar driving mechanism. A statistical survey of the daytime ionogram data at Wallops shows a preponderance of daytime sporadic-E events occurring during the local summer months, a seasonal dependence that is well-established for nighttime sporadic-E conditions in the northern hemisphere. No clear correlation is observed between the daytime sporadic-E events and magnetic storms, suggesting that the daytime sporadic-E events are not necessarily driven by the disturbance dynamo. Rather, we speculate that the same large wind shears that are believed to be the main engine for the nighttime sporadic-E and QP echoes, may also be at work during the daytime. The existence of enhanced plasma density layers during the daytime and their role in generating QP- echoes during the day remain open questions.
SA13A-1091
Preliminary report of DC electric field measurements in the ionosphere by Kagoshima sounding rocket experiments
S-310-37 and S-520-23 sounding rocket experiments are carried out at Uchinoura Space Center (USC) in 2007. The purpose of S-310-37 rocket experiment is an integrated observation of the high electron temperature layer in the Sq current focus during the winter daytime over USC. In order to measure the field-aligned electric field due to the Sq current, we develop the three-dimensional electric field detector (EFD). The EFD measures three components of electric field by using 3 pair of probe antenna. S-310-37 sounding rocket was launched at 11:20 LT on January 16, 2007. The apex of rocket trajectory was about 138 km. As a result of rocket measurement, it is clearly seen three components of electric field are fluctuated at the altitude from about 90 km to 120 km during the ascent. Particularly the electric field component parallel to the rocket spin axis is fluctuated in the region where the electron temperature is high. The purpose of S-520-23 rocket experiment is the investigation of the process of momentum transportation between the atmospheres and the plasma in the thermosphere during the summer evening time at mid latitudes. The electric filed and VLF/MF band receiver (EVMR) is loaded on this sounding rocket. The EVMR measures the two components of electric field by using 2 pair of probe antenna in order to obtain a dynamics of plasma particle in the ionosphere. S-520-23 sounding rocket was launched at 19:20 LT on September 2, 2007. The apex was about 279 km. The DC electric field was measured by the EVMR onboard S-520-23 sounding rocket. In this presentation, we report on the result of DC electric field measurement of two sounding rockets. In particular we will discuss about the relation between DC electric field and high electron temperature layer in the ionosphere using the results of S-310-37 sounding rocket experiments. Then we will show the preliminary report of DC electric field in the ionospheric E and F region measured by S-520-23 sounding rocket experiments.
SA13A-1092
Investigation of Electron Density Profile in the ionospheric D and E region by Kagoshima rocket experiment
The radio wave propagation characteristic in the lower ionosphere is important because of its effect on commercial radio communication, navigation, and broadcast services. The electron density is of primary interest in this region because the high ion-neutral collision frequencies result in radio wave absorption. In order to investigate the ionization structure in the ionospheric D and E region by using the propagation characteristics of MF-band and LF-band radio waves, S-310-37 and S-520-23 sounding rocket experiments have been carried out at Uchinoura Space Center (USC). S-310-37 sounding rocket was launched at 11:20 LT on January 16, 2007. The apex of rocket trajectory was about 138 km. Then S-520-23 sounding rocket was launched at 19:20 LT on September 2, 2007. The apex was about 279 km. As a common measurement, these sounding rockets measure the fields intensities and the waveform of radio waves from NHK Kumamoto broadcasting station (873kHz, 500kW) and JJY signals from Haganeyama LF radio station (60kHz, 50kW). The approximate electron density profile can be determined from the comparison between these experimental results and propagation characteristics calculated by the full wave method. We will get the most probable electron density profile in the ionosphere. In presentation, we will show the propagation characteristic of LF/MF radio waves measured by two sounding rocket experiments. Then we will discuss the analysis method and the estimated electron density profile in the ionosphere.