SA11B-01 INVITED
Detailed features of the low latitude ionosphere-thermosphere system, as derived from CHAMP observations
The CHAMP satellite, launched in July 2000, provides an extensive and valuable base of ionospheric and thermospheric measurements at low altitudes (~400 km) for more than 7 years. CHAMP carries a varity of advanced instrumentation such as a three-axes accelerometer sensing the ambient air density and thermospheric winds. The very sensitive magnetometer on board is able to detect faintest currents. Furthermore radio occultation and GPS topside sounding help to image the structure of the ionospheric electron density. These observations are accompanied by the local electron density and temperature measurements of the Langmuir probe. The CHAMP data base disclosed several climatological aspects of the upper atmosphere. One prominent feature of the thermosphere at low magnetic latitudes is the mass density anomaly showing in many respects resemblance with the equatorial ionisation anomaly. The ionisation anomaly itself has recently been shown to exhibit a pronounced 4-peaked longitudinal structure in the post-sunset local time sector (e.g. Immel et al., 2006). We could show that this longitudinal structure is also present during day time hours. Furthermore, it could be deduced from CHAMP data that the thermospheric zonal wind also yields a wave-4 pattern, but the phase of this wind component switches sign between day time and evening hours. Reasons for these observations are still under investigation. Another rather novel result is the identification of faint magnetic signatures caused by equatorial spread-F (plasma bubbles). Based on a systematic investigation the global distribution of the bubble's magnetic signature has been derived and a detailed climatological picture of their occurrence rate could be drawn.
SA11B-02 INVITED
Study the Upper Atmosphere Using FORMOSAT 3 / COSMIC GPS Radio Occultation Data
New opportunities for studying the upper atmosphere phenomena have become available after the launch of the satellite constellation FORMOSAT-3/COSMIC (F3/C), providing GPS radio occultation data which enables researchers to investigate the upper atmosphere globally in three-dimension. With more than 2500 soundings of the atmosphere every day, vertical electron density profiles in the ionosphere as well as temperature profiles in the stratosphere are available for the study of global ionospheric plasma structures and stratospheric temperature variations over the continents and the oceans, where ground-based observations are limited. In this talk, new results from our efforts in investigating several interesting phenomena in the upper atmosphere using the F3/COSMIC data will be presented. Future applications of the GPS radio occultation data will be discussed.
SA11B-03
Ionospheric Electron Density Derived by Using the TIP and GOX of FORMOSAT- 3/COSMIC
The tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) onboard FORMOSAT-3/COSMIC are employed to measure the OI 135.6 nm intensities and derive the electron density profiles in the ionosphere, respectively. Due to its very high sensitivity ~600 counts/Rayleigh and rather narrow nadir pointing 3.8¢X circular field-of-view, the TIP provides accurate characterization of ionospheric electron density gradients in the horizontal direction. Meanwhile, a technique of the low earthquake orbital (LEO) tomography is applied to analyze the GOX data accurately obtaining the F2-peak electron density, NmF2, and the height, hmF2. Here, we combine the two observations to carry out the GOX-TIP tomographic inversions.
SA11B-04
The effect of the vertical ExB drift on the longitudinal plasma density structure in low-mid latitudes
We investigate the temporal evolution of the longitudinally periodic plasma density structure in low-mid latitudes and its association with the vertical ExB drift pattern using the ROCSAT-1, TIMED/GUVI, DMSP, and FORMOSAT- 3/COSMIC data. The preliminary ROCSAT-1 observations show that the signatures of the periodic density structure occur before 0900 LT and are well correlated with the morphology of the vertical ExB drift. The density peaks develop in the regions where the upward ion velocity in the morning is larger than that in the neighboring longitudes. The growth of the density peaks in the afternoon depends on the persistence of the upward ExB drift. We will further investigate the seasonal, local time, and altitudinal variations of the density structure and ExB drift pattern by analyzing multiple satellite data. We will also conduct the SAMI2 model simulations to investigate the impact of the vertical ExB drift in the morning on the longitudinal density structure in the afternoon and at night.
SA11B-05
Multi-dimensional numerical modeling of the ionospheric electron density based on the FORMOSAT-3/COSMIC GPS radio occultation data
The FORMOSAT-3 (FS3)/COSMIC program uses the radio occultation technique to receive dual-frequency GPS carrier phase signals from six low Earth orbiting satellites and approach ray-path total electron content (TEC) measurements. Using the Abel inversion through TEC values, we can collect about seventeen hundreds of vertical profiles of the ionospheric electron density within one day and than retrieve the ionospheric characteristics (e.g. foF2 and hmF2) and vertical total electron density (VTEC). The retrieved ionospheric parameters and electron density results have been used to produce numerical maps and models representing the complex properties on a world-wide scale. Here we present a two-dimensional (2D) approach from the surface spherical harmonics analysis for mapping foF2, hmF2, and VTEC data. Another approach can be generalized to the 3D case (2D surface spherical harmonics and vertical EOFs) for modeling the ionospheric electron density. The derived numerical maps and models have also been examined through the International Reference Ionosphere (IRI) model.
SA11B-06
IDA4D – a new ionospheric imaging algorithm using non-linear ground-based and spaced- based data sources
New data assimilative methods combining ground and spaced-based ionospheric data are used to investigate the dynamics of the mid and low-latitude ionosphere. Data sources that are both linearly and non-linearly related to electron density can for the first time be ingested into the four-dimensional (4D) ionospheric imaging algorithm "Ionospheric Data Assimilation Four Dimensional" (IDA4D). This innovative step to use nonlinear data sources allows previously unused ionospheric data to be included in a data assimilation process that now takes in nine types of measurements to produce highly accurate ionospheric maps on a global scale, with formal error estimates. IDA has been in development for over 15 years, and is a mature, well validated algorithm that has been used for a number of scientific investigations. In the last year the IDA algorithm has been improved in two ways. First, IDA now solves for the log of electron density in a non-linear iterative method. This assures that the electron density is positive definite. Second, the algorithm uses high-latitude drift velocities obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm in a high-latitude forward prediction model. This provides a much improved capability for imaging high-latitude plasma structures. In addition to algorithm improvements, several new data sources have been added to IDA. The addition of the non-linear methodology has allowed the ingestion of non-linear data sources. These include time delay versus frequency obtained from ionosondes, EUV data from the GUVI sensor on the TIMED satellite and the TIP sensor on COSMIC. In addition, the other data sources on COSMIC including occultations and Tri-band beacon data are routinely ingested by IDA4D. Finally, new linear data sources that are now ingested by IDA4D include data from the DORIS array and CITRIS receiver. The new IDA4D algorithm is used to investigate the ionospheric system response to magnetic storms. Images of electron density are presented for several recent magnetic storms. The relationship between the observed ionospheric structures and the underlying physical mechanisms that cause them is discussed. Also discussed are innovative methods that investigate the relative importance of the underlying physical processes using the new algorithm in ways that were previously not possible.
SA11B-07
Measurements of the Thermospheric Wind Vector, Temperature and Relative Densities on the ANDE mission
A satellite in low Earth orbit moves at 8 km/s, much faster than the average molecular RMS speed - around 1 km/s, depending on molecular mass. A spectrometer whose aperture points into the ram detects a molecular flux with angular distribution that depends on the air temperature. We describe a new method to obtain the neutral wind vector, temperature and relative densities of major species (O and N2) in the thermosphere; it requires measurement of the angular distribution of the molecular flux and its energy distribution at an angle near the angle of maximum flux. The angle of the flux peak gives the direction of the total velocity vector in the satellite frame of reference. The energy distribution gives the magnitude of the total velocity vector. Then the full wind vector follows from the total velocity vector, the satellite velocity vector, and the spectrometer pointing angle. We have analyzed the fluxes produced by a Maxwellian gas drifting into a spectrometer aperture at a known satellite velocity to determine the required level of precision of the energy and angle measurements. Current technologies enable the energy-angle measurements, and the amount of data required to obtain the wind, temperature and relative densities is small enough that it can be transmitted to the ground for analysis. To achieve temperature/wind errors of 1K/10m/s we need to sample the angular distribution over 3 full-widths (25 deg) with angular resolution of 2 deg, and sample the energy spectrum with a resolution of 1 part in 20. The proposed measurement scheme can detect Maxwellian as well as non-Maxwellian distributions in the gas because it must measure these distributions explicitly – revealing any departure from Maxwellian immediately. We will discuss our implementation of this method in the Atmospheric Neutral Density Experiment (ANDE) mission of the U.S. Naval Research Laboratory.
SA11B-08
Investigations Based on the 3D Distribution of Optical Emissions at High Latitudes Obtained by ALIS
In this paper recent results from ALIS, the Auroral Large Imaging System, are presented. ALIS is a powerful system in Northern Scandinavia capable of doing 3D tomographic spectroradiometry. At present ALIS consists of six stations, spaced about 50 km. Each station has a CCD imager with a six-position filter wheel equipped with narrow-band interference filters. The field-of-view is roughly half all-sky. A positioning system enables imaging from several sites with overlapping fields-of-view for any desired part of the sky. To study the electrodynamics of an auroral arc ALIS images were used for tomographic reconstruction of the 3D distribution of the volume emission rate of aurora, and from that the initial differential particle flux was deduced. This particle flux was used as input into an auroral ionosphere model and ionospheric conductivities were calculated. Imaging of black aurora made it possible to draw conclusions about the causing mechanisms. In an experiment involving the EISCAT Heating facility the formation of an auroral arc was stimulated, leading to conclusions about the importance of a feedback mechanism.