SA33B-1321
Derivation of temperature and density from Langmuir probe observations with a small surface-to-probe area ratio
We present the dataset from two separate payloads of the EQUIS II sounding rocket campaign. The rockets were launched into thin radar scattering layers that were observed as precursors to nighttime Equatorial Spread-F. The payloads carried an RF Plasma Impedance Probe and a fixed-bias DC Langmuir probe (DCP) on one axial boom, and an internally heated sweeping Langmuir probe (SLP) that was guarded on one side on a second axial boom. The ratio of the payload surface area to the cumulative area of the sweeping Langmuir probe instrument and its guard was only about 250. We present a charging model for the payload and instrument combination to understand the problems associated with small surface-to-probe area ratio and then correlate the instrument observations with model output. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not accurate. The ion saturation region analysis of the SLP I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the impedance probe. The derived temperatures agree reasonably well with the IRI model, but also show unusual structure at small scale. Our results suggest that even with a small surface-to-probe area ratio it is possible to derive absolute plasma density and temperature from a sweeping Langmuir probe.
SA33B-1322
Model Simulation of the Equatorial Electrojet in the Peruvian and Philippine Sectors
Between 100 and 120 km above the Earth's magnetic equator, the equatorial electrojet (EEJ) flows as an enhanced eastward current in the daytime E region ionosphere which can induce a magnetic perturbation on the ground. Calculating the difference between the horizontal components of magnetic perturbation at magnetometers near the equator and about 6-9 degrees away from equator, ¡µH, provides us information about the strength of the EEJ. The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE- GCM) is capable of simulating the EEJ current and its magnetic perturbation on the ground. The simulated diurnal, seasonal (March equinox, June solstice, December solstice), and solar activity (F10.7 = 80, 140 and 200) variations of ¡µH in the Peruvian (75¢XW) and Philippine (120¢XE) sectors, and the relation of ¡µH to the ionospheric vertical drift velocity, are presented in this paper. Agreement between simulated and observed magnitudes of ¡µH is improved by modifying the standard daytime E region photochemistry in the TIE-GCM in order to better simulate observed E region electron densities.
SA33B-1323
Mysterious stripes observed over amazon by the PALSAR onboard ALOS satellite
From the analysis of all the images acquired by the Phased array type L-band SAR (PALSAR), which is a L-band synthetic aperture radar onboard Advanced Land Observing Satellite (ALOS) operational from May 2006 during April 2006 to December 2006, we found that several tens of images collected mainly in October, November and December of 2006 were interfered by the intensity variations, many small-width stripes along the satellite track, that are possibly caused by the ionospheric instability related to the disturbance of electron density due to the solar-earth daily interaction. The number of the interfered samples reaches to sixty, and all occurred in the nighttime in the Amazon. The interfered region reaches to 300km in east-west direction and 1000km or more in north-south direction. Since the width of the stripe is several hundred meters in range direction, the interference can be interpreted as phenomena that the ionospheric scintillation at the equatorial Amazon caused by the generation of the plasma bubbles that relates to the neutralization of the plasmatic atmosphere after the dark and their nonuniform diffuse. This stripe can be interpreted as the local TEC variation interfered the intensity of the SAR images. This is explained as the additive phenomena of two facts, 1) variation of the Total electron Contents (TEC) caused inuniformity of the refraction, and thus the ununiform compression of the image in range direction, 2) rotation of the polarimetric plane of the linear polarization L-band SAR caused by the number of the electrons density and the geomagnetic field. In this paper, we analyzed the several samples of this scintillation at the equatorial region, and obtain the quantitative TEC variation. As a result, it found that the PALSAR can measure the structure of the TEC distribution much more precisely than using the GPS.
SA33B-1324
Daytime 150-km Echoes Observed by the Multi-beam Equatorial Atmosphere Radar in Indonesia
The so-called "150-km echoes" observed in the daytime equatorial ionosphere have been least understood for more than 40 years. They were studied with the Jicamarca VHF radar for the most part and also observed by other radars installed in the equatorial regions. Recently, 150-km echoes were observed with the Gadanki MST radar in India (6.3° dip latitude), which is the first observation outside the equatorial electrojet belt [ Patra et al., 2006]. Therefore, it is important to investigate the latitudinal variation of 150-km echoes for further understanding. The 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20°S, 100.32°E, - 10.14° dip latitude) has the unique capability of rapid beam scanning on a pulse-to-pulse basis. We conducted an experiment for 150-km echoes with EAR in August 2007, and detected clear necklace-shape echoes between 145~km and 160~km altitude successfully. This is the first evidence that 150-km echoes exist 10° away from the dip equator. We used three radar beams with azimuth angles of 165°, 180° and 195° and zenith angles were set to be perpendicular to the geomagnetic field (21°-22°). By synthesizing Doppler velocities from three directions, we can estimate vertical and zonal drift velocities on the plane perpendicular to the geomagnetic field. The vertical and westward velocities are 5-20~m~s-1 and 20- 50~m~s-1, respectively, which resemble typical 150-km echoes observed by the Jicamarca radar. Further observation with the EAR will shed light on the generation mechanism of these echoes.
SA33B-1325
Ionospheric Electron Density Measurements Using COSMIC
At 0140 UTC on April 15, 2006, the joint Taiwan-U.S. COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate and Formosa Satellite mission #3; hereafter COSMIC) mission, a constellation of six micro-satellites, was launched into a 512-km orbit from Vandenberg Air Force Base in California. Using on-board propulsion these satellites have been deployed to their final orbits at 800 km with 30 degrees of separation. This process has taken about 17 months following the launch. There are three instruments aboard each COSMIC satellite: the GPS Occultation Experiment (GOX), the Tri-Band Beacon (TBB), and the Tiny Ionospheric Photometer (TIP). These three instruments constitute a unique suite of instruments for studying the Earth's ionosphere. The GOX instrument operates by inferring the slant total electron content (the integral of the electron density along the line-of-sight) between the COSMIC satellites and the GPS satellites as a function of tangent height above the Earth's limb. These data can be inverted to produce electron density profiles in the E and F regions of the ionosphere. The TBB is a three frequency radio beacon that radiates coherently at 150, 400, and 1067 MHz. When the relative phases of the signals are measured between the COSMIC satellites and ground-based or space-based receivers, the total electron content along the line-of-sight can be determined. By making the measurements from a set of receivers, the two-dimensional distribution of electrons beneath the satellite can be determined using tomographic techniques. The TIP instrument measures the optical signature of the natural decay of the ionosphere produced via ecombination of the O+ ions and electrons. The TIP measurements can be used to characterize the morphology and dynamics of the global ionosphere. Additionally, the TIP measurements can be inverted in conjunction with the GPS occultation measurements, using tomographic techniques, to produce the two- dimensional distribution of electrons beneath the satellite. We present an overview of the COSMIC mission, the instruments, and their application to ionospheric sensing.
SA33B-1326
GUVI limb observations of the Equatorial Ionization Anomaly
High altitude limb scans from Global Ultra Violet Imager (GUVI) contain signatures of the Equatorial Ionization Anomaly (EIA) observed using 1356 Å recombination emissions. This paper reports observations of the geomagnetic quiet time EIA and its global behavior at all local times, longitudes and seasons. Limb data is prepared for analysis using reduction techniques that remove from the limb file, contaminating signatures due to stars, glints and low altitude day time neutral atmosphere glow due to photoelectrons. A simple comparison of the subtracted data at different longitudes, seasons and magnetic activity reveal significant EIA variability with each of these factors. This data set integrated in altitude, is used to develop the global morphology of the quiet time EIA using metrics such as the magnetic latitudes of the north and south crest and the crest radiances that are extracted from the EIA structures. Observations from year 2003 to 2005 clearly show development in the anomaly strength between 11:00 to 14:00 LT. Signatures of the pre-reversal drift enhancement due to enhanced post-sunset F-region vertical drifts appear strongly during December solstice seasons between 19:00 to 21:00 local time at solar maximum periods. However this effect is found to be unexpectedly absent during equinox. Also observed is the lack of any EIA activity during June solstice during all the three years.
SA33B-1327
Occurrence characteristics of plasma bubble derived from global ground-based GPS receiver networks
Occurrence characteristic of plasma bubble was studied with ground-based GPS receiver networks. The coverage of the observation with global grond-based GPS receivers is wider than that with the other observatinal instruments because of the large number of receivers. The physical characteristics of plasma bubble occurrence were studied in detail with this novel data set. 23 GPS receivers around the dip equator were used to reveal occurrence of plasma bubble from 2000 to 2006. Monthly and semiannual occurrence rates for all longitudinal regions were studied. Characteristics of the monthly occurrence rates were different among the regions. Although it was found that sunset time lag effect plays an important role for the monthly variation, two asymmetries which could not be explained with the sunset time lag scenario were found: (1) asymmetry between two solstices and (2) asymmetry between two equinoxes. (1) was found in all of the regions. The F-region conductivity integrated along the geomagnetic field line, ΣFP, could affect on this solstice asymmetry. (2) was found in every region. (2) in the Central Pacific region was found for seven years from 2000 to 2006. Semiannual occurrence rates from 2000 to 2006 were used to study the year-to-year variation from the high solar activity period to the low solar activity period. The dependency of plasma bubble occurrence on the solar activity was different among the regions. In the Asian region, the occurrence rates decreased from 70% in 2002 to 10% in 2006. In the Atlantic region, on the other hand, the occurrence rates were between 20% and 50%, and did not show linear decrease as the solar activity. Occurrence rates against the latitude/altitude were also investigated in the Asian region in 2004. It was found that the occurrence was high and constant below 700km altitude on the dip equator. They began to decrease when the the altitude was higher than 700km, and was almost zero where the HODE was higher than 900km.
SA33B-1328
Ionospheric Scintillation Effects on GPS
Abstract. Ionospheric scintillation of Global Positioning System (GPS) signals threatens navigation and military operations by degrading performance or making GPS unavailable. Scintillation is particularly active, although not limited to, a belt encircling the earth within 20 degrees of the geomagnetic equator. As GPS applications and users increases, so does the potential for detrimental impacts from scintillation. We examined amplitude scintillation data spanning seven years from Ascension Island, U.K.; Ancon, Peru; and Antofagasta, Chile in the Atlantic/Americas longitudinal sector at as well as data from Parepare, Indonesia; Marak Parak, Malaysia; Pontianak, Indonesia; Guam; and Diego Garcia, U.K.; in the Pacific longitudinal sector. From these data, we calculate percent probability of occurrence of scintillation at various intensities described by the S4 index. Additionally, we determine Dilution of Precision at one minute resolution. We examine diurnal, seasonal and solar cycle characteristics and make spatial comparisons. In general, activity was greatest during the equinoxes and solar maximum, although scintillation at Antofagasta, Chile was higher during 1998 rather than at solar maximum.
SA33B-1329
Altitude latitude mapping of plasma depletions
Plasma depletions, if generated at the geomagnetic equator, are expected to appear in the all sky images as dark bands extending pole ward. The all sky observations conducted from Kavalur (12.5¢ªN, 78.8¢ªE; 4.6¢ªN, geomagnetic), INDIA, but showed dark patches in 630.0 nm entering the imager field of view (FOV) from the northern edge in the post-sunset period. These patches gradually extended towards equator and became fully extended dark bands in the North-South direction by midnight. The series of such images appeared to be the airglow signatures of irregularities that are probably generated at off-equatorial latitudes and mapped to the lower or equatorial latitudes. Similar features were observed in several nights. This appearance of depletions as dark patches from the northern edge of the FOV is explained in this work
SA33B-1330
The Low-latitude Ionosphere as Observed by TIMED/GUVI and TOPEX/Jason and Comparisons With the IRI Model
Long term measurement datasets available from several recent satellite missions provide essential information for better understanding the electrodynamics of ionosphere, especially in the low-latitude region. The TOPEX and Jason satellites have obtained the total electron content (TEC) over the oceans from ~1200 km orbit between 1992-present. TIMED/GUVI has retrieved the F-region electron density profile below ~550 km from 2002-present. The availability of these datasets allows us to examine the structure of the low-latitude ionosphere over a solar cycle. We will also present the detailed comparisons of our results with those from IRI model with an emphasis on variations in local time, longitude and over the solar cycle.
SA33B-1331
A Prediction Model for Solar-Driven Ionospheric Electric Fields at Arbitrary Locations
In an earlier work [Rothwell and Jasperse, 2006] we derived the global ionospheric electric field produced by the Region-1 and Region-2 currents. Despite the simplifying assumptions in that work of both the dipole and spin axis being aligned perpendicular to the ecliptic plane we found promising agreement with Jicamarca vertical drift data. However, in order to extend the model to arbitrary geographic locations we now take into account 1) the tilt of the magnetic dipole, as well as local IGRF modifications in the B-field, 2) a seasonal, solar-driven ionospheric conductance model which is accurate near the terminators, and 3) the Region-1 and Region-2 currents properly defined in magnetic coordinates. For example, the Region-1 and-2 currents are fixed in the inertial frame so that at a given geographic location there is a daily variation in the ionospheric electric field due to this effect. As in the previous work, Region-1 and Region-2 currents are related, using the Hill-Siscoe transpolar potential model, to the solar wind data as measured at L1 by the ACE satellite. In this way, we intend to build a useful Space Weather Forecasting tool by which the time-dependent, solar-driven ionospheric electric field is defined at any geographic location. Rothwell, P. L., and J. R. Jasperse(2006) Modeling the connection of the global ionospheric electric fields to the solar wind, J. Geophys. Res., 111, A3211, Doi:10.1029/2004JA010992.
SA33B-1332
Generation and characteristics of equatorial spread F plasma bubbles during intense magnetic storms
Magnetic storms represent very large disturbances in the magnetosphere and ionosphere. Equatorial spread F (ESF) is a process that causes plasma density irregularities in the equatorial F region. However, it is not well understood how magnetic storms affect the generation of ESF plasma bubbles. We will present the measurements of the evening equatorial ion density and velocity by the Defense Meteorological Satellite Program (DMSP) satellites and the Jicamarca incoherent scatter radar during twenty-three intense magnetic storms with minimum Dst value of smaller than -100 nT. The radar measurements show that penetration electric field during southward interplanetary magnetic field (IMF) is eastward in the evening sector and lifts the equatorial F region there. The DMSP measurements show that deep equatorial ion density depletions (ESF plasma bubbles) are generated after the IMF turns southward. The time delay between the IMF southward turning and the first DMSP detection of ion density depletions becomes shorter when the interplanetary electric field during southward IMF, correspondingly an eastward penetration electric field in the evening equatorial ionosphere, is larger. The results of this study provide strong evidence that enhanced magnetic activity increases the generation of ESF plasma bubbles during the main phase of magnetic storms. We will also present the observations of a case in which the plasma density depletions occurred at middle magnetic latitudes, as well as at equatorial latitudes. The depletions at middle latitudes (20-46 deg) were identified as the extension of depleted flux tubes into these latitudes. It implies that the plasma bubbles might have reached the altitude of 6800 km over the magnetic equator. The observations may represent the highest altitude/latitude of plasma bubbles that has ever been reported in the literature.
SA33B-1333
Relation between the variations of the solar wind and the noon-time equatorial ionospheric electric fields
We compare the solar wind measurements from ACE satellite with the vertical plasma drift (observed by JULIA radar) and the EEJ magnetic signals (observed at HUA observatory) from the South American equatorial sector. The aim is to understand the effect of solar wind on the variations of the electric field in the noon time equatorial ionosphere. We restrict our study to local noon time conditions, geomagnetically active days and while interplanetary Bz is negative. The estimates of electric field intensities (E_VS) at equatorial plain of the magnetosphere were made from ACE data using a combination of Volland-Stern and Siscoe-Hill models (Burke et al, 2007). The JULIA and magnetometer data were high-pass filtered to remove the regular daily variations. The relation between the data set will be presented as a coherence spectrum. In addition, the use of the ACE measurements to improve the climatological models of EEJ during geomagnetically active days will be explored.
SA33B-1334
The CHAMP data base of Equatorial Spread-F magnetic signatures
Novel possibilities to detect Equatorial Spread-F (ESF) events are given by the magnetic signatures of the depleted plasma tubes. The diamagnetic effect enhances the total magnetic field in regions of low plasma density. We use 7 years (2001-2007) of almost continuous high quality magnetic field observations on board the CHAMP satellite to reconstruct the global climatology of the ESF magnetic signatures at about 400 km altitude. Our results compare very well with existing ESF climatologies based on satellite observations of electron density, especially in longitudinal and seasonal (S/L) dependences. We find an excellent agreement with the S/L distribution of the equatorial prereversal vertical plasma drift velocity derived from ROCSAT-1 observations. These results prove that the vertical plasma drift acting on the F-layer height is the dominant contributor to the ESF occurrence. The increasing CHAMP data set spanning different solar cycle phases reveals the existence of more, larger and stronger ESF events for high solar flux level conditions. These characteristics are reflected in the extended local time and the higher L-values where ESFs are observed at high solar flux levels. CHAMP also provides observations of the transverse magnetic ESF signatures. These deflections imply the existence of field- aligned currents. Such observations will be used for characterizing the electrodynamic state of the ESF event.
SA33B-1335
Distributions of Pre-sunrise Plasma Heating in the Low- and Mid-latitude Topside Ionosphere
Pre-sunrise ionospheric heating above F layer peak was first observed by Carlson (1966) with incoherent backscatter radar at Arecibo Ionospheric Observatory during winter season. Photoelectrons streaming from sunlit magnetic conjugate ionosphere were concluded to produce the observed ionosphere heating. Recently global distributions of ion temperature were available from Ionospheric Plasma and Electrodynamics Instrument (IPEI) onboard the first satellite of Republic of China, ROCSAT-1, to study the pre-sunrise ion heating (Chao et al., 2003). The results showed that the most enhanced pre-sunrise heating was located in the longitude sector between 165° E and 195°E in the southern hemisphere (South Pacific region) during June solstice and between 75° W and 15° W in the northern hemisphere (North Atlantic region) during December solstice. In this study, we have compared with electron temperature distributions observed two decades ago by Hinotori satellite. The two distributions match very well in the 0400-0500 LT sector. We will also verify the distributions with results from SAMI2 model for more details.