SA31A-01
Overview of 2006 COSMIC December Campaign
In conjunction with FORMOSAT-3/COSMIC satellite observations an ionosphere observation campaign was conducted during December 20-21 2006 to collect extensive data from ground-based and satellite borne instruments. In this paper we present an overview of the campaign and survey the collected campaign data. In addition to validate COSMIC electron density profiles and TEC deduced from COSMIC GPS radio occultation receivers, the COSMIC December campaign was organized to study E layer structures, scintillations, and assessment of inversion techniques. The GPS radio occultation receivers and Tiny Ionospheric Photometer onboard the FORMOSAT-3/COSMIC satellites provide TEC, electron density profiles, scintillation amplitudes, and ionospheric 135.6-nm UV airglow emissions. Incoherent scatter radar measurements were taken from Jicamarca, Arecibo, Millstone Hill, Mu, and Chungli radars as ground truth. In addition the extensive campaign dataset includes worldwide ground TEC data from GPS receivers, VHF beacon receivers, high cadence digisonde ionograms, scintillation monitoring indices, and airglow images. FORMOSAT-2 satellite also participated in the COSMIC campaign by taking snapshots of 630 nm airglow images at mid-latitudes over Taiwan and Japan. Future plan of the campaign study is discussed. Collaborative analyses of the COSMIC December campaign data are encouraged to improve space weather forecasting.
SA31A-02
A Comparison of Ionosphere Profile Observed by FORMOSAT-3/COSMIC and Ionosonde Radar
Six FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology Ionosphere and Climate) satellites were launched into a low earth orbit at 518 km at 0140 UTC on 15 April 2006. The six satellites will be placed into six different orbits with 30 degrees separation in longitude at 800 km mission orbit and covers the entire global ionosphere, providing over 2,500 sounding data per day. The main payload of the satellite, GOX (Global Positioning Satellite Occultation Experiment), observes the ionosphere between 90 km and 800 km while the occultation line of sight from GPS horizontally passes through the ionosphere. The ionosphere data as collected through the line of sight from the GPS radio signals passing through the E and F region can sweep across horizontal distances that range from 100 km to more than 3000 km in some cases. Consequently, the electron density profiles as collected through the radio occultation can span in wide regions that will be useful for the space weather study. Although there are no other electron density profiles in wide regions by the radio occultation technique, the comparison of the electron density profiles by radio occultation with the localized ionograms near the same regions observed by the ionosonde ground radar stations can be accomplished. In this paper, we will use the ionograms recorded by ionosonde stations during the 20-21 December 2006 FORMOSAT-3/COSMIC campaign and compare these ground measured radar data with the GPS radio occultation ionospheric profiles. This result is important to validate the reliability of FORMOSAT-3/COSMIC ionospheric observation using the radio occultation technique.
SA31A-03
Characterization of Ionospheric Scintillation Using Simultaneous Formosat-3/COSMIC Radio Occultation Observations and AFRL SCINDA Ground Scintillation Measurements
Ionospheric scintillation at low latitudes has been studied using ionospheric radio occultation (RO) measurements by the FORMOSAT-3/COSMIC micro-satellites in conjunction with ground-based data from the Scintillation Network Decision Aid (SCINDA) station at Kwajalein Atoll. The Air Force Research Laboratory has developed the SCINDA network for monitoring low-latitude ionospheric total electron content (TEC) and scintillation associated with equatorial spread F. The network currently consists of sixteen stations distributed around the globe and the data have been used to conduct numerous studies on the characteristics and climatology of equatorial scintillation. The present study focuses on COSMIC RO and SCINDA data during the three COSMIC campaigns in 2006. Radio occultation events are selected by requiring that ionospheric scintillation was detected by the SCINDA VHF scintillation monitor at Kwajalein, and that the occultation ray path intersected the Kwajalein longitude below the satellite altitude, which varied from 500 to 800 km for the six FORMOSAT-3 satellites. In order to exclude tropospheric effects, only GPS signal amplitudes from FORMOSAT-3 with ray path tangent altitudes above 100 km are considered. Locations of ionospheric scintillation are estimated by triangulation using the satellites and the SCINDA ground station. Airglow images at Kwajalein are also used to confirm occurrence of equatorial ionospheric scintillations. For the selected events, large amplitude L1 and L2 scintillations tend to occur at altitudes below 200 km at frequencies around 0.5 Hz. The results are discussed as a potential path toward better specifying the occurrence of equatorial scintillations.
SA31A-04
Simultaneous Analysis of COSMIC Ionospheric Occultations and Airglow Images During Periods of Equatorial Spread F
GPS-LEO radio occultation measurements are an important source of atmospheric and ionospheric state parameter data, particularly in locations not served by incoherent scatter or MST radars. Classical radio occultation theory invokes the assumption of locally spherical symmetry through the Abel transform to invert the refractive index profile, and thus the electron density and other parameters. While it is well-known that departures from spherical symmetry near the tangent point are detrimental to this inversion, the effects of horizontal gradients have not been studied in detail. One source of severe localized electron density gradients are depletions associated with equatorial spread F. These depletions are readily imaged from the ground as dark regions in otherwise bright recombination airglow emissions. Ground-based imaging of these emissions can provide a two-dimensional map of the horizontal gradients in the ionosphere. Thus, exploiting the field-aligned nature of the depletions, airglow images may be extruded along the geomagnetic field to form an approximate three- dimensional representation of the depleted flux tubes. In this study, we present several cases from the COSMIC mission illustrating the effects of horizontal gradients on occultation ray paths that traverse depleted flux tubes. Depleted flux tubes are identified using a narrow-field airglow imager at Cerro Tololo, Chile, operating in a field- aligned viewing geometry.
SA31A-05
Equatorial Total Electron Content (TEC) at Low and High Solar Activity
Total Electron Content derived from ionosonde data recorded at Korhogo (Lat=9.33 N, Long =5.43 W, Dip = 0.67 S) are compared to the Internatial Reference Ionosphere (IRI) model predicted TEC for high (1999) and low (1994) solar activity conditions. The result shows that the TEC has a solar activity and seasonal dependence. The IRI predicted values are closer to the observed TEC at high solar activity. However, at low solar activity the IRI overestimates the observed TEC. The deviation is more prominent in equinox during the time range 0900 to 2300 local time. The deviation is estimated to 60% of the observed TEC.
SA31A-06
Recent Results on Bottomside Sinusoidal Irregularities
We have used TEC data collected by a set of 12 GPS receivers located in South America, a UHF scintillation receiver system from Ancon, and bottomside profiles from the Jicamarca digisonde to investigate the ionospheric conditions that lead to the onset of BSS plasma irregularities. We have examined 20 months of observations extending between September 2001 and April 2003 to find 18 events that contain BSS-type irregularities. To qualify as a possible BSS event, the following 3 conditions were required to occur simultaneously: (1) strong or moderate levels of UHF scintillations, (2) absence of TEC depletions, and (3) ionograms containing frequency- type spreading. On December 21, 2002 the digisonde reported that the F-layer peak was higher than 600 km altitude between 03 and 06 UT. The high altitude of the F-layer was accompanied by a large latitudinal displacement of the anomaly that remained away from the magnetic equator for many hours after sunset. The ROCSAT satellite passed south of Jicamarca at 0528 UT observing density structures with 1 km-scale oscillations that are the prominent characteristic of BSS structures. The ROCSAT measurements imply that BSS irregularities are associated with frequency-type ionograms. Prior to the initiation and during the BSS irregularities, the drift meter on-board ROCSAT detected an upward drift equal to 50 m/s. This paper also reports the results of 2 ionospheric models that have been conducted to explain the formation of BSS-type irregularities.
SA31A-07
On the efficiency factor for Jicamarca incoherent scatter measurements
Sulzer and Gonzalez (1999) found that electron coulomb collisions have an important effect on the incoherent scattering of radio waves by a plasma at small aspect angles. The primary effect of electron coulomb collisions on incoherent scattering at small aspect angles is the narrowing of the spectrum. Another interesting effect of the collisions is the control of the efficiency factor (Milla and Kudeki, 2006), which is defined as a proportionality factor between the plasma electron density and the normalized total scattering cross section. For unmagnetized plasmas or the case of large aspect angles, the efficiency factor is approximately 1/(1+Te/Ti). Milla and Kudeki (2006), however, pointed out that the efficiency factor is far more complicated for small aspect angles. An analytical expression of the efficiency factor for small aspect angles does not exist yet. In this work, proper efficiency factor for Jicamarca measurements were obtained using numerical integration of the incoherent scatter spectrum including magnetic field and coulomb effects. The results were used to correct backscattered power profiles measured at Jicamarca. Corrected power profiles were compared with electron density profiles measured simultaneously using Faraday rotation. A good agreement between corrected power profiles and electron density profiles has been found. This result not only improves electron density measurements at Jicamarca, but also validates the formulation of Woodman (2006) and Kudeki and Milla (2006) based on the coulomb effects discovered by Sulzer and Gonzalez (1999).
SA31A-08
Characterization of the Direct Penetration of Magnetospheric Electric Field Convection at the Equator
The remarkable variations of terrestrial magnetic field and electrodynamics parameters at equator latitudes during a severe magnetic storm would be due to the magnetospheric disturbances which are connected to the ionosphere of high latitudes. The ionosonde data and the magnetic data recorded at Korhogo (9.34° N; 5.43° W) are used to characterize the disturbances observed in the equatorial region following the mechanism of direct penetration of magnetospheric convection electric field from high latitudes to the equator during the magnetic storm of November 18, 1993. The H component of the magnetic field for the disturbed day was compared to quiet day used as reference day. The electrodynamics parameters are obtained by inverting the ionograms with the NHPC code program (Reinish, 1996). The variation of the H component of magnetic fields during the disturbed day shows a negative deflection (different from the variation of quiet day) which lasts approximately 3 hours (1600 - 1900) and represents a westward disturbance of the zonal electric field. That corresponds to the inversion of the equatorial electrojet current during a time period of 3 hours attesting the direct penetration of the magnetospheric electric field from high latitudes towards the magnetic equator. The analysis of the electrodynamic parameters at equatorial latitudes shows an increase of F2 region electron density during this event simultaneously to an inversion of the vertical drift which flows downward for this time interval (1600 - 1900). The event is followed by a resurgence and intensification of the eastward zonal electric field and thus the re- establishment of the eastward normal electrojet current as a result of the reinforcement of the upward vertical drift simultaneously to a fall of F2 layer electronic density.
SA31A-09
Spectral Study of the Equatorial Electric and Magnetic Fields
We report on the spectral analysis of four years of daytime electric and magnetic field data obtained near the magnetic equator. The former were obtained using the JULIA radar system at the Jicamarca Radio Observatory using the so-called 150 km echo, which can be used reliably to determine the zonal electric field component during daytime. The magnetic field data were obtained using magnetometers located at Jicamarca and Piura in Peru. Due to the nighttime data gap, we can study variations with periods longer than two days and shorter than eight hours. Our goal for the longer periods is to study the variability of atmospheric drivers of the equatorial electrojet. This is straightforward for the electric field, but requires subtracting the ring current and other external effects from the magnetic field data. This is done by using the Gonzales/Anderson technique and employing the two magnetic field measurements. The electrojet strength decreased almost linearly over the four-year period as the solar cycle wound down. Spectral analysis reveals a clear semi-annual peak with maxima at the equinoxes and a secondary peak with a period of fourteen days. The latter seems to indicate that the lunar gravitational tide adds constructively to the semi-diurnal solar thermal tide. At higher frequencies the data must be parsed according to magnetic activity and solar wind conditions due to the importance of penetrating electric fields from the solar wind, and will be presented in this format.
SA31A-10
First Light for the Spatial Heterodyne Spectrometer to Detect Thermospheric Neutral Oxygen Density via Bowen Fluorescence at 844.6 nm
This project involves the spectroscopic observation of neutral oxygen via Bowen fluorescence at 844.0 nm using the Spatial Heterodyne Spectrometer. This will allow for the determination of neutral oxygen densities in the thermopshere, and for improved forward modeling of the dynamics of that important region between 250 and 500 km (where neutral oxygen is the dominant species). The values for the neutral oxygen density will be derived from the observations following the technique developed by Dr. Redgie Lancaster. The specific relations between O and O+ in the thermosphere and ionosphere -- involving charge exchange equilibrium and ion energy balance -- will be constrained with this data. The data will also probe the inferred discrepancy between the neutral oxygen density values calculated from O I airglow observations at 6300 Angstroms and those calculated from MSIS theory. The Spatial Heterodyne Spectrometer (SHS) is a novel kind of interferometer, capable of high-resolution spectroscopy without internal scanning mechanisms. It thus combines the etendue and compactness advantages conventional interferometers (such as the Michelson and Fabry-Perot) enjoy over slit spectrometers with a greatly increased robustness that makes it particularly suited to studies from space platforms or in harsh environments on Earth. Such applications in astronomy and atmospheric science are now being developed. The SHS developed for this project will make ground-based observations of Bowen fluorescence at the Millstone Hill Observatory beginning in March 2007. The expected signal strength is in the range of a few to tens of Rayleighs, observed around sunset, and the SHS will observe it with a signal-to-noise ratio of 600, including a 3- Angstrom narrowband filter.
SA31A-11
Investigating Coupling in the Mesosphere and Lower Thermosphere Through Tidal Features Detected in OH (6,2) and O2(0,1) Emissions
Tidal features have been detected in OH Meinel (6,2) and O2atmospheric (0,1) rotational temperatures obtained at Adelaide, Australia (34.9° S, 138.6° E) and South Pole (90° S). Rotational temperatures obtained from the OH (6,2) and the O2atm (0,1) bands are in general agreement and exhibit the same trends. Wavelike modulations and tidal spectral peaks at 6, 8 and 12 hours were simultaneously observed in the rotational temperatures of the OH (6,2) and the O2atm (0,1) bands. Because the two bands peak at different altitudes (~87 km and ~95 km, respectively), the amplitudes and phases at the two altitudes are used to calculate vertical wavelengths, phase speeds, and direction of propagation of the tides. Seasonal and annual variations in the tidal amplitudes are determined and compared to model outputs. Non- linear coupling and modulation of the tides by planetary waves is also investigated.
SA31A-12
Mesospheric Gravity wave momentum fluxes and their seasonal variation over a low latitude region Trivandrum (8.5°N, 77°E), India
Gravity waves play a profound role in the energetics and dynamics of the MLT region. Mainly generated in the lower atmosphere they propagate vertically upwards, thus carrying energy and momentum fluxes from lower atmosphere to MLT region where they attain maximum wave amplitudes. Determining the gravity wave momentum fluxes is a crucial requirement in understanding the momentum and energy budgets of the MLT region. Earlier studies have been carried out using VHF and MF radars, which have limited seasonal and height coverage. To understand the global morphology of gravity wave momentum fluxes, continuous measurements of winds are required in MLT region. Meteor wind radars are well suited for this purpose owing to their uninterrupted data coverage. Using two years of data (2004-2006) from All-sky SKiYMET Meteor Wind Radar at Space Physics Laboratory (SPL), Trivandrum (8.5°N, 77°E) operating at a VHF frequency of 35.25 MHz and a pulse repetition frequency of 2144 Hz, an attempt has been made to estimate the momentum fluxes of gravity waves in the MLT region (82-98km). Seasonal variation in the momentum fluxes is also estimated. The detailed study will be presented.
SA31A-13
Momentum fluxes of gravity waves and their role in Stratospheric Semi annual Oscillation
Deposition of energy and momentum fluxes carried by the vertically propagating waves alters the mean flow, which are in turn responsible for the maintenance of periodic oscillation. The need of the hour is to quantify the amount of momentum deposition by the various wave motions. Among all other waves in the atmosphere, the contribution of gravity waves in driving the periodic oscillations is very significant. Divergence/convergence of the energy and momentum fluxes carried by the gravity waves accelerate/ decelerate the mean flow which in turn partly responsible for the maintenance of QBO and SAO, which are the characteristic features of the equatorial region. Once the contribution of gravity waves is quantified it will be very helpful to parameterize these waves in the general circulation models, which are otherwise posing a great challenge to the scientific community. The difficulty in parameterizing these waves arises as its source mechanism and propagation characteristics exhibit a wide range of variability in both temporal and spatial scales. As part of middle atmospheric dynamics program (MIDAS 2002-2007), an effort has been made to study the role of gravity waves in the generation of different phases SAO. Rayleigh Lidar observation over Gadanki has been utilized to estimate the gravity wave momentum fluxes and elucidate its seasonal variations. An extensive study has been carried out to estimate the relative contribution of gravity waves in driving SAO during three different cycles of SAO. It is quite interesting to note that gravity waves of periodicities 30 minutes- 4hour contribute about 30%-50% towards the mean flow acceleration. The contribution of gravity waves towards the mean flow acceleration varies from cycle to cycle. The detailed study will be presented.
SA31A-14
Short-Period Mesospheric Gravity Waves and Diurnal Tidal Interactions at a Critical Layer
The US Maui-MALT program is designed to investigate the properties and dynamics of the low-latitude mesosphere and lower thermosphere region (MLT) in exceptional detail. On June 29, 2003, the University of Illinois Meteor Wind Radar (MWR) at Kihei, Maui (20.8°N, 156.4°W) observed a diurnal tidal wave with an amplitude twice as large as normal at mesospheric height (80--100 km) for 7 hours (1400--2100 UT). At the same time, the Utah State University Mesospheric Temperature Mapper (MTM) measured OH and O2 band emission intensities and temperatures at nearby Haleakala Crater, Maui (20.8°N, 156.2°W). The MTM observed a short-period gravity wave (GW) event propagating through this region for most of the night from 600 to 1500 UT. The GWs disappeared from the O2 band data (peak altitude: ~94 km) and the OH band data (~87 km) around 1400 UT and 1430 UT, respectively. Qualitative and quantitative investigations of relationship between the observed GW dissipations and the increasing background wind field show the following. 1. The wave dissipation observed in both emissions was caused by wave absorption at a critical layer (CL) when the background wind speed exceeded the wave phase speed. 2. The wave absorption at the CL appears to accelerate the background wind. 3. The acceleration occurred over a wide altitude range (80--100 km) because the CL was moving down in association with downward progression of the diurnal tidal wave. 4. The change in background wind speed caused by the GW absorption at the CL was comparable with the induced tidal effect.
SA31A-15
Two-Station Height Measurements of Mesospheric Bores at Equatorial latitudes
Since their discovery in the early 1990s mesospheric bores have become a topic of considerable interest. These are most unusual gravity wave events that are characterized in the nightglow emissions by a sharp leading front usually followed by a coherent train of waves that grow in number with time. Recent coordinated imaging and Na lidar wind/ temperature measurements have established the coexistence of mesospheric temperature inversion layers which act as a duct supporting the horizontal propagation of the bores. Depending on the altitude of the thermal duct, the optical signatures of the bore induced in the near infrared OH Meinel bands (peak altitude ~87 km), O2 (0,1) band (altitude ~94 km), and the OI (557.7 nm) line (altitude ~96 km) will be quite different. However, to date there have been no direct height measurements of such bore events. This poster presents novel two-station measurements of mesospheric bores imaged near simultaneously in the OH emission at equatorial latitudes during 2006--2007. The observations were made from north-eastern Brazil using two all-sky CCD cameras, one located at São João do Cariri (7°S, 36°W) and operated by the Federal University of Campina Grande. The second camera, from Utah State University, was located at Monteiro (7.9°S, 37.1°W) giving a site separation of ~85 km. At least four bore events have been identified in both data sets. Their signatures are faint but sufficient to permit an initial investigation of their height ranges.
SA31A-16
A Campaign to Study Equatorial Ionospheric Phenomena over Guam
With the development of a series of ground-based and space-based experiments, the United States Air Force Academy (USAFA) is in the process of planning a campaign to investigate the relationship between equatorial ionospheric plasma dynamics and a variety of space weather effects, including: 1) ionospheric plasma turbulence in the F region, and 2) scintillation of radio signals at low latitudes. A Digisonde Portable Sounder DPS-4 will operate from the island of Guam (with a magnetic latitude of 5.6° N) and will provide measurements of ionospheric total electron content (TEC), vertical drifts of the bulk ionospheric plasma, and electron density profiles. Additionally, a dual-frequency GPS TEC/scintillation monitor will be located along the Guam magnetic meridian at a magnetic latitude of approximately 15° N. In campaign mode, we will combine these ground-based observations with those collected from space during USAFA's FalconSAT-3 and FalconSAT-5 low-earth orbit satellite missions, the first of which is scheduled to be active over a period of several months beginning in the 2007 calendar year. The satellite experiments are designed to characterize in situ irregularities in plasma density, and include measurements of bulk ion density and temperature, minority-to- majority ion mixing ratios, small scale (10 cm to 1 m) plasma turbulence, and ion distribution spectra in energy with sufficient resolution for observations of non-thermalized distributions that may be associated with velocity- space instabilities. Specific targets of investigation include: a) a comparison of plasma turbulence observed on- orbit with spread F on ionograms as measured with the Digisonde, b) a correlation between the vertical lifting of the ionospheric layer over Guam and the onset of radio scintillation activity along the Guam meridian at 15° N magnetic latitude, and c) a correlation between on-orbit turbulence and ionospheric scintillation at 15° N magnetic latitude. These relationships may provide further clues into understanding the trigger mechanisms responsible for instigating disturbances in the ionospheric plasma, thus resulting in a turbulent radio propagation medium that may cause outages of radio based communication and navigation systems.