SA12A-01 INVITED
WIND, FERIX-2 and ISUAL F-region imaging: Ionospheric Observation Campaigns over Japan in 2007
In the middle/low latitude ionosphere, coupling processes between plasma and neutral atmosphere is important, which is a key to understand ionospheric structures of the spatial scale of 10-1000km. Under international collaboration between scientists from Japan, Taiwan and USA, we are now conducting number of observation campaigns over Japan region. WIND (Wind measurement for Ionized and Neutral atmospheric Dynamics study) is a F-region rocket experiment to study neutral-plasma coupling processes. ISAS/JAXA successfully launched the S-520-23 sounding rocket from Uchinoura Space Center on September 2, 2007. The rocket was equipped with in-situ instruments for plasma-parameters. The Li-release experiment was conducted at the rocket downleg to measure the neutral wind. A dual-band beacon (DBB) transmitter was on board of the rocket, and we received the signal at five stations including one boat under the rocket trajectory. FERIX-2 (F- and E-Region Ionosphere Coupling Study-2) is multi-radar experiment to reveal F-region and E- region coupling processes in the ionosphere. Simultaneous measurement of F-region and E-region FAIs with the MU radar and a portable VHF radar obtained much data showing the coupling through geomagnetic field line. In parallel to these observations we conducted limb imaging of the airglow in the F-region by means of ISUAL on the FORMOSAT-2 satellite in December 2006 and June 2007. Data from FORMOSAT-3/COSCMIC satellites are valuable to support these observations. In the presentation we will overview preliminary results from these observation campaigns, and discuss future collaboration for the study of middle-low latitude ionosphere.
SA12A-02 INVITED
Modeling the Impact of Terrestrial Weather on Thermosphere Ionosphere Structure
Recent observations have revealed unambiguous signatures of the impact of terrestrial weather on the upper atmosphere. The manifestation are either spatial, indicating a longitude dependence in ionospheric features, or temporal, indicating multi-day periodicities from planetary wave forcing. A new model of Integrated Dynamics through Earth's Atmosphere (IDEA) that self-consistently combines a Whole Atmosphere Model (WAM) with a Global Ionosphere Plasmasphere (GIP), together with a solution of global electrodynamics has been used to begin to interpret the observations. The model was developed under a NASA sponsored collaborative project between the University of Colorado and National Weather Service's (NWS) Environmental Modeling and Space Environment Centers. The model was specifically designed to understand and interpret the recent observations, and determine the physical processes responsible for the longitude dependent ionospheric spatial structure and planetary wave (PW) modulation of the upper atmosphere. The model simulates ionospheric variability and is used to begin to quantify and separate the impact of either neutral dynamics, composition, and electrodynamics at mid and low latitudes.
SA12A-03
Traveling ionospheric disturbances observed by GPS network in North America and Millstone Hill IS radar
We report the daytime traveling ionospheric disturbances (TIDs) observed by the GPS receiver network in North America and the Millstone Hill incoherent scatter radar (MH-ISR) during Jan 20-23, 2007. Analysis of the high- resolution wide-coverage total electron content (TEC) maps from the GPS network revealed that the daytime TIDs have a wavelength of 300-1,000 km and a propagation velocity of 100-200 m/s. The daytime TIDs propagate southeastward prior to noon while the TIDs post-noon propagate southwestward. These TIDs are superimposed on each other around the post-noon period. The MH-ISR simultaneously observed periodic electron density fluctuations showing downward phase propagation in the ionospheric F-region. Perturbations with a period of ~1 hour in the F-region electron density correspond to the perturbations observed in the GPS-TEC measured above the MH-ISR. The maximum phases of perturbations in both GPS and ISR datasets are seen during the transition of detrended wind direction from southward to northward. The wind direction was calculated using the MH-ISR ion drift data in the altitude range 230-400km. These observational results indicate that the daytime TIDs are caused by atmospheric gravity waves generated in the auroral latitudes.
SA12A-04
TIMED/SABER Observations of the Storm-Time E-Region: Morphology, Chemistry, and Energetics
A new data product derived from TIMED/SABER measurements of 4.3 um limb emission is the NO+(v) volume emission rate (VER). We have found NO+(v) VER to be versatile analysis tool for studying the E-region response to solar-geomagnetic storms. Enhancements in nighttime 4.3 um emission during storm periods are due to vibrational excitation of NO+ (i.e., NO+(v)), caused by auroral dosing and subsequent ion-neutral chemical reactions, followed by radiative emission at 4.3 um. The NO+(v) VER is derived by (1) removing the background CO2 infrared emission using SABER observations and non-LTE radiation transfer models, and (2) by performing a standard Abel inversion on the residual radiance. Since NO+ is the terminal E-region ion, the NO+(v) VER is an excellent proxy for characterizing the morphology of the E-region response to magnetic disturbances. Analysis of the April 2002 and Halloween 2003 storm periods reveal spatial structure in the NO+(v) VER that is difficult to understand: large enhancements at mid-latitudes, well outside the region of strong auroral precipitation, and a bi- modal distribution in the vertical peak. The maximum NO+(v) VER for each profile occurs at roughly 110 km or 130 km. The International Reference Ionosphere (IRI) model indicates that the E-region electron density peak always occurs at roughly 110 km. In this paper we seek to understand the horizontal and vertical structure of the SABER- derived NO+(v) VER during the April 2002 and Halloween 2003 storm periods by utilizing both measurements and detailed modeling of the E-region chemistry, energetics, and radiation transfer. The morphology of the SABER-derived NO+(v) will be compared with radio occultation profiles of E-region electron densities measured by CHAMP, and with incoherent scatter radar measurement data available through the CEDAR database. In addition, we will model the NO+(v) VER by dynamically driving the field-line interhemispheric plasma (FLIP) model with particle precipitation energy characteristics observed by the NOAA/POES satellites. The FLIP model provides the ion and neutral density inputs for our NO+(v) kinetics model, which provides the NO+(v) densities for the 4.3 um non-LTE radiation transfer calculations used simulate the NO+(v) VER. The modeled NO+(v) VER provides a diagnostic approach to understanding the mechanisms responsible for the spatial structure observed in the SABER-derived NO+(v) VER.
SA12A-05
A multi-instrument technique for localization of radio wave scintillation in the equatorial ionosphere
Although ground-based scintillation monitoring has revealed much about the irregularities that cause scintillation, this technique has limited geographic coverage and requires knowledge of the irregularity altitude to infer scale information. GPS radio occultation experiments provide a source of scintillation measurements at geographically diverse locations and geometries impossible with ground-based scintillation monitors. In their simplest form, radio occultation experiments localize regions of scintillation to the ray path between the transmitter and receiver. Radio wave back-propagation techniques have been employed in the past to compute the range to irregularities; however, it is also instructive to obtain a three-dimensional view of irregularity regions. We present a new technique that integrates GPS radio occultations with ground-based narrow-field airglow imaging. Plasma depletions seen in the airglow images are extruded along the geomagnetic field to create a three-dimensional representation of the depleted flux tubes. Intersections between the depleted flux tubes and occultation ray paths are computed, yielding an estimate for the altitude distribution of scintillation irregularities. We present results of 26 coincident imaging/occultation observations in the South American sector during the 2006--2007 spread F season.
SA12A-06
GUVI Equatorial Plasma Bubble Imaging and Climatology, 2002-2007
Since its launch on-board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite in December 2001, the Global Ultraviolet Imager (GUVI) has over five years of observations of the nightside equatorial ionosphere. GUVI is capable of detecting and imaging plasma bubbles within the northern and southern equatorial arcs. An automated algorithm was developed to locate the peaks of the equatorial arcs and detect the presence of equatorial plasma bubbles. This algorithm was integrated with a tomographic imaging model and a statistical inversion technique to reconstruct electron density and produce multi- dimensional images of plasma depletion structures. A database of plasma bubble reconstructions is under development, with results from over five years of GUVI data. Climatological statistics of plasma bubble occurrence from this database are presented, including the effects of longitudinal, seasonal, geomagnetic, and solar cycle variations on plasma bubble occurrence. The relationship between the latitudinal separation and peak electron density values of the equatorial arcs and plasma bubble occurrence is also discussed.
SA12A-07
Neutral Density Holes, Patches, Fountains, and Jets in the Earth's Upper Atmosphere
Recent satellite measurements have indicated that the thermosphere exhibits a significant amount of spatial structure and fairly rapid temporal variations. This structure and variability can result from geomagnetic storms and sub-storms, mesoscale ionospheric structures, traveling atmospheric disturbances that propagate away from the auroral oval, upward propagating tides and gravity waves from the lower atmosphere, and both rapid time variations and spatial structure in the magnetospheric energy inputs. For example, during geomagnetic disturbances and near discrete auroral features, observations have shown the thermosphere to be highly structured, with spatial scales varying from 50 to 500 km. The thermosphere was also observed to exhibit fairly rapid temporal variations, with time scales as short as 10 minutes. In addition, during periods of enhanced plasma convection, the neutral winds can become supersonic in relatively narrow regions of the polar cap. The variability and structure of the thermosphere can be associated with mesoscale (100 - 1000 km) plasma structures, such as propagating plasma patches, auroral and boundary blobs, equatorial plasma bubbles, polar cap arcs, discrete auroral arcs, sub-auroral ion drift (SAID) events, and storm-enhanced densities (SEDs). The mesoscale ionospheric structures may not only affect the local thermosphere, but the cumulative effect of multiple plasma structures may affect the global mean thermospheric wind and temperature. The thermospheric variability and structure can appear in the form of propagating atmospheric holes, neutral gas fountains, neutral density patches, and transient neutral jets. The variability associated with these and other neutral gas disturbances have been modeled with a time-dependent, high-resolution, global model of the thermosphere- ionosphere system and the simulation results and supporting measurements will be presented.
SA12A-08
Assessment of the non-hydrostatic effect in general circulation models (GCMs)
Under hydrostatic equilibrium, a typical assumption used in global thermosphere ionosphere models, the pressure gradient in the vertical direction is exactly balanced by the gravity force. Using the Global Ionosphere Thermosphere Model (GITM), which solves the complete vertical momentum equation, the primary characteristics of non-hydrostatic effects on the upper atmosphere are investigated. Our results show that after a sudden intense enhancement of high-latitude Joule heating, the vertical pressure gradient force can locally be 25 percent larger than the gravity force, resulting in a significant disturbance away from hydrostatic equilibrium. This disturbance is transported from the lower altitude source region to high altitudes through an acoustic wave, which has been simulated in a global circulation model for the first time. Due to the conservation of perturbation energy, the magnitude of the vertical wind perturbation increases with altitude and reaches 150 (250) m/s at 300 (430) km during the disturbance. The upward neutral wind lifts the atmosphere and raises the neutral density at high altitudes by a factor of two. While the time scale of the buoyancy acceleration perturbation is around 5-10 minutes in this case, the large vertical wind (above 50 m/s) at 300 km altitude lasts for a significantly longer time, and depends on the lifetime of the forcing. These large vertical winds are observed and are not typically reproduced by hydrostatic models of the thermosphere and ionosphere.