SA23A-01
Wave Coupling Between the Lower and Upper Atmospheres
We are developing a thermosphere-ionosphere-plasmasphere data assimilation model that will be used as an upper atmospheric component of a comprehensive surface-to-space meteorological model. The ionosphere - plasmasphere data assimilation model was developed as part of an effort called the Global Assimilation of Ionosphere Measurements (GAIM). This data assimilation model is based on a physics-based model of the ionosphere-plasmasphere system that covers the E-region, F-region, topside ionosphere, and plasmasphere (from 90 –30,000 km). This model is capable of assimilating real-time (or near real -time) data from a variety of sources, including bottomside Ne profiles from ionosondes, slant GPS/TEC from a network of stations, in situ Ne from DMSP satellites, line-of-sight UV emissions measured by satellites, and occultation data. The data are assimilated via an ensemble Kalman filter technique. In addition to the global Ne distribution, the data assimilation model also provides global distributions of the self- consistent drivers (neutral winds, O/N2 composition, and electric fields). The thermosphere data assimilation model has been constructed from a physics-based, global, thermosphere model using an ensemble Kalman filter technique. This model will be able to assimilate UV radiances from the SSUSI and SSULI instruments, in situ winds and densities along satellite tracks, and inferred neutral parameters from incoherent scatter radars. The goal is to couple the thermosphere-ionosphere-plasmasphere data assimilation model to the Navy's troposphere weather model (NOGAPS-ALPHA) at 90 km, and this will yield a complete surface-atmosphere-space weather model. To date, time-dependent wave fields from NOGAPS- ALPHA were imposed at the lower boundary of the upper atmosphere model and the effect on the thermosphere was studied. Simulations were conducted with progressively better spatial and temporal resolutions, which allowed us to incorporate a wide spectrum of waves. These and other results will be presented.
SA23A-02
Thermospheric signatures of sudden stratospheric warming
We present experimental evidence of a link between the lower atmosphere and mid-latitude thermosphere and ionosphere using observations of neutral winds and ion temperatures by Millstone Hill ISR (42.6N, 288.5E) during stratospheric warming of January 2008. Temperature data reveal alternating regions of cooling in the large altitude range (150-300 km above ground) and warming in a narrow altitude band (120- 140 km above ground). Both warming and cooling variations reach 70-80K (11-16% of the background temperature) and are pronounced mostly in the morning and afternoon hours. The temporal and altitudinal variation in the temperature anomaly suggests it might be related to semidiurnal modulation, and the amplitude of semidiurnal tide in wind data is increased around the time of maximum in stratospheric warming. We rule out seasonal trend, solar flux and geomagnetic activity as significant causes of such variation and suggest that it is associated with stratospheric warming. Alternating areas of warm and cold vertical zones in the atmosphere are a well established phenomena, with mesospheric cooling accompanying stratospheric warming. Our observations show for the first time that areas of warming and cooling extend to altitudes of upper thermosphere (up to 300 km) and suggest that processes responsible for generation of sudden stratospheric warmings may also impact the lower and upper thermosphere and ionosphere.
SA23A-03
Nonmigrating Tides in Exosphere Temperature From CHAMP and GRACE Accelerometer Measurements
Exosphere temperatures are derived from inter-calibrated densities measured by accelerometers on the CHAMP and GRACE satellites, and are used to elucidate the longitude structure of the upper thermosphere (ca. 400-500 km) under quiet (Kp < 3) geomagnetic conditions. The near-polar orbits of CHAMP and GRACE precess in local time at different rates, thus enabling complete local time sampling as a function of longitude within 72-day windows moving forward daily from Aug 2005 to Aug 2006, and from Oct 2003 to Oct 2004; thus 72-day running vector-mean nonmigrating tides are revealed during these periods. Wave-4 longitude structures are often seen, suggesting connection with deep convective activity and latent heat release in the tropical troposphere. Many individual tidal components, e.g., DE3, DE2, SE2, etc., reveal the same seasonal-latitudinal variabilities as those in temperatures at 110 km measured by TIMED/SABER.
SA23A-04 INVITED
Neutral Ion Coupling Explorer satellite measurements of thermospheric composition, winds and temperatures.
A new Small Explorer mission, the Neutral Ion Coupling Explorer (NICE) mission, was selected for study by NASA to specifically address neutral ion coupling in the Earth's atmosphere. The main goal of NICE is to study neutral-ion coupling at low latitudes where the densest plasma in geospace is created and where a number of remarkable interactions between the plasma and neutral gas occur even in the relative absence of high-latitude forcing. NICE will study this region from a ~24 degree inclination 550 km circular orbit, residing entirely on closed magnetic field lines. The relatively fast precession of low-inclination orbit is favorable for frequent sampling of all local times for the determination of tidal structures. It is now widely recognized that the neutral thermosphere has a strong influence on the ionosphere and that Earth's ionosphere at quiet times is actually tidally dominated. The NICE concept is unique in simultaneously providing measurements of the parameters relevant to ion production and motion across the entire altitude range of the low-latitude ionosphere. The science payload consists of 3 remote sensing instruments viewing the atmospheric limb (1) a dual Doppler Fabry-Perot Interferometer (FP), scanning in altitude to measure neutral wind vector and temperature altitude profiles in the E- and F-regions, (2) a Far Ultraviolet (FUV) imager to measure daytime neutral composition and image the nighttime F-layer intensity distributions, and (3) an Extreme Ultraviolet (EUV) altitude profiler to retrieve daytime F-layer properties. In addition, an Ion Velocity Meter (IVM) measures the in-situ ion drifts. NICE will take advantage of an elegant choice of orbit and instrument viewing geometries to make coordinated and complementary observations at all local times, with optimal conjunction of measurements occurring near the equator. The observations are accompanied by a suite of advanced numerical models and analysis techniques.
SA23A-05 INVITED
Variations of the thermosphere in response to geomagnetic forcing: our current understanding and some future plans
This presentation uses both models and observations to summarize thermospheric variability, particularly as it pertains to geomagnetic storms. The ability to analyze both the data and models simultaneously has given us a greater understanding of the physical processes that lead to these observed changes. These forcing mechanisms are also briefly described here. As well as these storm-time issues, there are significant discrepancies even in quiet times. One example of such a discrepancy is the anomaly in electron densities that occurs over the South Pacific and Antarctica in the southern summer – the Weddell Sea anomaly. Efforts are in progress to help us past these bottle necks so that we can understand the causes of all of the variability that is seen in the thermosphere. One example of such work is the NASA GOLD mission, which is briefly described here. GOLD will image thermospheric temperatures and composition from geosynchronous orbit permitting us to obtain a greater understanding of how the simultaneous temporal and spatial changes in these fields are related.
SA23A-06
New Perspectives on the Thermosphere and Ionosphere From the RAIDS Experiment on the ISS
The Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of three photometers, three spectrometers, and two spectrographs that is manifested to fly on the Japanese Experiment Module-Exposed Facility aboard the International Space Station (ISS) in 2009. The RAIDS experiment measures many airglow features across the wavelength range 50-874 nm important for remote sensing of the thermosphere and ionosphere. The primary scientific objectives of the RAIDS experiment are to study the temperature of the lower thermosphere (100-200 km), to measure composition and chemistry of the lower thermosphere and ionosphere, and to develop capabilities to monitor the dayside ionosphere via the OII 83.4 nm emission. We will present an overview of the combination of measurements RAIDS will make to provide a new perspective on the thermosphere-ionosphere system, new techniques for thermospheric-ionospheric remote sensing, and a new vantage point from the ISS to add to the growing collection of data for more robust volumetric thermospheric specification.
SA23A-07
Utilizing Data Assimilation and Small Satellites to Better Understand the Thermospheric Density Structure
Most satellite missions focus on measuring as much physics as possible in single or a very small number of locations. These missions typically have the problem of determining whether the effects that they are measuring are propagated or locally developed features. Further, the extent of the features often can not be determined. Utilizing models and modern data assimilation techniques, it is possible to take a series of simultaneous measurements of a single quantity, such as the mass density, at multiple points to reconstruct the time-dependent structure of the thermosphere. Within the model, other quantities can be determined self-consistently, such as the wind and temperature structure. We will present initial results from a Kalman Filter data assimilation technique within the Global Ionosphere Thermosphere Model (GITM), showing quantitative improvement in the global thermospheric mass density utilizing only a few point measurements. Further, we will discuss an idea for multi-satellite mission to investigate the dynamical global thermospheric density and wind response to strong high-latitude inputs utilizing these techniques.
SA23A-08
A New Atmospheric Neutral Analyzer Instrument for Thermospheric Composition, Density and Wind Velocity Measurements on the ISWEAT Micro-Satellite
We present the concept of a new atmospheric neutral analyzer (ANA) instrument and its unique capability to measure thermospheric composition, density and wind velocity, and the proposed Ionospheric Space Weather Effects in the Auroral Thermosphere (ISWEAT) micro-satellite. Using the 'Quicksat' micro-satellite bus, the ISWEAT will carry ANA as well as a dual-frequency GPS receiver (DGR) and a fluxgate magnetometer (FMG) to study the effects of magnetic storms and substorms on the thermosphere. ANA will combine the techniques of radio-frequency ion mass spectrometry and CCD-based low-energy ion velocity imaging, respectively, to measure mass- resolved 2-dimensional velocity distribution functions of atmospheric neutral species, including their 'non-thermal' components ('high-energy tails'). The DGR will measure the satellite position and velocity to cm and cm/s precision, respectively, as well as the large-scale ionospheric total electron contents (TEC), while FMG will measure magnetic field perturbations due to field-aligned current structures. The primary objective of ISWEAT is to use these measurements to study the effects of thermospheric expansion and associated ionospheric changes on 'anomalous' satellite drags at auroral latitudes during magnetic storms and substorms. Results of our mission concept study will be presented.