SA33B-01
Global Model Comparison With Observations of the Ionosphere During September 2005
A comparison between results from the Global Ionosphere Thermosphere Model (GITM) and data from Millstone Hill during the September 2005 incoherent scatter world month (ISWM) is presented. One dimensional GITM is used to simulate the ionosphere for the entire month, and comparisons between electron densities, electron temperatures and ion temperatures are performed. It is found that 1D GITM can reproduce the state of the ionosphere to as high as 20% accuracy over the course of the month. The largest errors between the model and observations occur during the geomagnetic storm that begins on September 10th. Therefore, 3D GITM was also used to perform a more realistic simulation of the ionosphere during the storm. The model indicates that enhanced electron densities throughout the 10th are a result of upwelling of molecular rich (N2) air above Millstone Hill, which supports the conclusions made by Goncharenko et. al. (2006). A comparison of the results and the data show that the RMS errors using 3D GITM are not significantly better than the errors using 1D GITM. However, the cross correlation between 3D GITM and the observations, in most cases, is significantly higher than the cross correlation between 1D GITM and the observations. This indicates that the high latitude dynamics associated with the storm propagate to the mid-latitudes. Therefore, the global effects of a storm must be accounted for in order to accurately simulate the ionosphere in the Millstone Hill region.
SA33B-02
Doppler shift observations of severe tropospheric weather effects in the ionosphere
Tropospheric severe weather events are regarded as an important natural source of infrasound. They influence the ionosphere through the upward propagating waves. Due to temperature profile in the lower atmosphere, the infrasonic waves are focused upwards and most of the radiated energy can propagate to the upper atmosphere. Detection of infrasonic waves requires sampling in short intervals or preferably continuous measurements. Most of recent instruments for ionospheric sounding cannot detect ionospheric plasma fluctuations in the infrasonic range. The Doppler shift measurements started at the Institute of Atmopheric Physics, Prague in 2004. They enable us to monitor ionospheric wave activity in the acoustic and gravity wave domain. We focus on wave phenomena in the infrasonic range linked to severe tropospheric weather. Here, we compare the impact on the ionosphere of severe weather in summer and in winter. The analysed summer severe tropospheric events were represented by slowly passing cold front, which brought severe convective storms to the monitored region. They were accompanied by tornadoes, supercell development; the observed height of cumulonimbus cloud tops exceeded significantly the height of summer tropopause. As a winter severe weather case, we selected the day with a windstorm and a quickly passing cold front. Due to the fast movement of the frontal surface, convective storms developed on the cold front. Significant gravity wave and infrasonic wave activity was observed during all summer and winter events studied.
SA33B-03
Testing of the satellite electron temperature data base with incoherent scatter radar electron temperature measurements
Electron temperature (Te) in the topside ionosphere and plasmasphere is an important parameter because thermal electrons play a key role in the energy balance of these regions. There are two principal sources of Te measurements - in-situ satellite and ground based Incoherent Scatter Radar (ISR). Since the mid-nineteensixties when radars and satellite instruments began observing Te a large volume of data has been collected by these two techniques. Occasional comparisons of results of these two methods showed agreements but also disagreements. We have built a large database of electron temperature based on all available satellite measurements, the greatest volume of which is represented by DMSP data. Especially DMSP data statistically show surprisingly high values for low solar activity and daytime (Bilitza, 2006). To investigate this discrepancy we have compared Millstoen Hill incoherent scatter measurements with simultaneous satellite measurements during DMSP overflights of the station. Results of this study are shown, discussion is presented and possible implications on empirical Te modeling are pointed out. Bilitza D., Truhlik V., Richards P.G., Abe T., and Triskova L.: Solar Variations of Mid-Latitude Electron Density and Temperature: Satellite Measurements Model Calculations, Advances in Space Research, in press, 2006.
SA33B-04
Wavelet-based Analysis of Sporadic E Layer Variability in Midlatidutes
We apply wavelet analysis to time series describing state of ionosphere at heights of E region. Our study focuses mainly on occurrence of sporadic E layer and corresponding changes in plasma motion as measured by digisonde DPS4. This analysis involves vertical ionospheric sounding measurements recorded during period of low solar activity during summer time. Two high sampling rate campaigns were performed in Pruhonice Observatory (50N, 14.6E). Using DPS 4 equipment two types of the data, ionograms and plasma drift, were recorded and further analysed. Our data sets consist of time series of critical frequencies foEs, corresponding maxima hEs and particle drifts at two frequencies in the height range 90 km - 150 km. Dominant oscillation modes, their persistence and prevailing plasma motion are discussed.
SA33B-05
Searching for Dominant Oscillation Modes and Phase Synchronization in Ionospheric, Solar and Geomagnetic Time Series
Enhanced Monte Carlo Singular Space and Wavelet based methods are used to detect possible oscillatory modes in long-term time series describing state of ionosphere, neutral atmosphere, solar activity and geomagnetic activity. These modes are extracted from raw data, their instantaneous phases are computed and their relations are studied using the tools of synchronization and coherence.
SA33B-06
Validation of the Utah State University Global Assimilation of Ionospheric Measurements (GAIM) Model
The Utah State University Global Assimilation of Ionospheric Measurements (GAIM) model version 2.3 uses the Ionosphere Forecast Model (IFM), a physics-based model, and a Kalman filter using Gauss-Markov relaxation as a basis for assimilating a set of real-time measurements to produce a specification and forecast of the ionosphere. This model has recently been implemented at the Air Force Weather Agency (AFWA) for operational use. As part of that process, the Air Force Research Laboratory (AFRL) has performed extensive validations of GAIM. The primary focus of the work has been to determine if an operational GAIM will perform better than the current operational ionospheric model (the Parameterized Real-Time Ionospheric Specification Model, PRISM). In this presentation, we will discuss our results that illustrate that GAIM is generally superior to both climatology (IFM) and PRISM. We will also discuss data preprocessing, the robustness of GAIM, and some of the validation questions that remain unanswered.
SA33B-07
Midlatitude Nighttime hmF2 and NmF2 Retrieval from TIMED/GUVI Disk Measurements
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 global ionosphere. These observations span all local times and large variations in solar and geomagnetic activity. Multi- dimensional electron density profiles can be tomographically reconstructed from ultraviolet brightness observations of the nightside ionosphere. An existing tomographic model has been modified to optimally retrieve hmF2 and NmF2 from GUVI disk measurements despite the low signal-to-noise ratio of UV observations of the midlatitude ionosphere. This information is relevant for use in climatological and data assimilation models. After the forward model and retrieval method are described, results over five years of GUVI data are presented along with an error analysis and validation with incoherent scatter radar measurements and ionosonde profiles.