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This paper describes the latest version of the International Reference Ionosphere (IRI) model. IRI-2012 includes new models for the electron density and ion densities in the region below the F-peak, a storm-time model for the auroral E-region, an improved electron temperature model that includes variations with solar activity, and for the first time a description of auroral boundaries. In addition, the thermosphere model required for baseline neutral densities and temperatures was upgraded from MSIS-86 to the newer NRLMSIS-00 model and Corrected Geomagnetic coordinates (CGM) were included in IRI as an additional coordinate system for a better representation of auroral and polar latitudes. Ongoing IRI activities towards the inclusion of an improved model for the F2 peak height hmF2 are discussed as are efforts to develop a \textquotedblleftReal-Time IRI\textquotedblright. The paper is based on an IRI status report presented at the 2013 IRI Workshop in Olsztyn, Poland. The IRI homepage is at\ IRImodel.org.
Published by: Advances in Space Research Published on: 04/2015
YEAR: 2015   DOI: 10.1016/j.asr.2014.07.032
A methodology for evaluating the science benefit of adding space weather sensor data from a modest number of small satellites to the Utah State University Global Assimilation of Ionospheric Measurements\textemdashFull Physics (GAIM-FP) model is presented. Three orbital scenarios are presented, two focusing on improved coverage of narrowly specified regions of interest, and one on global coverage of the ionosphere as a whole. An Observing System Simulation Experiment is used to obtain qualitative and quantitative results of the impact of the various orbital scenarios on the ionospheric specifications. A simulated \textquotedbllefttruth\textquotedblright run of the ionosphere is obtained from a first principle model of the ionosphere/plasmasphere model and used to generate global simulated Global Positioning Satellite total electron content (GPS-TEC) data as well as in situ plasma density observations. Initially, only GPS data were assimilated by GAIM-FP, and the results of this limited run were compared to the truth run. Next, the simulated in situ plasma densities corresponding to our three orbital scenarios were assimilated together with the GPS data, and the results were compared to both the truth run and the limited GPS-TEC only GAIM-FP run. These model simulations have shown that adding a constellation of small satellites/sensors in addition to global TEC inputs does indeed converge the GAIM-FP model closer to truth in the situations described.
Published by: Radio Science Published on: 04/2015
YEAR: 2015   DOI: 10.1002/2014RS005426
During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7\textendash17 March 2012 caused geomagnetic storms that strongly affected high-latitude ionosphere in the Northern and Southern Hemisphere. GPS phase scintillation was observed at northern and southern high latitudes by arrays of GPS ionospheric scintillation and TEC monitors (GISTMs) and geodetic-quality GPS receivers sampling at 1 Hz. Mapped as a function of magnetic latitude and magnetic local time (MLT), the scintillation was observed in the ionospheric cusp, the tongue of ionization fragmented into patches, sun-aligned arcs in the polar cap, and nightside auroral oval and subauroral latitudes. Complementing a companion paper (Prikryl et al., 2015a) that focuses on the highlatitude ionospheric response to variable solar wind in the North American sector, interhemispheric comparison reveals commonalities as well as differences and asymmetries between the northern and southern high latitudes, as a consequence of the coupling between the solar wind and magnetosphere. The interhemispheric asymmetries are caused by the dawn\textendashdusk component of the interplanetary magnetic field controlling the MLT of the cusp entry of the storm-enhanced density plasma into the polar cap and the orientation relative to the noon\textendashmidnight meridian of the tongue of ionization.
Prikryl, P.; Ghoddousi-Fard, R.; Spogli, L.; Mitchell, C.; Li, G.; Ning, B.; Cilliers, P.; Sreeja, V.; Aquino, M.; Terkildsen, M.; Jayachandran, P.; Jiao, Y.; Morton, Y.; Ruohoniemi, J.; Thomas, E.; Zhang, Y.; Weatherwax, A.; Alfonsi, L.; De Franceschi, G.; Romano, V.;
Published by: Annales Geophysicae Published on: 01/2015
YEAR: 2015   DOI: 10.5194/angeo-33-657-2015
The Earth\textquoterights ionosphere is a highly dynamic region that is almost constantly in a state of flux. Solar radiation, geomagnetic activity, chemical reactions, and natural dynamics all act to perturb the state of the ionosphere. The ionosphere changes on time scales of hours to days, with the fine-scale ionospheric structures that are frequently observed lacking in global physics-based models due to time-step and spatial resolution constraints. To properly specify the ionosphere, data is needed, thus data assimilation. The Utah State University GAIM-GM model uses a data assimilation method to correct a physics-based model of the ionosphere using 5 different data types, divided into 9 different data sources. Multiple data types are necessary because the data from any individual data source will not be sufficient for global reconstructions. The GAIM-GM specification (in real-time) can then be used to correct for ionospheric propagation delays, thereby improving geo-location and communications. The focus here is to show the quantitative effects that multiple data types have on GAIM-GM ionospheric specifications for a relatively quiet day (April 19) in 2012.
Published by: Space Weather Published on: 11/2014
YEAR: 2014   DOI: 10.1002/2014SW001104
Space weather impacts on communications are often presented as a\ raison d\textquoterightetre\ for studying space weather (e.g., Solar and Space Physics: A Science for a Technological Society, 2013). Here we consider a communications outage during Operation Anaconda in Afghanistan that may have been related to ionospheric disturbances. Early military operations occurred during the peak of solar cycle 23 when ionospheric variability was enhanced. During Operation Anaconda, the Battle of Takur Ghar occurred at the summit of a 3191 m Afghan mountaintop on 4 March 2002 when the ionosphere was disturbed and could have affected UHF Satellite Communications (SATCOM). In this paper, we consider UHF SATCOM outages that occurred during repeated attempts to notify a Quick Reaction Force (QRF) on board an MH-47H Chinook to avoid a \textquotedbllefthot\textquotedblright landing zone at the top of Takur Ghar. During a subsequent analysis of Operation Anaconda, these outages were attributed to poor performance of the UHF radios on the helicopters and to blockage by terrain. However, it is also possible that ionospheric anomalies together with multipath effects could have combined to decrease the signal-to-noise ratio of the communication links used by the QRF. A forensics study of Takur Ghar with data from the Global Ultraviolet Imager on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission showed the presence of ionospheric bubbles (regions of depleted electron density) along the line of sight between the Chinook and the UHF communications satellites in geostationary orbit that could have impacted communications. The events of 4 March 2002 motivated us to develop the Mesoscale Ionospheric Simulation Testbed model, which can be used to improve warnings of potential UHF outages during future military operations.
Published by: Space Weather Published on: 10/2014
YEAR: 2014   DOI: 10.1002/2014SW001081
LBH dayglow emissions in the ionosphere, produced by the photoelectrons impact on the nitrogen molecules, are the most prominent molecular signals in the far ultraviolet range. Imaging the LBH dayglow emissions from the space can be a powerful method to monitor the state of the upper atmosphere. According to direct excitation theory and spherical geometry, the spectral characteristics of the LBH emission are analyzed and a revised method (RAURIC) to calculate the column emission rate of the LBH dayglow emissions for large field of view is given. Two main limitations of AURIC, that are the definition of the observation azimuth angle and the treating of the solar zenith angle as a constant along a line of sight, are improved in RAURIC. The column emission rates of the LBH bands in the range of 140\~180 nm are calculated with the method. Comparisons with results from AURIC show great agreement in nadir, while RAURIC should be used in other lines of light, especially for large field of view. This work provides a solid basis for simulating the image of ionospheric LBH dayglow emissions and the data inversion technique.
Published by: Chinese Journal of Geophysics Published on: 03/2014
YEAR: 2014   DOI: 10.1002/cjg2.2014.57.issue-210.1002/cjg2.20099