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Rastatter L.,NASA | Kuznetsova M.M.,NASA | Glocer A.,NASA | Welling D.,University of Michigan | And 14 more authors.
Space Weather | Year: 2013

This paper reports the metrics-based results of the Dst index part of the 2008-2009 GEM Metrics Challenge. The 2008-2009 GEM Metrics Challenge asked modelers to submit results for four geomagnetic storm events and five different types of observations that can be modeled by statistical, climatological or physics-based models of the magnetosphere-ionosphere system. We present the results of 30 model settings that were run at the Community Coordinated Modeling Center and at the institutions of various modelers for these events. To measure the performance of each of the models against the observations, we use comparisons of 1 hour averaged model data with the D st index issued by the World Data Center for Geomagnetism, Kyoto, Japan, and direct comparison of 1 minute model data with the 1 minute D st index calculated by the United States Geological Survey. The latter index can be used to calculate spectral variability of model outputs in comparison to the index. We find that model rankings vary widely by skill score used. None of the models consistently perform best for all events. We find that empirical models perform well in general. Magnetohydrodynamics-based models of the global magnetosphere with inner magnetosphere physics (ring current model) included and stand-alone ring current models with properly defined boundary conditions perform well and are able to match or surpass results from empirical models. Unlike in similar studies, the statistical models used in this study found their challenge in the weakest events rather than the strongest events. Key Points A large set of models that specify DST have been evaluated Five skill scores were used to evaluate models Statistical models perform best but physics-based models can compete ©2013. American Geophysical Union. All Rights Reserved.

Kelley M.C.,Cornell University | Ilma R.R.,Cornell University | Eccles V.,Space Environment Corporation
Journal of Geophysical Research: Space Physics | Year: 2012

We provide an explanation for a long-standing (more than 35 years) discrepancy between theory and rocket experiments concerning the peak height of the electrojet current and the magnitude of magnetic field perturbation. The arbitrary correction of the electron-neutral collision frequency by a factor of 4, which has been used to explain these problems, is not necessary if the field line-integrated conductivities are used. Recent research using ground-based magnetometers and CHAMP have also used this constant connection to classical collision theory. These methods arbitrarily change the electron-neutral collision frequency. A field line-integrated theoretical study of the electrojet by G. Haerendel and J. V. Eccles, implemented in this paper, explains the height of the electrojet using classical collision frequency. Furthermore, we argue that since the correction factor is independent of the driving electric field, it is unlikely that anomalous electron collision frequency due to a nonlinear plasma instability (gradient drift) is involved. Copyright 2012 by the American Geophysical Union.

Rice D.,Space Environment Corporation | Sojka J.J.,Space Environment Corporation
Advances in Space Research | Year: 2015

The IRI2012 provides ionospheric modeling from 1 January 1958 through the present and near future. However, archives of ionogram films exist dating back to the late 1940s, and are potentially valuable for studying long-term trends and change. IRI is very useful for the analysis and interpretation of the films, so Space Environment Corporation (SEC) has modified IRI2012 to extend its operations back to 1 January 1950. This paper describes results from IRI2012 and observations from the Washington DC ionosonde WA938 (38.7°N, -77.1°E) for 1951 (active post-solar maximum) and 1954 (quiet solar minimum). The comparison shows general agreement between the extended IRI2012 and the ionosonde observations. A nighttime enhancement found in IRI results is observed in some ionograms, with modification by atmospheric waves. A significant discrepancy between IRI and observations was found in nighttime 1954 solar minimum results. © 2014 COSPAR.

Rice D.D.,Space Environment Corporation | Sojka J.J.,Space Environment Corporation | Eccles J.V.,Space Environment Corporation | Schunk R.W.,Utah State University
Radio Science | Year: 2012

The Space Environment Group of the National Institute of Information and Communications Technology, Tokyo, Japan, operates four ionosondes at Okinawa, Yamagawa, Kokubunjii, and Wakkanai in the Asian sector. Okinawa is located at the lowest latitude and lies at the northern edge of the northern equatorial anomaly, while Wakkanai is located at the higher latitudes of the midlatitude ionosphere. For this study, ionograms obtained from the Internet are analyzed using the automated Expert System for Ionogram Reduction (ESIR). An anomalous 3day f oF 2 enhancement observed by the Wakkanai ionosonde from 9 to 11 October 2009 forms the basis for this study. The scientific question being addressed pertains to the remarkably quiescent geomagnetic activity experienced during the extended solar minimum between cycles 23 and 24 that enables a search for the ionospheric response to weather in the lower atmosphere. The analysis of the ionograms from these four stations using the proprietary ESIR technique provides an extended database of electron density profiles that describes the ionospheric variability as a function of latitude, local time, and season. In addition, independent observations of the ionospheric TEC used by the USU Global Assimilation of Ionospheric Measurements (GAIM) model verify the anomalous ionospheric behavior as well as establishing its extent. Typical solar minimum conditions were seen during this study, with geomagnetic activity restricted to well-characterized corotating interaction region (CIR) events. After eliminating geomagnetic and solar disturbances as drivers of the October 2009 anomaly, the presence of Typhoon Melor is suggested as a possible source mechanism for the ionospheric anomaly. © 2012 by the American Geophysical Union.

Eccles V.,Space Environment Corporation | Rice D.D.,Space Environment Corporation | Sojka J.J.,Space Environment Corporation | Valladares C.E.,Boston College | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

Data from the Low-Latitude Ionospheric Sensor Network are used to examine ionospheric electrodynamics during quiet, low solar conditions from September to November 2009. The ground-based magnetometers and the Jicamarca Vertical Incidence Pulsed Ionospheric Radar ionosonde in the Peruvian Sector are used to identify the neutral winds and plasma drifts that control the large-scale plasma structure of the ionosphere. It is observed that the solar- and lunar-driven semidiurnal tides have a significant influence on the background electrodynamics during this period of extreme solar minimum. The lunar tidal influence of the ionosphere electrodynamics is a large component of the variation of the vertical drift during the geophysically quiet study period. A significant portion, though not all, of the variation through the lunar month can be attributed to the lunar semidiurnal tide. Copyright 2011 by the American Geophysical Union.

Yuan T.,Utah State University | Fish C.,Utah State University | Sojka J.,Utah State University | Rice D.,Space Environment Corporation | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

It is well known that there is a strong correlation between the formation of a descending sporadic E layer (Es) and the occurrence of large upper atmospheric zonal wind shears, most likely driven by solar thermal tides and/or gravity waves. We present new results of Es perturbation events captured between 13 and 17 July 2011 (UT days 194-198) as part of a coordinated campaign using a wind/temperature Na lidar at Utah State University [41.7°N, 111.8°W], and a Canadian Advanced Digital Ionosonde (CADI; Scientific Instrumentation Ltd., Saskatoon, Saskatchewan, Canada) and SkiYMet meteor wind radar, both located at nearby Bear Lake Observatory [41.9°N, 111.4°W]. During this period, the CADI detected strong descending E s on 2 days (195 and 197) when large modulations of the top-side mesospheric Na layer occurred in synchronism with strong oscillations in the ionosonde E region echoes. A weakening in the descending E layer echoes was observed on the other 2 days (196 and 198) coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km. Both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for Es formation and its downward propagation. Further investigation indicates that the weakening tidal amplitudes and the occurrence of the Es events were also influenced by a strong quasi-two-day period modulation, suggesting significant quasi-two-day wave (QTDW) interactions with the tides. Indeed, a nonlinear, wave-wave interaction-induced 16-hour period child wave was also detected, with amplitude comparable to that of the prevailing tides. These interaction processes and their associated effects are consistent with earlier Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model studies of nonlinear interactions between the migrating tidal waves and the QTDW and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the Es. Key PointsEs induces large perturbations of Na abundance in lower thermosphereEs weakening is coincident with weakening of zonal wind tidesThe damping of tidal amplitude is the result of interaction between PW and Tide © 2012. American Geophysical Union. All Rights Reserved.

Eccles J.V.,Space Environment Corporation | St. Maurice J.P.,University of Saskatchewan | Schunk R.W.,Utah State University
Journal of Geophysical Research A: Space Physics | Year: 2015

The evening prereversal enhancement (PRE) of the vertical plasma drift has important consequences for the Appleton density anomaly and the stability of the nighttime ionosphere. Simplified simulations were used to review the three competing theories of the PRE origin, to explore their relative importance, and to indentify their interdependence. The mechanisms involved in the generation and climatology of the PRE are, first, a curl-free electric field response to rapid changes in the vertical electric field associated with the nighttime F region dynamo; second, a divergence of Hall currents in the E region away from the magnetic equator; and, third, the moderating effect of the large Cowling conductivities in the equatorial E region. The simulations indicate that the equatorial Cowling conductivity creates an important current path that limits the other two mechanisms prior to equatorial sunset and releases them after equatorial sunset. The curl-free mechanism is the dominant mechanism when the terminator and magnetic meridian are aligned in part due to the accelerating F region zonal wind. When the solar terminator is not aligned with the magnetic meridian, there is an interaction involving all three mechanisms contributing to the magnitude and timing of the PRE. Finally, the altitude profile of the PRE decays more quickly with altitude when the curl-free mechanism dominates as compared to when the Hall current mechanism dominates. ©2015. American Geophysical Union. All Rights Reserved.

Eccles V.,Space Environment Corporation | Vo H.,Atmospheric Science Group | Thompson J.,Space Environment Corporation | Gonzalez S.,Atmospheric Science Group | Sojka J.J.,Space Environment Corporation
Space Weather | Year: 2011

We describe the reduction of the Arecibo Observatory incoherent scatter radar electron density profiles from 1966 to 2006 into a standardized database of electron density profiles useful for the assessment of ionospheric models. The database of electron density profiles covers approximately 700 days of observation over nearly 4 solar cycles and all seasons. These data are averaged into climatological conditions with special attention at maintaining a normal profile shape in altitude. The reduced profile database and the climatological average profiles are provided to the Community Coordinated Modeling Center for open access by the community and their efforts to generate ionosphere model metrics and skill scores. Copyright 2011 by the American Geophysical Union.

Eccles V.,Space Environment Corporation | Thompson J.,Space Environment Corporation | Sojka J.J.,Space Environment Corporation | Vo H.,Atmospheric Science Group | Gonzalez S.,Atmospheric Science Group
Space Weather | Year: 2011

Due to the paucity of ionospheric density observations, ionospheric models are important for constructing the day-to-day 3-D specifications of electron density. Quality specifications are required to mitigate ionospheric influences on modern GPS navigation and communications technologies. The Arecibo Radar Observatory Incoherent Scatter Radar has provided F region electron density profiles spanning 50 years and 4 solar cycles. We have collected, reduced, and cleaned the Arecibo radar electron density profiles to create a "ground truth database" for use in the metric assessment of the accuracy of empirical and physics-based ionospheric models. The metrics and skill assessments within this Assessment of Ionospheric Models package are described herein. The assessment package will be implemented at the Community Coordinated Modeling Center to provide a Web-based generator of metrics and skill scores based on several electron density profile parameters: peak density values, peak density altitudes, and the shape of the electron density profile with altitude. This Assessment of Ionospheric Models package will greatly assist in improving current models of the ionosphere. Copyright 2011 by the American Geophysical Union.

Agency: NSF | Branch: Standard Grant | Program: | Phase: AERONOMY | Award Amount: 90.64K | Year: 2012

This goal of this project is to investigate the long-term behavior of the mid-latitude ionosphere near Washington, D.C., using historical ionosonde measurements obtained from 1936 to 1957 in order to extend existing data by more than two decades prior to the 1957 International Geophysical Year (IGY), when ionospheric observation became widespread. The archival data is currently stored on 35 mm films, and the first goal of this effort is to digitize the records using a film scanning device to be developed for this project. The data will be converted into ionospheric state parameters (electron density profiles) using an automated procedure, the Expert System Ionosonde Reduction (ESIR), previously developed by the investigators. The new data set will be analyzed in conjunction with an existing database of hand-scaled ionogram values, obtained from an ionosonde located near Washington, D.C. (1957-1968) and Wallops Island (1967-2009), in order to assess long-term trends in the ionospheric parameters. A specific scientific focus of the trend analysis is the quantification of secular cooling of the upper atmosphere, an outstanding question in aeronomy. The new, extended dataset will be made available to the wider community.

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