SEASONS (Space Environment Applications, Systems, and Operations for National Security) is a biennial conference that brings together members of the military, government, university, and contractor sectors who have an interest and stake in the space environment. The purpose of the conference is to provide participants an opportunity to discuss the impacts of space weather on DoD and intelligence community systems, as well as the applications and requirements for space weather sensors and algorithms to mitigate these impacts and enhance operations. The SEASONS 2018 conference will be held in the Kossiakoff Center at the Johns Hopkins University Applied Physics Laboratory (APL) from Wednesday, 7 November 2018, through Friday, 9 November 2018.

Space weather impacts on communications are often presented as a raison d ' etre 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 “hot” 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.

A comprehensive database of plasma bubble reconstructions is under development, with results reported here from more than 5 years of Global Ultraviolet Imager (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. Since its launch on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite in December 2001, GUVI has more than 7 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 multidimensional images of plasma depletion structures.

Coincident and near-coincident Global Ultraviolet Imager (GUVI) and Special Sensor Ultraviolet Spectrographic Imager (SSUSI) plasma bubble images provide a unique opportunity to image the evolution of a single feature over a large longitude and time range. SSUSI and GUVI are currently the only two UV imagers that can provide low-Earth orbit measurements capable of reconstructing a multidimensional electron density map. New imaging techniques applied to years of UV data provide a powerful tool for observing and understanding ionospheric electron density and equatorial plasma bubbles. GUVI, launched on board the TIMED satellite in December 2001, and SSUSI on board the DMSP F16 satellite launched in October 2003 have several overlapping years of observations of the nightside ionosphere. The low-Earth orbit of the DMSP and TIMED satellites allows for tomographic reconstruction of altitude versus longitude bubble cross sections from UV disk images. GUVI is at an altitude of 625 km in an orbit that precesses through all local solar times in just 60 days, and SSUSI is at an altitude of 830 km in a fixed 0800/2000 local solar time orbit. We have developed a technique for tomographic retrievals of electron density maps from GUVI observations. We are able to produce three-dimensional maps of ionospheric electron density. We discuss the adaptation of the tomographic imaging technique to SSUSI data and present initial results. Electron density reconstructions are accompanied by discussion and analysis of plasma bubble drift rates and the morphology and time changes in the tilt of the bubbles as they drift through the ionosphere.

The SpreadFEx campaign was conducted with the goal of investigating potential neutral atmospheric dynamics influences in seeding plasma instabilities and bubbles extending to higher altitudes from September to November 2005, with primary measurements in Brazil. In this paper, we present the results of space-based UV and ground-based optical observations in support of this campaign. Specifically, we present multi-dimensional electron density images obtained tomographically from the 135.6 nm emissions measured by the GUVI instrument aboard the TIMED satellite that result from radiative recombination of O+ and compare those with the corresponding 630.0 nm OI images recorded in the Brazilian sector. The GUVI results provide altitude vs. longitude information on depleted regions in the ionospheric plasma density that are complementary to the single-height latitude-longitude images obtained with the airglow imager.

We describe the use of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on the Defense Meteorological Satellite Program (DMSP) F16 satellite to produce 3D ionospheric electron density profiles and the coupling of these profiles with a high frequency (HF) radio propagation tool. These 3D reconstructions, produced via tomographic inversion, show the locations and shapes of density depleted regions and irregularities in the equatorial ionosphere. The radio propagation tool characterizes the effect of these bubbles on the refraction of HF skywave signal paths. We present examples of anomalous refraction occurring in and around density depleted regions seen in SSUSI reconstructions and the calculation of instantaneous Maximum Usable Frequency (MUF).

A tomographic forward and inverse model is presented that enables the recovery of three‐dimensional ionospheric structures from space‐based optical observations. In this paper we apply the technique to the Global Ultraviolet Imager (GUVI) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The forward model is based on GUVI observation geometry to simulate radiance observations of a model ionosphere. This model incorporates the physics of the 1356 Å emission and the pattern of line‐of‐sight measurements out of the plane of the orbit into a discrete matrix representation of the GUVI observation. The application of matrix inversion techniques to the discrete observation matrix allows a multidimensional electron density profile to be reconstructed from the GUVI brightness measurements. Appropriate regularization functionals are incorporated to constrain the reconstructed solution. A smoothness constraint with a nonconvex penalty function ensures smoothness while preserving edges in the reconstructed image, an attribute which is crucial for the reconstruction of sharp ionospheric gradients. Results using GUVI data are shown to demonstrate the applicability of this technique.

Recently the Global Ultraviolet Imager (GUVI) on‐board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has detected far ultraviolet (FUV) images of plasma depletions in the low‐latitude and equatorial ionosphere. A model of GUVI observation geometry was developed to simulate radiance observations of a model ionosphere. We report on results in reconstructing multi‐dimensional electron density profiles from GUVI brightness measurements through the use of statistical inversion techniques. These results enable the global observation and characterization of the structure of plasma bubbles and provide a means to quantify the level of depletion in the structures. Results are compared with corresponding JULIA observations for validation. The ability to globally image and characterize equatorial plasma bubbles provides a powerful tool for understanding this elusive space weather phenomenon.