Robert J. Redmon

Dynamics of the high‐latitude ionospheric irregularities during the 17 March 2015 St. Patrick's Day storm: Ground‐based GPS measurements

We report first results on the study of the high-latitude ionospheric irregularities observed in worldwide GPS data during the St. Patricks Day geomagnetic storm (17 March 2015). Multisite GPS observations from more than 2500 ground-based GPS stations were used to analyze the dynamics of the ionospheric irregularities in the Northern and Southern Hemispheres. The most intense ionospheric irregularities lasted for more than 24 h starting at 07 UT of 17 March. This period correlates well with an increase of the auroral Hemispheric Power index. We find hemispheric asymmetries in the intensity and spatial structure of the ionospheric irregularities. Over North America, the ionospheric irregularities zone expanded equatorward below ~45°N geographic latitude. Additionally, the strong midlatitude and high-latitude GPS phase irregularities in the auroral oval were found to be related to the formation of storm enhanced density and deepening of the main ionospheric trough through upper atmosphere ionization by energetic particle precipitation. Significant increases in the intensity of the irregularities within the polar cap region of both hemispheres were associated with the formation and evolution of the storm enhanced density/tongue of ionization structures and polar patches.

Comparison of magnetic perturbation data from LEO satellite constellations: Statistics of DMSP and AMPERE

During the past decade engineering-grade magnetic field measurements from the low Earth orbiting (LEO) Iridium constellation of communication satellites have been available to the geospace science community as a tool to map field-aligned currents. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) applied to Iridium measurements markedly improved the temporal and spatial resolution of these data. We developed new methods to compare data from the latest improvement to AMPERE with those from a constellation of four LEO Defense Meteorological Satellite Program (DMSP) spacecraft that carry high-resolution magnetometers. To perform the comparisons, we transformed all data to a common coordinate frame and altitude (110 km) and developed a means of computing spacecraft magnetic conjunctions. These conjunctions yield discrepancies in the magnetic field perturbations measured at each proximate spacecraft. During the geomagnetic disturbance of 29–30 May 2010, the vector differences in the horizontal perturbations at closest approach (typically a few tens of kilometers) had mean, median, and standard deviation values of 132 nT, 112 nT, and 90 nT, respectively. The DMSP spacecraft tend to report larger perturbations in the northern polar cap and cusp regions, especially during active intervals. We attribute some of the differences to limitations of spacecraft-attitude knowledge that propagate into AMPERE data. Overall, for the magnetic storm, we provide clear evidence that AMPERE data can provide high-resolution auroral zone data in good agreement with DMSP data for use in data assimilation algorithms. Such dual-use commercial data can provide important global augmentation to the nations space weather monitoring capabilities.

Low-energy ion precipitation structures associated with pulsating auroral patches

Pulsating auroras often appear in forms of geo-stable or slowly convecting “patches.” These patches can maintain their rough shape and size over many sequences of luminosity pulsations, yet they slowly drift with ionospheric E × B convection. Because of these characteristics, there has long been a speculation that the pulsating auroral patch (PAP) is connected to flux tubes filled with enhanced cold plasma. In this study, we perform a survey on pulsating auroral events when the footprints of low-Earth-orbit satellites traversed the PAPs, with a focus on the low-energy particle signatures associated with the PAPs. As a result, we identified, in a majority (~2/3) of events, the existence of a low-energy ion precipitation structure that is collocated with the PAP, with core energies ranging from several tens of eV up to a few hundred eV. This result supports the hypothesis that a PAP connects to flux tubes filled with enhanced cold plasma. We further propose that the plasma outflows from the ionosphere are the origin of such cold plasma flux tubes. We suggest that the PAP is formed by a combination of high-energy electrons of a magnetospheric origin, the low-energy plasma structure of an ionospheric origin, and certain ELF/VLF waves that are intensified and modulated in interactions with both the hot and cold plasma populations.

Evaluation of OVATION Prime as a forecast model for visible aurorae

This study evaluates the ability of the OVATION Prime auroral precipitation model to provide operational forecasts of the visible aurora. An operational implementation would primarily provide the general public with some guidance for viewing the aurora. We evaluate the likelihood that if aurorae are predicted to be visible at a location, they will be seen there within the hour. Nighttime model forecasts were validated with Polar Ultraviolet Imager data for Kp ≥ 3 and for the years 1997 and 1998. The overall forecasts for a visible aurora to occur or to not occur were correct 77% of the time. The most important prediction for public auroral viewing is that the visible aurora will occur, and these forecasts were correct 86% of the time.

A statistical study of midlatitude spread F at Wallops Island, Virginia

[1] An ionosonde study using data from Wallops Island, Virginia (37.95°N, 284.53°E, 67.5° dip angle), over a full solar cycle from 1996 to 2006 has been conducted. A pattern recognition algorithm is used to analyze these ionograms in order to determine the statistics of midlatitude spread F. An ionogram displays spread F both horizontally and vertically, which are defined as range and frequency spread F, respectively. Range and frequency spreading can occur either simultaneously or separately. Seasonal and solar cycle variations have been studied using the data set; both are significant and are somewhat different for range and frequency spread F. Correlations of spread F duration with F 10.7, Kp, and AE are investigated. The results provide insights into causative sources for both types of midlatitude spread F.

Modes of high-latitude auroral conductance variability derived from DMSP energetic electron precipitation observations: Empirical orthogonal function analysis

We provide the first ever characterization of the primary modes of ionospheric Hall and Pedersen conductance variability as empirical orthogonal functions (EOFs). These are derived from six satellite years of Defense Meteorological Satellite Program (DMSP) particle data acquired during the rise of solar cycles 22 and 24. The 60 million DMSP spectra were each processed through the Global Airlglow Model. Ours is the first large-scale analysis of ionospheric conductances completely free of assumption of the incident electron energy spectra. We show that the mean patterns and first four EOFs capture ∼50.1 and 52.9% of the total Pedersen and Hall conductance variabilities, respectively. The mean patterns and first EOFs are consistent with typical diffuse auroral oval structures and quiet time strengthening/weakening of the mean pattern. The second and third EOFs show major disturbance features of magnetosphere-ionosphere (MI) interactions: geomagnetically induced auroral zone expansion in EOF2 and the auroral substorm current wedge in EOF3. The fourth EOFs suggest diminished conductance associated with ionospheric substorm recovery mode. We identify the most important modes of ionospheric conductance variability. Our results will allow improved modeling of the background error covariance needed for ionospheric assimilative procedures and improved understanding of MI coupling processes.

Large‐amplitude electric fields in the inner magnetosphere: Van Allen Probes observations of subauroral polarization streams

The subauroral polarization stream (SAPS) is an important magnetosphere-ionosphere (MI) coupling phenomenon that impacts a range of particle populations in the inner magnetosphere. SAPS studies often emphasize ionospheric signatures of fast westward flows, but the equatorial magnetosphere is also affected through strong radial electric fields in the dusk sector. This study focuses on a period of steady southward interplanetary magnetic field (IMF) during the 29 June 2013 geomagnetic storm where the Van Allen Probes observe a region of intense electric fields near the plasmapause over multiple consecutive outbound duskside passes. We show that the large-amplitude electric fields near the equatorial plane are consistent with SAPS by investigating the relationship between plasma sheet ion and electron boundaries, associated field-aligned currents, and the spatial location of the electric fields. By incorporating high-inclination DMSP data we demonstrate the spatial and temporal variability of the SAPS region, and we suggest that discrete, earthward propagating injections are driving the observed strong electric fields at low L shells in the equatorial magnetosphere. We also show the relationship between SAPS and plasmasphere erosion, as well as a possible correlation with flux enhancements for 100s keV electrons.

Geomagnetic main field modeling with DMSP

The Defense Meteorological Satellite Program (DMSP) launches and maintains a network of satellites to monitor the meteorological, oceanographic, and solar-terrestrial physics environments. In the past decade, geomagnetic field modelers have focused much attention on magnetic measurements from missions such as CHAMP, Orsted, and SAC-C. With the completion of the CHAMP mission in 2010, there has been a multiyear gap in satellite-based vector magnetic field measurements available for main field modeling. In this study, we calibrate the special sensor magnetometer instrument on board DMSP to create a data set suitable for main field modeling. These vector field measurements are calibrated to compute instrument timing shifts, scale factors, offsets, and nonorthogonality angles of the fluxgate magnetometer cores. Euler angles are then computed to determine the orientation of the vector magnetometer with respect to a local coordinate system. We fit a degree 15 main field model to the data set and compare with the World Magnetic Model and Orsted scalar measurements. We call this model DMSP-MAG-1, and its coefficients and software are available for download at http://geomag.org/models/dmsp.html. Our results indicate that the DMSP data set will be a valuable source for main field modeling for the years between CHAMP and the recently launched Swarm mission.

Forecasting scintillation activity and equatorial spread F

When transionospheric radio waves propagate through an irregular ionosphere with plasma depletions or “bubbles,” they are subject to sporadic enhancement and fading, which is referred to as scintillation. Communication and navigation systems may be subject to these detrimental effects if the scintillation is strong enough. It is critical to have knowledge of the current ionospheric conditions so that system operators can distinguish between the natural radio environment and system-induced failures. In this paper we briefly describe the Forecasting Ionospheric Real-time Scintillation Tool UHF scintillation forecasting technique, which utilizes the observed characteristic parameter h′F from a ground-based, ionospheric sounder near the magnetic equator. The prereversal enhancement in vertical E × B drift velocity after sunset is the prime driver for creating plasma depletions and bubbles. In addition, there exists a “threshold” in the h′F value at 1930 LT, h′Fthr, such that, on any given evening, if h′F is significantly above h′Fthr, then scintillation activity is likely to occur, and if it is below h′Fthr, scintillation activity is unlikely to occur. We use this technique to explain the lack of scintillation activity prior to the Halloween storm in October 2003 in the Peruvian longitude sector. In addition, we have carried out a study which forecasts the occurrence or nonoccurrence of equatorial spread F (ESF), on a night-to-night basis, in five longitude sectors. The overall forecasting success is greater than 80% for each of the five longitude sectors.

Localized thermosphere ionization events during the high‐speed stream interval of 29 April to 5 May 2011

We analyze localized ionospheric-thermospheric (IT) events in response to external driving by a high-speed stream (HSS) during the ascending phase of the Solar Cycle 24. The HSS event occurred from ~ 29 April to 5 May, 2011. The HSS itself (and not the associated corotating interaction region) caused a moderate geomagnetic storm with peak SYM-H = −55 nT and prolonged auroral activity. We analyze TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) measurements of nitric oxide (NO) cooling emission during the interval as a measure of thermospheric response to auroral heating. We identify several local cooling emission (LCE) events in high to subauroral latitudes. Individual cooling emission profiles during these LCE events are enhanced at ionospheric E layer altitudes. For the first time, we present electron density profiles in the vicinity of the LCE events using collocated COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) radio occultation (RO) measurements. Measurements at local nighttime show the formation of an enhanced E layer (about 2.5 times increase over the undisturbed value) at ≥100 km altitude. Daytime electron density profiles show relatively smaller enhancements in the E layer. We suggest that the IT response is due to additional ionization caused by medium energy electron (>10 keV) precipitation into the subauroral to high-latitude atmosphere associated with geomagnetic activity during the HSS event.