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Evolution of Swarm-derived Equatorial Electrojet Signatures Using Vector Magnetic Measurements
Patrick Alken1, Astrid Maute2, Art Richmond2, Gary Egbert3, Heikki Vanhamäki4, Arnaud Chulliat1, Gauthier Hulot5
1University of Colorado at Boulder, United States of America; 2High Altitude Observatory, Boulder, CO, USA; 3Oregon State University, USA; 4University of Oulu, Finland; 5Institut de Physique du Globe de Paris, Paris, France
The Swarm Level-2 equatorial electric field (EEF) and equatorial electrojet (EEJ) product is based on a single satellite approach and uses only scalar field data. While this product currently produces good estimates of the eastward EEJ current strength at the magnetic equator, it may be possible to derive estimates of the other components of the current by using the full vector measurements along with the Swarm constellation configuration. In particular we are interested in the possibility of recovering estimates of the EEJ vertical and meridional current system. In this study we investigate two possible approaches toward this goal. The first is based on fitting Spherical Elementary Current Systems (SECS) to the low and mid latitude magnetic data. This approach is used routinely to investigate high-latitude ionospheric current systems but has not been used frequently at low and mid latitudes. The second approach is to use the TIEGCM physics-based ionosphere model to derive empirical orthogonal functions (EOFs) which contain statistically significant information about the spatial geometries of the various ionospheric current systems. These EOFs are then fit to the Swarm constellation data and the resulting currents are compared with the SECS method.
11:45am - 12:00pm
Constellation Strategies for Observing Plasma Bubbles in the Terrestrial Ionosphere
Jeff Klenzing1, Joe Huba2, Rob Pfaff1, Russell Stoneback3
1NASA / GSFC, United States of America; 2Naval Research Laboratory, United States of America; 3The University of Texas at Dallas, United States of America
The low-latitude ionosphere is home to many plasma irregularities such as plasma bubbles that wreak havoc on critical radio waves, including GPS, radar, and communication signals. Observations of plasma bubbles were first reported nearly eighty years ago, but day-to-day variability of bubble formation remains a significant question in ionospheric physics. While satellite observations provide important information about longitudinal variability, the chosen satellite orbit strongly affects the observations of the density depletions and hence may influence their interpretation. For example, the C/NOFS satellite had an elliptical orbit with a 65-day precession period of perigee through all local times, limiting the potential observation of low-altitude bubbles in the post-sunset sector. Using the SAMI3 model and comparisons to the C/NOFS database, we will discuss the effect of different orbital parameters (e.g., altitude, inclination, circular vs elliptical) on optimizing the detection of plasma bubbles by in situ satellite instrumentation, as well as improvements offered by using multiple spacecraft. Applications to DMSP, Swarm, and GDC will be discussed.
12:00pm - 12:15pm
Relation Between Diamagnetic Effects and Formation of the Nighttime Ionospheric Plasma Density Enhancements
Ewa Slominska1, Jan Blecki2, Roger Haagmans3, Jan Slominski2
1OBSEE, Poland; 2CBK PAN, Poland; 3European Space Agency
The interest of this study is focused on the mechanism governing the phenomenon of the nighttime electron density enhancements observed in the upper layer of the ionosphere. This type of ionospheric behavior is particularly interesting when phenomena such as the Weddell Sea Anomaly (WSA) or the mid-latitude nighttime summer anomaly (MSNA) are considered. Numerous studies make an attempt to provide concise explanation of mechanism responsible for the observed anomalies, focusing mainly on the interaction between ionosphere and thermosphere, with thermospheric winds considered as major drivers of phenomena. But it is still unclear why mentioned anomalies are confined only to certain regions.
Approach presented in this study concentrates on the role of diamagnetic currents, which so far has not been considered in the context of the WSA or MSNA. Spatial variations of ionospheric plasma density are often accompanied by signatures in the magnetic field strength because of the diamagnetic effect. Diamagnetic currents can be expressed as the effect of forces on a plasma due to gradients in the plasma pressure, resulting from variations in electron density. Such signatures have been observed in the equatorial and low-latitude ionosphere. This study expands discussion to mid-latitude regions, concentrating on spatial and temporal trends of magnetic field fluctuations.
Joint analysis utilizes Swarm MAG_HR and LP electron density data. Initial analysis of residuals derived from the scalar magnetic field exhibits pronounced structures of intensified emissions spatially corresponding to regions where density anomalies are detected.
12:15pm - 12:30pm
Electromagnetic Features of Equatorial Field Aligned Plasma Irregularities as Observed by the Swarm Mission
Juan Rodríguez-Zuluaga1,2, Claudia Stolle1,2
1GFZ German Research Centre for Geosciences, Germany; 2Faculty of Science, University of Potsdam, Germany
The electromagnetic properties of F-region field-aligned irregularities (FAIs) are key parameters in the understanding of their spatial and temporal distribution. So far, electric and magnetic fields associated with FAIs have been studied mostly by simulations and theoretical models, and in a minor fraction by observations. In this work, some static and dynamic electromagnetic characteristics of equatorial FAIs are investigated using observations from the Swarm constellation. First, the spatial and temporal distribution of irregularities are presented based on their magnetic response of their related field-aligned and pressure-gradient-driven currents. Second, the direction of their associated electromagnetic energy flow deduced from the Poynting theorem is shown for some selected events. The results are discussed in the light of numerical simulations and theoretical models.