Ion drift meter research

The final activity period for the DE project has been particularly productive. This period has seen the final delivery of geophysical data sets to the National Space Science Data Center, the granting of three Ph.D. degrees from cumulative work on the project, the operation of automatic data access and display routines for the data, and an increased effort in research and publication of the data. As before the research activities, largely devoted to studies involving the dynamics of the ionosphere, utilize data from the IDM and the RPA and thus the work is not easily attributable to one or the other of these separately funded efforts. In this final report we provide brief descriptions of the work accomplished in the final phase of the program. The Dynamics Explorer program has provided a significant opportunity for much of the community to participate in the data analysis and interpretation. The data, now residing in the national space science data center, are a great legacy that should continue to yield important results for many years

Modeling subauroral polarization streams during the 17 March 2013 storm

The subauroral polarization streams (SAPS) are one of the most important features in representing magnetosphere‐ionosphere coupling processes. In this study, we use a state‐of‐the‐art modeling framework that couples an inner magnetospheric ring current model RAM‐SCB with a global MHD model Block‐Adaptive Tree Solar‐wind Roe Upwind Scheme (BATS‐R‐US) and an ionospheric potential solver to study the SAPS that occurred during the 17 March 2013 storm event as well as to assess the modeling capability. Both ionospheric and magnetospheric signatures associated with SAPS are analyzed to understand the spatial and temporal evolution of the electrodynamics in the midlatitude regions. Results show that the model captures the SAPS at subauroral latitudes, where Region 2 field‐aligned currents (FACs) flow down to the ionosphere and the conductance is lower than in the higher‐latitude auroral zone. Comparisons to observations such as FACs observed by Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), cross‐track ion drift from Defense Meteorological Satellite Program (DMSP), and in situ electric field observations from the Van Allen Probes indicate that the model generally reproduces the global dynamics of the Region 2 FACs, the position of SAPS along the DMSP, and the location of the SAPS electric field around L of 3.0 in the inner magnetosphere near the equator. The model also demonstrates double westward flow channels in the dusk sector (the higher‐latitude auroral convection and the subauroral SAPS) and captures the mechanism of the SAPS. However, the comparison with ion drifts along DMSP trajectories shows an underestimate of the magnitude of the SAPS and the sensitivity to the specific location and time. The comparison of the SAPS electric field with that measured from the Van Allen Probes shows that the simulated SAPS electric field penetrates deeper than in reality, implying that the shielding from the Region 2 FACs in the model is not well represented. Possible solutions in future studies to improve the modeling capability include implementing a self‐consistent ionospheric conductivity module from inner magnetosphere particle precipitation, coupling with the thermosphere‐ionosphere chemical processes, and connecting the ionosphere with the inner magnetosphere by the stronger Region 2 FACs calculated in the inner magnetosphere model.Key PointsSAPS simulation using BATS‐R‐US coupled with ring current model RAM‐SCBComparisons done with AMPERE, DMSP, and Van Allen Probes observationsCaptured the basic physics and mechanism of SAPSPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111134/1/jgra51638.pd

Source of the low-altitude hiss in the ionosphere

We analyze the propagation properties of low-altitude hiss emission in the ionosphere observed by DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions). There exist two types of low-altitude hiss: type I emission at high latitude is characterized by vertically downward propagation and broadband spectra, while type II emission at low latitude is featured with equatorward propagation and a narrower frequency band above ∼fcH+. Our ray tracing simulation demonstrates that both types of the low-altitude hiss at different latitude are connected and they originate from plasmaspheric hiss and in part chorus emission. Type I emission represents magnetospheric whistler emission that accesses the ionosphere. Equatorward propagation associated with type II emission is a consequence of wave trapping mechanisms in the ionosphere. Two different wave trapping mechanisms are identified to explain the equatorial propagation of Type II emission; one is associated with the proximity of wave frequency and local proton cyclotron frequency, while the other occurs near the ionospheric density peak

Earth's ion upflow associated with polar cap patches: global and in-situ observations

We report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the polar cap region during a geomagnetic storm. Our observations indicate strong fluxes of upwelling O+ ions originating from frictional heating produced by rapid antisunward flow of the plasma patch. The statistical results from the crossings of the central polar cap region by Defense Meteorological Satellite Program F16–F18 from 2010 to 2013 confirm that the field-aligned flow can turn upward when rapid antisunward flows appear, with consequent significant frictional heating of the ions, which overcomes the gravity effect. We suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected. These observations give new insight into the processes of ionosphere-magnetosphere coupling

Plasma-neutral interactions in the lower thermosphere-ionosphere : The need for in situ measurements to address focused questions

The lower thermosphere-ionosphere (LTI) is a key transition region between Earth's atmosphere and space. Interactions between ions and neutrals maximize within the LTI and in particular at altitudes from 100 to 200 km, which is the least visited region of the near-Earth environment. The lack of in situ co-temporal and co-spatial measurements of all relevant parameters and their elusiveness to most remote-sensing methods means that the complex interactions between its neutral and charged constituents remain poorly characterized to this date. This lack of measurements, together with the ambiguity in the quantification of key processes in the 100-200 km altitude range affect current modeling efforts to expand atmospheric models upward to include the LTI and limit current space weather prediction capabilities. We present focused questions in the LTI that are related to the complex interactions between its neutral and charged constituents. These questions concern core physical processes that govern the energetics, dynamics, and chemistry of the LTI and need to be addressed as fundamental and long-standing questions in this critically unexplored boundary region. We also outline the range of in situ measurements that are needed to unambiguously quantify key LTI processes within this region, and present elements of an in situ concept based on past proposed mission concepts.Peer reviewe

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

The lower-thermosphere-ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200 km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI.Peer reviewe

Ionospheric Convection at High Latitudes / Clips from Bill Hanson\u27s 1974 presentation

At high latitudes plasma motions driven by the interaction of the magnetosphere with the solar wind are usually characterized in terms of an instantaneous distribution of the electrostatic potential. This potential distribution typically displays large-scale convection cells within which the direction and magnitude of the plasma flows are dependent on the solar wind speed and the solar wind magnetic field. Early observations show a remarkable consistency between the configuration of the electric potential, the associated current distributions that must accompany them and the auroral precipitation of energetic electrons, which carry a significant fraction of the current. Since the observational description of the convection, the current and the auroral precipitation, models of the solar wind magnetosphere interaction have been utilized to describe the associated interaction between the solar wind and the magnetosphere and the closure paths of the currents that flow through the ionosphere. In this way the drivers for the potential seen in the ionosphere and its dependence on solar wind conditions have been further understood. Still a point of discussion is the relative roles of so-called viscous interaction and merging in developing the ionospheric potential at different times. Currents in the ionosphere may originate from regions near the dayside magnetopause and from regions in the magnetospheric tail and these regions may not operate in unison. Thus, recent observations have focused on describing separately the spatial and temporal evolution of convection features on the dayside and the nightside. Changes in the magnetospheric drivers may be applied over small spatial and temporal scales but produce a more global reconfiguration of the major features of the convection pattern such as the convection reversal boundary and the low latitude extent of the auroral zone, which evolve on time scales of minutes to hours. How the plasma responds to these changes at different local times and latitudes is now being actively studied. Recent observations of ionospheric convection driven by the solar ind/magnetosphere interaction show that the volume over which this influence can be seen extends throughout the ionosphere to the magnetic equator. As the sphere of influence of the convection pattern changes significant changes in the plasma transport properties are produced with sometimes, dramatic changes in the plasma number density also appearing at a given location. In this brief review we will describe some key observations that illustrate the challenges associated with identifying the convection drivers, the ionospheric responses and the effects on the ionospheric plasma

Coordinated Satellite Observations of the Very Low Frequency Transmission Through the Ionospheric D Layer at Low Latitudes, Using Broadband Radio Emissions from Lightning

Both ray theory and full-wave models of very low frequency transmission through the ionospheric D layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low-inclination Communication/Navigation Outage Forecast System satellite to test this semiquantitatively, for broadband very low frequency emissions from lightning. Approximate ground-truthing of the incident wavefields in the Earth-ionosphere waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes<26deg. Thus, our conclusions, too, must be limited to the near-equatorial region and are not necessarily predictive of midlatitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of very low frequency lightning emissions through the D layer, at a level exceeding model predictions by at least an order of magnitude. We show that kilometric-scale D-layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D-layer transmission for transmission from powerful man-made radio beacons

EFFECTS OF LASER PULSE SHAPE AND BEAM PROFILE ON ELECTROMAGNETICALLY-INDUCED TRANSPARENCY Publication No.

Supervising Professor: Cyrus D. Cantrell Effects of a Gaussian pulse shape and beam profile on Electromagnetically-Induced Trans-parency (EIT) are studied in a strong probe laser intensity regime under the context of laser pulse propagation. By adopting a pulse-sequencing method, we show that EIT for an intense probe laser can be realized when both incident laser envelopes having both temporal and transverse radial profiles. A proper selection of two relevant parameters, i.e. time peak location and beam diameter, of two injected lasers will implement this pulse-sequencing technique into our numerical experiments on EIT and lead to an enhanced EIT behavior for a strong probe laser beam. vi TABLE OF CONTENTS Dedication....................................................................... i

Combined Contribution of Solar Illumination, Solar Activity, and Convection to Ion Upflow Above the Polar Cap

By analyzing a five‐year period (2010–2014) of Defense Meteorological Satellite Program (DMSP) plasma data, we investigated ion upflow occurrence, speed, density, and flux above the polar cap in the northern hemisphere under different solar zenith angle (SZA), solar activity (F10.7), and convection speed. Higher upflow occurrence rates in the dawn sector are associated with regions of higher convection speed, while higher upflow flux in the dusk sector is associated with higher density. The upflow occurrence increases with convection speed and solar activity but decreases with SZA. Upflow occurrence is the lowest when the SZA > 100° and the convection speeds are low. While, the upflow velocity and flux show a clear seasonal dependence with higher speed in the winter and higher flux in the summer during low convection conditions. However, they are detected for the first time to be both higher in summer during high convection conditions. These results suggest that ion upflow in the polar cap is controlled by the combination of convection, solar activity, and solar illumination