11 research outputs found
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
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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
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
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
Global Assimilation of Ionospheric Measurements (GAIM)
The ionosphere is a highly dynamic medium that exhibits weather disturbances at all latitudes, longitudes, and altitudes, and these disturbances can have detrimental effects on both military and civilian systems. In an effort to mitigate the adverse effects, we are developing a physics-based data assimilation model of the ionosphere and neutral atmosphere called the Global Assimilation of Ionospheric Measurements (GAIM). GAIM will use a physics-based ionosphere-plasmasphere model and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. Some of the data to be assimilated include in situ density measurements from satellites, ionosonde electron density profiles, occultation data, ground-based GPS total electron contents (TECs), two-dimensional ionospheric density distributions from tomography chains, and line-of-sight UV emissions from selected satellites. When completed, GAIM will provide specifications and forecasts on a spatial grid that can be global, regional, or local. The primary output of GAIM will be a continuous reconstruction of the three-dimensional electron density distribution from 90 km to geosynchronous altitude (35,000 km). GAIM also outputs auxiliary parameters, including N m F 2, h m F 2, NmE, hmE, and slant and vertical TEC. Furthermore, GAIM provides global distributions for the ionospheric drivers (neutral winds and densities, magnetospheric and equatorial electric fields, and electron precipitation patterns). In its specification mode, GAIM yields quantitative estimates for the accuracy of the reconstructed ionospheric densities
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