H. Carlson - Academia.edu (original) (raw)
Papers by H. Carlson
On 20-Dec-1998, the EISCAT Svalbard Radar was running in field-aligned mode from 0600-1200 UT. Th... more On 20-Dec-1998, the EISCAT Svalbard Radar was running in field-aligned mode from 0600-1200 UT. The auroral arc was observed by meridian scanning photometer to move from equatorward of the radar beam to poleward and back again while the radar was running, allowing measurements of the neutral temperature while the radar was measuring on closed field lines. When the auroral arc moved equatorward across the beam, 50 minutes of heating events were observed. Ion upflow is seen near all optical events, but only some show strong ion heating. Using the measured neutral temperature it is possible to estimate the scalar difference between the neutral wind and ion drift, assuming that frictional heating is the dominant ion heating mechanism. The strongest heating events do not appear to coincide spatially with optical events, rather they occur north or south of an optical event. This indicates that the heating events are caused by joule heating from reconnection-related transient flow channels.
Throughout the last decade we have carried out a several campaigns involving the EISCAT Svalbard ... more Throughout the last decade we have carried out a several campaigns involving the EISCAT Svalbard Radar. Using a combination of fast azimuth and elevation scans we have detected a series of meso-scale features in the F-region polar ionosphere, including meso-scale flow channel events and polar cap patches of enhanced electron density. We have found examples of extreme plasma density being transported all the way across the polar cap. We have also studied the growth of F-region plasma irregularities. In this talk we review some of our findings.
The character of the polar ionosphere is determined by the solar wind history, as is performance ... more The character of the polar ionosphere is determined by the solar wind history, as is performance capabilities of high latitude GNSS and communications systems. For system design we have learned key climatology of structuring of the polar cap ionosphere (cause) and of system performance (effect). For operations however, currently each significant new discovery both: defines better solutions, and rearranges priorities on scientific challenges to overcoming obstacles to system reliability. In 2007 we discovered that onset of structuring in polar cap patches (which dominate polar disruptions of GNSS/communications systems) was not by the mechanism accepted for over two decades (gradient drift), but a cusp mechanism (shear driven) creating outage regions far faster (~ minute) and closer (>500 km) to population centers than suspected. Discoveries since, including new cusp shear mechanisms, underscore cusp/polar cap dynamics challenges including self-consistent electrodynamics among: co...
Journal of Geophysical Research, 1966
ABSTRACT
Bulletin of the …, 2000
... Those who worked with him came to know the signs of yet another of his creative ideas-the bre... more ... Those who worked with him came to know the signs of yet another of his creative ideas-the breaking of an engaging smile, the brightening of the twinkle in his eye, the lightning pace of the ` `if/then/else' ` thought process that followed, and then his all-engaging question, ` `Now ...
Journal of Geophysical Research: Space Physics
Effect of the Ionosphere on Space Systems and Communications, 1975
The character of the polar ionosphere is determined by the solar wind history, as is performance ... more The character of the polar ionosphere is determined by the solar wind history, as is performance capabilities of high latitude GNSS and communications systems. For system design we have learned key climatology of structuring of the polar cap ionosphere (cause) and of system performance (effect). For operations however, currently each significant new discovery both: defines better solutions, and rearranges priorities on scientific challenges to overcoming obstacles to system reliability. In 2007 we discovered that onset of structuring in polar cap patches (which dominate polar disruptions of GNSS/communications systems) was not by the mechanism accepted for over two decades (gradient drift), but a cusp mechanism (shear driven) creating outage regions far faster (~ minute) and closer (>500 km) to population centers than suspected. Discoveries since, including new cusp shear mechanisms, underscore cusp/polar cap dynamics challenges including self-consistent electrodynamics among: convection models, summation of reconnection and transient flow events, and current-sheet boundary-interfaces.
Radio Sci, 1994
Since the end of the 1970s, we have seen enormous progress in our understanding of the polar iono... more Since the end of the 1970s, we have seen enormous progress in our understanding of the polar ionosphere and its structuring. With this benchmark issue of Radio Science it is appropriate to reflect briefly on that passage and some key questions that lie ahead. The discussion here will concentrate on the winter hemisphere, in keeping with the conditions under which most of the data studied to date have been gathered. The polar ionosphere alternates between two states, depending on whether the interplanetary magnetic field (IMF) is southward or northward. The former state is characterized by-• 100-1000 km islands of enhanced F region plasma, originating in sunlit upper midlatitudes, entering and traversing the polar cap. They become highly structured and produce severe scintillation. Despite much progress on the source, evolution, and ultimate fate of this polar plasma, we remain challenged by the process(es) which chop entering plasma into such islands. For northward IMF we have learned much about the near-Earth processes determining the character of polar cap arcs, velocity structure and electrodynamics, and energetics. A remaining challenge is to relate these structures to the topology and driving physical processes in the magnetosphere and solar wind. Here we sketch the principles behind the progress and the context of several key problem areas ahead.
Geophysical Research Letters, Oct 15, 1994
Polar patches are regions within the polar cap where the F-region electron concentration and airg... more Polar patches are regions within the polar cap where the F-region electron concentration and airglow emission at 630 nm are enhanced above a background level. They have been observed for over a decade [e.g. Weber et al., 1986 and the references therein] but as yet the processes responsible for their •brmation are still controversial. Anderson et al.
On 20-Dec-1998, the EISCAT Svalbard Radar was running in field-aligned mode from 0600-1200 UT. Th... more On 20-Dec-1998, the EISCAT Svalbard Radar was running in field-aligned mode from 0600-1200 UT. The auroral arc was observed by meridian scanning photometer to move from equatorward of the radar beam to poleward and back again while the radar was running, allowing measurements of the neutral temperature while the radar was measuring on closed field lines. When the auroral arc moved equatorward across the beam, 50 minutes of heating events were observed. Ion upflow is seen near all optical events, but only some show strong ion heating. Using the measured neutral temperature it is possible to estimate the scalar difference between the neutral wind and ion drift, assuming that frictional heating is the dominant ion heating mechanism. The strongest heating events do not appear to coincide spatially with optical events, rather they occur north or south of an optical event. This indicates that the heating events are caused by joule heating from reconnection-related transient flow channels.
Throughout the last decade we have carried out a several campaigns involving the EISCAT Svalbard ... more Throughout the last decade we have carried out a several campaigns involving the EISCAT Svalbard Radar. Using a combination of fast azimuth and elevation scans we have detected a series of meso-scale features in the F-region polar ionosphere, including meso-scale flow channel events and polar cap patches of enhanced electron density. We have found examples of extreme plasma density being transported all the way across the polar cap. We have also studied the growth of F-region plasma irregularities. In this talk we review some of our findings.
The character of the polar ionosphere is determined by the solar wind history, as is performance ... more The character of the polar ionosphere is determined by the solar wind history, as is performance capabilities of high latitude GNSS and communications systems. For system design we have learned key climatology of structuring of the polar cap ionosphere (cause) and of system performance (effect). For operations however, currently each significant new discovery both: defines better solutions, and rearranges priorities on scientific challenges to overcoming obstacles to system reliability. In 2007 we discovered that onset of structuring in polar cap patches (which dominate polar disruptions of GNSS/communications systems) was not by the mechanism accepted for over two decades (gradient drift), but a cusp mechanism (shear driven) creating outage regions far faster (~ minute) and closer (>500 km) to population centers than suspected. Discoveries since, including new cusp shear mechanisms, underscore cusp/polar cap dynamics challenges including self-consistent electrodynamics among: co...
Journal of Geophysical Research, 1966
ABSTRACT
Bulletin of the …, 2000
... Those who worked with him came to know the signs of yet another of his creative ideas-the bre... more ... Those who worked with him came to know the signs of yet another of his creative ideas-the breaking of an engaging smile, the brightening of the twinkle in his eye, the lightning pace of the ` `if/then/else' ` thought process that followed, and then his all-engaging question, ` `Now ...
Journal of Geophysical Research: Space Physics
Effect of the Ionosphere on Space Systems and Communications, 1975
The character of the polar ionosphere is determined by the solar wind history, as is performance ... more The character of the polar ionosphere is determined by the solar wind history, as is performance capabilities of high latitude GNSS and communications systems. For system design we have learned key climatology of structuring of the polar cap ionosphere (cause) and of system performance (effect). For operations however, currently each significant new discovery both: defines better solutions, and rearranges priorities on scientific challenges to overcoming obstacles to system reliability. In 2007 we discovered that onset of structuring in polar cap patches (which dominate polar disruptions of GNSS/communications systems) was not by the mechanism accepted for over two decades (gradient drift), but a cusp mechanism (shear driven) creating outage regions far faster (~ minute) and closer (>500 km) to population centers than suspected. Discoveries since, including new cusp shear mechanisms, underscore cusp/polar cap dynamics challenges including self-consistent electrodynamics among: convection models, summation of reconnection and transient flow events, and current-sheet boundary-interfaces.
Radio Sci, 1994
Since the end of the 1970s, we have seen enormous progress in our understanding of the polar iono... more Since the end of the 1970s, we have seen enormous progress in our understanding of the polar ionosphere and its structuring. With this benchmark issue of Radio Science it is appropriate to reflect briefly on that passage and some key questions that lie ahead. The discussion here will concentrate on the winter hemisphere, in keeping with the conditions under which most of the data studied to date have been gathered. The polar ionosphere alternates between two states, depending on whether the interplanetary magnetic field (IMF) is southward or northward. The former state is characterized by-• 100-1000 km islands of enhanced F region plasma, originating in sunlit upper midlatitudes, entering and traversing the polar cap. They become highly structured and produce severe scintillation. Despite much progress on the source, evolution, and ultimate fate of this polar plasma, we remain challenged by the process(es) which chop entering plasma into such islands. For northward IMF we have learned much about the near-Earth processes determining the character of polar cap arcs, velocity structure and electrodynamics, and energetics. A remaining challenge is to relate these structures to the topology and driving physical processes in the magnetosphere and solar wind. Here we sketch the principles behind the progress and the context of several key problem areas ahead.
Geophysical Research Letters, Oct 15, 1994
Polar patches are regions within the polar cap where the F-region electron concentration and airg... more Polar patches are regions within the polar cap where the F-region electron concentration and airglow emission at 630 nm are enhanced above a background level. They have been observed for over a decade [e.g. Weber et al., 1986 and the references therein] but as yet the processes responsible for their •brmation are still controversial. Anderson et al.