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Featured researches published by J. R. Dudeney.


Journal of Geophysical Research | 1995

HF radar signatures of the cusp and low-latitude boundary layer

K. B. Baker; J. R. Dudeney; R. A. Greenwald; M. Pinnock; Patrick T. Newell; A. S. Rodger; N. Mattin; C.-I. Meng

Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environment Modeling (GEM) program. It is therefore important to establish clear intercalibrations between different ground-based instruments and satellites in order to clearly place the ground-based observations in context with the corresponding in situ satellite measurements. HF-radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis. In this paper we report on an intercalibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labrador, and Halley Station, Antarctica, and the Defense Meteorological Satellite Program (DMSP) satellites. The DMSP satellite data are used to provide clear identifications of the ionospheric cusp and the low-latitude boundary layer (LLBL). The radar data for eight cusp events and eight LLBL events have been examined in order to determine a radar signature of these ionospheric regions. This intercalibration indicates that the cusp is always characterized by wide, complex Doppler power spectra, whereas the LLBL is usually found to have spectra dominated by a single component. The distribution of spectral widths in the cusp is of a generally Gaussian form with a peak at about 220 m/s. The distribution of spectral widths in the LLBL is more like an exponential distribution, with the peak of the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to those observed in the cusp.


Journal of Geophysical Research | 1994

A new mechanism for polar patch formation

A. S. Rodger; Michael Pinnock; J. R. Dudeney; K. B. Baker; R. A. Greenwald

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. Previous observations have demonstrated that polar patches can be readily identified in Polar Anglo-American Conjugate Experiment (PACE) data. Here PACE data and those from complementary instruments are used to show that some polar patches form in the dayside cusp within a few minutes of the simultaneous occurrence of a flow channel event (short-lived plasma jets ∼2 km s−1) and azimuthal flow changes in the ionospheric convection pattern. The latter are caused by variations of the y-component of the interplanetary magnetic field. The physical processes by which these phenomena cause plasma enhancements and depletions in the vicinity of the dayside cusp and cleft are discussed. Subsequently, these features are transported into the polar cap where they continue to evolve. The spatial scale of patches when formed is usually 200-1000 km in longitude and 2°-3° wide in latitude. Their motion after formation and the velocity of the plasma within the patches are the same, indicating that they are drifting under the action of an electric field. Occasionally, patches are observed to occur simultaneously in geomagnetic conjugate regions. Since some of these observations are incompatible with the presently-accepted model for patch formation involving the expansion of the high latitude convection pattern entraining solar-produced plasma, further modeling of the effects of energetic particle precipitation in the cusp, the consequences of flow channel events on the plasma concentrations, and the time dependence of plasma convection as a result of interplanetary magnetic field By changes is strongly recommended. Such studies could be used to determine the relative importance of this new mechanism compared with the existing theory for patch formation as a function of universal time and season.


Geophysical Research Letters | 1998

Strong flow bursts in the nightside ionosphere during extremely quiet solar wind conditions

A. D. M. Walker; M. Pinnock; K. B. Baker; J. R. Dudeney; J. P. S. Rash

Results of an HF radar study of convection during an extended quiet solar wind interval on March 10 1997 are presented. After thirty hours during which the solar wind met the criteria for quiet conditions the HF radars at Sanae and Halley in Antarctica showed strong activity on the night side. Flow bursts with velocities of more than 2000 m s−1, corresponding to electric fields exceeding 100 m V m−1 were observed. These occurred quasi-periodically for almost two hours on the night-side with a repetition time of several minutes. It is concluded that they map to a region well inside the magnetotail. It is suggested that they are associated with sporadic energy release during reconfiguration of the tail magnetic field, and that this can occur even during an extended quiet solar wind period.


Journal of Atmospheric and Solar-Terrestrial Physics | 1991

Studies of conjugate plasma convection in the vicinity of the Harang discontinuity

J. R. Dudeney; A. S. Rodger; M. Pinnock; J. M. Ruohoniemi; K. B. Baker; R. A. Greenwald

Abstract Two case studies are presented of the large-scale nightside ionospheric plasma convection observed simultaneously in the two polar regions using HF backscatter radars. The case studies occur during geomagnetically quiet conditions, and for one of the two periods the interplanetary magnetic field (IMF) is known to be northwards. For both cases plasma generally convects westward in the evening and eastward in the morning. The times at which the nightside flow reversal (the Harang discontinuity) occurs is observed to differ by several hours between the two hemispheres, and between the two study periods. For the case where IMF data are available, the nightside plasma flow is shown to respond to a step change in the IMF y -component (becoming less negative), with a time delay of about 25 min. In the southern hemisphere, the flow reversal appeared simply to be shifted to later magnetic local times, whilst for the northern hemisphere the evening westward flow was disrupted by the occurrence of eastward flow ahead of the Harang discontinuity. The general features of the observed convection are not consistent with the Heppner and Maynard (1987, J. geophys. Res. 92 , 4467) convection models, which exclude any significant association between the Harang discontinuity and the state of the IMF. The results are more in agreement with the MHD simulations for northward IMF of Ogino et al . (1985, J. geophys. Res. 90 , 10835). The latter invoke nightside reconnection cells whose behaviour is dependent upon the IMF y -component in the same sense as for our observations.


Journal of Geophysical Research | 1999

A very large scale flow burst observed by the SuperDARN radars

Nozomu Nishitani; Tadahiko Ogawa; M. Pinnock; M. P. Freeman; J. R. Dudeney; J.-P. Villain; K. B. Baker; Natsuo Sato; Hisao Yamagishi; Haruhisa Matsumoto

We examined the dynamics of the ionospheric plasma in the dayside sector by using the HF radar data at Iceland West and at Finland from 1100 to 1230 UT on September 5, 1995. During that period, the solar wind density was high and the IMF was strongly southward. The dayside magnetopause was highly compressed nearly to the geosynchronous orbit. The two radars simultaneously detected a poleward flow burst in the noon sector which, assuming uniformity of flow in the region of the data gap (1.5 MLT) between the two radars, showed a magnetic local time extent of 5 hours. This local time extent is 2 to 3 hours wider than previous results. The maximum poleward plasma velocity of the flow burst is ∼750 m/s, and the latitudinal size of the flow burst region is ∼100 to 200 km. This flow burst region initially expanded in longitude up to 5 hours, and then shifted poleward with a phase speed of 400 to 670 m/s. The flow burst has a duration of ∼20 min. This large-scale poleward flow burst is likely to be due to large-scale reconnection occurring at the dayside magnetopause and subsequent convection as the magnetic field lines are transported across the polar cap.


Journal of Geophysical Research | 1990

Simultaneous conjugate observations of dynamic variations in high-latitude dayside convection due to changes in IMF By

R. A. Greenwald; K. B. Baker; J. M. Ruohoniemi; J. R. Dudeney; M. Pinnock; N. Mattin; J.M. Leonard; R. P. Lepping


Geophysical Research Letters | 1990

Simultaneous HF-radar and DMSP observations of the cusp

K. B. Baker; R. A. Greenwald; J. M. Ruohoniemi; J. R. Dudeney; M. Pinnock; Patrick T. Newell; M. E. Greenspan; C.-I. Meng


Annales Geophysicae | 1994

Simultaneous two hemisphere observations of the presence of polar patches in the nightside ionosphere

A. S. Rodger; Michael Pinnock; J. R. Dudeney; J. Waterman; O. de la Beaujardiere; K. B. Baker


Journal of Geophysical Research | 1991

The intense magnetic storm of December 19, 1980: Observations at L = 4

Edgar A. Bering; J. R. Benbrook; Robert Haacke; J. R. Dudeney; L. J. Lanzerotti; Carol G. Maclennan; Theodore J. Rosenberg


Journal of Geophysical Research | 2002

Radar observations of magnetospheric activity during extremely quiet solar wind conditions

A. D. M. Walker; K. B. Baker; M. Pinnock; J. R. Dudeney; J. P. S. Rash

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A. S. Rodger

British Antarctic Survey

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M. Pinnock

British Antarctic Survey

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K. B. Baker

Johns Hopkins University

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Michael Pinnock

Natural Environment Research Council

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K. B. Baker

Johns Hopkins University

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C.-I. Meng

Johns Hopkins University Applied Physics Laboratory

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