High-latitude plasma structure and scintillation

Clayton Coker,1 Gary S. Bust,2 Richard A. Doe,3 and Thomas L. Gaussiran II2

Received 15 November 2002; revised 22 September 2003; accepted 3 October 2003; published 17 February 2004.

[1] Observations of high-latitude plasma structure and scintillation are presented from theJanuary 2001 scintillation campaign timeframe. Comparisons are made using the all-skyimager and two beacon-satellite ground receivers located at Sondrestrom, Greenland. TheCoherent Ionospheric Doppler Receiver (CIDR) observes 150- and 400-MHz signalstransmitted from low-Earth-orbiting satellites. The 250-MHz polar beacon-satellite systemobserves signals from highly elliptical orbiting satellites. F region patches, F regionprecipitation arcs, and auroral arcs were observed. Intermediate-scale structure wasobserved on the leading and trailing edges of patches prior to exiting the polar cap.Banded structure was observed across an F region arc. Additional beacon-satellitereceivers in Greenland and Alaska provide a unique opportunity to study the spatialdistribution and temporal evolution of patch structures and their associatedscintillation. INDEX TERMS: 2407 Ionosphere: Auroral ionosphere (2704); 2439 Ionosphere:

Ionospheric irregularities; 2475 Ionosphere: Polar cap ionosphere; 2494 Ionosphere: Instruments and

techniques; KEYWORDS: scintillation, beacon satellite, polar cap

Citation: Coker, C., G. S. Bust, R. A. Doe, and T. L. Gaussiran II (2004), High-latitude plasma structure and scintillation,

Radio Sci., 39, RS1S15, doi:10.1029/2002RS002833.

1. Introduction

[2] Ionospheric scintillation affects positioning, com-munication, space tracking, and surveillance systems athigh and low latitudes. Radio signals passing through theionosphere are rapidly modulated in phase and ampli-tude, causing interruptions and errors in signal tracking.This results in position errors, reduction in availablesatellite-to-ground data transmission bandwidths, errorsin target tracking, and poor-resolution surveillance.Aside from these direct effects, scintillation has anindirect effect. System errors can be attributed to scin-tillation by mistake, thus masking real problems anddelaying their resolution. Knowledge of current iono-spheric conditions and predictions about the develop-ment and evolution of plasma structures leading toscintillation effects are a critical element to mitigatingsystem errors.[3] With the proliferation of Coherent Ionospheric

Doppler Receiver (CIDR) receivers, tracking Navy Iono-

spheric Monitoring Satellites (NIMS), and the launch ofadditional satellites carrying the Coherent Electromag-netic Radio Tomography (CERTO) beacon, especiallythose in low inclination orbits (e.g., PICOsat andCNOFS), the capability exists to utilize CIDR receiversin the study of ionospheric plasma structure and scintil-lation. The development and validation of using CIDR asan ionospheric scintillation instrument builds on previousstudies using GPS total electron content (TEC) andtomography to specify a three-dimensional region ofelectron density interest [Coker et al., 2001, 1996; Bustet al., 2001]. The potential for using beacon receivers forscintillation studies at high latitudes has been demon-strated previously [Kersley et al., 1995; Fremouw et al.,2001].[4] This paper focuses on the investigation of scin-

tillation structures at high latitudes within the contextof observed F region patches and arcs. For this study,comparisons are made between CIDR phase scintilla-tions, a 250-MHz polar beacon-satellite system, and anall-sky camera in Greenland. The primary motivationfor studying patches is to be able to specify and predicttheir scintillation effects on operational systems, in-cluding navigation, communication, and radar applica-tions [Behnke et al., 1995; Reinking et al., 2001;Fremouw and Ishimaru, 1992]. The irregularity struc-ture and scintillation effects associated with patcheshave previously been investigated [Kersley et al., 1995;Basu et al., 1994], as well as the climatology of

RADIO SCIENCE, VOL. 39, RS1S15, doi:10.1029/2002RS002833, 2004

1Praxis Inc., Washington, DC, USA.2Center for Ionospheric Research, Applied Research Laboratories,

University of Texas, Austin, Texas, USA.3SRI International, Menlo Park, California, USA.

Copyright 2004 by the American Geophysical Union.

0048-6604/04/2002RS002833

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scintillation effects [Secan et al., 1997; Fremouw andSecan, 1984].

2. Background

[5] Additionally, an initial study has demonstrated thescintillation capabilities of the CIDR receiver. This wasaccomplished by performing bench tests using a simu-lator and by comparing observations made at highlatitudes from CIDR, a 250-MHz polar beacon-satellitesystem, and an all-sky camera in Greenland.[6] Four CIDR receivers are deployed along the west

coast of Greenland. The receivers typically collect data ata 1-Hz data rate, though capability exists to collect up toa KHz rate. For this study the receiver at Sondrestromcollected at a 10-Hz rate, corresponding to an approxi-mately 400 m minimum scale size observable in the Fregion. The CIDR scintillation observations sweepthrough a large geographic region in a relatively shorttimeframe, providing ‘‘snapshot’’ coverage of a largearea. By themselves, these observations will help answera number of important questions regarding scintillationstructures, especially on the dayside of the polar cap andat equatorial latitudes, where optical cameras are unableto detect high-altitude structures. In the following sec-tion, observations of high-latitude plasma structure andscintillation are presented from the January 2001 scintil-lation campaign timeframe. Comparisons are made usingthe all-sky imager and beacon-satellite ground receiverslocated at Sondrestrom, Greenland. F region patches, Fregion precipitation arcs, and auroral arcs were observed.Patches, islands of high-density plasma traveling anti-sunward across the polar cap, occur in the dark polarionosphere when the interplanetary magnetic field isdirected southward, Bz < 0; while precipitation arcs occurfrequently for Bz north conditions [Carlson, 1994].Intermediate-scale structure was observed on the leadingand trailing edges of patches prior to exiting the polarcap. Additional beacon-satellite receivers, distributedalong the west coast of Greenland, provide an extendedcoverage area for tracking patches through the polar cap.Observations from the distributed receivers provide ad-ditional information on the spatial distribution and tem-poral evolution of patch structures and their associatedscintillation.

3. Results

[7] We present three comparisons between observa-tions made by the all-sky imager using the 630.0-nmfilter, the 250-MHz measurements, and phase scintilla-tions from detrended 150-MHz CIDR phase measure-ments. Alternatively, the detrended 400-MHz CIDRphase measurements are used and scaled to 150 MHz.All the data are for the period of January 2001. Figure 1

compares an F region patch (Bz = �5 nT) with observedphase scintillations from the CIDR at Sondrestrom. Theupper panel presents a 630.0-nm all-sky image of thepatch, with the NIMS satellite pass superposed over it.The open circles show regions of scintillation. The lowerpanel shows the sigma-sub-phi of the observed phasescintillation. The patch is traveling in the antisunwarddirection (south) toward the more luminous auroralregion. This patch was one of several observed by theall-sky imager. Phase scintillations of up to 7 radians areobserved along the leading and trailing edges of thepatch. This observation is somewhat unusual in thatthe mechanism that produces scintillation in patches,the gradient drift instability [Crowley, 1996], predictslarger scintillation on the trailing edge of the patch. Thissame patch crossed the 250-MHz system line-of-sight(LOS) 20 min earlier, resulting in similarly elevatedamplitude scintillation, S4 values 0.5–0.6. By the timethe NIMS satellite intersects the 250-MHz system LOS,250-MHz S4 values have fallen to 0.2 and the NIMSphase scintillation has also fallen to moderately lowvalues (1–2 radians). The lower panel of Figure 1 showsthe clear correlation between the observed phase scintil-lations and the patch region. The phase scintillationclearly rises at the low-latitude edge of the patch. Whilenot as sharp a boundary, it also appears that the high-latitude boundary of the patch is again associated withincreased phase scintillations.[8] Figure 2 presents a comparison between an ob-

served large stable auroral arc and the observed phasescintillations. The time history of 630.0-nm emissionsshows that a large-scale brightness gradient advancesfrom south to north in about 20 min. This is a classicsubstorm onset signature for magnetic local time (MLT) =21 [Akasofu, 1977]. The sharp poleward edge of thestructure is the boundary of the open and closed fieldlines in the polar cap/auroral zone transition [Doe et al.,1997; Gallagher et al., 1993]. The phase scintillationfrom CIDR shows that the more-significant scintillationoccurs on the edges of the auroral arc. The 250-MHzsystem penetration point is also located along the pole-ward edge of this region, as indicated by the triangle inthe top panel, where moderately high S4 values areconsistent with results of the phase scintillation measure-ments from the satellite pass. It is also interesting to notethe amount of spatial structure in the vicinity of the arc.The phase scintillations show three, and possibly fourdistinct structure peaks, near the equatorward boundaryof the arc. A smaller scintillation peak is observed alongthe poleward boundary of the arc.[9] Figure 3 presents comparisons between observed

spatial scintillations and a premidnight soft F regionprecipitation arc (Bz = +5 nT), where the Kelvin-Hem-holtz instability is the mechanism responsible for pro-ducing scintillation [Crowley, 1996]. The satellite passes

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Figure 1. An all-sky image of an F region patch with a NIMS satellite pass superposed over it.See color version of this figure at back of this issue.

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Figure 2. A large, relatively stable auroral arc is present as the satellite crosses over it. See colorversion of this figure at back of this issue.

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Figure 3. A NIMS satellite pass crossing over a premidnight soft F region precipitation arc. Seecolor version of this figure at back of this issue.

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over the arc and then over a quiet region between arcs atthe point of closest approach to the 250-MHz systemLOS. In this quiet region between arcs the phase scin-tillation from NIMS and amplitude scintillation from the250-MHz system are at relatively low levels: 1–2radians and S4 value 0.25, respectively. Phase scintilla-tion is observed as the NIMS satellite passes over the arc,oscillating between 2 and 4 (sometimes 6) radians.Fifteen minutes earlier, this same arc crossed over the250-MHz system LOS, resulting in elevated amplitudescintillation, S4 value 0.4. Note that for this case thephase scintillations occur across the entirety of the arcand again demonstrate smaller-scale structure within theoverall spatially scintillating region.

4. Summary

[10] We have shown how the data from the CIDRreceivers deployed in Greenland as a tomography arraycan be used as a spatial phase scintillation measure-ment instrument. The advantage of using the CIDRreceivers, and low-Earth-orbiting satellites, is that weare able to obtain the horizontal variation in phasescintillation as the satellite passes by overhead. Polarorbiting satellites observe variations primarily in lati-tude. Thus the observed phase scintillations provide aspatial map in latitude of ionospheric fluctuations athigh latitudes.[11] Initial simulations were carried out on the CIDR at

Applied Research Laboratories, University of Texas,Austin (ARL:UT) to demonstrate that the observationsdid indeed track phase scintillations. The CIDR does notrecord amplitude measurements and therefore cannotobserve amplitude scintillations. A validation study withthe 250-MHz polar beacon-satellite system at Greenlandwas completed and demonstrated the field utility ofCIDR as a scintillation device.[12] We have presented results from the validation

study that compare spatial phase scintillations observedwith the CIDR receiver to images from the all-skycamera. The results clearly demonstrate correlationsbetween structures observed by the all-sky camera, thepolar beacon-satellite system, and the CIDR observa-tions. The spatial overlaying of the phase scintillationson the all-sky images clearly demonstrates the advan-tages of having spatial maps of scintillations. In Figure 1the phase scintillations indicate small-scale structuringon both the leading and trailing edge of the patch. Thiskind of result, were it to hold up under increasedanalysis, could for a large number of cases have impor-tant consequences for the understanding of the underly-ing dynamics associated along the edges of patches.Similarly, Figures 2 and 3 show what appears to besmall-scale structuring in the phase scintillations withinlarger scintillating regions. Increased analysis at small

scales can potentially provide insight into the dynamicspatial scales of processes in the magnetosphere.[13] For this study we only looked at a single CIDR

located at Sondrestrom. However, all four receivers inthe Greenland array can collect high-rate data and beanalyzed for spatial scintillations. In such a study wewould be able to map the latitudinal variations in phasescintillations from �60–80 degrees geomagnetic lati-tude. Considering that the Greenland array sees 30+passes per day, there is good potential for routinemonitoring of spatial scintillations. In addition, a sim-ilar array exists in Alaska, and a five-receiver array willbe deployed along the east coast this summer, coinci-dent with the Millstone Hill incoherent scatter radar(ISR) and extending from northern Canada to BlockIsland.

[14] Acknowledgments. We thank Keith Groves of AFRLfor providing the 250-MHz scintillation data.

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������������G. S. Bust and T. L. Gaussiran II, Center for Ionospheric

Research, Applied Research Laboratories, University of Texas

at Austin, P. O. Box 8029, Austin, TX 78713-8029, USA.

(gbust@arlut.utexas.edu; gauss@arlut.utexas.edu)

C. Coker, Naval Research Laboratory Code 7607, 4555

Overlook Ave., S.W., Washington, DC 20375, USA. (ccoker@

ssd5.nrl.navy.mil)

R. A. Doe, SRI International, 333 Ravenswood Ave., Menlo

Park, CA 94025, USA. (doe@sri.com)

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Figure 1. An all-sky image of an F region patch with a NIMS satellite pass superposed over it.

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Figure 2. A large, relatively stable auroral arc is present as the satellite crosses over it.

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Figure 3. A NIMS satellite pass crossing over a premidnight soft F region precipitation arc.

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