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GEOPHYSICAL RESEARCH LETTERS,VOL. 25, NO. 20, PAGES3791-3793, OCTOBER15, 1998

Comment on the source region of traveling convection vortices by A. G. Yahnin et al.
Y. I. Feldstein Institute of Terrestrial M·gnetism, Ionosphere ·nd R·dio W·ve Propagation, Troitsk, Moscow Region, Russi·

Abstract.

The sourceregionsof traveling convection and discrete precipitations equatorward of the LLBL

vortices (TCV) observed the dayside in magnetosphereare denoted "traditional CPS" and "traditional BPS",
outsidethe near noon sectorhave been mapped to mag- respectively,by analogy to the nightside notation. netospheric locations within the outer radiation belt, Feldsteinand Galperin [1985, hereafterFG85; 1993,

[1991,herebut not to the Central PlasmaSheet(CPS) as claimed hereafterFG93] and Galperinand Feldstein by Yahninand Motefta [1996]and Yahninet al. [1997]. after GF91; 1996, hereafterGF96] haveshownthat the
Their suggested connectionbetween TCV and the CPS is based on the unjustified application of terminology traditionally usedfor the auroral precipitation structure in the nightside magnetospheric sector[Winninghamet al. 1975]to the late morning-noon sector.This is a case wherean important finding on the location of TCV with respectto natural magnetospheric boundarieshas been presentedusing misleadingterminology,which leads to an incorrect physical interpretation of the result. Hence this Comment emphasizesthe need for a critical reexamination and modification of the "traditional" termi-

terms BPS and CPS, as commonly used during the last 20 years, are not appropriate descriptions of auroral energetic-plasmaprecipitation in the night sector. In fact, CPS and BPS denote precipitations which have absolutely no relation to either the central plasma sheet or the boundary plasma sheet in the magnetotail. Accordingto FG85 and GF96, the precipitation region can be divided into three parts with increasinggeomagnetic latitude: equatorial diffuse precipitations, structured

nology concerning the plasma domain structure in the magnetosphere.

precipitations accelerated of particles(discrete auroral forms inside the auroral oval), and weak low-energy electronprecipitationwith VDIS-2 (velocity-dispersed ion structures the second of type) just polewardof the
bright auroral oval. These three characteristic plasma

Yahninand Motefta [1996]and Yahninet al. [1997; structuresare mapped along magnetic field-linesto the hereafterY97] usedlow-altitudesatelliteparticle mea- nightside magnetosphereas follows: to the Remnant
surementsto determine the magnetosphericdomain in Layer, a region of large-scalesunward convectionwithwhich the travelling TCV-related currents originated. in the outer radiation belt (RL); to the Central PlasSpectrograms low-energy of particles(E < 20 keV) ma Sheet, a region mainly comprised of hot plasma on measuredby the DMSP satellites were used to select the stretched field lines on both sides of the magnetotail boundariesof plasma precipitation regionswith various current sheet; and to the Boundary Plasma Sheet at the particle characteristics. These regions were then iden- boundaries of the tail lobes and the plasma sheet in the tified with magnetospheric plasma domainssuchas the upper and lower parts of the tail, including the Plasma

CPS, BPS (boundaryplasmasheet), LLBL (low lat- SheetBoundary Layer(PSBL) and Low EnergyLayers itude boundarylayer), and so on. The coordinates (LEL) [FG85;GF96]. Correspondingly, of PSBLis characthe precipitation-regionboundarieswere determinedby
terized by the presenceof VDIS-2, and the LEL salient

means the automatedmethodof Newell et al. [1991] feature is counterstreaming, very low-energy electron of and Newell and Meng [1992]. On the basisof the tradi- and ion beams.
tional terminologyfor plasmaprecipitation regionsused A special analysis of simultaneous plasma measureby Newellet al. [1991],Y97 concluded that the fociiand ments by geosynchronous satellites and by low-altitude
trajectories of TCV lie inside the central plasma sheet

satellitesabove auroral regionswas performed by Hones

near the CPS/BPS boundary.

et al. [1996].Their result was: "our analysisof the full

Until recently, the most widely used descriptions of data set refutes the view that the auroral oval of disnightsideauroral precipitation-regionstructuresand cor- crete forms maps to the plasma sheet boundary layer respondingterminology were those proposedby Win- and that the equatorward diffuse aurora is the main ninghamet al. [1975; hereafterW75]. Accordingto portion of the plasma sheet. The analysis supports, inW75, the area of auroral electron precipitation in the stead,the opinionof Feldsteinand Galperin[1985]that near-midnight sectoris located poleward from the outer the auroral oval is the mapping of the plasma sheet's radiation belt, and is composed diffuseand structured full thicknessand the diffuse aurora maps into the outer of precipitations from the central and boundary plasma radiation belt". Thus, as demonstrated by the in situ sheets(CPS and BPS), respectively.Under the cate- measurementsof high-altitude satellites, diffuse plasgorization of auroral precipitations in the dayside sec- ma precipitations equatorwards of the auroral oval are tor proposed Newell and Meng [1992], the diffuse mapped to the regionof the outer radiation belt but not by to the central plasma sheet. The discovery of the LEL

Copyright bythe 1998 American Geophysical Union.
Paper number GRL-1998900054.
0094-8276/98/GRL-1998900054$05.00
3791

structureat the outeredgeof the plasmasheet[Parkset al. 1992]also supportsthe correctness the mapping of scheme FG85 for the plasmasheetperiphery [Feldby stein and Galperin 1994]. Further improvementof this
schemeand algorithms developed for automatic iden-


3792

FELDSTEIN Y.I.: COMMENT ON YAHNIN ET AL.
TSYGRNENKO'$MODEL( 1995 )

tiffcation plasma of structure boundaries the basis on
of low-altitudeDMSP spectrograms presented are by Newell et al. [1996].
have continued to use the erroneous

Newell et al. [1991] extended the identification of CPS/BPS by W75 to the daysidesector. Sincethen,
some researchers

t ,Re
·i"·: ·;.·': x:o:: .....

I ,Re
5

terminology of "traditional CPS" and "traditional B PS" mapping to the central plasma sheetand boundary plasma sheet, respectively. Below I demonstrate that the
use of this "traditional" notation can lead to incor-

rect conclusionsabout the magnetosphericsourcesof geophysicalphenomena observedfrom Earth, using the

)

work of Yahnin and Morefro [1996]and Yahnin et al. [1997]as examples.
For 5 events detected by ground-basedobservations,
Y97 found that the TCV focii were located in the "tra-10 -10

ditional CPS" region, so they concludedthat the TCV sourceswere really placed in the central plasma sheet.

For two cases (June28, 1986and December 1990), 17,
I was able to calculate the magnetospheric magnetic field from observations using the empirical model of
b) RLEXEEV'$ MOBELI 1gg6 I

Tsy#anenko [1995, hereafter T95] and the conceptual, paraboloid modelof Alezeev al. [1996,hereafter et A96].
The parameters which serve as an input for the T95

,Re

t¾'Ro

modelare the solarwindpressure (P), the IMF components(By and Bz), Dst indices, and the geomagnetic dipoleorientation(angle xlt). The A96 model requires
two additional parameters the geocentric distance to the inner boundary of the magnetotaft current sheet, and the magnetic flux from the polar cap -- which were determined from DMSP plasma observations. Figure 1 presents the results of mapping the TCV focus location to the magnetosphere for the June 28

x=
-5

')

·':.,·::

event(·t = 75Ü, MLT = 1000h), usingthe predictions of the T95 model(Figurela) and the A96 model(Figure lb). The projectionof the field-linewith the TCV
focus at its footpoint in the northern hemisphere is de-

pictedin the meridional v/X 2 + y2) andequatorial (Z, (X, Y) planes.Figurelb alsoshows modeled the magnetopause location in the corresponding planes. The field-line threading the TCV location in both models doesnot bend far to the magnetosphericnight side and doesnot map to the central plasma sheet, which is located in the night side of the magnetosphereaccordingto any standard textbook. Instead, the magnetic field-line threading the TCV focusis located within the outer radiation belt at a distance · IRe from the magnetopause at apex of the field line. Mapping the TCV focus to the magnetospherefor the December 17 event gives similar results. Additional confirmation of the TCV location in the outer ra-

Figure 1. TCV focus mapping the magnetosphere to on June 1986using Tsy#anenko and(b) 28, (a) [1995] Alezeev al. [1996] et paraboloid external magnetic-field
models. The magnetic field-line the meddional in plane is presented left, andits projection the equatoriat to al planeis shown right. For the paraboloid at model
corresponding planes included well. is as

(b), themodeled location themagnetopause of in the

to incorrectly identify the TCV sourcepositions. TCV sourcesare indeed located well within the magnetoelectrons according to NOAA-10 satellite observations sphere, as shown by Y97, but in the outer radiation (Y97). This boundarycoincides with the auroral oval belt rather than the central plasma sheet. Hence, the currentsrelated to the TCV originatenot equatorial boundary and, hence, with the boundary be- field-aligned tween the "traditional CPS and BPS". Note that Yahin the plasma sheet, as Y97 stated, but in the outer radiation belt is its position inside the poleward bound-

ary of the regionof trapped energetic > 30 keV) (E

nin et al. [1995] carried out similar mapping of the
TCV foci to the magnetosphereusing of the Tsy#a-

diation belt.

This incorrect

treatment

could be evaded

if the papersunder consideration critically reassess the as nenko[1989]magneticfield model, whereas present traditionalCPS/BPS identification, doneby Newell the paper relies on the up-to-date T95 and A96 magnetic- et al. [1996],FG85, FG93 and GF91. field models. The misunderstanding magnetospheric of TCV sources Therefore,the usageof "traditional CPS/BPS" ter- discussedabove testifies once more to the desirability of revisionand the fulfillmentof the followminologywhenidentifyingthe structuralboundaries of a terminology of plasmaprecipitationat low latitudes led Yahnin et al. ing recommendation IAGA WorkingGroupIIF/III4


FELDSTEIN

Y.I.: COMMENT

ON YAttNIN

ET Aoe.

3793

("Extension the AuroralOvalandPolarCapinto the of Magnetosphere") the IAGA Assembly Boulder, at in
July 1995: "The community should decouple nomenclature of ionosphericpopulationsfrom magnetospherIAGA WG recommendation have been used by Newell

Hones, E. W., M. F. Thomsen, G. D. Reeves, L. A.Weiss, D. L. McComas and P. T. Newell, Observational determination of magnetic connectivity of the geosynchronous

region of the magnetosphereto the auroral oval, J. Geo-

ic populations, creatinga set of operational definitions phys. Res., 101, 2629-2640, 1996. which are model independent". Efforts to apply this Newell, P. T., Ya. I. Feldstein, Yu. I. Galperin and C.-

et al. [1996] Feldstein Galperin and and [1996].
Acknowledgments. I am grateful to Y. I. GMperin
and L. I. Gromova for discussions,J. Karpen as a language copyeditor. This work was supportedin part by the 96-0566279 and INTAS grant 95-0932.

I. Meng, The morphology of nightside precipitation, J. Geophys. Res., 101, N5, 10737-10748, 1996. Newell, P. T. and C.-I. Meng, Mapping the dayside ionosphere to the magnetosphereaccordingto particle precipitation characteristics, Geophys. Res. Left., 19, 609-612,
1992.

Newell, P. T., S. Wing, C.-I. Meng and S. Sigillito, The auroral oval position, structure and intensity of precipitation from 1984 onwards: an automated online data base, J.
Geophys. Res., 96, 5877-5882, 1991. Parks, G. K., R. Fitzenreiter, K. W. Ogilvie, C. Y. Huang, K. A. Anderson, J. Dandouras, L. A. Frank, R. P. Lin, M. McCarthy, H. Reme, J. A. Sauvaud and S. Wetden, Lowenergy particle layer outside of the plasma sheet bound-

References

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GMperin, Yu. I. and Ya. I. Feldstein,Mapping of the precipitation regionsto the plasmasheet, J. Geomag. Geoelectr., ·8, 857-875, 1996.

(Received March 25, 1998;accepted July 30, 1998.)