Res. Vol. 16, No. 1, pp. (1)13-(1)16, 1995 Copyright 0 1995 COSPAR Printed io Great Britain. All rights resewed. 0273-l 177l95 $9.50 + 0.00
INCLUDING AURORAL OVAL BOUNDARIES IN THE IRI MODEL
AtthetsstfnusnationalRefereaceI~(IRI)W~it’cnraa,~tbatfulyn~~afthe model should include a repmsentatioaof the aamml oval bom&ri& In this paper we review the difflxe4ltexisting parameterkationsof the aamfal oval discassiag theirdata base, bolmdsq criteria. ~fonn~~n,andovaalluseNnessfa:l3U.Asrf~candidatefat~iatoIRI we recommendthe pammeterkatknof the Feldstein/ll ovals by Holzworthand Meag f.?J.Ways of [email protected]
this model into IRI are discussed.We will also addre3sadjustabilitywith usexquvided baundahescrhoundary-relatedparameteJrs,tobet&~storm-~stlldka. INTRODUCXION ~~watisthe~~onkthehigh-latltwlei~~,w~bu:auropa~y~(i)dre polarcap q$oa, (ii) the regionof maximumprecipitationof energeticekctmns, aad (iii) the traasitioa ~C~~~~~Cf~~~~~~~~ f sly circularia shapeoffset fromthe magneticpole by a few deg s conccpt~ftbeauronilovalwastirstusedbyF~~~kIukI96otodesaibGopticat(ali-sLycantaa) m duringthe IGY 1957158.Imagersoa DE1 andORlatersatelliteshaveprovidedas with the globalvisaal ~tion of this concept.They have also documeatedthattlz oval is highly dyaamkal ~gequatcwwardd~gmagneticallydisturbed~~.~ovalis~y~~with~ regioa of precipitatingenergeticelectrons(as illusaaud Figm~ I), since they areprkuuily respa&bk fartheaurora,aadalsowiththe~/~~wind-induoebiancoawxstioaat~k~(suleFigon2). A numhexof empiricaland semi-empiricalmodels have been developed from satellite data for the precipitatioafluxes as well as the convectioapat&as. Ia the folk* sectkns we will brieflydiscass themastimpcPtantonesandthanfocusonaliLely~~foa~~~~~k~.
1. Schematicill~tration of the regionsof partick przcipitatknandofthevisualaurora.
Fig. 2. The oval and the high-latitudeioa
D.BiIi&a f /
5:A 5:40 5:45 5:50 5:55 76.9 85.0 66.8 49.4 32.2 6:06 6:W.i 6:18 17:48 IS:06 18:12 f&12
Fig_ 3. Total
ion density as measured by DMSP on Sep 3, 1987and as predicted by IRL FHW auroralboundariesare shown forQ=O (Kp=O+).
XIIthis section we will give a brief overview of existing models for the specikation of am-oral boundaries. Fefdstein and Starkov f4J’presentedamoral ovals for seven levels of geomaguetk activity s~rn~ observations on a large vohkme of all-sky camera fiims taken during the ~~~~ Geophysical Yesr (Kiy) from f957 to 19% Activity leveb are ciassified with the l5-min Q index (crt;) that will be explained in more detail in the next section. Hokworth and Meng );1(established simple rn~~e~~ representations of the seven ovals using a third-order &urier fonnukt that describes the corrected geomagnetic latitude (CCL) of the polward and equatorward boundaries in terms of the mqnetic local time (MLT in the cotrected geomagnetic coordinate system). In the ruknder of the paper we will refer to this model as FHA& A number of statistical models have been developed for the precipitating electron energy flux and the resulting amoral zone conductauces (height-integrated HaU and m conductivities). Wallis and Buying /5/ used ISIS 2 rn~~rnen~ to obtain the local time and invariant latitude dependent ~ondu~~~ for quiet and active Gary cities. 30,407 ~vid~ AE-C and D woos were the basis for the model by Spiro et al. /6/that hsts the fluxes and conductance in terms of invariant faaitudeand~timeforf~~~~of~~activity&~~byttreAEindex.Hardydat~/retied on data from three sat&&es (DMSP-F2, -EQ, P78-1) ~wrn~~g 14.1 million flux speea to establish flux and conductances maps in CCL&&T-space for seven levels of magnetic activity as specjfredbythe~pindex,TheN~~~modetis~an~Erommcllr:r;bran6oooO~ passes/g/. Data were averaged secording to magnetic latitude, MLT, and total power input far each pass the total ~w~~~t was estimated from the flux dataand an activity index (I-10) was assigned. Amoral boundaries are obtained hrn such modeis simply (and also ~ew~~i~y) by choosing a minimum flux or conductance level. An often used estimate is a conductance of I mho for the equatorward as well as polward boundary. The minimum integral energy flux recommended for def* aurora! oval boundaries in the NQAAQ’IRtX model is 0.25 ergs cm* s-r /2!. In Piiure 4, bound&es defined in this way from the DMSP model /71 are compared with the FfcM oval m The example shows that the ~nd~~~ and flux criteria are not fully ~~~e and &at both akria prsdictaI;trger~~~~~the~~The~~~~~tDdsC oflargest energy fiux and correspond to a minimum ~gh~e f&x of about 1 ergs cm-a s-r and a minimum ~ndu~~~ofabouts~~weatso~~on~daysideihe~~~atsdefinedby the~conductanceisse~~~iower~theone~by~pade;csen~~. A somewhat different approaeb was chosen for NCAR’s Thermoapheric General Circulation Made1 (TGCM). Its pammetekation of the aurora! oval /91 is tight to the reversal boundary between sunward and anti-sunward ion convection as defimedin Heelis’s/IO/ semi-empirkal convecticmmodel ‘lbe radius of the center of the am-oralzone is positioned a few degrees qm&xwatd Of~~~~*M~ details can be found in 191.
model can be updated with these values by adjusting the FHW parameter (A,) that pr~rn~a~iy decent the oval radius. Best resUhscan be expected, if the vaIuesfar a wide range of MLF, at &xii two values axerequired
WDC-A for ~~rn~e~ since 1957. In many cases IRI users might have easiexaccess x. Therefore it would be de&able to know the appear Kp range for which the diffment KP Fe~ds~~ ovals are valid. A direct relation between Q and Kp is ~f~colt to establish, since the two indices correspond to different time scales. In their comparative study, Szuszczewiczetal‘/3/assumetbe following conversion algorithm: Kp = 0.33 Q for Qc3 and Kp = Q - 2 for QZI#(Kp=X stands here for X-, X0, X+) based on the deftition of the two indices. Comparisons with aanxal images takea by satellites bond help to provide a better ~~i~~tio~ of the m ovals in uxms of the Kp index.
1. Y.I. Feller,
3, E.P.S twig and amx& quakes 613 (1993).
et aL, ~~~rnea~ during the solsti
and empirical mode#corn Safe ~~p~~ of 1987,Ann,
4, Y.I. Fe~~~~ and G.V. S~kov, Dy~ics Planet. @MMS&. 15,209 (196~. 5. D.D. Res. 86,
and E.E. Bu 981).
of auroraI belt and polar g~m~oetic
~rnp~~ models of height integra
di J* G~~~k~~~
6. R.W. Sptio* P.H. Reiff, and LJ. h&her, Jr,, Pnxipifating electron energy flux and auroraI xoae conical - an empirical model, J. G~~~~y~.Rex, 87,8215-8227 (1982). 7. D.A. Hardy, US. Gussenhoven, R. Raistrick, and W.J. McNeil, Statistical and functional nqxesentation of the pattern of auroml energy flux, number flux;,and conductivity, J. Geophys.Res. 92,12275-12294 (1987). z!
nductivity 8 (1987).
9, R.G, Rob& and EK. Ridiey, An auroraI model for the MZAR ~~~~c M), AM. G~op~~~~ 5A, #6,369-382 (1987). model IO. R& Heelis, J.K. Lowell, and R.W. Spiro, A model of the ~gb-~~ pattern, J. Gtx#y~ Res. 87,6339 (1982).