ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-31-529-2013 New plasmapause model derived from CHAMP field-aligned current signatures Heilig B. https://orcid.org/0000-0002-7964-0048 1 2 Lühr H. https://orcid.org/0000-0002-1599-6758 1 GFZ German Research Centre for Geosciences, Telegrafenberg, 1473 Potsdam, Germany Tihany Geophysical Observatory, Geological and Geophysical Institute of Hungary, Kossuth L. u. 91., 8237 Tihany, Hungary 19 03 2013 31 3 529 539 Copyright: © 2013 B. Heilig 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/31/529/2013/angeo-31-529-2013.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/31/529/2013/angeo-31-529-2013.pdf

We introduce a new model for the plasmapause location in the equatorial plane. The determination of the <I>L</I>-shell bounding the plasmasphere is based on magnetic field observations made by the CHAMP satellite in the topside ionosphere. Related signals are medium-scale field-aligned currents (MSFAC) (some 10 km scale size). The mid-latitude boundary of these MSFACs is used for determining the plasmapause. We are presenting a procedure for detecting the MSFAC boundary. Reliable <I>L</I>-values are obtained on the night side, whenever the solar zenith angle is below 90°. This means, the boundary is not determined well in the 08:00 to 16:00 magnetic local time (MLT) sector. The radial distance of the boundary is closely controlled by the magnetic activity index Kp. Over the Kp range 0 to 9, the <I>L</I>-value varies from 6 to 2 <I>R</I><sub>E</sub>. Conversely, the dependence on solar flux is insignificant. For a fixed Kp level, the obtained <I>L</I>-values of the boundary form a ring on an MLT dial plot with a centre somewhat offset from the geomagnetic pole. This Kp and local time dependent feature is used for predicting the location of the MSFAC boundary at all MLTs based on a single <I>L</I>-value determination by CHAMP. We compared the location of the MSFAC boundary during the years 2001–2002 with the <I>L</I>-value of the plasmapause, determined from in situ observations by the IMAGE spacecraft. The mean difference in radial distance is within a 1 <I>R</I><sub>E</sub> range for all local times and Kp values. The plasmapause is generally found earthward of the FAC boundary, except for the duskside. By considering this systematic displacement and by taking into account the diurnal variation and Kp-dependence of the residuals, we are able to construct an empirical model of the plasmapause location that is based on MSFAC measurements from CHAMP. Our new model PPCH-2012 agrees with IMAGE in situ observations within a standard deviation of 0.79 <I>R</I><sub>E</sub>.

 References Binsack, J.&nbsp;H.: Plasmapause observations with the M.I.T. experiment on IMP 2, J. Geophys. Res., 72, 5231–5237, 1967. Brace, L.&nbsp;H. and Theis, R. F.: The Behavior of the Plasmapause at Mid-Latitudes: Isis 1 Langmuir Probe Measurements, J. Geophys. Res., 79, 1871–1884, 1974. Brandt, P. C., Goldstein, J., Anderson, B. J., Korth, H., Immel, T. J., Roelof, E. C., DeMajistre, R., Mitchell, D. G., and Sandel, B.: On the Relation Between Electric Fields in the Inner Magnetosphere, Ring Current, Auroral Conductance, and Plasmapause Motion, in: Inner Magnetosphere Interactions: New Perspectives From Imaging, edited by: Burch, J., Schulz, M., and Spence, H., Geophysical Monograph 159, AGU, Washington D.C., 159–166, 2005. Brice, N.&nbsp;M.: Bulk Motion of the Magnetosphere, J. Geophys. Res., 72, 5193–5211, 1967. Carpenter, D. L. and Anderson, R. R.: An ISEE/Whistler model of Equatorial Electron Density in the Magnetosphere, J. Geophys. Res., 97, 1097–1108, 1992. Carpenter, D. L., Park, C. G., and Miller, T. R.: A model of substorm electric fields in the plasmasphere based on whistler data, J. Geophys. Res., 84, 6559–6563, 1979. Carpenter, D. L., Giles, B. L., Chappel, C. R., Décréau, P. M. E., Anderson, R.R., Persoon, A. M., Smith, A. J., Corcuff, Y., and Canu, P.: Plasmasphere Dynamics in the Duskside Bulge Region: a New Look at an Old Topic, J. Geophys. Res., 98, 19243–19271, 1993. Foster, J. C., Rideout, W., Sandel, B., Forrester, W. T., and Rich, F. J.: On the relationship of SAPS to storm-enhanced density. J. Atmos. Sol.-Terr. Phys., 69, 303–313, 2007. Goldstein, J., Sandel, B. R., and Reiff, P. H.: Electric fields deduced from plasmapause motion in IMAGE EUV images, Geophys. Res. Lett., 31, L01801, https://doi.org/10.1029/2003GL018386, 2004. Goldstein, J., Wolf, R. A., Burch, J., and Sandel, B.: Magnetospheric model of subauroral polarization stream, J. Geophys. Res., 110, A09222, https://doi.org/10.1029/2005JA011135, 2005. Kan, J.&nbsp;R. and Lee, L.&nbsp;C.: Energy coupling function and solar wind-magnetosphere dynamo, Geophys. Res. Lett., 6, 577–580, 1979. Kikuchi, T., Lühr, H., Kitamura, T., Saka, O., and Schlegel, K.: Direct penetration of the polar electric field to the equator during a DP 2 event as detected by the auroral and equatorial magnetometer chains and the EISCAT radar, J. Geophys, Res., 101, 17161–17173, 1996. Kippenhahn, R. and Möllenhoff, C.: Elementare Plasmaphysik, B.I. Wissenschaftsverlag, Mannheim, 1975. Larsen, B.&nbsp;A., Klumpar, D.&nbsp;M., and Gurgiolo, C.: Correlation between plasmapause position and solar wind parameters, J. Atmos. Sol.-Terr. Phys., 69, 334–340, 2007. Lemaire, J.&nbsp;F.: The formation of the light-ion-trough and peeling off the plasmasphere, J. Atmos. Sol.-Terr. Phys., 63, 1285–1291, 2001. Lühr, H., Lockwood, M., Sandholt, P. E., Hansen, T. L., and Moretto, T.: Multi-instrument ground-based observations of a travelling convection vortices event, Ann. Geophys., 14, 162–181, <a href="http://dx.doi.org/10.1007/s00585-996-0162-z">https://doi.org/10.1007/s00585-996-0162-z</a>, 1996. Matsui, H., Foster, J.&nbsp;C., Carpenter, D.&nbsp;L., Dandouras, I., Darrouzet, F., De&nbsp;Keyser, J., Gallagher, D.&nbsp;L., Goldstein, J., Puhl-Quinn, P.&nbsp;A., and Vallat, C.: Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective From CLUSTER and IMAGE, Space Sci. Rev., 145, 107–135, https://doi.org/10.1007/s11214-008-9471-8, 2009. Maus, S., Rother, M., Hemant, K., Stolle, C., Lühr, H., Kuvshinov, A., and Olsen, N.: Earth's lithospheric magnetic field determined to spherical harmonic degree 90 from CHAMP satellite measurements, Geophys. J. Int., 164, 319–330, https://doi.org/0.1111/j.1365-246X.2005.02833.x, 2006. Nishida, A.: Formation of the plasmapause, or magnetospheric plasma knee, by combined action of magnetospheric convection and plasma escape from the tail, J. Geophys. Res., 71, 5669–5679, 1966. O'Brien, T.&nbsp;P. and Moldwin, M.&nbsp;B.: Empirical plasmapause models from magnetic indices, Geophys. Res. Lett., 30, 1152, https://doi.org/10.1029/2002GL016007, 2003. Pedatella, N. M. and Larson, K. M.: Routine determination of the plasmapause based on COSMIC GPS total electron content observations of the midlatitude trough, J. Geophys. Res., 115, A09301, https://doi.org/10.1029/2010JA015265, 2010. Pierrard, V., Goldstein, J., Nicolas, A., Jordanova, V.&nbsp;K., Kotova, G.&nbsp;A., Lemaire, J.&nbsp;F., Liemohn, M.&nbsp;W., and Matsui, H.: Recent progress in physics-based models of the plasmasphere, Space Sci. Rev., 145, 193–229, 2009. Richmond, A.&nbsp;D.: Ionospheric electrodynamics using magnetic apex coordinates, J. Geomagn. Geoelectr., 47, 191–212, 1995. Ritter, P. and Lühr, H.: Curl-B technique applied to Swarm constellation for determining field-aligned currents, Earth Planets Space, 58, 463–476, 2006. Rother, M., Schlegel, K., and Lühr, H.: CHAMP observation of intense kilometer-scale field-aligned currents, evidence for an ionospheric Alfvén resonator, Ann. Geophys., 25, 1603–1615, <a href="http://dx.doi.org/10.5194/angeo-25-1603-2007">https://doi.org/10.5194/angeo-25-1603-2007</a>, 2007. Wang, H., Lühr, H., and Ma, S.&nbsp;Y.: Solar zenith angle and merging electric field control of field-aligned currents: A statistical study of the Southern Hemisphere, J. Geophys. Res., 110, A03306, https://doi.org/10.1029/2004JA010530, 2005.