Midday auroral breakup events and related energy and momentum transfer from the magnetosheath

Combined observations by meridian-scanning photometers, all-sky auroral TV camera and the EISCAT radar permitted a detailed analysis of the temporal and spatial development of the midday auroral breakup phenomenon and the related ionospheric ion flow pattern within the 71°–75° invariant latitude radar field of view. The radar data revealed dominating northward and westward ion drifts, of magnitudes close to the corresponding velocities of the discrete, transient auroral forms, during the two different events reported here, characterized by IMF |BY/BZ| 2, respectively (IMF BZ between −8 and −3 nT and BY > 0). The spatial scales of the discrete optical events were ∼50 km in latitude by ∼500 km in longitude, and their lifetimes were less than 10 min. Electric potential enhancements with peak values in the 30–50 kV range are inferred along the discrete arc in the IMF |BY/BZ| 2 case. Joule heat dissipation rates in the maximum phase of the discrete structures of ∼ 100 ergs cm−2 s−1 (0.1 W m−2) are estimated from the photometer intensities and the ion drift data. These observations combined with the additional characteristics of the events, documented here and in several recent studies (i.e., their quasi-periodic nature, their motion pattern relative to the persistent cusp or cleft auroral arc, the strong relationship with the interplanetary magnetic field and the associated ion drift/E field events and ground magnetic signatures), are considered to be strong evidence in favour of a transient, intermittent reconnection process at the dayside magnetopause and associated energy and momentum transfer to the ionosphere in the polar cusp and cleft regions. The filamentary spatial structure and the spectral characteristics of the optical signature indicate associated localized ˜1-kV potential drops between the magnetopause and the ionosphere during the most intense auroral events. The duration of the events compares well with the predicted characteristic times of momentum transfer to the ionosphere associated with the flux transfer event-related current tubes. It is suggested that, after this 2–10 min interval, the sheath particles can no longer reach the ionosphere down the open flux tube, due to the subsequent super-Alfvenic flow along the magnetopause, conductivities are lower and much less momentum is extracted from the solar wind by the ionosphere. The recurrence time (3–15 min) and the local time distribution (∼0900–1500 MLT) of the dayside auroral breakup events, combined with the above information, indicate the important roles of transient magnetopause reconnection and the polar cusp and cleft regions in the transfer of momentum and energy between the solar wind and the magnetosphere.

[1]  R. Lundin Solar wind energy transfer regions inside the dayside magnetopause. II: Evidence for an MHD generator process , 1984 .

[2]  R. M. Robinson,et al.  On calculating ionospheric conductances from the flux and energy of precipitating electrons , 1987 .

[3]  M. Saunders Origin of the cusp Birkeland currents , 1989 .

[4]  Wolfgang Baumjohann,et al.  Solar Wind-Magnetosphere Coupling: Processes and Observations , 1987 .

[5]  M. Kivelson,et al.  The Magnetohydrodynamic Response of the Magnetospheric Cavity to Changes in Solar Wind Pressure , 1990 .

[6]  Charles J. Farrugia,et al.  What are flux transfer events , 1988 .

[7]  Stanley W. H. Cowley,et al.  The impact of recent observations on theoretical understanding of solar wind-magnetosphere interactions. , 1986 .

[8]  M. Freeman,et al.  Pressure-driven magnetopause motions and attendant response on the ground , 1989 .

[9]  D. Southwood Magnetopause coupling processes and ionospheric responses: a theoretical perspective , 1989, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[10]  L. Blomberg,et al.  Multisatellite and ground-based observations of transient ULF waves , 1989 .

[11]  Stanley W. H. Cowley,et al.  Initial EISCAT observations of plasma convection at invariant latitudes 70°–77° , 1984 .

[12]  A. Egeland,et al.  Auroral and magnetic variations in the polar cusp and cleft — Signatures of magnetopause boundary-layer dynamics , 1988, Astrophysics and Space Science.

[13]  M. Lockwood,et al.  Eastward propagation of a plasma convection enhancement following a southward turning of the interplanetary magnetic field , 1986 .

[14]  David J. Southwood,et al.  The ionospheric signature of flux transfer events , 1987 .

[15]  W. I. Axford Magnetic Field Reconnection , 1984 .

[16]  R. Lundin Processes in the Magnetospheric Boundary Layer , 1987 .

[17]  C. Meng,et al.  Cusp width and Bz : Observations and a conceptual model , 1987 .

[18]  Mike Lockwood,et al.  Dayside auroral activity and magnetic flux transfer from the solar wind , 1989 .

[19]  Wolfgang Baumjohann,et al.  The magnetopause for large magnetic shear: AMPTE/IRM observations , 1986 .

[20]  I. Papamastorakis,et al.  Evidence for magnetic field reconnection at the Earth's magnetopause , 1981 .

[21]  J. Burch Quasi-neutrality in the polar cusp , 1985 .

[22]  Lou‐Chuang Lee,et al.  A mechanism for the generation of cusp region hydromagnetic waves , 1988 .

[23]  Per Even Sandholt,et al.  IMF control of polar cusp and cleft auroras , 1988 .

[24]  Christopher T. Russell,et al.  ISEE observations of flux transfer events at the dayside magnetopause , 1979 .

[25]  J. Lemaire Impulsive penetration of filamentary plasma elements into the magnetospheres of the Earth and Jupiter , 1977 .

[26]  D. Luckey,et al.  Auroral electron energy derived from ratio of spectroscopic emissions 1. Model computations , 1974 .

[27]  Rickard N. Lundin,et al.  Auroral morphology of the midday oval , 1986 .

[28]  F. Mozer Electric field evidence on the viscous interaction at the magnetopause , 1984 .

[29]  Wolfgang Baumjohann,et al.  The Magnetospheric Response to 8-Minute Period Strong-Amplitude Upstream Pressure Variations , 1989 .

[30]  M. Lockwood,et al.  OBSERVATIONS AT THE MAGNETOPAUSE AND IN THE AURORAL IONOSPHERE OF MOMENTUM TRANSFER FROM THE SOLAR WIND , 1988 .

[31]  Göran Marklund,et al.  Auroral arc classification scheme based on the observed arc-associated electric field pattern , 1983 .

[32]  L. V. Medford,et al.  Possible evidence of flux transfer events in the polar ionosphere , 1986 .

[33]  M. Kuznetsova,et al.  Magnetopause stability threshold for patchy reconnection , 1986 .

[34]  David J. Southwood,et al.  Theoretical aspects of ionosphere-magnetosphere-solar wind coupling , 1985 .

[35]  Christopher T. Russell,et al.  A survey of dayside flux transfer events observed by ISEE 1 and 2 magnetometers , 1984 .

[36]  H. Rishbeth,et al.  Ionospheric response to changes in the interplanetary magnetic field observed by EISCAT and AMPTE–UKS , 1985, Nature.

[37]  A. Hasegawa,et al.  Generation of Field Aligned Current During Substorm , 1979 .

[38]  Per Even Sandholt,et al.  Signatures in the dayside aurora of plasma transfer from the magnetosheath , 1986 .

[39]  F. Mozer,et al.  Comparison of S3-3 polar cap potential drops with the interplanetary magnetic field and models of magnetopause reconnection , 1983 .

[40]  Christopher T. Russell,et al.  Flux transfer events: Scale size and interior structure , 1984 .

[41]  B.J.I. Bromage Errors in velocities determined from EISCAT data , 1984 .

[42]  C. D. Anger,et al.  Characteristics of dayside 5577Å and 3914Å aurora , 1977 .

[43]  C. Clauer,et al.  Observation of interplanetary magnetic field and of ionospheric plasma convection in the vicinity of the dayside polar cleft , 1984 .

[44]  S. Cowley The causes of convection in the Earth's magnetosphere: A review of developments during the IMS , 1982 .

[45]  M. Lockwood,et al.  The dependence of high-latitude dayside ionospheric flows on the North-South component of the IMF: a high time resolution correlation analysis using EISCAT polar and AMPTE UKS and IRM data , 1988 .

[46]  K. Glassmeier,et al.  Ground-based and satellite observations of traveling magnetospheric convection twin vortices , 1989 .

[47]  Per Even Sandholt,et al.  Electrodynamics of the polar cusp ionosphere: a case study , 1989 .

[48]  K. Schindler On the role of irregularities in plasma entry into the magnetosphere , 1979 .

[49]  Per Even Sandholt,et al.  Large‐ and small‐scale dynamics of the polar cusp , 1985 .

[50]  D. Stern The origins of Birkeland currents , 1983 .

[51]  M. Lockwood,et al.  EISCAT observations of bursts of rapid flow in the high latitude dayside ionosphere , 1986 .

[52]  T. Hill,et al.  Solar wind plasma injection at the dayside magnetospheric cusp , 1977 .

[53]  Manfred Scholer,et al.  Magnetic flux transfer at the magnetopause based on single X line bursty reconnection , 1988 .

[54]  M. Lockwood,et al.  Flow in the high latitude ionosphere: measurements at 15s resolution made using the EISCAT ‘Polar’ experiment , 1988 .

[55]  A. Egeland,et al.  Impulsive Pi bursts associated with poleward moving auroras near the polar cusp , 1988 .

[56]  J. Kan A theory of patchy and intermittent reconnections for magnetospheric flux transfer events , 1988 .

[57]  B. Lybekk,et al.  On the spatial relationship between auroral emissions and magnetic signatures of plasma convection in the midday polar cusp and cap ionospheres during negative and positive IMF Bz : A case study , 1986 .

[58]  C. Clauer,et al.  Modeled ground magnetic signatures of flux transfer events , 1987 .

[59]  K. Glassmeier,et al.  Observations of a possible ground signature of flux transfer events , 1985 .

[60]  A. Wright The evolution of an isolated reconnected flux tube , 1987 .

[61]  M. Lockwood,et al.  Response time of the high-latitude dayside ionosphere to sudden changes in the north-south component of the IMF , 1988 .

[62]  R. Nakamura,et al.  Midday Auroral Breakup , 1989 .

[63]  N. Fukushima EQUIVALENCE IN GROUND GEOMAGNETIC EFFECT OF CHAPMAN--VESTINE'S AND BIRKELAND--ALFVEN'S ELECTRIC CURRENT-SYSTEMS FOR POLAR MAGNETIC STORMS. , 1969 .

[64]  C. Clauer,et al.  Observations of ionospheric convection vortices: Signatures of momentum transfer , 1988 .

[65]  R. Lundin,et al.  IMF By dependence of region 1 Birkeland currents near noon , 1988 .

[66]  Wolfgang Baumjohann,et al.  Solar wind dynamic pressure variations and transient magnetospheric signatures , 1989 .

[67]  R. Elphic Multipoint observations of the magnetopause: Results from ISEE and AMPTE , 1988 .

[68]  M. Lockwood,et al.  The effect of rapid changes in ionospheric flow on velocity vectors deduced from radar beam-swinging experiments , 1989 .

[69]  M. Lockwood,et al.  A survey of simultaneous observations of the high-latitude ionosphere and interplanetary magnetic field with EISCAT and AMPTE-UKS , 1986 .

[70]  J. Holtet,et al.  Dayside Auroral Activity and Related Magnetic Impulses in the Polar Cusp Region , 1988 .

[71]  R. Roble,et al.  Excitation of O(1D) atoms in aurorae and emission of the [OI]6300-Å line , 1986 .

[72]  Lou‐Chuang Lee,et al.  A theory of magnetic flux transfer at the Earth's magnetopause , 1985 .

[73]  C. R. Clauer,et al.  Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind , 1988 .

[74]  E. Friis-Christensen Solar Wind Control of the Polar Cusp , 1986 .

[75]  M. Lockwood,et al.  Ionospheric ion upwelling in the wake of flux transfer events at the dayside magnetopause , 1988 .