Ionospheric plasma convection in the southern hemisphere

The first ionospheric plasma convection maps ordered by the y- and z-components of the IMF using only data from the southern hemisphere are presented. These patterns are determined from line-of-sight velocity measurements of the Polar Anglo-American Conjugate Experiment (PACE) located at Halley, Antarctica, with the majority of the observations coming from 65°–75° magnetic latitude. For IMF Bz positive and negative conditions, the observed plasma motions are consistent with a standard two cell pattern. For the periods from dusk through midnight to dawn, flow speeds are at least twice as large for Bz negative component compared with Bz positive. The observations about noon are significantly different from each other. For Bz positive, little ordered plasma motion is observed. For Bz negative, there are large anti-sunward flows the orientation of which is ordered by IMF By. These By orientated flows are consistent with theoretical predictions, and are anti-symmetric to those reported from the northern hemisphere. The two most significant differences from previous observations are that the convection reversal in the late morning sector for By negative conditions occurs at about a 4° lower latitude than the Heppner and Maynard (1987) model. This may be due to a seasonal bias in the PACE dataset. Also, the separatrix between eastward and westward flow near midnight has a very different shape dependent upon the orientation of IMF By. For positive By conditions, the separatrix is observed at progressively lower latitudes at later local times, but for By negative conditions, the separatrix appears at increasingly higher latitudes at later times.

[1]  B. Reinisch,et al.  Response of the polar cap F region convection direction to changes in the interplanetary magnetic field: Digisonde measurements in northern Greenland , 1991 .

[2]  G. Crowley,et al.  Polar cap convection for Bz northward , 1992 .

[3]  Mike Lockwood,et al.  Excitation and decay of solar-wind driven flows in the magnetosphere-ionosphere system , 1992 .

[4]  D. Rees,et al.  First measurements of thermospheric winds in Antarctica by an optical ground-based method , 1985, Nature.

[5]  A. Lui,et al.  By -dependent convection patterns during northward interplanetary magnetic field , 1984 .

[6]  S. Quegan,et al.  The role of ion drift in the formation of ionisation troughs in the mid- and high-latitude ionosphere—a review , 1992 .

[7]  J. Heppner.  Empirical models of high latitude electric fields , 1977 .

[8]  N. Maynard,et al.  Empirical high‐latitude electric field models , 1987 .

[9]  M. Brown,et al.  Dawn-dusk (y) component of the interplanetary magnetic field and the local time of the harang discontinuity , 1984 .

[10]  Y. Kamide,et al.  Interplanetary magnetic field control of high-latitude electric fields and currents determined from Greenland Magnetometer Data , 1985 .

[11]  E. Stassinopoulos,et al.  Temporal variations in the Siple Station conjugate area , 1984 .

[12]  R. Greenwald,et al.  Studies of conjugate plasma convection in the vicinity of the Harang discontinuity , 1991 .

[13]  R. Greenwald,et al.  Simultaneous conjugate observations of dynamic variations in high‐latitude dayside convection due to changes in IMF By , 1990 .

[14]  Y. Feldstein,et al.  Equivalent ionospheric currents above Antarctica during the austral summer , 1990, Antarctic Science.

[15]  H. J. Hansen,et al.  Associated ground‐based observations of optical aurorae and discrete whistler waves , 1990 .

[16]  P. Reiff,et al.  IMF By-dependent plasma flow and Birkeland currents in the dayside magnetosphere: 2. A global model for northward and southward IMF , 1985 .

[17]  Mike Lockwood,et al.  Dependence of convective flows and particle precipitation in the high‐latitude dayside ionosphere on the X and Y components of the interplanetary magnetic field , 1991 .

[18]  J. M. Ruohoniemi,et al.  Drift motions of small‐scale irregularities in the high‐latitude F region: An experimental comparison with plasma drift motions , 1987 .

[19]  T. Hill.  Solar-Wind Magnetosphere Coupling , 1983 .

[20]  R. Schunk,et al.  Theoretical study of the seasonal behavior of the global ionosphere at solar maximum , 1989 .

[21]  Charles J. Farrugia,et al.  The earth's magnetosphere under continued forcing - Substorm activity during the passage of an interplanetary magnetic cloud , 1993 .

[22]  C. Meng,et al.  Low‐altitude observations of the conjugate polar cusps , 1988 .

[23]  S. Wing,et al.  A new magnetic coordinate system for conjugate studies at high latitudes , 1989 .

[24]  C. Meng,et al.  Some low‐altitude cusp dependencies on the interplanetary magnetic field , 1989 .

[25]  J. V. Evans,et al.  Empirical models for the plasma convection at high latitudes from Millstone Hill observations , 1987 .

[26]  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 .

[27]  G. Caudal,et al.  A SAFARI-EISCAT comparison between the velocity of F region small-scale irregularities and the ion drift , 1985 .

[28]  J. Fontanari,et al.  Seasonal dependence of high‐latitude electric fields , 1991 .

[29]  R. Greenwald,et al.  An HF phased‐array radar for studying small‐scale structure in the high‐latitude ionosphere , 1985 .

[30]  Robert L. McPherron,et al.  Semiannual variation of geomagnetic activity , 1973 .

[31]  R. W. Spiro,et al.  A model of the high‐latitude ionospheric convection pattern , 1982 .

[32]  C. Meng,et al.  Dipole tilt angle effects on the latitude of the cusp and cleft/low‐latitude boundary layer , 1989 .

[33]  R. A. Greenwald,et al.  HF ray tracing at high latitudes using measured meridional electron density distributions J.P. Villain Laboratoire de Sondages Electromagntiques de l'Environnement Terrestre, Universitde Toulon , 1984 .