Driving dayside convection with northward IMF: Observations of a sounding rocket launched from Svalbard
N. C. Maynard, W. J. Burke, R. F. Pfaff, E. J. Weber, D. M. Ober, D. R. Weimer, J. Moen, S. Milan, K. Måseide, P. -E. Sandholt, A. Egeland, F. Søraas, R. Lepping, S. Bounds, M. H. Acuña, H. Freudenreich, L. C. Gentile, D. A. Hardy, J. A. Holtet, M. Lester, J. S. Machuzak, J. H. Clemmons, P. Ning, J. Stadsnes, and T. van Eyken
Mission Research Corporation, Nashua, New Hampshire
The first sounding rocket flights into the darkened dayside cusp were launched from the new SvalRak range at Ny-Ålesund in the Svalbard archipelago in early December 1997. Extensive ground-based observations of auroral emissions and radar backscatter provided contexts for interpreting in situ measurements. Realtime measurements from the Wind satellite allowed flight time selection with foreknowledge of impending conditions. NASA rocket flight 36.153 was launched near local magnetic noon while the interplanetary magnetic field (IMF) was dominated by positive BX and had a lesser northward BZ component. The westward trajectory carried it toward auroral forms associated with the morning boundary layer. the rich set of vector dc electric and magnetic fields, energetic particles, thermal plasma, plasma waves, and optical emissions gathered by the rocket reveal a complex electrodynamic picture of the cusp/boundary-layer region. four factors were instrumental in separating temporal and spatial effects: (1) near the winter solstice the Earth's magnetic dipole was tilted away from the Sun, (2) at the UT of the flight the dipole axis was rotated toward dawn, (3) the variability of solar wind driving was low, and (4) BX was the dominant IMF component. Our analysis leads us to conclude that no signatures of dayside merging in the northern hemisphere were detected in either the rocket or the correlative ground-based measurements. Electric field variations inferred from interplanetary data directly correlate with those observed by the sounding rocket with significantly shorter lag times than predicted for simple propagation between Wind and the Earth. The entire data set suggests that convection structures in the northern hemisphere were stirred by merging of the IMF with closed field lines in the southern hemisphere. In the process, open flux was added to the northern polar cap. Subsequent motions of adiaroic polar cap boundaries were detected by the rocket instruments. The observations thus indicate the IMF BX played a significant role in driving the resulting convection, and in the timing of the interaction process.
J. Geophys. Res., Vol. 105, A3, 5245-5264, 2000.