FIELD LINE RESONANT PULSATIONS ASSOCIATED WITH A STRONG DAYSIDE IONOSPHERIC SHEAR CONVECTION FLOW REVERSAL

We discuss a set of coordinated observations from the arrays of Greenl and ground magnetometers, Sondrestrom incoherent scatter radar, and th e DMSP, GOES 7, and IMP 8 satellites during 1000-1400 UT on August 4, 1991. The work presented here follows work presented by Clauer and Rid ley [1995]. In the previous work we show that this particular interval is characterized by a large positive interplanetary magnetic field (I MF) B-y and near-zero IMF B-z components. Associated with these condit ions is a very strong ionospheric convection shear reversal boundary i n the dayside noon and prenoon sector in the northern hemisphere. The convection reversal boundary is observed to be very dynamic, showing w ave-like displacements of several degrees in invariant latitude with a tailward phase propagation. These variations are associated with magn etic pulsations with a period of about 34 min. We have suggested that these waves are produced by a Kelvin-Helmholtz instability at the shea r convection reversal boundary. We present here a more detailed analys is of the magnetic variations from the Greenland arrays of magnetomete rs. Our new findings show that equatorward of the convection reversal boundary there is power in the pulsation spectra in bands with periods of about 34, 17, 12, and 8 min. Examination of the northward componen t of the pulsations along a meridional chain of stations ranging from 76.23 degrees to 66.86 degrees invariant latitude shows high coherence between stations and a change in relative phase of about 160 degrees over the observed latitude range for the 8-min. pulsations. These obse rvations are consistent with the expected signature of a field line re sonance. We suggest that the source of the resonance is the disturbanc e generated at the shear convection reversal boundary which then produ ces resonances on nearby equatorward closed field lines. In this case we suggest that the source is the Kelvin-Helmholtz wave established at the east-west convection shear which develops near local noon and pre noon regions during large IMF B-y positive conditions. This is possibl y the first observation of the field line resonance associated with su ch a source.