A TRIPLE CURRENT SHEET MODEL FOR ADJOINING CORONAL HELMET STREAMERS

The highly structured magnetic field and plasma properties observed in the heliospheric extension of the coronal streamer belt have been int erpreted as evidence for multiple current sheets originating at corona l helmet streamers. We explore the linear stability of a simple case: a triple current sheet: as would exist above two neighboring helmets o f the same polarity. The behavior of the triple current sheet when per turbed by small disturbances can be described (in the incompressible l imit) by MHD Orr-Sommerfeld and Squire equations, which we solve with a Chebyshev-tau method. We show the velocity and magnetic fields which characterize the three unstable modes and describe the modal dependen ce on fieldwise wavenumber and current sheet separation, At long wavel engths an unexpected phenomenon occurs: two modes degenerate into unst able traveling modes, We also explore the three-dimensional behavior a nd the modal variation with both large and small values of the resisti vity and viscosity, We conclude that the magnetic topology in closely packed streamers is susceptible to instabilities with growth times of the order of hours. Our predictions indicate that the resultant plasmo id structures should be observable with the large angle and spectromet ric coronagraph (LASCO) and ultraviolet coronagraph spectrometer (UVCS ) instruments on the upcoming Solar and Heliospheric Observatory (SOHO ) mission.