A MODIFIED LOWER-HYBRID DRIFT INSTABILITY AS A POSSIBLE MECHANISM FORTHE GENERATION OF MAGNETIC NOISE BURSTS IN THE MAGNETOTAIL NEUTRAL SHEET

A linear local kinetic analysis of a modified lower hybrid drift (LHD) instability near the neutral plane of a current sheet with a normal c omponent of the magnetic field B(z) is carried out. It is shown that i n nearly drift-free configurations the stabilizing effects of high pla sma beta (cross-field wave-particle resonance) are significantly reduc ed in comparison with straight or current-free magnetic field geometri es. A parameter alpha(0) characterizing the degree of local deviation of the system from the drift-free configuration is introduced. The sig n of this parameter characterizes the direction of the bounce averaged electron drift and depends on the value of the local gradient of the normal component of the magnetic field. It is shown that a modified LH D mode can be excited if this parameter exceeds a critical value alpha (cr). For quiet time magnetostatic models of the magnetotail the param eter alpha0 is below but very close to the critical value. It is sugge sted that in the course of magnetospheric convection the threshold con dition for instability development could be locally satisfied which sh ould result in generation of low-frequency magnetic noise burst (f < 1 Hz) at the neutral sheet.