  The influence of the magnetic field shear is studied on the $E\times B$
(and/or Gravitational) and the Current Convective Instabilities (CCI) occuring
in the High latitude F-layer ionosphere. It is shown that magnetic shear
reduces the growth rate of these instabilties. The magnetic shear induced
stabilization is more effective at the larger scale sizes ($\geq$ tens of
kilometers) while at the scintillation causing intermediate scale sizes ($\sim$
a few kms), the growth rate is largely unaffected. The eigen mode structure is
localised about a rational surface due to finite magnetic shear and has broken
reflectional symmetry due to centroid shift of the mode by equilibrium parallel
flow or current.
