Abstract
An investigation is made of the stability of the Ekman boundary layer flow with a thermally unstable stratification based on perturbation analysis. Three different types of the instability associated with the flow may be found, preference of which depends on Reynolds number, and Richardson number. The thermal instability, which is of gravitational origin modified by the shear flow, is dominant for Ri_??_10-3, while the other two, which are of inertial origin modified by the thermal stratification, are found for Ri_??_10-3 where the Richardson number Ri is taken to be positive for unstable stratification. One of the inertial instabilities may occur for low Reynolds number ranging 55_??_Re_??_150 and the other predominates for Re_??_ 150. Stability properties of the three different types and characteristics of the associated unstable perturbations are examined in detail by means of numerical solution of the perturbation equations. It is noticed that both the types of the inertial instability are slightly influenced by thermally unstable stratification in the range of Ri_??_10-3.
