High stratification case N= 100 and n= 3 (k= 3π/H with ⁠) for an a= 4, 10° band at 15° latitude. Symmetric case. Top panel: the eigenfunction. Note the large value at the equator. Bottom panel: linear development of the instability (note that the vertical axis has been expanded to aid visibility). The eigenvalue is σ= 0.955 ı.