The instability of upper tropospheric shear lines

Shear lines in the upper troposphere are created when strips of cold polar air are advected into midlatitudes. The subsequent dynamical evolution has potentially significant impact on the mixing of stratospheric and tropospheric air. The instability of idealized shear lines with varying Rossby numbers are studied with a primitive equation model. The results are compared with earlier quasigeostrophic solutions. There is good agreement in the range of Rossby numbers investigated (up to 1.5).