Fig. 5: Climatological potential vorticity gradient and zonal mean zonal wind in the mechanistic model.

Figure shows meridional cross-sections of (a) meridional gradient in PV and (b) zonal mean zonal wind. Black contours (solid for positive values, dashed for negative values) represent their climatologies in the reference model run (HS), shading represents the difference between the TIL and reference runs (HSTIL-HS). Contour interval in (a) is: 0.3 x 10⁻⁶ PVU m⁻¹, i.e., ..., −0.15, 0.15, 0.45, ...; contour interval in (b) is: 5 m s⁻¹, i.e., ..., −2.5, 2.5, 7.5, ... Black dashed and dotted lines represent the tropopause height in the TIL and reference runs, respectively. Grey contours in (a) represent the difference in buoyancy frequency (N²; in 10⁻⁴ s⁻²) between the TIL and the reference runs (HSTIL-HS), where only contours for ± 1 and ± 2.5 × 10⁻⁴ s⁻² were plotted for clarity; and in (b) grey dashed contours represent the imposed temperature anomaly (in K) in the equilibrium temperature profile. Grey diamond and star in (b) represent the latitude of the maximum 850hPa zonal mean zonal wind (i.e., the latitude of the eddy-driven jet stream) in the TIL and the reference runs, respectively.