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The impact on the troposphere

In Figure 4 we compare the average wind speed at 200 hPa in the first and second half of the 40-day period, for the propagating and non-propagating cases respectively. To highlight the jet stream we only plot the contours greater than 30 m/s. In the propagating case, the axis of Atlantic jet stream shifted to south by about 5 degrees of latitude, and the alignment of the axis became more zonal, in the post warming period. The Pacific jet stream did not change much except for somewhat south movement near the exit of the jet (140W-170W). On the other hand, in the non-propagating case the position of Atlantic jet stream remained almost unchanged, and the Pacific jet stream also moved somewhat to south near the exit. It seems that the Atlantic jet stream was more sensitive to the downward propagating stratospheric warm anomaly than the Pacific jet stream. The shift of the upper tropospheric jet stream over Atlantic Ocean affected tropospheric weather systems such as Atlantic storm tracks.

Figure 4. (a) Averaged wind speed at 200 hPa in the propagating case. Blue contours are Day 1- 20 average and red contours are Day 21 - 40 average. Contour interval is 10 m/s. Contours of wind speed less than 30 m/s are omitted. (b) Same as (a) except for the non-propagating case.