What they say about the polar vortex and weather

Jennifer Francis wrote:Figure 4 presents measures of wave phase speed. While FV12 did not present wave speeds, we speculated that larger amplitude waves should have slower wave speeds. Her measure of phase speed for waves at 500 hPa slows with time, supporting our speculation. She then measures speeds at the 250 hPa level and finds no change in speed. This much higher level is near the tropopause, often above the jet stream, and can be affected by dynamics of the stratosphere. The stratosphere is cooling with increasing greenhouse gases, leading to very different dynamical changes. Why did she choose to analyze this level? My only guess is to deliberately cast doubt on FV12.

This winter the UK has been affected very severely by an exceptional run of winter storms, culminating in serious coastal damage and widespread, persistent flooding.

This period of weather has been part of major perturbations to the Pacific and North Atlantic jet streams driven, in part, by persistent rainfall over Indonesia and the tropical West Pacific.

The North Atlantic jet stream has also been unusually strong; this can be linked to exceptional wind patterns in the stratosphere with a very intense polar vortex.

This paper documents the record-breaking weather and flooding, considers the potential drivers and discusses whether climate change contributed to the severity of the weather and its impacts.