Moist adiabatic scaling explains mean and fast upper-level jet stream wind response to climate change

Tiffany Shaw, Osamu Miyawaki

The upper-level jet stream exhibits a robust increase in strength and shear under climate change. Previous work also noted a fast-get-faster response and connected it diagnostically to the Clausius-Clapeyron relation. Here we derive a moist adiabatic scaling that explains the upper-level jet stream wind response. Given the daily surface air temperature distribution and assuming a moist adiabatic atmosphere, the upper-level mean and fast jet stream wind increase by ∼2%/K and the jet stream shear increases by ∼4%/K across a climate model hierarchy. The scaling shows the increase of the surface moisture gradient following the Clausius-Clapeyron relation dominates the response. The scaling connects the increasing surface moisture gradient to the upper-level temperature gradient thereby reconciling dry and moist perspectives. The results show record-breaking upper-level jet stream wind and increased clear-air turbulence are tied to the Clausius-Clapeyron relation and are therefore robust and well-understood consequences of climate change.