The Response of Synoptic-Scale Weather to Jet Stream Characteristics: a Lagrangian perspective.

The position and intensity of storm tracks undergo significant changes in response to temporal and spatial variations in atmospheric forcing. Comprehending these changes from the viewpoint of individual cyclones and anticyclones is crucial both from a physical perspective, as they are the main drivers of energy and moisture, and because they are a leading cause of severe weather in the midlatitudes. This study delves into the impact of the jet characteristics on individual cyclones and anticyclones, focusing on their maximum strength and growth time. By utilizing tracks of cyclones and anticyclones spanning over 80 years of ERA5 reanalysis data, we identify unique temporal and spatial variations in maximum strength and growth time. These variations are then clarified through a detailed examination of how these properties respond to the characteristics of the jet. 

 

The study reveals that the vertical shear of the jet increases the maximum strength at low and medium regimes and decreases it for intense shear values, potentially playing a significant role in phenomena characterized by extreme shear, such as the midwinter minimum. Breaking down the storm maximum strength into the responses due to growth time and Lagrangian growth rate (effective average growth rate of the individual storms) indicates that while the Lagrangian growth rate is linear with vertical shear, as expected by linear theory, the saturation of maximum strength results from a decrease in growth time with vertical shear. The horizontal shear of the jet, which is less widely studied, was found to reduce the growth time of cyclones and anticyclones significantly. Additionally, horizontal shear has a smaller effect on the Lagrangian growth rate, with cyclones on the poleward side of the jet growing faster and anticyclones on the equatorward side growing faster. These findings provide insights into predicting how changes in jet characteristics in past and future climates influence midlatitude weather through the effect on cyclone and anticyclone activity.