Statistical Relationship between Atmospheric Rivers and Extratropical Cyclones

In this study, some general relationships between atmospheric rivers (ARs) and extratropical cyclones (ECs) have been revealed for the first time based on analysis of 36-year global AR and EC datasets. Composites of atmospheric variables around mid-latitude ARs show that a strong cyclone is located poleward and westward of the AR centroid, which confirms the close link between the AR and EC. In addition to the cyclone, a pronounced anticyclone is located equatorward and eastward of the AR, which has not been emphasized before. This anticyclone is an essential component in the AR-EC system, whose presence leads to stronger horizontal pressure gradient that forces moisture to be transported along a narrow corridor within the warm sector of the cyclone. It is further found that the strength of ARs is better correlated with the pressure gradient between the cyclone and anticyclone than with the cyclone intensity.