Statistical Relationship between the Atmospheric River and Extratropical Cyclone

An atmospheric river is a narrow corridor or filament of concentrated moisture in the atmosphere. Previous studies have suggested close relationship between the atmospheric river and the warm conveyor belt of an extratropical cyclone. In this study, the relation between the atmospheric rivers and extratropical cyclones were explored statistically using datasets of the objectively identified atmospheric river and extratropical cyclone for 36 years (1979-2014). A composite map of sea level pressure with respect to the centroid of the atmospheric rivers and the center of the cyclones reveals that the atmospheric rivers are companied by cyclones and located within the warm conveyor belt of the cyclones, which is consistent with previous studies. Thecomposite map also shows an anticyclone at the equatorial flank of the cyclone, in contrast to the composite map with respect to the center of the cyclones only, in which the anticyclone is not evident. This suggests that the presence of the cyclone alone is not the sufficient condition for the occurrence of the atmospheric river. The accompanied anticyclonic circulation at the equatorial side of the cyclone that generates strong pressure gradient and narrow band of enhanced water vapor transport is a key factor for the occurrence of the atmospheric river. Other statistical relations between the atmospheric rivers and extratropical cyclones will also be discussed.