Examination of the Association and Difference between the Atmospheric Rivers and Extratropical Cyclones

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, possible association and difference between the atmospheric rivers and extratropica cyclones were explored making use of the objectively identified atmospheric river and extratropical cyclone datasets. Composite maps of a set of atmospheric parameters with respect to the centroid of the atmospheric rivers and the center of the cyclones identified for 36-years (1979-2014) reveal that statistically the atmospheric rivers company the cyclones and locate within the warm conveyor belt of the cyclones, which is consistent with previous studies. However, in contrast to the composite cyclone map, which shows the single cyclone, the composite atmospheric river map shows an anticyclone at the equatorial flank of the cyclone. It is argued 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 equatorical 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.