Roles of Wet and Dry Components of Moist Isentropic Mass Circulation in
Changing the Extratropical Surface Temperature in the Northern
This study separates the dry and wet components of the moist isentropic
mass circulation (MIMC) on daily timescale and investigates their
relationships with extratropical surface temperature changes in winter.
Results derived from ERA5 reanalysis data (1979-2018) show that, the
MIMC is composed of a poleward warm branch (WB) in upper layers, which
is dominated by the wet component in mid-latitude troposphere but by the
dry component to the rest, and an equatorward cold branch below,
dominated by the dry component. The stronger wet component of WB in
50-70N (WB_W) is a better precursory indicator than the dry component
(WB_D) for the Arctic surface warming in winter, because of its
dominant role in modifying the downward longwave radiation via water
vapor-related processes. The stronger WB_D is coupled with negative
Arctic Oscillation and a stronger equatorward transport of colder air,
thus a better precursor for the cold events in the mid-latitudes.