Arctic Response to an MJO-Like Tropical Heating in an Idealized GCM

Using an initial-value approach with an idealized general circulation model, the mechanisms by which the Madden-Julian oscillation (MJO) influences the Arctic surface air temperature (SAT) are investigated. Model calculations corresponding to MJO phases 1 and 5 are performed, as previous studies have shown that these two phases are associated with a cooling and warming of the Arctic surface, respectively. Observed MJO-like tropical heating profiles are specified, with the phase 5 (phase 1) heating taking on a more zonally localized (uniform) spatial structure. A large ensemble of model runs is performed, where the initial flow of each ensemble member consists of the winter climatology together with an initial perturbation that is selected randomly from observational data. The model calculations show that MJO phase 5 (phase 1) is followed by a strengthening (weakening) in the poleward wave activity propagation out of the tropics, which leads to an increase (decrease) in Arctic SAT. Examination of the corresponding eddy momentum flux convergence and mass streamfunction fields shows that an eddy-induced mean meridional circulation warms (cools) the Arctic for phases (phase 1). Further Arctic warming (cooling) takes place through changes in the planetary-scale, poleward eddy heat flux. In addition, calculations with a passive tracer added to the model show an increase (decrease) in the high-latitude tracer concentration for MJO phase 5 (phase 1). These results suggest that the observed changes in Arctic downward infrared radiation associated with the MJO may be associated with changes in poleward moisture transport.