Relationship Between the Madden-Julian Oscillation and High-Latitude Surface Air Temperature During Boreal Winter
The relationship between the Madden-Julian oscillation (MJO) and the high-latitude wintertime surface air temperature (SAT) is examined based on NCEP-NCAR reanalysis daily data during 1979-2016. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, where Phase 2 (Phase 6) corresponds to the enhanced (reduced) convection over the Indian Ocean and Maritime Continent, is used. A significant positive SAT anomaly over northern high-latitude region of (60°-90°N, 180°-60°W) is found 5-15 days following MJO Phase 2, while a negative SAT anomaly appears over the same region about 5-15 days after the MJO is detected in Phase 6, as the tropical forcing changes sign. An analysis of the lagging composite of the geopotential height at 500 hPa indicates that the Arctic SAT anomaly is a result of a north-eastward propagating Rossby wave train associated with the tropical convection anomaly of the MJO, which may have great impacts on intraseasonal SAT variability over high latitude. An analysis of the wave activity flux indicates that the north-eastward propagating Rossby wave train is likely a result of Rossby energy propagation. Composite maps of the specific humidity at 700 hPa also show close relationship with the SAT signals in high latitudes, due to the positive relationship between mid-troposphere specific humidity and downward longwave radiation. These analyses suggest that large-scale circulation anomalies associated with the MJO convection may have great impacts on high-latitude SAT signals, which can result from both advective and radiative processes. Hence, the MJO phases provide useful information for the extended-range forecast of high-latitude surface air temperature during boreal winter.