Northern Hemisphere Sea Level Pressure Synchronization and Its Effect on Northern Hemisphere Temperature Variability

We consider monthly anomalies of zonally averaged sea level pressure (SLP) in the Northern Hemisphere (NH) from two reanalysis products. A measure of synchronization utilizing correlation coefficient in a five-year sliding window across all latitude pairs is computed over this data. It is found that there have been two NH SLP synchronization episodes since the 1890s, which are significant to approximately three standard deviations. Similar statistically significant synchronization events are seen in simulations of 42 global climate models (GCM) with the dominant synchronization pattern in GCMs proving dynamically consistent with observations. Furthermore, a GCM-based NH temperature anomaly composite shows a flattening of temperature time series in a decade prior to the synchronization episodes, a brief warming trend just after episodes, and a cooling trend thereafter, all of which agrees with the temperature structure around the observed synchronization episode seen in the 1890s. NH sea ice concentration anomalies are also composited from global climate models and show a decrease in ice concentration approximately one to two years after the maximum increase in temperature and an increase in ice concentration one to two years after the maximum decrease in temperature. These results have substantial implications for climate prediction up to a decade in advance