April 2015, "On the relationship between the North Atlantic Oscillation and early warm season temperatures in the southwestern US," Journal of Climate, American Meteorological Society
We report here that the North Atlantic Oscillation (NAO), which has been known to directly affect winter weather conditions in western Europe and the eastern United States of America, is also linked to surface air temperature over the broad southwestern United States (SWUS) region encompassing California, Nevada, Arizona, New Mexico, Utah, and Colorado in the early warm season. We have performed monthly timescale correlations and composite analyses using three different multi-decadal temperature datasets. Results from these analyses reveal that NAO-related upstream circulation positively affects not only the means, but also the extremes of the daily maximum and minimum temperatures in SWUS. This NAO effect is primarily linked with the positioning of upper-tropospheric anti-cyclones over the western US that are associated with development of the positive NAO phase, through changes in low-tropospheric wind directions as well as suppression of precipitation and enhanced short-wave radiation at the surface. The effect is observed in SWUS only during the March-June period because the monthly migration of anti-cyclones over the western US follows the migration of the NAO center over the subtropical Atlantic Ocean. The link between the SWUS temperatures and NAO has been strengthened in the last 30-year period (1980-2009) compared to the previous 30-year period (1950-1979). In contrast to the NAO-SWUS temperature relationship, the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) show only marginal correlation strengths in several limited regions for the same 60-year period.".
Can we predict the AMO?
We are not yet capable of predicting exactly when the AMO will switch, in any deterministic sense. Computer models, such as those that predict El Niño, are far from being able to do this. What is possible to do at present is to calculate the probability that a change in the AMO will occur within a given future time frame. Probabilistic projections of this kind may prove to be very useful for long-term planning in climate sensitive applications, such as water management.
Is the AMO a natural phenomenon, or is it related to global warming?
Instruments have observed AMO cycles only for the last 150 years, not long enough to conclusively answer this question. However, studies of paleoclimate proxies, such as tree rings and ice cores, have shown that oscillations similar to those observed instrumentally have been occurring for at least the last millennium. This is clearly longer than modern man has been affecting climate, so the AMO is probably a natural climate oscillation. In the 20th century, the climate swings of the AMO have alternately camouflaged and exaggerated the effects of global warming, and made attribution of global warming more difficult to ascertain."