Flood Risk and Vulnerability Analysis Project - Atlantic Climate ...

Southern Oscillation (ENSO). The AMO has already been discussed in Section 3.4.3. The
other three oscillations will be considered in order.
Figure 3-24. Schematic of the global or Meridional Overturning
Circulation (MOC). From Kuhlbrodt et al, (2007).
The NAO is presented at Figure 3-25. During a positive phase of the NAO, the atmospheric
pressure difference between the Azores high (also called the Bermuda high) and the Icelandic
low is larger than average and results in an intensified south-westerly circulation over eastern
North America which prevents Arctic air from plunging southward during winter, so that it veers
to the east instead, resulting in colder temperatures over Newfoundland and Labrador and
increased snow fall over the east coast region. In the summer, these strong westerlies tend to
steer tropical storms away from the Gulf of Mexico, to the northeast, then north and finally
northwest over the Atlantic Ocean, making them more likely to reach the Maritimes and
Newfoundland. The higher summer sea surface temperature (SST) in the northeast Atlantic -
driven by the AMO, is also associated with a positive phase of the NAO. This helps the tropical
storms to conserve greater intensity while moving to higher latitudes as explained in Section
3.4.3.
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