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

middle of North America as it would during a negative phase of the AO and is instead deflected
to the east, bringing colder temperatures than usual over Newfoundland and Labrador. As with
the NAO, a positive phase of the AO tends to deflect tropical storms away from the Gulf of
Mexico over to the Atlantic Ocean increasing the potential for landfall in Atlantic Canada.
Figure 3-26. The Positive and Negative Phases of the Arctic Oscillation.
Finally, for completeness, the ENSO, whose effects on Newfoundland climate are indirect and
slight, will be discussed. ENSO itself is a coupled ocean-atmosphere oscillation in the tropical
Pacific Ocean and atmosphere. During an El Nino phase of ENSO, the atmospheric pressure
difference between the eastern and western tropical Pacific decreases and the trade winds
weaken, allowing warm western Pacific water to propagate eastward along the equator, pooling
along the coast of South America, where cold water normally sits as a result of coastal
upwelling. The La Nina phase is the opposite with particularly intensified easterly trade winds
and a cold water pool in the east. El Nino years generally see a significant decrease in the
number of tropical storms in the North Atlantic. Maps of precipitation departure from normal
prepared by Environment Canada (http://www.ec.gc.ca/adsc-cmda) indicate drier winter
conditions over Newfoundland during El Nino years. Similar maps for La Nina years indicate a
tendency for winters with slightly higher precipitation than normal.
The IPCC 2007 report (IPCC, 2007) presents an extensive review of already observed changes
in the atmospheric and oceanic circulation as well as further global warming induced anticipated
TA1112733 page 77