Atlantic Multidecadal Oscillation


A USGS publication "Cycles of Hurricane Landfalls on the Eastern United States Linked to Changes in Atlantic Sea-surface Temperatures" [] states: "AMO variability is related to variation in density-driven, global ocean circulation patterns that involve movement of warm equatorial surface waters into high latitudes of the North Atlantic Ocean and the subsequent cooling and sinking of these surface waters into the deep ocean (thermohaline circulation). Warm phases of the AMO represent intervals of faster thermohaline circulation, which transports more warm equatorial waters to high latitudes of the North Atlantic. Cold phases of the AMO represent intervals of slower thermohaline circulation and thus less transport of warm equatorial waters to high latitudes of the North Atlantic."

effect on arctic ocean temperature

A study published in 2009 (Levitus et al: "Barents Sea multidecadal variability", Geophysical Research Letters, Vol.36, 2009) provides the following figure showing "Monthly temperature (C) in the Barents Sea for the 100-150 m layer, from 1900 to 2006. Years without all 12 months of data are not plotted. The red line is the Atlantic Multidecadal Oscillation Index" []. This shows a strong correspondence between Arctic - Barents Sea - sea temperatures and the AMO.


Research Links Long Droughts In U.S. To Ocean Temperature Variations (United States Geological Survey (2004, March 10).) []: "researchers believe that such large and sustained shifts in U.S. precipitation are linked with the natural variability of sea surface temperatures, the mechanisms are not well understood and cannot yet be used to help predict the likelihood of droughts. These sea surface temperature variations are characterized by climatic indices dubbed the Pacific Decadal Oscillation, or PDO, and the Atlantic Multidecadal Oscillation, or AMO. ... Both negative and positive PDO "events" in the North Pacific Ocean tend to last 20-30 years, with recent research increasingly associating these events with regional temperature and precipitation variability across the country. ... The researchers were able to correlate two of the three leading modes of drought frequency with PDO and AMO variations. ... McCabe and his coauthors suggest that large-scale droughts in the United States are likely to be associated with positive AMO -- the kind of warming of sea surface temperatures that occurred over the North Atlantic in the 1930s, 50s, and since 1995."


Cycles of Hurricane Landfalls on the Eastern United States Linked to Changes in Atlantic Sea-surface Temperatures (USGS) []: "Historical observations suggest that the very active hurricane seasons of 2004 and 2005 may be part of a natural cycle in Earth's climate system that is related to changes in mean sea-surface temperature (SST) in the North Atlantic Ocean." The following figure compares landfalling major hurricanes for the negative and positive phases of the AMO.

Summary of 2008 Atlantic Tropical Cyclone Activity and Verification of Author's Seasonal and Monthly Forecasts (Philip J. Klotzbach and William M. Gray, Department of Atmospheric Science Colorado State University, Nov. 2008) []: "The global warming arguments have been given much attention by many media references to recent papers claiming to show such a linkage. Despite the global warming of the sea surface that has taken place over the last 3 decades, the global numbers of hurricanes and their intensity have not shown increases in recent years except for the Atlantic. The Atlantic has seen a very large increase in major hurricanes during the 14-year period of 1995-2008 (average 3.9 per year) in comparison to the prior 25-year period of 1970-1994 (average 1.5 per year). This large increase in Atlantic major hurricanes is primarily a result of the multi-decadal increase in the Atlantic Ocean thermohaline circulation (THC) that is not directly related to global sea surface temperatures or CO2 gas increases. Changes in ocean salinity are believed to be the driving mechanism. These multi-decadal changes have also been termed the Atlantic Multidecadal Oscillation (AMO)."