Oceanic Oscillations and Correlation to Climatic Phenomena

[last update: 2008/12/31]

This document describes the Pacific and Atlantic Ocean oscillations that have been identified and correlated to climatic event – temperature, drought, hurricanes, etc. The document contains the following sections:

• Pacific Decadal Oscillation (PDO)
• Atlantic Multi-decadal Oscillation (AMO)
• North Atlantic Oscillation (NAO)

It is only in recent years that scientists are starting to recognize the influence of oceanic cycles in influencing climate. For example, a recent study – “Oceanic Influences on Recent Continental Warming”, by Compo, G.P., and P.D. Sardeshmukh, (Climate Diagnostics Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, and Physical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration), Climate Dynamics, 2008)

[http://www.cdc.noaa.gov/people/gilbert.p.compo/CompoSardeshmukh2007a.pdf] states: “Evidence is presented that the recent worldwide land warming has occurred largely in response to a worldwide warming of the oceans rather than as a direct response to increasing greenhouse gases (GHGs) over land. Atmospheric model simulations of the last half-century with prescribed observed ocean temperature changes, but without prescribed GHG changes, account for most of the land warming. … Several recent studies suggest that the observed SST variability may be misrepresented in the coupled models used in preparing the IPCC's Fourth Assessment Report, with substantial errors on interannual and decadal scales. There is a hint of an underestimation of simulated decadal SST variability even in the published IPCC Report.”

Joseph D’Aleo has conducted a correlation analysis between the PDO, AMO and temperatures [http://icecap.us/images/uploads/US_Temperatures_and_Climate_Factors_since_1895.pdf] and [http://intellicast.com/Community/Content.aspx?a=127]. The following figures are from D’Aleo’s analysis.

The following figure shows the 5-year means of PDO, AMO and PDO + AMO.

The next figure shows the US temperature anomalies as calculated by NASA’s James Hansen (2001). The periods when the temperature anomalies are positive correspond almost exactly to when the PDO+AMO changes between warm and cool phases.

The following figure compares the PDO+AMO with the US average annual temperatures. D’Aleo calculated an r-squared of 0.85 between the two – an extremely good correlation.

The next figure compares the same temperature data with atmospheric CO2. D’Aleo calculated an r-squared of 0.44 between the two – a fair correlation, but poor in comparison to the PDO+AMO correlation. Although correlation does not prove causation, lower correlation proves less.

The Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) was defined by fisheries scientist Steven Hare in the mid-1990’s, based on observations of Pacific fisheries cycles. The PDO index is calculated from sea surface temperatures and sea level pressures. An overview of the PDO is given by Nathan Mantua (Joint Institute for the Study of the Atmosphere and Oceans, University of Washington) [http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm]. The PDO goes through warm and cool phases of the cycle with phases typically lasting about 30 years. The causes of the oscillation are currently unknown. A good source of information on the PDO is http://jisao.washington.edu/pdo/. The following figure is from that web site and shows the monthly PDO index from 1900 to September 2008.

PDO Index 1900 – September 2008

The recent phases of the PDO can be seen in the above figure, with a cool phase starting around 1945 and switching to a warm phase in 1977. It appears that 2008 may be the start of the next cool phase. According to the above-mentioned PDO web site: “Major changes in northeast Pacific marine ecosystems have been correlated with phase changes in the PDO; warm eras have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras have seen the opposite north-south pattern of marine ecosystem productivity.”

The following figure is from the NASA Earth Observatory, April 2008. It shows the sea surface temperature anomaly in the Pacific Ocean from April 14–21, 2008 as measured by satellite. The anomaly compares the recent temperatures with an average from 1985–1997. Places where the Pacific was cooler than normal are blue, places where temperatures were average are white, and places where the ocean was warmer than normal are red. [http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=18012 ]. The NASA article states: “while the La Niña was weakening, the Pacific Decadal Oscillation—a larger-scale, slower-cycling ocean pattern—had shifted to its cool phase. … The shift in the PDO can have significant implications for global climate, affecting Pacific and Atlantic hurricane activity, droughts and flooding around the Pacific basin, the productivity of marine ecosystems, and global land temperature patterns.”

Sea Surface Temperature Anomaly April 14-21, 2008 Compared to 1985 – 1997 Average

Hare and Mantua (“Empirical evidence for North Pacific regime shifts in 1977 and 1989”, Progress in Oceanography, 2000) [http://www.iphc.washington.edu/Staff/hare/html/papers/ei/ei.pdf] state: “It is now widely accepted that a climatic regime shift transpired in the North Pacific Ocean in the winter of 1976–77. This regime shift has had far reaching consequences for the large marine ecosystems of the North Pacific. Despite the strength and scope of the changes initiated by the shift, it was 10–15 years before it was fully recognized. Subsequent research has suggested that this event was not unique in the historical record but merely the latest in a succession of climatic regime shifts.”

Addressing the Washington Policymakers in Seattle, WA, Dr. Don Easterbrook (Dept. of Geology, Western Washington University) said that “shifting of the Pacific Decadal Oscillation (PDO) from its warm mode to its cool mode virtually assures global cooling for the next 25-30 years and means that the global warming of the past 30 years is over.” [http://icecap.us/images/uploads/WashingtonPolicymakersaddress.pdf] 

The following table summarizes North American climate anomalies associated with PDO (from [http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm]).

Pacific and North American climate anomalies associated with extreme phases of the PDO
Climate Anomalies	Warm Phase PDO	Cool Phase PDO
Ocean surface temperatures in the northeastern and tropical Pacific	Above average	Below average
October-March northwestern North American air temperatures	Above average	Below average
October-March Southeastern US air temperatures	Below average	Above average
October-March southern US/Northern Mexico precipitation	Above average	Below average
October-March Northwestern North America and Great Lakes precipitation	Below average	Above average
Northwestern North American spring time snow pack and water year (October-September) stream flow	Below average	Above average
Winter and spring time flood risk in the Pacific Northwest	Below average	Above average

Another good source of information on the PDO is: http://www.intellicast.com/Community/Content.aspx?a=126.

Many studies have shown that the major climatic events in the US are linked to cycles in ocean temperatures. Here are some PDO examples:

NASA Explains 'Dust Bowl' Drought (NASA/Goddard Space Flight Center (2004, March 19).) [http://www.sciencedaily.com/releases/2004/03/040319072053.htm]: “cooler than normal tropical Pacific Ocean temperatures and warmer than normal tropical Atlantic Ocean temperatures contributed to a weakened low-level jet stream and changed its course. The jet stream, a ribbon of fast moving air near the Earth's surface, normally flows westward over the Gulf of Mexico and then turns northward pulling up moisture and dumping rain onto the Great Plains. As the low level jet stream weakened, it traveled farther south than normal. The Great Plains dried up and dust storms formed. Analysis of other major U.S. droughts of the 1900s suggests a cool tropical Pacific was a common factor.”

Temperature of Pacific Ocean Influences Midwest Rains (University Of Illinois At Urbana-Champaign (1997, September 11).) [http://www.sciencedaily.com/releases/1997/09/970911034536.htm]: “The flood of 1993 and the drought of 1988 raised serious questions about the causes of summertime climatic fluctuations over the central United States … sea-surface temperatures in the Pacific Ocean affect both the position and the intensity of the jet stream over the central United States, which in turn modifies the circulation pattern from the gulf. "Warmer sea-surface temperatures shift the jet stream farther south, leading to more storm activity, which pumps more moisture up from the gulf," Ting said. "In contrast, cooler sea-surface temperatures shift the jet stream farther north, resulting in reduced storm activity and drier conditions.” 

The Significance of the 1976 Pacific Climate Shift in the Climatology of Alaska (Geophysical Institute, University of Alaska, 2004) [http://climate.gi.alaska.edu/ResearchProjects/pages/AKpaper10.html]: “In 1976, the North Pacific region, including Alaska, underwent a dramatic shift to a climate regime that saw great increases in winter and spring temperatures … The shift in the climate regime now  is known to have coincided with a shift in the phase of the Pacific Decadal Oscillation (PDO). …all of the regions in sub- Arctic Alaska have experienced a net cooling since 1977.”

Don Easterbrook (Geologist at Western Washington University) published the following figure showing the correspondence between PDO and glaciers on Mount Baker, Washington [http://www.ac.wwu.edu/~dbunny/research/global/215.pdf]

Tropical Pacific Decadal Variability and Global Warming (Amy J. Bratcher & Benjamin S. Giese, Department of Oceanography, Texas A&M University, Geophysical Research Letters, 29(19), 2002) [http://www.agu.org/pubs/crossref/2002/2002GL015191.shtml]: “An analysis of ocean surface temperature records show that low frequency changes of tropical Pacific temperature lead global surface air temperature changes by about 4 years. Anomalies of tropical Pacific surface temperature are in turn preceded by subsurface temperature anomalies in the southern tropical Pacific by approximately 7 years. The results suggest that much of the decade to decade variations in global air temperature may be attributed to tropical Pacific decadal variability. The results also suggest that subsurface temperature anomalies in the southern tropical Pacific can be used as a predictor for decadal variations of global surface air temperature. Since the southern tropical Pacific temperature shows a distinct cooling over the last 8 years, the possibility exists that the warming trend in global surface air temperature observed since the late 1970's may soon weaken.”

The following figure shows the annual mean temperature anomalies for the two 5x5 degree grids covering the Pacific Northwest coast of the U.S. -- western Oregon and Washington from 1900 to 2007. This data is from the Hadley Climatic Research Unit (HadCRU) as used by the IPCC.

The following figure shows the average of the two grids shown above. The next figure superimposes the two-grid average annual temperature anomaly (changed to green) on the Pacific Decadal Oscillation (PDO). A strong correlation exists between the PNW coastal temperatures and the PDO.

The Atlantic Multi-Decadal Oscillation (AMO)

The Atlantic Multi-Decadal Oscillation (AMO) is a fluctuation in de-trended sea surface temperatures in the North Atlantic Ocean. It was identified in 2000 and the AMO index was defined in 2001 as the 10-year running mean of the detrended Atlantic SST anomalies north of the equator. There is a significant negative correlation with US continental rainfall with less rain during a positive AMO index. (H.A. Dijkstra, “On the physics of the Atlantic Multidecadal Oscillation”, Institue for Marine and Atmospheric Research, Netherlands, 2005)  [http://www.knmi.nl/publications/fulltexts/drsg2006.pdf]

A USGS publication “Cycles of Hurricane Landfalls on the Eastern United States Linked to Changes in Atlantic Sea-surface Temperatures” [http://pubs.usgs.gov/circ/1306/pdf/c1306_ch2_a.pdf] 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.”

The following figure is from the NOAA AMO web site [http://www.aoml.noaa.gov/phod/amo_flarain.php]. The upper figure shows the AMO index since 1860, while the lower figure shows the smoothed anomaly of central Florida rainfall (shaded curve) and the amount of water flowing into Florida Lake Okeechobee. This shows the correlation between the AMO and the rainfall in Florida.

The AMO has a cycle length of approximately 70 years (i.e. a warm phase plus a cold phase). The following figure shows the annual AMO from 1958 to 2006 [http://intellicast.com/Community/Content.aspx?a=127] (See this link for more description of the AMO as well as the North Atlantic Oscillation and Arctic Oscillation).

The AMO affects regional temperatures in the Arctic area of the northern Atlantic. The following figure shows the temperature anomalies for the only 2 long-term stations in Iceland (from the NOAA GHCN database). Temperatures are recently approaching those observed in the 1930’s. The next figure compares the Iceland temperatures with the AMO shown previously. There is a strong correlation between the two.

The following figure shows the temperature anomalies for the available long-term or recent stations in Greenland (from the NOAA GHCN database). Temperatures are recently matching those observed in the 1930’s. The next figure shows the average temperature anomalies from those same stations, while the following figure compares the average anomalies with the AMO shown previously. Again, there is a strong correlation between the two.

The following figure shows occurrence of major hurricanes in the Atlantic. The next figure superimposes the hurricane data on the AMO plot shown previously.

The following figure is from a study reported in 2008 using oxygen isotopes in Caribbean coral (“Caribbean Coral Tracks Atlantic Multidecadal Oscillation and Past Hurricane Activity”, Hetzinger et al, Geology 2008)

[http://www.ifm-geomar.de/fileadmin/personal/fb1/me/nkeenlyside/paper/Hetzinger_etal_2008Geology.pdf]. The figure shows (A) a comparison between coral δ18O and the index of accumulated cyclone energy (ACE) for the North Atlantic averaged using a 5 yr running filter; and (B) a comparison between coral δ18O and the AMO index (North Atlantic SST averaged between 0 and 70°N) using an 11 yr running filter.

Many studies have shown that the major climatic events in the US are linked to cycles in ocean temperatures. Here are some AMO examples:

Cycles of Hurricane Landfalls on the Eastern United States Linked to Changes in Atlantic Sea-surface Temperatures (USGS) [http://pubs.usgs.gov/circ/1306/pdf/c1306_ch2_a.pdf]: “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) [http://tropical.atmos.colostate.edu/Forecasts/2008/nov2008/nov2008.pdf]: “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).”

Research Links Long Droughts In U.S. To Ocean Temperature Variations (United States Geological Survey (2004, March 10).) [http://www.sciencedaily.com/releases/2004/03/040310080316.htm]: “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.”

The AMO also influences rainfall in India and the African Sahel. The following figure is from a study Impact of Atlantic Multidecadal Oscillations on India/Sahel Rainfall and Atlantic Hurricanes (Zhang and Delwoth, Geophysical Research Letters, Vol. 33, 2006) [http://www.gfdl.noaa.gov/reference/bibliography/2006/roz0603.pdf] showing the correspondence between the AMO (a) and the Sahel rainfall (b), India rainfall (c) and hurricanes (e).

The following figure shows the combined effect of PDO and AMO on drought in the United States [http://oceanworld.tamu.edu/resources/oceanography-book/oceananddrought.html]. Further information on these drought relationships can be found at [http://www.pnas.org/content/101/12/4136.full] 

The North Atlantic Oscillation (NAO)

The North Atlantic Oscillation (NAO) is a major mode of atmospheric variability in the Northern Hemisphere, particularly in winter. The NAO index is calculated based on the difference between the normalized sea level pressures over Gibraltar (or Portugal, or the Azores) (subtropical high) and Southwest Iceland (polar low).

The following figure shows the winter NAO since 1823 based on Gibraltar. [http://www.cru.uea.ac.uk/~timo/projpages/nao_update.htm]

The following figure shows the winter NAO since 1864 based on Lisbon, Portugal and Reykjavik, Iceland. [http://www.cgd.ucar.edu/cas/jhurrell/Docs/naobook.ch1.pdf]

Updated NAO data can be found at http://ioc3.unesco.org/oopc/state_of_the_ocean/atm/nao.php

The different phases of the NAO result in different winter conditions over the North Atlantic, with the following general trends [http://www.ldeo.columbia.edu/res/pi/NAO/]:

Positive NAO Index	Negative NAO Index
More and stronger winter storms crossing the Atlantic Ocean on a more northerly track	Fewer and weaker winter storms crossing on a more west-east pathway
Warm and wet winters in Europe	Moist air into the Mediterranean and cold air to northern Europe
Cold and dry winters in northern Canada and Greenland	Milder winter temperatures in Greenland
US east coast experiences mild and wet winter conditions	US east coast experiences more cold air outbreaks and hence snowy weather conditions

The following figures show the general patterns of the NAO positive and negative modes (from NOAA Airmap [http://airmap.unh.edu/background/nao.html], which provides a comprehensive explanation of NAO effects on the eastern US).

A study of the NAO climate effects on barn swallow breeding (“North Atlantic Oscillation (NAO) effects of climate on the relative importance of first and second clutches in a migratory passerine bird”) http://www3.interscience.wiley.com/journal/118942055/abstract?CRETRY=1&SRETRY=0  “The size of first clutches increased with increasing NAO values, and clutch size increased during the study period. [1970-2000] … in years with high NAO index values first broods were relatively larger than second broods compared to years with low NAO values. Similarly, the breeding success of first relative to second broods was larger in years with high NAO index values compared to years with low NAO values”

An article in Science Daily (“North Atlantic Warming Tied To Natural Variability”, Jan 2008 [http://www.sciencedaily.com/releases/2008/01/080103144416.htm]) reported on a Duke University study of North Atlantic temperatures and their relation to the NAO. “while the North Atlantic Ocean's surface waters warmed in the 50 years between 1950 and 2000, the change was not uniform. In fact, the subpolar regions cooled at the same time that subtropical and tropical waters warmed. "It is premature to conclusively attribute these regional patterns of heat gain to greenhouse warming," … water in the sub-polar ocean --- roughly between 45 degrees North latitude and the Arctic Circle --- became cooler as the water directly exchanged heat with the air above it. …NOA[sic] -driven winds served to "pile up" sun-warmed waters in parts of the subtropical and tropical North Atlantic south of 45 degrees” … "We suggest that the large-scale, decadal changes...associated with the NAO are primarily responsible for the ocean heat content changes in the North Atlantic over the past 50 years," the authors concluded.”

Studies have found correlations between NAO and Indian monsoon. The study “Interannual and long-term variability in the North Atlantic Oscillation and Indian summer monsoon rainfall” (Dugam, Kakade and Verma, Indian Institue of Tropical Meteorology, 1997 [http://cat.inist.fr/?aModele=afficheN&cpsidt=2068184]) investigated 108 years of NAO / monsoon data and found that: “The decadal scale analysis reveals that the NAO during winter (December-January-February) and spring (March-April-May) has a statistically significant inverse relationship with the summer monsoon rainfall of Northwest India, Peninsular India and the whole of India. The highest correlation is observed with the winter NAO. The NAO and Northwest India rainfall relationship is stronger than that for the Peninsular and whole of India rainfall on climatological and sub-climatological scales.”

A study of the multi-decadal low frequency oscillation (LFO) of the NAO [http://denali.frontier.iarc.uaf.edu:8080/~igor/research/pdf/50yr_web.pdf] stated: “observations over the past 135 years showed that the recent decrease in ice extent in the Nordic Seas is within the range of natural variability since the 18th century. A combination of century- and half-a-century-long data records and model integrations leads us to conclude that the natural low-frequency oscillation (LFO) exists and is an important contributor to the recent anomalous environmental conditions in the Arctic. There is evidence that the LFO has a strong impact on ice and ocean variability”.

More information on the NAO can be found at: www.climate4you.com/NAOandAO.htm