AGW Observer

Observations of anthropogenic global warming

Papers on Atlantic Multidecadal Oscillation and climate

Posted by Ari Jokimäki on December 16, 2010

This is a list of papers on Atlantic Multidecadal Oscillation and its effects to the climate. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

100-year mass changes in the Swiss Alps linked to the Atlantic Multidecadal Oscillation – Huss et al. (2010) “Thirty new 100-year records of glacier surface mass balance, accumulation and melt in the Swiss Alps are presented. The time series are based on a comprehensive set of field data and distributed modeling and provide insights into the glacier-climate linkage. Considerable mass loss over the 20th century is evident for all glaciers, but rates differ strongly. Glacier mass loss shows multidecadal variations and was particularly rapid in the 1940s and since the 1980s. Mass balance is significantly anticorrelated to the Atlantic Multidecadal Oscillation (AMO) index assumed to be linked to thermohaline ocean circulation. We show that North Atlantic variability had a recognizable impact on glacier changes in the Swiss Alps for at least 250 years.” Huss, M., R. Hock, A. Bauder, and M. Funk (2010), 100-year mass changes in the Swiss Alps linked to the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., 37, L10501, doi:10.1029/2010GL042616. [Full text]

Evidence of multidecadal climate variability and the Atlantic Multidecadal Oscillation from a Gulf of Mexico sea-surface temperature-proxy record – Poore et al. (2009) “A comparison of a Mg/Ca-based sea-surface temperature (SST)-anomaly record from the northern Gulf of Mexico, a calculated index of variability in observed North Atlantic SST known as the Atlantic Multidecadal Oscillation (AMO), and a tree-ring reconstruction of the AMO contain similar patterns of variation over the last 110 years. Thus, the multidecadal variability observed in the instrumental record is present in the tree-ring and Mg/Ca proxy data. Frequency analysis of the Gulf of Mexico SST record and the tree-ring AMO reconstruction from 1550 to 1990 found similar multidecadal-scale periodicities (~30–60 years). This multidecadal periodicity is about half the observed (60–80 years) variability identified in the AMO for the 20th century. The historical records of hurricane landfalls reveal increased landfalls in the Gulf Coast region during time intervals when the AMO index is positive (warmer SST), and decreased landfalls when the AMO index is negative (cooler SST). Thus, we conclude that alternating intervals of high and low hurricane landfall occurrences may continue on multidecadal timescales along the northern Gulf Coast. However, given the short length of the instrumental record, the actual frequency and stability of the AMO are uncertain, and additional AMO proxy records are needed to establish the character of multidecadal-scale SST variability in the North Atlantic.” Richard Z. Poore, Kristine L. DeLong, Julie N. Richey and Terrence M. Quinn, Geo-Marine Letters, Volume 29, Number 6, 477-484, DOI: 10.1007/s00367-009-0154-6.

Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation – Chylek et al. (2009) “Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910–1940 and 1970–2008) by a significant 1940–1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale, (b) the Arctic warming from 1910–1940 proceeded at a significantly faster rate than the current 1970–2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi-decadal time scale.” Chylek, P., C. K. Folland, G. Lesins, M. K. Dubey, and M. Wang (2009), Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., 36, L14801, doi:10.1029/2009GL038777. [Full text]

Atlantic Warm Pool acting as a link between Atlantic Multidecadal Oscillation and Atlantic tropical cyclone activity – Wang et al. (2008) “Multidecadal variability of Atlantic tropical cyclone activity is observed to relate to the Atlantic Multidecadal Oscillation (AMO), a mode manifesting primarily in sea surface temperature (SST) in the high latitudes of the North Atlantic. In the low latitudes of the North Atlantic, a large body of warm water called the Atlantic Warm Pool (AWP) comprises the Gulf of Mexico, the Caribbean Sea, and the western tropical North Atlantic. AWP variability occurs on both interannual and multidecadal timescales as well as with a secular variation. The AWP multidecadal variability coincides with the signal of the AMO; that is, the warm (cool) phases of the AMO are characterized by repeated large (small) AWPs. Since the climate response to the North Atlantic SST anomalies is primarily forced at the low latitudes and the AWP is in the path of or a birthplace for Atlantic tropical cyclones, the influence of the AMO on Atlantic tropical cyclone activity may operate through the mechanism of the AWP-induced atmospheric changes. The AWP-induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability. More specifically, an anomalously large (small) AWP reduces (enhances) the vertical wind shear in the hurricane main development region and increases (decreases) the moist static instability of the troposphere, both of which favor (disfavor) Atlantic tropical cyclone activity. This is the most plausible way in which the AMO relationship with Atlantic tropical cyclones can be understood.” Wang, C., S.-K. Lee, and D. B. Enfield (2008), Atlantic Warm Pool acting as a link between Atlantic Multidecadal Oscillation and Atlantic tropical cyclone activity, Geochem. Geophys. Geosyst., 9, Q05V03, doi:10.1029/2007GC001809. [Full text]

The Atlantic multidecadal oscillation and extreme daily precipitation over the US and Mexico during the hurricane season – Curtis (2008) “The tail of the distribution of daily precipitation for August–September–October was examined over the United States and Mexico in relation to the Atlantic Multidecadal Oscillation (AMO). As expected from previous studies linking the AMO to hurricane activity, Florida and the coastal Southeast US showed an increase in precipitation intensity when the Atlantic was in a warm phase (AMO+). Also during AMO+ Northwest Mexico was dry and exhibited a reduction of extreme events and the Mid-Atlantic Appalachian Mountains showed evidence of an increase in heavy precipitation compared to when the Atlantic was cool. It is proposed that the aforementioned decadal variations in extreme rainfall are forced by changes in the large-scale surface winds and air temperature in conjunction with the AMO. Namely, an anomalous cyclonic circulation is observed off the Southeast coast, leading to a reduction of moisture flux into the decaying North American monsoon, and an increase in moisture flux into the Mid-Atlantic. Further, the Mid-Atlantic shows a relatively strong increase in the mid-tropospheric lapse rate. Thus, the unique combination of low-level humidity, potential instability, and elevated topography are consistent with an enhanced risk of intense rainfall during AMO+.” Scott Curtis, Climate Dynamics, Volume 30, Number 4, 343-351, DOI: 10.1007/s00382-007-0295-0.

Impact of the Atlantic Multidecadal Oscillation on North Pacific climate variability – Zhang & Delworth (2007) “In this paper, we found that the Atlantic Multidecadal Oscillation (AMO) can contribute to the Pacific Decadal Oscillation (PDO), especially the component of the PDO that is linearly independent of El Niño and the Southern Oscillation (ENSO), i.e. the North Pacific Multidecadal Oscillation (NPMO), and the associated Pacific/North America (PNA) pattern. Using a hybrid version of the GFDL CM2.1 climate model, we show that the AMO provides a source of multidecadal variability to the North Pacific, and needs to be considered along with other forcings for North Pacific climate change. The lagged North Pacific response to the North Atlantic forcing is through atmospheric teleconnections and reinforced by oceanic dynamics and positive air-sea feedback over the North Pacific. The results indicate that a North Pacific regime shift, opposite to the 1976–77 shift, might occur now a decade after the switch of the observed AMO to a positive phase around 1995.” Zhang, R., and T. L. Delworth (2007), Impact of the Atlantic Multidecadal Oscillation on North Pacific climate variability, Geophys. Res. Lett., 34, L23708, doi:10.1029/2007GL031601. [Full text]

A Hemispheric Mechanism for the Atlantic Multidecadal Oscillation – Dima & Lohmann (2007) “The physical processes associated with the ~70-yr period climate mode, known as the Atlantic multidecadal oscillation (AMO), are examined. Based on analyses of observational data, a deterministic mechanism relying on atmosphere–ocean–sea ice interactions is proposed for the AMO. Variations in the thermohaline circulation are reflected as uniform sea surface temperature anomalies in the North Atlantic. These anomalies are associated with a hemispheric wavenumber-1 sea level pressure (SLP) structure in the atmosphere that is amplified through atmosphere–ocean interactions in the North Pacific. The SLP pattern and its associated wind field affect the sea ice export through Fram Strait, the freshwater balance in the northern North Atlantic, and consequently the strength of the large-scale ocean circulation. It generates sea surface temperature anomalies with opposite signs in the North Atlantic and completes a negative feedback. The authors find that the time scale of the cycle is associated with the thermohaline circulation adjustment to freshwater forcing, the SST response to it, the oceanic adjustment in the North Pacific, and the sea ice response to the wind forcing. Finally, it is argued that the Great Salinity Anomaly in the late 1960s and 1970s is part of AMO.” Dima, Mihai, Gerrit Lohmann, 2007: A Hemispheric Mechanism for the Atlantic Multidecadal Oscillation. J. Climate, 20, 2706–2719, doi: 10.1175/JCLI4174.1. [Full text]

Climate impacts of the Atlantic Multidecadal Oscillation – Knight et al. (2006) “The Atlantic Multidecadal Oscillation (AMO) is a near-global scale mode of observed multidecadal climate variability with alternating warm and cool phases over large parts of the Northern Hemisphere. Many prominent examples of regional multidecadal climate variability have been related to the AMO, such as North Eastern Brazilian and African Sahel rainfall, Atlantic hurricanes and North American and European summer climate. The relative shortness of the instrumental climate record, however, limits confidence in these observationally derived relationships. Here, we seek evidence of these links in the 1400 year control simulation of the HadCM3 climate model, which produces a realistic long-lived AMO as part of its internal climate variability. By permitting the analysis of more AMO cycles than are present in observations, we find that the model confirms the association of the AMO with almost all of the above phenomena. This has implications for the predictability of regional climate.” Knight, J. R., C. K. Folland, and A. A. Scaife (2006), Climate impacts of the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., 33, L17706, doi:10.1029/2006GL026242. [Full text]

Atlantic Ocean Forcing of North American and European Summer Climate – Sutton & Hodson (2005) “Recent extreme events such as the devastating 2003 European summer heat wave raise important questions about the possible causes of any underlying trends, or low-frequency variations, in regional climates. Here, we present new evidence that basin-scale changes in the Atlantic Ocean, probably related to the thermohaline circulation, have been an important driver of multidecadal variations in the summertime climate of both North America and western Europe. Our findings advance understanding of past climate changes and also have implications for decadal climate predictions.” Rowan T. Sutton and Daniel L. R. Hodson, Science 1 July 2005,
Vol. 309 no. 5731 pp. 115-118, DOI: 10.1126/science.1109496. [Full text]

A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D. – Gray et al. (2004) “We present a tree-ring based reconstruction of the Atlantic Multidecadal Oscillation (AMO) which demonstrates that strong, low-frequency (60–100 yr) variability in basin-wide (0–70°N) sea surface temperatures (SSTs) has been a consistent feature of North Atlantic climate for the past five centuries. Intervention analysis of reconstructed AMO indicates that 20th century modes were similar to those in the preceding ∼350 yr, and wavelet spectra show robust multidecadal oscillations throughout the reconstruction. Though the exact relationships between low-frequency SST modes, higher frequency (∼7–25 yr) atmospheric modes (e.g., North Atlantic Oscillation/Arctic Oscillation), and terrestrial climates must still be resolved, our results confirm that the AMO should be considered in assessments of past and future Northern Hemisphere climates.” Gray, S. T., L. J. Graumlich, J. L. Betancourt, and G. T. Pederson (2004), A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D., Geophys. Res. Lett., 31, L12205, doi:10.1029/2004GL019932. [Full text]

The Atlantic Multidecadal Oscillation and its relation to rainfall and river flows in the continental U.S. – Enfield et al. (2001) “North Atlantic sea surface temperatures for 1856–1999 contain a 65–80 year cycle with a 0.4 °C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr [2000]. AMO warm phases occurred during 1860–1880 and 1940–1960, and cool phases during 1905–1925 and 1970–1990. The signal is global in scope, with a positively correlated co‐oscillation in parts of the North Pacific, but it is most intense in the North Atlantic and covers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Niño‐Southern Oscillation are also significantly changed between AMO phases.” Enfield, D. B., A. M. Mestas‐Nuñez, and P. J. Trimble (2001), The Atlantic Multidecadal Oscillation and its relation to rainfall and river flows in the continental U.S., Geophys. Res. Lett., 28(10), 2077–2080, doi:10.1029/2000GL012745. [Full text]

Is There a Dominant Timescale of Natural Climate Variability in the Arctic? – Venegas & Mysak (2000) “A frequency-domain singular value decomposition performed jointly on century-long (1903–94) records of North Atlantic sector sea ice concentration and sea level pressure poleward of 40°N reveals that fluctuations on the interdecadal and quasi-decadal timescales account for a large fraction of the natural climate variability in the Arctic. Four dominant signals, with periods of about 6–7, 9–10, 16–20, and 30–50 yr, are isolated and analyzed. These signals account for about 60%–70% of the variance in their respective frequency bands. All of them appear in the monthly (year-round) data. However, the 9–10-yr oscillation especially stands out as a winter phenomenon. Ice variability in the Greenland, Barents, and Labrador Seas is then linked to coherent atmospheric variations and certain oceanic processes. The Greenland Sea ice variability is largely due to fluctuations in ice export through Fram Strait and to the local wind forcing during winter. It is proposed that variability in the Fram Strait ice export depends on three different mechanisms, which are associated with different timescales: 1) wind-driven motion of anomalous volumes of ice from the East Siberian Sea out of the Arctic (6–7-yr timescale); 2) enhanced ice motion forced by winter wind anomalies when they align parallel to the Transpolar Drift Stream (9–10-yr timescale); 3) wind-driven motion of old, thick, and very low salinity ice from offshore northern Canada into the outflow region (16–20-yr timescale). Also, a marked decreasing trend in ice extent since around 1970 (30–50-yr timescale) is linked to a recently reported warming in the Arctic. The Barents Sea ice variability is associated with the nature of the penetration of Atlantic waters into the Arctic Basin, which is affected by two distinct mechanisms: 1) changes in the intensity of the northward-flowing Norwegian Current, which is linked to variability in the North Atlantic oscillation (NAO) pattern (9–10-yr timescale); and 2) changes in the upper-ocean temperature of the Norwegian Current waters, which is likely related to the advection of temperature anomalies by the ocean gyres (16–20-yr timescale). Ice variability in the Labrador Sea, on the other hand, appears to be mainly determined by thermodynamical effects produced by the local wind forcing, which is closely related to the NAO pattern (9–10-yr timescale), and by oceanic advection of ice anomalies into this sea from the Greenland–Irminger Sea by the East Greenland Current (6–7-yr timescale).” Venegas, Silvia A., Lawrence A. Mysak, 2000: Is There a Dominant Timescale of Natural Climate Variability in the Arctic?. J. Climate, 13, 3412–3434. [Full text]

Observed and simulated multidecadal variability in the Northern Hemisphere – Delworth & Mann (2000) “Analyses of proxy based reconstructions of surface temperatures during the past 330 years show the existence of a distinct oscillatory mode of variability with an approximate time scale of 70 years. This variability is also seen in instrumental records, although the oscillatory nature of the variability is difficult to assess due to the short length of the instrumental record. The spatial pattern of this variability is hemispheric or perhaps even global in scale, but with particular emphasis on the Atlantic region. Independent analyses of multicentury integrations of two versions of the GFDL coupled atmosphere-ocean model also show the existence of distinct multidecadal variability in the North Atlantic region which resembles the observed pattern. The model variability involves fluctuations in the intensity of the thermohaline circulation in the North Atlantic. It is our intent here to provide a direct comparison of the observed variability to that simulated in a coupled ocean-atmosphere model, making use of both existing instrumental analyses and newly available proxy based multi-century surface temperature estimates. The analyses demonstrate a substantial agreement between the simulated and observed patterns of multidecadal variability in sea surface temperature (SST) over the North Atlantic. There is much less agreement between the model and observations for sea level pressure. Seasonal analyses of the variability demonstrate that for both the model and observations SST appears to be the primary carrier of the multidecadal signal.” T. L. Delworth and M. E. Mann, Climate Dynamics, Volume 16, Number 9, 661-676, DOI: 10.1007/s003820000075. [Full text]

An oscillation in the global climate system of period 65–70 years – Schlesinger & Ramankutty (1994) “IN addition to the well-known warming of 0.5 °C since the middle of the nineteenth century, global-mean surface temperature records display substantial variability on timescales of a century or less. Accurate prediction of future temperature change requires an understanding of the causes of this variability; possibilities include external factors, such as increasing greenhouse-gas concentrations and anthropogenic sulphate aerosols, and internal factors, both predictable (such as El Niño) and unpredictable (noise). Here we apply singular spectrum analysis to four global-mean temperature records, and identify a temperature oscillation with a period of 65–70 years. Singular spectrum analysis of the surface temperature records for 11 geographical regions shows that the 65–70-year oscillation is the statistical result of 50–88-year oscillations for the North Atlantic Ocean and its bounding Northern Hemisphere continents. These oscillations have obscured the greenhouse warming signal in the North Atlantic and North America. Comparison with previous observations and model simulations suggests that the oscillation arises from predictable internal variability of the ocean–atmosphere system.” Michael E. Schlesinger & Navin Ramankutty, Nature 367, 723 – 726 (24 February 1994); doi:10.1038/367723a0.

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