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  • 1
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    Max-Planck-Institut für Meteorologie
    In:  MPI-Report, 273 . Max-Planck-Institut für Meteorologie, Hamburg, Germany, . pp.
    Publication Date: 2019-08-07
    Type: Report , NonPeerReviewed
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  • 2
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    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 26 (9). p. 1329.
    Publication Date: 2018-02-13
    Description: The coupling on decadal time scales of the mid‐latitude and tropical Pacific via an oceanic ‘bridge’ in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model. Results indicate that in the tropics decadal anomalies of isopycnal depth are forced by Ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid‐latitudes of either hemisphere. In the coupled model, temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere, but are lag correlated between southern hemisphere mid‐ and low‐latitudes. However, anomaly magnitudes on the equator are small. These results suggest that the oceanic ‘bridge’ to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial Pacific. Coupling to the southern mid‐latitudes via temperature anomalies on isopycnals remains an intriguing possibility.
    Type: Article , PeerReviewed
    Format: text
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 2416-2433, doi:10.1175/JCLI4103.1.
    Description: North Pacific decadal oceanic and atmospheric variability is examined from a 650-yr control integration of the Community Climate System Model version 2. The dominant pattern of winter sea surface temperature (SST) variability is similar to the observed “Pacific decadal oscillation,” with maximum amplitude along the Kuroshio Extension. SST anomalies in this region exhibit significant spectral peaks at approximately 16 and 40 yr. Lateral geostrophic heat flux divergence, caused by a meridional shift of the Kuroshio Extension forced by basin-scale wind stress curl anomalies 3–5 yr earlier, is responsible for the decadal SST variability; local surface heat flux and Ekman heat flux divergence act as a damping and positive feedback, respectively. A simple linear Rossby wave model is invoked to explicitly demonstrate the link between the wind stress curl forcing and decadal variability in the Kuroshio Extension. The Rossby wave model not only successfully reproduces the two decadal spectral peaks, but also illustrates that only the low-frequency (〉10-yr period) portion of the approximately white noise wind stress curl forcing is relevant. This model also demonstrates that the weak and insignificant decadal spectral peaks in the wind stress curl forcing are necessary for producing the corresponding strong and significant oceanic peaks in the Kuroshio Extension. The wind stress curl response to decadal SST anomalies in the Kuroshio Extension is similar in structure but opposite in sign and somewhat weaker than the wind stress curl forcing pattern. These results suggest that the simulated North Pacific decadal variability owes its existence to two-way ocean–atmosphere coupling.
    Description: The first author gratefully acknowledges financial support from NOAA’s Office of Global Programs (grant to C. Deser) and the CCSM Project Office.
    Keywords: Decadal variability ; Fluxes ; Rossby waves ; Wind stress ; Coupled models
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Climate Dynamics 36 (2011): 2295-2312, doi:10.1007/s00382-010-0764-8.
    Description: The winter response of the coupled atmosphere-ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra-tropics. The direct response consists of positive SST anomalies along the Kuroshio Extension and a baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North Pacific. The low-level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer, especially in late winter. The inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the Pacific Inter-Tropical Convergence Zone which drives an equivalent barotropic anomalous ridge over the North Pacific. Although the tropically-driven component of the North Pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically-forced atmospheric teleconnection.
    Description: We gratefully acknowledge financial support from NOAA’s Office of Global Programs (grant to C. Deser and Y.-O. Kwon). Y.-O. Kwon is also supported through the Claudia Heyman Fellowship of the WHOI Ocean Climate Change Institute.
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 25 (2012): 2622–2651, doi:10.1175/JCLI-D-11-00301.1.
    Description: This study presents an overview of the El Niño–Southern Oscillation (ENSO) phenomenon and Pacific decadal variability (PDV) simulated in a multicentury preindustrial control integration of the NCAR Community Climate System Model version 4 (CCSM4) at nominal 1° latitude–longitude resolution. Several aspects of ENSO are improved in CCSM4 compared to its predecessor CCSM3, including the lengthened period (3–6 yr), the larger range of amplitude and frequency of events, and the longer duration of La Niña compared to El Niño. However, the overall magnitude of ENSO in CCSM4 is overestimated by ~30%. The simulated ENSO exhibits characteristics consistent with the delayed/recharge oscillator paradigm, including correspondence between the lengthened period and increased latitudinal width of the anomalous equatorial zonal wind stress. Global seasonal atmospheric teleconnections with accompanying impacts on precipitation and temperature are generally well simulated, although the wintertime deepening of the Aleutian low erroneously persists into spring. The vertical structure of the upper-ocean temperature response to ENSO in the north and south Pacific displays a realistic seasonal evolution, with notable asymmetries between warm and cold events. The model shows evidence of atmospheric circulation precursors over the North Pacific associated with the “seasonal footprinting mechanism,” similar to observations. Simulated PDV exhibits a significant spectral peak around 15 yr, with generally realistic spatial pattern and magnitude. However, PDV linkages between the tropics and extratropics are weaker than observed.
    Description: M. Alexander, A. Capotondi, and J. Scott’s participation was supported by a grant from the NSF Climate and Large-scale Dynamics Program. Y.-O. Kwon gratefully acknowledges support from a WHOI Heyman fellowship and a grant from the NSF Climate and Largescale Dynamics Program. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy.
    Description: 2012-10-15
    Keywords: Atmosphere-ocean interaction ; El Nino ; ENSO ; La Nina ; Pacific decadal oscillation ; Climate models
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 6
    Publication Date: 2020-05-15
    Description: Polar amplification – the phenomenon where external radiative forcing produces a larger change in surface temperature at high latitudes than the global average – is a key aspect of anthropogenic climate change, but its causes and consequences are not fully understood. The Polar Amplification Model Intercomparison Project (PAMIP) contribution to the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016) seeks to improve our understanding of this phenomenon through a coordinated set of numerical model experiments documented here. In particular, PAMIP will address the following primary questions: (1) what are the relative roles of local sea ice and remote sea surface temperature changes in driving polar amplification? (2) How does the global climate system respond to changes in Arctic and Antarctic sea ice? These issues will be addressed with multi-model simulations that are forced with different combinations of sea ice and/or sea surface temperatures representing present-day, pre-industrial and future conditions. The use of three time periods allows the signals of interest to be diagnosed in multiple ways. Lower-priority tier experiments are proposed to investigate additional aspects and provide further understanding of the physical processes. These experiments will address the following specific questions: what role does ocean–atmosphere coupling play in the response to sea ice? How and why does the atmospheric response to Arctic sea ice depend on the pattern of sea ice forcing? How and why does the atmospheric response to Arctic sea ice depend on the model background state? What have been the roles of local sea ice and remote sea surface temperature in polar amplification, and the response to sea ice, over the recent period since 1979? How does the response to sea ice evolve on decadal and longer timescales? A key goal of PAMIP is to determine the real-world situation using imperfect climate models. Although the experiments proposed here form a coordinated set, we anticipate a large spread across models. However, this spread will be exploited by seeking “emergent constraints” in which model uncertainty may be reduced by using an observable quantity that physically explains the intermodel spread. In summary, PAMIP will improve our understanding of the physical processes that drive polar amplification and its global climate impacts, thereby reducing the uncertainties in future projections and predictions of climate change and variability.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
    Publication Date: 2022-06-29
    Description: The possibility that Arctic sea ice loss weakens mid-latitude westerlies, promoting more severe cold winters, has sparked more than a decade of scientific debate, with apparent support from observations but inconclusive modelling evidence. Here we show that sixteen models contributing to the Polar Amplification Model Intercomparison Project simulate a weakening of mid-latitude westerlies in response to projected Arctic sea ice loss. We develop an emergent constraint based on eddy feedback, which is 1.2 to 3 times too weak in the models, suggesting that the real-world weakening lies towards the higher end of the model simulations. Still, the modelled response to Arctic sea ice loss is weak: the North Atlantic Oscillation response is similar in magnitude and offsets the projected response to increased greenhouse gases, but would only account for around 10% of variations in individual years. We further find that relationships between Arctic sea ice and atmospheric circulation have weakened recently in observations and are no longer inconsistent with those in models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed , info:eu-repo/semantics/article
    Format: application/pdf
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  • 8
    Publication Date: 2022-05-26
    Description: Meteorological data have been gathered from a moored surface buoy at 34°N, 70°W in the Long Term Upper Ocean Study (LOTUS) experiment. The meteorological results from the first year of LOTUS are encouraging; the data returned from redundant sensors agree closely. Surface heat fluxes calculated from the observations show the annual cycle of heat transfer to the mixed layer. This report documents the meteorological sensors on the LOTUs-3 (May 1982-october 1982) and LOTUS-4 (November 1982-March 1983) surface buoys. It describes in detail the telemetry of the meteorological data via the ARGOS satellite system. The measurements returned from LOTUS-3 are presented and evaluated. Monthly heat fluxes at the sea surface are computed using the bulk formulas and compared with the long-term means. The errors in the heat fluxes have been estimated.
    Description: Prepared for the Office of Naval Research under Contract N00014-76-C-0197; NR 083-400.
    Keywords: Meteorology ; Oceanus (Ship : 1975-) Cruise OC119 ; Oceanus (Ship : 1975-) Cruise OC129 ; Endeavor (Ship: 1976-) Cruise EN97
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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