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  • 1
    Online Resource
    Online Resource
    American Meteorological Society ; 2013
    In:  Journal of Climate Vol. 26, No. 7 ( 2013-04-01), p. 2302-2328
    In: Journal of Climate, American Meteorological Society, Vol. 26, No. 7 ( 2013-04-01), p. 2302-2328
    Abstract: Constraining the low-frequency (LF) behavior of general circulation models (GCMs) requires reliable observational estimates of LF variability. This two-part paper presents multiproxy reconstructions of Niño-3.4 sea surface temperature over the last millennium, applying two techniques [composite plus scale (CPS) and hybrid regularized expectation maximization (RegEM) truncated total least squares (TTLS)] to a network of tropical, high-resolution proxy records. This first part presents the data and methodology before evaluating their predictive skill using frozen network analysis (FNA) and pseudoproxy experiments. The FNA results suggest that about half of the Niño-3.4 variance can be reconstructed back to A.D. 1000, but they show little LF skill during certain intervals. More variance can be reconstructed in the interannual band where climate signals are strongest, but this band is affected by dating uncertainties (which are not formally addressed here). The CPS reliably estimates interannual variability, while LF fluctuations are more faithfully reconstructed with RegEM, albeit with inevitable variance loss. The RegEM approach is also tested on representative pseudoproxy networks derived from two millennium-long integrations of a coupled GCM. The pseudoproxy study confirms that reconstruction skill is significant in both the interannual and LF bands, provided that sufficient variance is exhibited in the target Niño-3.4 index. It also suggests that FNA severely underestimates LF skill, even when LF variability is strong, resulting in overly pessimistic performance assessments. The centennial-scale variance of the historical Niño-3.4 index falls somewhere between the two model simulations, suggesting that the network and methodology presented here would be able to capture the leading LF variations in Niño-3.4 for much of the past millennium, with the caveats noted above.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    RVK:
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2013
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 2
    Online Resource
    Online Resource
    American Meteorological Society ; 2021
    In:  Journal of Climate Vol. 34, No. 10 ( 2021-05), p. 4169-4188
    In: Journal of Climate, American Meteorological Society, Vol. 34, No. 10 ( 2021-05), p. 4169-4188
    Abstract: Surface temperature is a vital metric of Earth’s climate state but is incompletely observed in both space and time: over half of monthly values are missing from the widely used HadCRUT4.6 global surface temperature dataset. Here we apply the graphical expectation–maximization algorithm (GraphEM), a recently developed imputation method, to construct a spatially complete estimate of HadCRUT4.6 temperatures. GraphEM leverages Gaussian Markov random fields (also known as Gaussian graphical models) to better estimate covariance relationships within a climate field, detecting anisotropic features such as land–ocean contrasts, orography, ocean currents, and wave-propagation pathways. This detection leads to improved estimates of missing values compared to methods (such as kriging) that assume isotropic covariance relationships, as we show with real and synthetic data. This interpolated analysis of HadCRUT4.6 data is available as a 100-member ensemble, propagating information about sampling variability available from the original HadCRUT4.6 dataset. A comparison of Niño-3.4 and global mean monthly temperature series with published datasets reveals similarities and differences due in part to the spatial interpolation method. Notably, the GraphEM-completed HadCRUT4.6 global temperature displays a stronger early twenty-first-century warming trend than its uninterpolated counterpart, consistent with recent analyses using other datasets. Known events like the 1877/78 El Niño are recovered with greater fidelity than with kriging, and result in different assessments of changes in ENSO variability through time. Gaussian Markov random fields provide a more geophysically motivated way to impute missing values in climate fields, and the associated graph provides a powerful tool to analyze the structure of teleconnection patterns. We close with a discussion of wider applications of Markov random fields in climate science.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    RVK:
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
    Online Resource
    Online Resource
    American Meteorological Society ; 2015
    In:  Journal of Climate Vol. 28, No. 19 ( 2015-10-01), p. 7717-7740
    In: Journal of Climate, American Meteorological Society, Vol. 28, No. 19 ( 2015-10-01), p. 7717-7740
    Abstract: This study formulates the design of optimal observing networks for past surface climate conditions as the solution to a data assimilation problem, given a realistic proxy system model (PSM), paleoclimate observational uncertainties, and a network of current and proposed observing sites. The method is illustrated with the design of optimal networks of coral δ18O records, chosen among candidate sites, and used to jointly infer sea surface temperature (SST) and sea surface salinity (SSS) fields from the Community Climate System Model, version 4, last millennium simulation over the 1850–2005 period. It is shown that an existing paleo-observing network accounts for approximately 20% of the SST variance, and that adding 25 to 100 optimal pseudocoral sites would boost this fraction to 35%–52%. Characterizing the SST variance alone, or jointly with the SSS, leads to similar optimal networks, which justifies using coral δ18O records for SST reconstructions. In contrast, the network design for reconstructing SSS alone is fundamentally different, emphasizing the hydroclimatic centers of action of El Niño–Southern Oscillation. In all cases, network design depends strongly on the amplitude of the observational error, so replicates may be more beneficial than the exploration of new sites; these replicates tend to be chosen where proxies are already informative of the large-scale climate field(s). Finally, extensions to other types of paleoclimatic observations are discussed, and a path to operationalization is outlined.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    RVK:
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
    Online Resource
    Online Resource
    American Association for the Advancement of Science (AAAS) ; 2020
    In:  Science Vol. 367, No. 6485 ( 2020-03-27), p. 1477-1481
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 367, No. 6485 ( 2020-03-27), p. 1477-1481
    Abstract: The El Niño–Southern Oscillation (ENSO) shapes global climate patterns yet its sensitivity to external climate forcing remains uncertain. Modeling studies suggest that ENSO is sensitive to sulfate aerosol forcing associated with explosive volcanism but observational support for this effect remains ambiguous. Here, we used absolutely dated fossil corals from the central tropical Pacific to gauge ENSO’s response to large volcanic eruptions of the last millennium. Superposed epoch analysis reveals a weak tendency for an El Niño–like response in the year after an eruption, but this response is not statistically significant, nor does it appear after the outsized 1257 Samalas eruption. Our results suggest that those models showing a strong ENSO response to volcanic forcing may overestimate the size of the forced response relative to natural ENSO variability.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    RVK:
    RVK:
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2020
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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  • 5
    Online Resource
    Online Resource
    Institute of Mathematical Statistics ; 2015
    In:  The Annals of Applied Statistics Vol. 9, No. 1 ( 2015-3-1)
    In: The Annals of Applied Statistics, Institute of Mathematical Statistics, Vol. 9, No. 1 ( 2015-3-1)
    Type of Medium: Online Resource
    ISSN: 1932-6157
    Language: Unknown
    Publisher: Institute of Mathematical Statistics
    Publication Date: 2015
    detail.hit.zdb_id: 2376910-5
    detail.hit.zdb_id: 2253657-7
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  • 6
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2018
    In:  Journal of Geophysical Research: Atmospheres Vol. 123, No. 23 ( 2018-12-16)
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 123, No. 23 ( 2018-12-16)
    Abstract: iCAM5 can simulate the observed anticorrelation between stratiform rainfall fraction and precipitation oxygen isotope ratios All models can simulate the observed relationship between outgoing longwave radiation and precipitation oxygen isotope ratios The contribution of convective processes to precipitation oxygen isotope ratios is very site dependent
    Type of Medium: Online Resource
    ISSN: 2169-897X , 2169-8996
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2018
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 2969341-X
    SSG: 16,13
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  • 7
    Online Resource
    Online Resource
    Past Global Changes (PAGES) ; 2018
    In:  Past Global Change Magazine Vol. 26, No. 2 ( 2018-11), p. 71-71
    In: Past Global Change Magazine, Past Global Changes (PAGES), Vol. 26, No. 2 ( 2018-11), p. 71-71
    Type of Medium: Online Resource
    ISSN: 2411-605X , 2411-9180
    URL: Issue
    Language: Unknown
    Publisher: Past Global Changes (PAGES)
    Publication Date: 2018
    detail.hit.zdb_id: 2779253-5
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  • 8
    Online Resource
    Online Resource
    Elsevier BV ; 2017
    In:  Earth and Planetary Science Letters Vol. 459 ( 2017-02), p. 362-371
    In: Earth and Planetary Science Letters, Elsevier BV, Vol. 459 ( 2017-02), p. 362-371
    Type of Medium: Online Resource
    ISSN: 0012-821X
    RVK:
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2017
    detail.hit.zdb_id: 300203-2
    detail.hit.zdb_id: 1466659-5
    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2010
    In:  Environmental Fluid Mechanics Vol. 10, No. 1-2 ( 2010-4), p. 257-273
    In: Environmental Fluid Mechanics, Springer Science and Business Media LLC, Vol. 10, No. 1-2 ( 2010-4), p. 257-273
    Type of Medium: Online Resource
    ISSN: 1567-7419 , 1573-1510
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2010
    detail.hit.zdb_id: 2037932-8
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  • 10
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2013
    In:  Geochemistry, Geophysics, Geosystems Vol. 14, No. 2 ( 2013-02), p. 457-469
    In: Geochemistry, Geophysics, Geosystems, American Geophysical Union (AGU), Vol. 14, No. 2 ( 2013-02), p. 457-469
    Abstract: The paleoclimate database should be structured in a machine‐readable format This is possible using semantic technologies and simple design principles This format would accelerate the inference made from paleoclimate observations
    Type of Medium: Online Resource
    ISSN: 1525-2027 , 1525-2027
    URL: Issue
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2013
    detail.hit.zdb_id: 2027201-7
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