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Cited by 5Climate variability and modelsOceanographic and Atmospheric ProcessesStatistical Methods and Applications

Sea surface temperature patterns in the Tropical Atlantic: Principal component analysis and nonlinear principal component analysis

Open access
Kenfack, Christian Sadem, Mkankam, François Kamga, Alory, Gaël, Penhoat, Yves du, Hounkonnou, Mahouton Norbert, Vondou, Derbetini Appolinaire, Jr., Bawe Gerard Nfor·2017·Terrestrial, Atmospheric and Oceanic Sciences
DOI 10.3319/tao.2016.08.29.01
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Abstract

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AI snapshot

Written from the paper’s full text.

TL;DR

This study applies linear PCA and neural-network nonlinear PCA (NLPCA) to monthly tropical Atlantic SST anomalies (1950–2005) to compare how each represents Atlantic Cold Tongue, Atlantic Niño, and Atlantic dipole variability. NLPCA explains slightly more variance and captures nonlinear/asymmetric states—especially canonical/non-canonical Atlantic Niño and dipole displacement—that linear PCA misses.

Key findings

  • The first two PCA EOF modes together account for 52% of total monthly SST variance (EOF1 36%, EOF2 16%). The first two NLPCA modes explain marginally more: NLPCA mode 1 explains 38% versus 36% for PCA mode 1, and NLPCA mode 2 explains 22% versus 16% for PCA mode 2.
  • PC1 correlates with the Atlantic Niño SST index at 0.82; PC2 correlates with the Atlantic dipole index at 0.66; NLPC2 correlates with the Atlantic dipole index at 0.9. NLPC1 correlates with the normalized ACT index at 0.85, compared with 0.8 for PC1.
  • NLPCA mode 1 represents the ACT as quasi-linear but captures both strong and weak ACT states and canonical/non-canonical Atlantic Niño states; the paper reports Atlantic Niño spatial variability is more linear than Pacific ENSO. NLPCA mode 2 captures the Atlantic dipole with a displaced southern lobe and more pronounced asymmetry/nonlinearity than the ACT.
  • Composite analysis shows strong and weak ACT patterns are quasi-symmetric, with a spatial correlation of -0.99, but NLPCA provides continuous states rather than only composite means.

Methods

  • Used monthly NOAA ERSST SST data at 2° × 2° resolution over 26°S–22°N, 30°W–20°E, from 1950 to 2005; computed monthly SST anomalies relative to the annual cycle and removed linear trends at each spatial location.
  • Applied PCA/EOF analysis, then retained 20 PCs by the Guttman-Kaiser criterion (99% total variance) as input to an NLPCA neural network with m = 3 and 3931 parameters, following Hsieh (2004).
  • Compared PCA and NLPCA modes, principal/nonlinear principal component time series, correlation maps, and composites for warm/cold ACT events during JJA.

Limitations

  • Stated: mechanisms controlling the tropical Atlantic mean state are not fully understood, and future analysis is needed to explore West African monsoon rainfall using NLPCA. NLPCA cannot be used directly on observed or modelled SST data and requires initial dimensionality reduction; larger m increases nonlinear capability but may lead to overfitted solutions.
  • Evident: the analysis is limited to one SST reconstruction, 1950–2005, and 2° × 2° resolution, and no formal significance testing is reported in the text. The NLPCA parameter count (3931) greatly exceeds the number of time points, which the paper itself flags as an overfitting concern.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3319/tao.2016.08.29.01

Cites

68 of 69 references verified1 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

3 of 43 cited sources checked · 1 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    There is interannual variability in the ACT spatial pattern in the Gulf of Guinea, which is not fully understood.

    “Caniaux et al. (2011) shows that there is interannual variability in the ACT spatial pattern in GoG, which is not fully understood.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites Caniaux et al. (2011) source
  • Findingown data

    The spatial distribution of the reconstructed SST anomaly varies with each selected value of u.

    “It observed that the spatial distribution varies with each selected value of u .”
    Quote in the paperNot a substantial claim
  • Findingown data

    Figs. 8b, 8c, 8d show the displacement of the southern counterpart of the dipole, which confirms the asymmetry of the meridional mode.

    “Figs.8b, 8c, 8d show the displacement of southern counterpart of the dipole, which confirms the asymmetry of the meridional mode.”
    Quote in the paperSubstantial claim
  • Findingown data

    The correlation coefficient between PC1 and the Atlantic Niño SST index is 0.82.

    “In addition, the correlation coefficient between PC1 and Atlantic Niño SST index is 0.82.”
    Quote in the paperSubstantial claim
  • Findingown data

    ACT distribution is quasi-linear in space.

    “and ACT distribution is quasi-linear in space.”
    Quote in the paperNot a substantial claim
  • May combine two claims. 45
  • Classified as probably not a substantial claim. 11

  • May combine two claims.

    Findingcitation

    By multiplying EOF1 with its related PC, typical ACT cold years are 1990, 1992, 1997, 2005 and warm years are 1984, 1987, 1998.

    “By multiplying EOF1 with its related PC, we observe some typical ACT cold years, such as 1990, 1992, 1997, 2005and warm years 1984, 1987and 1998(Caniaux et al., 2011).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites Caniaux et al., 2011 source

      Section 2.2 identifies 1992 and 2005 among the coldest ACT years and 1984 and 1987 among the warmest. It does not identify 1990 or 1997 as cold years, or 1998 as a warm year, and the passages found do not describe an EOF1–PC calculation. The paper uses an ACT temperature index for the reported classifications. (LLM, conf=0.87)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Two primary modes of interannual variability have been identified in the tropical Atlantic: the equatorial and meridional modes.

    “Within the last decades, two primary modes of interannual variability have been identified in the tropical Atlantic (e.g.Servain andMerle, 1993, Xie et al., 1999)): the equatorial and meridional modes.”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites Servain andMerle, 1993

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Xie et al., 1999 source

      The Observational Background (page unavailable in our copy) favors two tropical Atlantic modes: an equatorially symmetric monopole and an antisymmetric dipole. But it describes the monopole as interannual and the dipole as decadal, so it does not support calling both modes interannual. (LLM, conf=0.88)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingown data

    The SSTAs show a remarkable meridional gradient, with significant positive anomalies spreading from the North African coast into the northwestern tropical Atlantic and significant negative anomalies in the south.

    “The SSTAs show a remarkable meridional gradient, with significant positive anomalies spreading from the North African coast into the northwestern tropical Atlantic and significant negative anomalies in the south.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The high correlation coefficient between NLPCA mode 1 and PCA1 confirms the result that ACT distribution is quasi-linear in space.

    “This result is confirmed by the high correlation coefficient between NLPCA mode 1 and PCA1.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    During strong gradient events the core of the southern lobe is centered around 15°W; during some weak events it is around 20°W.

    “During the strong gradient (meridional gradient between the two lobes, Fig. 8a) events the core of the southern lobe is centered around 15°W during the strong gradient and around 20°W during some weak events (Fig. 8f).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The Atlantic dipole in Fig. 8a is similar to that in Fig. 8f but the southern lobe is not located at the same place.

    “The Atlantic dipole in Fig. 8a is similar to that in Fig. 8f but the southern lobe is not located at the same place.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    EOF1 mode accounts for up to 36% of the total variance, with the region of largest amplitude around the Angola coast.

    “EOF1 mode (Fig. 2a) accounts for up to 36% of the total variance with the region of largest amplitude around the Angola coast.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    There is a local maximum in the tropics which has a sign, indicating that the two regions are quite strongly out of phase.

    “There is, however, a local maximum in the tropics which has a sign, indicating that the two regions are quite strongly out of phase.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The largest SSTA is located in the eastern part during average weak ACT events and centered in the same region during average strong ACT events.

    “The largest SSTA is located in the eastern part during average weak ACT events and centered in the same region during average strong ACT events.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    NLPCA SSTA mode 2 explains 22% of the total data variance, compared to 38% for NLPCA SST mode 1.

    “For the observational SST data, NLPCA SSTA mode 2 explains 22% of the total data variance, compared to 38% for NLPCA SST mode 1.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingnone given

    The nonlinearity of the sinuosity observed in Fig. 4a is modest, and the maximum of PC1 is less than the absolute value of the minimum of PC1.

    “The non linearity of the sinuosity observed in Fig.4a is modest and the maximum of PC1 is less than the absolute value of the minimum of PC1.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    The first NLPCA mode explains 38.6% of the variance of the given EOFs, i.e. 38% of the total variance of SSTA, compared to 36% explained by the first PCA.

    “The first mode (Fig.4) of NLPCA explains 38.6% of the variance of the given EOFs, i.e 38% of the total variance of SSTA compared to 36% explained by the first PCA.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    One of these patterns can be captured by conventional PCA analysis but does not capture the quasi-symmetry presented by strong and weak ACTs.

    “One of these patterns can be captured by a conventional PCA analysis but does not capture the quasi symmetry presented by strong and weak ACTs.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The asymmetry of SSTA in the evolution of NLPCA mode 1 is modest; the canonical and non-canonical Atlantic El Niño event is observed which cannot be pointed out by linear mode 1.

    “The asymmetry of SSTA in the evolution of NLPCA mode 1 is modest; the canonical and non canonical Atlantic El Niño event is observed which cannot be pointed out by linear mode 1.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    The weak gradient between the two lobes is observed in the sequence map, and this weakening of the meridional mode is consistent with previous works.

    “Also the weak gradient between the two lobes is observed in the sequence map; this weakening of the meridional mode is consistent with previous works (Tokinaga et al., 2011).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Tokinaga et al., 2011

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Findingown data

    Fig. 6e, f and g characterized the non-canonical Atlantic Niño with negative anomalies in the northern tropical Atlantic, and Fig. 6h characterized the canonical Atlantic Niño with positive anomalies in the northern tropical Atlantic.

    “The results presented in Fig.6.e,f and g characterized the non canonical Atlantic Niño with negative anomalies in the northern tropical Atlantic and Fig.6h characterized the canonical Atlantic Niño with positive anomalies in the northern tropical Atlantic.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The first rotated PCA explained 31% of the total variance, versus 36% by the first PCA mode.

    “In this paper, in terms of variance, the first rotated PCA explained 31% of the total variance (not shown), versus 36% by the first PCA mode.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Fig. 7a and Fig. 7b bear a strong resemblance to Fig. 6h and Fig. 6a, respectively, and are strongly similar to EOF1.

    “Fig. 7a and Fig. 7b, respectively, bears a strong resemblance to Fig. 6h and Fig. 6a; and are strongly similar to EOF1.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    The correlation coefficient between the normalized ACT index, nonlinear principal component and linear principal component are respectively 0.85 and 0.8.

    “The correlation coefficient between the normalized ACT index, nonlinear principal component and linear principal component are respectively 0.85 and 0.8.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Composite analysis shows just two steps of ACT, determining a quasi-symmetry.

    “The quasi-symmetry determined by a composite analysis (Fig. 7) shows just two steps of ACT.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The main characteristic of the Atlantic dipole is captured, with the South Pole shifted towards the coast with different signs.

    “The main characteristic of the Atlantic dipole is captured, with the South Pole shifted towards the coast with different signs.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingcitation

    The south lobe is missing in Figs. 8b, 8c, 8d.

    “We also observed that the south lobe is missing in Figs.8b, c, d.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingnone given

    The two composite maps correspond to the SSTA patterns of an average warm and cold ACT event, respectively.

    “These two maps correspond to the SSTA patterns of an average warm and cold ACT event, respectively.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Findingnone given

    Fig. 6a represents the coldest year and Fig. 6h the year of the warmest ACT, which is not the warmest year but the year of weak ACT corresponding to Atlantic Niño.

    “Fig.6a represents the coldest year and Fig.6h the year of the warmest ACT, which is not the warmest year but the year of weak ACT corresponding to Atlantic Niño.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    NLPCA mode 1 explains 38% of the total variance in the SST field, in contrast to 36% for the first PCA mode, while NLPCA SST mode 2 explains 22% of the total data variance compared to 16% by the linear PCA mode 2.

    “It was observed that a NLPCA mode 1 explains 38% of the total variance in the SST field, in contrast to 36% for the first PCA mode while NLPCA SST mode 2 explains 22% of the total data variance compared to 16% by the linear PCA mode 2.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    The Atlantic equatorial mode, which is similar to ENSO in the Pacific Ocean, has been recognized and, considering Hsieh (2004), it is observed that it is less linear than ENSO.

    “The Atlantic equatorial mode which is similar to El Niño/Southern Oscillation (ENSO) in the Pacific Ocean has been recognized and considering the Hsieh (2004) work, it is observed that it is less linear than the latter.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Hsieh (2004) source

  • May combine two claims.

    Findingreasoning

    PCA mode 1 also characterizes average ACT variability, but only as a standing oscillation, so it is unable to evaluate the weak asymmetry in spatial pattern between average warm and cold events manifested in the 1D NLPCA.

    “PCA mode 1 also characterizes average ACT variability, but only as a standing oscillation, so it is unable to evaluate the weak asymmetry in spatial pattern between average warm and cold events manifested in the 1D NLPCA.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    In terms of explained variance, NLPCA mode 1 is generally greater than PCA mode 1, but the difference is not as much as that between PCA mode 2 and NLPCA mode 2, which are very large and with NLPCA mode 2 being greater than PC mode 2.

    “in terms of explained variance, NLPCA mode 1 is generally greater than PCA mode 1 however the difference is not as much as that between PCA mode 2 and NLPCA mode 2, which are very large and with the NLPCA mode 2 being greater than PC mode 2.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    The two approximations are equally well correlated with the original data over the central band of the Atlantic Ocean, where the NLPCA correlations are somewhat higher than those of the PCA approximation, except in the Northwest part of the Ocean.

    “The two approximations are equally well correlated with the original data over the central band of the Atlantic Ocean, where the NLPCA correlations are somewhat higher than those of the PCA approximation, except in the Nothwest part of the Ocean.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Kramer (1991) used neural networks to extend PCA to the extraction of nonlinear relationships in a dataset, defining nonlinear principal component analysis (NLPCA).

    “Since the 1980s, models of neural networks have been developed and Kramer (1991) used them to extend PCA abilities to the extraction of nonlinear relationships in a dataset, which defines the nonlinear principal component analysis (NLPCA).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Kramer (1991) source

  • May combine two claims.

    Premisereasoning

    Conventional PCA can only extract linear structures from data, so nonlinear structures are either missed or misinterpreted by these methods.

    “The weakness of this conventional method is that only linear structures can be extracted from data.This limitation means that nonlinear structures are either missed or misinterpreted by these methods.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    When trade winds intensify in the western Atlantic, the equatorial thermocline slope increases and negative SST anomalies develop in the Gulf of Guinea, reinforcing the ACT; conversely, when trade winds weaken, the slope decreases and positive SST anomalies develop in the Gulf of Guinea.

    “When the trade winds intensify in the western Atlantic, the equatorial thermocline slope increases and negative SST anomalies develop in the GoG, reinforcing the ACT; conversely, when trade winds weaken, the equatorial thermocline slope decreases and positive SST anomalies develop in the GoG (Servain and Amault, 1995).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Servain and Amault, 1995

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data

    NLPCA gives a more accurate description of the El Niño states than the first PCA mode, which did not fully represent the canonical and non-canonical Atlantic Niño.

    “In addition, it gives a more accurate description of the El Niño states (Fig. 6) than the first PCA mode (Fig. 2a), which did not fully represent the canonical and non-canonical Atlantic Niño.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The Atlantic Niño is much weaker than its Pacific counterpart.

    “However, the Atlantic Niño is much weaker than its Pacific counterpart (Carton and Huang, 1994, Latif and Grötzner, 2000, Servain et al., 2003, Zebiak, 1993).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Carton and Huang, 1994 source
    • cites Latif and Grötzner, 2000 source
    • cites Servain et al., 2003 source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Chen et al. (2010) applied NLPCA on SST in the South China Sea and showed that it accounts for more variance than linear PCA and brings a finer analysis of interannual variability.

    “Also, in the South China Sea, Chen et al. (2010) applied NLPCA on SST and showed that this statistical method accounts for more variance of the total variables in comparison with linear PCA and brings a finer analysis of interannual variability.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Chen et al. (2010) source

  • May combine two claims.

    Premisecitation

    The equatorial mode is mainly responsible for SST variability in the Gulf of Guinea and is identified by abnormal changes in the equatorial thermocline slope resulting from zonal-wind anomalies in the western tropical Atlantic.

    “The equatorial mode is responsible for SST variability in the GoG mainly, and is identified by abnormal changes in the equatorial thermocline slope resulting from zonal-wind anomalies in the western tropical Atlantic.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Servain and Amault, 1995

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    ENSO influence on the tropical Atlantic is strongest in the North Tropical Atlantic, with Atlantic warming occurring 4-5 months after the mature phases of Pacific warm events.

    “Many observational (Enfield et al., 1997) and modeling (Huang et al., 2002) studies have shown that the ENSO influence on the tropical Atlantic is strongest in the North Tropical Atlantic, with Atlantic warming occurring 4-5 months after the mature phases of Pacific warm events (Xie and Carton, 2004).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Enfield et al., 1997

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Huang et al., 2002 source
    • cites Xie and Carton, 2004

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The Atlantic dipole exhibits decadal time scales.

    “This is not surpring because it is observed in some studies (Rajagopalane et al., 1998, Servain, 1991) that the Atlantic dipole exhibits decadal time scales.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Rajagopalane et al., 1998

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Servain, 1991 source

  • May combine two claims.

    Interpretationreasoning

    The second NLPCA mode has fully captured the Atlantic dipole pattern, unlike PCA mode 2, which only captured part.

    “This means that the second NLPCA mode has fully captured the Atlantic dipole pattern, unlike PCA mode 2, which only captured part.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The spatial variation of the meridional mode changes, meaning that the phenomenon cannot happen in the same place every year.

    “Thus the spatial variation of the meridional mode changes meaning that the phenomenon cannot happen in the same place every year.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    The sequential evolution of the phenomenon from Fig. 8a to Fig. 8h is interrupted, implying that the phenomenon is not observed each year.

    “When observing the Atlantic dipole structure, we may realise that the sequential evolution of the phenomenon from Fig. 8a to Fig. 8h is interrupted, implying that the phenomena is not observed each year which is not also suprising as results.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    NLPCA explains variances extracted by PCA and gives more information, which is not obvious by analysis with the PCA.

    “So, NLPCA explains variances extracted by PCA and gives more information, which is not obvious by analysis with the PCA.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The spatial distribution is best described by NLPCA than PCA, and the variance may be represented by these first NLPCA modes.

    “The spatial distribution is best described (Fig.6) by NLPCA than PCA, and the variance may be represented by these first NLPCA modes.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    The second NLPCA mode yields a more accurate description of the Atlantic dipole than the second PCA mode, which did not fully represent the displacement of the center of action located in the southern part.

    “Thereby yielding a more accurate description of the Atlantic dipole (Fig. 8) than the second PCA mode (Fig. 2b), which did not fully represent the displacement of the center of action located in the southern part.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    NLPCA is not so constrained, and therefore its power lies in characterizing more complex lower-dimensional structures.

    “NLPCA is not so constrained, and therefore its power lies in characterizing more complex lower-dimensional structures (Monahan, 2001).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Monahan, 2001 source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The northern and southern hemispheres appear to act independently.

    “It was pointed out by Houghton and Tourre (1992) and confirmed by Metha (1998) that the northern and southern hemispheres appear to act independently.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Houghton and Tourre (1992) source
    • cites Metha (1998)

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S2 (checkable).

    Interpretationreasoning

    NLPCA can give more information about this variability.

    “NLPCA can give more information about this variability.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    NLPCA has the advantage of no a priori specification of a time series over which to composite, and provides a full 1D approximation to the data, in contrast to the absence of approximation in composite analysis.

    “However, NLPCA has the advantage of no a priori specification of a time series (e.g.periods) over which to composite, and provides a full 1D approximation to the data, in contrast to the absence of approximation in composite analysis.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Warm events (Atlantic Niños) are associated with reduced cold tongue development.

    “The warm events (Atlantic Niños) are associated with reduced cold tongue development(Carton and Huang, 1994).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Carton and Huang, 1994 source

  • May combine two claims.

    Interpretationreasoning

    The fact that ACT is almost linear gives the impression that NLPCA is not necessary, but the implementation of only linear PCA hides this weak nonlinearity.

    “The fact that we observed that ACT is almost linear gives the impression that NLPCA is not necessary, but the implementation of only linear PCA hides this weak nonlinearity.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Composite analysis can only give the mean state of ACT, but PCA and NLPCA can approximate the real state.

    “The latter can only give the mean state of ACT but PCA and NLPCA can approximate the real state.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    NLPCA shows different states of ACT, isolating different patterns and their associated amplitudes which may be missed by means or averaging.

    “But NLPCA shows different states of ACT; isolating different patterns and their associated amplitudes which may be missed by the means or averaging.”
    Quote in the paperSubstantial claim
52 of 52

  • The paper relies on this without support.

    NLPCA has never been applied in the tropical Atlantic region, to the authors' knowledge.

    “While PCA has been frequently used in the above studies of tropical Atlantic variability, NLPCA has never been applied in this region, to our knowledge.”

  • The paper relies on this without support.

    The mechanisms controlling the mean state of the tropical Atlantic are not fully understood.

    “Overall, the mechanisms controlling the mean state of the tropical Atlantic are not fully understood.”

  • The paper relies on this without support.

    The mean state of the tropical Atlantic is important as an indicator for predicting future atmospheric circulation.

    “However, its mean state is important as an indicator for predicting future atmospheric circulation.”
3 of 3

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Fig. 8f's displacement is described in the wrong direction

    Minor

    The southern lobe is placed at 15°W in Fig. 8a and 20°W in Fig. 8f. Moving from 15°W to 20°W is a westward shift, not an eastward one.

  • Atlantic mode is described as both more and less linear than Pacific ENSO

    Minor

    One passage says the Atlantic mode's spatial variability is more linear than Pacific ENSO; the conclusion says the Atlantic equatorial mode is less linear than its Pacific counterpart.

  • Fig. 7 composites are matched to the opposite ACT states

    Minor

    The text identifies Fig. 7a as strong ACT and Fig. 7b as weak ACT, while Fig. 6a and Fig. 6h are identified as strong and weak ACT, respectively. The stated resemblance pairs Fig. 7a with weak Fig. 6h and Fig. 7b with strong Fig. 6a instead.

  • First-mode NLPC values are not equally spaced

    Minor

    The eight listed values have unequal successive gaps: the first is 2.16 and the second is 0.41. They therefore are not equitably spaced from minimum to maximum as stated.

4 of 4

Cites

Flagged first, then by citations

1 of the 70 references couldn’t be matched to a known paper.

Research works printed but not linked: 5

  1. Czaja, A., Vaart, P. V. D.,Marshall, J.: A diagnostic study of the role of remote forcing in tropical Atlantic variability, J. Climate, 15, 3280-3290, 2002. Doi: 10.1175/1520- 0442(2002)015%3C3280:adsotr%3E2.0.co;2 · DOI
  2. Hastenrath, S., Lamb, P.J.: Climatic Atlas of the Tropical Atlantic and Eastern Pacific Ocean, the University of Wisconsin Press, Madison, 15, 97 charts, 1977.
  3. Houghton, R.W.: Seasonal variations of the subsurface thermal structure in the Gulf of Guinea, Journal of Physical Oceanography, 13, 2070-2081, 1983. Doi:10.1175/1520- 0485(1983)013%3C2070:svotst%3E2.0.co;2 · DOI
  4. Picaut, J: Propagation of the seasonal upwelling in the eastern equatorial Atlantic, Geophys. Res. Lett., 13, 18-37, 1983. Doi: 10.1175/1520- 0485(1983)013%3C0018:potsui%3E2.0.co;2 · DOI
  5. YUKO, O., and Shang-Ping,X.: Some Overlooked Features of Tropical Atlantic Climate Leading to a New Nio-Like Phenomenon, American Meteorological Society, 19, 5859-5879, 2006. Doi: 10.1175/jcli3928. · DOI

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Authors
Kenfack, C. S., Mkankam, F. K., Alory, G., Penhoat, Y. D., Hounkonnou, M. N., Vondou, D. A., & Jr., B. G. N.
Affiliations
  • Laboratoire d’Études en Géophysique et Océanographie Spatiales (FR)
  • Université d'Abomey-Calavi (BJ)
Venue
Terrestrial, Atmospheric and Oceanic Sciences
Publisher
Springer Science and Business Media LLC
Published
2017
Volume
28
Issue
3
Pages
395-410
ISSN
1017-0839 (ISSN-L)
DOI
10.3319/tao.2016.08.29.01
OpenAlex
W2748480688
Semantic Scholar
063b16b0242467364390427c922f1964b35830ed
Cited by
5
References
70
Citations by year
2024: 1 · 2022: 1 · 2020: 2 · 2018: 1
FWCI
0.56
Type
journal article
Language
en
Open access
Licence
other-oa
Locations
  • Terrestrial Atmospheric and Oceanic Sciences (publishedVersion, other-oa)
  • HAL (Le Centre pour la Communication Scientifique Directe) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
African Union
Topics
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate variability and models
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Oceanographic and Atmospheric Processes
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods and Applications
Keywords
sea surface temperature, tropical Atlantic, spatial patterns, principal component analysis, nonlinear principal component analysis, climate variability

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Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-16.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-16.

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