Skip to content

Research at St Andrews

Dynamics of ITCZ width: Ekman processes, non-Ekman processes, and links to sea surface temperature

Research output: Contribution to journalArticlepeer-review

Standard

Dynamics of ITCZ width : Ekman processes, non-Ekman processes, and links to sea surface temperature. / Byrne, Michael P.; Thomas, Rhidian.

In: Journal of the Atmospheric Sciences, Vol. 76, No. 9, 09.2019, p. 2869-2884.

Research output: Contribution to journalArticlepeer-review

Harvard

Byrne, MP & Thomas, R 2019, 'Dynamics of ITCZ width: Ekman processes, non-Ekman processes, and links to sea surface temperature', Journal of the Atmospheric Sciences, vol. 76, no. 9, pp. 2869-2884. https://doi.org/10.1175/JAS-D-19-0013.1

APA

Byrne, M. P., & Thomas, R. (2019). Dynamics of ITCZ width: Ekman processes, non-Ekman processes, and links to sea surface temperature. Journal of the Atmospheric Sciences, 76(9), 2869-2884. https://doi.org/10.1175/JAS-D-19-0013.1

Vancouver

Byrne MP, Thomas R. Dynamics of ITCZ width: Ekman processes, non-Ekman processes, and links to sea surface temperature. Journal of the Atmospheric Sciences. 2019 Sep;76(9):2869-2884. https://doi.org/10.1175/JAS-D-19-0013.1

Author

Byrne, Michael P. ; Thomas, Rhidian. / Dynamics of ITCZ width : Ekman processes, non-Ekman processes, and links to sea surface temperature. In: Journal of the Atmospheric Sciences. 2019 ; Vol. 76, No. 9. pp. 2869-2884.

Bibtex - Download

@article{1acbc4d0711f413a82423c48e257ee2b,
title = "Dynamics of ITCZ width: Ekman processes, non-Ekman processes, and links to sea surface temperature",
abstract = "The dynamical processes controlling the width of the intertropical convergence zone (ITCZ) are investigated using idealized and CMIP5 simulations. ITCZ width is defined in terms of boundary layer vertical velocity. The tropical boundary layer is approximately in Ekman balance, suggesting that wind stress places a strong constraint on ITCZ width. A scaling based on Ekman balance predicts that ITCZ width is proportional to the wind stress and inversely proportional to its meridional gradient. A toy model of an Ekman boundary layer illustrates the effects of wind stress perturbations on ITCZ width. A westerly wind perturbation widens the ITCZ whereas an easterly perturbation narrows the ITCZ. Multiplying the wind stress by a constant factor does not shift the ITCZ edge, but ITCZ width is sensitive to the latitude of maximum wind stress. Scalings based on Ekman balance cannot fully capture the behavior of ITCZ width across simulations, suggesting that non-Ekman dynamical processes need to be accounted for. An alternative scaling based on the full momentum budget explains variations in ITCZ width and highlights the importance of horizontal and vertical momentum advection. Scalings are also introduced linking ITCZ width to surface temperature. An extension to Lindzen-Nigam theory predicts that ITCZ width scales with the latitude where the Laplacian of SST is zero. The supercriticality theory of Emanuel is also invoked to show that ITCZ width is dynamically linked to boundary layer moist entropy gradients. The results establish a dynamical understanding of ITCZ width that can be applied to interpret persistent ITCZ biases in climate models and the response of tropical precipitation to climate change.",
keywords = "Tropics, Atmospheric circulation, Convergence/divergence, Hadley circulation, Momentum, General circulation models",
author = "Byrne, {Michael P.} and Rhidian Thomas",
note = "This project has received funding from the EU{\textquoteright}s Horizon 2020 Research and Innovation Programme under the Marie Sk{\l}odowska-Curie Grant Agreement 794063. We also acknowledge support from the Imperial College London Research Fellowship Scheme.",
year = "2019",
month = sep,
doi = "10.1175/JAS-D-19-0013.1",
language = "English",
volume = "76",
pages = "2869--2884",
journal = "Journal of the Atmospheric Sciences",
issn = "0022-4928",
publisher = "AMER METEOROLOGICAL SOC",
number = "9",

}

RIS (suitable for import to EndNote) - Download

TY - JOUR

T1 - Dynamics of ITCZ width

T2 - Ekman processes, non-Ekman processes, and links to sea surface temperature

AU - Byrne, Michael P.

AU - Thomas, Rhidian

N1 - This project has received funding from the EU’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Grant Agreement 794063. We also acknowledge support from the Imperial College London Research Fellowship Scheme.

PY - 2019/9

Y1 - 2019/9

N2 - The dynamical processes controlling the width of the intertropical convergence zone (ITCZ) are investigated using idealized and CMIP5 simulations. ITCZ width is defined in terms of boundary layer vertical velocity. The tropical boundary layer is approximately in Ekman balance, suggesting that wind stress places a strong constraint on ITCZ width. A scaling based on Ekman balance predicts that ITCZ width is proportional to the wind stress and inversely proportional to its meridional gradient. A toy model of an Ekman boundary layer illustrates the effects of wind stress perturbations on ITCZ width. A westerly wind perturbation widens the ITCZ whereas an easterly perturbation narrows the ITCZ. Multiplying the wind stress by a constant factor does not shift the ITCZ edge, but ITCZ width is sensitive to the latitude of maximum wind stress. Scalings based on Ekman balance cannot fully capture the behavior of ITCZ width across simulations, suggesting that non-Ekman dynamical processes need to be accounted for. An alternative scaling based on the full momentum budget explains variations in ITCZ width and highlights the importance of horizontal and vertical momentum advection. Scalings are also introduced linking ITCZ width to surface temperature. An extension to Lindzen-Nigam theory predicts that ITCZ width scales with the latitude where the Laplacian of SST is zero. The supercriticality theory of Emanuel is also invoked to show that ITCZ width is dynamically linked to boundary layer moist entropy gradients. The results establish a dynamical understanding of ITCZ width that can be applied to interpret persistent ITCZ biases in climate models and the response of tropical precipitation to climate change.

AB - The dynamical processes controlling the width of the intertropical convergence zone (ITCZ) are investigated using idealized and CMIP5 simulations. ITCZ width is defined in terms of boundary layer vertical velocity. The tropical boundary layer is approximately in Ekman balance, suggesting that wind stress places a strong constraint on ITCZ width. A scaling based on Ekman balance predicts that ITCZ width is proportional to the wind stress and inversely proportional to its meridional gradient. A toy model of an Ekman boundary layer illustrates the effects of wind stress perturbations on ITCZ width. A westerly wind perturbation widens the ITCZ whereas an easterly perturbation narrows the ITCZ. Multiplying the wind stress by a constant factor does not shift the ITCZ edge, but ITCZ width is sensitive to the latitude of maximum wind stress. Scalings based on Ekman balance cannot fully capture the behavior of ITCZ width across simulations, suggesting that non-Ekman dynamical processes need to be accounted for. An alternative scaling based on the full momentum budget explains variations in ITCZ width and highlights the importance of horizontal and vertical momentum advection. Scalings are also introduced linking ITCZ width to surface temperature. An extension to Lindzen-Nigam theory predicts that ITCZ width scales with the latitude where the Laplacian of SST is zero. The supercriticality theory of Emanuel is also invoked to show that ITCZ width is dynamically linked to boundary layer moist entropy gradients. The results establish a dynamical understanding of ITCZ width that can be applied to interpret persistent ITCZ biases in climate models and the response of tropical precipitation to climate change.

KW - Tropics

KW - Atmospheric circulation

KW - Convergence/divergence

KW - Hadley circulation

KW - Momentum

KW - General circulation models

U2 - 10.1175/JAS-D-19-0013.1

DO - 10.1175/JAS-D-19-0013.1

M3 - Article

VL - 76

SP - 2869

EP - 2884

JO - Journal of the Atmospheric Sciences

JF - Journal of the Atmospheric Sciences

SN - 0022-4928

IS - 9

ER -

Related by author

  1. Radiative effects of clouds and water vapor on an axisymmetric monsoon

    Byrne, M. P. & Zanna, L., 15 Oct 2020, In: Journal of Climate. 33, 20, p. 8789-8811

    Research output: Contribution to journalArticlepeer-review

  2. Monsoons Climate Change Assessment

    Wang, B., Biasutti, M., Byrne, M. P., Castro, C., Chang, C-P., Cook, K., Fu, R., Grimm, A. M., Ha, K-J., Hendon, H., Kitoh, A., Krishnan, R., Lee, J-Y., Li, J., Liu, J., Moise, A., Pascale, S., Roxy, M. K., Seth, A., Sui, C-H. & 5 others, Turner, A., Yang, S., Yun, K-S., Zhang, L. & Zhou, T., 6 May 2020, In: Bulletin of the American Meteorological Society. p. 1-60 60 p.

    Research output: Contribution to journalArticlepeer-review

  3. Advances in understanding large-scale responses of the water cycle to climate change

    Allan, R. P., Barlow, M., Byrne, M. P., Cherchi, A., Douville, H., Fowler, H. J., Gan, T. Y., Pendergrass, A. G., Rosenfeld, D., Swann, A. L. S., Wilcox, L. J. & Zolina, O., 4 Apr 2020, In: Annals of the New York Academy of Sciences. Early View, 27 p.

    Research output: Contribution to journalReview articlepeer-review

  4. Controls on the width of tropical precipitation and its contraction under global warming

    Donohoe, A., Atwood, A. R. & Byrne, M. P., 29 Aug 2019, In: Geophysical Research Letters. Early View, 10 p.

    Research output: Contribution to journalArticlepeer-review

  5. Response of the intertropical convergence zone to climate change: location, width and strength

    Byrne, M. P., Pendergrass, A., Rapp, A. & Wodzicki, K., 9 Aug 2018, In: Current Climate Change Reports. First Online, 16 p.

    Research output: Contribution to journalArticlepeer-review

Related by journal

  1. Journal of the Atmospheric Sciences (Journal)

    Richard Kirkness Scott (Editor)

    2006 → …

    Activity: Publication peer-review and editorial work typesEditor of research journal

  2. Journal of the Atmospheric Sciences (Journal)

    Riwal Plougonven (Editor)

    2005 → …

    Activity: Publication peer-review and editorial work typesEditor of research journal

  3. Journal of the Atmospheric Sciences (Journal)

    David Gerard Dritschel (Editor)

    2005 → …

    Activity: Publication peer-review and editorial work typesEditor of research journal

  4. Journal of the Atmospheric Sciences (Journal)

    Ali Reza Mohebalhojeh (Editor)

    2005 → …

    Activity: Publication peer-review and editorial work typesEditor of research journal

Related by journal

  1. The stability of Mars' annular polar vortex

    Seviour, W., Waugh, D. & Scott, R. K., May 2017, In: Journal of the Atmospheric Sciences. 74, 5, p. 1533-1547

    Research output: Contribution to journalArticlepeer-review

  2. The Troposphere-to-Stratosphere Transition in Kinetic Energy Spectra and Nonlinear Spectral Fluxes as Seen in ECMWF Analyses

    Burgess, B. H., Erler, A. R. & Shepherd, T. G., Feb 2013, In: Journal of the Atmospheric Sciences. 70, 2, p. 669-687 19 p.

    Research output: Contribution to journalArticlepeer-review

  3. Revisiting vacillations in shallow-water models of the stratosphere using potential-vorticity-based numerical algorithms

    MirRokni, S. M., Mohebalhojeh, A. R. & Dritschel, D. G., 1 May 2011, In: Journal of the Atmospheric Sciences. 68, 5, p. 1007-1022 16 p.

    Research output: Contribution to journalArticlepeer-review

  4. A barotropic model of the angular momentum-conserving potential vorticity staircase in spherical geometry

    Dunkerton, T. J. & Scott, R. K., 2008, In: Journal of the Atmospheric Sciences. 65, 4, p. 1105-1136

    Research output: Contribution to journalArticlepeer-review

ID: 261267534

Top