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Impact of intra-daily SST variability on ENSO characteristics in a coupled model

Impact of intra-daily SST variability on ENSO characteristics in a coupled model
Impact of intra-daily SST variability on ENSO characteristics in a coupled model
This paper explores the impact of intra-daily Sea Surface Temperature (SST) variability on the tropical large-scale climate variability and differentiates it from the response of the system to the forcing of the solar diurnal cycle. Our methodology is based on a set of numerical experiments based on a fully global coupled ocean–atmosphere general circulation in which we alter (1) the frequency at which the atmosphere sees the SST variations and (2) the amplitude of the SST diurnal cycle. Our results highlight the complexity of the scale interactions existing between the intra-daily and inter-annual variability of the tropical climate system. Neglecting the SST intra-daily variability results, in our CGCM, to a systematic decrease of 15% of El Niño—Southern Oscillation (ENSO) amplitude. Furthermore, ENSO frequency and skewness are also significantly modified and are in better agreement with observations when SST intra-daily variability is directly taken into account in the coupling interface of our CGCM. These significant modifications of the SST interannual variability are not associated with any remarkable changes in the mean state or the seasonal variability. They can therefore not be explained by a rectification of the mean state as usually advocated in recent studies focusing on the diurnal cycle and its impact. Furthermore, we demonstrate that SST high frequency coupling is systematically associated with a strengthening of the air-sea feedbacks involved in ENSO physics: SST/sea level pressure (or Bjerknes) feedback, zonal wind/heat content (or Wyrtki) feedback, but also negative surface heat flux feedbacks. In our model, nearly all these results (excepted for SST skewness) are independent of the amplitude of the SST diurnal cycle suggesting that the systematic deterioration of the air-sea coupling by a daily exchange of SST information is cascading toward the major mode of tropical variability, i.e. ENSO.
Diurnal cycle Coupled climate model El Niño-Southern Oscillation Ocean–atmosphere interactions
0930-7575
681-707
Masson, Sébastien
3c93954e-649f-478b-a35e-d06879fb5d12
Terray, Pascal
7b49a30e-8d8f-42c2-84f6-1555ee4d72bd
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635
Takahashi, Keiko
d13fea86-af23-4a25-bf92-987256b81375
Masson, Sébastien
3c93954e-649f-478b-a35e-d06879fb5d12
Terray, Pascal
7b49a30e-8d8f-42c2-84f6-1555ee4d72bd
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Luo, Jing-Jia
d17819b4-b29e-4b43-a81f-7465e3c8b628
Yamagata, Toshio
94509afb-faba-4a4b-9709-2d0dbb8f8635
Takahashi, Keiko
d13fea86-af23-4a25-bf92-987256b81375

Masson, Sébastien, Terray, Pascal, Madec, Gurvan, Luo, Jing-Jia, Yamagata, Toshio and Takahashi, Keiko (2012) Impact of intra-daily SST variability on ENSO characteristics in a coupled model. Climate Dynamics, 39 (3-4), 681-707. (doi:10.1007/s00382-011-1247-2).

Record type: Article

Abstract

This paper explores the impact of intra-daily Sea Surface Temperature (SST) variability on the tropical large-scale climate variability and differentiates it from the response of the system to the forcing of the solar diurnal cycle. Our methodology is based on a set of numerical experiments based on a fully global coupled ocean–atmosphere general circulation in which we alter (1) the frequency at which the atmosphere sees the SST variations and (2) the amplitude of the SST diurnal cycle. Our results highlight the complexity of the scale interactions existing between the intra-daily and inter-annual variability of the tropical climate system. Neglecting the SST intra-daily variability results, in our CGCM, to a systematic decrease of 15% of El Niño—Southern Oscillation (ENSO) amplitude. Furthermore, ENSO frequency and skewness are also significantly modified and are in better agreement with observations when SST intra-daily variability is directly taken into account in the coupling interface of our CGCM. These significant modifications of the SST interannual variability are not associated with any remarkable changes in the mean state or the seasonal variability. They can therefore not be explained by a rectification of the mean state as usually advocated in recent studies focusing on the diurnal cycle and its impact. Furthermore, we demonstrate that SST high frequency coupling is systematically associated with a strengthening of the air-sea feedbacks involved in ENSO physics: SST/sea level pressure (or Bjerknes) feedback, zonal wind/heat content (or Wyrtki) feedback, but also negative surface heat flux feedbacks. In our model, nearly all these results (excepted for SST skewness) are independent of the amplitude of the SST diurnal cycle suggesting that the systematic deterioration of the air-sea coupling by a daily exchange of SST information is cascading toward the major mode of tropical variability, i.e. ENSO.

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More information

Published date: August 2012
Keywords: Diurnal cycle Coupled climate model El Niño-Southern Oscillation Ocean–atmosphere interactions
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 350998
URI: https://eprints.soton.ac.uk/id/eprint/350998
ISSN: 0930-7575
PURE UUID: 333816e5-9e80-4bf0-9e29-eba175a33a7e

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Date deposited: 12 Apr 2013 10:42
Last modified: 18 Jul 2017 04:29

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Contributors

Author: Sébastien Masson
Author: Pascal Terray
Author: Gurvan Madec
Author: Jing-Jia Luo
Author: Toshio Yamagata
Author: Keiko Takahashi

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