TY - JOUR
T1 - Impact of intra-daily SST variability on ENSO characteristics in a coupled model
AU - Masson, Sébastien
AU - Terray, Pascal
AU - Madec, Gurvan
AU - Luo, Jing Jia
AU - Yamagata, Toshio
AU - Takahashi, Keiko
N1 - Funding Information:
This work is a part of the EU-Japan collaboration build around the SINTEX-F coupled model. It is also a contribution to the MOU between the Earth Simulator Center (ESC), CNRS and IFREMER. All the computationally expensive experiments analysed in the study were performed on the Earth simulator. Our sensitivity experiments with 301 levels in the ocean have been double thanks to the outstanding computational performances offered by this unique supercomputer. S. Masson and G. Madec were supported by ANR (INLOES project). P. Terray benefited from the financial support from the Indo-French CEFIPRA project (No. 3907/1). Many thanks to R. Benshila, C. Talandier, A. Caubel, E. Maisonnave, M.A. Foujols, C. Levy, Y.Meursedoif, F. Pinsard, C. Deltel, S. Denvil and P. Brochard who have come to the ESC to implement, optimize and run the simulations. Their visit at the ESC was greatly facilitated by the kind help of A. Kurita, R. Itakura, A. Toya and M.-E. Demory. Graphics have been prepared using the SAXO package of S. Masson.
PY - 2012/7
Y1 - 2012/7
N2 - 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.
AB - 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.
KW - Coupled climate model
KW - Diurnal cycle
KW - El Niño-Southern Oscillation
KW - Ocean-atmosphere interactions
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U2 - 10.1007/s00382-011-1247-2
DO - 10.1007/s00382-011-1247-2
M3 - Article
AN - SCOPUS:84864395074
SN - 0930-7575
VL - 39
SP - 681
EP - 707
JO - Climate Dynamics
JF - Climate Dynamics
IS - 3
ER -