Cassou Christophe

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Cassou
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Christophe
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  • Preprint
    Coupled atmosphere–mixed layer ocean response to ocean heat flux convergence along the Kuroshio Current Extension
    ( 2010-01-28) Kwon, Young-Oh ; Deser, Clara ; Cassou, Christophe
    The winter response of the coupled atmosphere-ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra-tropics. The direct response consists of positive SST anomalies along the Kuroshio Extension and a baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North Pacific. The low-level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer, especially in late winter. The inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the Pacific Inter-Tropical Convergence Zone which drives an equivalent barotropic anomalous ridge over the North Pacific. Although the tropically-driven component of the North Pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically-forced atmospheric teleconnection.
  • Article
    Supplement to Cirene : air-sea interactions in the Seychelles-Chagos thermocline ridge region
    (American Meteorological Society, 2009-01) Vialard, Jérôme ; Duvel, J. P. ; McPhaden, Michael J. ; Bouruet-Aubertot, Pascale ; Ward, Brian ; Key, E. ; Bourras, Denis ; Weller, Robert A. ; Minnett, Peter ; Weill, A. ; Cassou, Christophe ; Eymard, L. ; Fristedt, Tim ; Basdevant, C. ; Dandonneau, Y. ; Duteil, O. ; Izumo, T. ; de Boyer Montegut, C. ; Masson, S. ; Marsac, F. ; Menkes, C. ; Kennan, S.
    The Vasco—Cirene field experiment, in January—February 2007, targeted the Seychelles—Chagos thermocline ridge (SCTR) region, with the main purpose of investigating Madden—Julian Oscillation (MJO)-related SST events. The Validation of the Aeroclipper System under Convective Occurrences (Vasco) experiment (Duvel et al. 2009) and Cirene cruise were designed to provide complementary views of air—sea interaction in the SCTR region. While meteorological balloons were deployed from the Seychelles as a part of Vasco, the Research Vessel (R/V) Suroît was cruising the SCTR region as a part of Cirene.
  • Article
    Cirene : air-sea iInteractions in the Seychelles-Chagos thermocline ridge region
    (American Meteorological Society, 2009-01) Vialard, Jérôme ; Duvel, J. P. ; McPhaden, Michael J. ; Bouruet-Aubertot, Pascale ; Ward, Brian ; Key, E. ; Bourras, Denis ; Weller, Robert A. ; Minnett, Peter ; Weill, A. ; Cassou, Christophe ; Eymard, L. ; Fristedt, Tim ; Basdevant, C. ; Dandonneau, Y. ; Duteil, O. ; Izumo, T. ; de Boyer Montegut, C. ; Masson, S. ; Marsac, F. ; Menkes, C. ; Kennan, S.
    The Vasco—Cirene program ex-plores how strong air—sea inter-actions promoted by the shallow thermocline and high sea surface temperature in the Seychelles—Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and air—sea flux observations in this region in Jan-uary—February 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers. Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles—Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.