Cirene: Air-Sea Interactions in the Seychelles-Chagos Thermocline Ridge Region

Jérôme Vialard (1) , Jean-Philippe Duvel (2) , Michael J. Mcphaden (3) , Pascale Bouruet-Aubertot (4) , Brian Ward (5) , Erica Key , Denis Bourras (6) , R. Weller (7) , P. J. Minnett (8) , Alain Weill (6) , Christophe Cassou (9) , Laurence Eymard (1) , T. Fristedt (10) , Claude Basdevant (2) , Yves Dandonneau (1) , Olaf Duteil (1) , Takeshi Izumo (11) , Clément de Boyer Montégut (11) , Sébastien Masson (1) , F. Marsac (12) , Christophe E. Menkès (1) , Sean C. Kennan (13)

1 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
2 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
3 PMEL - NOAA Pacific Marine Environmental Laboratory [Newport]
4 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
5 ODU - Old Dominion University [Norfolk]
6 ESTER - LATMOS
7 WHOI - Woods Hole Oceanographic Institution
8 University of Miami [Coral Gables]
9 CERFACS - Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique
10 FOI - Swedish Defence Research Agency [Stockholm]
11 FRCGC - Frontier Research Center for Global Change
12 THETIS - Thons tropicaux et écosystèmes pélagiques : taxies, interactions et stratégies d'exploitation
13 NIWA - National Institute of Water and Atmospheric Research [Wellington]

The Vasco–Cirene program explores how strong air–sea interactions 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 oceanographic cruise collected oceanic, atmospheric, and air–sea flux observations in this region in January–February 2007. The contemporaneous Vasco field experiment complemented these measurements 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 January 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 cooling 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.

Domaines: Océan, Atmosphère; Climatologie

Jérôme Vialard, Jean-Philippe Duvel, Michael J. Mcphaden, Pascale Bouruet-Aubertot, Brian Ward, et al.. Cirene: Air-Sea Interactions in the Seychelles-Chagos Thermocline Ridge Region. Bulletin of the American Meteorological Society, 2009, 90 (1), pp.45-61. ⟨10.1175/2008BAMS2499.1⟩. ⟨hal-00361422⟩