The Cirene project

The “CIRENE” campaign Jan-Feb 2007

P.I. J. Vialard jv@lodyc.jussieu.fr

The Cirene project

A brief summaryWhere?In the western Indian Ocean, between 5°S and 10°S

When?In January-February 2007

Why?To study the strong SST response to the MJO in this

region.

The Cirene project

MJO & oceanic response

Intraseasonal variability of the convectionSummer: active & break phases of the monsoonWinter: MJO

Many recent studies indicate strong SST responses & possible feedback: e.g. Sengupta & Ravichandran, 2001; Harrison and Vecchi 2001; Duvel et al. 2004; Duvel and Vialard, 2006; Vecchi and Harrison, 2002; etc…

Contours: mean OLR Colors: 10-80 day standard deviation

The Cirene project

SST response to the MJO

Case study: Duvel et al. (2004)30.5

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Buoy TMI

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One of the 2 strong SSTsignals due to the MJO

in early 1999

The Cirene project

Statistical study: Duvel and Vialard (2006)

SST response to the MJO

OLR

SST

Observed SST response associated with large-scale OLR 10-80 day variability

Other region of strong SST

response

No strong SST response in western

Pacific

« Cirene  region »

The Cirene project

SST response to the MJODuvel and Vialard (2006)

The 53°E-81°E, 3°S-9°S region is highly responsive to MJO in winter (especially in January)

15-day low passed filtered time series of TMI SST, NOAA OLR, NCEP surface wind and heat fluxes in the CIRENE region

The Cirene project

SST response to the MJO

Probably largely driven by heat fluxes (solar and latent) but questions remain on the role of vertical mixing and Ekman pumping.

Models and re-analyses don’t allow to close budget (underestimation of variability)

Role of diurnal cycle?

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Buoy TMI

1D Modelling of the role of diurnal cycle in COAREModèle 1D

(Bernie et al. 2005)

The Cirene project

Scientific questions ?

Coupling between SST and convection at intraseasonal scale in winter in the “Cirene” region.

Processes driving the SSTRespective role of fluxes / Ekman pumping and mixing?Role of the diurnal cycle?Role of thermocline in maintaining shallow mixed layerWhy such a warm SST in a shallow thermocline & upwelling region?

Biogeochemical response of the ocean to the MJOChlorophyll-a signal?Influence on the heat budget?

Ocean feedback on the atmosphere?Influence of local against large scale conditions?

The Cirene project

Two components

The Vasco experiment (PI: J-P. Duvel)Deployment of Aeroclippers and pressurised baloons from the Seychelles (Jan-Feb 2007)

The Cirene experiment (PI: J. Vialard)Oceanographic campaign with the Ifremer ship « Le Suroît », starting from the Seychelles (Jan-Feb 2007)

The Cirene project

Two components

Seychelles ATLAS mooring

Cirene campaign AREAVASCO aeroclippers and pressurised baloons

The Cirene project

VASCO ExperimentStatistics of multi-scale variability for a large region south of the equator

Diurnal to intraseasonalSurface parametersTop of the atmospheric boundary layer

Aeroclipper measurementsSmall scale structure of the surface atmospheric and oceanic parameters in convectively suppressed or active conditions

• Surface flux• SST variability (warm-layer diurnal cycle for suppressed conditions)• SSS variability (impact of rain events)

Large scale dynamics at the surface

Pressurized Balloon measurementsLarge scale dynamics and thermodynamics (T,RH) around 850hPa

The Cirene project

Quasi-Lagrangian Trajectories for

Pressurized Balloons and Aéroclippers

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Maximum convective activity BPs and Aeroclippers in this low-level westerly jet

VASCO Experiment

The Cirene project

Vasco Pilot experiment - February 2005

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Pressurized Balloons Aeroclippers

5 pressurised balloons and 4 Aéroclippers launched from Mahé between February 10 and February 25, 2005.Flight until March 17 for the 1st pressurised balloons (31 days).

The Cirene project

T P Q

Isopycnal pressurized balloons

GPS Argos positioning and data transmission

2.5m

The Cirene project

Atmospheric gondola

T, RH, P, Relative Wind

Onboard computations

Ocean gondola

SST SSS Speed

Security positioning and transmission (GPS, ARGOS)

Tension (computation of height)

Science positioning and transmission (GPS, ARGOS)

60 m

for V=0

Aéroclipper6m

The Cirene project

The Cirene experiment

The Cirene project

In a few words…2 legs, start, stopover and return in SeychellesInstruments deployment:

One ATLAS and one ADCP mooring (collaboration PMEL, to retrieve)12 Argo profilers (PROVOR)3 “dragged” surface buoys (collaboration WHOI, to retrieve)XBT (every 3h) and radiosondes (two to four times a day)

Long stations (2 x 12 days at ~ 67°30’E, 8°S) CTD with L-ADCP, PAR, transmissiometer, fluorimeter2 à 4 water samples (~5-7 levels) a day (Chlorophyll, nutrients, salinity)Autonomous micro)structure profiler 0-100m (ASIP, B. Ward)

Continuous measurementsAir sea fluxes measurements (CETP-CNRM-DT INSU instrument)RSMAS (U. Miami): radiometers, sky camera, radiative fluxes…

The Cirene project

Cirene, first legPreparation: 5-8 januaryLeg 1: 9-29 januaryStopover 30-31 januaryLeg 2: 1-20 februaryEnd: 21 february

The Cirene project

Cirene, second legPreparation: 5-8 januaryLeg 1: 9-29 januaryStopover 30-31 januaryLeg 2: 1-20 februaryEnd: 21 february

The Cirene project

ADCP & ATLAS MooringAt 67°E, 8°S, where there is a significant SST and flux signal-

ATLAS: long and shortwave fluxes, Tair, humidity, pressure, wind, 14 T sensors in upper 500m, 9 S sensors in upper 140m, 4-5 currentmeters

The Cirene project

The Cirene measurements(B. Ward, WHOI)

High resolution near surface profiler: diurnal cycle.

The Cirene project

The Cirene measurements(B. Ward, WHOI)

The Cirene project

The Cirene measurementsWHOI drifting buoys

3 balls float24 nodes thermistance chain with .5m resolutionSelf-recording thermometers (every 5 m from 15 to 60m)Deep-drogue the buoys at ~500 to 1000m to slow them down. Will be deployed aroundship at beginning of 1Dstation period & recoveredat the end.

The Cirene project

The Cirene measurementsFluxes measurementsContinuous measure air-sea fluxes (momentum, heat, freshwater) with a 15% accuracy over 30minutes periodsMeasured quantities for turbulent component of the fluxes: platform motion (6 degrees of freedom) and wind, temperature, humidity with two samplings (1 Hz=accurate low frequency sampling and 50Hz: turbulence)Numerical simulations of flow around ship to correct for distortion effects

Refractometer (q)

The Cirene project

Cirene measurementsRSMAS (P. Minett et al.) M-AERI

Radiation package

Microwaveradiometer

Optical rain gauge

All sky camera

Weather station

The Cirene project

The Cirene analyses

Document the amplitude of the fluxes and upper ocean response the amplitude of the diurnal cycleThe atmospheric signals…

associated with a MJO in the Cirene region

Evaluate upper ocean heat and salt budget based on observations.

Process studies with a 1D ocean model, and with a 1D ocean-atmosphere column model.

The Cirene project

Vasco-Cirene complementarityVASCO

Large-scale dynamical perturbations• Low-level jet around 850hPa and surface wind

Statistics of multi-scale variability of surface parameters for a (hopefully) large region• Diurnal to intraseasonal

CIRENEPrecise local measurements of diurnal to intraseasonal evolutions of the vertical structures for the Ocean and the Atmosphere

VASCO gives to CIRENE:The large-scale environment of the CIRENE measurements

• Link between CIRENE measurements and satellite/analysed fields (Spatial homogeneity, …)

A larger statistics for the same region and season for perturbations at the air-sea interface

• Wind gusts, Warm-layer, Salinity, Surface fluxes, etc.

CIRENE gives to VASCOPhysical interpretation of Aeroclipper observations

• Origin of SST and SSS variability• Potential impact of observed surface flux perturbation (diurnal, …) on the ocean mixed layer

Radiosondes for the vertical structure of the atmosphere