Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: J. M. Molines x
  • Refine by Access: All Content x
Clear All Modify Search
A. Lamy, C. Millot, and J. M. Molines

Abstract

Bottom and atmospheric pressure, sea level, wind, current and temperature measurements have been obtained during summer in the coastal zone of the Gulf of Lions. Relations between these parameters are estimated mainly with coherence analysis. First, it is shown that the atmospheric pressure forcing is small and that the sea level and bottom pressure spectra are very similar. Then the characteristics of tides are computed with a least-squares method. Removing the tidal signal from the original time series allows us to study in a clearer way the inertial frequency band: arguments for the possible occurrence of sea surface oscillations at this frequency are discussed. At lower frequencies, large sea level variations are due to the wind. At frequencies higher than the tidal ones, very energetic signals are connected with natural oscillations of the Gulf of Lions induced by atmospheric pressure perturbations of a relatively small scale. This paper is concerned with regional oceanograhy, but the results (mainly those about natural oscillations) corroborate the interest of filtering in the frequency domain.

Full access
A. M. Treguier, C. Lique, J. Deshayes, and J. M. Molines

Abstract

Correlations between temperature and velocity fluctuations are a significant contribution to the North Atlantic meridional heat transport, especially at the northern boundary of the subtropical gyre. In satellite observations and in a numerical model at ⅞° resolution, a localized pattern of positive eddy heat flux is found northwest of the Gulf Stream, downstream of its separation at Cape Hatteras. It is confined to the upper 500 m. A simple kinematic model of a meandering jet can explain the surface eddy flux, taking into account a spatial shift between the maximum velocity of the jet and the maximum cross-jet temperature gradient. In the Gulf Stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth. The numerical model suggests that the meandering of the Gulf Stream could account, at least in part, for the large eddy heat transport (of order 0.3 PW) near 36°N in the North Atlantic and for its compensation by the mean flow.

Full access
A. M. Treguier, J. Le Sommer, J. M. Molines, and B. de Cuevas

Abstract

The authors evaluate the response of the Southern Ocean to the variability and multidecadal trend of the southern annular mode (SAM) from 1972 to 2001 in a global eddy-permitting model of the DRAKKAR project. The transport of the Antarctic Circumpolar Current (ACC) is correlated with the SAM at interannual time scales but exhibits a drift because of the thermodynamic adjustment of the model (the ACC transport decreases because of a low renewal rate of dense waters around Antarctica). The interannual variability of the eddy kinetic energy (EKE) and the ACC transport are uncorrelated, but the EKE decreases like the ACC transport over the three decades, even though meridional eddy fluxes of heat and buoyancy remain stable. The contribution of oceanic eddies to meridional transports is an important issue because a growth of the poleward eddy transport could, in theory, oppose the increase of the mean overturning circulation forced by the SAM. In the authors’ model, the total meridional circulation at 50°S is well correlated with the SAM index (and the Ekman transport) at interannual time scales, and both increase over three decades between 1972 and 2001. However, given the long-term drift, no SAM-linked trend in the eddy contribution to the meridional overturning circulation is detectable. The increase of the meridional overturning is due to the time-mean component and is compensated by an increased buoyancy gain at the surface. The authors emphasize that the meridional circulation does not vary in a simple relationship with the zonal circulation. The model solution points out that the zonal circulation and the eddy kinetic energy are governed by different mechanisms according to the time scale considered (interannual or decadal).

Full access
I. Shulman, J. C. Kindle, D. J. McGillicuddy Jr., M. A. Moline, S. H. D. Haddock, D. Nechaev, and M. W. Phelps

Abstract

The focus of this paper is on the development of methodology for short-term (1–3 days) oceanic bioluminescence (BL) predictions and the optimization of spatial and temporal bioluminescence sampling strategies. The approach is based on predictions of bioluminescence with an advection–diffusion–reaction (tracer) model with velocities and diffusivities from a circulation model. In previous research, it was shown that short-term changes in some of the salient features in coastal bioluminescence can be explained and predicted by using this approach. At the same time, it was demonstrated that optimization of bioluminescence sampling prior to the forecast is critical for successful short-term BL predictions with the tracer model. In the present paper, the adjoint to the tracer model is used to study the sensitivity of the modeled bioluminescence distributions to the sampling strategies for BL. The locations and times of bioluminescence sampling prior to the forecast are determined by using the adjoint-based sensitivity maps. The approach is tested with bioluminescence observations collected during August 2000 and 2003 in the Monterey Bay, California, area. During August 2000, BL surveys were collected during a strong wind relaxation event, while in August 2003, BL surveys were conducted during an extended (longer than a week) upwelling-favorable event. The numerical bioluminescence predictability experiments demonstrated a close agreement between observed and model-predicted short-term spatial and temporal changes of the coastal bioluminescence.

Full access