Three-dimensional ageostrophic motion in mesoscale vortex dipoles

22 pages, 30 figuresThe three-dimensional motion of mesoscale baroclinic dipoles is simulated using a nonhydrostatic Boussinesq numerical model. The initial conditions are two ellipsoidal vortices of positive and negative potential vorticity anomalies. The flow is moderately ageostrophic with a maximum absolute Rossby number equal to 0.71. The trajectory of the dipole is related to the maximum potential vorticity anomaly and size of the vortices. Three cases are considered depending on the curvature of the dipole trajectory: negative, close to zero, and positive. The ageostrophic flow strongly depends on the distance between the ellipsoidal vortices d0. For small d0 the vortices move steadily as a compact dipole, and the vertical velocity w has an octupolar three-dimensional pattern. The horizontal ageostrophic velocity is due to the advective acceleration of the flow, particularly the centripetal acceleration. The speed acceleration is only relatively important at the rear and front parts of the dipole axis, where the flow curvature is small but where the flow confluence and diffluence are, respectively, large. The geostrophy is maximal at the dipole center, on the dipole axis, where both curvature and speed acceleration are minimal. As d0 increases, the dipole self-propagating velocity and the extreme values of |w| decrease, and vortex oscillations highly distort the octupolar pattern of w. In all cases, as is typical of balanced mesoscale geophysical flows, the vertical velocity is related to the advection of vertical vorticity by the horizontal shear velocity.We acknowledge FPU Grant AP2002-1895 and a research grant from the Spanish Ministerio de Ciencia y Tecnología (REN2002-01343).Peer reviewe

Spontaneous generation of inertia–gravity waves during the merging of two baroclinic anticyclones

22 pages, 26 figures, 1 tableThe spontaneous generation and propagation of short-scale inertia–gravity waves (IGWs) during the merging of two initially balanced (void of IGWs) baroclinic anticyclones is numerically investigated. The IGW generation is analyzed in flows with different potential vorticity (PV) anomaly, numerical diffusion, numerical resolution, vortex aspect ratio, and background rotation. The vertical velocity and its vertical derivative are used to identify the IGWs in the total flow, while the unbalanced flow (the waves) is diagnosed using the optimal PV balance approach. Spontaneous generation of IGWs occurs in all the cases, primarily as emissions of discrete wave packets. The increase of both the vortex strength and vortex extent isotropy enhances the IGW emission. Three possible indicators, or theories, of spontaneous IGW generation are considered, namely, the advection of PV, the material rate of change of the horizontal divergence, and the three-dimensional baroclinic IGW generation analogy of Lighthill sound radiation theory. It is suggested that different mechanisms for spontaneous IGW generation may be at work. One mechanism is related to the advection of PV, with the IGWs in this case having wave fronts similar to the PV isosurfaces in the upper layers, and helical patterns in the deep layers. Trapped IGWs are ubiquitous in the vortex interior and have annular wave front patterns. Another mechanism is related to the spatially coherent motion of preexisting IGWs, which eventually cooperate to produce mean flow, in particular larger-scale horizontal divergence, and therefore larger-scale vertical motion, which in turns triggers the emission of new IGWs.We acknowledge an FPU grant (AP2002-1895) and a research grant (CGL2005-01450/CLI) from the Spanish Ministerio de Educación y Ciencia.Peer reviewe

Flujo en balance de mesoscala, velocidad vertical, y emisión espontánea de ondas inercio-gravitatorias

Memoria de tesis doctoral presentada por Enric Pallàs Sanz para optar al grado de Doctor en Física Aplicada por la Universitat Politécnica de Catalunya (UPC), realizada bajo la dirección del Dr. Álvaro Viúdez Lomba del Institut de Ciències del Mar (ICM-CSIC).-- 179 pagesPeer Reviewe

Diagnosing Mesoscale Vertical Motion from Horizontal Velocity and Density Data

19 pages, 22 figures, 1 appendixThe mesoscale vertical velocity is obtained by solving a generalized omega equation (ω equation) using density and horizontal velocity data from three consecutive quasi-synoptic high-resolution surveys in the Alboran Sea. The Atlantic Jet (AJ) and the northern part of the Western Alboran Gyre (WAG) were observed as a large density anticyclonic front extending down to 200-230 m. The horizontal velocity uh in the AJ reached maxima of 1.2 m s-1 for the three surveys, with extreme Rossby numbers of ζ/f ≈ -0.9 in the WAG and +0.9 in the AJ (where ζ is the vertical vorticity and f is the Coriolis parameter). The generalized ω equation includes the ageostrophic horizontal flow. It is found that the most important >forcing> term in this equation is (fζph + ∇h e) · ∇h 2uh, where ζ ph is the horizontal (pseudo) vorticity and e is the buoyancy. This term is related to the horizontal advection of vertical vorticity by the vertical shear velocity, uhz · ∇hζ. Extreme values of the diagnosed vertical velocity w were located at 80-100 m with max[w] ⊂ [34, 45] and min{w} ⊂ [-64, -34] m day-1. Comparison with the quasigeostrophic (QG) ω equation shows that, because of the large Rossby numbers, non-QG terms are important. The differences between w and the QG vertical velocity are mainly related to the divergence of the ageostrophic part of the total Q vector (Qh ≡ ∇ huh · ∇h e) in the ω equation. © 2005 American Meteorological SocietyPeer Reviewe

Jornada de portes obertes a l'Institu del Ciències del Mar - Setmana de la Ciència 2003

Colección de DVDs del Institut de Cièncias del Mar (ICM-CSIC), volúmen 29Entrevistas con motivo de Jornada de Puertas abiertas del Instituto de Ciencias del Mar (ICM-CSIC) durante la Semana de la Ciencia del año 2003Peer reviewe

Ocean Front Detection with Glider and Satellite-Derived SST Data in the Southern California Current System

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region

Ocean Front Detection with Glider and Satellite-Derived SST Data in the Southern California Current System

This study proposes a method to detect ocean fronts from in situ temperature and density glider measurements. This method is applied to data collected along the CalCOFI Line 90, south of the California Current System (CCS), over the 2006–2013 period. It is based on image-processing techniques commonly applied to sea surface temperature (SST) satellite data. Front detection results using glider data are consistent with those obtained in other studies carried out in the CCS. SST images of the Multi-scale Ultra-high Resolution (MUR) dataset were also used to compare the probability of occurrence or front frequency (FF) obtained with the two datasets. Glider and MUR temperatures are highly correlated. Along Line 90, frontal frequency exhibited the same maxima near the transition zone (~130 km offshore) as derived from MUR and glider datasets. However, marked differences were found in the bimonthly FF probability with high (low) front frequency in spring-summer for glider (MUR) data. Methodological differences explaining these contrasting results are investigated. Thermohaline-compensated fronts are more abundant towards the oceanic zone, although most fronts are detected using both temperature and density criteria, indicating a significant contribution of temperature to density in this region

Heat Content Anomaly and Decay of Warm‐core Rings: the Case of the Gulf of Mexico

In this study, we harness the 25‐year satellite‐altimeter record, in concert with a vast array of in‐situ measurements, to estimate the heat content anomaly of 32 warm‐core rings in the Gulf of Mexico (GoM). The decay rate of these mesoscale eddies is studied in detail, and it is shown that they release the majority of their heat as they drift in the central GoM (away from topographic obstacles). The surface heat fluxes from the eddies is shown to be small in comparison to the total rate of heat loss from the eddies, suggesting that heat is primarily released towards the surrounding watermasses. Integrating the total heat evolution equation over the warm‐core rings yields an estimate of their effective lateral diffusivity coefficient. The long term impact of warm‐core rings on heat and salt balance in the GoM is also discussed

Intrathermocline Eddies Embedded within an Anticyclonic Vortex Ring

High‐resolution hydrographic measurements reveal the presence of three Intra‐Thermocline Eddies (ITEs) embedded within a Loop Current Eddy (LCE). ITEs are lenticular bodies of nearly homogeneous water which contrasts with the well stratified surrounding water. Their radii and thickness ranged between [19‐32] km and [150‐250] m. Negative relative vorticity within their cores (down to ‐0.85 times the Coriolis frequency), along with a large negative stratification anomaly, result in low Ertel Potential Vorticity (PV) and intense negative Ertel Potential Vorticity Anomalies (PVA). Vortex stretching and relative vorticity have comparable contributions to PVA, resulting in Burger numbers of order unity. The similarity of thermohaline properties within the ITE's cores and the surrounding LCE water, suggests that these ITEs likely form by intense mixing events followed by Rossby adjustment