In this paper a process study aimed at analyzing the low-frequency variability of intrinsically oceanic origin of the Gulf Stream (GS) and GS extension (GSE) is presented. An eddy-permitting ...reduced-gravity nonlinear shallow water model is implemented in an idealized North Atlantic Ocean, with schematic boundaries including the essential geometric features of the coastline and a realistic zonal basin width at all latitudes. The forcing is provided by a time-independent climatological surface wind stress obtained from 41 years of monthly ECMWF fields. The model response yields strong intrinsic low-frequency fluctuations on the interannual to decadal time scales. The modelled time-averaged GS/GSE flows are found to exhibit several features that can also be deduced from satellite altimeter data, such as the Florida Current seaward deflection, the GS separation at Cape Hatteras, and the overall structure of the GSE. The intrinsic low-frequency variability yields two preferred states of the GSE differing in latitudinal location that also have their counterpart in the altimeter data. A preliminary analysis of the variability in terms of dynamical systems theory is carried out by using the lateral eddy viscosity as the control parameter. A complex transition sequence from a steady state to irregular low-frequency variability emerges, in which Hopf and global bifurcations can be identified.
The weakly nonlinear finite amplitude evolution of mixed baroclinic/barotropic instabilities of an eastward zonal jet is considered in a two-layer QG-model on a mid-latitude beta-plane. Linear ...friction is included and is essential to the momentum transport. The focus is two parameter regimes, one corresponding to the Gulf Stream and the other to the Antarctic Circumpolar Current. In the latter case, the nonlinear self-interaction of the most unstable mode causes upgradient momentum transport and therefore sharpens the jet. The analysis of this example leads to a clear description of the physics of this process. It also indicates why upgradient momentum transport does not occur in the Gulf Stream regime.
It has been reported by the Blanchards, that the attacks of offensively motivated rats produce a very characteristic wound distribution on the body of opponents, the back region being the most ...prominent target area. We now report that the distribution of wounds on male intruders produced by male resident Wistar rats in a resident-intruder paradigm, depends on the experimental situation used. Rats solitarily housed in small cages (0.1 m2), produced most wounds (57%) on the upper back, about 14% on the lower back, whereas head and belly were much less bitten. Rats housed in larger cages (0.52 m2) with a female ("territorial situation") produced about 39% of the wounds on the back, equally divided over the anterior and posterior parts. In this situation the head (21%) and the belly (23%) were more frequently bitten than in the other test situations. In a large colony (5.7 m2), practically all wounds were situated dorsally (81%), the majority (58.5%) on the lower part of the back. It was concluded that the distribution of wounds over the body of the intruder was at least partly determined by the possibility of escape.
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