The Mellor‐Yamada level‐2 and 2 1/2, Niiler, and Garwood one‐dimensional mixed‐layer models were compared for some simple forcing experiments and were tested by simulating changes in the mixed layer at ocean stations November and Papa for the year 1961. The ocean station simulations show that the models can be tuned to give fairly good results. However, the need to readjust model constants when changing locations suggests that there is room for improving some of the mixing parameterizations. The sensitivity of the model simulations to certain “external” parameterizations, including surface heat flux, seawater turbidity, and ambient diffusivity below the mixed layer, was investigated. The year‐long simulations were found to be very sensitive to the seawater turbidity. Increasing the turbidity from Jerlov optical type I to type III causes a maximum increase in the monthly mean SST at November of 3°C or more. The simulations are most sensitive to seawater turbidity during summer when the mixed‐layer remains shallow. For the ambient diffusivity a decrease from 0.4 to 0.01 cm2/s results in a maximum increase in the monthly mean SST at November and Papa of 0.5 and 1.5°C, respectively. The effects of using a constant ambient diffusivity are most noticeable in late summer when the seasonal thermocline is strongest. The effects are larger at Papa than at November because of the stronger summer seasonal thermocline at Papa. Best results at November and Papa were obtained by using the observed optical water types (I and II, respectively) and relatively small values for ambient diffusivity (less than 0.2 cm2/s).

Quantum mechanics hinders our ability to determine the state of a physical system in two ways: individual measurements provide only partial information about the observed system (because of Heisenberg uncertainty), and measurements are themselves invasive-meaning that little or no refinement is achieved by further observation of an already measured system. Theoretical methods have been developed to maximize the information gained from a quantum measurement while also minimizing disturbance, but laboratory implementation of optimal measurement procedures is often difficult. The standard class of operations considered in quantum information theory tends to rely on superposition-basis and entangled measurements, which require high-fidelity implementation to be effective in the laboratory. Here we demonstrate that real-time quantum feedback can be used in place of a delicate quantum superposition, often called a 'Schrödinger cat state', to implement an optimal quantum measurement for discriminating between optical coherent states. Our procedure actively manipulates the target system during the measurement process, and uses quantum feedback to modify the statistics of an otherwise sub-optimal operator to emulate the optimal cat-state measurement. We verify a long-standing theoretical prediction and demonstrate feedback-mediated quantum measurement at its fundamental quantum limit over a non-trivial region of parameter space.

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[1] A numerical simulation of the Gulf of Mexico (GoM) using the Navy Coastal Ocean Model (NCOM) is used to identify the pathways by which fresh water discharged by major rivers in the northern Gulf is exported away from the region. The NCOM, a new primitive equation ocean model with a hybrid sigma/geopotential level vertical coordinate, is described along with its application to the GoM region. Trajectories from surface drifters are analyzed to show evidence of the seasonally shifting alongshore and crossshelf transport in the region. The model results are used to determine the preferred locations and times of year for cross-shelf and along-shelf export of low-salinity water from the northern GoM. The annual cycle of local wind stress plays an important role in shifting the export pathway of the fresh water discharged from the major rivers (primarily the Mississippi River) toward the east in the spring/summer, where it can be transported offshore by the currents associated with deep ocean mesoscale eddies, and toward the west in the fall/winter, where it is transported southward along the Mexican coastline as a coastally trapped current.