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Western boundary currents (WBCs) modulate the global climate and dominate regional ocean dynamics. Despite their importance, few direct comparisons of the kinematic structure of WBCs exist, due to a lack of equivalent sustained observational data sets. Here we compare multiyear, high‐resolution observations (1 km, hourly) of surface currents in two WBCs (Florida Current and East Australian Current) upstream of their separation point. Current variability is dominated by meandering, and the WBCs exhibit contrasting time‐mean velocities in a Eulerian coordinate frame. By transforming to a jet‐following coordinate frame, we show that the time‐mean surface velocity structure of the WBC jets is remarkably similar, considering their distinct local wind, bathymetry, and meandering signals. Both WBCs show steep submesoscale kinetic energy wavenumber spectra with weak seasonal variability, in contrast to recent findings in other ocean regions. Our results suggest that it is the mesoscale flow field that controls mixing and ocean dynamics in these regions. Western boundary currents (WBCs) are warm, strong currents that flow along the western sides of the world's ocean basins. They dominate the climate and ecology of some of the most densely populated coastlines on Earth. Considering their importance, there is surprisingly little knowledge of how different WBCs compare. In this paper we use high‐resolution measurements to study the mean structure and variability of two WBCs, in the North Atlantic and South Pacific, and show that while they differ in their variability, they are remarkably similar in their time‐mean. We discovered this by transforming the coordinate frame in which we viewed them, so that the variability of the meandering currents does not affect the mean calculation. We quantify the amount of variability at different spatial scales and show that for these WBC regions, variability is dominated by the large‐scale flow field, with no seasonal cycle at the smaller scales, in contrast to studies of other ocean current regimes. These high‐resolution results provide an updated view of WBC systems globally and can be used by numerical modelers to evaluate the performance of their models, helping to improve forecasts of a changing climate. Multiyear surface velocity data of the Florida Current and East Australian Current are compared at 1 km/1 hr scales with high frequency radarDespite contrasting local wind, bathymetry, and meandering, the time‐mean structure of their jet speed and lateral shear are almost identicalEddy kinetic energy submesoscale wavenumber spectra are steep, with weak seasonal variability across both upstream western boundary currents

Marine heatwaves (MHWs) are becoming more common with record events occurring around the world and unprecedented biological impacts including mass mortality and habitat shifts. However, little is known about the statistical characteristics of MHWs due to the lack of long‐term in situ observations. Using two historical data sets spanning from 1953 (and 1992) to 2016, we use a seasonally varying climatology and temperature anomalies to identify and characterize MHW events down to 100 m depth in coastal waters off southeastern Australia. We show that MHWs regularly extend the full depth of the water column, with a maximum intensity below the surface. Extreme temperatures at depth are driven by local downwelling favorable winds that mix the water column and reduce the stratification. These results show the importance of considering subsurface hydrography and that sea surface temperature is insufficient to fully understand MHWs which are having disastrous ecological consequences in coastal regions globally. We present the first subsurface analysis of coastal MHWs (marine heatwaves) using a 60+ year data setMHWs regularly extend to the seafloor mostly during weak stratification driven by downwelling windsMHWs are most intense at depth, indicating a pressing need for more subsurface temperature records

The East Australian Current (EAC) dominates the ocean circulation along south-eastern Australia, however, little is known about the submesoscale frontal instabilities associated with this western boundary current. One year of surface current measurements from HF radars, in conjunction with mooring and satellite observations, highlight the occurrence and propagation of meanders and frontal eddies along the inshore edge of the EAC. Eddies were systematically identified using the geometry of the high spatial resolution (~1.5 km) surface currents, and tracked every hour. Cyclonic eddies were observed irregularly, on average every 7 days, with inshore radius ~10 km. Among various forms of structures, frontal eddies associated with EAC meanders were characterized by poleward advection speeds of ~0.3–0.4 m/s, migrating as far as 500 km south, based on satellite imagery. Flow field kinematics show that cyclonic eddies have high Rossby numbers (0.6–1.9) and enhance particle dispersion. Patches of intensified surface divergence at the leading edge of the structures are expected to generate vertical uplift. This is confirmed by subsurface measurements showing temperature uplift of up to 55 m over 24 h and rough estimates of vertical velocities of 10s of meters per day. While frontal eddies propagate through the radar domain independently of local wind stress, upfront wind can influence their stalling and growth, and can also generate large cold core eddies through intense shear. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal or deep waters, influencing physical and biological dynamics, and connectivity over large distances. Cyclonic eddies occur frequently along the East Australian Current (30°S) on average every 7 days over a 12 month periodFrontal eddies with high Rossby number (0.6–1.9) and inshore radius ~10 km propagate downstream all year round at 0.3–0.4 m/sCyclonic frontal eddies influence biology through vertical uplift favoring local production or entrainment of productive water over 100s of km

Mesoscale cyclonic eddies are known to be highly productive. Less well‐known are the dynamics and productivity of smaller cyclonic eddies, known as frontal eddies, that form on the landward side of western boundary currents. In this study, we investigate the physical and biogeochemical properties of two contrasting cyclonic eddies in the East Australian Current (EAC). The first (“Murphy”), a mesoscale cyclonic eddy that formed at ∼28°S with a diameter of ∼160 km and high surface chlorophyll‐a concentrations, which lived ∼47 days. The second (“Freddy”), a smaller frontal eddy (∼35 km diameter) that formed from a shelf water billow ∼7 days prior to sampling at ∼31.5°S and was advected off the shelf along the EAC front (from ∼200 m to 4000 m of water). Both eddies were at least 1000 m deep with a similar steric height anomaly. We introduce and employ “the method of closest approach” using shipboard ADCP velocities to estimate the eddy centers, which reveals significant tilting through the water column. We estimate rotation rates of 4–10 days and 1–9 days and Rossby numbers 0.25–0.1 and 0.6–0.1, from the surface to 600 m for Murphy and Freddy, respectively. High‐resolution altimetry measurements from the SARAL/AltiKA satellite provide estimates of the ageostrophic component of rotation. Our results show that the frontal eddy is significantly more ageostrophic, energetic, and productive than the mesoscale cyclone, despite its small size and short life (∼4 weeks). We suggest that frontal eddies have potential to contribute significantly to the net productivity of the Tasman Sea region. We present the first depth observations of a small cold core eddy which formed along the landward front of the East Australian Current. We contrast the observations with a typical larger cold core eddy. The observations were collected from a dedicated cruise aboard a research vessel. We show that this small Frontal Eddy is very dynamic feature. It rotates rapidly, extends to more than 1000 m in depth and is highly productive. We believe these features make a significant contribution to the productivity of western boundary current regions. We contrast a suite of 3‐D observations of a cyclonic frontal eddy (∼35 km), and a mesoscale cyclonic eddy (∼160 km) in the Tasman SeaThe frontal eddy was short lived (∼ 4 weeks), deep (∼1000 m), highly ageostrophic, and dynamic. Both eddies were tiltingBoth eddies were productive, however the productivity of the frontal eddy which formed on the shelf was proportionately higher

In this paper we present MGtoolkit: an open-source Python package for implementing metagraphs - a first of its kind. Metagraphs are commonly used to specify and analyse business and computer-network policies alike. MGtoolkitcan help verify such policies and promotes learning and experimentation with metagraphs. The package currently provides purely textual output for visualising metagraphs and their analysis results.

In this paper we presents a martingale method for analysing queues of M/G/1 type, which have been generalised so that the system passes through a series of phases on which the service behaviour may differ. The analysis uses the process embedded at departures to create a martingale, which makes possible the calculation of the probability generating function of the stationary occupancy distribution. Specific examples are given, for instance, a model of an unreliable queueing system, and an example of a queue-length-threshold overload-control system.

Temperature data collected in the shallow, tidally isolated reef flat/lagoon of Lady Elliot Island off Queensland, Australia, show marked variability under solar and tidal forcing. Sea level drops below the height of the protective lagoon rim for a few hours during low tide, effectively isolating the remaining water. Because the lagoon is shallow, its temperature change (from diurnal solar forcing and cooling) is amplified. We develop a simple analytical model to predict the time evolution of mean lagoon temperature, beginning with a well‐mixed control volume. This approach highlights the asymmetric flood/ebb physics of tidally isolated lagoons. After discussing the response of this model, we compare it with results from two idealized numerical simulations that illustrate differing aspects of lagoon temperature variability under “potential flow” and “prevailing current” situations. The conceptual model captures the essence of lagoon temperature variability and underscores the importance of solar‐lunar phasing. However, because of the well‐mixed assumption, it cannot reproduce sudden temperature transitions associated with new incoming water masses. Observations show that a slowly progressing thermal wave inundates the lagoon on rising tides. This wave is similar to our “potential flow” simulation in that it is approximately radially symmetric. On the other hand, it appears to advectively replace resident lagoon water, similar to our “prevailing current” simulations. We attempt to account for this behavior with a simple “frontal” modification to our conceptual model. Results show that this frontal model is able to capture the sudden temperature transitions present in the data and offers improved predictive capabilities over the well‐mixed model.