Realistic simulations of Central California reveal interactions between shoaling internal tidal bores and submesoscale currents on the inner-shelf (30-60 m depth). These interactions comprise collisions between internal tidal upwelling, ‘forward’ bores (FBs) with submesoscale currents (SMCs) in the form of surface layer density fronts or filaments with downwelling secondary circulation. Along-shore oriented FBs collide with both cross-shore (perpendicular interaction) or along-shore (parallel interaction) oriented SMCs. In perpendicular interaction, FBs colliding into cross-shore oriented SMCs refract around the offshore tip of the downwelling front or filament. SMCs generally survive perpendicular interaction, despite partial disruption of downwelling secondary circulation by FBs. An example of parallel interaction demonstrates (1) blocking of FB propagation by elevated mixing and dense filament formation on the inner-shelf and (2) the subsequent destruction of the dense filament coincident with a decrease in vertical mixing and FB propagation underneath it. For both perpendicular and parallel interaction, FB propagation is modulated by a varying medium introduced by SMC density and current structure. The computational evidence of these interactions corroborates recent observations of interactions between small-scale, nearshore currents in the real ocean. This study motivates further exploration of interactions between fronts, filaments, internal tidal bores, and vortices in the nearshore.

The science guiding the \EURECA campaign and its measurements are presented. \EURECA comprised roughly five weeks of measurements in the downstream winter trades of the North Atlantic — eastward and south-eastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, \EURECA marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or, or the life-cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso (200 km) and larger (500 km) scales, roughly four hundred hours of flight time by four heavily instrumented research aircraft, four global-ocean class research vessels, an advanced ground-based cloud observatory, a flotilla of autonomous or tethered measurement devices operating in the upper ocean (nearly 10000 profiles), lower atmosphere (continuous profiling), and along the air-sea interface, a network of water stable isotopologue measurements, complemented by special programmes of satellite remote sensing and modeling with a new generation of weather/climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that \EURECA explored — from Brazil Ring Current Eddies to turbulence induced clustering of cloud droplets and its influence on warm-rain formation — are presented along with an overview \EURECA’s outreach activities, environmental impact, and guidelines for scientific practice.

The connections between Greenland’s tidewater glaciers and the continental shelf waters are modulated by fjords that are geometrically complex with numerous modes of variability. These fjords transport heat towards the glaciers and meltwater away, with a renewal determined by a range of factors including buoyancy forcing at the surface (surface melt) and at depth (subglacial discharge), wind stresses, shelf currents, bathymetry, and mixing processes. This study aims to classify the various regimes of flow and fjord renewal over the diverse parameter space of Greenland fjords with an emphasis on investigating the role of shelf-driven variability and mixing. We conduct idealized numerical simulations using MITgcm to explore how fjord renewal is controlled by elements of the shelf and fjord geometry, and by thermodynamic and mechanical forcings, with domains consisting of idealized bays and shelves representative of Greenland. Specifically, we investigate the sensitivity of the renewal to the following dynamic/thermodynamic influences: (a) bathymetric sills and their influence on mixing, (b) horizontal constrictions (peninsulas, islands, turns), (c) ice cover, and (d) subglacial meltwater discharge. To explain our numerical model results, we develop dynamical theories for the exchange flow as a function of the geometric and forcing parameters.

Fjord circulation modulates the connection between marine-terminating glaciers and the ocean currents offshore. These fjords exhibit both overturning and horizontal recirculations, which are driven by water mass transformation at the head of the fjord via subglacial discharge plumes and distributed meltwater plumes. However, little is known about the interaction between the 3D fjord circulation and glacial melt and how relevant fjord properties influence them. In this study, high-resolution numerical simulations of idealized glacial fjords demonstrate that recirculation strength controls melt, which feeds back on overturning and recirculation. The overturning circulation strength is well predicted by existed plume models for face-wide melt and subglacial discharge, while relationships between the overturning, recirculation, and melt rate are well predicted by vorticity balance, reduced-order melt parameterizations, and empirical scaling arguments. These theories allow improved predictions of fjord overturning, recirculation, and glacial melt by taking intrafjord dynamics into account.

The modeling of physical phenomena oftentimes leads to partial differential equations (PDEs) that are usually nonlinear and can also be subject to various uncertainties. Solutions of such equations typically involve multiple spatial and temporal scales, which can be numerically expensive to fully resolve. On the other hand, for many applications, it is large-scale features of the solutions that are of primary interest. The closure problem of a given PDE system seeks essentially for a smaller system that governs to a certain degree the evolution of such large-scale features, in which the small-scale effects are modeled through various parameterization schemes. 
 We will present an approach to parameterize the unresolved small-scale dynamics using the resolved large scales for forced dissipative systems. We will show that efficient parameterizations can be explicitly determined as parametric deformations of geometric objects constructed from dynamically based analytical formulas. The minimizers are intimately tied to the conditional expectation of the original system. We will highlight, within a variational framework, a simple semi-analytic approach to determine such parameterizations based on backward-forward auxiliary systems and short solution data. Concrete examples arising from geophysical considerations will also be presented to illustrate the effectiveness of the approach.