Justin Michael Brown

Naval Postgraduate School | NPS · Department of Oceanography

Plain Language Summary In developing numerical models for liquids, such as seawater, it is often necessary to make approximations about some properties of the flow. These approximations can include the degree to which the flow can be compressed, the importance of planetary rotation, the proximity of boundaries, etc. The approximation that the fluid...

Though thermohaline staircases exist in a large fraction of the Arctic halocline, the interactions of such staircases with shear and turbulence are still largely unexplored. We perform a series of three-dimensional Direct Numerical Simulations with and without shear and demonstrate the capacity of shear to disrupt Arctic staircases. We force an osc...

This study explores the behavior of turbulent wakes generated by a sphere propagating with constant speed in a non-uniformly stratified fluid. The investigation is based on a series of high-resolution direct numerical simulations in which the background stratification is systematically varied. We consider one linear and three nonlinear density prof...

Though turbulence is often thought to have universal behavior regardless of origin, it may be possible to distinguish between the types of turbulence generated by different sources. Prior work in turbulence modeling has shown that the fundamental “constants” of turbulence models are often problem-dependent and need to be calibrated to the desired a...

Parameterizations of small-scale mixing are important in modeling the behavior of the World Ocean. These microstructure mixing processes do not exist in isolation, however, and larger-scale processes can affect their fluxes, which is an important consideration for general circulation models. We have developed a new pseudo-spectral hydrodynamic mode...

Arctic staircases mediate the heat transport from the warm water of Atlantic origin to the cooler waters of the Arctic mixed layer. For this reason, staircases have received much due attention from the community, and their heat transport has been well characterized for systems in the absence of external forcing. However, the ocean is a dynamic envi...

This study attempts to identify the equilibration mechanisms of baroclinic instability and investigate the effects of the orientation of the background flow and topography on eddy‐induced transport. The analysis is based on growth rate balance theory, which assumes that nonlinear equilibration occurs when the growth rate of the primary baroclinic i...

The Arctic halocline is generally stable to the development of double-diffusive and dynamic instabilities – the two major sources of small-scale mixing in the mid-latitude oceans. Despite this, observations show the abundance of double-diffusive staircases in the Arctic Ocean, which suggests the presence of some destabilizing process facilitating t...

Minor mixing processes—any fluid processes that mix material or transport heat other than convection or other large-scale flows—play a critical role in stellar evolution. These processes have been invoked through phenomenological models in order to explain away many issues in stellar evolution, such as the blue-red supergiant ratio problem and the...

Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive stars with solar metallicity and masses from 9.0 to 120 M. The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino...

Fingering convection (or thermohaline convection) is a weak yet important kind of mixing that occurs in stably-stratified stellar radiation zones in the presence of an inverse mean-molecular-weight gradient. Brown et al. (2013) recently proposed a new model for mixing by fingering convection, which contains no free parameter, and was found to fit t...

The processes of semi-convection and overshooting convection have been shown to have drastic impacts on the evolution of stars; in particular, the pre-supernova structure of massive stars depends strongly on the mixing prescription of semi-convection used in 1D stellar models. This has a significant impact on the properties of the supernova and the...

We explore the sensitivity of nucleosynthesis in massive stars to the truncation of supernova explosions above a certain mass. It is assumed that stars of all masses contribute to nucleosynthesis by their pre-explosive winds, but above a certain limiting main sequence mass, M BH, the presupernova star becomes a black hole and ejects nothing more. T...

A region of a star that is stable to convection according to the Ledoux criterion may nevertheless undergo additional mixing if the mean molecular weight increases with radius. This process is called fingering (thermohaline) convection and may account for some of the unexplained mixing in stars such as those that have been polluted by planetary inf...

We describe spectroscopic observations of 21 low-mass (<0.45 M_sun) white dwarfs (WDs) from the Palomar-Green Survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction of single, low-mass WDs is <30%. We discuss the potential formation channels for these single star...