Investigation of a sea breeze front in an urban environment

In this study, we examine the dynamics of a sea breeze front interacting with the heavily urbanized New York City area. In addition, we investigate the impact of the urban-influenced sea breeze front on transport and diffusion of simulated passive tracer plumes. We employ the U. S. Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS„µ) to perform a multiply nested simulation with data assimilation for the sea breeze event of 9 August 2004. Available surface and upper-air observations are used to validate the simulation. We also perform a sensitivity study in which the urban influence is removed (no-urban). The sea breeze front has characteristics of a density current, including an elevated head at the leading edge. The density current moves slowly and un-evenly across the city. Kelvin-Helmholtz billows form in the region of the density current head and the results show evidence of the occurrence of Kelvin-Helmholtz instability (KHI). The density current head is greatly elevated due to the enhanced surface roughness of the urban area; in the no-urban simulation, the head of the density current is not elevated to the same degree and KHI does not occur in this simulation. The sea breeze/density current has a large impact on transport and diffusion of simulated tracer plumes, not only changing the direction of plume motion due to the wind shift but also redistributing tracer material in the vertical so as to produce dramatic, rapid changes in near surface concentration as the front passes.