The influence of synoptic wind on land–sea breezes

Abstract

Particularly challenging classes of heterogeneous surfaces are ones where strong secondary circulations are generated, potentially dominating the flow dynamics. In this study, we focus on land‐sea breeze circulations (LSBs) resulting from surface thermal contrasts, in the presence of increasing synoptic pressure forcing. The relative importance and orientation of the thermal and synoptic forcings are measured through two dimensionless parameters: a heterogeneity Richardson number (measures the relative strength of geostrophic wind and convection induced by buoyancy), and the angle α between the shore and geostrophic wind. Large eddy simulations reveal the emergence of various regimes where the dynamics are asymmetric with respect to α. Along‐shore cases result in deep LSBs similar to the scenario with no synoptic background, irrespective of the geostrophic wind strength. Across‐shore simulations exhibit a circulation cell that decreases in height with increasing synoptic forcing. However, at the highest synoptic winds simulated, the circulation cell is advected away with sea‐to‐land winds, while a shallow circulation persists for land‐to‐sea cases. Scaling analysis that relates the internal parameters Qshore (net shore volumetric flux) and qshore (net shore advected kinematic heat flux) to the external input parameters results in a succinct model of the shore fluxes that also helps explain the physical implications of the identified LSBs. Finally, the vertical profiles of the shore‐normal velocity and shore‐advected heat flux are used, with the aid of k‐means clustering, to independently classify the LSBs into four regimes (canonical, sea‐driven, land‐driven, and advected), corroborating our visual categorization.This article is protected by copyright. All rights reserved.

How Many Parameters are Needed to Represent Polar Sea Ice Surface Patterns and Heterogeneity?

“…Section 6 will synthesize the findings and outline open questions that can guide future investigations of sea ice heterogeneity. (Baidya Roy, 2002;Bou-Zeid et al, 2004) in convective boundary layers (Courault et al, 2007;Maronga and Raasch, 2013), stable boundary layers (Huang et al, 2011), and coastlines (Allouche et al, 2023) to name a few; see Section 3.6 of Stoll et al (2020). This heterogeneous high-Reynolds number description aptly applies to the MIZ-ABL.…”

“…As a thought experiment, consider an ice-water surface with a very fine checkerboard pattern, and a sea ice fraction of f i = 0.5; this configuration will lead to statistically-homogeneous ice floes that are locally variable at the surface, but are effectively homogeneous in regards to the MIZ-ABL where turbulence will rapidly mix their small-scale signatures (Brutsaert, 2005;Mahrt, 2000;Bou-Zeid et al, 2004). However, two large patches of sea ice and water (meso-α heterogeneity, see Bou-Zeid et al (2020)), also with a sea ice fraction of f i = 0.5, will develop a large circulation closer to that of a sea breeze due to the abrupt transition between two large homogeneous surfaces (Porson et al, 2007;Crosman and Horel, 2010;Allouche et al, 2023). The dynamics and thermodynamics in this MIZ-ABL system, and the surface exchange therein, will thus be quite different over these two patterns even if the some key surface properties, e.g.…”

Unsteady Land-Sea Breeze Circulations in the Presence of a Synoptic Pressure Forcing

“…These include: (i) the transient difference Δθ(t) between land surface temperature θ L and sea surface temperature θ s and its natural time scale (usually 24 hours), (ii) the speed (M g ) and direction (α) of the synoptic pressure gradient forcing, (iii) the latitude as it influences the Coriolis parameter f and the associated time scale of inertial oscillations, (iv) land and sea roughness lengths for momentum and for heat, (v) land topography, and (vi) the height of the inversion and its strength. This vast parameter space prompted the authors of this manuscript submitted to Journal of Geophysical Research: Atmospheres 4 study to propose a reduction to a set of non-dimensional parameters (Allouche, Bou-Zeid, et al, 2023) to facilitate generalization of the physical findings and to guide numerical and experimental studies. In that prequel paper, we focused on analyzing the competing effects of synoptic forcing and thermal contrast under steady state conditions, identifying several distinct regimes of the LSBs and notable asymmetry in the synoptic effect when the geostrophic wind blew from land-to-sea or vice versa.…”

“…In this paper, we consider the same numerical setup introduced in (Allouche, Bou-Zeid, et al, 2023) for steady thermal contrasts, but here we account for the transient diurnal cycle of the surface temperature contrasts between land and sea Δθ(t) = θ L (t) -θ S . As the expression suggests, we impose a constant sea surface temperature (θ S ) and a timevarying land surface temperature (θ L (t)), while also including a constant synoptic pressure forcing.…”

Estimating scalar turbulent fluxes with slow-response sensors in the stable atmospheric boundary layer

“…For example, a constant flux surface layer that requires stationarity, planar homogeneity, absence of subsidence, and a high Reynolds number state may not be well established for surface flux measurements under stable conditions. The challenges are exacerbated by surface heterogeneity, such as over surfaces with mixed water and sea ice in polar regions that can accelerate the exchanges of gases, aerosols, and energy between the ocean surface and the atmosphere (Sharma et al, 2012;Fogarty and Bou-Zeid, 2023), and semi-infinite heterogeneity patches e.g., land-sea interfaces (Allouche et al, 2023). These observational challenges then propagate into theoretical and modeling considerations, prompting the need for improved estimates of scalar fluxes under stable conditions.…”