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The interactions among several stable-boundarylayer (SBL) processes occurring just after the evening transition of 2 July 2011 have been analysed using data from instruments deployed over the area of Lannemezan (France) during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. The near-calm situation of the afternoon was followed by the formation of local shallow drainage flows (SDFs) of less than 10m depth at different locations. The SDF stage ended with the arrival of a stronger wind over a deeper layer more associated with the mountain-plain circulation, which caused mixing and destruction of the SDFs. Several gravity-wave-related oscillations were also observed on different time series. Wavelet analyses and wave parameters were calculated from high resolution and accurate surface pressure data of an array of microbarometers. These waves propagated relatively long distances within the SBL. The effects of these phenomena on turbulent parameters (friction velocity and kinematic heat flux) have been studied through multi-resolution flux decomposition methods performed on high frequency data from sonic anemometers deployed at different heights and locations. With this method, we were able to detect the different time-scales involved in each turbulent parameter and separate them from wave contributions, which becomes very important when choosing averaging-windows for surface flux computations using eddy covariance methods. The extensive instrumentation allowed us to highlight in detail the peculiarities of the surface turbulent parameters in the SBL, where several of the noted processes were interacting and producing important variations in turbulence with height and between sites along the sloping terrain., Gobierno de España, INSU-CNRS (Institut National des Sciences de l'Univers, Centre national de la Recherche Scientifique, LEFE-IDAO program), Meteo-France, Observatoire Midi-Pyrenees (University of Toulouse), EUFAR (EUropean Facility for Airborne Research), European Cooperation in Science and Technology (COST), Unión Europea, Centre National de la Recherche Scientifique (CNRS), German Research Foundation (DFG), Netherlands Organization for Scientific Research (NWO), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

We analyze approximately four years of heat-flux measurements at two levels, profiles of air temperature, and multiple measurements of the water temperature collected at a coastal zone site. Our analysis considers underestimation of the sea-surface flux due to vertical divergence of the heat flux between the surface and the lowest flux level. We examine simple relationships of the heat flux to the wind speed and stratification and the potential influence of fetch and temperature advection. The fetch ranges from about 4 km to near 400 km. For a given wind-direction sector, the transfer coefficient varies only slowly with increasing instability, but decreases significantly with increasing stability. The intention here is not to recommend a new parameterization but rather to establish relationships that underly the bulk formula that could lead to assessments of uncertainty and improvement of the bulk formula.

Motivated by previous studies, we examine the underestimation of the sea surface stress due to the stress divergence between the surface and the atmospheric observational level. We analyze flux measurements collected over a 6-yr period at a coastal tower in the Baltic Sea encompassing a wide range of fetch values. Results are posed in terms of the vertical divergence of the stress scaled by the stress at the lowest observational level. The magnitude of this relative stress divergence increases with increasing stability and decreases with increasing instability, possibly partly due to the impact of stability on the boundary layer depth. The magnitude of the relative stress divergence increases modestly with decreasing wave age. The divergence of the heat flux is not well correlated with the divergence of the momentum flux evidently due to the greater influence of advection on the temperature. Needed improvement of the conceptual framework and needed additional measurements are noted.

A number of studies have indicated that non-stationarity of the wind field over the sea significantly disrupts the equilibrium between the wind, stress, and wave fields. However, no studies have systematically examined the impact of non-stationarity using a large dataset. Here, we examine the effect of non-stationarity of the wind field on the stress by analyzing six years of turbulent flux data from the Östergarnsholm site. On average, the impact of the non-stationarity on the stress and drag coefficient becomes important for wind speeds lessthan about 6 ms-1. Differences between the acceleration and deceleration stages are revealed by phase shifting the calculation of the non-stationarity with respect to the calculation of the stress and drag coefficient. The time structure of events is examined by selecting samples of large increases and decreases of the wind speed. Analyses needed for further progress are noted., Larry Mahrt was supported by the U.S. Office of Naval Research through Awards N00014-16-1-2600 and N00014-19-1-2469.

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1533-1541, doi:10.1175/JPO-D-17-0267.1., Our study analyzes measurements primarily from two Floating Instrument Platform (FLIP) field programs and from the Air–Sea Interaction Tower (ASIT) site to examine the relationship between the wind and sea surface stress for contrasting conditions. The direct relationship of the surface momentum flux to U2 is found to be better posed than the relationship between and U, where U is the wind speed and is the friction velocity. Our datasets indicate that the stress magnitude often decreases significantly with height near the surface due to thin marine boundary layers and/or enhanced stress divergence close to the sea surface. Our study attempts to correct the surface stress estimated from traditional observational levels by using multiple observational levels near the surface and extrapolating to the surface. The effect of stability on the surface stress appears to be generally smaller than errors due to the stress divergence. Definite conclusions require more extensive measurements close to the sea surface., This work was supported by the U.S. Office of Naval Research through Award N00014-16-1-2600. We, 2019-01-10

Over the last 100 years, boundary layer meteorology grew from the subject of mostly near-surface observations to a field encompassing diverse atmospheric boundary layers (ABLs) around the world. From the start, researchers drew from an ever-expanding set of disciplines—thermodynamics, soil and plant studies, fluid dynamics and tur-bulence, cloud microphysics, and aerosol studies. Research expanded upward to include the entire ABL in response to the need to know how particles and trace gases dispersed, and later how to represent the ABL in numerical models of weather and climate (starting in the 1970s–80s); taking advantage of the opportunities afforded by the development of large-eddy simulations (1970s), direct numerical simulations (1990s), and a host of instruments to sample the boundary layer in situ and remotely from the surface, the air, and space. Near-surface flux-profile relationships were developed rapidly between the 1940s and 1970s, when rapid progress shifted to the fair-weather convective boundary layer (CBL), though tropical CBL studies date back to the 1940s. In the 1980s, ABL research began to include the interaction of the ABL with the surface and clouds, the first ABL parameterization schemes emerged; and land surface and ocean surface model development blossomed. Research in subsequent decades has focused on more complex ABLs, often identified by shortcomings or uncertainties in weather and climate models, including the stable boundary layer, the Arctic boundary layer, cloudy boundary layers, and ABLs over heterogeneous surfaces (in-cluding cities). The paper closes with a brief summary, some lessons learned, and a look to the future. © 2019 American Meteorological Society.