Abstract
AbstractOver 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 turbulence, 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 (including cities). The paper closes with a brief summary, some lessons learned, and a look to the future.
Highlights
How do we define the atmospheric boundary layer (ABL)? Here are some definitions from textbooks:‘‘that part of the troposphere that is directly influenced by the presence of the earth’s surface, and responds to surface forcings with a timescale of about an hour or less’’ (Stull 1988, p. 2).‘‘the layer of air directly above the earth’s surface in which the effects of the surface are felt directly on time scales less than a day, and in which ‘‘lowest kilometer’’ or ‘‘lowest portion of the atmosphere, which intensively exchanges heat as well as mass and momentum with the earth’s surface’’ (Sorbjan 1989, p. 1).The time scales in these definitions are fundamental, but vary by an order of magnitude, a function of context and application
Many scientists recognized that the winds in the boundary layer could be represented by some form of the Ekman spiral; that the virtual potential temperature uy was well mixed during the day, and that radiative cooling at night led to a deepening temperature inversion
As measuring techniques improved to allow sampling of turbulence quantities, we were able to quantify vertical transport of heat and momentum so that, by midcentury, Monin– Obukhov similarity theory provided a framework under which we could relate those fluxes to their corresponding mean profiles
Summary
BRETHERTON,d FEI CHEN,a JIMY DUDHIA,a EVGENI FEDOROVICH,e KRISTINA B. PATTON,a JIELUN SUN,a,h MICHAEL TJERNSTRÖM,i AND JEFFREY WEILa a National Center for Atmospheric Research, Boulder, Colorado b CIRES, University of Colorado, Boulder, Boulder, Colorado c NOAA ESRL, Chemical Sciences Division, Boulder, Colorado d Department of Atmospheric Sciences, University of Washington, Seattle, Washington e School of Meteorology, University of Oklahoma, Norman, Oklahoma f NorthWest Research Associates, Whidbey Island, Washington g NorthWest Research Associates, Corvallis, Oregon h NorthWest Research Associates, Boulder, Colorado i Department of Meteorology, and Bolin Centre for Climate Research, Stockholm University, Sweden
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