Aircraft observations of the mean and turbulent structure of the atmospheric boundary layer during spring in the central Arctic

Autor: Bernard A. Walter, James E. Overland
Rok vydání: 1991
Předmět:
Zdroj: Journal of Geophysical Research. 96:4663
ISSN: 0148-0227
DOI: 10.1029/90jc02263
Popis: The NOAA P-3 research aircraft carried out measurements of the mean and turbulence structure of the planetary boundary layer on March 27 and 30, 1989, at 83°N, 10°E in the central Arctic. The ice motion was strongly decoupled from the atmosphere; surface winds were 2–3 m s−1 and winds at 100 m were 10 to 12 m s−1 on March 27 and 8 m s−1 on March 30. Geostrophic drag coefficients were 0.014 and 0.015. The mean vertical structure on both days is characterized by a shallow slightly stable layer ∼50 m deep at the surface with a 300-m-deep strong inversion above. Speed shear was 0.1 s−1 in the slightly stable layer and direction shear at the top of the layer was 15°–20° on March 27 and 35°–40° on March 30. Profiles of the Richardson number for each day showed that Ri was less than 0.25 in the slightly stable layer and rapidly increased above. A low level jet was located at the top of the slightly stable layer just below the level where the Richardson number became very large. Shear-induced turbulence at the top of the slightly stable layer resulted in a maximum of turbulence kinetic energy just below the wind maximum on March 27 and at the wind maximum on March 30. Heat flux profiles from the gust probe measurements showed a maximum of upward flux at the top of the slightly stable layer of 9 W m−2, implying that the flux was countergradient. This upward flux was responsible for maintaining the strength of the inversion above this level. Spectra of turbulent vertical velocity showed a peak at a wavelength of 350–400 m. The source of this peak is gravity waves from an upper level shear layer. It is speculated that the observed countergradient flux was a result of gravity waves and/or wave-turbulence eddy flux. Use of an E-e turbulence closure model allowed an estimation of the sensible heat flux from the air to the snow surface of 4 W m−2. This surface flux played only a secondary role in cooling the surface layer and establishing the structure of the boundary layer compared to inversion layer processes.
Databáze: OpenAIRE
Externí odkaz: