The variances of wind components in Low-Level Jets are mostly non-turbulent
Such winds, or Low-Level Jets (LLJs), are caused by the inertial oscillations emerging due to cease of turbulent mixing after sunset. Numerous measurements of vertical profiles of turbulent mixing within LLJs show contradictory results:some of them suggest decrase of mixing at the jet-core height, others suggest homogeneous mixing through the whole layer of the LLJ. In most of these studies the mixing is associated with observed varialnce of a wind component.
Continuous sodar measurements of wind profiles have been carried out at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics since 2008 in collaboration with Finnish Meteorological Institute.The station is located in a slightly inhomogeneous rural area about 45 km west of Moscow, Russia.
The detailed analysis of variances measured by three beams of the "Latan-3" sodar have shown a significant increase of variances of tilted wind components in zones of wind shear. It was shown that the variances are caused by quazi-regular motions of a sheared layer, rather than by turbulence within it. This conclusion agrees with the observations of decrase of horizontal wind component variations at the LLJ core height, however, it indicates that such a decrease is not connected to turbulence.
The study brings more light on the turbulence within nocturnal LLJ, and will help to better represent them in meteorological models.
More information:
Rostslav Kouznetsov, tel:+358 29 539 4360, rostislav.kouznetsov@fmi.fi
Kallistratova, Margarita A., Rostislav D. Kouznetsov, Valerii F.Kramar, Dmitrii D. Kuznetsov, 2013: Profiles of Wind Speed Variances within Nocturnal Low-Level Jets Observed with a Sodar. J. Atmos.Oceanic Technol., 30, 1970–1977 doi:10.1175/JTECH-D-12-00265.1