Turbulent Helicity and Potential Vorticity in Lower 25 meters of Atmosphere

Abstract:

The measuring procedure developed and results obtained as related to turbulent flux of vorticity <u_iω_j> and to covariation <ω_iG_j> between vorticity and temperature gradient Gi=∂T/∂x_i.The sum of the diagonal element of this matrix in Boussinesq approximation is proportional to potential vorticity.

 The main instrument used was set of 4 acoustical anemometer–termometer Gill as situated in the corners of rectangular tetrahedron. It was placed at the top of mast of variable height (3.5–25m).The base distance between sensors was equal to 0.7 m. The measurements were carried out of total duration near 100 hours both in stable and unstable stratification (at the Tsimlyansk Scientific Station in a uniform area of virgin steppe 700 x 650 m, August 2014).

 The correlation–covariation matrix was calculated between 10 parameters: u_i,ω_j,G_k,T. It turned out that sum of horizontal components of helicity <u₁ω₁+u₂ω₂> has negative sign, but for the vertical helicity <u₃ω₃> – positive. As a rule the absolute value of correlation coefficients related to all terms of the sum u_iω_i do not exceed 0.1. Correlations related to all other elements of turbulent flux of vorticity are few times more (in absolute value).

 The cospectra related to turbulent flux of vorticity and to all other mentioned above variables have been calculated in the frequency band of 10^-3-10 Hz. The maximal contribution into integral covariations supplies frequency band around 10^-1 Hz.

This work was supported by the Russian Science Foundation (Project No 14-27-00134).