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Temperature auto‐correlation and spectra functions in low‐wind meandering conditions
Author(s) -
Mortarini L.,
Maldaner S.,
Moor L. P.,
Stefanello M. B.,
Acevedo O.,
Degrazia G.,
Anfossi D.
Publication year - 2016
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2796
Subject(s) - anemometer , wind speed , spectral line , turbulence , eulerian path , atmospheric sciences , physics , field (mathematics) , meteorology , environmental science , geology , mathematics , lagrangian , astronomy , pure mathematics , mathematical physics
In quiet, clear sky conditions at night a remarkable feature may occur with respect to the wind near the surface. Like river flows, the wind may spontaneously start to meander without need for a specific trigger to initiate such motion. In addition to this regular and ‘slow’ motion, air parcels also experience chaotic motion due to weak background turbulence. Besides wind, temperature is also affected. The slow and regular response of temperature can be separated from its fast chaotic response, by plotting the ‘temperature variance’ as a function of frequency (black line, see Figure). At low frequencies a peak is found, as a signature of the aforementioned meandering motion. The red curve represents a theoretical fit. The gray line represents corresponding fluctuations of vertical wind velocities. The observational data consist of high‐frequency temperature and wind measurements from a sonic anemometer operated at 5m above the surface near the city of Turin, Italy.