The dynamical behaviour of the lifted temperature minimum

Ragothaman, S. and Narasimha, R. and Vasudeva Murthy, A.S. (2001) The dynamical behaviour of the lifted temperature minimum. Il nuovo cimento C, 24 C (3). pp. 353-376. ISSN 1826-9885

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Thispap er concernsa phenomenon called the RamdasP aradox by Lettau, referring to the occurrence of a minimum in the temperature some decimetres above ground on calm clear nights. Recently, Vasudeva Murthy, Srinivasan and Narasimha have proposed a theory that successfully reproduces the observed minima. We extend that work here to investigate the time evolution of near-ground temperature distributions through numerical simulations. It is demonstrated that, if the surface emissivity is not too close to unity, a lifted temperature minimum can appear shortly after sunset, but its subsequent evolution, depending strongly on ground cooling rate, can lead to i) monotonic growth, ii) near-steady state, or iii) growth followed by collapse. Solutions of the model to an appropriately formulated “turbulent transport episode” reveal that the lifted temperature minimum disappears after the commencement and reappears after the cessation of the gust in times of order 10–20 s, in qualitative agreement with the observations of Raschke. However, full recovery to the no-gust state takes times of order 103 safter the episode. This behaviour is identified with a two-time response of the cold layer, involving a quick radiative adjustment followed by a slow diffusive relaxation. It is concluded that the VSN model fully reproducesthe observed dynamical behaviour of the lifted temperature minimum, and provides a satisfactory basis for the study of the near-ground thermal environment.

Item Type: Article
Uncontrolled Keywords: Boundary layer structure and processes ; Reactive, radiative, or nonequilibrium flows
Subjects: 500 Scienze naturali e Matematica > 550 Scienze della Terra > 551 Geologia, Idrologia, Meteorologia
Depositing User: Marina Spanti
Date Deposited: 10 Mar 2020 18:33
Last Modified: 10 Mar 2020 18:33

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