Unravelling the turbulent structures of temperature variations during a gust front event: a case study
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Unravelling the turbulent structures of temperature variations during a gust front event: a case study Subharthi Chowdhuri1 · Kiran Todekar1 · Palani Murugavel1 · Anandakumar Karipot2 · Thara V. Prabha1 Received: 11 June 2020 / Accepted: 14 September 2020 © Springer Nature B.V. 2020
Abstract The simultaneous observations from a Doppler weather radar and an instrumented micrometeorological tower, offer an opportunity to dissect the effects of a gust front on the surface layer turbulence in a tropical convective boundary layer. We present a case study where a sudden drop in temperature was noted at heights within the surface layer during the passage of a gust front in the afternoon time. Consequently, this temperature drop created an interface which separated two different turbulent regimes. In one regime the turbulent temperature fluctuations were large and energetic, whereas in the other regime they were weak and quiescent. Given its uniqueness, we investigated the size distribution and aggregation properties of the turbulent structures related to these two regimes. We found that, the size distributions of the turbulent structures for both of these regimes displayed a clear power-law signature. Since power-laws are synonymous with scale-invariance, this indicated the passing of the gust front initiated a scale-free response which governed the turbulent characteristics of the temperature fluctuations. We propose a hypothesis to link such behaviour with the self-organized criticality as observed in the complex systems. However, the temporal organization of the turbulent structures, as indicated by their clustering tendencies, differed between these two regimes. For the regime corresponding to large temperature fluctuations, the turbulent structures were significantly clustered, whose clustering properties changed with height. Contrarily, for the other regime where the temperature fluctuations were weak, the turbulent structures remained less clustered with no discernible change being observed with height. Keywords Clustering · Convective surface layer · Gust front · Size distribution · Turbulent structures
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1065 2-020-09769-z) contains supplementary material, which is available to authorized users. * Subharthi Chowdhuri [email protected] 1
Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Dr. Homi Bhaba Road, Pashan, Pune 411008, India
2
Savitribai Phule Pune University, Ganeshkhind, Pune 411007, India
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Environmental Fluid Mechanics
1 Introduction Gust fronts are a typical phenomenon associated with convective outflows from thunderstorms that are growing in a relatively dry environment [17, 35, 48]. The evaporative cooling of rain and the associated downdrafts initiate the cold pool, which introduces cold and moist air into the dry and sub-saturated boundary layer. As the moist air interfaces with the dry surrounding air, the density differences betwee
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