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SUMMARY:Turbulence characteristics of non-neutral/ non-stationary flows in
  the atmospheric surface layer - Xiaojing Zheng (Chinese Academy of Scienc
 es)
DTSTART:20220329T110000Z
DTEND:20220329T113000Z
UID:TALK171158@talks.cam.ac.uk
DESCRIPTION:Under the influence of environmental and meteorological condit
 ions\, non-neutral (in the sense of thermal equilibrium) and non-stationar
 y (in the sense of statistics) flows are ubiquitous in the atmospheric sur
 face layer (ASL). This talk will introduce measurements on clean and sand-
 storm wind flows in the ASL based on a unique observation facility\, i.e.\
 , the Qingtu Lake Observation Array (QLOA) specifically designed to probe 
 the turbulence characteristics of wind flows in ASL. Preliminary results o
 n the turbulence coherent structures of non-neutral clean-air flows\, and 
 the evolution of the turbulence features during the whole process of sand-
 storm events characterized by non-stationary flows will be present. Firstl
 y\, the similarity between large-scale flow structures and temperature fie
 ld structures in the ASL with various scales under different stratificatio
 n stability conditions were analyzed\, and the results show that large-sca
 le flow structures have scale similarity at different scales with unstable
  stratification conditions\, and the scale ratio decreases with the therma
 l buoyancy. Further\, with unstable stratification conditions the inclinat
 ion angles of large-scale flow structures are scale-dependent\, i.e.\, the
  inclination angle of large-scale flow structure decreases with the scale.
  For the temperature field structures\, their streamwise scales display a 
 linear increase with height but a decrease with the thermal buoyancy. Then
 \, this talk will take a sand-storm as an example to demonstrate the varia
 tions of the turbulent kinetic energy during the growth\, stabilization an
 d decay stages. Analysis show that the large-scale coherent structures ori
 ginally exist in the growth stage of sandstorms with an energy fraction of
  75% rather than gradually forming. In addition to carrying a substantial 
 portion of energy\, the large-scale structures are active structures with 
 strong nonlinear energy transfer. Structures gain energy from the nonlinea
 r interaction in the growth stage\, but as time evolves\, the nonlinear in
 teraction in the stabilization and decay stages gradually weakens but main
 tains a balanced budget of energy. The energy fraction reduced to 40% in t
 he decay stage. These results will provide an insight for understanding th
 e turbulent characteristics of wind flows and sandstorm process in the ASL
  under the influence of heat.
LOCATION:Seminar Room 1\, Newton Institute
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