Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions
Monin–Obukhov similarity theory (MOST) applicability is limited in several conditions: e.g., weak wind and very-stable stratification; complex terrain; presence of non-local, submeso motions. In this work, two years of observations from three Arctic stations are considered, to characterize the near-...
Main Author: | |
---|---|
Other Authors: | |
Format: | Doctoral or Postdoctoral Thesis |
Language: | English |
Published: |
Alma Mater Studiorum - Università di Bologna
2020
|
Subjects: | |
Online Access: | http://amsdottorato.unibo.it/9235/ http://amsdottorato.unibo.it/9235/1/Schiavon_Mario_tesi.pdf |
id |
ftunivbologntesi:oai:amsdottorato.cib.unibo.it:9235 |
---|---|
record_format |
openpolar |
spelling |
ftunivbologntesi:oai:amsdottorato.cib.unibo.it:9235 2023-05-15T14:25:39+02:00 Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions Schiavon, Mario <1986> Drofa, Oxana 2020-03-26 application/pdf http://amsdottorato.unibo.it/9235/ http://amsdottorato.unibo.it/9235/1/Schiavon_Mario_tesi.pdf en eng Alma Mater Studiorum - Università di Bologna http://amsdottorato.unibo.it/9235/1/Schiavon_Mario_tesi.pdf urn:nbn:it:unibo-26126 Schiavon, Mario (2020) Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Geofisica <http://amsdottorato.unibo.it/view/dottorati/DOT250/>, 32 Ciclo. DOI 10.6092/unibo/amsdottorato/9235. info:eu-repo/semantics/openAccess FIS/06 Fisica per il sistema terra e il mezzo circumterrestre Doctoral Thesis PeerReviewed 2020 ftunivbologntesi 2021-06-03T13:40:42Z Monin–Obukhov similarity theory (MOST) applicability is limited in several conditions: e.g., weak wind and very-stable stratification; complex terrain; presence of non-local, submeso motions. In this work, two years of observations from three Arctic stations are considered, to characterize the near-surface turbulence exchange in the area, which presents critical conditions for MOST applicability: i.e., complex terrain and long-lasting stable conditions, which favour submeso motions like gravity waves. Particular attention is dedicated to the similarity relationship between the shear stress, τ , and the vertical velocity variance, <w^2>, which are key variables to characterize the vertical turbulence exchange. Besides the stability effect predicted by MOST and the topographic influence, the effect of submeso motions on the τ /<w^2> similarity relationship is considered. This is done by using spectral analysis and by defining a parameter,R_τ , which quantifies the relative low-frequency contribution to the shear stress, and thus the strength of the submeso effect. It is shown that submeso motions affect small-scale turbulence thus modifying the flux-variance similarity relationship, which, besides stability and surface characteristics, depends on R_τ . In particular, the efficiency of the vertical transport by small-scale turbulence (i.e., τ /<w^2>) diminishes for increasing submeso effect (i.e., increasing R_τ ). This connects MOST applicability with more profound characteristics of the turbulent flow—i.e., the different time scales of the flow and the interplay among them. Results has impacts on modelling closures. In particular, considering the budget of (i.e., the stream-wise component of the shear stress), a simple balance among shear production, buoyancy, and pressure redistribution does not hold when the submeso effect is significant (i.e., R_τ>>1). This demands for a modification of the closures and/or for an extension of the budget, with additional terms accounting for unsteadiness, vertical transport of third-order moments, and interaction of submeso motions with small-scale turbulence. Doctoral or Postdoctoral Thesis Arctic Arctic Università di Bologna: AMS Tesi di Dottorato (Alm@DL) Arctic |
institution |
Open Polar |
collection |
Università di Bologna: AMS Tesi di Dottorato (Alm@DL) |
op_collection_id |
ftunivbologntesi |
language |
English |
topic |
FIS/06 Fisica per il sistema terra e il mezzo circumterrestre |
spellingShingle |
FIS/06 Fisica per il sistema terra e il mezzo circumterrestre Schiavon, Mario <1986> Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
topic_facet |
FIS/06 Fisica per il sistema terra e il mezzo circumterrestre |
description |
Monin–Obukhov similarity theory (MOST) applicability is limited in several conditions: e.g., weak wind and very-stable stratification; complex terrain; presence of non-local, submeso motions. In this work, two years of observations from three Arctic stations are considered, to characterize the near-surface turbulence exchange in the area, which presents critical conditions for MOST applicability: i.e., complex terrain and long-lasting stable conditions, which favour submeso motions like gravity waves. Particular attention is dedicated to the similarity relationship between the shear stress, τ , and the vertical velocity variance, <w^2>, which are key variables to characterize the vertical turbulence exchange. Besides the stability effect predicted by MOST and the topographic influence, the effect of submeso motions on the τ /<w^2> similarity relationship is considered. This is done by using spectral analysis and by defining a parameter,R_τ , which quantifies the relative low-frequency contribution to the shear stress, and thus the strength of the submeso effect. It is shown that submeso motions affect small-scale turbulence thus modifying the flux-variance similarity relationship, which, besides stability and surface characteristics, depends on R_τ . In particular, the efficiency of the vertical transport by small-scale turbulence (i.e., τ /<w^2>) diminishes for increasing submeso effect (i.e., increasing R_τ ). This connects MOST applicability with more profound characteristics of the turbulent flow—i.e., the different time scales of the flow and the interplay among them. Results has impacts on modelling closures. In particular, considering the budget of (i.e., the stream-wise component of the shear stress), a simple balance among shear production, buoyancy, and pressure redistribution does not hold when the submeso effect is significant (i.e., R_τ>>1). This demands for a modification of the closures and/or for an extension of the budget, with additional terms accounting for unsteadiness, vertical transport of third-order moments, and interaction of submeso motions with small-scale turbulence. |
author2 |
Drofa, Oxana |
format |
Doctoral or Postdoctoral Thesis |
author |
Schiavon, Mario <1986> |
author_facet |
Schiavon, Mario <1986> |
author_sort |
Schiavon, Mario <1986> |
title |
Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
title_short |
Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
title_full |
Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
title_fullStr |
Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
title_full_unstemmed |
Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions |
title_sort |
turbulence in the atmospheric boundary layer: intercomparison among arctic stations, deviations from most, and submeso motions |
publisher |
Alma Mater Studiorum - Università di Bologna |
publishDate |
2020 |
url |
http://amsdottorato.unibo.it/9235/ http://amsdottorato.unibo.it/9235/1/Schiavon_Mario_tesi.pdf |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic Arctic |
genre_facet |
Arctic Arctic |
op_relation |
http://amsdottorato.unibo.it/9235/1/Schiavon_Mario_tesi.pdf urn:nbn:it:unibo-26126 Schiavon, Mario (2020) Turbulence in the atmospheric boundary layer: intercomparison among Arctic stations, deviations from MOST, and submeso motions, [Dissertation thesis], Alma Mater Studiorum Università di Bologna. Dottorato di ricerca in Geofisica <http://amsdottorato.unibo.it/view/dottorati/DOT250/>, 32 Ciclo. DOI 10.6092/unibo/amsdottorato/9235. |
op_rights |
info:eu-repo/semantics/openAccess |
_version_ |
1766298092754173952 |