Integral scales in the surface atmospheric boundary layer for Bora flows

master's thesis

• Title: Integralne skale u prizemnom atmosferskom sloju za buru
• Author: Katarina Vinković
• Mentor: Željko Večenaj (mentor)
• Committee member: Željko Večenaj (predsjednik povjerenstva)
• Committee member: Branko Grisogono (član povjerenstva)
• Committee member: Ines Ivančić (član povjerenstva)
• Committee member: Maja Telišman Prtenjak (član povjerenstva)
• Committee member: Ivica Sović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; Zagreb
• Defense date and country: 2017-04-27, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Geophysics; Meteorology and Climatology

Abstract

Mnogi numerički i klimatski modeli za prognozu vremena koriste prognostički oblik jednadžbe turbulentne kinetičke energije (TKE). Mjera disipacije TKE se parametrizira odgovarajućim omjerom TKE i takozvanom integralnom skalom duljine, što je otežano određenim numeričkim koeficijentom. U znanstvenoj zajednici ne postoji dogovor o jedinstvenoj formulaciji takve integralne skale. Stoga, u literaturi nalazimo različite oblike integralne skale. Međutim, one se najčešće izvode iz autokorelacijske funkcije i Fourierovog spektra komponenti brzine vjetra. To su, takozvane skale 1/e i skala prelaska nule te skala za koju normalizirani Fourierov spektar postiže maksimum. Cilj ovog rada je procjena integralne skale turbulencije i pripadnog numeričkog koeficijenta, po prvi put, za buru. Za analizu koristimo podatke prikupljene „WindMaster“ ultrasoničnim anemometrima na visinama 2, 5 i 10 m, u neposrednoj blizini novog Masleničkog mosta, s čestinom uzrokovanja od 20 Hz. U razdoblju od 09. listopada 2015. do 09. listopada 2016. godine izdvojeno je 48 epizoda bura u trajanju od otprilike 1206 sati. Tako veliki set podataka nam omogućava procjenu navedene integralne skale i numeričkog koeficijenta u svrhu testiranja parametrizacije TKE i disipacije TKE u prizemnom sloju za buru. Takozvana skala 1/e se pokazala najboljom za procjenu integralne skale turbulencije za buru. U konačnici, na temelju analiziranih podataka uočeno je znatno odstupanje numeričkog koeficijenta za buru u odnosu na vrijednosti korištenih u znanstvenoj zajednici, koje predlažu npr. Cuxart i sur. (2006), to nam ostavlja prostora za daljnja detaljnija istraživanja u budućnosti.

Abstract (english)

Many NWP and climate models use prognostic turbulence kinetic energy (TKE) equation. TKE dissipation ratio is parameterized via suitable ratio of TKE and so-called integral length scale for turbulence, which is weighted by a certain numerical coefficient. The scientific community does not have unique agreement on formulation of integral turbulence scales. Therefore, in literature we find various forms of those integral scales. However, usually they are derived from autocorrelation functions and Fourier spectra of wind speed components. These are the so-called 1/e and zero crossing scales and the scale at which a normalized Fourier spectra achieve their maximum value. The aim of this study is to evaluate integral turbulence scales and the related coefficient, for the first time for bora flows. For the analysis we used dana collected with „WindMaster“ ultrasonic anemometers at heights 2, 5 and 10 m, close to new Maslenica bridge, with a frequency sampling of 20 Hz. In the period from 09 October 2015 to 09 October 2016 recorded were 48 bora events with cumulative duration of 1206 hours. Such a large dataset gives us an opportunity to evaluate integral turbulence scales and the related numerical coefficient to test the parametrization of the TKE dissipation rate for the atmospheric surface boundary layer in bora flows. So-called 1/e scale proved to be the best estimate for the integral turbulence scale. At the end, based on the analyzed dataset, it has been observed a significant disagreement of the numerical coefficient for bora flows compared with values used in the literature, proposed by e.g. Cuxart et al. (2006). This leaves us space for further studies in future.

• Keywords: autokorelacijska funkcija; bura; integralne skale; TKE; turbulencija
• Keywords (english): autocorrelation function; bora; integral scales; TKE; turbulence
• Language: croatian
• URN:NBN: urn:nbn:hr:217:494078
• Study programme: Title: Fizika i geofizika; smjerovi: Seizmologija i fizika čvrste Zemlje, Meteorologija i fizička oceanografija; Study programme type: sveučilišni; Study level: diplomski; Academic / professional title: magistar/magistra fizike – geofizike (magistar/magistra fizike – geofizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-05-23 12:15:58