Utjecaj advekcije i rada sila na mahovitost bure

Local wind changes within the flow of the Adriatic Bora are investigated in the case of 8 December 2001 that was simulated with the WRF/ARW model in a 333 m horizontal resolution and with all relevant model variables archived during a 3 h time interval with 1 s temporal resolution. Along a selected cross section, two locations of strong gusts in the lee of a Dinaric mountain ridge are found - the upper one on the slope and the other over the sea close to the coastline; in between the wind is considerably weaker. About 16 to 18 gusts developed in the 3 h interval at both locations with an average period of approximately 8.5 min. The advective transport of kinetic energy (KE), the work of the unbalanced part of the pressure gradient force and the diffusion and dissipation of KE cause the local change ΔKE, and their quasi-periodic fluctuations lead to gusts and lulls. The results of the numerical simulation enable an estimation of the contributions of advection, the work of forces and of turbulence and dissipation effects. Advective contributions to local changes are more or less in the phase with ΔKE and ahead of the phase of KE, while the contributions of work are generally smaller and in the opposite phase: so in general the advection and the work effects oppose each other. The advection and the work effects are not spatially homogeneous, i.e. they cease and even change their sign between the two locations of the strongest gusts and so there is no continuous displacement of KE from the upper to the lower location by either of the two effects: their contributions interchange with each other down the slope.Lokalne promjene vjetra u buri istražene su u slučaju od 8. prosinca 2001. koji je bio simuliran WRF/ARF modelom s horizontalnom rezolucijom od 333 m i sa svim relevantnim modelskim varijablama arhiviranim tijekom 3-satnog vremenskog intervala s vremenskom rezolucijom od 1 s. Duž odabranog presjeka paralelnog s burom nađene su dvije lokacije u navjetrini Dinarida s jakim udarima – jedna na obronku planine i druga iznad mora blizu obale, dok je između njih vjetar znatno slabiji. U promatranom trosatnom intervalu razvilo se oko 16 do 18 udara vjetra s prosječnim periodom od približno 8,5 minuta. Advektivni transport kinetičke energije (KE), rad neuravnoteženog dijela sile gradijenta tlaka te difuzija i disipacija KE uzrokuju lokalnu promjenu ΔKE, i njihove kvazi-periodičke fluktuacije vode do pojave udara i zatišja. Rezultati numeričke simu- lacije omogućavaju procjenu doprinosa advekcije, rada sila te učinaka turbulencije i di- sipacije. Advekcijski doprinosi lokalnim promjenama su više ili manje u fazi s ΔKE i ispred faze KE, a doprinosi rada su općenito manji i u suprotnoj fazi. To znači da advekcija i rad općenito djeluju suprotno. Učinci advekcije i rada nisu prostorno homogeni, tj. oni prestaju ili čak mijenjaju predznak između dvije lokacije najjačih udara. Stoga nema kontinuiranog pomaka KE od više prema nižoj lokaciji koji bi bio uzrokovan bilo kojim od ova dva učinka: njihovi se doprinosi međusobno izmjenjuju niz obronak

Analysis of meteorology-chemistry interactions during air pollution episodes using online coupled models within AQMEII Phase-2

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).This study reviews the top ranked meteorology and chemistry interactions in online coupled models recommended by an experts’ survey conducted in COST Action EuMetChem and examines the sensitivity of those interactions during two pollution episodes: the Russian forest fires 25 Jul -15 Aug 2010 and a Saharan dust transport event from 1 Oct -31 Oct 2010 as a part of the AQMEII phase-2 exercise. Three WRF-Chem model simulations were performed for the forest fire case for a baseline without any aerosol feedback on meteorology, a simulation with aerosol direct effects only and a simulation including both direct and indirect effects. For the dust case study, eight WRF-Chem and one WRF-CMAQ simulations were selected from the set of simulations conducted in the framework of AQMEII. Of these two simulations considered no feedbacks, two included direct effects only and five simulations included both direct and indirect effects. The results from both episodes demonstrate that it is important to include the meteorology and chemistry interactions in online-coupled models. Model evaluations using routine observations collected in AQMEII phase-2 and observations from a station in Moscow show that for the fire case the simulation including only aerosol direct effects has better performance than the simulations with no aerosol feedbacks or including both direct and indirect effects. The normalized mean biases are significantly reduced by 10-20% for PM10 when including aerosol direct effects. The analysis for the dust case confirms that models perform better when including aerosol direct effects, but worse when including both aerosol direct and indirect effects, which suggests that the representation of aerosol indirect effects needs to be improved in the model.Peer reviewedFinal Published versio

CLUSTERING OF THE HIGH RESOLUTION BACKWARD TRAJECTORIES FOR

Abstract: High resolution backward air trajectories arriving at four measuring sites in Slovenia were calculated for months April to September of years 2003 and 2004. K-means clustering methodology was used for classification of trajectories into groups with similar curvature, length and direction. We investigated how different meteorological variables at trajectory receptor points differ between groups of similar trajectories (clusters). Analyses of trajectories reveal the most typical flow patterns and effects of alpine barrier on air mass travelling. Their influence on precipitation accumulation is discussed in more detail

Analiza trajektorija onečišćenja ozona u Sloveniji

Annual number of days with exceeded ozone threshold values at the ground level measuring stations in Slovenia ranges from a few days in the interior of the country to up to 25 days at the Mediterranean stations. The highest number of ozone exceedances is usually recorded in the southwestern part of Slovenia, close to the Adriatic Sea, where favorable meteorological conditions enhance ozone formation. Local emission sources in this part of the country cannot explain the measured level of pollution. In addition, high ozone concentrations are occasionally measured at some Slovenian rural sites. We performed an ozone analysis with respect to air mass origin to provide an insight into processes leading to the high measured values of near-ground ozone. Three dimensional back trajectories were computed with a 3 hour-time interval for four measuring sites in Slovenia, generating eight arrival times per day starting at 00 UTC, for the warm parts (April – September) of the years 2003 and 2004. Trajectory clustering was used to determine typical pathways of air masses. Ozone and basic meteorological characteristics of trajectory clusters were further analyzed and multiple comparison tests were applied to determine which pairs of clusters differ significantly in measured ozone. In addition, concentration weighted trajectory (CWT) and number density (ND) of »polluted trajectories« were calculated to provide additional information about possible emission source regions. Results suggest that high ozone concentrations appear most often in the short trajectory clusters of slow-moving air masses originated from SW. Moreover, CWT and ND fields confirm that high near-ground ozone levels in Slovenia are usually associated with trajectories originating from the area of the northern Adriatic Sea and its coastal regions. A heavily industrialized Po River Basin does not appear to have a significant direct impact on measured ozone concentrations in Slovenia, but may considerably contribute to the overall pollution over the northern Adriatic Sea together with coastal emissions.Godišnji broj dana s vrijednostima većim od graničnih na postajama za kakvoću zraka u Sloveniji kreće se od nekoliko dana u unutrašnjosti pa sve do 25 dana na postajama Mediterana. Najveći broj slučajeva povećanja ozona je zabilježen u jugozapadnom dijelu Slovenije, blizu Jadrana, gdje odgovarajući meteorološki uvjeti povećavaju stvaranje ozona. Lokalni izvori onečišćenja u ovom dijelu zemlje ne mogu objasniti mjereni nivo onečišćenja. Također, visoke koncentracije ozona su povremeno mjerene i na ruralnim postajama u Sloveniji. Izveli smo analizu ozona u odnosu na porijeklo zračnih masa koja nam je omogućila uvid u procese koji vode prema visoko mjerenim koncentracijama prizemnog ozona. Izračunate su trodimenzionalne trajektorije s 3-satnim vremenskim intervalom unatrag za 4 mjerne postaje u Sloveniji, generirajući vremena dolaska po danu počevši u 00:00 UTC, za topli dio (travanj – rujan) 2003. i 2004. godine. Korišteno je grupiranje trajektorija radi određivanja tipičnih staza zračnih masa. Dalje su se analizirali ozon i osnovne meteorološke karakteristike grupa trajektorija te su primijenjeni višestruki testovi usporedbe radi određivanja koji se par klastera razlikuje značajnije u mjerenom ozonu. Kao dodatak su izračunate otežane trajektorije koncentracija (CWT) i broj gustoće (ND) »trajektorija onečišćenja« radi dobivanja dodatnih informacija o mogućim regionalnim izvorima emisije. Rezultati sugeriraju da se visoke koncentracije ozona pojavljuju najčešće u klasterima kratkih trajektorija sporo-gibajućih jugozapadnih zračnih masa. Nadalje, CWT i ND polja potvrđuju da su visoke vrijednosti prizemnog ozona u Sloveniji uobičajeno povezane s trajektorijama koje potječu sa sjevernog dijela Jadrana i njegove obalne zone. Izrazito industrijalizirano područje bazena rijeke Po nema značajniji direktni utjecaj na mjerene koncentracije ozona u Sloveniji, ali može znatno doprinijeti sveukupnom onečišćenju nad sjevernim Jadranom zajedno s obalnim emisijama

Supporting the improvement of air quality management practices: The “FAIRMODE pilot” activity

This paper presents the first outcomes of the “FAIRMODE pilot” activity, aiming at improving the way in which air quality models are used in the frame of the European “Air Quality Directive”. Member States may use modelling, combined with measurements, to “assess” current levels of air quality and estimate future air quality under different scenarios. In case of current and potential exceedances of the Directive limit values, it is also requested that they “plan” and implement emission reductions measures to avoid future exceedances. In both “assessment” and “planning”, air quality models can and should be used; but to do so, the used modelling chain has to be fit-for-purpose and properly checked and verified. FAIRMODE has developed in the recent years a suite of methodologies and tools to check if emission inventories, model performance, source apportionment techniques and planning activities are fit-for-purpose. Within the “FAIRMODE pilot”, these tools are used and tested by regional/local authorities, with the two-fold objective of improving management practices at regional/local scale, and providing valuable feedback to the FAIRMODE community. Results and lessons learnt from this activity are presented in this paper, as a showcase that can potentially benefit other authorities in charge of air quality assessment and planning