Wind characteristics in the present and future climate obtained from regional climate models' simulations over broader Adriatic region

Jadran je područje kompleksne orografije stoga predstavlja izazov za realistično simuliranje polja vjetra regionalnim klimatskim modelima (RCM-ima). Analizirani RCM-i uključuju modele CORDEX inicijative s prostornim korakom od 0.11° i 0.44° te model ETH instituta u Zürichu s prostornim korakom od 0.11° i 0.02°. Simulirani prizemni vjetar usporedio se s prizemnim vjetrom standardne mreže kopnenih meteoroloških postaja, s podacima dobivenih pomoću QuikSCAT satelita te s podacima ERA-Interim reanalize za šire područje Jadrana. U svrhu evaluacije koristilo se nekoliko osnovnih (pristranost, standardna devijacija, itd.), izvedenih (mjere uspješnosti) i naprednih (EOF analiza i spektralna analiza) statističkih metoda. Ova analiza je rezultirala procjenom ograničenja u simuliranju tipičnih vjetrovnih režima današnjom generacijom RCM-a. Uspješnijima su se pokazale simulacije s manjim prostornim korakom mreže, osobito u obalnom području i kod ekstremnih brzina vjetra. Klimatske promjene u prizemnom vjetru odredile su se usporedbom polja strujanja u sadašnjoj i budućoj klimi iz CORDEX simulacija s prostornim korakom od 0.11°. Analizirao se utjecaj izbora RCM-a, rubnih uvjeta i scenarija koncentracije stakleničkih plinova (RCP4.5 i RCP8.5), a rasap među simulacijama je mjera vjerojatnosti određenih promjena. Polje strujanja analiziralo se u smislu promjena u raspodjeli brzina vjetra i u smjeru vjetra duž Jadrana. Dan je fokus na smjerove vjetra koji odgovaraju buri i jugu. Analiza je pokazala da se buduće promjene intenziviraju odabirom jačeg (RCP8.5) scenarija i približavanjem kraju 21. stoljeća. Buduće su promjene često istog reda veličine kao i interkvartilni raspon među simulacijama, međutim postoje naznake da će se broj događaja bure smanjiti duž Jadrana, ali će srednja brzina porasti u sjevernom Jadranu krajem stoljeća. Za jugo je pokazano da broj događaja u srednjem Jadranu raste, a srednja brzina vjetra opada. Buduće promjene u buri i jugu povezane su s promjenama u strujanju nad Jadranom koristeći podatke o polju tlaka svedenog na srednju morsku razinu te geopotencijalne visine 500 hPa plohe. Razvijen je novi algoritam za određivanje tipova vremena na sinoptičkoj skali nad širim jadranskim područjem. Pokazano je da se broj ciklona nad Jadranom, osobito zimi, smanjuje te su one uglavnom zamjenjene anticiklonalnim strujanjem.Extended abstract in the thesi

Određivanje utjecaja lokalnih meteoroloških uvjeta na kvalitetu zraka u Zagrebu primjenom generaliziranih aditivnih modela

This paper reports the estimated response of hourly mean concentrations of selected air pollutants, namely carbon monoxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2) and particulate matter with an aerodynamic diameter of up to 10 µm (PM10), to local scale meteorology in Zagreb, Croatia for the pe¬riod 2006–2012. A new method is applied here for the urban area of Zagreb. In a general model, a logarithm of hourly mean air pollutant concentrations is expressed as the sum of the nonlinear functions of meteorological and several time variables, with the latter included accounting for temporal variation in emissions. The model can be formulated within the framework of generalized additive models (GAMs) and is additive on the logarithmic scale, which results in multiplicative effects on the original scale. Although the model is nonlinear, it is simple and easy to interpret. It quantifies the impact of meteorological conditions and emissions on air pollution. A measure of the relative importance of each predictor, partial effects and statistical evaluation of the model are also presented. Overall, the results show that the most important predictors are those related to emissions. The aggregate impact of meteorological variables in the model explained 45% of variance in CO, 14% in SO2, 25% in NO2 and 24% in PM10. This indicates that meteorology, at least on a local scale, is a noticeable driver of air quality in Zagreb. Stable atmospheric conditions in the urban area favour the occurrence of higher concentrations of air pollutants. Convection processes dominate under unstable conditions, resulting in the dilution of pollutant concentrations within the boundary layer.U ovom se radu određuje utjecaj lokalnih meteoroloških uvjeta u Zagrebu na satnu koncentraciju odabranih polutanata: ugljikovog monoksida (CO), sumporovog dioksida (SO2), dušikovog dioksida (NO2) i lebdećih čestica aerodinamičkog polumjera do 10 µm (PM10) za razdoblje od 2006. do 2012. godine. Primijenjena je nova metodologija za urbano područje Zagreba. U modelu je logaritam satne koncentracije polutanata određen pomoću sume nelinearnih funkcija meteoroloških i nekoliko vremenskih varijabli. Uključene vremenske varijable opisuju vremenske promijene u emisijama. Takav model pripada generaliziranim aditivnim modelima (GAM) i aditivan je na logaritamskoj skali, što rezultira umnošcima na originalnoj skali. Iako je model nelinearan, rezultati se vrlo lako interpretiraju, opisujući utjecaj meteoroloških uvjeta i emisija na kvalitetu zraka pomoću relativne važnosti i parcijalnih utjecaja. Provedena je i statistička procjena uspješnosti modela. U konačnici, dobiveni rezultati su pokazali da su najvažnije varijable one koje opisuju emisije. Ukupni utjecaj meteoroloških varijabli u modelu objasnio je 45% varijance za CO, 14% za SO2, 25% za NO2 i 24% za PM10. Time je pokazano da meteorološki uvjeti, barem lokalno, osjetno utječu na kvalitetu zraka u Zagrebu. Stabilni atmosferski uvjeti u urbanom okruženju pogoduju većim koncentracijama navedenih polutanata. Pri nestabilnim atmosferskim uvjetima dominira konvekcija, koja razrjeđuje koncentracije polutanata unutar graničnog sloja

A Weather-Type Classification and Its Application to Near-Surface Wind Climate Change Projections over the Adriatic Region

The main goal of this study is to present a recently developed classification method for weather types based on the vorticity and the location of the synoptic centers relative to the Adriatic region. The basis of the present objective classification, applied to the Adriatic region, is the subjective classification developed by Poje. Our algorithm considered daily mean sea-level pressure and 500 hPa geopotential height to define one out of 17 possible weather types. We applied the algorithm to identify which weather type was relevant in the generation of the two typical near-surface winds over the Adriatic region, namely Bora and Sirocco. Two high-resolution (0.11°) EURO-CORDEX regional climate models were used, SMHI-RCA4 and DHMZ-RegCM4, forced by several CMIP5 global climate models and analyzed for two 30-year periods: near-present day and mid-21st century climate conditions under the high-end Representative Concentration Pathway (RCP8.5) scenario. Bora and Sirocco days were extracted for each weather type and a distribution over the 30-year period was presented. Our results suggest that in the winter season, climate model projections indicate a reduction in the main cyclonic types relevant in the formation of Bora over the entire Adriatic region and an increase in the number of anticyclonic types relevant in Sirocco events. In contrast, for the summer season, an increase in the main anticyclonic Bora-related weather types is found in the ensemble over the northern Adriatic region

Using a generalized additive model to quantify the influence of local meteorology on air quality in Zagreb

This paper reports the estimated response of hourly mean concentrations of selected air pollutants, namely carbon monoxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2) and particulate matter with an aerodynamic diameter of up to 10 µm (PM10), to local scale meteorology in Zagreb, Croatia for the pe¬riod 2006–2012. A new method is applied here for the urban area of Zagreb. In a general model, a logarithm of hourly mean air pollutant concentrations is expressed as the sum of the nonlinear functions of meteorological and several time variables, with the latter included accounting for temporal variation in emissions. The model can be formulated within the framework of generalized additive models (GAMs) and is additive on the logarithmic scale, which results in multiplicative effects on the original scale. Although the model is nonlinear, it is simple and easy to interpret. It quantifies the impact of meteorological conditions and emissions on air pollution. A measure of the relative importance of each predictor, partial effects and statistical evaluation of the model are also presented. Overall, the results show that the most important predictors are those related to emissions. The aggregate impact of meteorological variables in the model explained 45% of variance in CO, 14% in SO2, 25% in NO2 and 24% in PM10. This indicates that meteorology, at least on a local scale, is a noticeable driver of air quality in Zagreb. Stable atmospheric conditions in the urban area favour the occurrence of higher concentrations of air pollutants. Convection processes dominate under unstable conditions, resulting in the dilution of pollutant concentrations within the boundary layer.U ovom se radu određuje utjecaj lokalnih meteoroloških uvjeta u Zagrebu na satnu koncentraciju odabranih polutanata: ugljikovog monoksida (CO), sumporovog dioksida (SO2), dušikovog dioksida (NO2) i lebdećih čestica aerodinamičkog polumjera do 10 µm (PM10) za razdoblje od 2006. do 2012. godine. Primijenjena je nova metodologija za urbano područje Zagreba. U modelu je logaritam satne koncentracije polutanata određen pomoću sume nelinearnih funkcija meteoroloških i nekoliko vremenskih varijabli. Uključene vremenske varijable opisuju vremenske promijene u emisijama. Takav model pripada generaliziranim aditivnim modelima (GAM) i aditivan je na logaritamskoj skali, što rezultira umnošcima na originalnoj skali. Iako je model nelinearan, rezultati se vrlo lako interpretiraju, opisujući utjecaj meteoroloških uvjeta i emisija na kvalitetu zraka pomoću relativne važnosti i parcijalnih utjecaja. Provedena je i statistička procjena uspješnosti modela. U konačnici, dobiveni rezultati su pokazali da su najvažnije varijable one koje opisuju emisije. Ukupni utjecaj meteoroloških varijabli u modelu objasnio je 45% varijance za CO, 14% za SO2, 25% za NO2 i 24% za PM10. Time je pokazano da meteorološki uvjeti, barem lokalno, osjetno utječu na kvalitetu zraka u Zagrebu. Stabilni atmosferski uvjeti u urbanom okruženju pogoduju većim koncentracijama navedenih polutanata. Pri nestabilnim atmosferskim uvjetima dominira konvekcija, koja razrjeđuje koncentracije polutanata unutar graničnog sloja

Near-surface wind variability over the broader Adriatic region: insights from an ensemble of regional climate models

ISSN:0930-7575ISSN:1432-089

A New Approach for the Analysis of Deep Convective Events: Thunderstorm Intensity Index

In this study, an investigation of a new thunderstorm intensity index (TSII) derived from lightning data is performed, along with its relationship to rain, wind, hail and waterspouts as well as instability indices (CAPE, LI, KI, and DLS). The study area is located in the northeastern Adriatic and includes various terrain types in a relatively small area (coastal, flatlands, hills and valleys, and mountain regions). The investigated period covers 11 years (2008–2018). The mathematical algorithm standing behind the TSII is based on the well-established methodology of lightning jump, allowing us to recognize areas where intensification in thunderstorms occurred. Our results suggest that these areas (with a positive TSII) experience significantly higher rain intensities and have higher total amounts of precipitation compared with areas where thunderstorms did not generate a TSII. Moreover, 76% of thunderstorm hail cases were associated with the presence of a TSII within a 15 km distance. The maximum reported wind speed also has higher values on a day with a TSII. Out of 27 waterspout events associated with lightning, 77% were related to a TSII. Due to the good spatial (3 km × 3 km) and high temporal (2 min) resolution of lightning data, the TSII can recognize even a local and short-lived intense system that is often misread by radars and satellites due to their inferior temporal resolution. The TSII is designed to be used as a climatological and diagnostic variable that could serve in lieu of more established data sources (e.g., station measurements and observations, radar imagery, etc.) if they are unavailable

Micro-Scale Properties of Different Bora Types

In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used to test the Monin–Obukhov similarity theory, the surface layer stratification, the behavior of the terms in the prognostic turbulence kinetic energy equation, and the wind profiles. One of our main goals is to identify possible micro-scale differences between shallow and deep bora types because of the possible different mountain wave dynamics in those flows. We found that a turbulence averaging scale of 30 min is suitable for this location and is in agreement with previous bora studies. The wind speed power spectral densities of all selected bora episodes showed pulsations with periods of 2–8 min. This suggests that mountain wave breaking was present in all cases, regardless of flow depth and synoptic type. The stability parameter analysis confirmed the near-neutral thermal stratification of bora; a consequence of intensive mechanical mixing. No significant differences related to bora type were observed in other micro-scale parameters

Evaluation of the near-surface wind field over the Adriatic region: local wind characteristics in the convection-permitting model ensemble

We present the first evaluation of the wind field from the ensemble of kilometer-scale simulations from the CORDEX-Flagship Pilot Study on convection, with focus on the Adriatic region. Kilometer-scale climate models, also known as convection-permitting models (CPMs), produce a good representation of small-scale topographic features and consequently a more detailed depiction of dynamical and thermal circulations. These enable a reliable view of climate characteristics of the wind field, especially in coastal regions and over complex terrain, such as the Adriatic region. We investigate the (potential) added value introduced by CPMs compared to classical “cumulus-parametrized” regional climate models (RCMs), reanalysis and station observations. For this purpose, wind components at 10 m level are used at 3-hourly frequency. All simulations cover a 10-year period, extending from 2000 to 2009. In terms of the standard statistical parameters such as correlation coefficient and temporal standard deviation, CPMs are very dependent on their parent RCM performance. However, the orographic forcing emphasizes the potential added value and CPMs contain some fine spatial scale variability (i.e., stronger extremes by 25% and more accurate wind direction) that is absent in coarser RCMs and reanalysis. The potential added value is higher in the cold season compared to the warm season due to the proportion of severe wind events. CPMs reproduce well the typical wind regimes along the Adriatic coast, namely Bora and Sirocco. The benefit of using CPMs is especially pronounced in simulating Bora maximum wind speeds in northern Adriatic and Sirocco frequencies in southern Adriatic. Based on our overall analysis, we conclude that CPMs provide added value compared to coarser models, especially in the complex coastal terrain