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

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

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

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