20 years of Croatian participation in ALADIN and RC LACE projects

U radu je dan kratak osvrt na povijest sudjelovanja Hrvatske u ALADIN i RC LACE projektima. Hrvatski doprinos razvoju ALADIN modela obavlja se u okviru rada RC LACE grupe, pa je posebna pažnja posvećena upravo RC LACE suradnji. Naglašen je znanstveni i stručni doprinos hrvatskih znanstvenika na pojedinim temama, učešće Hrvatske u organizaciji ALADIN I RC LACE sastanaka, radionica i seminara. Od uključenja Hrvatske u ALADIN i RC LACE projekte realizirano je 68 dugotrajnijih boravaka 19 hrvatskih meteorologa u meteorološkim službama zemalja članica. U razdoblju od uspostave ALADIN/HR operative u Hrvatskoj do kraja 2014. godine 22 hrvatska meteorologa je radilo ukupno 593 mjeseci na temama razvoja modela i razvoju i održavanju lokalnog operativnog prognostičkog ALADIN sustava. Rezultat toga je, između ostalog, znatan broj znanstvenih i stručnih radova, te doprinos mnogobrojnim domaćim i međunarodnim znanstvenim projektima.The paper gives a brief overview of the history of Croatian participation in the ALADIN and RC LACE projects. Croatian contribution to the development of the ALADIN model is carried out in the framework of RC LACE cooperation. Therefore, the special emphasis is given to the research and development activities in RC LACE group. Detailed information are given on the scientific contribution of Croatian scientists to specific topics and Croatian role in ALADIN and RC LACE management and meetings, seminar and workshops organizations. From the beginning of ALADIN and RC LACE cooperation 19 Croatian scientists realized 68 visits to consortium countries. In the period from 2000 (start of the pre-operational run in Croatia) to 2014, 22 Croatian meteorologists worked a total of 593 months on model development as well as development and maintenance of the local operational ALADIN weather prediction system. The result is, among others, a substantial number of scientific papers and contributions to numerous national and international scientific projects

KARAKTERISTIKE SUHE FRONTE NAD ZAGREBOM I NJEZINI UZROCI

Proučavana je suha fronta koja je prešla preko Zagreba 6_7.1.1982. uz izrazit pad temperature i vlage pri tlu. Prikazane su detaljne analize dinamičkih veličina, kao što su statička stabilnost, vertikalno smicanje vjetra i transporti topline i momenta, na vremenskim vertikalnim presjecima prema radiosondažnim mjerenjima u Zagrebu. Pokazano je da ovu situaciju karakterizira postojanje sekundarne cirkulacije u blizini tropopauze. Ova se cirkulacija manifestira izraženim silaznim gibanjima, porastom temperature i padom vlage unutar frontalne zone koja slijedi hladnu frontu u donjoj troposferi. Silazna gibanja na prekidu tropopauze omogućavaju transport suhog zraka stratosferskog porijekla u niže slojeve. Posljedica tog procesa je smanjenje vlage u troposferi, a uz to i izostanak oborine unatoč izraženim frontalnim karakteristikama u polju temperature i vjetra

SEVERE BORA ON THE NORTHERN ADRIATIC PART I: STATISTICAL ANALYSIS

The results of statistical analysis of severe bora (wind N-E direction and mean hourly wind velocity ≥ 17.O m/s) occurrence at three locations on the northern Adriatic (Senj, Omišalj and Pula) are presented. Concerning the representativness of Senj it is shown that Senj\u27s bora is not representative for a broader area in the northern Adriatic. ln the 30-year period of observation (1957-1986) 434 cases with severe bora were registered in Senj. On the other locations severe bora was not so frequent. Long severe bora usually occurs only during the winter season. The wind velocity is more uniform in situations with the longer lasting bora. Its basic characteristic of long bora duration is shown to be valid mainly for bora in the cold season particularly in Senj. Although the great majority of cases the strongest bora occurs in Senj, there are situations with maximum bora gusts greater at other localities

Cold air outbreak and the Adriatic bora

The case studies of two cold air outbreaks in Zagreb which cause a local wind bora on the eastern Adriatic area are presented ( 17 December 1978 and 7 January 1982 ). The cold air outbreak on 17 December 1978 appeared as a shallow zone of large equivalent potential temperature drop ( Q e ) and NE wind with maximum at 800 m above ground. The stable layer which was placed above this zone was more expressed in terms of vertical Q e - rather than temperature-structure which was consequence of very humid and warm air advected from SW above the cold bora layer. This upstream bora layer characteristics and strengthening of cyclonic activity on the Tyrrhenian Sea caused a longlasting and strong bora associated with precipitation on the northern Adriatic . The strongest bora with maximum gusts of 35.2 m s -1 and with the longest duration of bora was 28-40 hours with the maximum gusts varying from 14.9 m s -1 to 34.7 m s -1 . In the case of 7 January 1982 , a strong bora, associated with anticyclone strengthening over the middle Europe , occurred along the entire Adriatic coast as a consequence of an expressed cold and dry air outbreak. The main characteristic in this situation was a narrow zone of sudden drop of Q e and NE wind with a maximum at 2.5 km altitude. The stability above this zone was smaller than in the first situation and the temperature fall occurred throughout the troposphere. Due to extremely dry air supply, the bora occurred without precipitation lasting from 16 to 31 hours and even 52 hours in Senj. The maximum gusts varied from 17.0 m s -1 to 35.4 m s -1 . Two case studies are not enough for a general conclusion but it should be emphasized that the bora had quite different characteristics in the considered frontal situations

ATMOSPHERIC TRANSPORT TO THE GAW REGIONAL STATION AT ZAVIŽAN AND RELATED PRECIPITATION CHEMISTRY

A study on the connection between the state of the atmosphere, as represented by cluster-mean trajectories, and the chemical composition of precipitation at the Croatian GAW regional station of Zavižan is presented. The trajectory cluster analysis has been done on the basis of daily backward trajectories calculated for 1996, using the HYSPLIT_4 trajectory model. The seasonal cluster analysis indicates four major flow directions in the region: 1) fast W-NW flow, 2) strong SW flow, 3) N-NE flow, 4) very short trajectories of different directions. The major transport route that brings higher levels of acidifying compounds to the region, is from the NW wind sector. The most polluted precipitation has been observed in spring with precipitation connected with three cluster means: NNW, SE and E

Bora wind load upon structures

Djelovanje vjetra, uz djelovanje potresa, čini dominantno horizontalno djelovanje kojem su izloženi građevinski objekti u svom vijeku trajanja. Posebni značaj ovog djelovanja je što je ono promjenjivo u vremenu, a po intenzitetu varira i ovisi o meteorološkim karakteristikama pojedinog područja, te se ne može unificirati. U postojećim opće prihvaćenim europskim standardima za proračun opterećenja građevinskih konstrukcija vjetrom koristi se maksimalna očekivana 10-minutna brzina vjetra. Tlak kojim vjetar te brzine djeluje na građevinu ukazuje na tzv. statičko opterećenje. Međutim, brzina vjetra u 10-minutnom intervalu može značajno varirati. To je posebno izraženo u slučaju mahovitog, turbulentnog vjetra kao što je bura. Analiza utjecaja turbulencije na opterećenje građevinskih konstrukcija olujnim vjetrom pokazala je da se pri projektiranju građevina na priobalju i otocima gdje brzina bure postiže ekstremne vrijednosti mora uzeti u obzir utjecaj turbulentne komponente vjetra na opterećenje građevinske konstrukcije ili tzv. dinamičko opterećenje. Primjer jedne od najjačih ikad izmjerenih bura na Jadranu pokazao je da je tlak vjetra, uzimajući u proračunu u obzir dinamičko opterećenje konstrukcije, gotovo 4 puta veći od onog koji se dobije uzimajući u obzir samo statičko opterećenje vjetrom.Wind action, together with the earthquake action, represents dominant horizontal action on structures in his lifetime. Special significance of this action is that it is changing over time and its intensity varies depending on the meteorological characteristics of each area, and cannot be unified. In existing Eurocodes wind load calculation is based on the reference wind speed defined as a maximum 10-minutes average wind speed to be expected in a 50 years period. Wind with the reference wind speed results with so called static wind load. However, in 10 minutes wind speed varies significantly. That is particularly case during the severe and turbulent bora wind. Due to its gusty character and extreme turbulence, estimates of wind load in the bora region have to include the dynamical wind load caused by bora turbulence. This is confirmed during the example situation of strong bora wind conditions by the values of the exposure coefficient of 4 times greater than the exposure coefficient obtained using only static wind load

SPATIAL BORA VARIATIONS IN RELATION TO COLD AIR OUTBREAK AND SURFACE PRESSURE GRADIENT

Bora wind on the northern Adriatic is associated with an upstream cold air outbreak although the most pronounced outbreaks are not always connecled with the strongest bora slorms. During the cold season between 1973 - 1982 in Zagreb only 3 strong cold air outbreaks were associated with severe bora in the northern Adriatic. ln these cases bora onset is almost simultaneous along the entire northern Adriatic coast, it lasts 1 - 2 days and its strength is nearly equal at all considered meteorological stations. The cut-off processes and blocking circulation pattern connected with the less pronounced long lasting cold air outbreak resulted with the longest bora duration. ln 12 considered severe bora situations a drop of temperature due to cold air outbreaks is followed by the characteristic mesoscale pressure field with low pressure area along the coast and islands and higher pressure in the upstream bora region. The estimated correlation coefficient between the cross mountain sea level pressure difference Δp and mean hourly bora velocity Vs show the stohastic significancy in all 12 severe bora cases. The relationship between Δp and Vs is stronger using Senj data than data measured at Omišalj and Pula what is a consequence of Senj\u27s specific location in relation to the mountain barrier. ln 3 most pronounced cold air outbreak situations the constants in the correlation expression obtained using Senj data are almost the same. Thay enable us to estimate the mean hourly bora wind speed in Senj for predicted Zagreb - Senj pressure differences in similar weather situations

Expected airflow regimen on the Sv. Rok (South) - Maslenica motorway route

Na primjeru trase autoceste Sv. Rok (jug) – Maslenica upozoreno je na značenje pravovremene izrade meteorološke podloge za potrebe projektiranja, izgradnje i uporabe prometnice. Analiza režima strujanja provedena je koristeći se izmjerenim podacima smjera koji su bili na raspolaganju i brzine vjetra na širem području autoceste i procijenjenom razdiobom smjera i brzine vjetra duž trase autoceste. Rezultati pokazuju da se može očekivati izloženost autoceste jakim i olujnim burama.The significance of timely preparation of meteorological data bases for the design, construction and use of transportation facilities is illustrated through the example of the Sv. Rok (South) - Maslenica Motorway route. The analysis of flow regimen was conducted based on measured directional data available at the time, wind speed in the wider motorway area, and the estimated wind direction and speed distribution along the motorway route. Results show that strong and gale-force winds may be expected along this motorway

Aerial Analysis of the Strongest North Adriatic ALPEX Bora Case

This paper presents the results of an aerial analysis of the bora case- on 6-7 March 1982 using aerological data from 10 stations in the region 40° - 49° N, 10° - 22° E. The objective analysis method has been constructed for the presentation of the isentropic surfaces and the two-dimensional isentropic divergence and the vertical component of vorticity. The objective analysis scheme considered seems to be capable of describing the main three-dimensional features of air flow during bora: the descent of a stable bora layer not only along the NE bora flow, but also perpendicular to this flow in the upstream region; the region of vertical divergence forming a "dead region" with strong turbulence downstream; the anticyclonic vorticity in the lee of the Alps and cyclonic circulation in the mid-Adriatic before the bora onset

SULPHUR-DIOXIDE CONCENTRATION IN THE NORTHERN ADRIATIC HEALTH RESORT AREA

The series of 1226 samples of 24-hours SO2 concentration data in Veli Lošinj during the period 1986-1989 have been analysed together with basic meteorological variables measured on Mali Lošinj at 3 climatological terms. The day-to-day synoptic weather types are examined in order to relate synoptic scale flow patterns to the SO2 concentration data. The pollution level in Lošinj area was found to be considerably lower than the minimum legal value of SO2 based on public health criteria which is 60 μgm-3 for 24 hours. Nevertheless, particular meteorological conditions such as anticyclonic situations with slight winds from SW-NW direction in winter and bora favourable conditions in spring produced the limited number of situations with 24-hour SO2 concentration level greater than 40 μgm-3. From the analysis of the effects of various meteorological elements wind speed and directions were found to be best correlated with the pollution concentration. It is shown that the worst cased air pollulion situations in areas of low emission rates are not necessarily stagnation periods but my be periods with good ventilation