THE METEOROLOGICAL ASPECTS OF THE DART FIELD EXPERIMENT AND PRELIMINARY RESULTS

DART (Dynamics of the Adriatic in Real-Time) is a project devoted to real time observational and modelling study of the Adriatic Sea involving a considerable number of organisations from Europe and US. Several ocean and wave models were run using different meteorological model outputs for input atmospheric conditions. Two field campaigns (research cruises) were organised, during March and August 2006. This paper presents the role of meteorology and operational meteorological models in an oceanographic research cruise. Real-time measurement and model capabilities are described in detail with brief analysis of two severe weather events

The Adriatic Sea wave response to severe Bura wind

Bura is a strong wind with severe gusts; it occurs suddenly and affects safety of life at sea. It has a large spatial variability and depends on an upstream terrain configuration. The quality of surface winds derived from meteorological models is the key issue (and input) in wave modelling. In this study we are addressing question of storm Bura wind and effect on wave field response. Increase in the predicted wind field resolution from 8 to 2 km using Aladin model dynamical adaptation enables high resolution wave forecast as well. There is little information about detailed structure of the wave field (significant height and direction) in the Adriatic Sea produced by severe Bura wind. Results for wave response of the Adriatic Sea for 13-18 of November 2004 storm are presented and discussed in detail, as well as differences due to forcing of the wave model with 8 km and 2 km ALADIN wind fields. Comparison of modelled wave response is made with in situ ADCP wave measurements

Alternative formulations for incorporating lateral boundary data into limited area models

Limited-area models (LAMs) use higher resolutions and more advanced parameterizations of physical processes than global numerical weather prediction models, but suffer from one additional source of error-the lateral boundary condition (LBC). The large-scale model passes the information on its fields to the LAM only over the narrow coupling zone at discrete times separated by a coupling interval of several hours. The LBC temporal resolution can be lower than the time necessary for a particular meteorological feature to cross the boundary. A LAM user who depends on LBC data acquired from an independent prior analysis or parent model run can find that usual schemes for temporal interpolation of large-scale data provide LBC data of inadequate quality. The problem of a quickly moving depression that is not recognized by the operationally used gridpoint coupling scheme is examined using a simple one-dimensional model. A spectral method for nesting a LAM in a larger-scale model is implemented and tested. Results for a traditional flow-relaxation scheme combined with temporal interpolation in spectral space are also presented

Modeliranje izvora i transporta zagađenja na jugoistočnu obalu Jadrana (Hrvatska)

In this study we analysed meteorological and oceanographic conditions that lead to the waste deposition along the southeast Croatian coast during the second half of November 2010. We used available in situ measurements, atmospheric products (reanalysis, remote sensing) as well as atmosphere and ocean numerical models. The measured meteorological data reveal that an intensive rainfall event occurred from 7 till 10 November 2010, over the parts of Montenegro and Albania. It was followed by a substantial increase of the river water levels indicating a possibility of flash floods, capable of splashing the waste material into a river and after to the Adriatic Sea (or to the sea directly). The currents that could bring this waste to Croatian coast are likely intensified by the strong wind from southeast direction. In order to test these two hypotheses we set a number of numerical drifter experiments with trajectories initiated over southeast Adriatic during the intensive rainfall events following their path in space and time. The numerical drifter trajectory experiments that resulted with drifters reaching the right position (southeastern Adriatic coast) at exact time the waste was observed were initiated on 00:00 and 12:00 UTC of 10 November 2010 during the mentioned high precipitation event.U ovom radu analizirali smo meteorološke i oceanografske uvjete koji su mogli doprinijeli nakupljanju otpada na jugoistočnoj obali Jadrana tijekom druge polovice studenog 2010. Pritom smo koristili dostupna mjerenja, produkate modela te daljinska mjerenja. Mjereni meteorološki podaci ukazuju na period intenzivne oborine nad područjem Albanije i Crne Gore, u period od 7. do 10. studenog 2010. Nakon događaja uslijedio je značajan porast razine lokalnih rijeka. Upravo ovaj podatak ukazuje na mogućnost bujičnih poplava koje su mogle navedeni otpad odnjeti u rijeke i zatim u Jadran (ili izravno u Jadran). Također je opaženo da su površinske morske struje, povoljne za transport otpada do hrvatske obale, bile intenzivnije usljed jakog vjetra iz smjera jugoistoka. U svrhu provjere navedenih hipoteza proveli smo niz numeričkih eksperimenata pomoću numeričkih driftera simuliranih na području jugoistočnog Jadrana, upravo tijekom perioda s opaženom jakom oborinom, a čije smo putanje računali u prostoru i vremenu. Eksperimenti s putanjama koje su stigle do traženog područja (jugoistočna obala Jadrana) u pravom vremenskom trenutku (kada je zabilježeno nakupljanje otpada) započele su gibanje u 00 i 12 UTC 10. studenog 2010, upravo tijekom spomenutog događaja s velikom količinom oborine

MAP IOP 15 CASE STUDY

The paper presents the ability of forecasting severe bura events on the Adriatic coast using the ALADIN model operationally used at the Croatian Meteorological Service. Both versions currently in use, the LACE and the Croatian version, as well as the dynamical adaptation of the surface wind field from the latter have been tested on a MAP IOP 15 case. The MAP IOP 15 took place between 5th and 10th November 1999. The strongest bura was recorded around 12 UTC on 7th November. Different versions of the same numerical model have been used on different domains and resolutions. The output surface wind fields from the 8-km resolution Croatian domain have been dynamically adapted to orography with a 2-km resolution, and both results have been compared to the measured data. The latter method proved to be very useful for locations where bura is the most severe, like the Maslenica bridge. The impact of a better representation of orography on the forecasted wind field in the mountainous parts of the coast is visible in the increased spatial variability of the field

Poboljšanje operativne prognoze opasnih vremenskih prilika numeričkim mezomodelom ALADIN

Severe weather represents storms, cyclones, fronts, severe wind or thick fog and other phenomena. Limited area models (LAM) can simulate or forecast such phenomena in higher resolution and using dedicated model set-up. This thesis explores the ALADIN (Aire Limitée Adaptation dynamique Développement InterNational) model capabilities to forecast threatening weather conditions for wider area of the Republic of Croatia. The research focuses on the consequences of a fast cyclone entering LAM domain through lateral boundary too quickly to be detected, frequency of such events, mechanism for automatic detection of such events and methods to treat the problem in the operational forecast. The solution will be applied to events with severe weather such as windstorms and/or intensive precipitation. This thesis deals with problems of temporal interpolation of the lateral boundary conditions (LBC) for a limited area model (LAM). The LBCs are taken from a large scale model and usually available with an interval of several hours. However, these data are used at the lateral boundaries every model timestep, which is usually several minutes. Therefore, the LBCs are interpolated in time. In practice, the LBCs are usually interpoated with a 3 h temporal resolution. This can be too infrequent to resolve rapidly moving storms. This problem is expected to be worse with increasing horizontal resolution. In order to detect intensive disturbances in surface pressure moving rapidly through the model domain, a filtered surface pressure field (MCUF - monitoring of the coupling update frequency) is computed operationally in the ARPEGE global model of Météo France. The field is distributed in the coupling files along with conventional meteorological fields used for LBCs for the operational forecast using ALADIN LAM in the Meteorological and Hydrological Service of Croatia (DHMZ). Here an analysis is performed of the MCUF field for the LACE coupling domain for the period since 23rd of January 2006, when it became available, until 15th of November 2014. The MCUF field is a good indicator of rapidly moving pressure disturbances (RMPDs). Its spatial and temporal distribution can be associated to the usual cyclone tracks and areas known to be supporting cyclogenesis. Alternative set of coupling files from IFS operational run in ECMWF is also available operationally in DHMZ with 3 h temporal resolution but the MCUF field is not available. Here, several methods are tested that detect RMPDs in surface pressure a posteriori from the IFS model fields provided in the coupling files. MCUF is computed by running ALADIN on the coupling files from IFS. The coupling error function [There are many functions called error function in the literature, this work focuses on the coupling error function] (that shows when the temporal interpolation misses the storm) is computed using one time step integration of ALADIN on the coupling files without initialization, initialized with digital filter initialization (DFI) or scale selective DFI (SSDFI). Finally, the amplitude of changes in the mean sea level pressure is computed from the fields in the coupling files. The results are compared to the MCUF field of ARPEGE and the results of same methods applied to the coupling files from ARPEGE. Most methods give a signal for the RMPDs, but DFI reduces the storms too much to be detected. The coupling error function without filtering and amplitude have more noise, but the signal of a RMPD is also stronger. The methods are tested for NWP LAM ALADIN, but could be applied to other LAMs and benefit the performance of climate LAMs. Usually, LAMs use higher resolutions and more advanced parameterizations of physical processes than global numerical weather prediction models, but suffer from one additional source of error - the LBCs. The large scale model passes the information on its fields to LAM only over the narrow coupling zone at discrete times separated by a coupling interval of several hours. The LBC temporal resolution can be lower than the time necessary for a particular meteorological feature to cross the boundary. A LAM user who depends on LBC data acquired from an independent prior analysis or parent model run can find that usual schemes for temporal interpolation of large scale data provide LBC data of inadequate quality. The problem of a quickly moving depression that is not recognized by the operationally used gridpoint coupling scheme is examined using a simple one-dimensional model. A spectral method for nesting a LAM in a larger scale model is implemented and tested. Results for a traditional flow-relaxation scheme combined with temporal interpolation in spectral space are also presented. The work presented here shows that more frequent LBCs are important for forecasting small storms even when they develop inside the domain. Missing a storm in a LAM forecast due to infrequent LBCs has lead to a model tuning that enhances storm development. Unfortunately, the same tuning is not very supportive for the fog development.Prošireni sažetak na hrvatskom jeziku u disertacij

Poboljšanje operativne prognoze opasnih vremenskih prilika numeričkim mezomodelom ALADIN

Severe weather represents storms, cyclones, fronts, severe wind or thick fog and other phenomena. Limited area models (LAM) can simulate or forecast such phenomena in higher resolution and using dedicated model set-up. This thesis explores the ALADIN (Aire Limitée Adaptation dynamique Développement InterNational) model capabilities to forecast threatening weather conditions for wider area of the Republic of Croatia. The research focuses on the consequences of a fast cyclone entering LAM domain through lateral boundary too quickly to be detected, frequency of such events, mechanism for automatic detection of such events and methods to treat the problem in the operational forecast. The solution will be applied to events with severe weather such as windstorms and/or intensive precipitation. This thesis deals with problems of temporal interpolation of the lateral boundary conditions (LBC) for a limited area model (LAM). The LBCs are taken from a large scale model and usually available with an interval of several hours. However, these data are used at the lateral boundaries every model timestep, which is usually several minutes. Therefore, the LBCs are interpolated in time. In practice, the LBCs are usually interpoated with a 3 h temporal resolution. This can be too infrequent to resolve rapidly moving storms. This problem is expected to be worse with increasing horizontal resolution. In order to detect intensive disturbances in surface pressure moving rapidly through the model domain, a filtered surface pressure field (MCUF - monitoring of the coupling update frequency) is computed operationally in the ARPEGE global model of Météo France. The field is distributed in the coupling files along with conventional meteorological fields used for LBCs for the operational forecast using ALADIN LAM in the Meteorological and Hydrological Service of Croatia (DHMZ). Here an analysis is performed of the MCUF field for the LACE coupling domain for the period since 23rd of January 2006, when it became available, until 15th of November 2014. The MCUF field is a good indicator of rapidly moving pressure disturbances (RMPDs). Its spatial and temporal distribution can be associated to the usual cyclone tracks and areas known to be supporting cyclogenesis. Alternative set of coupling files from IFS operational run in ECMWF is also available operationally in DHMZ with 3 h temporal resolution but the MCUF field is not available. Here, several methods are tested that detect RMPDs in surface pressure a posteriori from the IFS model fields provided in the coupling files. MCUF is computed by running ALADIN on the coupling files from IFS. The coupling error function [There are many functions called error function in the literature, this work focuses on the coupling error function] (that shows when the temporal interpolation misses the storm) is computed using one time step integration of ALADIN on the coupling files without initialization, initialized with digital filter initialization (DFI) or scale selective DFI (SSDFI). Finally, the amplitude of changes in the mean sea level pressure is computed from the fields in the coupling files. The results are compared to the MCUF field of ARPEGE and the results of same methods applied to the coupling files from ARPEGE. Most methods give a signal for the RMPDs, but DFI reduces the storms too much to be detected. The coupling error function without filtering and amplitude have more noise, but the signal of a RMPD is also stronger. The methods are tested for NWP LAM ALADIN, but could be applied to other LAMs and benefit the performance of climate LAMs. Usually, LAMs use higher resolutions and more advanced parameterizations of physical processes than global numerical weather prediction models, but suffer from one additional source of error - the LBCs. The large scale model passes the information on its fields to LAM only over the narrow coupling zone at discrete times separated by a coupling interval of several hours. The LBC temporal resolution can be lower than the time necessary for a particular meteorological feature to cross the boundary. A LAM user who depends on LBC data acquired from an independent prior analysis or parent model run can find that usual schemes for temporal interpolation of large scale data provide LBC data of inadequate quality. The problem of a quickly moving depression that is not recognized by the operationally used gridpoint coupling scheme is examined using a simple one-dimensional model. A spectral method for nesting a LAM in a larger scale model is implemented and tested. Results for a traditional flow-relaxation scheme combined with temporal interpolation in spectral space are also presented. The work presented here shows that more frequent LBCs are important for forecasting small storms even when they develop inside the domain. Missing a storm in a LAM forecast due to infrequent LBCs has lead to a model tuning that enhances storm development. Unfortunately, the same tuning is not very supportive for the fog development.Prošireni sažetak na hrvatskom jeziku u disertacij

ALADIN/HR: TESTING THE NEW SUB-GRID SCALE OROGRAPHY REPRESENTATION ON BURA CASES

Especially important for the coastal area of Croatia is the wind forecast, particularly during the bura windstorm episodes. Current operational version of ALADIN model is rather satisfactory for the wind field forecast, although in many cases the wind speed is somewhat overestimated. A modified subgrid scale orography representation was introduced and tested. The envelope was removed and to compensate for the loss of volume, changes in gravity wave drag parametrisation were introduced. New orography representation resulted in slight enhancement of upstream and general decrease of downstream wind speed, as well as reduction of mountain wave amplitude