Comparison of an Automated Classification System with an Empirical Classification of Circulation Patterns over the Pannonian Basin, Central Europe

The aim of the study is to compare the performance of the two classification methods, based on the atmospheric circulation types over the Pannonian basin in Central Europe. Moreover, relationships including seasonal occurrences and correlation coefficients, as well as comparative diagrams of the seasonal occurrences of the circulation types of the two classification systems are presented. When comparing of the automated (objective) and empirical (subjective) classification methods, it was found that the frequency of the empirical anticyclonic (cyclonic) types is much higher (lower) than that of the automated anticyclonic (cyclonic) types both on an annual and seasonal basis. The highest and statistically significant correlations between the circulation types of the two classification systems, as well as those between the cumulated seasonal anticyclonic and cyclonic types occur in winter for both classifications, since the weather-influencing effect of the atmospheric circulation in this season is the most prevalent. Precipitation amounts in Budapest display a decreasing trend in accordance with the decrease in the occurrence of the automated cyclonic types. In contrast, the occurrence of the empirical cyclonic types displays an increasing trend. There occur types in a given classification that are usually accompanied by high ratios of certain types in the other classification

Regional climate hindcast simulations within EURO-CORDEX: evaluation of a WRF multi-physics ensemble

In the current work we present six hindcast WRF (Weather Research and Forecasting model) simulations for the EURO-CORDEX (European Coordinated Regional Climate Downscaling Experiment) domain with different configurations in microphysics, convection and radiation for the time period 1990?2008. All regional model simulations are forced by the ERA-Interim reanalysis and have the same spatial resolution (0.44°). These simulations are evaluated for surface temperature, precipitation, short- and longwave downward radiation at the surface and total cloud cover. The analysis of the WRF ensemble indicates systematic temperature and precipitation biases, which are linked to different physical mechanisms in the summer and winter seasons. Overestimation of total cloud cover and underestimation of downward shortwave radiation at the surface, mostly linked to the Grell?Devenyi convection and CAM (Community Atmosphere Model) radiation schemes, intensifies the negative bias in summer temperatures over northern Europe (max ?2.5 °C). Conversely, a strong positive bias in downward shortwave radiation in summer over central (40?60%) and southern Europe mitigates the systematic cold bias over these regions, signifying a typical case of error compensation. Maximum winter cold biases are over northeastern Europe (?2.8 °C); this location suggests that land?atmosphere rather than cloud?radiation interactions are to blame. Precipitation is overestimated in summer by all model configurations, especially the higher quantiles which are associated with summertime deep cumulus convection. The largest precipitation biases are produced by the Kain?Fritsch convection scheme over the Mediterranean. Precipitation biases in winter are lower than those for summer in all model configurations (15?30%). The results of this study indicate the importance of evaluating not only the basic climatic parameters of interest for climate change applications (temperature and precipitation), but also other components of the energy and water cycle, in order to identify the sources of systematic biases, possible compensatory or masking mechanisms and suggest pathways for model improvement.The contribution from Universidad de Cantabria was funded by the Spanish R&D programme through projects CORWES (CGL2010-22158-C02-01) and WRF4G (CGL2011-28864), co-funded by the European Regional Development Fund. M. García-Díez acknowledges financial support from the EXTREMBLES (CGL2010-21869) project

Εφαρμογή καινοτόμου μεθοδολογίας αξιολόγησης και βελτιστοποίησης του μοντέλου WRF για τη μελέτη καταιγιδοφόρων δραστηριοτήτων στην περιοχή της Θεσσαλίας

The present PhD dissertation investigated the capability of a state of the art numerical prediction model to represent convective activity in the region of Thessaly, Central Greece. The mesoscale meteorological model Weather Research and Forecasting (WRF), was tested in order to discover the optimal configuration able to simulate convective events. An ensemble of twelve different model configurations was put under test, simulating days with high convective activity. The impact of microphysics (MP), cumulus convection (CU) and planetary boundary layer (PBL) schemes was investigated and the best performing combination was chosen. Three MP schemes (Ferrier, WRF single-moment 6-classes, and Goddard), two CU schemes (Kain Fritch and Betts-Miller-Janjić) and two PBL (Yonsei University and Mellor-Yamada- Janjić) were tested. In the first stage, results of the simulations for seven individual cases were statistically evaluated against surface observations and radar data using classic statistical methods. The best performing setup was chosen and further evaluated in the second stage by widening the experimental sample. Thirty six more cases were selected and classified according to the prevailing synoptic conditions. Statistics were obtained for every synoptic type assuring that the selected setup performs adequately in every case. The final stage involved the application of a novel statistical method for the evaluation of the original ensemble of simulations. The new method belongs to the spatial methods, that do not perform a point to point evaluation, but they rather try to distinguish similarities between the observed and forecast fields. The particular method employed, Method for Object Based Diagnostic Evaluation (MODE), uses objects, discrete entities inside the field, and examines their characteristics. The similarity of the characteristics between the observed and forecast objects, as expressed by the appropriate metrics, provides the performance of the model. In the present study the field of reflectivity was used to derive the objects. The result of this novel method confirmed that the model setup, selected primarily using classic statistical methods has the best performance according to the new method too. This way the WRF-ARW model, with this configuration, can be a useful tool in every situation where a high convective event should be studied employing a numerical weather prediction model.Η παρούσα διδακτορική διατριβή διερεύνησε την ικανότητα ενός αριθμητικού μοντέλου πρόγνωσης καιρού στην αναπαράσταση καταιγιδοφόρων δραστηριοτήτων στην περιοχή της Θεσσαλίας. Το μετεωρολογικό μοντέλο μέσης κλίμακας WRF, δοκιμάστηκε προκειμένου να βρεθεί η βέλτιστη διαμόρφωση ικανή να προσομοιώνει την καταιγιδοφόρο δραστηριότητα. Ένα σύνολο δώδεκα διαφορετικών διαμορφώσεων του μοντέλου τέθηκε υπό δοκιμή, προσομοιώντας ημέρες με υψηλή καταιγιδοφόρο δραστηριότητα. Εξετάστηκε η επίδραση των σχημάτων μικροφυσικής (MP), ανωμεταφοράς (CU) και πλανητικού οριακού στρώματος (PBL) και επιλέχθηκε ο συνδυασμός με τις καλύτερες επιδόσεις. Χρησιμοποιήθηκαν τρία σχήματα μικροφυσικής (Ferrier, WSM6 και Goddard), δύο σχήματα ανωμεταφοράς (Kain Fritch και Betts-Miller-Janjic) και δύο σχήματα οριακού στρώματος (Yonsei University και Mellor-Yamada-Jancic). Στο πρώτο στάδιο, τα αποτελέσματα των προσομοιώσεων αξιολογήθηκαν στατιστικά για επτά μεμονωμένες περιπτώσεις χρησιμοποιώντας παρατηρήσεις επιφάνειας και δεδομένα ραντάρ με τη χρήση κλασικών στατιστικών μεθόδων. Ο συνδυασμός με τις καλύτερες επιδόσεις επιλέχθηκε και αξιολογήθηκε περαιτέρω στο δεύτερο στάδιο διευρύνοντας το πειραματικό δείγμα. Προστέθηκαν τριάντα έξι περισσότερες περιπτώσεις και ταξινομήθηκαν σύμφωνα με τις επικρατούσες συνοπτικές συνθήκες. Λαμβάνοντας στατιστικά για κάθε συνοπτικό τύπο διασφαλίστηκε ότι ο επιλεγμένος συνδυασμός παράγει ικανοποιητικά αποτελέσματα σε κάθε περίπτωση. Το τελευταίο στάδιο αφορούσε την εφαρμογή μιας νέας στατιστικής μεθόδου για την αξιολόγηση του αρχικού συνόλου προσομοιώσεων. Η νέα μέθοδος ανήκει στις χωρικές μεθόδους, οι οποίες δεν εκτελούν αξιολόγηση σημείο προς σημείο, αλλά προσπαθούν να διακρίνουν τις ομοιότητες μεταξύ των παρατηρούμενων και των προσομοιωμένων πεδίων. Η συγκεκριμένη μέθοδος που χρησιμοποιείται, η Μέθοδος για τη Διαγνωστική Αξιολόγηση Βάσει Αντικειμένων (MODE), χρησιμοποιεί αντικείμενα, διακριτές οντότητες μέσα στο πεδίο, και εξετάζει τα χαρακτηριστικά τους. Η ομοιότητα μεταξύ των παρατηρούμενων και των προσομοιωμένων αντικειμένων, όπως αυτή εκφράζεται χρησιμοποιώντας τις κατάλληλες μετρικές, χαρακτηρίζει την απόδοση του μοντέλου. Στην παρούσα μελέτη χρησιμοποιήθηκε το πεδίο της ανακλαστικότητας για την εξαγωγή των αντικειμένων. Το αποτέλεσμα αυτής της νέας μεθόδου επιβεβαίωσε ότι η διαμόρφωση του μοντέλου, που επιλέχθηκε αρχικά με κλασσικές στατιστικές μεθόδους, έχει την καλύτερη απόδοση και σύμφωνα με τη νέα μέθοδο. Με αυτό τον τρόπο το μοντέλο WRF-ARW, με τη συγκεκριμένη διαμόρφωση μπορεί να είναι ένα χρήσιμο εργαλείο στη μελέτη καταιγιδοφόρου δραστηριότητας στην περιοχή της Θεσσαλίας

Sensitivity of a Mediterranean Tropical-Like Cyclone to Physical Parameterizations

The accurate prediction of Mediterranean tropical-like cyclones, or medicanes, is an important challenge for numerical weather prediction models due to their significant adverse impact on the environment, life, and property. The aim of this study is to investigate the sensitivity of an intense medicane, which formed south of Sicily on 7 November 2014, to the microphysical, cumulus, and boundary/surface layer schemes. The non-hydrostatic Weather Research and Forecasting model (version 3.7.1) is employed. A symmetric cyclone with a deep warm core, corresponding to a medicane, develops in all of the experiments, except for the one with the Thompson microphysics. There is a significant sensitivity of different aspects of the simulated medicane to the physical parameterizations. Its intensity is mainly influenced by the boundary/surface layer scheme, while its track is mainly influenced by the representation of cumulus convection, and its duration is mainly influenced by microphysical parameterization. The modification of the drag coefficient and the roughness lengths of heat and moisture seems to improve its intensity, track, and duration. The parameterization of shallow convection, with explicitly resolved deep convection, results in a weaker medicane with a shorter lifetime. An optimum combination of physical parameterizations in order to simulate all of the characteristics of the medicane does not seem to exist

Numerical Study of the Medicane of November 2014

A hurricane-like cyclone with an `eye', eyewall convection and strong winds affected central Mediterranean basin on 7-8 November 2014. The maximum observed sustained wind speed was 22 m/s (tropical storm strength) at Lampedusa. Significant damages were reported from this island and the coastal regions of eastern Sicily. Thus, it is essential to study medicanes and calibrate the numerical weather prediction models in order to simulate them adequately. Operational ECMWF analyses are used together with the non-hydrostatic Weather Research and Forecasting numerical model with the Advanced Research dynamic solver (WRF-ARW ver 3.7.1). The aims of this study are to simulate the system and investigate the sensitivity of the model on the microphysical scheme, the number of vertical levels and the global input dataset. The main characteristics of the medicane are represented in good agreement with observations and analyses, but, no single setup is able to provide the best reproduction of all its features