Deterministic methods for prediction of tropical cyclone tracks

ABSTRACT. The paper presents a state-of-art review of different objective techniques available for tropical cyclone track prediction. A brief description of current theories of tropical cyclone motion is given. Deterministic models with statistical and dynamical methods have been discussed. Recent advances in the understanding of cyclone structure and motion aspects have led to improved prediction of tropical cyclones. There has been considerable progress in the field of prediction by dynamical methods. High resolution Limited Area Models (LAM) as well as Global Circulation Models (GCM) are now being used extensively by most of the leading operational numerical weather prediction (NWP) centres in the world The major achievements towards improvement of such models have come from improved horizontal resolution of the models, inclusion of physical processes, use of synthetic and other non-conventional data in the data assimilation schemes and nudging method for initial matching of analysed cyclone centres with corresponding observations. A brief description of further improvement in deterministic approach for prediction of tropical cyclone tracks is outlined.

Variability of Saharan Cyclone Tracks, I: Climatology Study

Objectively, Saharan cyclones have been detected for the period from 1967 to 2019 using mean sea level pressure (SLP); their tracks have been specified from nearest neighbor cyclonic positions and classified into long/short tracks depending on the area of influence of the cyclones. Additionally, the detected long tracks have been objectively classified into five main routes directed generally eastward, northeastward and northward, accounting for approximately 41.6%, 19.7% and 30.4% of the total long tracks, respectively. Mainly for long tracks, three cyclogenesis areas, where more than 99% of cyclones are generated, were identified, with more than 61% generated in the Atlas region. Moreover, four far cyclolysis areas were identified, where approximately 74% of these cyclones terminated, with more than 66% of them terminating in the eastern study region. Furthermore, statistical analysis indicated that Saharan cyclones are commonly generated in the spring and summer, with ~35.3% and 46.3%, respectively. However, the highest numbers occur in spring in the northern Saharan and in summer in the southern Saharan, with ~49.1% and 57.7%, respectively. Temporally, the monthly distribution indicates that most of the cyclones moving along the five main routes are generated in warm months, namely, May to August. Approximately 85% of these cyclones have a lifespan of three days, while only 1% span more than five days.

Simulating synthetic tropical cyclone tracks for statistically reliable wind and pressure estimations

The design of coastal protection measures and the quantification of coastal risks at locations affected by tropical cyclones (TCs) are often based solely on the analysis of historical cyclone tracks. Due to data scarcity and the random nature of TCs, the assumption that a hypothetical TC could hit a neighboring area with equal likelihood to past events can potentially lead to over- and/or underestimations of extremes and associated risks. The simulation of numerous synthetic TC tracks based on (historical) data can overcome this limitation. In this paper, a new method for the generation of synthetic TC tracks is proposed. The method has been implemented in the highly flexible open-source Tropical Cyclone Wind Statistical Estimation Tool (TCWiSE). TCWiSE uses an empirical track model based on Markov chains and can simulate thousands of synthetic TC tracks and wind fields in any oceanic basin based on any (historical) data source. Moreover, the tool can be used to determine the wind extremes, and the output can be used for the reliable assessment of coastal hazards. Validation results for the Gulf of Mexico show that TC patterns and extreme wind speeds are well reproduced by TCWiSE.

Variabilität trockenheitsrelevanter Zirkulationstypen im südlichen Mitteleuropa

<p>Im Rahmen des bilateralen Forschungsprojekts WETRAX+ (WEather Patterns, Cyclone TRAcks and related precipitation eXtremes) wird unter anderem der Zusammenhang zwischen großräumigen atmosphärischen Zirkulationstypen und Trockenperioden im südlichen Mitteleuropa unter dem Einfluss des Klimawandels untersucht. Das Untersuchungsgebiet umfasst dabei Österreich sowie Teile Deutschlands, der Schweiz und der Tschechischen Republik.</p> <p>Für eine, auf den Niederschlag konditionierte Zirkulationstypklassifikation wurden atmosphärische Variablenfelder aus gegitterten täglichen JRA55-Reanalysedaten (Japanische Meteorologische Agentur 2018) und tägliche Niederschlagsdaten auf Basis von 1756 Wetterstationen im Untersuchungsgebiet (Zentralanstalt für Meteorologie und Geodynamik 2018) für den Beobachtungszeitraum 1961 bis 2017 verwendet. Zur Abschätzung künftiger Veränderungen wurden sechs verschiedene regionale Klimamodellläufe (Treibhausgasszenario RCP 8.5) der Euro-Cordex – Initiative herangezogen.</p> <p>Die großräumigen atmosphärischen Zirkulationstypen werden unter Verwendung einer nicht-hierarchischen Clusteranalyse, die in der COST733 Classification Software bereitgestellt wird, abgeleitet. Den resultierenden Zirkulationstypen können Eigenshaften (trocken, feucht, warm, kalt) zugeordnet werden. Die trockenheitsrelevanten Zirkulationstypen werden hinsichtlich Trends,  Persistenzen, Veränderungen der monatlichen Auftrittshäufigkeiten und der  typinternen Variabilität untersucht. Bei der Übertragung der Zirkulationstypen auf die Klimamodelldaten wird jeder Einzeltag des Projektions-Zeitraums demjenigen Zirkulationstypen zugeordnet, zu dessen Zentroidfeldern die betreffenden Einzelfelder die geringste euklidische Distanz aufweisen.</p> <p>Im Beobachtungszeitraum zeigen die Analysen, dass das Auftreten trockenheitsrelevanter Zirkulationstypen signifikant häufiger mit höheren Temperaturen und einer geringeren relativen Luftfeuchte einhergeht. Erste Ergebnisse der Analyse für die Klimazukunft ergeben für die Monate April bis September eine Zunahme zentraler Hochdruckgebiete über Mittel- und Osteuropa, während antizyklonale Trogvorderseiten mit resultierender, südwestlicher Anströmungsrichtung für das Untersuchungsgebiet seltener auftreten.</p>