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Areal extremity of windstorms in the Czech Republic
Polášek, Jan Ferdinand ; Kašpar, Marek (advisor) ; Pop, Lukáš (referee)
Areal extremity of windstorms in the Czech Republic Abstract This thesis deals with the extremeness of events with strong winds in the Czech Republic in the period from 1961 to 2009. The first part is dedicated to the principles of air flow dynamics and to wind climatology. The second part describes theoretical distributions used for evaluating the extremeness of wind speed and presents various computation methods of distribution parameters and interpolation methods of converting point data to spatial information. At the end of this part, two modern indices are introduced: WEI (Weather Extremity Index) and SSI (Storm Severity Index) which use return periods and wind speeds for evaluating the extremeness of windstorms, respectively. The third part contains an application of the methods to the pre-processed data from meteorological stations. The fourth section presents the files of 50 most extreme and 50 seasonally most abnormal windstorms selected by both indices which determine in different ways the extremeness, the affected area and duration of each event. The spatial and temporal aspects of the events are discussed as well, along with their seasonal and interannual variability and causal synoptic conditions. Among extreme wind events, most of them are synoptic scale windstorms related to great horizontal...
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Analysis of stability conditions during heavy rains in the Czech republic
Marek, Lukáš ; Kašpar, Marek (advisor) ; Zacharov, Petr (referee)
In this thesis I describe the conceptual model of three kinds of instability in terms of precipitation. I describe ways of evaluating their presence in the atmosphere. They are: conditional instability, potential instability and symmetric instability. I have selected three events with strong precipitation in the Czech Republic so that the formation of each of them is with high probability involved in just one of the three kinds of instability. Events are first described using distance and station measurements. Through the NWP model COSMO are created prognostic fields of precipitation and several derived thermodynamic quantities for each event. On the horizontal (for the whole country) and vertical (for selected areas of the Czech Republic) distribution of these variables are demonstrated favourable conditions for the occurrence of the types of instability in the atmosphere. In the event of conditional instability the rainfall occurs in areas with high CAPE and negative or very small positive vertical lapse rate of potential temperature. The event with the potential instability is characterized by the occurrence of negative vertical lapse rate of equivalent potential temperature in the broad layers. The occurrence of symmetric instability suggests a number of indicators. The necessary occurence...
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Measures of extremity in meteorology
Polášek, Jan Ferdinand ; Kašpar, Marek (advisor) ; Pecho, Jozef (referee)
Measures of extremity in meteorology Abstract This work deals with the methods of extremity quantification of meteorological variables and weather events. The first part is dedicated to the expression of variables by generalized extreme value distribution (GEV) and presents various computation methods of distribution parameters. The second part is dedicated to the extremity of wind storms, heat waves, droughts and heavy precipitation. The third part contains the application of the method based on the order of values and GEV distribution. We evaluate the extremity and abnormality of high daily mean temperatures at the station Milešovka and in the reanalysis ERA-40 and NCEP/NCAR for the grid point representing the Czech Republic. It is shown that the days with positive abnormality of temperature occur more frequently in the warm half-year. The method based on the order of values underestimates the return period of temperature extremes in most cases in comparison with the method based on the GEV distribution. The method based on the GEV distribution is sensitive to various input data. The design values for the station Milešovka increase with the return period more rapidly than reanalysis design values. Keywords: extremity, GEV function, Milešovka, reanalysis, temperature extreme, return period
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Potential instability of thermal stratification in the territory of the CR
Turková, Edita ; Kašpar, Marek (advisor) ; Müller, Miloslav (referee)
This work deals with the conditions of creating and releasing potential instability of temperature stratification, its occurrence in the CR and its influence on the weather. The first part of the work contains a theoretical basis necessary for the understanding of potential instability. Firstly, we describe the adiabatic processes which lead to the genesis of static instability and stability. Then we formulate a criterion of the occurrence and strength of potential instability given by the negative vertical gradient of adiabatic equivalent potential temperature. The second part contains the evaluation of daily, annual and year-on-year variability of the occurrence and strength of potential instability in the layer 850-700 hPa in aerologic station Praha-Libuš from 2000 to 2010. Instability shows no trend in annual frequency there. The highest frequency and strength of instability are observed in the afternoon and during summer months. At the end of the second part, we discuss meteorological conditions during the event when we may expect the release of potential instability. The event is characterized by strong potential instability, upward motions and low CAPE and is accompanied by showers and thunderstorms near Prague. Keywords: potential instability, static stability, adiabatic process
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Convective environment indicies and their comparison
Marek, Lukáš ; Müller, Miloslav (advisor) ; Kašpar, Marek (referee)
In this work I created the overwiew of instability indices and other characteristics of convective environment which can be found in the literature. On the basis of variables, which the instability indices are calculated from, I suggested their categorization. It was created five groups of instability indices: (i) indices of isobaric levels differences, (ii) indices of rising air parcel, (iii) indices of potential temperatures, (iv) indices of the energy potential of convection and (v) indices of wind shear. In addition to these five categories it was created the sixth category consists of other thermodynamic characteristics. In the last chapter I used the upper air soundings data and values of instability indices of the University of Wyoming for one storm in Prague and I compared instability indices to each other. The group of the indices of potential temperatures was the most successful in the storm forecast, except the Rackliff index. The bulk Richardson number from the group of indices of wind shear forecasted a supercell storm correctly. The work could be used for creation of instability climatology of the Czech Republic on the basis of the selected instability indices. Keywords: instability index, convection, convective storm
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Time variability of the vertical copmponent of wind speed and its relationship to other meteorological variables in the Czech Republic
Zeman, Šimon ; Kašpar, Marek (advisor) ; Müller, Miloslav (referee)
Title: Time variability of the vertical component of wind speed and its relationship to other meteorological variables in the Czech Republic Author: Bc. Šimon Zeman Department: Physical Geography and Geoecology Supervisor: RNDr. Marek Kašpar, Ph.D. Abstract: The large-scale vertical velocity of the horizontal scale up to thousands of kilometers has been studied in the presented study. These "centimeters" motions have a significant interest in the formation of cloud and precipitation bands in midlatitudes frontal cyclones. The formation and distribution of large-scale vertical motion in the frontal midlatitude cyclone are mentioned. For the statistical analysis, the data from the reanalysis project ECMWF ERA-40 were used for the Czech territory from 1957 - 2002. From March to July, higher frequency of ascend motions was found. In contrast, descent motions dominated. between September and January. Interannual variability of vertical velocity showed increased frequency of descent motions in the period 1972 - 1982 and increasing frequency of ascend motions between 1983 - 1988. Relationship of vertical velocity and high precipitation has a moderate correlation with exponential regression. Relationship of absolute vorticity advection and vertical velocity have a weak negative correlation. Keywords: vertical...
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