National Repository of Grey Literature 40 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Possibilities of Using of Remote Detection Data for Convective Storms Intensity Nowcasting
Valachová, Michaela ; Žák, Michal (advisor)
Title: Possibilities of Using of Remote Detection Data for Convective Storms Intensity Nowcasting Author: Michaela Valachová Department: Department of Atmospheric Physics Supervisor: Mgr. Michal Žák, Ph.D., Department of Atmospheric Physics Abstract: Evolution of 60 isolated convective storms from 2016 and 2017, which formed in the region of Central Europe, is studied by means of multi-sensor observations. According to the reports from the European Severe Weather Da- tabase, two categories of storms are classified: severe and non-severe. Based on radar, lightning and satellite measurements, trends of storm characteristics are analyzed to ascertain their typical behavior. Lightning stroke rates and their change could well warn about the ability of the storm to become severe, therefore a Lightning jump algorithm was proposed within this work. From individual case studies follows that methods of remote sensing offer comprehensive information about convective storm life-cycles. In order to objectively determine crucial variables for estimating the storm se- verity, logistic regression models and regularized regressions (elastic net) are employed. In total 53 variables from the first 30, 60 and 90 minutes of the moni- tored storm lifetime are used to show their predictive skill. Results of the models indicate...
Precipitation nowcasting for the warm part of the year
Mejsnar, Jan ; Sokol, Zbyněk (advisor) ; Jaňour, Zbyněk (referee) ; Žák, Michal (referee)
Current precipitation nowcasting systems primarily use the extrapolation of observed radar reflectivity. I used the extrapolation and studied limits of the forecast using the concept of the decorrelation time (DCT). I used data from two radars covering the territory of the Czech Republic from warm parts of four years and calculated DCT in dependence on several selected conditions describing the state of the atmosphere. I found that the mean DCT for the extrapolation is 45.4 minutes. On average the increase of the DCT in comparison when the persistence forecast is employed is 13.4 minutes. However, in dependence on current conditions the DCT may increase or decrease in more than 40 %. I also explored time evolution of the DCT during two storm events. I found that the DCT may significantly change in time, which is the consequence of changing character of the atmosphere during the storm development.
Single-Step Purification of Raw Biogas to Biomethane Quality by Hollow Fiber Membranes without any Pre-Treatment – Innovation in Biogas Upgrading.
Žák, Michal
Herein, a radical innovation in biogas production is presented using a single-step membrane purification technology without any necessary pre-treatment steps for contaminant removal. Asymmetric hollow fiber membranes with a thin, selective, non-porous layer made from polyester carbonate on the bore side were successfully used in a single-step raw biogas upgrading process at biogas plant Choťovice in Czech Republic.\n
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On the assessment of urbanization application in weather forecasting model
Nováková, Tereza ; Halenka, Tomáš (advisor) ; Žák, Michal (referee)
Built-up areas represent an artifiial impait to natural environment with large spatial variability and speiifi meihaniit radiationt thermal and ihemiial properties. Despite of inireasing horizontal resolution of numeriial weather prediition modelst the impait of loial built-up area on mesosynoptiv weather phenomena is still not well resolved. Therefore it is neiessary to use some of urban environment modelst whiih were designed to parameterize speiifi urban prosiessest not expliiitly resolved inside the grid box. In the thesis main urban iharaiteristiis are explained (impait on the struiture of boundary layert radiation and heat balanie of urban environment or urban heat island)t basii priniiples of urbanization appliiation in the numeriial weather model are desiribedt as well as different urban parameterizations available in numeriial model WRFe (Weather Reseaih and Feoreiasting). Number of validation experiments were performed for summer and winter episode in non-hydrostatii mode at 3t3 km resolutiont where different urban parametrizationst antropogenii heat adjustment and impait of mosaii land-use were tested. April 2018 Prague weather foreiast was verifiated in ionsideration of urban heat island.
Possibilities of Using of Remote Detection Data for Convective Storms Intensity Nowcasting
Valachová, Michaela ; Žák, Michal (advisor) ; Bližňák, Vojtěch (referee) ; Simon, André (referee)
Title: Possibilities of Using of Remote Detection Data for Convective Storms Intensity Nowcasting Author: Michaela Valachová Department: Department of Atmospheric Physics Supervisor: Mgr. Michal Žák, Ph.D., Department of Atmospheric Physics Abstract: Evolution of 60 isolated convective storms from 2016 and 2017, which formed in the region of Central Europe, is studied by means of multi-sensor observations. According to the reports from the European Severe Weather Da- tabase, two categories of storms are classified: severe and non-severe. Based on radar, lightning and satellite measurements, trends of storm characteristics are analyzed to ascertain their typical behavior. Lightning stroke rates and their change could well warn about the ability of the storm to become severe, therefore a Lightning jump algorithm was proposed within this work. From individual case studies follows that methods of remote sensing offer comprehensive information about convective storm life-cycles. In order to objectively determine crucial variables for estimating the storm se- verity, logistic regression models and regularized regressions (elastic net) are employed. In total 53 variables from the first 30, 60 and 90 minutes of the moni- tored storm lifetime are used to show their predictive skill. Results of the models indicate...
Multimodel weather forecast comparison
Žáček, Ondřej ; Žák, Michal (advisor) ; Brožková, Radmila (referee)
This thesis analyses comparison and verification of three global numeric weather models, GFS, ECMWF, NEMS. The research subjects are make comparison of their 48-hour forecast with, for this thesis created, index correspondence of models and evaluate predictability of weather. Next, introduce basic verification methods and their application to forecast verification, from previously mentioned models, against surface observations with resolution 2 ř x 2 ř lat/lon between 1. 6. 2017-28. 2. 2018. Results show, that the worst predictability is at areas with continental glaciers, extensive world mountain ranges and at ITCZ area. The best predictability is observed in subtropical anticyclones over the oceans. Verification of temperature we find out significant smoothing of diurnal cycle in all three models. Biases of relative humidity are strongly negative corelated with temperature bias, skill score for relative humidity is worse than for temperature. Performance of mean sea level pressure is the best for all verification metrics from all analysed quantities. Wind speed is for most world overestimated. Results of 3-hour precipitation depends on treshold. Models overestimate frequency of low intensity precipitation, opposite results are observed for high intensity precipitation, break occur at interval...
Separation of Gasses by Supported Liquid Membranes.
Izák, Pavel ; Žitková, Andrea ; Žák, Michal ; Vejražka, Jiří ; Kárászová, Magda ; Petrusová, Zuzana
Two swollen polyamide thin-film composite membranes were tested for effective CO2/CH4 separation. It was found that the water wettability has a key role for the separation of binary mixture representing a raw biogas, i.e. containing CO2 and CH4. The transport properties were analyzed by means of a mathematical model simulating gas permeation. A new modification of the mass transport coefficient model provided the concentration profiles of individual components on both sides of the membrane (inaccessible in experiments). Furthermore, the model enabled the evaluation of the mass transport coefficients of the gases in the mixture under varying stream flow rates and arrangements with respect to the membrane separation cell size. Therefore, the possibility of scale-up was discussed for both membranes and flow cell arrangement. Although the mathematical model was developed for a flat sheet membrane configuration, the results can be applied for a real spiral wound module with a wider surface.
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Extreme precipitation in low mountain ranges in Central Europe: a comparative study between the Vosges and the Ore mountains
Minářová, Jana ; Müller, Miloslav (advisor) ; Žák, Michal (referee) ; Caumont, Olivier (referee)
of the doctoral dissertation Extreme precipitation is related to flooding which is one of the most frequent natural hazards in Central Europe. Detailed understanding of extreme precipitation is the precondition for an efficient risk management and more precise projections of precipitation, which include uncertainties, especially at regional scale. The thesis focuses on extreme precipitation in the Ore Mountains (OM) and the Vosges Mountains (VG); two low mountain ranges in Central Europe experiencing orographic effect on precipitation. Based on state of the art about precipitation in OM and VG, a currently missing analysis of the temporal distribution of precipitation in VG was needed prior to the analysis of extremes. The original dataset of daily precipitation totals from 14 weather stations used in the initial study was extended to 168 stations covering a broader area of VG. The study of temporal distribution of precipitation during 1960-2013 led to a classification of stations: (i) mountainous stations with winter maxima and highest mean annual totals due to orographic enhancement of precipitation, (ii) stations on leeward slopes with two maxima (summer and winter), (iii) lee side stations with summer maxima and lowest mean annual totals due to rain shadow and more continental character, and...

National Repository of Grey Literature : 40 records found   1 - 10nextend  jump to record:
See also: similar author names
10 ŽÁK, Martin
3 Žák, Marek
10 Žák, Martin
1 Žák, Matúš
1 Žák, Matěj
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