|
|
Coupling processes of various timescales in the middle atmosphere
Kuchař, Aleš ; Pišoft, Petr (advisor) ; Koucká Knížová, Petra (referee) ; Thiéblemont, Rémi (referee)
The thesis deals with the manifestation of coupling processes of various timescales in the middle atmosphere. Longer and shorter timescales are represented here by the 11-year solar cycle (SC) and orographic gravity waves (oGWs) considered on the intraseasonal timescale of the north hemisphere winter, respectively. The first two chapters deal with the application of rigorous attribution the variability of temperature, ozone and circulation characteristics in the stratosphere and lower mesosphere with regard to the SC using multiple nonlinear techniques (support vector regression and neural networks) besides the multiple linear regression approach. The aliasing of the SC with volcanic eruptions or the El Niňo Southern Oscillation is qualitatively assessed and its impact on conclusions about the top-down coupling mechanisms discussed. The last chapter examines the role of parametrized oGWs in the lower stratosphere. The Himalayan hotspot reveals common features with sudden stratospheric warmings such as the residual circulation amplification leading to a warming and ozone enrichment in the polar latitudes of the lower stratosphere.
|
|
|
Use of machine learning methods for satellite data processing
Doležalová, Anežka ; Pišoft, Petr (advisor) ; Piskala Gvoždíková, Blanka (referee)
Meteorological features, such as clouds, can be observed in 2 ways - from ground stations and, more recently in the last decades, by distance methods. The fact that the two views mentioned are different makes it not easy to compare them. In our work, we use MSG data, such as level 1.5 data and NWC SAF product cloud type, and cloud determination at ground stations by observers from CHMI. Based on these data, we build ML models that best determine from the input satellite data the categories that would be observed by the ground-based observer. It is necessary to select the appropriate model type for this task, set the most suitable parameters and also deal with the imbalanced representation of the different meteorological phenomena and associated cloud categories.
|
|
| |
|
|
Uncertainty of regional climate models outputs
Kliková, Barbora ; Kalvová, Jaroslava (advisor) ; Pišoft, Petr (referee)
This thesis focuses on examination of the ability of regional climate models (RCMs) to simulate precipitation patterns in the Czech Republic and on evaluation of uncertainties due to different global climate models (GCMs) driving the same RCM and due to different RCMs driven by a single GCM. Model outputs of regional climate models RCAO and HIRHAM driven by global climate models HadAM3H and ECHAM for period 1961-1990 were analyzed. It was shown that spatial variability of mean annual precipitation totals is mainly influenced by RCM. The global driving model determines areal mean and minimum values of precipitation totals for the Czech Republic. Both regional models overestimate the mean annual precipitation totals over most of the area, more markedly with driving model ECHAM. After the analysis of the further precipitation characteristics in selected grid points, it was shown that models RCAO and HIRHAM simulate most of the characteristics differently. Most of the characteristics were not expressed well by the models; the results of the model RCAO were better. Further, the model results distinctively differ between chosen areas. This variability is more noticeable for HIRHAM.
|
|
| |
|
|
Quasi-biennial oscillation of zonal winds in the tropical stratosphere
Kupčihová, Zuzana ; Pišoft, Petr (advisor) ; Mikšovský, Jiří (referee)
This thesis is about phenomenon of the quasi-biennial oscillation-the alternation of westerly and easterly zonal wind in the equatorial stratosphere with a mean period of 28 months. The structure of the thesis is following. Firstly it describes the general division of the atmosphere with the emphasis on vertical division according to the temperature, which is the most common in meteorology. Furthermore it depicts conditions in the stratosphere; temperature and mean zonal wind flow at the 100 hPa, 10 hPa level and comparision for the summer and winter months. The work introduces important stratospheric phenomena such as polar vortex, sudden stratospheric warming, Brewer-Dobson circulation. The entire third chapter is devoted to the quasi-biennial oscillation. The basic characteristic, the theory of formation and different impacts on the tropical and extratropical region are described. The whole thesis is summerized in the epilogue.
|
|
|
Spatial variability of precipitation annual cycles
Zíková, Naděžda ; Kalvová, Jaroslava (advisor) ; Pišoft, Petr (referee)
This thesis enquires into the spatial variability of precipitation annual cycles and its representation by regional climate models. Goal is to find suitable metrics that could describe spatial character of the precipitation field and consequently evaluate model results. For complete understanding the issue, there is an introduction to modeling with regional climate models and also parameters of the precipitation in the Czech Republic. The main part of the thesis is an application of different methods of descripiton on the results of the regional climate models (including the Czech model ALADIN) and CRU data. Results of the models are compared to observed data transferred into the regular grid. Each method is applied on the model results and assessed with regard to advantages and disadvantages. The metrics that were found useful are recommended for the further evaluation of the spatial variability of precipitation annual cycles. The ALADIN model seems to be quite successfull, weak points are only modelling of the precipitation in spring and the effect of the continentality and oceanity on the precipitation annual cycles.
|
|
| |
|
|
New Perspective on the Role of Gravity Waves in the Stratospheric Dynamics and Variability
Šácha, Petr ; Pišoft, Petr (advisor) ; Dameris, Martin (referee) ; Rieder, Harald (referee)
This thesis is concerned with the role of internal gravity waves (IGWs) in the stratospheric dynamics and variability demonstrating the effect of spatiotemporal distribution of their activity on the stratospheric dynamics and transport. The first part introduces a theoretical overview of the most recent as well as classical approaches used for description of the wave-mean interaction in the middle atmosphere. Methodology for an IGW analysis from the GPS radio occultation density data is described in the next chapter and the advantages of utilization of density data are listed. The third chapter presents results describing the peculiar dynamics and anomalous IGW activity in the Eastern Asia/Northern Pacific region. An important part is dedicated to a discussion of accuracy limits and usability of different IGW activity proxies. The possible impact of the localized IGW activity is investigated using a mechanistic middle and upper atmosphere model in the last chapter. Sensitivity simulations are used to demonstrate an important role of the spatial distribution of IGW activity for a formation of planetary waves and for the longitudinal variability of the Brewer-Dobson circulation. Implications for the middle atmospheric and climate change research are discussed along with consequences for parameterizations of...
|
|
| |
guest ::
