Number of found documents: 130
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Comparision of devices for monitoring of the ionosphere at the observatory Průhonice
Beran, L.; Chmelař, P.; Rejfek, Luboš; Chum, Jaroslav; Mošna, Zbyšek
2015 - English
This document is about comparison of the methods ad systems for the measurement of the ionosphere used at the geophysical observatory Pruhonice (50N, 14.5E). Three systems for ionospheric monitoring are installed at the station. The first system for the monitoring of the ionosphere is Digisonde, the second system is countinuous Doppler sounding. Each system has its banefits and weaknesses which are compared in this paper. Keywords: digisonde; GNSS receiver; continuous Doppler sounding; ionosphere; Total Electron Content (TEC) Available at various institutes of the ASCR
Comparision of devices for monitoring of the ionosphere at the observatory Průhonice

This document is about comparison of the methods ad systems for the measurement of the ionosphere used at the geophysical observatory Pruhonice (50N, 14.5E). Three systems for ionospheric monitoring ...

Beran, L.; Chmelař, P.; Rejfek, Luboš; Chum, Jaroslav; Mošna, Zbyšek
Ústav fyziky atmosféry, 2015

Drivers of soil moisture trends in the Czech Republic between 1961 and 2012
Trnka, M.; Brázdil, R.; Balek, J.; Semerádová, D.; Hlavinka, P.; Možný, M.; Štěpánek, P.; Dobrovolný, P.; Zahradníček, P.; Dubrovský, Martin; Eitzinger, J.; Fuchs, B.; Svoboda, M.; Hayes, M.; Žalud, Z.
2015 - English
Soil moisture dynamics and their temporal trends in the Czech Republic are forced by various drivers. Our analysis of temporal trends indicates that shifts in drought severity between 1961 and 2012 and especially in the April, May, and June period, which displayed such results as a 50% increase in drought probability during 1961–1980 in comparison to 2001–2012. We found that increased global radiation and air temperature together with decreased relative humidity (all statistically significant at p < 0.05) led to increases in the reference evapotranspiration in all months of the growing season; this trend was particularly evident in April, May, and August, when more than 80% of the territory displayed an increased demand for soil water. These changes, in combination with the earlier end of snow cover and the earlier start of the growing season (up to 20 days in some regions), led to increased actual evapotranspiration at the start of the growing season that tended to deplete the soil moisture earlier, leaving the soil more exposed to the impacts of rainfall variability. These results support concerns related to the potentially increased severity of drought events in Central Europe. The reported trend patterns are of particular importance with respect to expected climate change, given the robustness and consistency of the trends shown and the fact that they can be aligned with the existing climate model projections. Introduction Keywords: soil moisture; Czech Republic; climate change Available at various institutes of the ASCR
Drivers of soil moisture trends in the Czech Republic between 1961 and 2012

Soil moisture dynamics and their temporal trends in the Czech Republic are forced by various drivers. Our analysis of temporal trends indicates that shifts in drought severity between 1961 and 2012 ...

Trnka, M.; Brázdil, R.; Balek, J.; Semerádová, D.; Hlavinka, P.; Možný, M.; Štěpánek, P.; Dobrovolný, P.; Zahradníček, P.; Dubrovský, Martin; Eitzinger, J.; Fuchs, B.; Svoboda, M.; Hayes, M.; Žalud, Z.
Ústav fyziky atmosféry, 2015

HF Doppler Radar Observations of Geomagnetic Pulsations
Fišer, Jiří; Chum, Jaroslav
2014 - English
Geomagnetic pulsations interact with the ionosphere, which influences the propagation properties of high frequency (HF) radio waves. In this work we present results of an experimental study focused on investigation of relations between the geomagnetic pulsations observed on the ground and the Doppler frequency shift oscillations observed remotely in the ionosphere by a Doppler sounding system in the Czech Republic. We study mainly the dependence of phase shift between them on various parameters. Keywords: Doppler sounding; ionosphere; geomagnetic pulsations Available at various institutes of the ASCR
HF Doppler Radar Observations of Geomagnetic Pulsations

Geomagnetic pulsations interact with the ionosphere, which influences the propagation properties of high frequency (HF) radio waves. In this work we present results of an experimental study focused ...

Fišer, Jiří; Chum, Jaroslav
Ústav fyziky atmosféry, 2014

Device for Measurement of Optical Visibility
Rejfek, L.; Brázda, V.; Fišer, Ondřej
2013 - English
This paper is about a proposed device for the optical visibility measurement. This device is usable for monitoring of the fog mightiness. The principle of device is based on comparison of attenuation on two optical links. The fog mightiness is determined by the using of the Beer-Lambert Law. The philosophy of electrical arrangement is also explained. Keywords: Beer-Lambert Law; Optical Links; Optical Visibility; Mightiness of the Fog; Absorbance; Transmittance Available at various institutes of the ASCR
Device for Measurement of Optical Visibility

This paper is about a proposed device for the optical visibility measurement. This device is usable for monitoring of the fog mightiness. The principle of device is based on comparison of ...

Rejfek, L.; Brázda, V.; Fišer, Ondřej
Ústav fyziky atmosféry, 2013

Subseasonal temperature trends in Europe (1961-2000) and their links to atmospheric circulation
Cahynová, Monika; Pokorná, Lucie
2013 - English
We use daily maximum and minimum temperatures and the daily temperature range from 136 stations in Europe in the period 1961–2000 to precisely locate their seasonal and subseasonal trends within the year. Linear trends are calculated for moving “subseasons” of 10, 20, 30, 60, and 90 days, each shifted by one day. Over most of Europe, the observed warming is greatest in winter. In Iceland and the Mediterranean, a pronounced warming is only present in summer. Significant autumn cooling was found in Eastern and Southeastern Europe for both TX and TN. Other non-warming periods occur in Western and Central Europe in February, April, and late June. Trends of DTR are inconclusive. Changes in the frequency of atmospheric circulation types usually explain a substantial part of the observed climatic trends; however, the influence varies between regions, times of the year, subseason lengths, numbers of circulation types, and input variables for the classification of circulation types. Keywords: air temperature; daily temperature range; trend; atmospheric circulation; classification Available at various institutes of the ASCR
Subseasonal temperature trends in Europe (1961-2000) and their links to atmospheric circulation

We use daily maximum and minimum temperatures and the daily temperature range from 136 stations in Europe in the period 1961–2000 to precisely locate their seasonal and subseasonal trends within the ...

Cahynová, Monika; Pokorná, Lucie
Ústav fyziky atmosféry, 2013

Analysis of temporal variability and spatial characteristics of heat waves in central Europe using extremity index
Lhotka, Ondřej; Kyselý, Jan
2013 - English
Heat waves have severe consequences on natural environment and society. Th e majority of studies defined heat waves from station data only, so there is a need to examine these events not only from the aspect of point characteristics of air temperature and duration, but also from the view of their spatial extent. In this study, heat waves over Central Europe were analysed using the gridded E-OBS dataset. Th e extremity index of heat waves, which takes into account their spatial extent, duration, and peak temperature, was proposed and used to analyse variability of heat waves over Central Europe from 1950 to present. We delimited 220 hot days and 21 heat waves and computed the extremity index for each heat wave. Th e eight most signifi cant heat waves based on the extremity index were visualized. Temporal variability of hot days and heat waves was analysed and we demonstrate that the number of hot days and the severity of heat waves have been increasing. Keywords: heat waves; central Europe; extremity index Available at various institutes of the ASCR
Analysis of temporal variability and spatial characteristics of heat waves in central Europe using extremity index

Heat waves have severe consequences on natural environment and society. Th e majority of studies defined heat waves from station data only, so there is a need to examine these events not only from the ...

Lhotka, Ondřej; Kyselý, Jan
Ústav fyziky atmosféry, 2013

On Forward and Backward Scattering from Fog and Rain Drops
Fišer, O.; Rejfek, Luboš; Brázda, Vladimír
2013 - English
This contribution deals with the backward and forward scattering on dielectrical spheres. The well-known Rayleigh, Mie and Optical regions are discussed for frequencies regions 0.05 to 70 GHz and for optical wavelength of 830 nm. Some of our results fit the published one, some of them are different and the explanation of possible reasons is added. Also the formulas necessary to compute the radar reflectivity or attenuation due to fog and rain are presented. Keywords: Forward scattering; backward scattering; efficiency factor; Rayleigh region; Mie region; Optical region; mlha; déšť Available at various institutes of the ASCR
On Forward and Backward Scattering from Fog and Rain Drops

This contribution deals with the backward and forward scattering on dielectrical spheres. The well-known Rayleigh, Mie and Optical regions are discussed for frequencies regions 0.05 to 70 GHz and ...

Fišer, O.; Rejfek, Luboš; Brázda, Vladimír
Ústav fyziky atmosféry, 2013

Occurrence Rate of Equatorial Noise Emissions as a Function of the McIlwain's Parameter
Hrbáčková, Zuzana; Santolík, Ondřej
2012 - English
We report results of a statistical analysis of equatorial noise (EN) emissions based on the data set collected by the four Cluster spacecraft between January 2001 and December 2010. We have investigated a large range of the McIl- wain’s parameter from L 1 to L 11 thanks to the change of orbital parameters of the Cluster mission. We have processed data from the STAFF-SA instruments which analyze measurements of electric and magnetic field fluctuations onboard and provide us with hermitian spectral matrices. We have used linear polarization of magnetic field fluctuations as a selection criterion. Propagation in the vicinity of the geomagnetic equator has been used as an additional criterion for recognition of EN. We have identified about 6000 equatorial passages of all four spacecraft during the investigated time period and about 2000 passages in which we observed EN emissions. We demonstrate that EN can occur almost at all the analyzed L shells. However, the occurrence rate at L shells below 2 and above 8.5 is very low. At L shells above 10 the occurrence rate is zero. We show that EN is dependent on the magnetic local time. Keywords: Cluster spacecraft; Earth's magnetosphere; equatorial noise emission; magnetic local time Available at various institutes of the ASCR
Occurrence Rate of Equatorial Noise Emissions as a Function of the McIlwain's Parameter

We report results of a statistical analysis of equatorial noise (EN) emissions based on the data set collected by the four Cluster spacecraft between January 2001 and December 2010. We have ...

Hrbáčková, Zuzana; Santolík, Ondřej
Ústav fyziky atmosféry, 2012

Rain impact on FSO link attenuation based on theory and measurement
Brázda, V.; Schejbal, V.; Fišer, Ondřej
2012 - English
The FSO link becomes a usual mean of modern wireless communications. But it suffers from atmospheric particles causing attenuation. That´s why this random attenuation must be carefully considered by the FSO link design. As it is known the most serious atmospheric phenomenon is fog, and low cloudiness. But the rain attenuation (night mare of mm wave links) is not negligible on optical links, too. In this contribution we focus on rain attenuation from theoretical as well as experimental point of view. Statistics and rain event analysis are shown. There is an overview and a comparison of several formulas for rain attenuation derived from DSD or rain rate. Rain is not the worst phenomena for the transmission but we can’t neglect its influence on FSO. Only full understanding of influence of real atmosphere can lead to solution of a high availability of FSO systems. Keywords: Free-space optics; atmospheric attenuation; rain rate Available at various institutes of the ASCR
Rain impact on FSO link attenuation based on theory and measurement

The FSO link becomes a usual mean of modern wireless communications. But it suffers from atmospheric particles causing attenuation. That´s why this random attenuation must be carefully considered by ...

Brázda, V.; Schejbal, V.; Fišer, Ondřej
Ústav fyziky atmosféry, 2012

The STEREO/Waves Goniopolarimetric Products for Centre de Données de la Physique des Plasmas
Krupař, Vratislav; Cecconi, B.; Maksimovic, M.; Nguyen, Q. N.; Santolík, Ondřej
2011 - English
We present results on the calibration of the HFR receiver, a part of the S/Waves instrument onboard the STEREO spacecraft. The HFR provides us with GP measurements in the frequency range 125–1975 kHz. The obtained data products will be archived in the Plasma Physics Data Center: CDPP. This paper contains a description of used methods and summarizes outputs of the calibration. Keywords: Solar Radio Emissions; Goniopolarimetric inversion Available at various institutes of the ASCR
The STEREO/Waves Goniopolarimetric Products for Centre de Données de la Physique des Plasmas

We present results on the calibration of the HFR receiver, a part of the S/Waves instrument onboard the STEREO spacecraft. The HFR provides us with GP measurements in the frequency range 125–1975 ...

Krupař, Vratislav; Cecconi, B.; Maksimovic, M.; Nguyen, Q. N.; Santolík, Ondřej
Ústav fyziky atmosféry, 2011

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