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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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
Influence of Non-vertical Echoes to Ionogram Scaling
Kouba, Daniel; Koucká Knížová, Petra
2011 - English
Digisonde DPS 4 replaced the older ionosonde IPS 42 KEL Aerospace in the Observatory Pruhonice in January 2004. Additional information about the wave polarization enables us to determine and to distinguish exactly between ordinary and extraordinary wave traces on the ionogram records. This new ability basically changes scaling of the ionograms comparing to the ionograms obtained by classical ionosondes. Digisonde measurements show that in some cases the interpretation of ionograms based on classical ionospheric soundings may lead to the systematic errors, which affect classical ionograms interpretation. We demonstrate possible significant misinterpretations of the ionograms obtained using the classical equipment that is not able to distinguish between ordinary and extraordinary modes and records only time of flight of the electromagnetic sounding pulse. We show the necessity to be careful in using an old ionosonde measurements and scaled data for further analysis.
Keywords:
Digisonde; ionogram interpretation; spread F
Available at various institutes of the ASCR
Influence of Non-vertical Echoes to Ionogram Scaling
Digisonde DPS 4 replaced the older ionosonde IPS 42 KEL Aerospace in the Observatory Pruhonice in January 2004. Additional information about the wave polarization enables us to determine and to ...
Evaluating drought risk for permanent grasslands under present and future climate conditions
Trnka, Miroslav; Schaumberger, A.; Formayer, H.; Eitzinger, Josef; Hlavinka, Petr; Semerádová, Daniela; Dubrovský, Martin; Možný, M.; Thaler, S.; Žalud, Zdeněk
2011 - English
Over the past years, the changing climate has affected parts of Czech Republic and Austria by drought spells of the intensity and extend that was unprecedented in previous decades. These events had a significant impact on agricultural areas, especially on the grasslands. The idea behind the GIS monitoring relies on hypothesis that the effect of weather and climate conditions on the grassland production can be estimated by models that describe certain natural processes in a simplified manner and in spatialized form.
Keywords:
climatic change; drouhgt stress; grasslands; modelling; yield
Available at various institutes of the ASCR
Evaluating drought risk for permanent grasslands under present and future climate conditions
Over the past years, the changing climate has affected parts of Czech Republic and Austria by drought spells of the intensity and extend that was unprecedented in previous decades. These events had a ...
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