Number of found documents: 251
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Models of FSO link attenuation due to fog, rain and wind derived from measurement
Fišer, Ondřej; Brázda, Vladimír; Chládová, Zuzana; Pešice, Petr; Svoboda, Jaroslav; Schejbal, V.
2011 - English
The Institute of Atmospheric Physics of the Czech Academy measures atmospheric attenuation on 60 m experimental FSO link while wavelength being 830 and 1550 nm. The measurement lasts three years. In this contribution we show dependences of FSO link attenuation on visibility, rain rate and selected wind parameters. We show that the measured attenuation values are higher than the theoretical values derived by the Kim formula. The sonic temperature is surprisingly very well correlated with attenuation. Keywords: Free-space optics; atmospheric attenuation; visibility; rain rate; wind parameters; sonic temperature Available at various institutes of the ASCR
Models of FSO link attenuation due to fog, rain and wind derived from measurement

The Institute of Atmospheric Physics of the Czech Academy measures atmospheric attenuation on 60 m experimental FSO link while wavelength being 830 and 1550 nm. The measurement lasts three years. In ...

Fišer, Ondřej; Brázda, Vladimír; Chládová, Zuzana; Pešice, Petr; Svoboda, Jaroslav; Schejbal, V.
Ústav fyziky atmosféry, 2011

Scaling Analysis Applied to Ionospheric, Solar and Geomagnetic Data
Mošna, Zbyšek; Koucká Knížová, Petra
2011 - English
Scaling analysis based on structure function zeta(q) computed using wavelet analysis and spectrum D(h) is used to study possible connection of ionospheric system with the solar and geomagnetic activity. Data from six ionospheric stations (critical frequency foF2), solar flux F10.7 and geomagnetic indices AE, Kp and Dst are used. Data of foF2 show scale invariance in the period range 2–32 day. Scaling properties of ionospheric data show strong dependence on geomagnetic latitude of the station. Similar distribution of values of scaling exponents h for ionospheric and geomagnetic activity AE and Kp suggests connection between these systems. Values of h for foF2 and F10.7 have different distribution which suggests weak connection between these systems at chosen periods. Keywords: Scaling analysis; structure function; ionosphere; critical frequencies; ionosféra Available at various institutes of the ASCR
Scaling Analysis Applied to Ionospheric, Solar and Geomagnetic Data

Scaling analysis based on structure function zeta(q) computed using wavelet analysis and spectrum D(h) is used to study possible connection of ionospheric system with the solar and geomagnetic ...

Mošna, Zbyšek; Koucká Knížová, Petra
Ústav fyziky atmosféry, 2011

Multi-band Whistler-mode Chorus Emissions Observed by the Cluster Spacecraft
Macúšová, Eva; Santolík, Ondřej
2011 - English
Whistler-mode chorus emissions are one of the most significant mechanisms causing the acceleration of electrons in the outer Van Allen radiation belt to relativistic energies. They consist of individual wave packets divided into two frequency bands separated close to the source region by a gap at 1/2 of the electron cyclotron frequency (fce). This configuration is called banded chorus and it is correlated with magnetic activity. Landau damping is one of the possible explanations describing the existence of the gap. On the other hand, the role of ducts in its formation was also discussed. We present several events of chorus combined with noisy or shapeless chorus-like emissions that are arranged in three or more frequency bands with two or more gaps and are observed mostly in a magnetic latitude range from 3 to 10 degrees on the both sides of the equator. We investigate possible influences of the magnetic local time (MLT), the Kp index, the McIlwain parameter and the plasma density on the formation of these multi-band emissions. Keywords: Cluster spacecraft; Whistler-mode chorus emissions Fulltext is available at external website.
Multi-band Whistler-mode Chorus Emissions Observed by the Cluster Spacecraft

Whistler-mode chorus emissions are one of the most significant mechanisms causing the acceleration of electrons in the outer Van Allen radiation belt to relativistic energies. They consist of ...

Macúšová, Eva; Santolík, Ondřej
Ústav fyziky atmosféry, 2011

Automatic Visualization Method of Height–Time Development of Ionospheric Layers
Mošna, Zbyšek; Koucká Knížová, Petra
2010 - English
An automatic method for visualization of variability of ionospheric plasma in terms of ionospheric layers is presented. Here, we use the virtual reflection height for visualization. We directly plot the height–time dependence using original raw digisonde outputs. It gives us an opportunity to promptly visualise the ionospheric digital data and locate events of the interest for further analysis. In this paper, we present a variability in height of E-layer with a special focus on the sporadic E-layer. The proposed method is applicable for any ionospheric region. Keywords: Ionospheric Layers; Visualization; vizualizace Available at various institutes of the ASCR
Automatic Visualization Method of Height–Time Development of Ionospheric Layers

An automatic method for visualization of variability of ionospheric plasma in terms of ionospheric layers is presented. Here, we use the virtual reflection height for visualization. We directly plot ...

Mošna, Zbyšek; Koucká Knížová, Petra
Ústav fyziky atmosféry, 2010

Systematic Analysis of Equatorial Noise Using Data of the Cluster Mission
Hrbáčková, Zuzana
2010 - English
The four spacecraft of the Cluster mission are collecting a unique data set. We use data measured between 2002 and 2009. These data are unique not only by their quantity but also because the spacecraft changed their orbits during their operational phase and therefore we have data from a large area around the Earth. We focus our analysis on observations of equatorial noise (EN) which is an intense electromagnetic emission generated by unstable ion distributions. It occurs in the inner magnetosphere and propagates close to the geomagnetic equator between the local proton cyclotron frequency and local lower hybrid frequency. We make systematic analysis of EN using data from the STAFF-SA instruments onboard the four spacecraft of the Cluster mission. Keywords: Analysis; Equatorial Noise; Cluster Mission; analýza Available at various institutes of the ASCR
Systematic Analysis of Equatorial Noise Using Data of the Cluster Mission

The four spacecraft of the Cluster mission are collecting a unique data set. We use data measured between 2002 and 2009. These data are unique not only by their quantity but also because the ...

Hrbáčková, Zuzana
Ústav fyziky atmosféry, 2010

Dopady lidské činnosti na horní atmosféru
Laštovička, Jan
2010 - Czech
Trendy v teplotě mezosféry, elektronové koncentraci v dolní ionosféře, elektronové koncentraci a výšce jejího maxima v E vrstvě, elektronové koncentraci v maximu F1 vrstvy, hustotě termosféry a iontové teplotě ve vrstvě F kvalitativně souhlasí s následky zesíleného skleníkového efektu a tvoří konzistentní scénář globálních změn v horní atmosféře. Byly identifikovány tři skupiny parametrů, které nezapadají do tohoto scénáře, F2 vrstva ionosféry, vodní pára v mezosféře a dynamika mezosféry a dolní termosféry. V článku je podána informaci o pokroku v globálním scénáři dlouhodobých trendů v horní atmosféře se zaměřením na ty tři otevřené problémy. K dlouhodobým trendům přispívá několik dalších faktorů, jmenovitě antropogenní změny stratosférického ozónu, změny koncentrace vodních par v mezosféře, dlouhodobé změny geomagnetické aktivity a magnetického pole Země Trends in the mesospheric temperature, electron concentration in the lower ionosphere, electron concentration and height of its maximum in the E region, electron concentration in the F1-region maximum, thermospheric neutral density and F-region ion temperature qualitatively agree with consequences of the enhanced greenhouse effect and form a consistent pattern of global change in the upper atmosphere. Three groups of parameters were identified as not-fitting this global pattern, the F2 region ionosphere, mesospheric water vapour, and the mesosphere/lower thermosphere dynamics. The paper reports progress in development of the global pattern of trends with emphasis to these three open problems. There are several other factors contributing to long-term trends, namely the stratospheric ozone depletion, mesospheric water vapour concentration changes, long-term changes of geomagnetic activity and of the Earth’s magnetic field. Keywords: Upper atmosphere; long-term trends; human activity; vodní pára; koncentrace Available at various institutes of the ASCR
Dopady lidské činnosti na horní atmosféru

Trendy v teplotě mezosféry, elektronové koncentraci v dolní ionosféře, elektronové koncentraci a výšce jejího maxima v E vrstvě, elektronové koncentraci v maximu F1 vrstvy, hustotě termosféry a ...

Laštovička, Jan
Ústav fyziky atmosféry, 2010

Statistical Study of the Ionospheric Density Variation Related to the 2010 Chile Earthquake and Measured by the DEMETER Satellite
Píša, David; Santolík, Ondřej; Parrot, M.
2010 - English
Statistical Study of the Ionospheric Density Variation Related to the 2010 Chile Earthquake and Measured by the DEMETER Satellite. Keywords: Whistler-mode Chorus; Emissions; hustota; studium Available at various institutes of the ASCR
Statistical Study of the Ionospheric Density Variation Related to the 2010 Chile Earthquake and Measured by the DEMETER Satellite

Statistical Study of the Ionospheric Density Variation Related to the 2010 Chile Earthquake and Measured by the DEMETER Satellite.

Píša, David; Santolík, Ondřej; Parrot, M.
Ústav fyziky atmosféry, 2010

Estimation of the Apparent Source Size of Solar Radio Emissions Using SVD: An Application to Type III Radio Bursts at Long Wavelengths Observed by STEREO and Wind
Krupař, Vratislav; Santolík, Ondřej; Cecconi, B.; Maksimovic, M.
2010 - English
Type III radio bursts are intense solar radio emissions. They are frequently observed by the S/Waves instruments on-board the STEREO spacecraft. We describe a wave propagation analysis using the Singular Value Decomposition (SVD) which can be directly applied to spectral matrices measured by the High Frequency Receiver (HFR; a part of the S/Waves experiment). We have found an empirical relation between the decomposed spectral matrices and apparent source sizes for waves with a low degree of polarization. We present a joint observation of a type III radio burst by the STEREO and Wind spacecraft during small separation distances. We obtain consistent results for the apparent source size and k-vector direction using different analysis method for the measurements of the STEREO and Wind spacecraft. We demonstrate that SVD can be an effective tool for the wave analysis of radio emissions with very extended sources. Keywords: Solar Radio; SVD; Wavelengths; STEREO; vlnění; analýza Available at various institutes of the ASCR
Estimation of the Apparent Source Size of Solar Radio Emissions Using SVD: An Application to Type III Radio Bursts at Long Wavelengths Observed by STEREO and Wind

Type III radio bursts are intense solar radio emissions. They are frequently observed by the S/Waves instruments on-board the STEREO spacecraft. We describe a wave propagation analysis using the ...

Krupař, Vratislav; Santolík, Ondřej; Cecconi, B.; Maksimovic, M.
Ústav fyziky atmosféry, 2010

Different Spectral Shapes of Whistler-mode Chorus Emissions
Macúšová, Eva; Santolík, Ondřej
2010 - English
Different Spectral Shapes of Whistler-mode Chorus Emissions are presented here. Keywords: Whistler-mode Chorus; Emissions; studenti; režim ložiska Available at various institutes of the ASCR
Different Spectral Shapes of Whistler-mode Chorus Emissions

Different Spectral Shapes of Whistler-mode Chorus Emissions are presented here.

Macúšová, Eva; Santolík, Ondřej
Ústav fyziky atmosféry, 2010

Study of Chance for Good DDA Drift Velocity Estimation for Ionospheric F-region Drift Measurements
Kouba, Daniel; Koucká Knížová, Petra
2010 - English
Estimation of the plasma drift velocity measured by Digisonde depends on the number of reflection points and their distribution. In the paper we divide and analyse plasma drift measurements according to the number of reflection points. A detailed study of Digisonde drift measurement quality has not been published yet. Two extreme groups are selected for further detail analysis, the first one with less than 100 reflection points and the second with more than 800 points. Within the data in these groups we detect annular and diurnal variability. Measurements containing low number of the reflection points occur mainly around equinoxes and during day-time. On the contrary, maximum occurrence of the measurements with more than 800 points is in winter and summer. The lowest chance to register extreme number of the reflections is during afternoon and around sunset. Keywords: Drift Velocity; DDA; Estimation; F-region; rychlost; výhybky Available at various institutes of the ASCR
Study of Chance for Good DDA Drift Velocity Estimation for Ionospheric F-region Drift Measurements

Estimation of the plasma drift velocity measured by Digisonde depends on the number of reflection points and their distribution. In the paper we divide and analyse plasma drift measurements according ...

Kouba, Daniel; Koucká Knížová, Petra
Ústav fyziky atmosféry, 2010

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