Number of found documents: 128
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Earth-space path propagation characteristics in the climatic conditions of the Czech Republic from Alphasat Ka/Q band experiment
Fišer, Ondřej; Brázda, Vladimír; Pešice, Petr; Grabner, M.
2017 - English
The objective of the activity is to prepare, realize and conduct experimental research of the influence of atmospheric phenomena on the Earth-space path propagation characteristics at 20 and 40 GHz (Ka/Q) bands in the specific climatic conditions of the Czech Republic (CR). The scientific approach is based on the comprehensive measurements of physical parameters of atmosphere together with concurrent measurements of propagation characteristics on the Earth-space path and on 10 collocated terrestrial paths with star configuration. The proposed activity will utilize the ESA Alphasat Mission Ka/Q experiment that is designed to investigate the propagation characteristics on slant paths in Europe and elsewhere. Keywords: satellite communication; atmosphere; atmospheric attenuation; propagation characteristics Available at various institutes of the ASCR
Earth-space path propagation characteristics in the climatic conditions of the Czech Republic from Alphasat Ka/Q band experiment

The objective of the activity is to prepare, realize and conduct experimental research of the influence of atmospheric phenomena on the Earth-space path propagation characteristics at 20 and 40 GHz ...

Fišer, Ondřej; Brázda, Vladimír; Pešice, Petr; Grabner, M.
Ústav fyziky atmosféry, 2017

Seasonal Variation in Propagation Directions of Acoustic Gravity Waves in the Thermosphere
Fišer, Jiří; Chum, Jaroslav
2016 - English
We investigate seasonal behaviour of acoustic gravity waves (AGWs) in\nthe thermosphere. For this purpose, measurements of HF Doppler sounding stations\noperated by or in cooperation with our institute are used. These measurements\nare compared with previously reported studies which employed different techniques\nof ionospheric observations. The propagation of AGWs is found to have strong\nseasonal dependence. AGWs in summer generally tend to propagate poleward in\nsummer and equatorward in winter. Keywords: thermosphere; acoustics gravity waves; ionosphere; HF Doppler sounding Available at various institutes of the ASCR
Seasonal Variation in Propagation Directions of Acoustic Gravity Waves in the Thermosphere

We investigate seasonal behaviour of acoustic gravity waves (AGWs) in\nthe thermosphere. For this purpose, measurements of HF Doppler sounding stations\noperated by or in cooperation with our ...

Fišer, Jiří; Chum, Jaroslav
Ústav fyziky atmosféry, 2016

Observation and modelling of local wind circulation in the complex topography of Svalbard archipelago
Chládová, Zuzana; Láska, K.; Hošek, Jiří
2016 - English
The atmospheric boundary layer processes over Svalbard fjords are strongly influenced by complex topography and sea ice occurence. In this study we point at foehn winds and low level jets in surrounding of Petuniabukta in central part of Spitsbergen. We used the Weather Research and Forecasting mesoscale model. The low level jets and wind have been successfilly simulated by the model. Keywords: Svalbard; model evaluation; low level jets; föhn Available at various institutes of the ASCR
Observation and modelling of local wind circulation in the complex topography of Svalbard archipelago

The atmospheric boundary layer processes over Svalbard fjords are strongly influenced by complex topography and sea ice occurence. In this study we point at foehn winds and low level jets in ...

Chládová, Zuzana; Láska, K.; Hošek, Jiří
Ústav fyziky atmosféry, 2016

Measurements of electromagnetic signals generated by lightning and atmospheric discharges associated with transient luminous events
Zemanová, Hana; Santolík, Ondřej; Kolmašová, Ivana
2016 - English
This paper focuses on the measurement techniques of extremely low\nfrequency EM waves generated by lightning. Basic types of lightning and transient\nluminous events along with the definition and properties of Schumann resonance are\npresented. We also show the description of our measurement site in Nov´y Kostel,\nwhich uses one horizontal magnetic antenna.\n Keywords: magnetosphere; lightning; extremely low frequency waves (ELF); transient luminous events; Schumann resonance; Novy Kostel Available at various institutes of the ASCR
Measurements of electromagnetic signals generated by lightning and atmospheric discharges associated with transient luminous events

This paper focuses on the measurement techniques of extremely low\nfrequency EM waves generated by lightning. Basic types of lightning and transient\nluminous events along with the definition and ...

Zemanová, Hana; Santolík, Ondřej; Kolmašová, Ivana
Ústav fyziky atmosféry, 2016

HF Doppler Observations of Ionospheric Disturbances over Taiwan
Fišer, Jiří; Chum, Jaroslav
2015 - English
Results of observations of traveling ionospheric disturbances (TIDs) by the multipath continuous HF Doppler sounding system operating in Taiwan are presented. We analysed one-year long period of measurements from April 2014 to March 2015 and investigated horizontal velocities and azimuths of propagation of medium scale traveling ionospheric disturbances (MSTIDs) with periods from 4 min to 60 min. Horizontal velocities range from ≈ 100 m s−1 to ≈ 300 m s−1 and MSTIDs propagate preferentially south-eastward in the local winter and preferentially northward in the local summer. The disturbances rarely propagate with azimuth in the range of 200–290◦ . Keywords: traveling ionospheric disturbances; ionosphere; HF Doppler sounding Available at various institutes of the ASCR
HF Doppler Observations of Ionospheric Disturbances over Taiwan

Results of observations of traveling ionospheric disturbances (TIDs) by the multipath continuous HF Doppler sounding system operating in Taiwan are presented. We analysed one-year long period of ...

Fišer, Jiří; Chum, Jaroslav
Ústav fyziky atmosféry, 2015

Comparison of parametric methods for radar signal processing
Rejfek, Luboš; Burešová, Dalia; Fišer, O.; Brázda, V.
2015 - English
The paper deals with comparison of parametric power spectral density methods for the utilization in the meteorological radar (pulse radar of frequency modulated pulses). We have compared duration of signal processing requested by single methods involved in the test. The methods used are the Auto Regressive model, MUSIC method, Eigen Vector algorithm and CAPON. The best results we have obtained for the AR model. Keywords: PSD method; MUSIC; Eigen Vector algorithm; CAPON; Auto Regressive (AR) model; frequency modulated radar Available at various institutes of the ASCR
Comparison of parametric methods for radar signal processing

The paper deals with comparison of parametric power spectral density methods for the utilization in the meteorological radar (pulse radar of frequency modulated pulses). We have compared duration of ...

Rejfek, Luboš; Burešová, Dalia; Fišer, O.; Brázda, V.
Ústav fyziky atmosféry, 2015

Automated eddy covariance data quality control for long-term measurements
Šigut, L.; Mauder, M.; Sedlák, Pavel; Pavelka, M.; Špunda, V.
2015 - English
Estimation of matter and energy exchange using the eddy covariance method is often organized into regional or global networks. To achieve comparability among sites, it is important to standardize and specify the methodology used. Currently, quality control (QC) is one of the most time-demanding steps in data processing within the Czech Carbon Observation System. Although manual QC (MQC) enables consideration of more complex test applications, it is often difficult to document. The aim of this study was to establish an automated QC (AQC) scheme based on available literature and post-processing software and test its effectivity and reliability on sites comprising an agroecosystem and a mature European beech forest. AQC successfully flagged low-quality CO2 fluxes and provided estimates of net ecosystem productivity similar to estimates based on MQC. The tests’ efficiency was particularly high for the agroecosystem, where AQC removed 13% less data than did MQC. We conclude that the adopted AQC displays satisfactory performance, especially for sites with low canopy heights. Keywords: eddy covariance; data quality control Available at various institutes of the ASCR
Automated eddy covariance data quality control for long-term measurements

Estimation of matter and energy exchange using the eddy covariance method is often organized into regional or global networks. To achieve comparability among sites, it is important to standardize and ...

Šigut, L.; Mauder, M.; Sedlák, Pavel; Pavelka, M.; Špunda, V.
Ústav fyziky atmosféry, 2015

Heat waves over Central Europe in ALADIN-Climate/CZ regional climate model: evaluation and future projections
Lhotka, Ondřej; Farda, A.; Kyselý, Jan
2015 - English
We evaluated a simulation of Central European heat waves and analysed possible changes of their characteristics in the future climate using the ALADIN-Climate/CZ regional climate model with 25km horizontal grid spacing. Lateral boundary conditions were provided by the ARPEGE global climate model, using historical forcing and the SRES A1B scenario. Observed data were taken from the E-OBS gridded data set. Heat waves were evaluated over 1970−1999 and changes in their characteristics were assessed for 2020−2049. Their definition is based on exceedance of the 90th percentile of summer daily maximum temperature calculated separately for modelled and observed data. ALADIN-Climate/CZ simulates characteristics for the recent climate quite well, especially the overall severity of heat waves. In contrast, temperature amplitude was considerably overestimated. This model projects an increase in overall heat wave severity by a factor of 2 to 3 in the future climate, primarily driven by an increasing number of events. The study shows that ALADIN-Climate/CZ is generally capable of simulating Central European heat waves, which gives more credibility to model projections of future heat waves. Keywords: heat waves; regional climate models; ALADIN-Climate/CZ Fulltext is available at external website.
Heat waves over Central Europe in ALADIN-Climate/CZ regional climate model: evaluation and future projections

We evaluated a simulation of Central European heat waves and analysed possible changes of their characteristics in the future climate using the ALADIN-Climate/CZ regional climate model with 25km ...

Lhotka, Ondřej; Farda, A.; Kyselý, Jan
Ústav fyziky atmosféry, 2015

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.; 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.; Dubrovský, Martin; Eitzinger, J.; Fuchs, B.; Svoboda, M.; Hayes, M.; Žalud, Z.
Ústav fyziky atmosféry, 2015

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