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Dependence of the Sweep Rate of Whistler-mode Chorus Emissions on the Plasma Density
Macúšová, Eva ; Santolík, Ondřej ; Gurnett, D. A. ; Pickett, J. S. ; Nunn, D. ; Trakhtengerts, V. Y. ; Demekhov, A. G. ; Titova, E. E. ; Kozelov, V. ; Rycroft, M. J.
Whistler-mode chorus consists of intense electromagnetic wave packets generated by a nonlinear mechanism involving wave-particle interactions. Chorus wave packets are discrete frequency-time structures in a frequency range from a few hundreds of Hz to several kHz changing their frequency on a time scale from a few tenths of seconds to a few seconds. The source region of chorus emissions is localised close to the geomagnetic equatorial plane. Our investigation is based on multipoint measurements of the wideband (WBD) plasma wave instruments on board the four Cluster spacecraft. We investigate the sweep rate of the chorus frequency as a Whistler-mode chorus consists of intense electromagnetic wave packets generated by a nonlinear mechanism involving wave-particle interactions. Chorus wave packets are discrete frequency-time structures in a frequency range from a few hundreds of Hz to several kHz changing their frequency on a time scale from a few tenths of seconds to a few seconds. The source region of chorus emissions is localised close to the geomagnetic equatorial plane. Our investigation is based on multipoint measurements of the wideband (WBD) plasma wave instruments on board the four Cluster spacecraft. We investigate the sweep rate of the chorus frequency as a function of the cold plasma density in the equatorial plane and then we compare it A theoretical model, numerical simulations and also our preliminary results from the measurements predict an increasing sweep rate with decreasing cold plasma density.
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Statistical analysis of equatorial noise emissions as a function of magnetic local time
Hrbáčková, Zuzana ; Němec, F. ; Santolík, Ondřej
The four spacecraft of the Cluster mission collect a unique data set since January 2001. We process the time period from January 2001 to December 2009. The spacecraft changed their orbits over the last few years, resulting in the data set with excellent coverage of a wide range of radial distances from the Earth, especially in the equatorial plane. We focus on the statistical analysis of whistler-mode waves called the equatorial noise (EN). These intense wave emissions are generated by unstable ion distributions. They propagate close to the geomagnetic equator at frequencies between the local proton cyclotron frequency and the lower hybrid frequency. Polarization of the magnetic field fluctuations corresponding to these emissions is linear. We processed data from the STAFF-SA instruments which preanalyze data from electric and magnetic field fluctuations onboard and provide us hermitian spectral matrices. We use the data measured at radial distances from about 2 to 11 RE to show the dependence of the occurrence of EN on the magnetic local time (MLT). We show from the statistical analysis that EN is occurred at all research radial distances within 10◦ from the geomagnetic equator and the maximum occurrence rate of EN is during the daytime especially in the afternoon sector.
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Multi-band Whistler-mode Chorus Emissions Observed by the Cluster Spacecraft
Macúšová, Eva ; Santolík, Ondřej
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.
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Calibration of the STEREO/WAVES Instrument in the Solar Wind
Krupař, Vratislav ; Maksimovic, M. ; Cecconi, B. ; Santolík, Ondřej
The S/WAVES instrument onboard the STEREO spacecraft measures electromagnetic waves in the solar wind. This unique project allows us to investigate properties of type II and type III radio bursts related with solar flares and propagation of coronal mass ejections (CMEs) in the interplanetary medium, respectively. In this paper we present properties of the High Frequency Receiver (HFR) receiver which covers the frequency range 125 kHz–16.025 MHz. We have compared the gains from the two HFR channels and we have found significant variations of these gains with time. We have proposed a solution for correcting these gain variations and improving the S/WAVES HFR calibrations in order to get as accurate goniopolarimetric measurements as possible.
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Applied research at the Institute of Atmospheric Physics Prague
Fišer, Ondřej ; Jaroš, J. ; Brázda, V.
This article describes the research performed at the Milesovka observatory. The base of this research is the measurement of the signal attenuation on the experimental free space optic link. Concurrently the pertinent meteorological parameters are measured and compared to the attenuation. First of all, visibility, liquid water content, wind speed + other wind parameters and rain rate are sampled and statistically evaluated including diurnal variations.
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Scaling Analysis Applied to Ionospheric, Solar and Geomagnetic Data
Mošna, Zbyšek ; Koucká Knížová, Petra
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.
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The impact of rain precipitation on dust concentration in the atmosphere
Fišák, Jaroslav ; Bartůňková, Kristýna
In this contribution the impact of precipitation on the amount of dust in the air is studied. Two precipitation characteristics are used: precipitation amount and time of precipitation duration. For the determination of dust concentrations dry filtering method was used. By this method the air is being sucked in by the suction pump over the head with filter. The exposition of the filter lasted approximately one weak. The time of samples collecting was not absolutely constant. Therefore it was necessary to choose relative characteristics. Precipitation amount for daily exposition of the filter was used. Even more difficult was to characterize the time of precipitation duration. In this case percent expression of precipitation duration to the time of filter exposition was used.
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Influence of Non-vertical Echoes to Ionogram Scaling
Kouba, Daniel ; Koucká Knížová, Petra
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.
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The effect of high long-lasting solar/geomagnetic activity on pressure fields in the winter northern lower atmosphere
Bochníček, Josef ; Davídkovová, Hana ; Hejda, Pavel ; Huth, Radan
The effect of high long-lasting solar/geomagnetic activity on stratospheric and tropospheric pressure distributions was investigated in the winter Northern Hemisphere. The analysis concerns winter period (December 1 – March 30) in 1952-2003. Solar activity is characterized by 30 day means of R number, geomagnetic activity by 30 day means of daily sum of Kp index. Stratospheric and tropospheric pressure distributions are described by 30 day mean anomalies in geopotential height (GPH) at 50 hPa/500 hPa. GPH anomalies are computed as the difference between the long-term 30 day averages (covering 33 year period, 1970-2003) and actual 30 day averages. Data are taken from the NCEP/NCAR reanalysis
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