Adriena Ondrášková

On the transformation of planetary waves of tropospheric origin into waves in radio wave absorption in the lower ionosphere

SummaryCalculations are carried out of upward propagation of a tropospherically forced 10-day planetary wave into the upper middle atmosphere with the use of the COMMA-R model of the University of Cologne, of its transformation into a wave in electron density by means of the model of the Comenius University, and of its final transformation into a wave in radio wave absorption in the lower ionosphere applying the computer code of the Geophysical Institute. The calculations show that the absorption may be used for investigating the planetary wave activity, particularly of its long-term trends. The possibility of propagation of planetary waves from the winter hemisphere to the summer hemisphere is illustrated, which could contribute to explanation of the occurrence of travelling planetary waves in the mesosphere in summer.

Photochemical response of neutral and ionized middle atmosphere composition to the strong solar proton event of October 1989

Abstract One of the strongest solar proton events (SPE) occurred in October 1989. Its forcing of the middle atmosphere chemistry including ionized components in the D-region is examined. The ionization rate, and ozone, NO and OH density temporal and spatial (vertical) deviations induced by the SPE, calculated by a 1-D time-dependent photochemical model separately for daytime and nighttime (not shown here), are used in a 1-D model of the lower ionosphere to calculate the response of ionized components to combined forcing by ionization rate and neutral chemical composition disturbances. The radio wave absorption caused by electron density disturbances after the SPE is calculated and compared with observations. The computed ozone values are compared with observations, as well.

A numerical model of ion concentration profiles in the lower ionosphere

SummaryA one-dimensional numerical model has been developed which gives the vertical profiles of the electron and ion concentrations at altitudes between 50 and 100 km. The model has been constructed for day-time ionization conditions in midlatitudes and yields a slightly abbreviated scheme of ion-molecular reactions. Neutral species concentrations have been compiled from various authors. Seasonal variations of temperature and the most important neutral species have been taken into account. For the purpose of this paper moderate solar fluxes in all required radiation bands have been considered.

A significant decrease of the fundamental Schumann resonance frequency during the solar cycle minimum of 2008-9 as observed at Modra Observatory

A significant decrease of the fundamental Schumann resonance frequency during the solar cycle minimum of 2008-9 as observed at Modra Observatory The Schumann resonances (SR) are electromagnetic eigenmodes of the resonator bounded by the Earths surface and the lower ionosphere. The SR frequency variability has been studied for more than 4 decades. Using data from the period 1988 to 2002, Sátori et al. (2005) showed that the SR fundamental mode frequency decreased on the 11-year time scale by 0.07 - 0.2 Hz, depending on which component of the field was used for estimation and likely also on the location of the observer. A decrease by 0.30 Hz from the latest solar cycle maximum to the minimum of 2009 is found in data from Modra Observatory. This extraordinary fall of the fundamental mode frequency can be attributed to the unprecedented drop in the ionizing radiation in X-ray frequency band. Although the patterns of the daily and seasonal variations remain the same in the solar cycle minimum as in the solar cycle maximum, they are significantly shifted to lower frequencies during the minimum. Analysis of the daily frequency range suggests that the main thunderstorm regions during the north hemisphere summer are smaller in the solar cycle minimum than in the maximum.

The determination of Schumann resonance mode frequencies using iterative procedure of complex demodulation

Abstract The more precise determination of instantaneous peak frequency of Schumann resonance (SR) modes, especially based on relatively short signal sequences, seems to be important for detailed analysis of SR modal frequencies variations. Contrary to commonly used method of obtaining modal frequencies by Lorentzian fitting of DFT spectra, the attempt was made to employ the complex demodulation method in iterated form. The results for SR signals contaminated with low-frequency noise and hum in various degree as well as the comparison with standard method are presented. Real signals of vertical electric field component picked up at the Astronomical and Geophysical Observatory of Comenius University at Modra, Slovakia, were the primary sources.

On the relation between the red sprites and the transients in the ELF band

On the relation between the red sprites and the transients in the ELF band Under favourable conditions sprites appear above large storms. Long continuing current in tens of ms in the parent +CG stroke radiates electromagnetic energy also in the Schumann resonance (SR) band. Optical and Extremely Low Frequency (ELF) observations at the Astronomical and Geophysical Observatory (AGO) near Modra are analyzed to find these two effects associated with +CG discharges. Since April 2007 dozens of sprites have been captured by automated all-sky TV system at AGO. A majority (77%) of the optical transient events are accompanied with the transients in the SR band. No ELF counterparts are found for 23% of the captured sprites. Our observations are compared with similar observations in Sopron and Nagycenk (NCK). Example of the optical frames, the associated ELF time plot and the Fourier as well as dynamic spectrum are presented for one of the events simultaneously observed at AGO and NCK.

The iterative complex demodulation applied on short and long Schumann resonance measured sequences

Abstract The precise determination of instantaneous frequency of Schumann resonance (SR) modes, with the possibility of application to relatively short signal sequences, seems to be important for detailed analysis of SR modal frequency variations. Contrary to commonly used method of obtaining modal frequencies by the Lorentz function fitting of DFT spectra, we employ the complex demodulation (CD) method in iterated form. Results of iterated CD method applied on short and long measured sequences are compared. Results for SR signals as well as the comparison with Lorentz function fitting are presented. Decrease of frequencies of all first four SR modes from the solar cycle maximum to solar cycle minimum has been found using also the CD method.

variations of the atmospheric chemical composition in the earths’s polar regions after solar proton flare on July 14, 2000 (photochemical simulation)

Altitude—temporal cross-sections q(z, t) of atmospheric ionization rates by solar protons above the polar regions were calculated using the GOES-10 satellite data on solar proton fluxes for the period of solar proton flare (SPF) on July 14, 2000. The values of q(z, t) were used further in calculations of variations of the atmospheric chemical composition during the flare in the northern and southern polar regions (70°N and 70°S) by two different 1D photochemical models of the atmosphere (neutral and charged components). The calculation results have shown considerable variation of the ozone content after SPF: a decrease of [O3] was about 80% at altitudes of 65–75 km above northern and 25% in the layer of 55–65 km above the southern polar region. Such decrease of the ozone content is a result of reactions with [NO] and [OH] whose concentrations have grown substantially during SPF. According to calculations, the increase of electron concentration during SPF has reached 3–4 orders of magnitude at altitudes of 50–80 km. A comparison of the calculation results with the observational data on [NO], [NO2], and [O3] from the UARS and HALOE satellites for 70°N have shown a good qualitative correspondence, however, for variations of nitric oxides there are quantitative discrepancies.

Simultaneous Measurements of Low-Frequency Natural Electric Field at Two Neighbouring Stations

Simultaneous Measurements of Low-Frequency Natural Electric Field at Two Neighbouring Stations The electromagnetic eigenmodes of Earth-ionosphere global resonator known as Schumann Resonances (SR) are excited by global lightning activity. The simultaneous measurements of electric field in the ELF (~5 - 100 Hz) frequency band at two observatories clearly reveal the global character of the resonator response to the excitation both in the permanent Schumann background as well as in isolated events (transients). It is shown that measurement of ELF electric field can be done with relatively simple equipment.

On Seasonal Variation of the 162 kHz Radio Wave Reflection Height: Model Calculations and Their Comparison with Experiments

The seasonal variation of the 162 kHz radio wave reflection height was measured indirectly at Panská Ves using the IPHA method described in Fišer and Matys (1992). The fact that these waves are reflected at the height where the electron concentration is about 3.5 × 108m−3was used to model this height using a 1-D model of the lower ionosphere electron concentration described by Ondrášková (1993). The comparison of the measurements and model results indicates that: 1. The annual mean of the reflection height derived from measurements is several km higher than that derived from the model; 2. the character of the modelled seasonal variation is different from the real variation shown in Fišer and Laštovička (1992). The differences are discussed.