János Lichtenberger

Total solar eclipse effects on VLF signals: Observations and modeling

During the total solar eclipse observed in Europe on August 11, 1999, measurements were made of the amplitude and phase of four VLF transmitters in the frequency range 16–24 kHz. Five receiver sites were set up, and significant variations in phase and amplitude are reported for 17 paths, more than any previously during an eclipse. Distances from transmitter to receiver ranged from 90 to 14,510 km, although the majority were 10,000 km. Negative phase changes were observed on most paths, independent of path length. Although there was significant variation from path to path, the typical changes observed were ∼3 dB and ∼50°. The changes observed were modeled using the Long Wave Propagation Capability waveguide code. Maximum eclipse effects occurred when the Wait inverse scale height parameter β was 0.5 km−1 and the effective ionospheric height parameter H′ was 79 km, compared with β=0.43 km−1 and H′=71 km for normal daytime conditions. The resulting changes in modeled amplitude and phase show good agreement with the majority of the observations. The modeling undertaken provides an interpretation of why previous estimates of height change during eclipses have shown such a range of values. A D region gas-chemistry model was compared with electron concentration estimates inferred from the observations made during the solar eclipse. Quiet-day H′ and β parameters were used to define the initial ionospheric profile. The gas-chemistry model was then driven only by eclipse-related solar radiation levels. The calculated electron concentration values at 77 km altitude throughout the period of the solar eclipse show good agreement with the values determined from observations at all times, which suggests that a linear variation in electron production rate with solar ionizing radiation is reasonable. At times of minimum electron concentration the chemical model predicts that the D region profile would be parameterized by the same β and H′ as the LWPC model values, and rocket profiles, during totality and can be considered a validation of the chemical processes defined within the model.

Temporal variability of the descent of high-altitude NOx inferred from ionospheric data

In this study we investigate periods of enhanced ionization in the mesosphere during Northern Hemisphere wintertime. Long-lasting ionization enhancements (days) are typically produced by solar proton events or by the descent of thermospheric NOX during periods of sustained downward vertical transport associated with a strong underlying polar vortex. Using a new application of ground-based low-frequency radio wave remote sensing, we study the mesospheric ionization conditions during the Northern Hemisphere winters spanning 2003-2004, 2004-2005, and 2005-2006. The winter 2003-2004 subionospheric radio wave propagation data from a transmitter in Iceland shows signatures of the descent of NOX through 80 km altitude starting on 13 January 2004, during the occurrence of a strong polar vortex, indicating a thermospheric source for the NOX. Similar analysis of radio wave propagation data in the Northern Hemisphere winter of 2004-2005 does not show a NOX descent event passing through the mesosphere, due to a lack of downward vertical transport as a result of a weak underlying polar vortex, despite the occurrence of significant solar proton ionization during January 2005. In 2005-2006 there were no significant ionization events and also no descent of significant amounts of thermospheric NOX, despite a strong polar vortex and strong vertical transport. We model the signature of the descent of NOX seen in the radio wave propagation data using the Sodankyla Ion Chemistry model, confirming that the levels of NOX in the mesosphere are similar to 100 times the usual background levels. The combination of strong NOX sources in the thermosphere and also a strong polar vortex is required for NOX to descend into the stratosphere with significant concentration levels.

Application of matched filtering and parameter estimation technique to low latitude whistlers

Abstract The Matched Filtering and Parameter Estimation (MFPE) technique developed for the analysis of mid/high latitude whistlers has been extended to analyze whistlers recorded at low latitude ground station Varanasi, India (geomagnetic latitude 14° 55′ N, longitude 153° 59′ E, L=1.07). Some of the whistlers recorded at Varanasi are found to have propagated along higher L-values (L>2). It has been argued that these whistlers after exiting the ionosphere have propagated towards the equator in the Earth-ionosphere waveguide. Trace splitting is observed below the nose frequency and above 2.0 kHz, a result in agreement with mid/high latitude whistlers. The trace splitting structure revealed by MFPE demonstrates the complexities of whistler wave propagation and is quite helpful in deriving information about high resolution features of the duct structure. The banded features observed in the dynamic spectrum are clearly seen in the output of the matched filter. The observed banded features may arise due to interference between the wavelets propagating in the duct/waveguide.

Whistler doublets and hyperfine structure recorded digitally by the signal analyzer and sampler on the active satellite

The signal analyzer and sampler (SAS) experiment was placed on the Active spacecraft as a collaborative effort between the Eotvos University (Budapest), the Technical University of Budapest, and IZMIRAN (Moscow). The scientific objective of the experiment was to study whistler/VLF ducted propagation, VLF duct structure, and the hyperfine structure of whistlers. Digitally sampled waveforms of several field components were transmitted in real time by the SAS telemetry system at 460.4 MHz. For the transmission 900-Hz wide bands were selected between 0.5 and 21.5 kHz or a single 5 kHz wide band was transmitted. Data were received in Budapest, Hungary and at Wallops Island, Virginia. Although the obtained data were processed for various purposes, here some results concerning the hyperfine structure of whistlers are presented. The studied whistlers, recorded as several pairs of closely spaced traces (doublets), were interpreted as ducted whistlers escaping at a high altitude from a single or two closely spaced narrow ducts and reaching the satellite directly from above or after reflection from below. The whistler traces were processed by a sophisticated matched filter technique which enabled us to obtain very high resolution dynamic (frequency-time-amplitude) spectra. The hyperfine structure of traces revealed by this technique demonstrates the complexity of whistler propagation. The observed splitting of traces may be explained, for example, in terms of a number of guided modes (waveguide mode splitting) or by the superposition of closely spaced ducting structures (duct splitting).

Correlation between global lightning and whistlers observed at Tihany, Hungary

Although the generation and propagation mechanisms for whistlers are fairly well understood, the location and extent of the lightning source region for the whistlers observed at a given station are ...

Searching for electromagnetic counterpart of LIGO gravitational waves in the Fermi GBM data with ADWO

Aims. The Fermi collaboration identified a possible electromagnetic counterpart of the gravitational wave event of September 14, 2015. Our goal is to provide an unsupervised data analysis algorithm to identify similar events in Fermi ’s Gamma-ray Burst Monitor CTTE data stream. Methods. We are looking for signals that are typically weak. Therefore, they can only be found by a careful analysis of count rates of all detectors and energy channels simultaneously. Our Automatized Detector Weight Optimization (ADWO) method consists of a search for the signal, and a test of its significance. Results. We developed ADWO, a virtual detector analysis tool for multi-channel multi-detector signals, and performed successful searches for short transients in the data-streams. We have identified GRB150522B, as well as possible electromagnetic candidates of the transients GW150914 and LVT151012. Conclusions. ADWO is an independently developed, unsupervised data analysis tool that only relies on the raw data of the Fermi satellite. It can therefore provide a strong, independent test to any electromagnetic signal accompanying future gravitational wave observations.

The Study of Electromagnetic Parameters of Space Weather, Micro-Satellite “Chibis-M”

Plasma-wave experiment on the micro-satellite “Chibis-M” is aimed at the solution of fundamental problem – a study of the interrelation of the plasma- wave processes connected with the manifestation in the ionosphere of solar – magnetosphere – ionosphere – atmosphere connections and the parameters of space weather. Specific fundamental problem is the search for universal laws governing transformation and dissipation of plasma-wave energy in the magnetosphere-ionosphere system. The solution of this problem will be achieved employing the coordinated Procedure: (1) Study in situ of the fluctuations of electrical and magnetic field, the parameters of thermal and epithermal plasma in the ionosphere near layer F during different helio- and geomagnetic conditions. (2) Study of the geomagnetic and geophysical parameters on the ground-based observatories with the time scales from 10–1 to 10–3 s. (3) Study of the interrelation of electromagnetic phenomena (spectra of ULF/VLF- waves) in different regions of near-earth space by means of via the comparative analysis of the wave measurements of those carry out simultaneously on different spacecrafts and ground geophysical stations. Micro-satellite “Chibis-M” now designed in IKI. Total mass of “Chibis-M” with support systems construction and scientific instruments is 40 kg.

Yield estimation and forecasting for winter wheat in Hungary using time series of MODIS data

ABSTRACT Wheat is one of the most important crops in Hungary, which represents approximately 20% of the entire agricultural area of the country, and about 40% of cereals. A robust yield method has been improved for estimating and forecasting wheat yield in Hungary in the period of 2003–2015 using normalized difference vegetation index (NDVI) derived from the data of the Moderate Resolution Imaging Spectroradiometer. Estimation was made at the end of June – it is generally the beginning of harvest of winter wheat in Hungary – while the forecasts were performed 1–7 weeks earlier. General yield unified robust reference index (GYURRI) vegetation index was calculated each year using different curve-fitting methods to the NDVI time series. The correlation between GYURRI and country level yield data gave correlation coefficient (r) of 0.985 for the examined 13 years in the case of estimation. Simulating a quasi-operative yield estimation process, 10 years’ (2006–2015) yield data was estimated. The differences between the estimated and actual yield data provided by the Hungarian Central Statistical Office were less than 5%, the average difference was 2.5%. In the case of forecasting, these average differences calculated approximately 2 and 4 weeks before the beginning of harvest season were 4.5% and 6.8%, respectively. We also tested the yield estimation procedure for smaller areas, for the 19 counties (Nomenclature of Territorial Units for Statistics-3 level) of Hungary. We found that, the relationship between GYURRI and the county level yield data had r of 0.894 for the years 2003–2014, and by simulating the quasi-operative forecast for 2015, the resulting 19 county average yield values differed from the actual yield as much as 8.7% in average.

PLASMON: Data assimilation of the Earth's plasmasphere

The principal source and loss mechanisms in the Earths radiation belts are currently not completely understood. Loss rates are important since they determine the duration of exposure of satellites to enhanced radiation conditions during a geomagnetic storm. The dominant loss process is relativistic electron precipitation via resonant interactions with a variety of wave modes. These interactions are governed by the characteristics of the plasmasphere. Current models provide an inadequate representation of the spatial and temporal evolution of the plasmasphere. In situ measurements of the plasmasphere provide only local characteristics and are thus unable to yield a complete global picture. Ground based measurements, based on the analysis of Very Low Frequency (VLF) whistlers and Field Line Resonances (FLRs), are able to describe large sections of the plasmasphere, extending over significant radial distances and many hours of local time. These measurements provide electron number and plasma mass densities. PLASMON is a funded FP7 project between 11 international partners. PLASMON intends to assimilate near real time measurements of plasmaspheric densities into a dynamic plasmasphere model. The VLF whistler analyses will be conducted by automatic retrieval of equatorial electron densities using data from AWDAnet. Equatorial mass densities will be constructed from FLR measurements along meridional magnetometer chains. The resulting model will facilitate the prediction of precipitation rates. The predicted rates will be compared to observations from the AARDDVARK network.

Inter-calibration of VAP-HOPE particle detectors to obtain the anisotropy of electron Pitch angle distribution

Whistler mode chorus waves play a key-role in the formation of prompt changes in outer radiation belts. Despite of that, the generation mechanism of chorus emissions is still a subject of debate. Many theories aim at explaining the results of empirical studies on wave-particle interaction. Validation requires a thorough investigation based on precise datasets. EMFISIS, HOPE and MagEIS on the Van Allen Probes provide excellent measurements of electromagnetic waves and particles for such studies. In this summary paper we present the reliability and efficiency of HOPE instrument from this point of view. The 5 polar pixels of HOPE have not been inter-calibrated yet, leading to inaccuracies in angular measurements and in pitch angle distribution (PAD) data also. A preliminary investigation of HOPE L1 datas count rates is presented, in the aim of using count ratios of neighboring pixels with overlapping pitch angle intervals. A list of cross-calibration data was produced for the entire mission. Finally, a case study on 14 November 2012 is presented to represent the efficiency of the corrected dataset, as defining isotropy or anisotropy in PADs. To calculate anisotropy of PADs is essential to determine times and energies of an electron population which presumably interacting/generating chorus wave emissions.