A new model to predict the electron density and effective recombination coefficient of the lower ionosphere under solar flare conditions is presented. This model relies on space-borne solar irradiance measurements in coincidence with ground recorded active transmissions of Very Low Frequency (VLF), (<30 kHz) signals. Use is made of the irradiance measured by broad-band radiometers onboard the satellites: GOES, SDO, and PROBA2. Measurements are made over succeeding and partly overlapping wavelength intervals of the instrument band-pass ranges altogether covering the range 0.1-20 nm. The aim is to determine the effectiveness of the particular instrument bandpass in producing changes in the ionization of the lower ionosphere (D-region) during solar X-ray flares. Ionization efficiency is evaluated using modelled Solar Spectral Irradiance for each flare separately and for each instrument as a function of its bandpass.The new model is based on coupling of the continuity equation with the Appleton relation and uses the concept of time delay - the time lag of the extreme VLF amplitude and phase behind the flare irradiance maximum. The solution of the continuity equation predicts the electron density time -height profile for 55-100 km altitude.An analysis of M to X class flares shows the flare-enhanced electron densities due to a particular ionizing wavelength domain are in good agreement for the case where irradiance is taken over the bandpass of (1) either GOES (0.1-0.8 nm) or SDO/ESP (0.1-7 nm) for up to 90 km (2) either SDO/ESP or PROBA2/LYRA (1-2 +6-20 nm) at heights above 90 km. The results agree within 22% for heights up to 90 km, and differ by at most a factor of 2 for heights above 90 km. Remarkable agreement is shown between measured and evaluated time delay; discrepancies are generally less than 8%. The effective recombination coefficient is deduced from the model itself and is found to be consistent with other independent estimates.

COST (European Cooperation in Science and Technology) is one of the longest-running European frameworks supporting cooperation among scientists and researchers across Europe. Its action ES0803 “Developing Space Weather Products and Services in Europe” involves the task “Exploitation, Dissemination, Education and Outreach”. To meet the objectives of this task, we describe how we developed and maintained the Space Weather Portal, initiated the electronic Journal of Space Weather and Space Climate, took care of the scientific organization of the annual European Space Weather Week conference and of two schools for scientists and students from the space weather community. We also describe several dissemination projects supported by the action, which target the non-specialist in the field of space weather.

In this study we analyze the Ground Level Enhancement Event No 70 observed on December 13, 2006, by correlating the observations from two research topics: Cosmic rays and Very Low Frequency (VLF < 30 kHz) wave propagation, as two ground based techniques for the detection of solar proton events, and their impact on the lower ionosphere. The observations have been endorsed from recordings of worldwide network ground based Neutron Monitors as well as by satellite data from the satellites GOES 12 (www.swpc.noaa.gov) and Pamela (www.pamela.roma2infn.it).We have evaluated the ionization rate for protons in the altitude range relevant to VLF propagation, and for galactic cosmic ray (GCR) background, finding that at energies up to similar to 2 GeV the ionization rate of solar protons exceeded the GCR ionization by 1.5 orders of magnitude.We have applied the Long Wave Propagation Capability (LWPC) code to evaluate the enhancement of the electron density from VLF signal perturbation and have inferred corresponding electron densities from the evaluated ionization rates and effective recombination coefficients from literature, to find the two independent sets in good agreement. (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

We present the numerical model for determining particle concentration in partially dissociated low pressure neutral hydrogen gas in a metal reaction cell where flowing gas is partially dissociated by a hot tungsten filament. Neutral hydrogen atoms and molecules in different vibrational states are taken into account. Available parameters for relevant surface processes (thermal dissociation, atom recombination, adsorption/desorption and vibrational relaxation) are used as initial input parameters. Calculated particle concentration distributions are compared to experimental data and qualitative agreement is obtained. Such a model is needed as a tool for indepth understanding and interpretation of results from our specific experiment and thus in turn enabling checking and evaluating rates and cross sections for the above surface processes.

The study presents a contribution to the modelling of processes with H2 molecules in both ground and vibrationally excited state and with H atoms. Attention is focused on the surface processes, which besides volume collisions, can influence significantly the vibrational population of hydrogen molecules. It is important to know this population since it opens a variety of low-energy channels at the cold edge of fusion plasmas. We have developed a simple kinetic model to estimate the particle fluxes formed by vibrational excitation and dissociation of hydrogen on metal surfaces, at low pressures and low temperatures. Comparison with the experiment shows that it grasps the main of the underlying physics: further improvements accompanied by more complete vibrational state-selective data are foreseen.

VLF (Very-Low-Frequency, 3-30 kHz) radio waves emitted from four single frequency transmitters located in Australia, USA, UK and Italy, have been permanently monitored in Belgrade by an AbsPAL receiver since August 2003. The collected data comprise a digitalized VLF wave amplitude and phase both recorded at 0.1 s time intervals for each of the four transmitters. Peculiarities, showing up in profiles of their time dependence curves, reveal effects of phenomena such as solar flares and magnetospheric electron precipitations among others. These features of solar activity may significantly influence the electron density distribution in the ionospheric D-region and consequently the characteristics of received radio signals. This work gives some insight into solar activity and space weather in general in their signatures in VLF signal recordings as well. Two examples show how sudden changes in the ionizing solar X-ray intensity in the ionosphere caused by a flare and solar eclipse, effect VLF signals recorded by the Belgrade receiver.

The electron distribution function in xenon in the low-energy region comprising the Ramsauer-Townsend minimum was obtained by solving the Boltzmann equation in the hydrodynamic approximation. for electric field to gas density ratios E/N in the. range (0.01 3) Td. The distortion of the electron distribution function due to the minimum is analysed and correlated to the behaviour of the electron transport coefficients: the drift velocity W-d and the ratio of the transverse and lonaitudinal diffusion coefficient to mobility,. D-T/mu and D-L/mu. The results are discussed in view of the different theoretical and experimental cross-section data used.