Ludwik Liszka

The high-latitude trough in ionospheric electron content

Abstract Results of 15 months observations of the ionospheric electron content made at Kiruna, Sweden are presented. Observations were made using the 40 and 41 MHz beacon of the S-66 satellite. Most of the night-time observations, except for the summer period, show a distinct trough in the electron content. Seasonal and diurnal variations of the trough and of the electron content are studied. Also the corresponding equivalent slab thickness obtained using ƒ 0 F2 data from six Scandinavian ionosondes and geomagnetic control of the trough are investigated. Some features of the diurnal variation of electron content during the summer agree with the hypothesis of ionospheric heating by photoelectrons from the sunlit magnetic conjugate ionosphere.

On the possible infrasound generation by sprites

Energetic electrons accelerated by electric fields in thunderstorms are assumed to be responsible for generation of luminous phenomena at altitudes above 30 km, so called sprites. If the generation of light in these phenomena is associated with local heating, it may also be expected that low frequency acoustic waves will be generated. Due to the cylindrical structure of the source the most of the acoustic energy will be radiated close to the horizontal plane along the entire height of the source. The infrasound form these phenomena is therefore unlikely to be detected immediately beneath the source. The search for infrasonic signals from the high altitude luminous phenomena was carried out during the recent years using data from the infrasonic networks operated by the Swedish Institute of Space Physics. During the night of May 26–27 1995, when a severe thunderstorm area passed over the Golf of Bothnia, it was possible to identify signals, most probably generated by sprites. The infrasonic observations made during that night are described in the present report. Similar, chirp-like signals were observed during some other occasions at Swedish stations during the recent years.

Infrasonic Observations of the Hekla Eruption of February 26, 2000

INTRODUCTION On February 26-27, 2000 infrasonic signals associated with the eruption of the Hekla Volcano, Iceland, were recorded by the Swedish infrasound network. This network is operated by the Swedish Institute of Space Physics and consists of 4 stations located in Kiruna, Jamton and Lycksele in Northern Sweden and Uppsala in Central Sweden. Each station consists of an array of 3 modified Lidstrommicrophones (see Appendix 1) with a 7 Hz low-pass filter, so that the effective frequency range is 0.5 6 Hz. A sampling rate of 18 Hz is used at all stations. The microphones at each array are located in the corners of a right angle triangle, where the perpendicular sides are 75 m long and oriented East-West and North-South. Shelters reduce wind noise at each array element. The Kiruna and Lycksele array data may be accessed at http://callisto.space.umu.se. Geographical coordinates for the stations are given in Table I.

The European Arctic: A Laboratory for Seismoacoustic Studies

The International Monitoring System (IMS) for verifying compliance with the Comprehensive Nuclear‐Test‐Ban Treaty (CTBT) comprises sensors associated with four monitoring technologies: seismic, infrasound, hydroacoustic, and radionuclide. The so‐called waveform technologies (seismic, infrasound, and hydroacoustic) are used to detect and locate events that could constitute treaty violations. All four technologies may be employed to investigate the nature of events, with the network of radionuclide sensors in place to provide evidence of a nuclear explosion. Historical, political, and technical issues surrounding the CTBT are discussed by Dahlman etxa0al. (2009, 2011). The global IMS infrasound network (Fig.xa01) is primarily to detect signals generated by atmospheric nuclear tests.nnnnFigure 1. nStatus of the International Monitoring System infrasound network in August 2014. Filled symbols are certified stations sending data to the International Data Center (IDC) in Vienna. White symbols indicate the treaty coordinates of stations planned or under construction.nnnnThe IMS infrasound network has been deployed over the last two decades (Brachet etxa0al. , 2010; Christie and Campus, 2010), and only with the network approaching completion has a realistic picture of its detection capability emerged (Le Pichon etxa0al. , 2009; Green and Bowers, 2010). The detectability of atmospheric signals is governed by a seasonally varying wind‐determined anisotropy. In the northern summer, the stratospheric winds blow predominantly east to west, facilitating the detection of infrasound at stations west of sources and inhibiting the detection at stations east of sources. In the northern winter, the winds blow in the opposite direction changing the sense of high and low detectability. The reverse patterns occur in the southern hemisphere. There is increasing interest in using infrasound for probing atmospheric structure (e.g., Lalande etxa0al. , 2012), and the broader properties and applications of infrasound are discussed by Evers and Haak (2009) and Hedlin etxa0al. (2012).nnIn October …

Energetic ion outflow from the dayside ionosphere and its relationship to the interplanetary magnetic field and substorm activity

Abstract The energetic ion outflow from the dayside ionosphere has been investigated for different AE and IMF conditions. Viking ion data, 1-min values of the AE index, and 5-min averaged IMF values have been used. An automated algorithm using principal component analysis has been used to categorize and classify the upflowing ion events (UFIs) into beams and conics. The Viking data cover altitudes between 6000 and 13,500 km, 0600 to 1800 magnetic local time, and 65 to 90° invariant latitude. Beams dominate the outflow prenoon and postnoon outside the cusp region, while conics are responsible for most of the cusp region outflow. Generally, the highest average number flux is found in the cusp region. The outflow intensity is higher for southward than for northward IMF, especially in the cusp and postnoon sector. Also, the outflow region increases slightly for southward IMF. However, the difference in outflow intensity and active area is stronger when the data are sorted according to quiet and active geomagnetic conditions using the AE index. The highest average UFI number flux is observed during the expansion phase of substorms, when the flux increase from quiet conditions ( AE ) is by a factor of 2, but even during growth and recovery phase the average UFI number flux is ∼30% higher than for quiet conditions. The results imply that the dayside energetic ion outflow is controlled partly by nightside (driven by the release of stored energy in the magnetotail, as observed in the AE index) and partly by dayside (directly driven, as observed in the polarity in the IMF B z component) activity.

A study of auroral zone ionospheric irregularities made simultaneously at Tromsö, Norway and Kiruna, Sweden

Abstract The results of observations of satellite scintillation at 54 Mc/s made simultaneously at Tromso, Norway (70° N, 19° E), and Kiruna, Sweden (68° N, 20° E), using sets of spaced receivers, are reported. In most cases the height and the thickness of the layer producing scintillation were the same at both stations. A type of fast and very regular fading observed at both stations is discussed.

Exploring the signature of polar lows in infrasound: the 19–20 November 2008 cases

Abstract We report in this study the infrasound signal measured consistently at four stations in Fennoscandia, associated with the development of two intense cyclones, called polar lows, over the Norwegian Sea. When conditions of propagation are favourable, the infrasound signal comes from the direction of the polar lows, and it follows their track. The results thus, tend to confirm those of a previous study who claimed that an outbreak of three polar lows generated clear infrasound to distances up to 1000 km, according to measurements acquired in Northern Norway and on Svalbard. Because the conditions of propagation of infrasound depend on the state of the atmosphere between the sources and the receivers, signals may remain undetected, which limits the capability of a systematic early warning system, and also of a global monitoring of polar lows. However, the recorded signals might reflect on-going source processes, since convection associated with the polar lows is detected using microwave satellite observations in the areas from which the signals emanate. This suggests that at least part of the signal is due to turbulence induced by convection, in agreement with the earlier study. Nevertheless, more evidence of broadband infrasound measurements of polar low cases have to be examined in order to be able to fully assess the role of other possible sources (swell, surf, lightnings, …). The addition in Northern Norway in late 2013 of the IS37 infrasound station of the International Monitoring Network, developed for the verification of the Comprehensive nuclear-Test-ban Treaty, will provide new opportunities to further investigate this issue.