Extremely periodic pulsating aurora observed near L=6: A new type pulsating aurora

Extremely periodic pulsating aurora, a new type pulsating aurora, was detected by three photometers (directing towards the zenith and 45° N and S in the meridian plane, for 427.8 nm emission) at Husafell in Iceland on 18-19 December 1985. We examined the characteristics of the pulsating auroras and their relationship to magnetic pulsations using the data obtained in Iceland and Syowa Station, the geomagnetically conjugate pair station in Antarctica. The characteristics of this event are as follows; 1) extremely regular periodic pulsating auroras with the frequency of -50 mHz were observed simultaneously on the 3 photometers, 2) the periodicity of the pulsation was extremely high, and the Q-value showed more than 20, 3) the intensity variation among the 3 photometers occurred with excellent coherency and simultaneously without time lag, suggesting that these pulsating auroras were not of a propagating type but a standing type, 4) there are no correlation between the optical pulsating auroras and magnetic pulsations on the ground. These characteristics suggest that the extremely periodic pulsating aurora on this event is not a common (popular) pulsating aurora but an exceptional type pulsating aurora which would occur under a certain condition in the magnetosphere

Assessment of Landslide-Induced Geomorphological Changes in Hítardalur Valley, Iceland, Using Sentinel-1 and Sentinel-2 Data

Publisher's version (útgefin grein)Landslide mapping and analysis are essential aspects of hazard and risk analysis. Landslides can block rivers and create landslide-dammed lakes, which pose a significant risk for downstream areas. In this research, we used an object-based image analysis approach to map geomorphological features and related changes and assess the applicability of Sentinel-1 data for the fast creation of post-event digital elevation models (DEMs) for landslide volume estimation. We investigated the Hítardalur landslide, which occurred on the 7 July 2018 in western Iceland, along with the geomorphological changes induced by this landslide, using optical and synthetic aperture radar data from Sentinel-2 and Sentinel-1. The results show that there were no considerable changes in the landslide area between 2018 and 2019. However, the landslide-dammed lake area shrunk between 2018 and 2019. Moreover, the Hítará river diverted its course as a result of the landslide. The DEMs, generated by ascending and descending flight directions and three orbits, and the subsequent volume estimation revealed that-without further post-processing-the results need to be interpreted with care since several factors influence the DEM generation from Sentinel-1 imagery.This research has been supported by the Austrian Science Fund (FWF) through the project MORPH (Mapping, monitoring and modelling the spatio-temporal dynamics of land surface morphology; FWF-P29461-N29) and the Doctoral Collage GIScience (DKW1237-N23), as well as by the Austrian Academy of Sciences (?AW) through the project RiCoLa (Detection and analysis of landslide-induced river course changes and lake formation).Peer Reviewe

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Debris flows are fast-moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris-flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris-flow release styles by integrating high-resolution multi temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris-flow triggering processes were previously hypothesized for this site: (i) slope failure, characterised by landslides evolving into debris flows, and (ii) the fire-hose effect, in which debris accumulated in pre-existing, steep-sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris-flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire-hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source-area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire-hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris-flow initiation in absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Publisher's version (útgefin grein)Debris flows are fast-moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris-flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris-flow release styles by integrating high-resolution multi-temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris-flow triggering processes were previously hypothesised for this site: (i) slope failure, characterised by landslides evolving into debris flows; and (ii) the fire-hose effect, in which debris accumulated in pre-existing, steep-sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris-flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire-hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source-area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire-hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris-flow initiation in the absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows.This work would not have been possible without a postgraduate studentship grant (NE/L002493/1) from the CENTA Doctoral Training Partnership funded by the UK Natural Environment Research Council (NERC) and the British Geological Survey University Funding Initiative Studentship (GA/14S/024, Ref: 284). We thank the NERC Airborne Research Facility Data Analysis Node for obtaining the aerial photography and LiDAR data, for the airborne survey project NERC ARSF 07217a in 2007 and for the airborne survey project NERC ARSF IG13‐11 in 2013. We thank the NERC Geophysical Equipment Facility for technical support and for the loan number 1001. We would like to show our gratitude to Jón Kristinn Helgason (Icelandic Meteorological Office), who provided expertise that greatly improved the manuscript. We acknowledge constructive comments and suggestions from two anonymous reviewers. C. Jordan publishes with permission from the Executive Director of the British Geological Survey.Peer Reviewe

Conjugacy of electron auroras observed by all-sky cameras and scanning photometers

Simultaneous auroral observations were carried out at the Syowa-Husafell conjugate pair of stations (L=6.1) in the period of August 28-September 30,1984. During the period of the campaign, conjugate auroral data were obtained on 4 nights of clear sky in the conjugate regions. In this paper, we show some initial results on the geomagnetic conjugacy of visible auroras observed by 5577Å scanning photometers and all-sky cameras in the selected event study of September 26,1984. The characteristics of the conjugacy of visible auroras are as follows, 1) Auroral breakups occur almost simultaneously in the northern and southern hemispheres. However, the poleward expansion speed is much larger at Syowa than at Husafell, 2) The east-west (EW) aligned auroral arcs appear at almost the same geomagnetic latitude in the IGRF model in both hemispheres. However, the EW-aligned auroras observed at Husafell show a large longitudinal displacement (more than 300km westward) relative to those observed at Syowa, 3) Isolated north-south aligned auroras show a good conjugacy in their shapes and locations, 4) The EW-aligned auroras generally show different movements and fine structures in both hemispheres