Features of the electron avalanche formation process in a strongly inhomogeneous electric field under high overvoltages

The simulation of the electron avalanche formation process in subnanosecond discharges of high pressure was carried out by means of the Monte-Carlo approach. The discharge gap under consideration was of the configuration “the finger-shaped cathode – the hemispherical anode”. The presence of a conic-shaped microprotrusion on a cathode surface was assumed. Such the electrode configuration provided the strongly inhomogeneous distribution of an electric field. A gas simulated was nitrogen at a pressure of 6 atm. An average electric field strength across the discharge gap was varied from 200 kV/cm up to 400 kV/cm. Microprotrusion height was varied from 0 um up to 30 um. The critical size and formation time of an electron avalanche were determined under various conditions simulated. The threshold electric field strength for electrons to transit into the continuous accelerating regime was calculated for various heights of the microprotrusion. The applicability of the non-self-consistent Monte-Carlo technique for the investigation of the runaway electron kinetics and the correct simulation of the runaway electron beam transport across the discharge gap was shown.

SNOW AVALANCHES ON THE SEREBRYANSKAYA DISTANCE OF THE WAY

This article presents the probability of avalanche formation, possible damages depending on the volume of the avalanche, the volume of snow avalanches, the type of snow avalanches, slope angle, slope roughness, snow cover height. The analysis of conditions and factors accompanying such a natural disaster as snowfalls and snowdrifts on the railway is made. Effective ways of dealing with snowdrifts on the railway are highlighted.

Snowiness as a factor for assessing the avalanche activity in poorly explored mountainous areas (on the example of the Baikal region)

The relevance of the study of snowiness in the Baikal region is due to the long-term existence of a stable snow cover, which determines the development of such dangerous natural phenomena as snow runup, snow loads, snow flows and avalanches, which can cause a serious damage to the infrastructure facil up, snow loads, snow flows and avalanches, which can cause a serious damage to the infrastructure facilities. The problem is aggravated by the lack of comprehensive studies of nival phenomena, which are not taken into account in the construction of such important industrial facilities as railway bridges, power lines, railways and highways. The purpose of the article is to assess the risks of unfavorable and dangerous phenomena of a nival nature in the Baikal region, as well as to develop methods of protection against them. The results of observations are presented. The total amount of precipitation was determined. The dynamics of snowfall indicators as indicators of the avalanche formation regime in the mountains of the Baikal region was carried out. The chronology of winters with different snowfall indicators was reconstructed. The amount of precipitation in the cold period was taken as a basic indicator. A scheme for assessing snowiness for poorly studied areas was developed. The calculation of values of the spatial correlation of snowfall indicators was carried out, which made it possible to identify areas with synchronous fluctuations in the amount of precipitation of the cold season for many years. It was established that dependences of the snow cover height and snow reserves on the terrain height remained unchanged. The dependences of snow cover indicators on different factors were identified.

Snow heterogeneous reactivity of bromide with ozone lost during snow metamorphism

Earth's snow cover is very dynamic on diurnal timescales. The changes to the snow structure during this metamorphism have wide-ranging impacts on processes such as avalanche formation and on the capacity of surface snow to exchange trace gases with the atmosphere. Here, we investigate the influence of dry metamorphism, which involves fluxes of water vapour, on the chemical reactivity of bromide in the snow. To this end, the heterogeneous reactive loss of ozone in the dark at a concentration of 5×1012–6×1012 molec. cm−3 is investigated in artificial, shock-frozen snow samples doped with 6.2 µM sodium bromide and with varying metamorphism history. The oxidation of bromide in snow is one reaction initiating polar bromine releases and ozone depletion. We find that the heterogeneous reactivity of bromide is completely absent from the air–ice interface in snow after 12 d of temperature gradient metamorphism, and we suggest that the burial of non-volatile bromide salts occurs when the snow matrix is restructuring during metamorphism. Impacts on polar atmospheric chemistry are discussed.

Snow heterogeneous reactivity of bromide with ozone lost during snow metamorphism

Earth's snow cover is very dynamic on diurnal time scales. The changes to the snow structure during this metamorphism have wide ranging impacts such as on avalanche formation and on the capacity of surface snow to exchange trace gases with the atmosphere. Here, we investigate the influence of dry metamorphism, which involves fluxes of water vapor, on the chemical reactivity of bromide in the snow. For this, the heterogeneous reactive loss of ozone at a concentration of 5–6 x 1012 molecules cm-3 is investigated in artificial, shock-frozen snow samples doped with 6.2 μM sodium bromide and with varying metamorphism history. The oxidation of bromide in snow is one reaction initiating polar bromine releases and ozone depletions. We find that the heterogeneous reactivity of bromide is completely absent from the air-ice interface in snow after 12 days of temperature gradient metamorphism and suggest that burial of non-volatile bromide salts occurs when the snow matrix is restructuring during metamorphism. Impacts on polar atmospheric chemistry are discussed.

Potential avalanche release in windthrow areas: the effect of snow height and terrain roughness

<p>Windthrow is an important disturbance agent in forest ecosystems and is expected to become more frequent and severe under climate change. Windthrow creates large amounts of surface roughness from downed trees, root plates and stumps. In mountain forests, these elements increase the surface roughness and provide a considerable protective effect against snow avalanches during the first years following a disturbance event. However, if large volumes of snow covers the surface roughness elements, a windthrow area may become prone to avalanche release. Snow accumulation produces terrain smoothing, which is an important factor in avalanche formation.</p><p>To assess the effect of snow accumulation on surface roughness in windthrow areas, we quantified terrain smoothing using a vector ruggedness measure and corresponding snow heights, based on digital surface models from summer and winter terrain produced from repetitive UAV flights. Additionally, the snowpack structure was examined using a digital snow micro penetrometer (SMP) to quantify the heterogeneity of snow stratigraphy and to monitor a possible development of weak snow layers over distances greater than 10-20 m, which may contribute to slab avalanche formation. Four study plots were selected to characterize different conditions: i) undisturbed forest, windthrow area with ii) high and iii) low surface roughness, and iv) an open meadow control plot. We then quantified how surface roughness is smoothed depending on the snow height, and at the same time characterized the snowpack structure and the extent of potential weak layers.</p><p>We found that increasing snow height leads to decreasing surface roughness, which can produce local release areas. We expect that with continuous increase of snow height, these release areas expand in size; however, further analyses of the snowpack structure will provide deeper insights in potential weak layer formation. Critical conditions for avalanche releases in windthrow areas may thus be defined based on scenarios for snow height and close-range sensing-based roughness data.</p>

Acoustic Emission investigation for avalanche formation and release: A case study of dry-slab avalanche event in Great Himalaya

Non-invasive monitoring of avalanche formation and release processes, through the use of Acoustic Emission (AE) technique, has been a research challenge since long time. In present investigation AE technique is implemented to monitor the avalanche formation and release processes through a case study of a natural avalanche event reported in Great Himalaya. The specialized AE sensor-arrestor arrays, established over the avalanche starting zone, in conjunction to a high speed multichannel AE acquisition system have successfully recorded the avalanche event passed through the course of instability development followed by release of avalanche. A new method is devised to compute the AE based instability index, and same has been applied to quantify the instability levels of a snowpack. The prominent AE parameters and instability indices are analyzed for different window scales with respect to different AE sensors. The effect of nivological and meteorological conditions and pit analyses collected during the avalanche formation process is also discussed. The critical instability was triggered possibly due to the excessive loading (during snowfall) of an unstable snowpack consisting of persistent weak layers which led to the avalanche release. An abnormal and abrupt increase in the AE activity was observed prior to the avalanche release. The increasing trends in instability indices have shown a good correlation to the avalanche formation and a sharp jump in instability index is attributed to a particular transition occurring across two different instability states of the snowpack. Thus, five conceptual states of snowpack are identified for instability evolution corresponding to four different transitions during avalanche formation and release processes.

ASSESSMENT OF SNOW AVALANCHE SUSCEPTIBILITY OF ROAD NETWORK - A CASE STUDY OF ALAKNANDA BASIN

<p><strong>Abstract.</strong> Snow avalanche occurring in a micro-climatic condition causing hydro-geo (Hydrological and geological) hazard to the deployed armed forces and nearby inhabitant to the North Western Himalaya about 3000 MSL. In recent years, frequencies of snow avalanche have increase and consequently the death toll have also surged to many folds. These unavoidable occurrences not only cause road blocks which disrupts transportation connectivity in the rugged terrain of Himalaya as well as loss of infrastructure and life. Here, in this study an attempt has been made to assess the susceptibility of road network of Alaknanda Basin from snow avalanche. Potential avalanche formation zones have been generated using Analytical Hierarchical Process (AHP) of Multi-Criteria Decision Making (MCDM. Advance Thermal Emission Reflection Radiometer (ASTER) Global Digital Elevation (GDEM) 30 meter has been used to generate static parameters like slope, aspect, curvature etc. using GIS platform. ISRO-Geosphere Biosphere Program Land Use Land Cover (LULC) used as another static parameter. Weights are generated using comparison matrix and ratings to different static parameter layers assigned on the basis of field visit and literature review while the road network are digitized from Google earth. A methodology has been prepared to categorize the road stretches on the basis of potential snow avalanche formation zone including hydrological processing. Buffer zone are assigned with weights according to potential snow avalanche formation zones. Later roads are intersected with sub basin with assigned values that resulted very high avalanche potential zonation, considered as most susceptible to snow avalanche hazard.</p>

Determining the drivers for snow gliding

Snow gliding is a key factor for snow glide avalanche formation and soil erosion. This study considers atmospheric and snow variables, vegetation characteristics, and soil properties, and determines their relevance for snow gliding at a test site (Wildkogel, Upper Pinzgau, Austria) during winter 2014/15. The time-dependent data were collected at a high temporal resolution. In addition to conventional sensors a snow melt analyzer was used. The analysis shows that the soil moisture at the soil surface had the largest influence on snow gliding during the first part of the winter (October to January). The soil moisture 1.5 cm below the soil surface was the second important variable in the first part of the winter, and the most important variable in the second part of the winter (February to May). A negative influence on snow gliding had the phytomass of mosses in autumn and spring caused by lower canopy heights at these sites. Furthermore, a higher portion of dwarf shrub phytomass reduces snow gliding, because its rigid structure can transfer forces to the soil. Further investigations may be focused on the freezing and melting processes in the uppermost soil layers, and at the soil surface.