Tomography-based observation of sublimation and snow metamorphism under temperature gradient and advective flow

Abstract. Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray micro-tomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. The sublimation of water vapor for saturated air flowing across the snow sample was experimentally determined via variations of the porous ice structure. The results showed that the exothermic gas-to-solid phase change is favorable vis-a-vis the endothermic solid-to-gas phase change, thus leading to more ice deposition than ice sublimation. Sublimation has a marked effect on the structural change of the ice matrix but diffusion of water vapor in the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong reposition process of water molecules on the ice grains is relevant for atmospheric chemistry.

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Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

The Cryosphere ◽

10.5194/tc-6-1141-2012 ◽

2012 ◽

Vol 6 (5) ◽

pp. 1141-1155 ◽

Cited By ~ 85

Author(s):

B. R. Pinzer ◽

M. Schneebeli ◽

T. U. Kaempfer

Keyword(s):

Temperature Gradient ◽

Physical Properties ◽

Time Lapse ◽

Phase Changes ◽

External Temperature ◽

Vapor Flux ◽

Snow Metamorphism ◽

Diffusion Enhancement ◽

Micro Tomography ◽

Snow Microstructure

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during temperature gradient metamorphism (TGM) under a constant gradient of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, in addition to the exact locations of these phase changes. We calculated the average time that an ice volume stayed in place before it sublimated and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snowpack where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60% of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of {temperature gradient metamorphism} produced by directly observing the changing microstructure sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

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Vapor flux and recrystallization during dry snow metamorphism under a steady temperature gradient as observed by time-lapse micro-tomography

The Cryosphere Discussions ◽

10.5194/tcd-6-1673-2012 ◽

2012 ◽

Vol 6 (3) ◽

pp. 1673-1714 ◽

Cited By ~ 3

Author(s):

B. R. Pinzer ◽

M. Schneebeli ◽

T. U. Kaempfer

Keyword(s):

Temperature Gradient ◽

Physical Properties ◽

Time Lapse ◽

Steady Temperature ◽

Data Set ◽

External Temperature ◽

Vapor Flux ◽

Snow Metamorphism ◽

Micro Tomography

Abstract. Dry snow metamorphism under an external temperature gradient is the most common type of recrystallization of snow on the ground. The changes in snow microstructure modify the physical properties of snow, and therefore an understanding of this process is essential for many disciplines, from modeling the effects of snow on climate to assessing avalanche risk. We directly imaged the microstructural changes in snow during metamorphism under a steady temperature gradient (STGM) of 50 K m−1, using in situ time-lapse X-ray micro-tomography. This novel and non-destructive technique directly reveals the amount of ice that sublimates and is deposited during metamorphism, and in addition the exact locations of these phase changes. From the four-dimensional data set, we calculated the average time that an ice volume stayed in place before it sublimated, and found a characteristic residence time of 2–3 days. This means that most of the ice changes its phase from solid to vapor and back many times in a seasonal snow pack, where similar temperature conditions can be found. Consistent with such a short timescale, we observed a mass turnover of up to 60 % of the total ice mass per day. The concept of hand-to-hand transport for the water vapor flux describes the observed changes very well. However, we did not find evidence for a macroscopic vapor diffusion enhancement. The picture of STGM that is produced by directly observing the microstructure of snow in situ sheds light on the micro-physical processes and could help to improve models that predict the physical properties of snow.

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Tomography-based monitoring of isothermal snow metamorphism under advective conditions

The Cryosphere Discussions ◽

10.5194/tcd-9-1021-2015 ◽

2015 ◽

Vol 9 (1) ◽

pp. 1021-1045

Author(s):

P. P. Ebner ◽

M. Schneebeli ◽

A. Steinfeld

Keyword(s):

Structural Dynamics ◽

Transport Process ◽

Laboratory Experiments ◽

Time Lapse ◽

Digital Geometry ◽

X Ray ◽

Effective Transport ◽

Snow Metamorphism ◽

Kelvin Effect ◽

Micro Tomography

Abstract. Time-lapse X-ray micro-tomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. Diffusion and advection across the snow pores were analysed in controlled laboratory experiments. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective transport properties. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Diffusion originating in the Kelvin effect between snow structures dominates and is the main transport process in isothermal snow packs.

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Vapor plumes in a tropical wet forest: spotting the invisible evaporation

10.5194/hess-2020-14 ◽

2020 ◽

Cited By ~ 1

Author(s):

César Dionisio Jiménez-Rodríguez ◽

Miriam Coenders-Gerrits ◽

Bart Schilperoort ◽

Adriana González-Angarita ◽

Hubert Savenije

Keyword(s):

Water Vapor ◽

Temperature Gradient ◽

Formation Process ◽

Forest Canopy ◽

Time Lapse ◽

Minor Importance ◽

Tropical Wet Forest ◽

Air Convection ◽

Rain Events ◽

Lifting Condensation Level

Abstract. Forest evaporation exports a vast amount of water vapor from land ecosystems into the atmosphere. Meanwhile, evaporation during rain events is neglected or considered of minor importance in dense ecosystems. Air convection moves the water vapor upwards leading the formation of large invisible vapor plumes, while the identification of visible vapor plumes has not been studied yet. This work describes the formation process of vapor plumes in a tropical wet forest as evidence of evaporation processes happening during rain events. In the dry season of 2018 at La Selva Biological Station (LSBS) in Costa Rica it was possible to spot visible vapor plumes within the forest canopy. The combination of time-lapse videos at the canopy top with meteorological measurements along the canopy profile allowed to identify the conditions required for this process to happen. This phenomenon happened only during rain events, where evaporation measurements showed contributions of 1.8 mm d−1. Visible vapor plumes during day time occurred on the presence of precipitation (P), air convection identified by the temperature gradient (Δϴv / Δz) at 2 m height, and a lifting condensation level at 43 m height (Zlcl.43) smaller than 100 m.

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Snow heterogeneous reactivity of bromide with ozone lost during snow metamorphism

10.5194/acp-2020-170 ◽

2020 ◽

Author(s):

Jacinta Edebeli ◽

Jürg C. Trachsel ◽

Sven E. Avak ◽

Markus Ammann ◽

Martin Schneebeli ◽

...

Keyword(s):

Water Vapor ◽

Temperature Gradient ◽

Snow Cover ◽

Atmospheric Chemistry ◽

Chemical Reactivity ◽

Trace Gases ◽

Heterogeneous Reactivity ◽

Surface Snow ◽

Avalanche Formation ◽

Snow Samples

Abstract. 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.

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Metamorphism during temperature gradient with undersaturated advective airflow in a snow sample

The Cryosphere ◽

10.5194/tc-10-791-2016 ◽

2016 ◽

Vol 10 (2) ◽

pp. 791-797 ◽

Cited By ~ 4

Author(s):

Pirmin Philipp Ebner ◽

Martin Schneebeli ◽

Aldo Steinfeld

Keyword(s):

Temperature Gradient ◽

Structural Dynamics ◽

Time Lapse ◽

Water Molecules ◽

Matrix Diffusion ◽

Snow Sample ◽

Advective Flow ◽

X Ray ◽

Chemical Content ◽

Snow Samples

Abstract. Snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow, which alters its microstructure and physical properties. Time-lapse X-ray microtomography is applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions. Cold saturated air at the inlet was blown into the snow samples and warmed up while flowing across the sample with a temperature gradient of around 50 K m−1. Changes of the porous ice structure were observed at mid-height of the snow sample. Sublimation occurred due to the slight undersaturation of the incoming air into the warmer ice matrix. Diffusion of water vapor opposite to the direction of the temperature gradient counteracted the mass transport of advection. Therefore, the total net ice change was negligible leading to a constant porosity profile. However, the strong recrystallization of water molecules in snow may impact its isotopic or chemical content.

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