Drifting snow and snow accumulation in complex arctic terrain

159 Pages·2013·16.68 MB·English

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Reports in Meteorology and Oceanography No. 3 - 2001
ISBN 82 - 90569 - 88 -2
ISSN 1502 - 5519
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Preface
This study was initiated by my supervisor Prof. Yngvar Gjessing in 1998. After three months of
postgraduate studies at the University courses on Svalbard, he asked me whether I was interested in
working as a Ph.D. student on the subject of drifting snow. After a weekend of consideration I
accepted under the condition that I could stay in Bergen for longer time spans. Since then, Prof.
Gjessing has been an inspiring supervisor who thoroughly discusses and supports all of a many
ideas of a student. I would like to express my gratitude for his designated help and untiring support.
Completing an university degree in foreign countries is still not the easiest way to proceed.
During the past five years of my master studies in Sweden and the time as Ph.D. student in Norway
my family and friends in Germany supported me in any possible way to continue my education
abroad and to keep in touch with the world at home.
Ten months of my Ph.D. period were spent with fieldwork in the high Arctic on Svalbard.
Successful fieldwork depends, among many other effects, primarily on a good cooperating field
team. The majority of the field measurements were done together with Ola Brandt, Martin Dahl,
Thomas Thiis and Jonas Johnsen. Their help and their input in the practical and scientific
discussions contributed largely to the success of my study and their friendship and company
supported me in person during the entire period.
Our security during the fieldwork periods is a major concern in the Arctic climate and was
supervized by the logistic staff at UNIS.
The new snow radar system, presented in this study, was developed in close cooperation with the
technical department at UNIS, in particular with Knut Sandaker who managed all the electronics of
the radar.
Special thanks to all the staff members and students at UNIS who helped in practice or just
contributed to keeping up a good spirit and a heartfelt social atmosphere on Spitsbergen.
During my stay in Bergen, my colleagues at the geophysical institute contributed with input and
critical discussion of the data processing and publication manuscripts. Anne Sandvik, who also gave
me an insight to the world of numerical modelling, did all the wind simulations for my study.
The digital elevation model of the study areas was kindly provided by the Norwegian Polar
Institute.
The linguistic quality of the thesis is improved by the tireless work of my language consultants
Petra Kuhn, Stefanie Frauciel and Carolyn Bright.
The project was funded by the Norwegian Research Council, project number 121740 / 410 and by
the University Courses on Svalbard, project number 9141.
Bergen June 2001, Christian Jaedicke
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Definition
The following terms for wind transported snow are used in this thesis:
snowdrift: snow accumulation resting on the ground
snow drift: the process of wind transport of snow
drifting snow: the ongoing process of snow drift
The terminology in papers 1 - 3 is changed accordingly!
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CONTENT
1. Introduction __________________________________________________________________3
1.1 Scope of this study_________________________________________________________________ 5
2. Background __________________________________________________________________5
2.1 Snow fences_______________________________________________________________________ 6
2.2 Traps and instruments _____________________________________________________________ 7
2.3 Wind tunnel ______________________________________________________________________ 8
2.4 Numerical simulations______________________________________________________________ 9
3. Theory______________________________________________________________________11
3.1 The snow surface_________________________________________________________________ 11
3.2 The wind________________________________________________________________________ 13
3.3 The drift ________________________________________________________________________ 16
3.3.1 Creep ______________________________________________________________________________16
3.3.2 Saltation____________________________________________________________________________16
3.3.3 Roughness over a snow surface __________________________________________________________20
3.3.4 Suspension__________________________________________________________________________21
3.3.5 Sublimation _________________________________________________________________________25
4. Field methods________________________________________________________________29
4.1 Snow distribution_________________________________________________________________ 29
4.1.1 Ground penetrating radar (GPR)__________________________________________________________29
4.1.2 Manual measurements _________________________________________________________________31
4.1.3 GPS and positioning___________________________________________________________________32
4.1.4 Total station _________________________________________________________________________32
4.2 Meteorological measurements ______________________________________________________ 33
4.3 Data processing __________________________________________________________________ 33
4.3.1 Snow distribution data _________________________________________________________________33
4.3.2 Meteorological data ___________________________________________________________________34
5. Field locations _______________________________________________________________34
5.1 Drønbreen_______________________________________________________________________ 34
5.2 Blekumbreen ____________________________________________________________________ 34
5.3 Adventdalen _____________________________________________________________________ 34
6. Meteorological conditions during snow drift _______________________________________36
6.1 Wind speed______________________________________________________________________ 36
6.2 Wind directions at low and high wind speeds__________________________________________ 36
6.3 Wind profiles ____________________________________________________________________ 36
6.4 Atmospheric stability _____________________________________________________________ 37
6.5 Sublimation from the snow surface__________________________________________________ 39
6.6 Sublimation during drift___________________________________________________________ 40
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6.7 Threshold friction velocities________________________________________________________ 40
6.8 Precipitation_____________________________________________________________________ 41
7. Numerical simulations_________________________________________________________42
7.1 Wind simulations_________________________________________________________________ 42
7.2 Drift model______________________________________________________________________ 44
7.3 Sublimation model________________________________________________________________ 46
7.4 Coupling of wind model and drift model _____________________________________________ 47
8. The included papers___________________________________________________________48
8.1 Changes in the snowdrift pattern caused by a building extension -Investigations through scale
modelling and numerical simulations ___________________________________________________ 48
8.2 The snowdrift pattern around a small hill in the high Arctic_____________________________ 48
8.3 Drifting snow in complex terrain – comparison of measured snow distribution and simulated
wind field __________________________________________________________________________ 49
8.4 Acoustic snowdrift measurements: Experiences from the FlowCapt instrument ____________ 49
8.5 Snow drift losses from an Arctic catchment on Spitsbergen: An additional process in the water
balance ____________________________________________________________________________ 50
8.6 High resolution snow distribution data from complex Arctic terrain – A tool for model validation
___________________________________________________________________________________ 50
8.7 The influence of drifting snow on the location of glaciers on western Spitsbergen ___________ 51
9. Concluding discussion_________________________________________________________52
10. List of symbols ______________________________________________________________54
11. References _________________________________________________________________55
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1. Introduction
Arctic regions and mountain ranges are characterized by their seasonal snow cover and low
vegetation. The wind has free access to the snow surface. Whenever the wind is strong enough it
moves the snow over the terrain. The snow is eroded in areas of high wind speeds such as mountain
ridges and exposed areas and is transported into accumulation areas such as lee slopes and surface
depressions, where, snowdrifts of several meters easily develop during a single storm event. The
wind transported snow causes severe problems for human activities in cold regions. This laid the
very foundation for the detailed study of the phenomenon.
Drifting snow is mainly a problem for the maintenance of roads and traffic lanes in the winter
season. Snowdrifts of only half a meter height are sufficient to block the traffic of motor-driven
vehicles and trains. Also the drifting snow itself can cause significant problems by decreasing
visibility and view. Such whiteout conditions prohibit traffic in affected areas (Fig.1). Large
resources of manpower and machinery are needed to clear off the snow and to guarantee road
safety. Around buildings as well, snowdrifts can cause severe problems for the accessibility of
entrances or emergency escapes (Fig. 2). In extreme cases, buildings are unemployable during the
entire winter season. This introduces an economical aspect to the problem. Farsighted design of
traffic lanes and buildings can prevent the worst drifting snow problems and save economic
resources in winter maintenance.
The snow avalanche activity in mountainous areas is closely related to drifting snow. Snow that is
transported by the wind into avalanche release zones is a major factor for the stability of avalanche
slopes (McClung and Schaerer, 1993). The wind loading can result in large snow cornices (Fig. 3)
and avalanche releases affecting infrastructure several kilometres down the valley.
On a larger scale, drifting snow has become an interesting part for the study of glacier and ice
sheet mass balances. Additional snow is transported to some glaciers by drifting snow. On the large
ice sheets of Greenland and Antarctica, snow mass is lost from the surface due to sublimation from
wind transported snow particles (Bintanja, 1998). Also the hydrology of snow-covered catchments
is affected by wind forced redistribution of snow. It influences the melting pattern in spring, which
again has an impact on the runoff pattern and the runoff chemistry (Ryden, 1979). Both are of
interest for drinking water and hydropower facilities.
The uneven snow cover caused by drifting snow has a major impact on the botany of cold regions
(Elvebakk, 1994, Campbell, 1997).
During precipitation events that occur simultaneously with strong winds, similar effects are
caused by the accumulating snow. These events play a major role for the snow distribution in
cold and wet climates such as the main land of Norway. The consideration of wind precipitated
snow in the theoretical approach is not very well developed and therefore not embodied in this
study. Furthermore, Spitsbergen has a very dry climate and drift occasions dominate over
precipitation events.
These differing aspects of drifting snow caused an intensive research activity over the past 50
years ranging from process studies to numerical modelling of drifting snow.
Summarizing reviews and lecture book chapters on snowdrift are given by Mellor (1965), Radok
(1977), Male (1980), Kind (1981, 1986) and Tabler et al. (1990b).