Transcript Slide 1

C-Change in GEES
Changing Permafrost
Environments
Session Three: Permafrost
Development
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
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Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
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Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Three Key Topics
• Surface Energy Balance
– Determines the temperature of the ground surface.
– Principally controlled by climate.
• Ground Thermal Regime
– Change in temperature with depth is controlled by the surface
temperature, the properties of the subsurface materials and the
duration of any surface temperature changes.
– Geothermal gradient determines permafrost thickness.
• Surface Boundary Layer
– Changing nature of the surface complicates the relationship
between climate and permafrost thickness.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Related variable
Surface
boundary
conditions
Surface energy
balance
Ground
thermal
properties
(+time)
CLIMATE
GROUND
SURFACE
TEMP.
GROUND
THERMAL
REGIME
MEAN ANNUAL
AIR TEMP.
Complex
relationship
MEAN ANNUAL
GROUND TEMP.
PERMAFROST
THICKNESS
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
1. Surface Energy Balance
Fig 1.2 IPCC (2001) IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the
Third Assessment Report of theIntergovernmental Panel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M.
Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA, 881pp
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
1. Surface Energy Balance
Temperature of the ground surface is
determined by:
• Balance of incoming vs.
outgoing radiation
– Short-wave and long-wave.
• Sensible heat exchange (e.g.
cold air mass above a ground
surface will cause it to cool).
• Latent heat exchange (related to
phase changes)
Midnight sun, Prudhoe Bay, Alaska (R I Waller)
– Condensation (will cause
ground to warm).
If balance is negative, the surface
– Evaporation (will cause ground
temperature will drop.
to cool).
If balance is positive, the surface
temperature will rise.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Outgoing
longwave
radiation
Sensible
heat flux
Latent heat
flux
(evaporation)
Refle
cted
(albe
do)
Incoming
solar
radiation
More incoming than outgoing
energy. Ground temperature rises
and energy flows into the ground.
Energy exchange at the ground surface during a sunny summer’s day.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Incoming
solar
radiation
Outgoing
longwave
radiation
Sensible
heat flux
Latent heat
flux
(condensation)
More outgoing than incoming
energy. Ground temperature falls
and energy flows out of the ground.
Energy exchange at the ground surface during a clear night (5am).
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Heat Balance Equation
Q* = QLE + QH + QG
Q*
QLE
QH
QG
= Net radiation (largely insolation)
= Latent heat flux
= Sensible heat flux
= Ground heat flux
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Heat Balance Equation
Q* = QLE + QH + QG
Net radiation
(shortwave &
longwave)
Drives
evaporation
e.g. Summer’s day
Energy flux into
the ground
Ground
surface heats
the air
(convection)
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
2. Ground Thermal Regime
Winter
Summer
Ground
surface
MAGT
(1)
Permafrost
thickness
(3)
(2)
OºC
isotherm
• Refers to the vertical change
in temperature with depth.
• Changes in the gradient (and
therefore permafrost
thickness) driven by:
1 Climate or ground surface
changes (affects MAGT).
2 Variations in the
geothermal heat flux.
3 Thermal conductivity of the
subsurface materials.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Subsurface Temperature Changes
Drop in surface temp.
0ºC
Temperature changes at the
ground surface influence
subsurface temperatures by
altering the ground thermal
regime.
Permafrost
thickens
Ground thermal regime “pulled across”
by shift in surface temperature.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Permafrost
thins
Permafrost
thickens
Theoretical responses to changes in surface temperature (T1 to T2) through time (d1 to d2).
Figure From: Harris, S.A. 1986. The Permafrost Environment. Croom Helm, Beckenham (p.25).
© Croom Helm Publishers
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Thermal Conductivity
0°C
MAGT
Permafrost
thickness
Low conductivity
High conductivity
• Thermal conductivity of the
substrate determines:
– the rapidity of substrate
temperature changes.
– the slope of the
geothermal gradient.
• E.g. High conductivity =
– rapid change in ground
temperatures.
– shallow geothermal
gradient – temp. changes
extend to a deeper level.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Table of average thermal conductivities for a variety of
materials
e.g. rocks are good
conductors of heat
…whilst snow is a
poor conductor
(insulator)
Table From: French, H.M. 2007. The Periglacial Environment (3rd ed.). Wiley & Sons, Chichester(p.87).
© Wiley and Sons
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
From: Terzaghi, K.
(1952) ‘Permafrost’ in
From theory to practice
in soil mechanics:
Selections from the
writings of Karl Terzaghi,
pp. 246-295. New York
and London: John Wiley.
In reality, the subsurface is likely to comprise a number of units with
different thermal conductivities, each influencing the geothermal gradient.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Duration and Depth
•
Changes in surface energy balance and ground surface temperature
occur at a variety of timescales.
•
Duration of temperature change dictates the depth to which the
temperature change extends:
– Diurnal changes: few centimetres.
– Seasonal changes: up to 10-20 m.
– Longer-term changes: up to around 1 km.
SYR Figure 2-3 IPCC, 2001:
Climate Change 2001:
Synthesis Report. A
Contribution of Working
Groups I, II, and III to the Third
Assessment Report of the
Integovernmental Panel on
Climate Change [Watson, R.T.
and the Core Writing Team
(eds.)]. Cambridge University
Press, Cambridge, United
Kingdom, and New York, NY,
USA, 398 pp
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Seasonal Fluctuations
• Seasonal temperature
fluctuations influence ground
temperatures in the upper few
tens of metres.
• MAGT measured at the point at
which seasonal temperature
variations cease.
Williams, P.J. & Smith, M.W. 1989. The Frozen
Earth. Studies in Polar Research. CUP, Cambridge.
Fig 1.6 p.12
http://www.cambridge.org/uk/catalogue/catalogue.as
p?isbn=9780521424233
Reproduced with the permission of Cambridge
University Press
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Based on data
from: Carson, J.E.
and Moses, H.
(1963) ‘The annual
and diurnal heat
exchange cycles in
upper layers of soil’
Journal of Applied
Meteorology 2 397406
Seasonal temperature changes at the ground surface are gradually
damped and delayed with increasing depth (become zero at the MAGT).
Figure From: Williams, P.J. & Smith, M.W. 1989. The Frozen Earth. Studies in Polar Research. CUP, Cambridge.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Long-term fluctuations
• Really thick sequences of permafrost require thousands of years
to form.
• Termed relict permafrost as they relate to colder past climate
regimes (usually Pleistocene).
– E.g. permafrost up to 700 m in thickness in the western
Canadian Arctic reflects persistently low temperatures and
non-glacial conditions over the last 40,000 years.
– Modelling suggests MAGT must have dropped to a sustained
-18°C to produce such a thickness of permafrost.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Theoretical model illustrating the
gradual downward propagation of a
stepwise temperature change
through time.
From Molochuskin, E.N. (1973) ‘The effect of thermal
abrasion on the temperature of the permafrost in the
coastal zone of the Laptev Sea. Proceedings of the
Second International Conference on Permafrost.
Yakutsk, USSR, USSR Contribution. Pp90-93.
Washington D.C.: National Academy of Sciences. Fig. 2
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
3. The Surface Boundary Layer
Reindeer moss on the floor of a forest in northern Finland (R I Waller)
• Relationship between climate
and permafrost thickness is
strongly influenced by a series of
boundary layer conditions.
E.g.
– Relief and aspect.
– Vegetation.
– Snow cover
– Presence of water bodies
and drainage.
– Fire.
• Determine local microclimate,
MAGT and permafrost thickness.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Boundary or Buffer Layer
Conceptual model describing
the complex relationship
between climate (atmosphere)
and permafrost (geothermal
regime).
Based on: Luthin, J.N and Guymon, G.L. (1974) ‘Soil
moisture-vegetation-temperature relationships in
Central Alaska’ Journal of Hydrology, 23, 233-246
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Relief & Aspect
• Relief and aspect affect the
receipt of incoming solar
radiation and the depth and
duration of snow cover.
• Pole-facing slopes:
– Lower receipt of insolation.
– Lower MAGT.
– Thicker permafrost.
– Thinner active layer (shorter
duration).
http://www.flickr.com/photos/7202153@N03/2402867494/
…and vice-versa…
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Vegetation
The tree line marking the boundary between tundra and boreal forest,
northern Finland (R.I. Waller).
• Can influence the surface
energy balance in a variety of
ways:
– Insulates ground surface –
reduces magnitude of
ground surface
temperature changes.
– Can also influence other
variables - e.g. vegetation
traps snow which
enhances insulating effect.
– Influence depends on type
of vegetation: e.g. scrub
traps snow, trees intercept
snow in their canopies.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Influence of Vegetation
Ground thermal regime
beneath tundra and forest in
the western Canadian Arctic.
Tundra offers less insulation
at the ground surface subsurface temperature
changes are greater and
extend deeper.
Figure From: Rouse, W.R. (1984)
‘Microclimate of Arctic tree line. 2: Soil
microclimate of tundra and forest. Water
Resources Research, 20, 1, 67-73.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Snow cover
• One of the most important factors.
• In general, insulates ground from the
extreme winter temperatures.
• BUT - timing and duration of
snowfall are critical:
– autumn snow will delay freezing.
– spring snow will delay thaw.
http://www.flickr.com/photos/vizpix/3775615775/
• Variations in snowpack thickness
can cause widespread local changes
in permafrost and active layer
thickness.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Fire & Water
Fire
• Many fires started by lightning in the Boreal Zone.
• Effect of fire on underlying permafrost depends upon duration of fire
and thermal conductivity of ground.
• Greatest effect occurs due to vegetation change and the resulting
change in the surface energy balance.
Water
• Supremely effective at buffering adjacent ground from temperature
fluctuations (high heat capacity).
• Saturation of substrate and state of water also influences its
thermal conductivity: dry - good insulator; wet & frozen - highly
conductive.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Influence of Water
Numerical simulation of the geothermal disturbances caused by
lakes at the ground surface (A-E).
Figure From: French, H.M. 2007. The Periglacial Environment (3rd ed.). Wiley & Sons, Chichester (p.91).
© Wiley and Sons
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Significance...
Surface
disturbance
C hange in
surface energy
balance
A ltered
geothermal
regime
A relatively slight surface
disturbance can induce a
disproportionately large
response...
C hange in
permafrost and
A L thickness
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Lecture Summary
• Changes to the ground thermal regime and permafrost thickness
are driven primarily by changes in the surface energy balance.
• The surface energy balance is principally determined by climate,
although its influence is modified by a complex series of additional
factors.
• The ground thermal regime is driven by the surface energy
balance, the geothermal heat flux and the thermal conductivity of
the substrate.
• Changes to the surface conditions can dramatically affect
permafrost and active layer thicknesses.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
References
French, H.M. 2007. The Periglacial Environment (3rd ed.). Wiley &
Sons, Chichester.
Harris, S.A. 1986. The Permafrost Environment. Croom Helm,
Beckenham.
Rouse, W.R. 1984. ‘Microclimate of Arctic tree line. 2: Soil
microclimate of tundra and forest. Water Resources Research, 20, 1,
67-73.
Luthin, J.N and Guymon, G.L. 1974. ‘Soil moisture-vegetationtemperature relationships in Central Alaska’ Journal of Hydrology, 23,
233-246
Williams, P.J. & Smith, M.W. 1989. The Frozen Earth. Studies in
Polar Research. CUP, Cambridge.
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
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1. Slide 14 – Figure showing theoretical responses to changes in surface temperature from: Harris, S.A. 1986. The
Permafrost Environment. Croom Helm, Beckenham, is the copyright of Croom Helm Publishers. Permission should be
sought from the copyright holders prior to re-use
2. Slide 16 – Table of thermal conductivities from: French, H.M. 2007. The Periglacial Environment (3rd ed.). Wiley & Sons,
Chichester, is the copyright of Wiley and Sons. Permission should be sought from the copyright holders prior to re-use
3. Slide 30 – Figure showing a numerical simulation of geothermal disturbances from: French, H.M. 2007. The Periglacial
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Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development
Item Metadata
Author
Dr Richard Waller
Stephen Whitfield
Institute – Owner
Keele University, School of Physical and Geographical Sciences
Title
Permafrost Development PowerPoint Presentation
Date Created
March 2010
Description
Part Three of Changing Permafrost Environments
Educational Level
3
Keywords (Primary keywords – UKOER &
GEESOER)
UKOER, GEESOER, surface, energy, thermal, conductivity,
heat, balance, snow cover, vegetation
Creative Commons License
Attribution-Non-Commercial-Share Alike 2.0 UK: England &
Wales
Dr Richard Waller, Keele University, [email protected]
C-Change in GEES: Changing Permafrost Environments – Permafrost Development