Download Incomplete DRAFT Ice Sheet Science Questions Traceability and

Team Updated Draft Ice Sheet
Science Goals and Assignments
September 27
OIB Ice Sheet Science Themes
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What is the present state of the ice sheet? What is the flux of ice from the polar ice sheets
and what is required to improve the estimates for the IPCC on the contribution of ice sheets
to global sea level rise [1]? OIB will collect surface elevation change data and ice thickness
measurements. In combination with available spaceborne radar interferometry
measurements of surface velocity, OIB will enable ongoing assessments of the evolution of
mass fluxes from the Greenland Ice Sheet and from important sectors of the Antarctic Ice
sheet .
How and why are the ice sheets changing? What causes observed abrupt changes in ice
sheet motion? Does a rapid change in a glacier always lead to a large change in the ice
sheet volume [2]? OIB will map the sea water cavity beneath ice shelves, depth of
grounded glaciers below sea level, how far inland they remain below sea level, and the
basal slopes. OIB will inform on subglacial geology and basal boundary conditions. These
data will feed ice sheet process studies and numerical models assessing areas capable of
sustained contribution to sea level rise.
How will the mass balance and dynamics of the ice sheets change in the future [1,2,3]?
High fidelity surface and basal topographies and other measurements (eg InSAR velocities
from other projects) will provide input to material properties, forcings and boundary
conditions.
What do we learn across glacier systems? By documenting changing glacier systems in
Alaska/Greenland/Antarctica can we identify common forcings and responses that drive
future evolution? The Greenland Ice sheet, rimmed by outlet glaciers, is an analog for the
future of the Antarctic Ice sheet, rimmed by outlet-glacier-fed ice shelves.
Alaskan/Canadian glaciers and ice caps are analogs for the eventual fates of both
Greenland and Antarctica. IceBridge will explore these relationships to identify key
processes and characteristize glacier systems where information on local processes can be
Ice Sheet Science Questions
A. Where are glaciers continuing to thin and where may they be slowing/
thickening (1,2)
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B.
What are the major forces and mechanisms causing the ice sheets to lose
mass and change velocity, and how are these processes changing over
time? (2, 3, 4)
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C.
How can the ICESat, OIB, Cryosat, ICESat -2 measurements be optimized to characterize
the state of the ice sheets over several decades?
How does the ice sheet/glacier surface topography, bed topography, bed geology, ice
shelves/tongues, and grounding line configurations effect ice dynamics?
How and how far are horizontal stresses transmitted in the ice sheet?
How far downstream do changing processes near the ice divide effect glacier flow
What is the important scale for measuring geophysical parameters so as to substantially
improve modeling fidelity?
Where is the subglacial water produced and where is it going?
What is the sliding law and can repeat measurements be used to refine estimates of the
sliding law parameters?
How do ocean, sea ice, ice sheet interactions influence ice sheet behavior
(1, 2,3, 4)
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How does the bathymetry beneath ice shelves and the ocean/ice sheet interaction
effect ice sheet/glacier flow dynamics?
How does bathymetry in fjords influence tide-water glaciers about Greenland?
Ice Sheet Science Questions
D.
When do ice shelves become unstable? (2,3,4)
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E.
What are yearly snow accumulation rates over the ice sheets? (1,3)
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F.
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H.
How do changing accumulation rates (and hence near surface densities and firn structure)
impact altimetry measurements
What is the relative importance of ice sheet surface melt, and melt hydrology
on ice sheet mass balance and dynamics? (1,2,3)
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G.
What creates "granularity" in ice shelves? By granularity, we mean the bumpy texture that
creates the meltwater features that exist on entities like the pre-collapse Larsen B Ice
Shelf. Why should water fill crevasses on Larsen in a geometry such that the fragments of
the ice shelf created during collapse can capsize rather than float "top up" as a tabular
iceberg? This (the development of the proper granularity) is the key constraint that
differentiates a stable ice shelf from an ice shelf that can collapse explosively.
At what scale are ice rises/rumples important for understanding ice shelf and upstream ice
sheet stability?
What are the surface-melt flow-patterns and how much surface melt drains directly from the
surface and how much drains through channels within the ice sheet?
How much annual surface melt refreezes in place and how much results in net wastage?
What is the magnitude and spatial distribution of basal melt/freeze on ice shelves?
Are there commonalities in bed geomorphology, surface/base hydrology etc,
that can be used to extend IceBridge-derived process-knowledge to glaciers
not overflown by IceBridge? (characterisitic systems like fast glaciers with
high slope, fast glaciers with low slope etc.) (4)
What is the current surface mass balance and dynamic thinning of ice sheets?
(1,2,4)
OIB Ice Sheet Program Goals
a)
b)
c)
d)
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e)
Make airborne altimetry measurements over the ice sheets and sea ice to
extend the record of observations begun by ICESat. (A-H)
Link the measurements made by aircraft, ICESat, ICESat-2, and CryoSat-2
to allow accurate comparison and production of a long-term, ice altimetry
record. (A-D, H)
Use airborne altimetry to monitor key, rapidly changing areas of ice in the
Arctic and Antarctic to maintain a long term observation record, improve
understanding of glacial dynamics and surface mass balance, and improve
predictive models of sea level rise and sea ice cover. (A-H)
In conjunction with altimetry measurements, collecting other remotely
sensed data, improve predictive models of sea level rise and sea ice cover,
especially the following: (A-H)
Ice thickness and structure;
Bed topography underlying land-based ice;
Bathymetry beneath floating ice shelves;
Snow accumulation and firn structure; and
Other geophysical constraints that will improve estimates of the
geothermal and oceanic heat flux.
Adapt existing instruments for airborne remote sensing of ice by
unmanned aerial systems such as NASA’s Global Hawk. (A-H)
Ice Sheet Observation Requirements
originally in section 1.3.1 of Draft Project Plan
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vi.
Provide a dataset for cross-calibration and validation of ice-sheet
elevations from satellite lidars (ICESat-1, ICESat-2, DesDynI-Lidar)
and radars (CryoSat-2 and Envisat). (a, b, c)
Provide a dataset for improving and linking ICESat and ICESat-2
the ice-sheet elevation time series, including better
characterization of ICESat-1 errors. (a,b)
Provide a data sets for investigating critical ice sheet processes
(c,d)
Provide a dataset for improving and comparing numerical models
of ice-sheet dynamics, especially maps of the bed beneath
glaciers and ice shelves. (a,b,c,d)
Provide a dataset for improving instrument simulation and
performance analysis in support of future missions, such as
ICESat-2 and DesDynI-Lidar. (a,c,d,e)
Collaborate with field programs that will enhance interpretationo
f ice bridge data. (d,e)
Science Requirements – Spatial Coverage
• Detailed requirements deleted here and
awaiting an update by Halloween
Process toward Requirements
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Assignments refering back to vu-graph 6
1. Michele/Scott, Duncan
2. Ben, Bea
3. Ken, Bea, Robin
4. Sophie, Eric, Eric, Robin, Ian, Ben
5. Scott , Bea(check with Science leads on Icesat
etc)
• 6. Michael, Ken, Mark
• What is the format of the requirements and level
of detail.
Issues and Random Thoughts
• Cal val sensor intercal plan
• Concise explanation/justification on each
objective/requirement
• Update tracability throughout the bullets
• Objectives and Requirements as a check list
for flight planning and instrument priorities
• What are the risks to the gravity measurement
inversions for sub ice shelf cavities in the
presence of undetected basal marine ice?