Land ice is losing mass to the worlds oceans at an accelerated rate. The
worlds glaciers contain much less ice than the ice sheets but contribute equally to
eustatic sea level rise and are expected to continue to do so over the coming
centuries if global temperatures continue to rise. It is therefore important to
characterize the mass balance of these glaciers and its relationship to climate
trends and variability. In the Canadian High Arctic, analysis of long-term surface
mass balance records shows a shift to more negative mass balances after 1987 and
is coincident with a change in the mean location of the July circumpolar vortex, a
mid-troposphere cyclonic feature known to have a strong influence on Arctic
summer climate. Since 1987 the occurrence of July vortices centered in the
Eastern Hemisphere have increased significantly. This change is associated with
an increased frequency of tropospheric ridging over the Canadian High Arctic,
higher surface air temperatures, and more negative glacier mass balance.
However, regional scale mass balance modeling is needed to determine whether
or not the long-term mass balance measurements in this region accurately reflect
the mass balance of the entire Canadian High Arctic.
The Canadian High Arctic is characterized by high relief and complex
terrain that result in steep horizontal gradients in surface mass balance, which can
only be resolved if models are run at high spatial resolutions. For such runs,
models often require input fields such as air temperature that are derived by
downscaling of output from climate models or reanalyses. Downscaling is often
performed using a specified relationship between temperature and elevation
(a lapse rate). Although a constant lapse rate is often assumed, this is not well
justified by observations. To improve upon this assumption, near-surface
temperature lapse rates during the summer ablation season were derived from
surface measurements on 4 Arctic glaciers. Near-surface lapse rates vary
systematically with free-air temperatures and are less steep than the free-air lapse
rates that have often been used in mass balance modeling. Available observations
were used to derive a new variable temperature downscaling method based on
temperature dependent daily lapse rates. This method was implemented in a
temperature index mass balance model, and results were compared with those
derived from a constant linear lapse rate. Compared with other approaches, model
estimates of surface mass balance fit observations much better when variable,
temperature dependent lapse rates are used. To better account for glacier-climate
feedbacks within mass balance models, more physically explicit representations
of snow and ice processes must be used. Since absorption of shortwave radiation
is often the single largest source of energy for melt, one of the most important
parameters to model correctly is surface albedo. To move beyond the limitations
of empirical snow and ice albedo parameterizations often used in surface mass
balance models, a computationally simple, theoretically-based parameterization
for snow and ice albedo was developed. Unlike previous parameterizations, it
provides a single set of equations for the estimation of both snow and ice albedo.
The parameterization also produces accurate results for a much wider range of
snow, ice, and atmospheric conditions.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/1250 |
| Date | 11 1900 |
| Creators | Gardner, Alex Sandy |
| Contributors | Martin J. Sharp (Earth and Atmospheric Sciences), Andrew B.G. Bush (Earth and Atmospheric Sciences), Jeffrey L. Kavanaugh (Earth and Atmospheric Sciences), Christian Haas (Earth and Atmospheric Sciences), Faye Hicks (Civil and Environmental Engineering), Jon Ove Hagen (Department of Geosciences, University of Oslo) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 8374985 bytes, application/pdf |
| Relation | Gardner, A. S. and M. Sharp, 2007: Influence of the Arctic Circumpolar Vortex on the mass balance of Canadian High Arctic glaciers. Journal of Climate, 20, 45864598., Gardner, A. S. and M. J. Sharp, 2009: Sensitivity of net mass balance estimates to near-surface temperature lapse rates when employing the degree-day method to estimate glacier melt. Annals of Glaciology, 50, 80-86., Gardner, A. S., M. J. Sharp, R. M. Koerner, C. Labine, S. Boon, S. J. Marshall, D. O. Burgess, and D. Lewis, 2009: Near-surface temperature lapse rates over Arctic glaciers and their implications for temperature downscaling. Journal of Climate, 22, 4281-4298., Gardner, A. S. and M. J. Sharp, 2010: A review of snow and ice albedo and the development of a new physically based broadband albedo parameterization. Journal of Geophysical Research, 115, F01009, dio: 10.1029/2009jf001444. |
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