Geoscience Reference
In-Depth Information
the Arctic Ocean domain, and uncertainties in the data, there is no clear seasonality
in the convergence of atmospheric energy transport. Notably, the July atmospheric
transport is larger than for January.
Compared to the atmospheric transports, the horizontal ocean flux terms are small.
Looking back to
Chapter 2
, we are led to conclude that, although the ice export
through the Fram Strait is extremely important for the freshwater budget of the Arctic
Ocean (it represents the primary sink), it has only a small influence on the heat bud-
get of the ocean. Because of the smallness of the ocean transport terms, the annual
cycle in total ocean heat storage is essentially determined by the net surface flux.
However, it is these small ocean transport terms that maintain the upward net surface
flux in the annual mean that is also seen for the polar cap domain (
Table 3.1
).
The summer gain in oceanic sensible heat is largest in June and July, and the
loss is largest in November and December. Ice melt (positive Li)
i
) occurs from June
through August and is largest in July when it is about twice as big as the sensible heat
gain. The strongest ice growth (negative Li)
i
) is indicated for October, followed by a
decline between November and December, and then another peak in January and
February. The autumn peak is expected; there is ample open water in which new ice
can grow. The second peak is somewhat puzzling. As argued by Serreze et al. (
2007
),
part of the explanation is again at issue with the data, specifically, difficulties in cal-
culating the storage changes in ocean sensible heat content from the hydrographic
data and uncertainties in the ERA-40 net surface heat fluxes. However, the pattern
is physically consistent with delayed ice growth in the warmer parts of the Arctic
Ocean domain, specifically, in the Barents Sea region. The Barents Sea region is
characterized by strong autumn and winter cooling and strong summer heating of the
upper ocean via the net surface flux. However, autumn cooling of the water column
in this region is delayed because of oceanic heat transport through the Barents Sea
opening (the Barents Sea Branch of the Atlantic inflow). Hence, even as the surface
waters cool, the ocean circulation keeps bringing heat into the region. The water col-
umn then cools strongly between November and December. However, there is still
enough heat storage to prevent much ice growth until January and February.
Focus Questions and Exercises
1) The earth's axial tilt is 23.5
o
. Imagine a world in which the axial tilt is instead
27.5
o
. Describe, qualitatively, how the seasonal cycles in components of
energy budgets of the Arctic atmosphere and ocean will differ from the case
with a 23.5
o
axial tilt.
2) Compare and contrast, qualitatively, the seasonal cycles of the major com-
ponents of the energy budget of the atmosphere for the north polar cap (the
region poleward of 70
o
N) with what you would expect to see for the south
polar cap (the region poleward of 70
o
S).
3) The vertically integrated horizontal convergence of water vapor into the Arctic
region counts as a heat gain by the atmosphere. Why?
