meetings/2008/HeimbachEGU08.txt

Sensitivities of sea-ice export through Fram Strait in a coupled ocean/sea-ice
adjoint modeling framework.

P. Heimbach, D. Menemenlis, J.-M. Campin, C. Hill, and M. Losch.

Submitted to the EGU2008 Session CR21: Modelling sea ice and ice-ocean
interactions.

The sensitivity of sea-ice export through Fram Strait to changes in various
elements of the ocean and sea-ice state, and to elements of the atmospheric
forcing fields through time and space is assessed by means of a coupled
ocean/sea-ice adjoint model.  The adjoint model furnishes full (two- or
three-dimensional) spatial sensitivity maps (also known as Lagrange
multipliers) of the export metric to a variety of model variables at any
chosen point in time, providing the unique capability to quantify major
drivers of sea-ice export variability.  The underlying model is the MIT ocean
general circulation model (MITgcm), which is coupled to a Hibler-type
dynamic/thermodynamic sea-ice model.  The configuration is based on the Arctic
face of the ECCO2 high-resolution cubed-sphere model, but coarsened to 36-km
horizontal grid spacing. The adjoint of the coupled system has been derived by
means of automatic differentiation using the software tool TAF. To assess the
sensitivity behavior with respect to different basic states, three five-year
adjoint simulations have been performed, using realistic atmospheric forcings,
(1) covering a phase of high NAO (1977 to 1981),
(2) covering a phase of low NAO (1989 to 1993), and
(3) covering the recent period (2003 to 2007).
The results show a complex interplay between atmospheric forcing patterns,
heat transport carried by extensions of the North Atlantic current, and
sea-ice evolution. Apparent dominant patterns on various time scales underline
the transient nature of the problem.
1	Sensitivities of sea-ice export through Fram Strait in a coupled ocean/sea-ice
2	adjoint modeling framework.
3
4	P. Heimbach, D. Menemenlis, J.-M. Campin, C. Hill, and M. Losch.
5
6	Submitted to the EGU2008 Session CR21: Modelling sea ice and ice-ocean
7	interactions.
8
9	The sensitivity of sea-ice export through Fram Strait to changes in various
10	elements of the ocean and sea-ice state, and to elements of the atmospheric
11	forcing fields through time and space is assessed by means of a coupled
12	ocean/sea-ice adjoint model. The adjoint model furnishes full (two- or
13	three-dimensional) spatial sensitivity maps (also known as Lagrange
14	multipliers) of the export metric to a variety of model variables at any
15	chosen point in time, providing the unique capability to quantify major
16	drivers of sea-ice export variability. The underlying model is the MIT ocean
17	general circulation model (MITgcm), which is coupled to a Hibler-type
18	dynamic/thermodynamic sea-ice model. The configuration is based on the Arctic
19	face of the ECCO2 high-resolution cubed-sphere model, but coarsened to 36-km
20	horizontal grid spacing. The adjoint of the coupled system has been derived by
21	means of automatic differentiation using the software tool TAF. To assess the
22	sensitivity behavior with respect to different basic states, three five-year
23	adjoint simulations have been performed, using realistic atmospheric forcings,
24	(1) covering a phase of high NAO (1977 to 1981),
25	(2) covering a phase of low NAO (1989 to 1993), and
26	(3) covering the recent period (2003 to 2007).
27	The results show a complex interplay between atmospheric forcing patterns,
28	heat transport carried by extensions of the North Atlantic current, and
29	sea-ice evolution. Apparent dominant patterns on various time scales underline
30	the transient nature of the problem.