FAMOUS

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Iceberg Calving

There’s a salinity drift in any FAMOUS control run as snow can accumulate on land - usually locations of ice-sheets - without any way of returning it to the ocean without direct local melting. To cancel this salinity drift, a water flux adjustment can be added to the ocean. Given that this field is mostly compensating for permanent snow accumulation on ice, we call it an iceberg calving field - it’s not really an iceberg parameterisation in any meaningful way.

The pattern for this field is derived from that used in HadCM3, scaled to match the FAMOUS salinity drift. I didn’t repeat the process by which the HadCM3 field was derived using various regional components. This is included in the Summer ‘07 FAMOUS release. In release versions of FAMOUS, up to XDBUA, salinity drift is still not zero, as the snow build up on land/ice is not constant - after 200 years running with the new iceberg field the original positive salinity drift has become a very small negative drift. In its present form the iceberg field is thus not suitable for really extended runs. It’s probably inappropriate for paleoruns anyway, seeing as it’s derived for modern conditions. I’ve got a re-calibrated version lying around that produces a rather smaller drift in the 1860 control climate on QUEST if anyone wants it. This field has been recalibrated again for the XFXWB climate.

Accumulating snow on land is not reduced when using the iceberg field, so it does actually “create” water in the system. This would only be apparent if the snow that had accumulated on the icesheets were to melt.

It’s not really desirable to have iceberg calving match the snow accumulation rate - iceberg calving is obvious dependent on the wider ice sheet growth/dynamics that we don’t have: having a constant rate is one thing, having a variable rate based on a (basically) arbitrary climate variable is just silly. It’s a quick fix that can be justified for a single, stable climate state - pretending we’ve got an iceberg model of any sort would be ingenuous.

Page last modified on August 16, 2011, at 10:57 AM by robin