The importance of cloud properties when assessing surface melting in an offline-coupled firn model over Ross Ice shelf, West Antarctica

Hansen, Nicolaj; Orr, Andrew ORCID: https://orcid.org/0000-0001-5111-8402; Zou, Xun; Boberg, Fredrik; Bracegirdle, Thomas J. ORCID: https://orcid.org/0000-0002-8868-4739; Gilbert, Ella ORCID: https://orcid.org/0000-0001-5272-8894; Langen, Peter L.; Lazzara, Matthew A.; Mottram, Ruth; Phillips, Tony ORCID: https://orcid.org/0000-0002-3058-9157; Price, Ruth ORCID: https://orcid.org/0000-0003-1981-9860; Simonsen, Sebastian B.; Webster, Stuart. 2024 The importance of cloud properties when assessing surface melting in an offline-coupled firn model over Ross Ice shelf, West Antarctica. The Cryosphere, 18 (6). 2897-2916. 10.5194/tc-18-2897-2024

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Official URL: https://tc.copernicus.org/articles/18/2897/2024/

Abstract/Summary

The Ross Ice Shelf, West Antarctica, experienced an extensive melt event in January 2016. We examine the representation of this event by the HIRHAM5 and MetUM high-resolution regional atmospheric models, as well as a sophisticated offline-coupled firn model forced with their outputs. The model results are compared with satellite-based estimates of melt days. The firn model estimates of the number of melt days are in good agreement with the observations over the eastern and central sectors of the ice shelf, while the HIRHAM5 and MetUM estimates based on their own surface schemes are considerably underestimated, possibly due to deficiencies in these schemes and an absence of spin-up. However, the firn model simulates sustained melting over the western sector of the ice shelf, in disagreement with the observations that show this region as being a melt-free area. This is attributed to deficiencies in the HIRHAM5 and MetUM output and particularly a likely overestimation of night-time net surface radiative flux. This occurs in response to an increase in night-time downwelling longwave flux from around 180–200 to 280 W m−2 over the course of a few days, leading to an excessive amount of energy at the surface available for melt. Satellite-based observations show that this change coincides with a transition from clear-sky to cloudy conditions, with clouds containing both liquid water and ice water. The models capture the initial clear-sky conditions but seemingly struggle to correctly represent cloud properties associated with the cloudy conditions, which we suggest is responsible for the radiative flux errors.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.5194/tc-18-2897-2024
ISSN:	1994-0416
Date made live:	27 Oct 2023 13:10 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/536178

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.5194/tc-18-2897-2024

ISSN:

1994-0416

Date made live:

27 Oct 2023 13:10 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/536178