Farrell Sinéad L.

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Farrell
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Sinéad L.
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  • Article
    Ice and ocean velocity in the Arctic marginal ice zone : ice roughness and momentum transfer
    (University of California Press, 2017-09-21) Cole, Sylvia T. ; Toole, John M. ; Lele, Ratnaksha ; Timmermans, Mary-Louise ; Gallaher, Shawn G. ; Stanton, Timothy P. ; Shaw, William J. ; Hwang, Byongjun ; Maksym, Ted ; Wilkinson, Jeremy P. ; Ortiz, Macarena ; Graber, Hans C. ; Rainville, Luc ; Petty, Alek A. ; Farrell, Sinéad L. ; Richter-Menge, Jackie A. ; Haas, Christian
    The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20–30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations of momentum transfer, and imply that the future Arctic system could become increasingly seasonal.
  • Article
    CryoSat-2 estimates of Arctic sea ice thickness and volume
    (John Wiley & Sons, 2013-02-28) Laxon, Seymour W. ; Giles, Katharine A. ; Ridout, Andy L. ; Wingham, Duncan J. ; Willatt, Rosemary ; Cullen, Robert ; Kwok, Ron ; Schweiger, Axel ; Zhang, Jinlun ; Haas, Christian ; Hendricks, Stefan ; Krishfield, Richard A. ; Kurtz, Nathan ; Farrell, Sinéad L. ; Davidson, Malcolm
    Satellite records show a decline in ice extent over more than three decades, with a record minimum in September 2012. Results from the Pan-Arctic Ice-Ocean Modelling and Assimilation system (PIOMAS) suggest that the decline in extent has been accompanied by a decline in volume, but this has not been confirmed by data. Using new data from the European Space Agency CryoSat-2 (CS-2) mission, validated with in situ data, we generate estimates of ice volume for the winters of 2010/11 and 2011/12. We compare these data with current estimates from PIOMAS and earlier (2003–8) estimates from the National Aeronautics and Space Administration ICESat mission. Between the ICESat and CryoSat-2 periods, the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods.