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Discussion papers
https://doi.org/10.5194/tc-2018-262
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2018-262
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jan 2019

Research article | 25 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Estimation of turbulent heat flux over leads using satellite thermal images

Meng Qu1, Xiaoping Pang1, Xi Zhao1,2, Jinlun Zhang2, Qing Ji1, and Pei Fan1 Meng Qu et al.
  • 1Chinese Antarctic Center of Surveying and Mapping, Wuhan University, Wuhan 430079, China
  • 2Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, Washington 98195-3770, USA

Abstract. Sea ice leads are an important feature in pack ice in the Arctic. Even covered by thin ice, leads can still serve as the prime window for heat exchange between the atmosphere and the ocean, especially in winter seasons. Lead geometry and distribution in the Arctic have been studied in previous studies using optical or microwave remote sensing data. But turbulent heat flux over lead area has only been measured on site during a few special expeditions. In this study, we derive turbulent 10 heat flux through leads at different scale using a combination of lead distribution from remote sensing images and meteorological parameters from a reanalysis dataset. Firstly, ice surface temperature was calculated from Landsat-8 Thermal Infrared Sensor (TIRS) and MODIS thermal images using split-window algorithm at 30 m and 1 km scales, respectively, then lead pixels are segmented from colder ice. Heat flux over lead area is calculated using two empirical models, including bulk aerodynamic formulae and a fetch-limited model with lead width from Landsat-8. Results show that, even though lead area 15 from MODIS is generally a little higher, the length of leads is underestimated by 72.9 % in MODIS data compared to that from TIRS due to the inability to resolve small leads. Heat flux estimated from Landsat-8 TIRS data using bulk formulae is 42.33 % larger than that from MODIS data. When fetch-limited model was applied, turbulent heat flux calculated from TIRS data is 31.87 % higher than that from bulk formulae. In both cases, small leads account for more than a quarter of total heat flux over lead, mainly due to its large area, though the heat flux estimated using fetch-limited model is 42.26 % larger. More contribution 20 from small leads can be expected at larger air-ocean temperature difference and stronger winds.

Meng Qu et al.
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Short summary
Can we ignore the contribution of small ice leads when estimating the turbulent heat flux? Combining bulk formulae and a fetch-limited model with surface temperature from MODIS and Landsat-8 Thermal Infrared Sensor (TIRS) images, we found small leads account for 25 % of the turbulent heat flux, due to its large total area. Estimated turbulent heat flux is larger from TIRS than that from MODIS with a coarser resolution, and larger using fetch-limited model than that using bulk formulae.
Can we ignore the contribution of small ice leads when estimating the turbulent heat flux?...
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