Polar Science 25 (2020) 100549 Available online 7 July 2020 1873-9652/© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Flow over a snow-water-snow surface in the high Arctic, Svalbard: Turbulent fuxes and comparison of observation techniques Anna Sj¨ oblom a, b, * , Andreas Andersson a, c , Anna Rutgersson a , Eva Falck b a Department of Earth Sciences, Uppsala University, Villav¨ agen 16, 75236, Uppsala, Sweden b Department of Arctic Geophysics, University Centre in Svalbard, P.O. Box 156, 9171, Longyearbyen, Norway c Department of Ecotechnology and Sustainable Building Engineering, Mid-Sweden University, Akademigatan 1, 83125, ¨ Ostersund, Sweden A R T I C L E INFO Keywords: Arctic Svalbard Turbulent fuxes Measuring techniques Air-sea interaction ABSTRACT From observations in a High Arctic valley and ice-free fjord in Svalbard during March and April 2013 we show that, while some caution needs to be applied, ordinary slow-response instruments placed over a snow-water- snow surface can be effectively used as a proxy for more sophisticated measuring techniques at complex sites such as leads or a polynyas. The turbulent fuxes of momentum, sensible and latent heat were measured at three locations with a snow-water-snow fetch. At the snow site upwind of the water, the stability was generally stable, the momentum fux small, and the sensible heat fux positive. Over the water however, the internal boundary layer that was formed gave on average an increased vertical gradient in wind speed, temperature, and humidity and turbulent heat fuxes exceeding 400 W m 2 . At the snow surface downwind of the water, the conditions were highly variable and all the fuxes were, on average, of very small magnitude. That the behaviour of the internal boundary layers can be highly variable is demonstrated through four case studies. This phenomenon is likely to increase in occurrence with a changing climate. 1. Introduction The sea ice cover in the Arctic is generally highly variable in terms of amount, size, and thickness. Openings, such as leads and polynyas can give rise to very large heat fuxes from the water to the atmosphere. Despite covering only a few percent of the Arctic Ocean, leads are thought to contribute with approximately 50% of this regions sensible heat fux to the atmosphere (e.g., Ruffeux et al., 1995). Moreover, polar regions are one of the most affected areas of the ongoing climate change with consequences for physical processes as well as biological systems (e.g., AMAP, 2011; Førland et al., 2011; Walsh et al., 2011). As Taylor et al. (2018) point out, air-sea exchanges are becoming increasingly important in a thawing Arctic. Regardless of their importance, direct observations in the Arctic are generally rare and observation campaigns short due to the challenging environmental conditions (e.g. severe weather conditions, logistical problems, or the lack of a power supply). Measurements over leads and polynyas possesses particular challenges since the size of the open water can change rapidly (e.g., Cottier et al., 2010) making the deployment of instrumentation somewhat demanding. Even if numerical models have increased in reliability (e.g., Renfrew and King, 2000; Esau, 2007), the need for more in-situ measurements still exists by which to populate and validate the models. Therefore, simple measuring techniques and cheap instrumentation that can be left unattended for long periods are required for better understanding of the processes. Several of the frst reports of successful measurements over leads and polynyas came in the 1970s–1980s (e.g., Andreas et al., 1979; Smith et al., 1983; den Hartog et al., 1983). Since then, both measuring techniques and a deeper understanding of the physical processes have been developed and Morales Maqueda et al. (2004) and Vihma et al. (2014) presented thorough reviews of the current state of knowledge. The increased use of aircraft (e.g., Tetzlaff et al., 2015) and icebreakers (e.g., Brooks et al., 2017) have made it possible to take observations from large ice-covered areas. In addition, the use of remote sensing observations is also growing (e.g., Crist´ obal et al., 2017) as a method to attain longer measurement time series. There are also examples of longer surface based observation campaigns on sea-ice, for example the one month period in 1992 where instruments were deployed over a lead in the Arctic during the LEADEX project. Or, the SHEBA experiment in the Canadian Arctic 1997–1998 (e.g., Persson et al., 1997; Pinto et al., 2003; Andreas et al., 2010a; Andreas et al., 2010b) that is still consid- ered to be one of the fnest datasets available. * Corresponding author. Department of Earth Sciences, Uppsala University, Villav¨ agen 16, 75236, Uppsala, Sweden. E-mail address: Anna.Sjoblom@geo.uu.se (A. Sj¨ oblom). Contents lists available at ScienceDirect Polar Science journal homepage: http://www.elsevier.com/locate/polar https://doi.org/10.1016/j.polar.2020.100549 Received 11 February 2020; Received in revised form 4 June 2020; Accepted 8 June 2020