Drag Coefficient Estimates

This data-set contains average drag coefficient estimates for the whole of the Arctic (resampled onto a 25 km polar stereographic grid) for each month from 11.2018 to 06.2022. The total drag coefficients are referenced to a height of 10 meters and a neutrally stratified atmosphere is assumed. The total drag is the sum of open water drag scaled with (1-A) where A is sea ice concentration (Spreen et al., 2008), drag due to floe edges incorporated via a constant derived from parameterization (Lüpkes et al., 2012) and scaled with A(1-A), as well as sea ice skin drag and sea ice obstacle form drag, both scaled with A. The sea ice form drag due to obstacles (e.g. ridges) is computed from sea ice feature averages (Garbrecht et al., 2002) derived from ICESat-2 ATL07 sea ice heights (for all 25 km grid cells filled by ICESat-2 ATL07 data) (Kwok et al., 2021). Each individual component is also given as a separate variable in the data-set. Obstacles below a threshold value of 20 cm and those that do not fulfill the Rayleigh Criterion (wherein if the trough between two peaks is smaller than the higher of two crests, only the higher one is considered) are omitted. Lastly, we scale up the ICESat-2 ATL07-derived form drag coefficients via a regression derived from comparing them to drag coefficients derived from topographic data collected during the 04.2019 NASA airborne Operation IceBridge ICESat-2 under-flights (Studinger, 2013). This is to deal with the sampling issues associated with resolution differences.


Drag is the force acting opposite to the relative motion of an object (sea ice floes) with respect to a surrounding fluid (atmosphere). The atmospheric drag coefficient helps quantify drag and thereby the sea ice—atmosphere momentum transfer. To retrieve the drag coefficient estimates, we use a parameterization developed by Garbrecht et al. 2002 that links sea ice—atmosphere form drag coefficients with surface feature height and spacing (both of which are also contained in the netCDF4 data files).

This dataset was developed in the study New estimates of pan-Arctic sea ice–atmosphere neutral drag coefficients from ICESat-2 elevation data (Mchedlishvili et al., 2023). For more information on the development as well as data time series, see the manuscript here.

Obstacle (Ridge) Height and Spacing

Data Availability

Drag coefficient estimate data are currently available for the period listed below

  • Nov 2018 - Jun 2022

For FTP access, connect to ftp://seaice.uni-bremen.de. The products are available in the directory "SurfaceRoughness/ICESat-2/". Please set your ftp client to "active mode". Otherwise no connection is possible. The user name is "anonymous" and no password is needed.

For HTTP access, visit https://data.seaice.uni-bremen.de/SurfaceRoughness/ICESat-2/DragCoefficients/, the structure is the same as for FTP.

The file names of the type "0.2mThresh_201904_10km_segment_TotalDC_modOIB" indicates that

  • A 0.2 m threshold was used
  • It is a map for the month of April 2019 (in this particular example)
  • The segment length over which obstacle height and spacing was averaged is 10 km
  • That it includes total drag coefficient data as well as components and constituents
  • And that is has the Operation IceBridge scaling coefficient (5.28) applied to obstacle form drag data


Mchedlishvili, Alexander; Lüpkes, Christof; Petty, Alek; Tsamados, Michel; Spreen, Gunnar (2023): New estimates of pan-Arctic sea ice–atmosphere neutral drag coefficients from ICESat-2 elevation data. The Cryosphere, 17(9), 4103-4131, https://doi.org/10.5194/tc-17-4103-2023

Garbrecht, Thomas; Lüpkes, Christof; Hartmann, Jörg; Wolff, Mareile (2002): Atmospheric drag coefficients over sea ice - validation of a parameterisation concept. Tellus Series A-Dynamic Meteorology and Oceanography, 54(2), 205, https://doi.org/10.3402/tellusa.v54i2.12129

Kwok, Ronald; Petty, Alek; Cunningham, G; Markus, T; Hancock, D; Ivanoff, A; Wimert, J; Bagnardi, M; Kurtz, Nathan; et al. (2021): ATLAS/ICESat-2 L3A Sea Ice Height, version 5. NASA National Snow and Ice Data Center DAAC, https://doi.org/10.5067/ATLAS/ATL07.005

Lüpkes, Christof; Gryanik, V M; Hartmann, Jörg; Andreas, Edgar L (2012): A parametrization, based on sea ice morphology, of the neutral atmospheric drag coefficients for weather prediction and climate models. Journal of Geophysical Research: Atmospheres, 117(D13), https://doi.org/10.1029/2012JD017630

Petty, Alek; Tsamados, Michel; Kurtz, Nathan (2017): Atmospheric form drag coefficients over Arctic sea ice using remotely sensed ice topography data, spring 2009–2015. Journal of Geophysical Research-Earth Surface, 122(8), 1472-1490, https://doi.org/10.1002/2017JF004209

Spreen, Gunnar; Kaleschke, Lars; Heygster, Georg (2008): Sea ice remote sensing using AMSR-E 89-GHz channels. Journal of Geophysical Research, 113(C2), https://doi.org/10.1029/2005JC003384

Studinger, Michael (2013): IceBridge ATM L1B Elevation and Return Strength, Version 2. NASA National Snow and Ice Data Center DAAC, https://doi.org/10.5067/19SIM5TXKPGT