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David Braaten, Prasad Gogineni, Claude Laird, Susanne Buchardt*, and Hilary Barbour

Spatial variability of interior ice-sheet accumulation determined with an FM-CW radar and connections to the NAO. David Braaten, Prasad Gogineni, Claude Laird, Susanne Buchardt*, and Hilary Barbour. * Centre for Ice and Climate, Univ. Copenhagen. Introduction.

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David Braaten, Prasad Gogineni, Claude Laird, Susanne Buchardt*, and Hilary Barbour

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  1. Spatial variability of interior ice-sheet accumulation determined with an FM-CW radar and connections to the NAO David Braaten, Prasad Gogineni, Claude Laird, Susanne Buchardt*, and Hilary Barbour * Centre for Ice and Climate, Univ. Copenhagen

  2. Introduction • Snow accumulation is important in understanding ice sheet mass balance and the accumulation/precipitation climatology. • Detecting near-surface internal layers with radar allow regional scale assessments of snow accumulation on time scales of 1 year or less. • Radar data permit spatial averaging to overcome local uncertainty caused by wind-generated surface features. • Regional scale assessments of accumulation on annual time scales can lead to an understanding of links between climate indices and ice-sheet accumulation.

  3. Radars

  4. Accumulation Radar – Surface based 16 “ 10.5 “

  5. Radar Range Profile Relative Dielectric Constant r = firn density (g cm-3) (Kovacs et al., 1995) Core density profile The range profile is constructed as follows: where: r(n) = depth of the nth range bin tstep = time extent of 1 range bin (Rink, 2006) Antenna to snow surface = 2 m; er = 1 Dielectric constant profile

  6. Greenland Depth Depth .5 m 1.2 m .6 m .7 m 1.3 m .8 m 1.4 m Pass 1 .9 m 1.7 km 1.5 m Snow Pit Snow Pit 1.0 m 1.6 m Summit Camp, Greenland Pass 2

  7. Tracked annual layers along traverse Ice Thickness = 2542 m Ice Thickness = 3085 m 375 km

  8. Radar Annual Accumulation: 1889 - 2007 185 km segment - Northern 1.2σ 0.6σ 0.6σ 1.2σ (Chen, 2013)

  9. Radar Annual Accumulation: 1889 - 2007 185 km segment - Southern 1.2σ 0.6σ 0.6σ 1.2σ (Chen, 2013)

  10. Climate Index - NAO North Atlantic Oscillation: a diagnostic quantity used to characterize atmospheric circulation patterns in the North Atlantic sector: 20°- 80° N; 90° W - 40° E. Used Hurrelland Deser (2009) principal component (PC)-based indices of the NAO that are determined by the Empirical Orthogonal Function (EOF) of sea level pressure (SLP) anomalies in the domain.

  11. Connection between Greenland accumulation and PC-NAO? Previous studies using ice core and model data say no. Do the regional partitioning and spatial averaging advantages of radar determined accumulation show a connection? The NAO shifts between a positive phase and a negative phase resulting in large changes in air temperature, storminess, winds, and precipitation. Large pressure gradient Weak pressure gradient

  12. Average Accumulation NGRIP NEEM

  13. NAO versus Accumulation: 1958-2006 • Radar annual accumulation • Gridded annual accumulation from Polar MM5 (Burgess et al., 2010) • NEEM ice core derived annual accumulations PC-NAO time series examined: • Annual • Winter (DJFM and DJF) • Spring (MAM) • Summer (JJA) • Fall (SON)

  14. Significant positive correlations between summer PC-NAO and 25 km-averaged radar accumulation time series (49 years)

  15. Summer PC-NAO and annual accumulation 25 km segment r= 0.391 P-value= 0.005

  16. Conclusions • Accumulation radar provides spatial averaging to overcome local redistribution of snow by wind. • Accumulation radar provides regional coverage allowing examination of different precipitation regimes. • Positive correlation found between summer PC-NAO and radar determined accumulation. • Climate models show summer NAO becomes increasingly positive in a warming world (Follandet al., 2009). • Takes us beyond the Clausius–Clapeyron equation (es(T)) to include large scale circulation for understanding future ice sheet mass balance.

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