Research ArticleCLIMATOLOGY

Surface-atmosphere decoupling limits accumulation at Summit, Greenland

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Science Advances  29 Apr 2016:
Vol. 2, no. 4, e1501704
DOI: 10.1126/sciadv.1501704
  • Fig. 1 Humidity profiles over Summit Camp.

    (A) Distribution of the ratio between the water vapor mixing ratio at the surface (~0.1 m) and at ~40 m taken from hourly averaged profiles between 2012 and 2014. (B) Saturation mixing ratios as a function of temperature (47). Theoretical summer and winter mixing lines with schematic depictions of where the air inlets in Fig. 2 would be sampling.

  • Fig. 2 Vertical profiles of the isotopic ratio (δ18O) and humidity at Summit Camp.

    (Top) Isotopic ratio profile. (Bottom) Water vapor mixing ratio profile. The seasonal profiles were generated as the average of all hourly profiles from the respective time window and reported relative to the value at the top inlet. Red (green) lines are generated from profiles during stable (unstable) periods (fig. S3), and the error envelope represents the 66th and 90th percentiles. The dotted line is the average of all profiles. Blue dots below the profiles are the average isotopic ratios measured from the firn interstitial vapor. The error envelop for the firn vapor is 1 SD.

  • Fig. 3 Rayleigh distillation and inversion strength.

    (A) Isotopic difference between collected rime and simultaneous vapor (Δ18O) plotted as a function of inversion strength measured as the difference between the surface and 10-m temperatures. (B) Evolution of the difference between the condensation reservoir and the initial vapor source as a function of fraction of moisture remaining (Fo). The coloring of points corresponds to the Fo values in (A). (C) Isotopic composition of the surface latent heat flux derived using the gradient method against the isotopic composition of the background vapor. Profiles were selected only when the correlation coefficient between inverse of the water vapor mixing ratio and δ18O exceeded 0.8 (43). Colored dots show the inferred isotopic fluxes and measured isotopic ratio of the vapor for 5°C bins. The fit of the derived flux against the background vapor intercepts with the 1:1 line at cold temperatures, providing a similar perspective on hydrological closure during the winter season as depicted in (A) and (B).

  • Fig. 4 Temperature inversions and accumulation at Summit Camp.

    (A) Seasonal cycle of inversion strength inferred by subtracting temperatures recorded at the uppermost and lowermost temperature probes. (B) Trend in winter (blue) and summer (red) inversion frequency. The error envelope shows the response of the trend to shifting the threshold for an “inversion event” between 2° and 4°C. A best-fit line through the annual data and 95% confidence interval on the fit are also shown. (C) Recent accumulation near Summit Camp assessed by looking at the burial rate of a series of bamboo poles (48). Best-fit lines for the different seasons [annual, NDJFM (November to March), and MJJAS (May to September)] and the 90% confidence interval for NDJFM (gray lines) are shown. (D) Comparison between winter accumulation from Summit and the nearby IceSat site using the same technique. The numbers correspond to the year (that is, “06” is 2006). The dotted line is the 1:1 line, and the solid line is the best-fit linear regression showing that there are local differences in total accumulation but interannual variability is consistent.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1501704/DC1

    fig. S1. Air temperature time series for the Summit research tower.

    fig. S2. Diagram showing the vapor sampling system.

    fig. S3. Hourly Bulk Richardson number calculated at the 2-m height using the 2D sonic wind and temperature data from the Summit Camp research tower.

    fig. S4. Isotopic difference between vapor and condensate.

    fig S5: Recent DJF and JJA temperature trends for Summit.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Air temperature time series for the Summit research tower.
    • fig. S2. Diagram showing the vapor sampling system.
    • fig. S3. Hourly Bulk Richardson number calculated at the 2-m height using the 2D sonic wind and temperature data from the Summit Camp research tower.
    • fig. S4. Isotopic difference between vapor and condensate.
    • fig. S5. Recent DJF and JJA temperature trends for Summit.

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