Latest Greenland ice sheet reflectivity

 




These albedo visualizations are discussed here and here.

About the Data

Surface albedo retrievals from the NASA Terra platform MODIS sensor MOD10A1 product beginning 5 March 2000 are available from the National Snow and Ice Data Center (NSIDC) (Hall et al., 2011). The daily MOD10A1 product is chosen instead of the MODIS MOD43 or MCD43 8-day products to increase temporal resolution. Release version 005 data are compiled over Greenland spanning March 2000 to October 2011. Surface albedo is calculated using the first seven visible and near-infrared MODIS bands (Klein and Stroeve, 2002; Klein and Barnett, 2003). The MOD10A1 product contains snow extent, snow albedo, fractional snow cover, and quality assessment data at 500m resolution, gridded in a sinusoidal map projection. The data are interpolated to a 5 km Equal Area Scalable Earth (EASE) grid using the NSIDC regrid utility April and after September, there are few valid data, especially in Northern Greenland because of the extremely low solar incidence angles. The accuracy of retrieving albedo from satellite or ground-based instruments declines as the solar zenith angle (SZA) increases, especially beyond 75 degrees, resulting in many instances of albedo values that exceed the expected maximum clear sky snow albedo of 0.84 measured byKonzelmann and Ohmura (1995). Here, we limit problematic data by focusing on the June–August period when SZA is minimal.

Stroeve et al. (2006) concluded that the MOD10A1 data product captured the natural seasonal cycle in albedo, but exhibited significantly more temporal variability than recorded by ground observations. We now understand that a dominant component of this assessed error is the failure of the MODIS data product to completely remove cloud effects. Inspection of the raw MOD10A1 images reveal an abundance of residual cloud artifacts (shadows, contrails, thin clouds, cloud edges) in the albedo product, presumably because the similar spectral properties between snow and some clouds results in obvious cloud structures. Another problem consists of spuriously low values, for example below 0.4 in the accumulation area where albedo is not observed by pyranometers at the surface to drop below 0.7, seen as linear stripe artifacts in the imagery. Because both the cloud shadows and stripes introduce abrupt daily departures from the actual albedo time series, it is possible to reject them using a multi-day sample. Thus, on a pixel-by-pixel basis, 11-day running statistics are used to identify and reject values that exceed 2 standard deviations (2 sigma) from an 11-day average. To prevent rejecting potentially valid cases data within 0.04 of the median are not rejected. The 11-day median is taken to represent each pixel in the daily data and has a smoothing effect on the albedo time series. June–August (JJA or summer) seasonal averages are generated from monthly averages of the daily filtered and smoothed data. Redundant data from the Aqua satellite MODIS instrument are not used in this study for simplicity, to reduce computational burdens, and given an Aqua MODIS instrument near infrared (channel 6) failure (Hall et al., 2008) that reduces the cloud detection capability. (http://nsidc.org/data/modis/ms2gt/). The interpolation method employs a trend surface through the surrounding four 500m grid cell values closest to the grid points. The resulting 5 km spatial resolution permits resolving the ablation area within the goals of this study. Major gaps in the time series occur 29 Jul – 18 August 2000 and 14 June – 7 July 2001. The frequency and quality of spaceborne albedo retrievals decreases in non-summer months as the amount of solar irradiance and solar incidence angles decrease. Also, in non-melting periods before

Works Cited

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
  • Hall, D. K. J. E. Box, K. Casey, S. J. Hook, C. A. Shuman, K. Steffen, Comparison of satellite-derived and in-situ observations of ice and snow surface temperatures over Greenland, Remote Sensing of Environment, 2008
  • Hall, D. K., Riggs, G. A., and Salomonson, V. V.: MODIS/Terra Snow Cover Daily L3 Global 500m Grid V004, January to March 2003, Digital media, updated daily. National Snow and Ice Data Center, Boulder, CO, USA, 2011.
  • Klein, A. G. and Barnett, A. C.: Validation of daily MODIS snow cover maps of the Upper  Rio Grande River Basin for the 2000–2001 snow year, Remote Sens. Environ., 86(2), 162–176, 2003.
  • Klein, A. G. and Stroeve, J. C.: Development and validation of a snow albedo algorithm for the MODIS instrument, edited by: Winther, J. G. S. R., Ann. Glaciol., 34, 45–52, 2002.
  • Konzelmann, T. and Ohmura, A.: Radiative fluxes and their impact on the energy-balance of the Greenland ice-sheet, J. Glaciol., 41(139), 490–502, 1995.

Follow my climate-cryosphere tweets on Twitter

10 Responses to “Latest Greenland ice sheet reflectivity”

  1. Greenland melt record likely Says:

    [...] the latest “noodle plot”2 (regularly updated here) for the ice sheet between elevations of 2,000 and 2,500 metres. 2012 (the black line) is well down [...]

  2. Rob Dekker Says:

    Dr. Box, thank you for showing the disturbing change in albedo at Greenland this year.
    Quick question with possibly significant consequences :
    We know that Greenland receives some 250 – 300 W/m^2 insolation ‘on the ice’ during June/July.
    With a change in albedo of 3 % to (as your recent numbers show) to 6 %, how much ice will melt over the entire ice sheet due to this change in albedo alone ?

    If we do the simple physics calculations of increased solar absorption of 3-6% albedo change, we get to a ice loss anomaly of some 7 – 14 cm or, over the entire 1.7 million km^2 ice sheet, an additional loss of 120 – 240 Gton per month (that the surface temps remain close to freezing on Greenland) due to this albedo anomaly alone.

    Please tell me that these calculations are not right, because if they are, we should be very concerned…

  3. Jason Box Says:

    Rob, I like this kind of calculation, do something similar in the attached, find the extra energy erodes 14 cm of the ‘cold content’ of the upper snow layers across the accumulation area… Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere Discuss., 6, 593-634, doi:10.5194/tcd-6-593-2012, 2012. DOWNLOAD LATEST, ACCEPTED VERSION

  4. Rob Dekker Says:

    Dr.Box, I’m sorry. I was mistaken about NOA. Indeed the summer NOA index (JJA) seems to be at record negative since 2007.
    http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.nao.monthly.b5001.current.ascii.table
    I’ll read your paper in more detail before drawing any conclusions regarding the origin of the temperature increases around Greenland.
    Still, could you please comment on the 4 polynomial orders of feedback, especially the snow cover anomaly over the Northern Hemisphere, and what this may mean for Greenland’s melt rate ?

  5. Darth Vader Says:

    The alberto of higher altitudes seems to be very low this year, but why is it that the alberto of lower altitudes is so much higher compared to other years?

  6. 97% of Greenland has experienced surface melting this month ,record temps expected next week . « toolwielder Says:

    [...] Figure 2. The albedo (reflectivity) of the Greenland Ice Sheet at its highest elevations (2,500 – 3,200 meters, or 8,200 – 10,500 feet) has steadily decreased in recent years as the ice has darkened due to increased melting and dark soot being deposited on the ice from air pollution. This July, the high elevations of Greenland were the darkest on record, which helped contribute to the record warm temperatures observed at the Greenland Summit. Image credit: Dr. Jason Box, Ohio State University. [...]

  7. Ghiacci artici: minimo assoluto di estensione! - Pagina 10 Says:

    [...] [...]

  8. Greenland’s extraordinary summer: melting records and ice island setting sail Says:

    [...] ice sheet at 3,200 meters, initiating surface melt over the whole vast sheet, ice sheet albedo has plummeted, and the Jakobshavn Isbrae’s calving front has retreated into the ice [...]

  9. Jason Box Says:

    The alberto of lower altitudes is so much higher compared to other years because that surface is already as low as it should get. The extreme lowest elevations, the albedo increases again because the impurities begin concentrating near the surface. An albedo increase at the lowest elevations, I suspect, is due to the ‘white ice’ area moving to higher elevations. This is very interesting, but of little consequence to the increasingly negative mass balance of the ice sheet.

    Jason

  10. Dramatic Lessons from the Arctic Big Melt of 2012 Says:

    [...] Greenland: Those circumstances as well as rising global temperatures will increase the rate of melting of the Greenland ice sheet, which is already accelerating. Total ice sheet mass loss in 2011 was 70 per cent larger than the 2003-2009 average annual loss rate of 250 gigatons per year. And now, today, we have news of a record melt in 2012 with another month of the melt season to go. And now the tipping point for Greenland’s ice sheet (eventual sea level rise of 7 metres) has been revised down from around 3ºC to just 1.6ºC (uncertainty range of 0.8-3.2ºC). At the current temperature rise of 0.8ºC we may have already reached Greenland’s tipping point, and with temperature rises in the pipeline (global emissions still rising, no reasonable agreement to reduce them), we are very likely to hit 1.6ºC in two, or three, decades. The albedo (reflective capacity of a surface, measured as a percentage) of the Greenland ice sheet, particularly the high-elevation areas where snow typically accumulates year-round, have reached a record low since satellite records began in 2000. This indicates that the ice sheet is absorbing more energy than normal. Albedo has dropped significantly in 2012 (black line). There are more charts here. [...]

Leave a Reply