Antarctic Hindcast Project


OVERVIEW: This 3-year project (June 2004-May 2007) was funded by the National Science Foundation's Office of Polar Programs (Glaciology). We employed the Polar MM5 to model variability and change in the surface mass balance (the net accumulation of moisture) over Antarctica in recent decades. This work is motivated by the need to understand the contribution to global sea level change of Antarctica, which holds about 90% of the fresh water on earth. It also provides an extremely valuable dataset of temperature, pressure, winds, moisture, etc. for the broader Antarctic research community that can be applied to a range of climate studies [download dataset #1] . Additional analyses combined model fields and observations to extend the Antarctic snowfall and near-surface temperature record further into the past [download dataset #2].

WORK PERFOMED:
Year 1: In year 1, two sets of simulations, each with different initial and boundary conditions, were run for the ~24-y period from January 1979-August 2002. The initial and boundary conditions for the two sets of runs were provided respectively by the (1) European Centre for Medium-Range Weather Forecasts 40-year Reanalysis (ERA-40), and (2) National Centers for Environmental Prediction - Department of Energy Reanalysis II (NCEP-II). This approach was been used so that uncertainty could be assessed by comparing the two resulting data sets. ERA-40 is the newest global atmospheric dataset and thus has employed the most modern assimilation techniques, especially exploiting the wealth of satellite data available during the past couple of decades. NCEP-II extends back to 1979 and is meant to be an improvement over the groundbreaking NCEP/NCAR Reanalysis, which had a few data assimilation problems that make analyzing climate change difficult (especially over Antarctica).

After subsequent analysis we chose to use the 17-y period spanning 1985-2001, rather than the entire 1979-2001 period, because agreement between the simulations for the longer period was not as good. The reason for this may be related to adjustments in the ERA-40 assimilation system after the onset of the modern satellite era and prior to the mid-1980s.

Year 2: In year 2 we built on the year 1 work by extending our analysis further into the past and then writing two papers. The first examines Antarctic snowfall variability and trends over the past two decades with Polar MM5, and the second assesses Antarctic snowfall variability and trends over the past 5 decades by blending ice core accumulation records with model simulations. The results are summarized below.

Year 3: In year 3 we continued to build on previous work by employing our novel technique developed originally to reconstruct Antarctic snowfall variability over the past 5 decades, to reconstruct near-surface Antarctic temperatures over the entire continent since 1960. By blending model simulations with near-surface temperature records from Antarctic stations, we were able to create a temperature record that fills in critical gaps in our spatial and temporal knowledge of Antarctic temperature variability. The record allows us to assess climate model projections and also to understand then sensitivity of snowfall to changes in near-surface temperature, which has important implications for global sea level rise. The results are summarized below.

FINDINGS: The first paper, entitled "Recent trends in Antarctic snow accumulation from Polar MM5 simulations", is in the July 2006 issue of Philosophical Transactions of the Royal Society, A. We found that there is broad agreement between the two Polar MM5 data sets for the annual precipitation trends for 1985-2001. These generally agree with ice core and snow stake accumulation records at various locations around the continent, indicating broad areas of both upward and downward trends. Averaged over the continent the annual trends are small and not statistically different from zero, suggesting that recent Antarctic snowfall changes do not mitigate current sea level rise. However, this result does not suggest that Antarctica is isolated from the recent climate changes occurring elsewhere on Earth. Rather, these are expressed by strong seasonal and regional precipitation changes.

Our modeling work made it clear that none of the current model datasets is adequate for reproducing accumulation variability and trends prior to the mid-1980s. Realizing the importance of extending the record of accumulation back further in time to obtain a longer perspective of the interdecadal variability of Antarctic snowfall, we created a 50-year time series of snowfall accumulation over the continent by blending model simulations with observations primarily from ice cores. This is the first time such a task has been undertaken. The results are published in the August 11, 2006 issue of the journal Science, in an article entitled "Insignificant change in Antarctic snowfall since the International Geophysical Year". As the title suggests, our findings indicate there has been little change in Antarctic snowfall over the past 5-decades. Rather, regions of upward and downward trends with no coherent, continental-scale increases or decreases occur over the continent in all decades.

Next we employed the same technique we used for snowfall (blending model data and observations) to reconstruct a record of Antarctic near-surface temperature back to 1960. Considering that there are only 15 long-term observational records of near-surface temperature over the entire continent of Antarctica (1-1/2 times the size of the U.S.), this record fills important gaps in our current knowledge of the spatial and temporal variability of Antarctic near-surface temperatures. Only two other such observational records - that depict temperatures over the entire continent - exist. We have collaborated with the creators of the other two datasets (Josefino Comiso and William Chapman) to perform the most comprehensive evaluation of Antarctic near-surface temperatures yet. The paper,entitled "New Antarctic temperature analysis suggests recent warming due to weaker SAM forcing", was recently submitted to Journal of Geophysical Research. The key finding is that temperatures over most of Antarctica have been warming subtly since the early 1990s, consistent with a leveling-off of trends in the Southern Hemisphere Annular Mode over the same period. This result contrasts with most recent results indicating the temperatures over Antarctica (other than on the Antarctic Peninsula) haven't changed much in recent decades.

CONTACTS:
David Bromwich, P.I. (bromwich.1@osu.edu)
Sheng-Hung Wang (wang.446@osu.edu)

PUBLICATIONS:

  • Bromwich, D. H., R. L. Fogt, K. E. Hodges, and J. E. Walsh, 2007: A tropospheric assessment of the E A-40, NCEP, and JRA-25 global reanalyses in the polar regions. J. Geophys. Res., 112 , doi:10.1029/2006JD007859. Full Text (PDF)
  • Bromwich, D. H., J. E. Box, R. L. Fogt, and A.J. Monaghan, 2007: Contributors to the Antarctic section of 'State of the Climate in 2006'. Bull. Amer. Meteorol. Soc., 88, s72-s74.
  • Monaghan, A. J., D. H. Bromwich, W. Chapman, and J. C. Comiso, 2007: New Antarctic temperature analysis suggests recent warming due to weaker SAM forcing. J. Geophys. Res., submitted June 2007. Full Text (PDF)
  • Monaghan, A. J., D. H. Bromwich, R. L. Fogt, S.-H. Wang, P. A. Mayewski, D. A. Dixon, A. A. Ekaykin, M. Frezzotti, I. D. Goodwin, E. Isaksson, S. D. Kaspari, V. I. Morgan, H. Oerter, T. D. van Ommen, C. J. van der Veen, and J. Wen, 2006: Insignificant change in Antarctic snowfall since the International Geophysical Year, Science, 313, 827-831. Animation of last 5 decades of Antarctic Snowfall
  • Monaghan, A. J., D. H. Bromwich, and S.-H. Wang, 2006: Recent trends in Antarctic snow accumulation from Polar MM5. Philosophical Trans. Royal. Soc. A, 364, 1683-1708. Full Text (PDF)
  • Wen, Jiahong, K. C. Jezek, A. J. Monaghan, S. Bo, R. Jiawen, P. Huybrechts, 2006: Accumulation variability and mass budgets of the Lambert Glacier-Amery Ice Shelf system at high elevations. Ann. Glaciol., 43, 351-360.
  • Fogt, R. L., and D. H. Bromwich, 2006: Decadal variability of the ENSO teleconnection to the high latitude South Pacific governed by coupling with the Southern Annular Mode. J. Climate, 19, 979-997. Full Text (PDF)
  • Bromwich, D. H., and R. L. Fogt, 2004: Strong trends in the skill of the ERA-40 and NCEP/NCAR Reanalyses in the high and middle latitudes of the Southern Hemisphere, 1958-2001. J. Climate, 17, 4603-4619. Full Text (PDF)

    ACTIVITIES AND OUTREACH:

  • Tours of our facilities at the Byrd Polar Research Center during 2005, 2006, and 2007.

  • Presentations to K-12 field trips to Byrd Polar Research Center during 2005, 2006, and 2007.

  • Invited Talk (D. Bromwich): 8th Conference on Polar Meteorology and Oceanography, San Diego, CA, USA, "Mesoscale modeling of the Antarctic atmosphere" (January 2005).

  • Talk (D. Bromwich): 8th Conference on Polar Meteorology and Oceanography, San Diego, CA, USA, "Decadal variability of the ENSO teleconnection to the South Pacific governed by coupling with the Antarctic Oscillation" (January 2005). Co-authored by R. Fogt.

  • Talk (D. Bromwich): 8th Conference on Polar Meteorology and Oceanography, San Diego, CA, USA, "Strong trends in the skill of the ERA-40 and NCEP/NCAR reanalyses in the high and middle latitudes of the Southern Hemisphere, 1958-2001" (January 2005). Co-authored by R. Fogt.

  • Talk (A. Monaghan), Byrd Polar Research Center Seminar Series, Columbus, OH, USA, "Toward understanding Antarctica's role in global sea level change: simulating Antarctic accumulation variability in recent decades" (May 2005). Co-authored by D. Bromwich and S-H. Wang.

  • Talk (A. Monaghan), Antarctic Automatic Weather Station - Antarctic Mesoscale Prediction System - Antarctic Meteorological Research Center Joint Annual Meeting, Columbus, OH, USA, "Toward understanding Antarctica's role in global sea level change: simulating Antarctic accumulation variability in recent decades" (June 2005). Co-authored by D. Bromwich and S-H. Wang.

  • Convener (D. Bromwich): International Association of Meteorology and Atmospheric Science 2005 Meeting, Beijing, China, "Symposium F2: Climate Variability and Change in the Polar Regions: Causality and Prediction" (August 2005).

  • Talk (D. Bromwich for Shengjie Ge): International Association of Meteorology and Atmospheric Science 2005 Meeting, Beijing, China, "Assessment of Polar MM5 and ECMWF pressure fields over Antarctica using GRACE" (August 2005). Co-authored by C-K. Shum, S-C. Han, and D. Bromwich.

  • Talk (D. Bromwich): International Association of Meteorology and Atmospheric Science 2005 Meeting, Beijing, China, "Toward understanding Antarctica's role in global sea level change: simulating Antarctic accumulation variability in recent decades" (August 2005). Co-authored by A. Monaghan and S-H. Wang.

  • Talk (D. Bromwich): International Association of Meteorology and Atmospheric Science 2005 Meeting, Beijing, China, "Decadal variability of the ENSO teleconnection to the high-latitude South Pacific governed by coupling with the Southern Annular Mode" (August 2005). Co-authored by R. Fogt.

  • Talk (A. Monaghan): West Antarctic Ice Sheet Initiative (WAIS) Annual Workshop, Sterling, VA, USA, " Recent variability and trends in Antarctic snow accumulation from Polar MM5 " (September 2005). Co-authored by D. Bromwich and S-H. Wang.

  • Poster (D. Bromwich): Workshop on Development of Improved Observations for Reanalyses, Greenbelt, MD, USA, "A comparison of ERA-40, NCEP-NCAR, and JRA-25 reanalyses in the high and middle latitudes of the Southern Hemisphere, 1958-2001" (September 2005). Co-authored by R. Fogt and S-H. Wang.

  • Invited Talk (A. Monaghan): Lamont-Doherty Earth Observatory Physical Oceanography Seminar, Palisades, NY, USA, "Recent trends in Antarctic snow accumulation" (October 2005). Co-authored by D. Bromwich and S-H. Wang.

  • Invited Talk (D. Bromwich): Royal Society Meeting on the Evolution of the Antarctic ice sheet: new understanding and challenges, London, U.K., "Recent variability and trends in Antarctic snow accumulation from Polar MM5 simulations" (October 2005). Co-authored by A. Monaghan and S-H. Wang.

  • Invited Talk (A. Monaghan), SCAR Workshop on the Antarctic Wind Field, Kuala Lumpur, Malaysia, "A Study of the Adélie Land Katabatic Wind Regime and Its Impact on Coastal Cyclonic Activity." (March 2006). Co-authored by D. Bromwich, D. Steinhoff, and R.L. Fogt.

  • Talk (D. Bromwich): 102nd Meeting of the Association of American Geographers, Chicago, IL, USA, "Recent trends in Antarctic snow accumulation from Polar MM5 simulations" (March 2006).

  • Co-organizer (D. Bromwich): Workshop on Atmospheric Reanalyses in the High Latitudes, Cambridge, U.K. (April 2006).

  • Community Talk (D. Bromwich): Columbus Senior Community Center, Columbus, OH, USA, "Contemporary Climate Change and Variability of the Arctic and Antarctic: Sign of Things to Come for Our World or Nothing to Worry About?" (September 2006).

  • Invited Talk (D. Bromwich): Ohio Supercomputing Center, Columbus, OH, USA, "Mesoscale Modeling of the Antarctic Atmosphere" (July 2006). Co-authored by A. Monaghan.

  • Invited Talk (D. Bromwich): XXIX Meeting of the Scientific Committee on Antarctic Research, Hobart, Australia, "Antarctic Precipitation" (July 2006).

  • Talk (A. Monaghan): West Antarctic Ice Sheet Initiative (WAIS) Annual Workshop, Eaton, WA, USA, "A high spatial resolution record of near-surface temperature over WAIS during the past 5 decades" (September 2006). Co-authored by D. Bromwich.

  • Talk (A. Monaghan), Byrd Polar Research Center Seminar Series, Columbus, OH, USA, "Changes in snowfall and near-surface temperature over Antarctica during the past 50 years" (October 2006). Co-authored by D. Bromwich.

  • Talk (D. Bromwich): Annual meeting of the Program on Arctic Regional Climate Assessment, Pasadena, CA, USA, "Antarctic Climate: Change or Multidecadal Variability?" (January 2007). Co-authored by A. Monaghan and R. Fogt.

  • Talk (D. Bromwich): Annual meeting of the American Association for the Advancement of Science, San Francisco, CA, USA, "Antarctic Climate: Change or Multidecadal Variability?" (January 2007). Co-authored by A. Monaghan and R. Fogt.

  • Invited Talk (A. Monaghan), SUNY Stony Brook Topics in Atmospheric and Oceanic Sciences Seminar Series, Stony Brook, NY, USA, "Changes in Snowfall and Near-Surface Temperature Over Antarctica During the Past 50 Years" (February 2007).

  • Talk (D. Bromwich): NASA Modeling, Analysis, and Prediction (MAPS) Program Science Meeting, College Park, MD, USA, "Potential NASA contributions to advancing atmospheric modeling in the Arctic and Antarctic" (March 2007).

  • Talk (D. Bromwich): Annual Meeting of the American Association of Geographers, San Francisco, CA, USA, "Changes in Snowfall and Near-Surface Temperature Over Antarctica During the Past 50 Years" (April 2007). Co-authored by A. Monaghan and R. Fogt.

  • Invited Talk (D. Bromwich): West Antarctic Links to Sea-Level Estimation (WALSE) Workshop, Austin, TX, USA, "Multidecadal Climate Variability and Change in Antarctica" (April 2007). Co-authored by A. Monaghan and R. Fogt.

  • Invited Talk (D. Bromwich): Joint Symposium of the American Polar Society and the Byrd Polar Research Center, Columbus, OH, USA, Antarctic Weather Forecasting: From IGY to IPY" (April 2007). Co-authored by A. Monaghan and R. Fogt.

  • Invited Talk (D. Bromwich): University of Wisconsin Department of Atmospheric and Oceanic Sciences Colloquium, Madison, WI, USA, "Multidecadal Climate Variability and Change in Antarctica" (May 2007). Co-authored by A. Monaghan and R. Fogt.

  • Invited Talk (D. Bromwich): National Science Foundation workshop on 'Setting the course for Antarctic Integrated and System Science (AISS)', Washington, DC, USA, "Global warming and Antarctica: Happening, imminent, or lost in the climatic noise" (June 2007)

  • Talk (K. Hines): Ninth Conference on Polar Meteorology and Oceanography, St. John's, Newfoundland, Canada, "Changes in Snowfall and Near-Surface Temperature Over Antarctica During the Past 50 Years in IPCC AR4 GCMs" (June 2007). Co-authored by A. Monaghan, D. Bromwich, R. Fogt, and D. Schneider.

  • Talk (D. Bromwich): Symposium XXIV of the International Union of Geodesy and Geophysics, Perugia, Italy, "Changes in Snowfall and Near-Surface Temperature Over Antarctica During the Past 50 Years in IPCC AR4 GCMs" (June 2007). Co-authored by A. Monaghan, R. Fogt, and D. Schneider.


    Data Products

    DATASET 1: 23-y Polar MM5 fields from Monaghan et al. (2006, P. Trans. Royal. Soc. A)

    INTRODUCTION: Available here are annually and seasonally resolved grids of atmospheric data simulated by Polar MM5 for the period Jan 1979-Aug 2002. The ERA-40 dataset provided the initial and boundary conditions for the simulations. Several publications documenting these data are currently being written. In the mean time, please refer to the information above, as well as the Polar MM5 Webpage for more information regarding the Polar MM5 and the quality of the simulations. The burden of validating the data provided is the responsibility of anyone choosing to download it.

    MODEL CONFIGURATION: The Polar MM5 simulations were performed on a 121 x 121 polar stereographic grid covering the Antarctic and centered over the South Pole. The model resolution is 60-km in each horizontal direction. Vertically, the domain contains 32 sigma levels ranging from the surface to 10 hPa. Atmospheric data (U,V,T,Q,P) and sea surface temperatures were provided by ERA-40. 25-km resolution daily sea ice concentration grids were provided by the National Snow and Ice Data Center to determine fractional ice coverage over ocean gridpoints. The model topography was interpolated from the 1-km resolution digital elevation model of Liu et al. (2001). Images of the model domain, topography and land use specifications can be found here. More information on the physics in Polar MM5 can be found on the Polar MM5 Webpage.

    KNOWN MODEL ISSUES:

  • The column integrated cloud ice and column integrated snow are currently suspect (these fields are included in the moisture files below). This is due to the time mean column snow being greater than the column cloud ice.

    CONSTANT FIELDS:
    Description
    Constants File

    SIMULATED FIELDS: (note that some Data files are up to 150 mb...right click on the file you desire and and choose the "save as" option to download to your computer)
    Parameter Annual
    (long-term 23-year annual means)
    Seasonal
    (long-term 23-year seasonal means)
    Annual
    (annual means for each of 23 years)
    Seasonal
    (seaonal means for each of 23 years)
    MOISTURE
    FIELDS
    Data /
    Description
    Data /
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    Data /
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    Data /
    Description
    FLUX
    FIELDS
    Data /
    Description
    Data /
    Description
    Data /
    Description
    Data /
    Description
    SURFACE
    FIELDS
    Data /
    Description
    Data /
    Description
    Data /
    Description
    Data /
    Description
    500 hPa
    FIELDS
    Data /
    Description
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    IMAGES OF LONG-TERM (23-y) MEANS:
    Variable Annual DJF MAM JJA SON
    Preciptation
    X X X X X
    Evaporation
    X X X X X
    Column Precipitable Water
    X X X X X
    Cloud Fraction
    X X X X X
    2-m Temperature
    X X X X X
    2-m Relative Humidty
    X X X X X
    10-m Wind Speed
    X X X X X
    Inversion Strength
    X X X X X
    Sfc Latent Heat Flux
    X X X X X
    Sfc Sensible Heat Flux
    X X X X X
    Sfc Incoming Longwave Radiation
    X X X X X
    Sfc Outgoing Longwave Radiation
    X X X X X
    Sfc Incoming Shortwave Radiation
    X X X X X
    Sfc Outgoing Shortwave Radiation
    X X X X X
    500-hPa Geopotential Height
    X X X X X


    DATASET 2: 50-y Antarctic snowfall accumulation from Monaghan et al. (2006, Science)

    INTRODUCTION: Available here are the decadal mean annual Antarctic snowfall accumulation (averaged by basin) for the decades 1955-64, 1965-74, 1975-84, 1985-94, 1995-04. The values were calculated by blending ice core, snow stake, and model snowfall fields, as described in Monaghan et al. (2006, Science).

    Download Excel Spreadsheet

     


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