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Understanding Permafrost Dynamics: The Role of Surface Frost Number in Climate Modelling

This report presents insights into the relationship between surface frost number and permafrost distribution, emphasizing the impact of temperature and snow cover variables. Through a detailed analysis of the frost number theory and its application in climate models, we explore how varying conditions contribute to the classification of permafrost into continuous, discontinuous, and sporadic types. Our findings reveal that the model aligns with observations and is sensitive to temperature shifts, providing essential data for understanding permafrost dynamics across different latitudes.

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Understanding Permafrost Dynamics: The Role of Surface Frost Number in Climate Modelling

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  1. Permafrost project team report Florence Marika Mathieu Meri Instructor: Drew Hugo Simberg: Frost

  2. Surface frost number • Defined by degree-day sums of freezing and thawing Tw (Ts) = average winter (summer) temperature Lw (Ls) = length of winter (summer)

  3. Surface frost number • Potential values range from 0 (no freezing) to 1 (no thawing) • Continuous permafrost expected poleward of locations at which F ≥ 0.67 • Extensive discontinuous permafrost when 0.6 < F < 0.67 • Sporadic permafrost when F > 0.5

  4. Surface frost number • Defines a latitudinal zonation of contemporary permafrost at continental scales • Not used for relict permafrost or over small areas (<500,000 km2) without numerous climate stations

  5. The theory behind the frost number

  6. The theory behind the frost number “Change over”

  7. Surface frost number • Used monthly climatological variables (air temperature, snow mass, and snow depth) as input for model • Data from MERRA Reanalysis

  8. Influence of snow cover on permafrost • Density, thickness, and duration of snow cover • The time of year at which the snow falls • Snow cover can be the critical factor determining the presence or absence of permafrost (e.g., Granberg, 1973) A+ = temperature amplitude with snow cover Zs = average snow thickness Z*s = damping depth in the snow

  9. Basic runs 1980-1989 1990-1999 2000-2009

  10. Experiments Snow thickness +25 % +50 %

  11. Experiments Snow thickness -25 % -50 %

  12. Experiments Air temperature +2ºC+4ºC/90º ×Latitude

  13. Conclusions • Model produces surface frost numbers that are consistent with observations (according to Drew) • Model is sensitive to temperature changes, but not so much to changes in snow cover thickness

  14. Snow density was kept constant, when snow depth was increased / decreased up to 50 %

  15. Average soil temperature at ~5m depth

  16. Total area: Observed Data • no permafrost : 23.14 mill sq Km • isolated permafrost : 3.48 mill sq Km • sporadic permafrost : 2.88 mill sq Km • discontinuous permafrost : 3.32 mill sq Km • continuous permafrost : 10.62 mill sq Km • all permafrost areas : 13.94 mill sq Km

  17. Merra Permafrost extent 1980-1990 • Area no permafrost : 35.56 mill sq Km • Area with permafrost : 7.88 mill sq Km

  18. Merra Permafrost extent 2002-2012 • Area no permafrost : 31.47 mill sq Km • Area with permafrost : 11.97 mill sq Km

  19. Error due to incorrect initial conditions

  20. One of Mathieu's mistakes

  21. One of Mathieu's mistakes

  22. One of Mathieu's mistakes

  23. Fortran vs. Matlab if (T<0) then do i=1,n … end do end if if T<0 for i=1:n … end end

  24. Credits Thanks to our “debugging team” : Antoine, Eric, Jake, & Drew

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