1 / 32

Snow Energy Balance T.H. Painter, NSIDC

Snow Energy Balance T.H. Painter, NSIDC. Energy Balance. Conservation of Energy. Energy Balance. Energy Balance Equation. where  = albedo S = solar irradiance L * = net longwave flux Q s = sensible heating flux Q v = latent heating flux Q g = ground heating flux

xuan
Download Presentation

Snow Energy Balance T.H. Painter, NSIDC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Snow Energy BalanceT.H. Painter, NSIDC

  2. Energy Balance Conservation of Energy

  3. Energy Balance

  4. Energy Balance Equation where  = albedo S = solar irradiance L* = net longwave flux Qs = sensible heating flux Qv = latent heating flux Qg = ground heating flux Qm = melting energy flux dU/dT = change in internal energy

  5. Snowpack Energy and Melt • Bring snowpack to 0 C (remove “cold content”) • Melt snow (overcome latent heat of fusion) • Get the water into and through the snowpack (complicated) • Melt enough that water drains when surface melt occurs (make the pack “ripe”)

  6. Solar Irradiance, S • TOA controlled by • Temperature of Sun • Emissivity of Sun • Planck’s Law • Locally controlled by • Atmospheric optical depth • Solar zenith angle (latitude and time of day) • Local slope and aspect

  7. Planck Equation where Mis the radiant exitance (W m-2m-1), h is Planck’s constant, c is the speed of light, k is Boltzmann’s constant,  is wavelength, T is temperature.

  8. Planck Curves

  9. Peak Wavelength of Emission Wien’s Displacement Law Willhelm Wien  in micrometers T in Kelvin

  10. Albedo • Controlled by snow grain size • Controlled by snow impurities • Controlled by snow density? • Controlled by irradiance spectrum dist, geometry, etc. • Range: 0.35 – 0.9

  11. Snow Albedo

  12. Spectral albedo  = 0.72  = 0.43

  13. Net Shortwave • Winter  = 0.85: (1-0.85)*700 = 105 W m-2 • Spring  = 0.55: (1-0.55)*1100 = 495 W m-2 Winter Spring

  14. Longwave (Terrestrial) Radiation • Controlled by temperature • Controlled by emissivity • Stefan-Boltzmann’s Law • Range of Emissivity: 0.97-0.99

  15. Planck Curves again

  16. Integrate Planck’s Equation where  is emissivity,  is the Stefan Boltzmann constant, and T is temperature in Kelvin

  17. Shortwave versus Longwave

  18. Longwave from Snow • Dry Snow • Ts = 253.15 K • M = 0.98 x 5.67 x 10-8 x 253.154 • M = 228 W m-2 • Melting Snow • Ts = 273.15 K • M = 0.98 x 5.67 x 10-8 x 273.154 • M = 309 W m-2

  19. Longwave Irradiance • Incoming longwave depends on atmospheric optical depth, cloud height, and temperature, as well as field of view (vegetation, etc.) Winter Spring

  20. Net Longwave • Dry Snow • Clear Sky L - L = 138 – 228 = -90 W m-2 • Cloudy L - L = 240 – 228 = 12 W m-2 • Wet Snow • Clear Sky L - L = 220 – 309 = -89 W m-2 • Cloudy L - L = 280 – 309 = -29 W m-2

  21. Sensible Heating • Turbulent exchange of atmospheric heat • Qs DS uz (Ta-Ts) • DS is the convective heat bulk transfer coefficient • uz is the wind speed at height z above the snow • Ta is the air temperature at height z • Ts is the snow surface temperature • Controlled by vertical gradient in temperature, surface roughness • Best measured through eddy-correlation

  22. Sensible Heating Senator Beck Alpine Study Plot, San Juan Mountains, CO

  23. Latent Heating • Turbulent exchange of latent release associated with sublimation or condensation • Qv Dv uz (ea-es) • Dv is the latent heat bulk transfer coefficient • uz is the wind speed at height z above the snow • ea is the water vapor pressure at height z • es is the snow surface vapor pressure • Controlled by vertical gradient in vapor, surface roughness • Best measured through eddy-correlation

  24. Latent Heating Senator Beck Alpine Study Plot, San Juan Mountains, CO

  25. Ground Heating • Ground heating flux due to temperature gradient, respective thermal conductivities, and infiltration of meltwater into soils • Generally small component of snowpack energy balance Where K is the thermal conductivity.

  26. Change in Internal Energy • AKA ‘Cold Content’ • Richard Armstrong will discuss the details of snowpack metamorphism and therein will discuss internal energy

  27. Melting Energy Flux • Residual in Energy Balance equation

  28. Spectral albedo Snowmelt flux SWE Snowmelt Modeling clean 0.72 dirty 0.43 SNTHERM.89 (CRREL- Jordan, 1990) Met inputs from 3500 m, Tokopah Basin, Sierra Nevada, CA

  29. Alpine Site Sub-alpine Site

  30. Energy Balance Sites • Solar irradiance (K&Z CM21) • Reflected solar (K&Z CM21) • Terrestrial irradiance (K&Z CG4) • Terrestrial emission (Everest IR) • Relative humidity • Wind speed and direction • Air temperature • Snow temperatures in stratigraphy

  31. Slope Correction to Albedo

  32. Energy Balance - 2005

More Related