1 / 19

Diagnosis of Performance of the Noah LSM Snow Model

Diagnosis of Performance of the Noah LSM Snow Model. *Ben Livneh, *D.P. Lettenmaier, and K. E. Mitchell *Dept. of Civil Engineering, University of Washington. Outline. Large-scale hydrologic model Problem Definition and Key Concepts Snow albedo Turbulent Exchange Energy Balance Issues

ingrid-palmer
Download Presentation

Diagnosis of Performance of the Noah LSM Snow Model

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. Diagnosis of Performance of the Noah LSM Snow Model *Ben Livneh, *D.P. Lettenmaier, and K. E. Mitchell *Dept. of Civil Engineering, University of Washington

  2. Outline • Large-scale hydrologic model • Problem Definition and Key Concepts • Snow albedo • Turbulent Exchange • Energy Balance Issues • Study Area [Noah – VIC models] • Results & Conclusions

  3. Background – NOAH LSM • NOAH LSM: (NCEP, OSU, Air Force, Hydrologic research lab) • Land scheme for suite of weather and atmospheric models (NOAA). • Partitioning of radiation (H, LE) • Characterizes soil moisture, snow cover, etc… • Focus: snow cover very important to both land and atmosphere.

  4. Problem: Excessive Snow Ablation • SEB = Rnet + H + LE + G + F • Numerous authors identified an excessive ablation (*melt + sublimation) problem • Chose to focus on: • Snow Albedo • Turbulent Exchange • Energy Balance Closure Noah SWE (mm) Observed SWE (mm) Mitchell et al, 2004

  5. Snow Albedo • % of reflected incident radiation • Determined mostly by character of snow surface • Effectively changes over time • *Noah presently uses fixed value (satellite) • *Problem: doesn’t capture the evolving amount of melt energy available Corps of Engineers, 1956; CA DMSP satellite image, 1979

  6. As used in VIC: Snow Albedo Decay Scheme • Maximum snow albedo: αmax = 0.85 • Daily value: • Accumulation season: • Melt Season: * t-days since last snowfall

  7. Turbulent Exchange • Highly efficient means for the transfer of temperature, vapor, and momentum • Important features: -surface roughness: hvegetation -air stability *Indicators of instability are: 1. Richardson#: 2. Monin-Obhukov stability length ratio : *Noah uses combined Monin-Obhukov stability correction method for Ch

  8. Noah: Surface Exchange and Stability Parameterization • Complex, iterative parameterization for combined surface exchange and stability! • Agglomeration of numerous components of boundary layer theory, runaway feedbacks requiring superimposed bounding. Surface Exchange Coeff. Temperature Roughness Length (Zilitenkovich (1995) Monin-Obukkhov Similarity Theory Friction Velocity Paulson (1970) functions, Monin-Obukkhov similarity, to derive height for surface exchange and stability

  9. As used in VIC: Surface Exchange • Straightforward, non-iterative scheme, considers CH and stability separately. • Surface Exchange based on Aerodynamic Resistance: Ra=1/CH (DHSVM: Soer, 1980) • Yields more realistic snow ablation: - timing and amount; - no run-away feedback.

  10. As used in VIC: Stability Correction • Non-neutral conditions, account for either enhanced or restricted heat transfer • Applied to aerodynamic resistance, Ra • Atmospheric instability (turbulence) Critical Richardson #: Stable (Ri > 0): Unstable (Ri < 0):

  11. Study areas • SNOTEL stations (AK, CA, CO, WA) *Daily: Tmin, Tmax, Pacc, SWE • Verify modifications in different snow types (alpine, maritime, low and high latitude, etc…) • SWE used as comparison tool • Panarctic (gridded data)

  12. Pan-arctic • Investigation of snow cover extents (Apr 1, 1999) • Noah slightly under-predicted snow cover, based on vegetation specific threshold (stability adj.) Noah Satellite Noah

  13. Conclusions • Major improvement seen with albedo decay scheme especially lower latitude sites… • Energy balance issues create further ablation problems, requiring additional analysis… • Pan-arctic simulations provide a reasonable estimation of snow cover extents, especially with an alternate stability correction.

  14. Thank you

More Related