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SUEWS_OHMCoefficients.rst

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SUEWS_OHMCoefficients.txt

OHM, the Objective Hysteresis Model (Grimmond et al. 1991) [G91OHM]_ calculates the storage heat flux as a function of net all-wave radiation and surface characteristics.

  • For each surface, OHM requires three model coefficients (a1, a2, a3). The three should be selected as a set.
  • The SUEWS_OHMCoefficients.txt file provides these coefficients for each surface type.
  • A variety of values has been derived for different materials and can be found in the literature (see: typical_values).
  • Coefficients can be changed depending on:
    1. surface wetness state (wet/dry) based on the calculated surface wetness state and soil moisture.
    2. season (summer/winter) based on a 5-day running mean air temperature.
  • To use the same coefficients irrespective of wet/dry and summer/winter conditions, use the same code for all four OHM columns (OHMCode_SummerWet, OHMCode_SummerDry, OHMCode_WinterWet and OHMCode_WinterDry).

Note

  1. AnOHM (set in RunControl.nml by StorageHeatMethod = 3) does not use the coefficients specified in SUEWS_OHMCoefficients.txt but instead requires three parameters to be specified for each surface type (including snow): heat capacity (AnOHM_Cp), thermal conductivity (AnOHM_Kk) and bulk transfer coefficient (AnOHM_Ch). These are specified in SUEWS_NonVeg.txt, SUEWS_Veg.txt, SUEWS_Water.txt and SUEWS_Snow.txt. No additional files are required for AnOHM.
  2. AnOHM is under development in v2018b and should NOT be used!
.. only:: html

    An example `SUEWS_OHMCoefficients.txt` can be found below:

    .. literalinclude:: sample-table/SUEWS_OHMCoefficients.txt


.. only:: latex

    An example `SUEWS_OHMCoefficients.txt` can be found in the online version.