More realistic air-ice/snow turbulent flux estimates over sea-ice

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The PI is responsible to closely follow the progress of the action, and especially to contact NEMO project manager if the delay on preview (or review) are longer than the 2 weeks expected.

1. Summary
2. Description
3. Implementation
4. Documentation updates
5. Preview
6. Tests
7. Review

Summary

Action	More realistic air-ice/snow turbulent flux estimates over sea-ice
PI(S)	Laurent Brodeau @ Ocean Next
Digest	Implementation of a bulk-transfer-coefficient parameterization for sea-ice-covered regions. This parameterization should consider sea-ice roughness and be able to handle extremely stable surface atmospheric layer conditions typical of sea-ice-covered regions.
Dependencies	no
Branch	source:/NEMO/branches/2020/dev_r13648_ASINTER-04_laurent_bulk_ice
Previewer(s)	Names
Reviewer(s)	Names
Ticket	#2369

Description

The work accomplished can be separated in two parts:

• Further development of the general SBCBKK interface (introduction of proper bulk parameterizations for ice-air exchanges, new air-sea bulk parameterizations + general improvements and simplifications)
• Further development of the STATION_ASF test-case (boolean sanity-check of the SBCBLK interface and sea-ice support "key_si3")

Implementation

Development of the general SBCBLK interface

(introduction of proper bulk parameterizations for ice-air exchanges, new air-sea bulk parameterizations + general improvements and simplifications)

• module "sbcblk_phy" becomes "sbc_phy" (outside SBC: ABL/ablmod.F90, ABL/sbcabl.F90)

• SBC/sbcblk.F90
  • old and uncomplete "Cdn10_Lupkes2015" & "Cdn10_Lupkes2012" are gone!
  • more efficient use of #if defined key_si3
  • new bulk algorithm available: "sbcblk_algo_andreas" (Andreas et al., 2015)
  • nn_iter_algo, number of iterations to be used in bulk algorithms now provided in "&namsbc_blk" namelist block

INTEGER :: nn_iter_algo ! Number of iterations in bulk param. algo ("stable ABL + weak wind" requires more)

• handling of new namelist parameters for air-ice bulk algorithms ()

     LOGICAL  ::   ln_Cx_ice_cst             ! use constant air-ice bulk transfer coefficients
     REAL(wp) ::   rn_Cd_i, rn_Ce_i, rn_Ch_i ! constant values for     "       "      "
     LOGICAL  ::   ln_Cx_ice_LU12            ! air-ice bulk transfer coefficients based on Lupkes et al., 2012)
     LOGICAL  ::   ln_Cx_ice_LG15            ! air-ice bulk transfer coefficients based on Lupkes & Gryanik, 2015)
  

• use of new global public arrays theta_air_zt and q_air_zt, potential air temperature and specific humidity at zt, respectively
  • theta_air_zt, the potential temperature, is computed from absolute temperature at zt (read in netCDF file) and q_air_zt if ln_tair_pot==.false. (new namelist parameter)

LOGICAL :: ln_tair_pot ! temperature read in files ("sn_tair") is already potential temperature (not absolute)

• "blk_oce_1" passes latent heat flux as output argument, (affects: ABL/sbcabl.F90)
• "blk_oce_2" passes latent heat flux as input argument, (affects: ABL/sbcabl.F90)
• "blk_oce_2" input argument "pqsr" removed because not used, (affects: ABL/sbcabl.F90)

• "SBC/sbcblk_algo_*.F90": various improvements
  • number of iterations now provided through namelist parameter into "&namsbc_blk"
  • neutral transfer coefficients now as OPTIONAL output arguments

• SBC/sbc_ice.F90: pp_cldf removed and declared into "sbc_phy" instead (affects: SBC/sbccpl.F90, SBC/sbcblk.F90, SBC/sbcmod.F90)

• SBC/sbc_oce.F90: declaration of global public arrays theta_air_zt and q_air_zt, potential air temperature and specific humidity at zt, respectively

• DOM/phycst.F90: add vkarmn2, square of von Karmán constant

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Development of the STATION_ASF test-case

(boolean sanity-check of the SBCBLK interface and sea-ice support "key_si3")

Documentation updates

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Preview

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Tests

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Test-case associated with this development:

• Test case name: STATION_ASF (C1D meets SAS). See ​https://github.com/NEMO-ocean/NEMO-examples/tree/master/STATION_ASF for a more complete introduction.

• Test case functionality: test-case STATION_ASF checks that all bulk algorithms available in NEMO, used to estimate the bulk transfer coefficients for turbulent air-sea and air-ice fluxes, are working properly. This is done by checking that all turbulent fluxes computed at the punctual location of STATION_ASF lie within a reasonable range.

• Test case setup: in STATION_ASF nemo.exe runs on one processor and needs only 2 lightweight netCDF files as input. These 2 files provide hourly time-series of sea-surface variables (SST, SSH), and surface atmospheric state (wind, temperature, humidity and downwelling radiative fluxes), respectively, at the punctual location of STATION_ASF. 1 year of simulation with STATION_ASF takes a few tens of seconds on 1 proc.

• Test case verification value: WILL BE boolean. Each computed turbulent flux (hourly time-series), namely evaporation, wind stress and sensible flux, will be checked for consistency during a whole year. This operation will be carried out with every bulk (air-sea and air-ice) parameterization algorithms available in NEMO, including the testing of different options: cool-skin/warm-layer and wave-pattern input).

• Status of the test case as for now: Exists on the official GitHub? for NEMO. Boolean output not ready yet, version for air-ice fluxes in progress.

Review

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