ORCHIDEE Development Section

TRENDY-v9 (2020)
CRUJRA v2.1 forcing

  1. Source Dataset
  2. ORCHIDEE forcing
  3. Interpolation to different resolution
  4. Testing CDO interpolation from 0.5° to 2°

1. Source Dataset

Variable Units Long name
tmp Degrees Kelvin Temperature at 2m
tmin Degrees Kelvin Minimum temperature at 2m
tmax Degrees Kelvin Maximum temperature at 2m
pres Pa Pressure
spfh kg/kg Specific humidity
vgrd m/s Meridional component of wind speed
ugrd m/s Zonal component of wind speed
dswrf J/m2 Downward solar radiation flux
dlwrf W/m2 Downward long wave radiation flux
pre mm/6h Total precipitation

2. ORCHIDEE forcing

ORCHIDEE Variable Conversion from CRUJRA Units Time shift Cell method
Tair tmp K 1 time-step backward,
so that the first data entry is at 06:00
(for compatibility with old driver)
timeplussix: instantaneous
PSurf pres Pa timeplussix: instantaneous
Qair spfh kg/kg timeplussix: instantaneous
Wind_N vgrd m/s timeplussix: instantaneous
Wind_E ugrd m/s timeplussix: instantaneous
Tmin tmin K none time: min(start)
Tmax tmax K time: max(start)
SWdown dswrf / (6*60*60) W/m^2 time: mean(start)
LWdown dlwrf W/m^2 time: mean(start)
Rainf pre / (6*60*60), if tmp >= 273.15
0, if tmp < 0
kg/m^2/s time: mean(start)
Snowf 0, if tmp >= 273.15
pre / (6*60*60), if tmp < 0
kg/m^2/s time: mean(start)


3. Interpolation to different resolution

ORCHIDEE Variable Interpolation Special treatment
Tair bilinear + nearest neighbor if nan
PSurf bilinear + nearest neighbor if nan
Qair bilinear + nearest neighbor if nan spfh → rh → interpolation → spfh
(see equations below)
Wind_N bilinear + nearest neighbor if nan
Wind_E bilinear + nearest neighbor if nan
Tmin bilinear + nearest neighbor if nan
Tmax bilinear + nearest neighbor if nan
SWdown bilinear + nearest neighbor if nan
LWdown bilinear + nearest neighbor if nan
Rainf nearest neighbor pre → Rainf (if tmp >= 0) → interpolation
Snowf nearest neighbor pre → Snowf (if tmp < 0) → interpolation

Saturated water vapor pressure (\(p_{ws}\), Pa) at given temperature (\(t\), °C):

\( p_{ws}(t) = 611.2 \cdot \exp\left(\frac{\large{17.67 \cdot t}}{\large{243.5 + t}}\right) \)

Specific humidity (\(SH\), g/g) to relative humidity (\(RH\), %) conversion at given temperature (\(t\), °C) and pressure (\(p\), Pa):

\(RH = \frac{\large{SH \cdot p \cdot 100}}{\large{p_{ws}(t) \cdot (SH \cdot 0.378 + 0.622)}} \)

Relative humidity (\(RH\), %) to specific humidity (\(SH\), g/g) conversion at given temperature (\(t\), °C) and pressure (\(p\), Pa):

\(p_w = RH/100 \cdot p_{ws}(t)\)

\(SH = \frac{\large{0.622 \cdot p_w}}{\large{p - 0.378 \cdot p_w}}\)

(humidity conversion adapted from https://onlineconversion.vbulletin.net/forum/main-forums/convert-and-calculate/322-relative-humidity-absolute-humidity)


4. Testing CDO interpolation from 0.5° to 2°

CDO interpolation methods tested:

orig
nn
bil
bilnn
con
anm
jan
ts