| When |
Who |
What |
| 2004/11/05/00 |
Ferrier |
Decreased the assumed number concentration of cloud droplets from
200 to 100 /cm**3, which reduces the threshold cloud water mixing ratio
for autoconversion to rain from 0.838 to 0.419 g/m**3. Also decreased
the maximum number concentration of precipitation ice particles from 20
to 10 per liter. Both changes are intended to lower the amount of
suspended condensate in the atmosphere, which should help reduce the
cool bias that has developed below clouds in the parallel.
Fixed a minor bug in ADJPPT1 that limits the amount of cloud water
from exceeding the autoconversion threshold
|
| 2004/11/04/12 |
Ferrier |
A new cloud cover scheme is introduced in order to increase
the presence of forecast partial cloudiness. Two adjustable
parameters in the scheme have been tuned to match the AFWA total
cloud cover product. The first parameter (STSDM) is the assumed
standard deviation of total grid-scale relative humidity in the grid
box, and it is set to 2%. The second parameter (RHsat) is the total
relative humidity associated with an assumed cloud fraction of 50%,
and it is set to the average of the threshold relative humidity for
the onset of grid-scale condensation (RHgrd) and a value of 100%
(i.e., 98.3% for the 32-km runs).
|
| 2004/11/02/00 |
Ferrier |
Changes intended for the 10/30 change but were left out: reduce longwave emmissivity for ice,
and removed a slight, accidential increase in the solar absorption of ice.
|
| 2004/10/30/00 |
Ferrier |
Changed the LW absorption coefficient for ice to be the same as
what's currently used in the operational Eta
|
| 2004/10/27/00 |
Ferrier |
In calculating longwave emissivities in cloudy layers,
the optical depths for cloud water and for ice (cloud ice and snow)
are obtained using the downwelling longwave relationships of Smith and
Shi (1992).
In calculating solar absorption, the optical depths for cloud
water and for ice (cloud ice and snow) are obtained using the relationships
described by eqs. (5.2), (5.3), and Table 9 from Hou et al. (2002), assuming
a constant effective radius of 10 microns for cloud water and 75 microns for
ice. For cloud water optical depths, equal weighting is assumed for
absorption of UV-VIS and near IR radiation.
In the operational radiation, a minimum optical depth is assumed
for grid-scale liquid water clouds consistent with a minimum mixing ratio
of 0.1 g/kg. This lower limit has been removed.
With respect to the EtaW, the biggest impact of these changes is
to increase the optical depths for ice clouds by a factor of 5 when calculating
(longwave) cloud emissivities. The net effect of all of the other changes are
minor (i.e., less than 2.5%).
|
| 2004/10/11/12 |
Ferrier |
The ice absorption coefficient was modified to be one
half of the value that's currently used in operations rather than 1/15
the value in the previous change
|
| 2004/10/08/00 |
Ferrier |
Reverted back to the operational code, except
with the modified precipitation assimilation.
Doubled the absorption coefficient for cloud water
based on values used in the GFS radiation. This change
is intended to increase solar absorption of radiation by
liquid water clouds at lower levels.
Decreased the absorption coefficient for ice by more
than an order of magnitude to be more consistent with values
used in the GFS radiation for an effective radius of 500 microns.
This change is intended to reduce the upper-level warm bias
believed to be caused by too much absorption of solar radiation by ice.
reduction in solar radiation passing through clouds at low sun angles.
|
| 2004/09/30/00 |
Ferrier |
Set RHsat in RADTN to RHgrd (0.967 for 32-km runs). This change is
intended to increase the amount of grid-scale cloudiness based on the latest
comparisons against the AFWA total product.
Set STSD in RADTN to .02 rather than .01, which assumes a standard
deviation of total grid-scale relative humidity of 2%
Multiply the cloud optical depths by a factor of 0.5+max(0., min(0.5, cosz(i) ) ),
which reduces the cloud optical depths by at most a factor of two starting at zenith
angles larger than 60 deg. This change is intended to cut down on the large
reduction in solar radiation passing through clouds at low sun angles.
|
| 2004/09/28/00 |
Ferrier |
Set RHsat in RADTN to RHgrd+STSD (=0.967+.01=0.977) rather than to 0.98
|
| 2004/09/25/00 |
Ferrier |
Assumed standard deviation of total relative humidity of 1% is assumed rather
than 2%, based on tuning experiments with AFWA total cloud product.
T_ICE=-10C rather than -25C, leading to less supercooled liquid water
XNCW=50.e6 (50 /cm**3) will lead to larger cloud droplets and easier formation
of rain
FLARGE=0.5 rather than 0.1 or 0.2 will reduce the number of small ice
crystals and reduce the solar absorption by ice
|
| 2004/09/24/12 |
Ferrier |
The assumed standard deviation of total relative humidity in the grid box
and the threshold relative humidity for the onset of grid-scale condensation
have been tuned to match the AFWA total cloud product, but using the
modifications to radiation that are currently running in the EtaL.
Cycled EDAS started from ETAL parallel as of 9/24/04
|