Mesoscale Parallel Experiment Log
- Experiment Name
Eta-12 with modified cloud microphysics, assimilation of GOES cloud top pressure,
assimilation of NEXRAD radial wind velocity data
- Parallel Slot
- Control Slot
- Ops Eta-12
- Start date of parallel experiment
- 12Z 2002/08/14 ; restarted from prod at 12Z 9/19/02
- End date of parallel experiment
- 00Z 2003/07/08
- Environmental Modeling Center scientists
- Abstract (including Motivation, Hypothesis and Method)
The Eta-12 is being used to test the impact
modifications to the cloud microphysics, assimilation of
NEXRAD radial wind data in the EDAS, and assimilation of
GOES cloud top pressure data in the EDAS
ETA MODEL CHANGES
I. Model changes : Cloud Physics
- 1. New grid-scale cloud properties are written and read in the restart files,
allowing for their cycling in the forecast system. Old arrays from the Zhao
et al. (1997) microphysics were removed from all code.
- 2. Arrays defining convective cloud-base and cloud-top properties used in
radiation are now properly reinitialized after being written to the model restart
files. Code was restructured to have convective cloud arrays used in radiation,
then written to restart files, and then reinitialized to no-cloud values using
a single set of arrays. Additional arrays that separate shallow from deep
convection have also been added to the model restart files.
- 3. Code is restructured so that cycling will produce the same forecast
as a longer forecast. For example, the forecasts will be the same if the
model is run for two 3-h forecasts (e.g., two EDAS cycles with no assimilation
of observations) compared to one 6-h forecast. In other words, the model
forecast does not depend on the reading of arrays that are read in at the end
of the restart files when restarting the model from the middle of the forecast
(i.e., a nonzero start time).
- 4. Whole array operations were found to be inefficient and were replaced
with explicit do-loop indexing.
- 5. Lower limits were placed to turbulent kinetic energy (Q2) throughout
the code, set to values of 0.2. This change affects the writing of Q2 to
restart files but does not affect the model integration, since lower limits
of Q2 are internally enforced in TURBL.
- 6. Longwave radiation is updated every hour along with shortwave radiation.
- 7. Inline compiler directives have been added at the beginning of numerous
subroutines, which allow for easy debugging of code. These directives override
compiler directives specified in the make files, and they are included in those
subroutines that call MPI routines. Now the code can be run with full trapping,
checks on array bounds, and checks on argument lists by just manipulating the makefile.
- 8. The lower limit for all hydrometeor mixing ratios is set to 1.e-12
for all model routines (parameter EPSQ).
- 9. Convective precipitation rates used to define optical properties of
convective clouds are now modified in the precipitation assimilation code.
- 10. Some of the values in array ZEFFIJ along the eastern boundary were
uninitialized. A small patch of code was added in GOSSIP to assign values at
these locations to values at the next grid point west (in from) the eastern boundary.
- 11. Tunable parameters in the microphysics defined based on grid resolution
in subroutine GSMCONST are restructured more clearly. These quantities are
assumed to vary linearly as a function grid resolution, but this functional
dependence can be easily changed in the future.
- 12. Probablistic freezing of rain as a function of temperature, as
parameterized by Lin et al. (1983) following Biggs (1953), has been correctly
coded in the grid-scale microphysics in GSMCONST and in GSMCOLUMN. What is
currently coded in operations is producing underflow errors and is effectively
not activated, however, this process is an extremely slow process and is not
expected to have much impact on precipitation forecasts.
- 13. A small bug was fixed in SFCDIF, in which on rare occasions
subscript ML for array ZEFF was out of range (i.e., larger than the upper
limit of 4). No discernible impact on the forecast is expected.
- 14. No dependence of cloud type (convective or grid scale) was seen
in the GFDL radiation driver, so the array ITYP was removed from RADFS.
- 15. The following changes were made in the representation of clouds in radiation.
a. Convective cloud fraction as a function of precipitation rate of
Slingo (1987) was increased by 20%, allowing for shallow, nonprecipitating
convective clouds to have an assumed cloud fraction of 10%.
b. Grid-scale cloud fraction is now parameterized following Xu and
Randall (1996), replacing the Randall (1994) formulation. Also,
relative humidity is now calculated using the same approach as in the
EGCP01 grid-scale microphysics. One change was made with respect to Xu
and Randall, however, in that a relative humidity of 100% or more will not
produce a cloud fraction of 1.0. Grid-scale cloud must be present in order
for nonzero cloud fractions to be represented. Grid-scale cloud is defined
as the sum of the mixing ratios of cloud water and total ice (i.e., ignoring rain).
c. The radiative effects from low-level clouds in the lowest 100 mb
and upper-level clouds above the tropopause are no longer ignored.
d. Absorption coefficients for convective clouds is assumed
to be 0.16 at temperatures <= -10C assuming ice is the dominant hydrometeor
category as in the grid scheme, 0.08 at warmer temperatures assuming water
is dominant at warmer temperatures. The values for these coefficients
is based on Harshvardhan et al. (1989). Absorption coefficients for
grid-scale cloud water is 0.08*min(1., Qw/Q0), where Qw is the cloud
water mixing ratio and Q0=0.1e-3 kg/kg. Absorption coefficients
for grid-scale ice is equal to 500*Qi, where Qi is the mixing ratio
for all ice particles (kg/kg). This value was derived based on the optical
properties for snow provided by Q. Fu (U. Washington, personal communication)
for ice particles. Operational code currently assumes the absorption
coefficients vary as functions of temperature for convective and grid-scale clouds.
e. Many of the algorithms for calculating cloud fraction were
simplified and numerous comments were added to allow future modifications
to be made much more easily and effectively.
II. Post changes : Cloud Physics
-1. Read in new, expanded restart files.
-2. Post new cloud fields (cloud water, cloud ice, rain, snow, and
total condensate) on pressure and Eta surfaces,.as well as original model
arrays (F_rain, F_ice, F_RimeF) on Eta surfaces for debugging.
-3. Post total cloud fraction from grid-scale and convective clouds
on Eta surfaces using the same algorithms as in the Eta radiation driver
(this is not true in the operational Eta post). Also post cloud-base and
cloud-top pressures from shallow, nonprecipitating convection, deep
convection, and grid-scale convection. The cloud efficiency parameter
used in the convective parameterization can now also be posted.
-4. Visibility calculations have been changed to use the new cloud
fields, responding to mixing ratios of cloud water, cloud ice, rain, and snow.
-5. The same method is used to calculate relative humidity (RH)
throughout the post. This currently is defined as RH with respect to
water at all levels, however, it will be very easy to calculate RH
with respect to ice(if desired) in the future. There were MANY subroutines that
used the ice/water flag from Zhao and Carr (1997) for calculating RH,
and the code was poorly structured and not always uniform throughout the post.
These blocks of code have been substituted with a simple subroutine call.
-6. The same lower limit for the condensate mixing ratio of EPSQ=1.e-12
is used throughout the post as it is used throughout the model. Small
changes were made to the include parameter file "params" that removed
the need to use the parameter file "cuparm" in WETBULB. The "cuparm"
file is no longer used in the post.
-7. Inline compiler directives have been added to the beginning
of numerous subroutines, as in the model, to allow for easy compiling
of code with or without traps, checks on array bounds,
and checks on argument lists by simply changing lines in the make file.
-8. Bug fixes identified by Tuccillo have been made to the J index
in FIXED, and an argument to MPI_ISEND in GRIBIT was changed that
solved the problem of the post occasionally failing due to segmentation faults.
III. Brief summary of changes : Cloud Physics
Changes were made allows the new cloud arrays to be written to the model
restart files and posted to grib files. Numerous changes were made in
the optical properties of grid-scale and convective clouds that should
increase the areal coverage of clouds, including modifications in the
calculation of cloud fraction and the absorption coefficient of clouds.
These changes will result in the radiative properties of the clouds being
more consistent with the other physical parameterizations. These changes
are also accurately reflected in the post, allowing the end user to review
many more aspects of the convective and grid-scale cloud properties simulated in the Eta.
IV. Model changes : Assimilation of GOES cloud top pressure data
- Prior to running each 3-hour EDAS segment, a pre-processing
program reads in the 3-hour's worth of GOES cloud top data from
the PREPBUFR file, and distributes the observations to the
appropriate assimilation hour and horizontal Eta grid box.
- During EDAS, at each physics time step and on each Eta grid
where observed cloud top is available, we zero out model cloud
water/cloud ice above the observed cloud top, and set the water
vapor mixing ratio to no more than saturation (original value or
grid-scale saturation value [w/r/t water if T > -10 C, otherwise
w/r/t ice], whichever is less). At the model level closest to the
observed cloud top, if the model air is sub-saturated (by an amount
of delta(Qv)), the air at this level is then moistened by the amount
of delta(Qv)*physDT/3600., i.e. it is moistened at a rate that would
bring it to saturation in 1 hour.
- The observed cloud top is also used as 'anchor' cloud top in
precipitation assimilation, i.e. in the event that we need to create
a layer of precipitating cloud, the observed cloud top is used in
the cloud creation.
OBSERVATIONAL AND ANALYSIS CHANGES
- Radial wind data from NEXRAD are assimilated using the eta 3DVAR analysis. The
raw data is converted into super-obs with a spatial resolution of 1 km and 6 degrees of
azimuth. All NEXRAD winds within +/- 1.5 hours of the analysis time are used.
- Define radar beam vertical extent to increase at the rate of
20m/km. This is about 20% larger than the actual beam size, to allow
for beam propagation uncertainty.
- Winds at all eta levels covered by the radar beam are adjusted so
that the observation is as close as possible to the interval between the
minimum and maximum wind at the selected levels. (The min and max are
not the actual min and max but those derived from a straight line fit to
the winds. This is done to simplify the computation of the gradient of
the forward model implied by this process).
- All winds, out to the maximum range of the radar can be used with
the above defined forward model. Bill Facey increased the
distance parameter in the superob code so that superobs are formed out
to the maximum radar range (250km).
- All VAD wind observation quality marks are collocated in the
vertical in 500m bins with the corresponding radar winds. If there is
no VAD observation, or if the quality mark is larger than 3, then the
corresponding radar winds are not used. This combines the bird
algorithm and other checks used on the VAD winds.
- If the beam envelope extends below the eta model terrain
height, the corresponding radar wind is not used.
- If the superob error is larger than 6m/sec, the radar wind is
- Gross checks are the same as for conventional winds (residual
- Experiment changes log
- Background links
- Evaluation of parallel results
Daily forecast maps
Daily forecast stats
Verification of precipitation and against rawinsonde / surface data
Mesoscale Parallel Home Page
Page Last Modified: August 15, 2002