www.csiro.au ccam regional climate modelling dr marcus thatcher research scientist december 2007
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www.csiro.au
CCAM Regional climate modelling
Dr Marcus Thatcher
Research Scientist
December 2007
CMAR RCM
Overview
This presentation describes CCAM climate downscaling
Specifically, we downscale from NCEP 2.5 deg reanalyses to 60 km resolution climate simulation
The output can then be processed using NCO toolkit for netCDF files to create climate averages, etc.
These results can then be compared to downscaled climate projections (e.g., CSIRO Mk3)
CMAR RCM
Regional Climate Modelling with CCAM
RCM is achieved with a multiple nesting procedure, by first downscaling to 60 km resolution and then downscaling to 15 km resolution
Mk3 CCAM 60km CCAM 15km
Comparison of average rainfall (mm/day) between Mk3, CCAM at 60 km resolution and CCAM at 15 km resolution for northern Queensland
CMAR RCM
Regional Climate Modelling with CCAM
The climate downscaling script can be found at
$HOME/ccam/scripts/clim/pd60_run
This script will generate a ten year downscaled climate run for Indonesia (this takes a long time to run!)
Today we will simply start the script running and examine the first month of output
CMAR RCM
Host model – NCEP reanalyses
Instead of preparing initial conditions, we must first prepare the host model from which to downscale.
Usually we downscale from NCEP 2.5 degree reanalyses
Alternatively we downscale from CSIRO Mk3 climate projections
However, any model once prepared on the CCAM grid can in theory be used (e.g., ERA-40)
Aerosols andCO2 data
Run 60 km CCAM for Indonesia
Process output for climatology
Host modelInterpolated to
C48 CCAM grid
CMAR RCM
Aerosol input
Next the aerosols for a particular year must be prepared for CCAM
This is achieved using the aero_m20.sh script.
The aerosol data files are located at
$HOME/ccam/stdin/sulfateA2.????
Note that the aerosol data files are valid from 1961 to 2100
Run 60 km CCAM for Indonesia
CO2 dataAerosols(aero_m20.sh)
CMAR RCM
CO2 input
The CO2 levels must also be specified for a CCAM climate run.
These files also are valid from 1961 to 2100 and are located at
$HOME/ccam/stdin/co2_data.????
Note that there is no preprocessing of CO2 files since (unlike aerosols), the CO2 levels are independent of position
However, the CO2 files only work for CCAM with 18 vertical levels. For different vertical resolution, the CO2 data files need to regenerated
Run 60 km CCAM for Indonesia
CO2 dataAerosols(aero_m20.sh)
CMAR RCM
CCAM namelist options for climate downscaling
The CCAM namelist for climate simulations is also slightly different to the NWP example.
CCAM switches used for climate simulations are listed as follows:
nbd = 0 (disable far field nudging)
mbd = 20 (spectral nudging)
kbotdav = 10 (nudge upper levels only)
CMAR RCM
Sigma levels
kbotdav=4 (typically NWP)
kbotdav=10 (typically climate)
CMAR RCM
CCAM climate simulation
When performing a climate simulation, we run only one month at a time.
Once the month simulation is complete, it creates a restart file which is used to initialise CCAM for the next month
CCAM simulation(Jan)
CCAM simulation(Feb)
CCAM simulation(Mar)
Restartfile
Restartfile
NCEP 2.5 degree reanalysis host model
(nudging)
CMAR RCM
CCAM restart files
If CCAM stops during a long climate run (e.g, electricity black-out), then the climate simulation can be restarted from the last restart file
Also, the restart files are usually archived so that CCAM can be restarted from any month during the climate simulation
CMAR RCM
CCAM climate simulation
CCAM restart files are called
$HOME/ccam/scripts/clim/RESTART/Restccam_NCEP_60.??????
Typically we tar the files from the same year
The daily CCAM output can be found at
$HOME/ccam/scripts/clim/daily
The monthly averaged CCAM output is
$HOME/ccam/scripts/clim/monthy_mean
The raw CCAM output (from which the above files can be regenerated) is
$HOME/ccam/scripts/clim/OUTPUT
CMAR RCM
CCAM output
Below is an example cc2hist namelist
&input
kta=720 ktb=999999 ktc=720
minlat = -20., maxlat = -10., minlon = 90., maxlon = 120.
use_plevs = T
plevs = 1000, 850, 700, 500, 300
&end
&histnl
htype=“ave"
hnames= "all" hfreq = 0
&end
Generate average
Use and definePressure levels(instead of sigmalevels)
Output domain
Every 12 hours
CMAR RCM
NCO toolkit for NetCDF files
CCAM output can also be processed using the NCO toolkit for manipulating NetCDF files
Specifically, the ncea program for averaging NetCDF files is a quick way to calculate the average climate (i.e., for study)
CMAR RCM
Other types of climate run
There are several different versions of CCAM climate runs, depending on the application
NCEP 2.5 deg reanalyses:
Used to test CCAM downscaling with ‘observed’ present day or historical weather behaviour.
CSIRO Mk3 control run:
Nesting CCAM in a simulated present day climate to test the performance of CCAM when there are biases in the host model
CSIRO Mk3 climate projection:
Nesting CCAM in simulated future climate to predict regional changes arising from increasing global temperatures.
CMAR RCM
Some RCM examples
The following slides show some examples of RCM with CCAM
In these examples we show Australia
However, during the tutorial we can start to create examples for Indonesia
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DJF
JJA
Obs Tmax CCAM-m
30-year run, downscaled from Mk3 CGCM
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DJF
JJA
Obs Tmin CCAM-m
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Obs Rainfall (mm/d) CCAM-m
DJF
JJA
CMAR RCM
Obs – 30 yr climatologyNew CCAM – 30 yr climatology10 ms-1 threshold
Tropical cyclone days/year – observed vs model
Latest 60 km simulations produce good climatology of “cyclone-like” vortices.Above shows example of C-CAM downscaled from Mk3 CGCM
CMAR RCM
Multiple nesting for climate simulations
Like the CCAM NWP forecasts, it is possible to downscale the 60 km climate run to 15 km resolution by multiple nesting of the forecast
However, given the small time step for the 15 km simulation, this takes a very long time to simulate (multiprocessor CCAM is a necessity)
CMAR RCM
Average maximum temperature (deg C)
OBS - Jan CCAM - Jan OBS - Apr CCAM - Apr
OBS - Jul CCAM - Jul OBS - Oct CCAM - Oct
CMAR RCM
Average minimum temperature (deg C)
OBS - Jan CCAM - Jan OBS - Apr CCAM - Apr
OBS - Jul CCAM - Jul OBS - Oct CCAM - Oct
CMAR RCM
Average rainfall (mm/day)
OBS - Jan CCAM - Jan OBS - Apr CCAM - Apr
OBS - Jul CCAM - Jul OBS - Oct CCAM - Oct
CMAR RCM
CCAM technical notes
Missing data in the highly stretched region is replaced with weather information from the previous, lower resolution forecast
CCAM uses a multiple stretched grid technique to ‘step down’ or downscale the forecast
8km
1km
60km
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Full nudging of far-field winds in the free atmosphere, with e-folding time ~24 h
Partial nudging
No nudging
(only SSTs)
Far-field nudging
Model uses NCEP or GCM winds only outside the inner red boundary
Model uses NCEP or GCM winds (and optionally other fields) at all points
Global nudging
Full nudging of fields in the free atmosphere, with e-folding time ~48 h
For long, variable-resolution climate runs (only), some nudging is desirable to assist the climatology in the coarsest part of the globe
CMAR RCM
8 km resolution
No hard boundaries at panel edges:Far-field nudging from 60 km model run on this panel
Rest of world8 km resolution throughoutthis panel About 50 km resolution
at this edge
CMAR RCM
Far field nudging
CMAR RCM
Advanced CCAM configuration
CCAM can now also use spectral downscaling, although it is slower than far field nudging
Spectral downscaling modifies the large scale structure of the atmosphere to be the same as the host model everywhere
8km
60km
The large scale structure of the atmosphereis nudged everywhere
Small scale structure is not perturbed
CMAR RCM
Spectral nudging
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Thank You
Marine and Atmospheric Research
Name Dr Marcus Thatcher
Title Research Scientist
Email Marcus.Thatcher@csiro.au
Contact CSIRO
Phone 1300 363 400
+61 3 9545 2176
Email enquiries@csiro.au
Web www.csiro.au
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