Intercomparison of Monsoon climatology and variability
by the use of atmospheric GCM
We propose that each GCM group participating this intercomparison makes two
kinds of simulations as follows.
1. Long term simulations
1) Observed SST run
- Simulation period: 1 January 1979 – 31 May 1998
- SST: use the AMIP II monthly mean sea surface temperatures for the AMIP II
period and OISST (NCEP) afterward. AMIP II uses OISST after Dec1981.
- Other conditions: use AMIP II conditions.
2) Climatological SST run
- Simulation period: same as the observed SST run
- For SST and sea-ice use the AMIP climatological cycle
- Soil moisture and snow can be calculated interactively by each model
Therefore, the long-term experiments are the extention of AMIP integration and we
are focusing here on the Monsoon/ENSO simulation
2. A set of ensemble experiment for 1997-98 El-Nino
- Simulation period: 1 January 1997 – 31 May 1998
- 10 simulations carrying out with same boundary condition but with
different initial conditions of 1 January 1997, 1996, 1995, 1994, …., 1989,
and 1988 from the long-term observed SST run.
- SST: weekly OISST (NCEP) for the same period.
- Other conditions: use the AMIP II conditions.
To make the intercomparison, each participating group is recommended to make the
following diagnostic results.
1. Long-term simulation statistics
1) Climatological mean
Summer (June, July, August) and Winter (December, January, February) means
a. Means over the AA Monsoon region (30E-180E, 40S-60N)
- precipitation
- sea level pressure (SLP)
- soil moisture
- wind vectors at 850 mb and 250 mb
b. Large scale features over the global tropics
- 200 mb eddy streamfunction and velocity potential
c. Global zonal mean circulation
- height-latitude section of zonal-mean zonal wind and temperature
d. Air-sea interaction statistics over the Pacific and Indian oceans
in the regions of (30E-90W, 60S-60N)
- wind stress
- net heat flux
2) Annual cycle based on 5-day mean climatological data
a. rms of precipitation
b. EOFs of precipitation and SLP over the AA Monsoon domain of 30E-180E and
40S-60N. Please consider the grid of same area for the EOF analysis.
A simplest way is to make a grid distance at each latitude proportional to
1/cos(latitude).
c. Time-latitude section of 5 day mean precipitation averaged over 70-90E and
110-130E for the latitude from 40S to 60N.
3) Interannual variability
a. rms of the summer and winter mean precipitation, soil moisture, SLP,
200mb streamfunction and velocity potential.
b. rms of the summer and winter mean wind stress and net heat flux over the
oceans between 60S and 60N.
b. Time series of various Monsoon and ENSO indices
- Webster and Yang monsoon index (Webster and Yang 1992)
- Goswami et al. monsoon index: Avg(v850mb, lat=10N-30N and long=70E110E) - Avg(v200mb, lat=10N-30N and long=70E-110E)
- Lau et al. Indice: Avg(u200mb, lat=42N-52N and long=110E-150E)
-Avg(u200mb, lat=27N-37N and long=110E-150E)
- Indian summer rainfall
- Tibetan anticyclone intensity based on 200mb streamfunction
- Southern Oscillation index: SLP(Tahiti)-SLP(Darwin)
- PNA index (Horel and Wallace 1981)
4) Intraseasonal variability in the time scale of 10-60 days
- rms maps of precipitation for summer and winter seasons.
- Time-latitude section of climatological (20yr mean) intraseasonal precipitation
averaged over 70-90E and 110-130E to show the northward propagation. Latitude
domain: 40S-60N.
- Time-longitude section of the velocity potential at 200mb averaged 5S-5N for
the three years of 1 June 1996 – 31 May 1998, to show the global eastward
propagation of the intraseasonal oscillations.
5) Compare the items 3) and 4) of the climatological SST run with those of the
observed SST run.
6) Make the relationships (lag correlation) between ENSO index and various
monsoon indices using the observed SST run.
7) Other analysis (suggested)
-EOF(200mb eddy streamfuction for winter months with the zonal-mean
eliminated) for the control and SST runs.
2. Ensemble experiment statistics for the 1997-98 El-Nino
1) Ensemble mean anomalies over the AA monsoon region (40S-60N, 30E-180E)
for the 1997 summer (June, July, August) and the 1997-98 winter (Dec 1997, Jan
and Feb 1998) and corresponding observations.
- precipitation
- vector winds at 850 mb and 200 mb
- soil moisture
- SLP
** Anomaly is defined by the deviation of the ensemble mean from the
climatological seasonal mean of the observed SST run.
2) Time series of monthly mean anomalies (12 time series, one each from 10 runs,
their ensemble mean, and observation) from January 1997 to May 1998.
- SO index
- various monsoon indices introduced above
3) Time-longitude section of monthly mean precipitation anomaly along the
equator. Anomaly is the deviation of the ensemble mean from the climatological
monthly mean of the observed SST run.
4) Intraseasonal variability of precipitation with a time scale of 10-60 days
- rms maps for summer and winter seasons using all ten runs.
- Compare the rms above with the corresponding rms of the SST run to find out
the impact of weekly SST in the intraseasonal variability.
- Time-longitude section of intraseasonal variation of precipitation along the
equator.
5) Monsoon-ENSO relationship
- Make the lag correlation between ENSO index and various monsoon indices
using all ten runs.
- The end –