NMM International Project Proposal, Clarifications
Impacts of ocean-atmosphere coupling and SST high frequency variability on the
coupled simulation of the mean state and variability of the Indian Summer Monsoon
LOCEAN-IPSL/LEGOS, France: Pascal Terray, Sébastien Masson and Fabien Durand
IITM, India: Roxy Mathew, VinuValsala
INGV-CMCC, Italy [newly proposed]: Silvio Gualdi, Annalisa Cherchi
Clarifications and updates
With reference to our proposal, we understand that some clarifications are required by the
MM committee:
1. How will the diurnal cycle be resolved from the upper ocean, as the resolution in the
ocean model is sparse in the upper ocean?
Concerning the first question, it has been suggested that a vertical resolution of 1m near the
surface and a coupling frequency of less than 2-3 hrs are required for resolving the SST
diurnal cycle in a coupled model (e.g. Bernie et al., 2005; see our initial proposal for more
details). We intend to check the impacts and benefits of optimizing both the coupling
frequency and vertical oceanic resolution by using a multi-model approach, with a focus on
the CFSv2 model.
The experiments already done with SINTEX-F2 in France, testing with the coupling
frequency for the SST alone, suggest that even with 10m oceanic vertical resolution near the
surface, there are some positive and significant changes due to changes in the coupling
frequency alone (Masson et al., 2012; Terray et al., 2012). As a start, we therefore intend to
make further coordinated experiments with CFSv2, along with different coupled models
available in the proposal to verify the benefits and impacts of modifying the coupling
frequency alone (for specific parameters like SST or wind stress or for all the air-sea
parameters together).
Presently, the coupling frequency used in CFSv2 is 30 minutes or 1 hr. We are planning to
experiment with this coupling frequency, decreasing it to up to one day or further increasing it
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to 10 minutes. Moreover, these variations of coupling frequency may be done for some
specific parameters alone (e.g. SST or systematically). Gathering all together, the results of
the different experiments will provide us a first knowledge about the impacts of resolving (or
more precisely, starting to resolve) the diurnal cycle with respect to the coupled simulation of
the monsoon. Such experiments with CFSv2 will be a good start to examine the sensitivity of
the model to the diurnal cycle, even if the coupling frequency is already very high in CFSv2.
In a second step and depending on the manpower allocated to the project, we can investigate
the benefits of increasing the oceanic resolution in CFSv2 and in other coupled models. For
the SINTEX coupled models family, we are planning to use the “new” version of NEMO with
75 vertical levels with 1m vertical resolution near the surface, which resolves the SST diurnal
cycle fully and comprehensively. Concerning CFSv2, the vertical oceanic resolution is
presently very coarse (10m) and we will examine if a higher resolution (< 10m) can be
achieved in MOM4.
If it falls under the vision of Monsoon Mission, and if the manpower is sufficient, we can
examine the possibilities of coupling NEMO with NCEP GFS as a stable version of NEMO
resolving comprehensively the diurnal cycle is already available. We may also before going
into this direction investigate in details the ocean biases in NEMO in comparison with MOM4,
especially in the tropics. Besides, since the French/Italian teams in the current proposal are
experts on NEMO, an active support on the ocean model can be expected. This may be an
added virtue as NCEP support is on the atmospheric model (GFS) only, and there is no active
support for IITM from GFDL [Ref: Dr. Roxy’s collaboration and visit to NCEP through
Monsoon Mission, 2012]. Coupling NEMO with NCEP GFS may thus be taken as an option,
if increasing the vertical resolution in MOM4 does not improve the simulations or required
others important and tedious adjustments in that model (as it was the case for NEMO).
2. How will this proposal help in improving CFSv2 coupled model and its Ocean model?
Concerning the second question, we would like to point out that in order to understand the
limitation or strength of a coupled model (e.g. CFSv2) it is useful (and even mandatory) to
compare it with other state-of-the art coupled models. While the goal is to improve the
monsoon simulation in the CFSv2 coupled model, the use of different CGCMS is crucial to
obtain robust results and avoid wrong conclusions due to compensating errors which are very
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common in current CGCMs.This is the pathway proposed in our MM project. More precisely,
this multi-model approach would be utilized to understand the biases in CFSv2 and to provide
guidance and clues about possibilities of improvements in the coupling and ocean components
of CFS model.
Concretely, the work on CFSv2 will be done through a team in IITM, which will be funded
by MM if this proposal is accepted and sufficient manpower is allocated to it, and by sharing
the modelling expertise available in France and Italy with the Indian team. We argue that this
will be a very efficient approach because all the partners involved in this MM proposal have
already a long and fruitful history of scientific collaborations and are highly motivated to
work together for improving monsoon simulation with CFSv2 or other coupled models from
the ocean point of view. As an illustration, Dr. Roxy Mathew has already closely worked and
co-authored with both French's and Italian's teams on the coupled model simulations of the
Asian Monsoon. Moreover, both the French and Italian partners of this project have
vast/excellent experience in developing and "directly" dealing with coupled models and also a
long history of collaborations. Our intention with this proposal is to provide a unique
combination of experts in monsoon variability, ocean and coupled modelling for improving
the monsoon simulation, especially CFS, from the point of view of the ocean.
Since the French and Italian partners of the project have presently only a limited view of the
performance and deficiencies of CFS as implemented and used in IITM, it is very difficult for
us to say more on that matter presently and before the real start of the project. This explains
why in the first phase of our proposal we proposed a detailed comparison of CFS simulations
with the other coupled models available in the French and Italian teams through a coordinated
set of sensitivity experiments with a specific focus on the role of the ocean and of the oceanatmosphere coupling. This first step hopefully will also provide guidance and pathways to
improve CFS skill and correcting deficiencies in a second step.
Further developments on the proposal
Our MM project was submitted in September 2012. Since this submission, we are happy to
inform the MM committee that Italian scientists from INGV-CMCC (Silvio Gualdi, Annalisa
Cherchi) who are international experts of monsoon variability and modelling will join our
MM proposal and will contribute actively to the proposed work and tasks by making all the
coupled and atmosphere-only experiments initially proposed with their own coupled models
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available at CMCC.CMCCmight provide some relevant contribution to our MM project, by
strengthening both the multi-model approach (enlarging also the number of possible
sensitivity experiments) and the analysis part of the project.
They could considerably strengthen our multi-model as they might make the proposed
sensitivity experiments (both coupled and un-coupled) using the new CMCCmodel based on
CAM (the NCAR atmospheric model), beside using the INGV-SINTEX model (which is
different in important aspects of SINTEX-F2, as an illustration the hydrological cycle is
closed in INGV-SINTEX; this is not the case in SINTEX-F2 and this aspect may be important
for monsoon variability, especially in regions like the Bay of Bengal). This means that we
will have now a pool of 4 different coupled models (with CFSv2 at IITM and SINTEX-F2 at
LOCEAN/IPSL) in order to test the importance and assess the role of ocean-atmosphere
coupling, SST diurnal cycle on the monsoon simulations. This will provide more robust
guidance for diagnosing problems in CFSv2 through a unique multi-model approach and
gathering together the strong expertise available in France and Italy about ocean and coupled
modelling to the Indian team participating to the proposal.
Finally, CMCC might extend the part concerning the role of the systematic error on the ISM
simulation and prediction, providing all theseasonal forecast hindcastsavailable at CMCC.
There is also thepossibilityto conduct specific sensitivity experiments through the use of the
seasonal forecastsystem at CMCC.
Importantly,
INGV-CMCC can also contribute to the project
with their own
computingresources that will be made available for the coordinated sensitivity experiments.
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