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members, are made from slightly different initial atmospheric and oceanic
conditions, which are designed to represent the uncertainties inherent in the
operational analyses. The details about the ECMWF monthly forecast system
along with its skill over the different geographical regions have been discussed
in Vitart (2004) and Vitart et al. (2008). As it will be shown, the model displays
some useful skill up to 18 days over some geographical regions including Asia.
It is also seen from the study of Vitart (2004) that for days 12-18, probabilistic
scores indicate that the monthly forecasting system performs generally better
than both climatology and the persistence of the previous weekly probabilities,
suggesting that forecasts at that time range could be useful.
2.2 NCEP's Climate Forecast System
Extended-range prediction is also carried out at Climate Prediction Centre,
National Centre for Environmental Prediction by using the dynamical model
outputs from CFS as discussed in Jon et al. (2008). The details about the
operational CFS are discussed in Saha et al. (2006). The operational CFS
(T62L64) is initialized four times daily from 00Z, 06Z, 12Z and 18Z with one
day delay (because of the availability of the ocean analysis). The atmospheric
component of the CFS is the NCEP atmospheric GFS model. The oceanic
component is the GFDL Modular Ocean Model Version 3 (MOM3). The ocean-
atmosphere coupling is nearly global (64°N-74°S) and no flux correction
applied. Thus, the CFS is a fully 'tier-1' forecast system. The skill of the seasonal
and monthly monsoon rainfall forecast is found to be reasonable in the CFS
(Pattanaik and Kumar, 2010).
2.3 Multi-model Ensemble (MME) Forecast
As discussed above, the ECMWF and the NCEP are routinely generating the
forecast from the coupled model. The products of the ECMWF monthly
forecasting system used here are based on weekly forecasts for two weeks
which updates on every Thursday and valid for week 1 (days 5-11) and week 2
(days 12-18). For the CFS there are four forecasts every day. The outputs from
these two models are used for generating the MME forecast based on following
steps: The ensemble means (51 members) from ECMWF forecast is considered
with forecast period for days 5-11 and days 12-18. Similarly, the ensemble
mean forecast from four members NCEP CFS valid for the same period as that
of ECMWF are used. The corresponding hindcast mean is calculated both from
ECMWF (18 years climatology) and the NCEP CFS (25 years climatology)
and interpolated into uniform grid of 0.5 degrees.
The corresponding hindcast
climatology is subtracted and the weekly anomaly for three weeks is calculated
both from ECMWF and the NCEP CFS. The anomaly for week 1 to week 2 is
calculated by giving equal weight to ECMWF and NCEP CFS model. The
product is generated on real time basis on every Friday with forecast for week
1 (Monday to Sunday) and week 2 (subsequent Monday to Sunday).
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