Geoscience Reference
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(iv) Cocos Island-Malacol and the corresponding TCI being referred to as
TCI (C-M).
(v) Cocos Island-New Delhi and the corresponding TCI being referred to
as TCI (C-N).
(vi) Il Nouvelle-New Delhi and the corresponding TCI being referred to
as TCI (I-N).
(vii) Il Nouvelle-Malacol and the corresponding TCI being referred to as
TCI (I-M).
The methods of computation of TCIs are as follows. In order to
study the low-frequency oscillation, annual oscillation was filtered from
MSLP data. This has been done by subtracting the 30 years' (1953-1982)
mean monthly values from the respective individual months. This monthly
anomaly time series was standardized using the standard deviation of the
respective anomaly time series. Then, difference is further standardized by
the standard deviation of the difference time series. This method is used for
all the above seven groups of stations for all the 12 months from January to
December to obtain the respective monthly TCI series. From these TCIs,
four standard seasonal series centered at January, April, July, and October
are also made. These are used in this study. The rainfall series for the
summer monsoon months (June to September) over India (AIR) and two
of its subregions viz., the Northwest India (NWR) and the Peninsular India
(PIR) have been prepared by Chattopadhyay and Bhatla.
2
They have used
area-weighted subdivisional rainfall in India during the period 1901-1990.
This data series from 1953 to 1982 was used in the present study.
To establish the relationships between the all India summer monsoon
rainfall and TCIs, lead/lag and contemporaneous correlation coecients
(CCs) were computed among them for several months/seasons prior to the
summer monsoon season and several months/seasons after the summer
monsoon season. Consistencies of the significant CCs were also tested
using sliding windows of different widths. The statistical significance of
the correlations was tested using the conventional two-tailed
-test.
t
3. Results and Discussion
To investigate the temporal degree of association among the seven different
TCIs and Indian summer monsoon rainfall anomalies viz., AIR, NWR, and
PIR, concurrent and lagged correlations (CCs) were computed. Thus, AIR,
NWR, and PIR seasonal monsoon rainfall anomalies have been correlated
