Murakami (1980a) used the outgoing longwave
radiation data derived from the NOAA
polar orbiting satellite to find some characteristic
features at long period (20–30 days) oscillation
of the Asian summer monsoon. The data has
been further studied to investigate the regional
nature of long and short period oscillations over
the South China Sea, Indonesia Sea and Bay of
Bengal during the winter (Murakami, 1980b;
1980c).
Prasad and Verma (1985) have analysed the
dominant eigen-vector pattern of the outgoing
long-wave radiation using eigen-vector analysis.
Their study shows annual cycle with pronounced
variations in the outgoing long-wave radiation
over the tropical belt between 10 N to 20 N.
They have also concluded that interannual variation
of the outgoing long-wave radiation for the
summer monsoon period shows a close association
with the large-scale monsoon rainfall over
India. The outgoing long-wave radiation data
has been used in monitoring and understanding
the tropical circulation changes and in modeling,
for, e.g., Chelliah and Arkin (1992), Kousky and
Kayano (1994), and Moron (1995). In the literature,
the details of the principal components
analysis technique are given by Grimmer
(1963), Kutzbach (1967), Kidson (1975),
Hastenrath (1978). In the present study, the
Empirical Orthogonal Function (EOF) or Principal
Component Analysis is used to compare the
dominant rainfall patterns from normal rainfall
records over India and the major modes of the
outgoing long-wave radiation data for the period
(1979–1988) during the monsoon period (June–
September). The analysis identifies the spatial
and temporal pattern characteristics of possible
physical significance. The El-Ni~no=Southern Oscillation
(ENSO) and its relationship with Indian
monsoon have also been examined.