Analysis of Cyclone Tracks of North Indian Ocean Using Cluster Analysis - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 92

events whereas the cluster 3 has short duration events. Cluster 1 is biggest
cluster but only 29% of the events have made landfall on the Indian coastline.

5.2.3 Maximum Intensity
For each of the cyclonic event the maximum intensity attained during its life
cycle is recorded as categorical variable. Each event may be classified as
Cyclonic Storm (wind speed 34-47 knots) or Severe Cyclonic Storm (wind
speed >47 knots). Table 1 presents the ratio of number of severe cyclonic storms
to cyclonic storms in each of the five clusters. Clusters 4 and 2 consist of
higher intensity events; most systems being classified as severe cyclonic storms,
suggests that these events may be of significance with regard to impact.

5.2.4 Seasonality
The frequency distribution of months in which the cyclone has occurred for
each of the five clusters is presented in Table 2. Clusters 1, 3 and 5 show peaks
in pre Monsoon (May) and post Monsoon (October-December). Clusters 2
and 5 have single peak, post Monsoon (October-December). The results are
similar to the past studies (Niyas, Srivastava and Hatwar, 2009) where the
frequency of tropical cyclones in the Indian seas is said to have a bi-modal
character, with two peaks, one from mid-April to mid-June and second from
October to December.

Table 2: Frequency distribution of months in which cyclones have occurred

Cluster Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total

1 1 3 1 16 194 6

2 1 1 1 2 2 17 13 37

3 1435 1 56 5

4 1 15 5 18 84 3

5 1 2 3 1 9 15 5 36

Total 237

6. Conclusion and Future Work

This study analyses the tropical cyclone characteristics for the North Indian
Ocean using the cluster analysis. Tropical cyclone tracks appear to be grouped
into clusters that are well defined and robust. These clusters correspond to
distinct regions of cyclone activity and type with distinct characteristics related
to genesis location, life span, maximum sustained intensity and probability of
landfall. Some of the clusters are particularly important because of high intensity,
and landfall location in vulnerable coastal belt. This provides a means for
analyzing the events of significance from impact point of view. In particular,
the clustering approach has grouped cyclones with higher maximum intensity
and longest life span into a single cluster (cluster 2) consisting of late season
events mostly occurring in the months of November-December.