Role of ENSO on CDs/TCs Frequency
Relationships between the frequency of CDs, TCs and severe TCs over NIO and the Nino 3.4 index during the pre-monsoon, monsoon and post-monsoon seasons in both the antecedent and concurrent modes have been studied by Mohapatra el al. (2015). Figure 6(a-c). shows the 30-year sliding CCs between frequency of (a) CDs
- (b) TCs and (c) severe TCs over the NIO during the post-monsoon season and Nino
- 3.4 index during the antecedent winter(JF)/pre-monsoon (MAM)/monsoon (JJAS) season and concurrent post-monsoon (OND) season based on the data of 1951— 2010. There is a persistently increasing negative relationship, after 1960, between frequency of CDs during the post-monsoon season and concurrent Nino 3.4 index, though not significant (Fig. 6a). The CCs have changed sign from positive to negative around 1960. Similar relationship exists with antecedent Nino 3.4 of JJAS. However, a positive relation is building up since mid-seventies between frequency of CDs during post-monsoon season and Nino 3.4 of winter/pre-monsoon seasons.
Fig. 6 The 30-year sliding correlation coefficients (CC) between frequency of a CDs, b TCs and c severe TCs over NIO during the post-monsoon season and Nino 3.4 SST during the antecedent winter (JF)/pre-monsoon (MAM)/monsoon (JJAS) season and concurrent post-monsoon (OND) season based on data of 1951-2010 (CCs significant at the 95 % confidence level are indicated by dotted lines)
In the case of TCs, significant negative relation has emerged since mid-seventies with concurrent Nino 3.4 and antecedent Nino 3.4 of monsoon season (Fig. 6b). Similar relation has emerged for severe TCs also (Fig. 6c).