ENSO and CW Days
Composite seasonal spatial maps of mean CW days over India for the 13 El Nino years as well as that of 15 La Nina years for the DJF season during the data period are shown in Fig. 11a, b. In the El Nino case, the composite map showed relatively reduced frequency of CW days over most areas of CCZ. However, in the case of La Nina, significantly more number of CW days were seen in most parts of CCZ. In the case of SCW also (Figures not presented), significant increase (decrease) in the frequency of the SCW days were observed in the northern and north-western parts of CCZ during La Nina (El Nino) years.
Fig. 11 Maps showing composite of average number of CW days during the AMJ season for the a 13 El Nino years and b 15 La Nina years
Trends in the Station-Wise Seasonal CW/SCW Days
In Fig. 12, red rising arrow (blue falling arrow) are used to represent stations with increasing (decreasing) trend in the CW days with filled arrows showing trends significant at the 95 % confidence level. Decreasing trends were observed in most of the stations (Fig. 12) north of about 18°N with significant trends observed in 23 stations (mostly from north and north-west parts of CCZ). On the other hand, two stations from south Peninsula (Ananthapur and Vellore) showed significant increasing trends. In case of SCW (figure not shown), decreasing trends were observed in many stations of CCZ with significant trends observed in 9 stations from north-western part and 4 stations from central part of CCZ. One station from south Peninsula (Ananthapur) showed significant increasing trend. The decreasing trends in the CW/SCW days was also corroborated by the increasing trends (figure not showed) in the season averaged (DJF) minimum temperature anomalies over
Fig. 12 Trends in the CW days of 86 stations during the DJF season for the period 1971-2010. Nonparametric Mann-Kendall test was used to test the significance of the trends. Red rising (blue falling) arrows represent the increasing (decreasing) trends. Filled arrows represent the trends significant at 5 % level (color figure online) most of the stations from the country (Chap. 2) for the period 1971-2010. Of the total stations, 38 stations showed significant increasing trends in the seasonal minimum temperature anomaly.