Features of the formation of the Central and East Pacific La Niña types

Abstract

In this paper the dataset of global ocean chlorophyll «a» (Chl a) concentration from the GlobColour project over the equatorial Pacific during the La Niña events from 1998 to 2018 is analyzed. GlobColour includes satellite sensors such as SeaWiFS, MODIS, MERIS and others. The study of changes in chlorophyll «a» concentration is carried out with an analysis of sea temperature and current distributions on the surface and over the ocean depth taken from the NCEP GODAS reanalysis from 1981 to 2018. Additionally the trade wind indices from 1979 to 2018 are used. The purpose of the work is to study the mechanisms of formation of two La Niña types, leading to the occurrence of different climatic anomalies in different regions of our planet. It is found that at the initial stage of the Central Pacific La Niña type origin the ocean chlorophyll «a» concentration over the center equatorial Pacific increases in six to eight times (from 0.1 mg/m3 to 0.8 mg/m3) and the thermocline depth in this area decreases to 50 m indicating the intensification of the central equatorial upwelling. During the East Pacific La Nina type the central equatorial upwelling is not formed and negative sea surface temperature anomalies are formed by increasing of the Peruvian upwelling supported intensification trade winds on the East Pacific equatorial sector. All obtained results are confirmed by a 95% statistically significant by Student's test. Thus, the work is demonstrated significant differences in the features of the two La Niña types formation at their initial stage of origin.