Appendix B.1 Composite analysis

For the purpose of extracting circulation structures associated with precipitation events at the equator, a composite analysis referring to the precipitation peak is performed. Composite analysis is a method to pick up possible characteristics of a group which is composed of a number of events that satisfy a given condition by, for instance, averaging the events. In the present study, the aim is to clarify peculiar circulation structures associated with precipitation events at the equator by averaging the related fields of physical quantities after shifting the field longitudinally referring to the position of precipitation peak at the equator so that the position of precipitation peak of each event coincides to each other. The method utilized here is the same as that of Numaguti and Hayashi (1991). The method of selecting precipitation peaks to be referred to is as follows.

1. Pick up longitudinal positions of precipitation peaks which are determined as the position where amount of precipitation exceeds a certain given threshold value at a given time.
2. When the precipitation amount for a picked peak is maximum in a give longitudinal area, then the peak is selected as one of the key points to be referred to for composite. Repeat these procedure for different time and different peaks, and correct the key points for composite.
3. Each data of circulation field of the time of a particular maximum event is shifted longitudinally so that the longitude of the key point coincides with 180 degree, and then added to the data of other maximum event and averaged.

We adopt the threshold value as 0.0007 [kg m-2 s-1] and the longitudinal area to determine a precipitation peak as 2000km.