E. Linacre and B. Geerts

7/'98

As in India, the onset, duration and end of the monsoonal period at Darwin, Australia is quite variable (1, 2). There is considerable variation from year to year, in all three features. Typically, the onset is in mid-December and the end in mid-March. But the onset date ranged from November 23rd to January 27th, a difference of two months, whilst the earliest and latest endings differed by more than three months, i.e. January 1st and April 6th, respectively (Fig 1).

Sometimes, the onset and the end are well-defined, but often their definition is subjective, in particular because the monsoon is often discontinuous, i.e. a sequence of wet spells and dry spells. The duration and/or timing of the Australian monsoon do not correlate well with El Niño events, however, the onset and end dates are related to the phase of Madden-Julian oscillation (3).

Fig 1. The dates of onset and end of the Australian summer monsoon at Darwin between 1952-1983 (from 1,2).