A meteorological overview of the pre-AMEX and AMEX periods over the Australian region

A synoptic analysis is presented of the tropospheric circulation patterns in the Australian region tropics for the month prior to AMEX Phase II (14 December 1986 to 14 January 1987) and for the AMEX Phase II period (15 January to 15 February 1987). These periods are chosen to be representative of two distinctly different tropical flow regimes: the pre-monsoon onset and monsoon regimes at Darwin. A significant feature shown by the analysis is the rapid evolution from a 'transition season' regime to a 'monsoon season' regime between the two periods. Data are presented showing the time and space scales of the variability of the wind and pressure fields for the six weeks leading up to AMEX and for the AMEX time period, and a synoptic description of the major weather systems affecting the northern Australian region is given. A preliminary analysis is presented describing the role of mesoscale monsoon squall lines in influencing the precipitation regime over northern Australia. Data are presented which show that a high proportion of rainfall received in Darwin during AMEX Phase II was from such weather systems.