Analysis - 2020 La Niña: a closer look
/Scientists around the world are busy reporting on the strength of the current La Niña. This is generally measured as the extent of the cooling in the Niño SST regions in the Tropical Pacific. Together with the trade winds and Walker Circulation (SOI), the stronger the La Niña, the moisture theoretically shifts towards Australia. A comparison of 2010 (a record strength event) ocean temperatures in Mid-Oct v 2020 shows a few notable differences; a cooler Coral Sea and cooler Arafura Sea (circled in red) to the north of Australia. These are important regions for convective moisture for weather systems and while cool now, will be watched with interest following basin-wide warming of the Indian Ocean at the end of November.
Other global climate researchers also point out the nuances among La Niña events and the similarities between 2020 La Niña and those of 1983-84 and 1988-89 (Nov-Jan rainfall, bottom panel). Check your farm rainfall records for these summers:
1983-84 La Niña: cooler waters through the Maritime Continent (Indonesia/Malaysia) saw the mid-latitudes achieve high decile rainfall through this period and less so through the northern tropics.
1988-89 La Niña: this La Niña arrived earlier than the current 2020 La Niña and brought fantastic rains in winter/spring. Southern areas of the continent fared much better than Qld through the analysis period.
If 2020-21 La Niña is characterised by more tropical forcing (SSTs driving the climate to change from dry to wet) over the Indian Ocean than the Maritime Continent north of Australia, then some caution for much anticipated wet season rains through Qld would be prudent. Close monitoring of the phase of the SAM (NSW and s Qld) and MJO activity will be critical in the following months.
