CSIRO PUBLISHING Journal of Southern Hemisphere Earth Systems Science, 2020, 70, 304–327 Seasonal Climate Summary https://doi.org/10.1071/ES19037 Seasonal climate summary for the southern hemisphere (spring 2017): equal-fifth warmest spring on record, with rainfall mixed Skie Tobin Bureau of Meteorology, GPO Box 1289, Melbourne, Vic. 3001, Australia. Email:
[email protected] Abstract. This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for spring 2017; an account of seasonal rainfall and temperature for the Australian region and the broader southern hemisphere is also provided. The tropical Pacific Ocean cooled from mid-winter, with an unusually late La Nin˜a becoming established by the end of spring. Spring was the equal-fifth warmest on record, in terms of area-averaged national mean temperature, and was characterised by exceptional September warmth over eastern Australia, while rainfall was mixed geographically and from month-to-month, but below average overall. Keywords: Antarctica, Australia, climate, climate drivers, ENSO, IOD, La Nin˜a, MJO, rainfall, SAM, seasonal climate summary, seasonal summary, southern hemisphere, temperature. Received 2 October 2019, accepted 20 January 2020, published online 17 September 2020 1 Introduction Fig. 2 shows the ENSO 5VAR Index over the same period, with This summary reviews the southern hemisphere and equatorial a three-month binomially weighted moving average. The climate patterns for spring 2017, with particular attention given 5VAR2 is a composite monthly ENSO index, calculated as to the Australasian and equatorial regions of the Pacific and the standardised amplitude of the first principal component of Indian ocean basins.