Coupled ocean-atmosphere summer heatwaves in the New Zealand region: an update
During austral warm seasons (November - March, NDJFM) of 1934/35, 2017/18, 2018/19 and 2021/22 the New Zealand (NZ) region experienced the most intense coupled ocean/atmosphere (MHW/AHW) heatwaves on record. Average temperature anomalies over land and sea were +1.2 to 1.4°C above average. Common to...
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| Published in: | Weather and climate : journal of the Meteorological Society of New Zealand 2023-01, Vol.42 (1), p.18-41 |
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| Main Authors: | , , , , , , , , , , , , , , |
| Format: | Article |
| Language: | eng |
| Online Access: | Get full text |
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| Summary: | During austral warm seasons (November - March, NDJFM) of 1934/35, 2017/18, 2018/19 and 2021/22 the New Zealand (NZ) region experienced the most intense coupled ocean/atmosphere (MHW/AHW) heatwaves on record. Average temperature anomalies over land and sea were +1.2 to 1.4°C above average. Common to all four events were maximum sea surface temperature (SST) anomalies to the west of the South Island of NZ. Atmospheric circulation anomalies showed a pattern of blocking high pressure over the Tasman Sea and Pacific Ocean to the south, and southeast of NZ, and reduced trough activity over and to the east of NZ, accompanied by strongly positive Southern Annular Mode conditions.
Hindcasts for 2017/18, 2018/19 and 2021/22 NDJFM indicate that positive temperature anomalies around 1°C occurred in the Tasman Sea, and near 1.5°C for the Chatham Rise. The temperature anomalies in the upper 50m of the ocean are consistent with the 500hPa atmospheric height anomalies. The temperature anomalies in the upper 50m of the ocean are consistent with the 500hPa atmospheric height anomalies and associated winds. The eastern Tasman Sea during August 2021 to July 2022 experienced the highest annual number of MHW days during the satellite-era (1981-present) from OISSTv2.1 data. Under 1.5°C of global warming the four events would have ERIs of 2-3 years, and with 2°C of warming all would be considered cool years relative to the +2°C climate. For the 1957-2022 period, the two most intense heatwaves have ERIs of between 30 to 150 years.
Major loss of glacial ice occurred from Southern Alps glaciers with rapid melt of seasonal snow in all cases. Slow advances in grape phenology since 1948 may be associated with increases in temperature over the same period. Cherries and apricot harvest dates advanced by one to two weeks. Marine impacts may be linked to starvation of kororā/Little Penguin (Eudyptula minor) chicks in the Bay of Plenty. Chicks weighed less and had a lower body condition score in 2020 and 2021 compared to 2019 and rescue calls in 2021 reached the highest volumes since 2015. The first record of warm-water prey species in the diet of yellow-eyed penguins at Moeraki occurred, as well as widespread sea-sponge bleaching around northern and southern NZ. |
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| ISSN: | 0111-5499 |