Iain McGregor / Stuff
An epic sunrise captured over Riversdale Beach, Wairarapa on June 9.
Scientists say the illuminating sunrises and sunsets in Aotearoa in recent weeks are likely caused by “afterglow” from the Tonga volcanic eruption six months ago.
Niwa said that since late May his forecast team had been inundated with messages across the motu from people who had noticed unusually vibrant skies before dawn and after dusk.
To understand the observations, the forecast team contacted their colleagues at the Lauder Atmospheric Research Station in central Otago, who confirmed that their ground-based Lidar (Light Detection and Ranging) instrument had detected unusual spikes in aerosols in the stratosphere, about 20-25 kilometers above New Zealand.
The aerosols come from the plume of gas and ash that was ejected during the eruption of the Hunga Tonga-Hunga Ha’apai volcano on January 15.
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They have dispersed around the world, with concentrations peaking in the New Zealand region since mid-May.
Researchers at the Pierre-Simon Laplace Institute in Paris, using satellite data analysis, found that stratospheric aerosol concentrations from the eruption tripled between 35°S and 45°S – the latitude where finds Aotearoa on the globe – since April.
Niwa forecaster Nava Fedaeff said stratospheric aerosols are changing the way light scatters.
“Usually when you see a sunrise or sunset, it’s the clouds that turn into the most vivid colors.
“However, when stratospheric aerosols are present following a volcanic eruption, they scatter and bend light as the sun dips or rises beyond the horizon, creating a glow in the sky with tints of blue. , purple and purple.”
Since the colors reach their greatest intensity after sunset or before it rises, Fedaeff said volcanic twilights are known as “afterglows.”
“These haunting scenes are made all the more striking by the twilight rays cast by the shadows of distant clouds or mountain barriers.”
This is not the first time that New Zealand has experienced this natural phenomenon. After the eruption of Mount Pinatubo in the Philippines in 1991, the sunset afterglows lingered in varying degrees for months, meaning New Zealanders were able to enjoy some more of those beautiful morning colors and evening.
When Pinatubo blew, it cooled the earth by 1°C for the next year and a half.
The eruption of the Hunga-Tonga-Hunga-Ha’apai volcano on January 15 filmed. (Video first posted April 2022).
Niwa atmospheric scientist Ben Liley said it was unlikely this time because the Tonga volcano had injected far less sulfur dioxide into the atmosphere – 0.4 million tonnes compared to 10 to 15 million tons of Pinatubo – instead, sending out a lot more water vapor because it burst underwater. .
“Sulfur dioxide is what often causes global cooling after an eruption.
“The scientific interest will be how water vapor changes the chemistry of the stratosphere, which would have had its own effects.”
Niwa’s lead atmosphere and climate scientist, Dr Olaf Morganstern, said that at sea level about 1% of the atmosphere is water, but in the stratosphere it drops to just a few parts per million of air molecules.
“A large volcanic eruption from an undersea volcano can substantially increase this. Stratospheric water vapor is a potent greenhouse gas, trapping Earth’s heat, so this increase would overwhelm the cooling effect of aerosols. .”