Colourful skies may be eruption after glow: Niwa

The sun rises over Dunedin last week. Niwa says the volcanic eruption in Tonga in January likely...
The sun rises over Dunedin last week. Niwa says the volcanic eruption in Tonga in January likely added aerosols into the stratosphere at New Zealand’s latitude, adding vibrancy to sunsets and sunrises. PHOTO: STEPHEN JAQUIERY otagoimages.co.nz
The violent eruption of an underground volcano in Tonga in January could be adding vibrance to recent sunsets and sunrises in New Zealand, Niwa says.

The environmental science research institute said yesterday its scientists believed aerosols originating from the plume of gas and ash ejected when the Hunga Tonga-Hunga Ha’apai volcano erupted had been concentrating in the stratosphere around New Zealand since mid-May.

A Paris institute had analysed satellite data that showed concentrations of stratospheric aerosols from the Tongan volcanic eruption had tripled between 35 degrees south and 45 degrees south since April.

Niwa forecaster Nava Fedaeff said stratospheric aerosols changed the way light scattered.

"Usually when you see a sunrise or sunset, it is the clouds that morph into the most vibrant colours.

"However, when stratospheric aerosols are present following a volcanic eruption, they scatter and bend the light as the sun dips or rises past the horizon, creating a glow in the sky
with hues of blue, purple, and violet."

Since the colours achieved their greatest intensity after the sun had set or before it had risen, Ms Fedaeff said volcanic twilights were known as "afterglows".

The colour and intensity of the afterglow was affected by the amount of haze and cloudiness along the path of light reaching the stratosphere.

This was not the first time a volcanic eruption had had an impact on New Zealand sunsets and sunrises, Niwa said.

After the Philippine volcano Mt Pinatubo erupted in 1991, sunset afterglows persisted to varying degrees for months, meaning New Zealanders could be treated to the vibrant morning and evening colours for a while longer.

When Mt Pinatubo blew 30 years ago, it cooled Earth’s temperature by 1degC for the next year and a-half.

However, Niwa said it was unlikely that would happen this time around, because the Tongan eruption had happened underwater and much less sulphur dioxide had entered the atmosphere.

 

 

 

 

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