“We’ve looked at clouds from both sides now, from up and down”

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NIWA scientists have been at work all weekend measuring the height of the volcanic ash clouds as they approached and passed over Lauder, in Central Otago. This work has been done to support predictions about the ash cloud and its effects.

Lauder's high tech instruments can profile the volcanic ash clouds from bottom to top, and give clues to their composition. 

“We have been operating our LIDAR (Light Detection and Ranging) instrument. It shoots a laser beam vertically upwards, and then we measure how much light is scattered back off the aerosols (small particles) and clouds,” says NIWA scientist Ben Liley.

The concentrations of particles at different heights can be calculated from the amount of laser light reflected back to a telescope, and the height of the ‘echo’ from the time delay, measured to billionths of a second.

The LIDAR works like RADAR, but instead of using radio waves, it emits beams of pulsed laser-light vertically and is sensitive enough to measure particles up to about 30 kilometres.

Aviation authorities wanted “confirmation that the time and height that the cloud is passing over New Zealand is accurate,” says Liley.

Lauder's observations of the volcanic ash suspended in the atmosphere confirmed that the international modelling effort to forecast the arrival was accurate for the Central Otago location.

“We started seeing the [cloud] plume on Saturday afternoon, and it first appeared between 8.5 -10 kilometres in altitude. The layer was about 2 kilometres thick, and it moved up in height so it was about 10 kilometres in altitude by early Sunday morning. It thickened up as the night went on," says Liley.

Early on Sunday morning a second layer, centred at about 9 kilometres in altitude, appeared. Over the course of Sunday it varied. Different layers came across but the cloud remained above 8 kilometres.

The volcanic ash clouds have passed for now and its back to ‘blue skies’ over Lauder.

Background:

Situated 35 kilometres from Alexandra in the South Island, NIWA’s Atmospheric Research Station at Lauder is well known throughout the international research community. The clear skies and isolation makes it perfect for observing atmospheric chemistry and radiation. Lauder specialises in measuring CFCs, Ozone, UV light levels and greenhouse gases and has a wide range of world class instruments.

Find out more on our Lauder page.

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Atmospheric Scientist
The purple beam in this photo is from a lidar (laser radar) measuring ozone above NIWA's atmospheric research station at Lauder, Central Otago. The instrument, worth NZ$2 million, was installed by the Dutch RIVM research group as part of the Network for the Detection of Stratospheric Change. [NIWA]
LIDARs in operation at NIWA's Lauder research station in Central Otago. The green beam is measuring the cloud plume. Ben Liley, NIWA
Research subject: Instrumentation