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Satellite image of the month - 2018

Showcasing some of the Met Office's satellite imagery from around the world showing weather in action, new views of the world and extra commentary on how we collect and create the images from our Satellite Applications team.

March 2018: Significant Saharan Dust Outbreak over Greece

22 March 2018 -  Large-scale transfer of Saharan dust as seen from Space.

Saharan dust from the Libyan Desert was lifted by strong winds blowing from North Africa towards Europe. These winds were a result of a low-pressure system in the central Mediterranean. Crete in particular was badly affected with very low visibility caused by airborne dust. While Saharan dust over Greece is not uncommon, this was a particularly large transfer of dust, estimated to be the biggest for at least a decade. The reduced visibility led to the closure of a local airport and orange skies over the region.

The image above is from the VIIRS instrument aboard the NOAA/NASA satellite, Suomi-NPP. This is a polar-orbiting satellite that orbits the earth every 101 minutes at an altitude of around 830 km. It shows a plume of dust reaching northwards from Africa towards Crete at 11:45 UTC on 22nd March.

The animation below enables the easy identification of dust. In this type of imagery, known as the 'Dust RGB',  the lifted dust is picked out as pink or purple colours that are brighter than the background. Thick ice clouds show up in red and orange colours. To produce these images we use a combination of data from infra-red channels from the SEVIRI instrument on-board the European geostationary satellite, Meteosat-11, operated by EUMETSAT. This satellite sits at nearly 36,000 km above the Earth and provides imagery of the full Earth disc every 15 minutes.

Credits: Met Office (images) , NOAA/NASA (data for top image), EUMETSAT (data for movie).

February 2018: Eruption of Mount Sinabung

19 February 2018 - Large eruption of an Indonesian volcano - as seen from above.

Mount Sinabung, located in Northern Sumatra, Indonesia, erupted on 19th February sending ash, sulphur dioxide (SO2) and ice high into the atmosphere and triggered flight warnings in the area.

These images are from the Advanced Himawari Imager on-board Himawari-8, a Japanese Meteorological Agency satellite. This satellite is in geostationary orbit, 36,000 km above the surface of the Earth. The false-colour image on the left uses channels from the visible and near-infra-red part of the spectrum and looks similar to a true-colour image; however, ice cloud appears as a cyan colour, allowing it to be distinguished from water cloud. Volcanic ash appears brown, close to its true colour, and can be seen spreading from the volcano at 05:30 UTC when this image was captured.

The image on the right is from the same time but uses three infra-red channels to create an image type we use to detect dust storms and volcanic ash. We can get a better idea of what is going on from this combination of IR channels, particularly when looking at a sequence of images. In the animation below, different coloured features appear from the volcano and move in different directions following the eruption. This clearly demonstrates wind shear in the region as erupted matter advects in various directions depending on how high in the atmosphere it reaches.

The colours in the imagery coming from the volcano show:

  • green: sulphur dioxide-rich plume
  • pink/red: ash-rich plume
  • yellow: mixture of ash and SO2
  • black: ice cloud

The orange, black and pale pink colours further away from the volcano are cloud unrelated to the eruption.

Credits: Met Office (images) , JMA (data).

January 2018: Two days in Winter

07/08 January 2018 - Snow on the mountains seen from 830 km up.

The UK and Ireland were mostly cloud-free on 7th January 2018, only for the Southern part of the UK to be blanketed by low cloud on 8th January, with the Highlands of Scotland clearing. This is shown in these false-colour images from the VIIRS instrument aboard the NOAA/NASA satellite, Suomi-NPP. The two images were made from data collected a day apart as the satellite passed over the UK on 7th (left image) and 8th January (right image).  This type of false-colour image highlights where snow is lying on the ground. They are created using five channels in the near-infra-red part of the spectrum so things look a little different to what the human eye would see. The white snow can be differentiated from the white cloud as it now appears in a bright orange colour, while cloud ranges between blue, white and yellow depending on the cloud properties.

The Alps have seen very high snowfall this winter and a cloud-free day over the mountains later in January showed the snow cover on the higher ground.

Credits: Met Office (images) , NOAA/NASA (data).