Satellite image of the month

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.

April 2017: Large dust outbreak in the Atlantic

April 2017 - Saharan dust being transported over the Atlantic

For a period in early April, scientists in Satellite Applications at the Met Office observed a Saharan dust outbreak off the West coast of Africa. Between 60-200 million tons of dust are typically lifted every year in the Sahara region up to 5 or 6 km in altitude, and most of it is transported by the trade winds across the Atlantic all the way to the American continent. Occasionally, dust plumes may also reach the United Kingdom. Dust affects radiation in the atmosphere. The dust combined with the hot and dry air of the Sahara forms the Saharan Air Layer over the Atlantic Ocean, which has significant effects on tropical weather and interferes with the development of hurricanes. Dust also acts as a nutrient source for oceanic microorganisms and it can favour the formation of ice clouds. Large uncertainties exist in the exact properties and the quantification of atmospheric dust. Since 2011, dust is predicted in the Met Office global forecast model.

There is a large year to year variability in the dust transport across the Atlantic, generally towards the Caribbean, but in the winter and spring also towards South America. African dust has been shown to be a major contributor to soils in the receptor regions, and is believed to be a major source of nutrients for the Amazon River Basin, mainly due to its content of minerals and phosphorous.

This event, of intensity larger than usual, shows a week-long episode of dust transport from West Africa to South America. It has been followed using passive and active satellite sensors. It is well observed from the EUMETSAT geostationary satellite Meteosat-10, as seen in the top image, which is a  3-channel 'Natural Colour' image from 3 April 2017 at 16:15 UTC. The dust crossing the Atlantic is highlighted as a brown/yellow haze against the dark oceanic background.

The lower image shows the dust plume as highlighted with the NASA space lidar CALIOP (circled). In lidar imagery, the vertical dimension is height above sea level and the horizontal dimension is the location of the satellite as it follows its orbit around the Earth. This image was acquired on 30 March 2017 at 03:45 UTC.

The image loops below shows satellite observations alongside modelled dust. The left loop shows Meteosat-10 observations of the dust plume travelling across the Atlantic. In this type of imagery (called "dust RGB") dust is highlighted in luminous pink colour. The features in dark red, dark blue and orange, instead, are cloud fields. The right loop shows the Met Office Unified Model representation of the dust plume crossing the Atlantic from West Africa to South America.

Meteosat-10 dust RGB imagery     Met Office Unified Model dust


March 2017: Cyclone Enawo.

7 March 2017 - A composite image of Cylone Enawo aproaching Madagascar using Meteosat-8 visible channel.

EUMETSAT's Meteosat-8 geostationary satellite has been moved to replace the aging Meteosat-7 and provide coverage centering on the Indian Ocean region. The image above, created at the Met Office, is a composite image. The clouds in the image are taken from a visible channel (at 0.6 μm) of the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on Meteosat-8. This is overlaid on NASA Blue Marble imagery, which provides the land and sea surface background.

The image shows Cyclone Enawo on 7th March, the time when it reached peak intensity just before making landfall on Madagascar.

February 2017: Green, swirling "eye".

20 February 2017 - Lake Maracaibo, Venezuela - duckweed outbreak

Looking like a great, green swirling eye from space, this is in fact an outbreak of duckweed on Venezuela’s Lake Maracaibo. The lake is brackish, connected to the Caribbean Sea by a narrow channel.  During heavy rains, mixing of the fresh rain water with the salty lake water can cause the duckweed, already present in the lake, to rapidly increase in amount giving the vibrant green colour. The influx of sea water through the channel causes currents in the lake giving the swirling appearance.

The Moderate-resolution Imaging Spectroradiometer (MODIS) on board NASA's Aqua satellite provides useful information on changes to the Earth's surface as well as information on atmospheric dynamics, water vapour, cloud and aerosols. This is a true-colour image, combining information from three visible channels on the instrument to give an image as it would appear to the human eye.

January 2017: Two images, one day apart, from NASA's Terra Satellite.

25 January 2017 - Rare snowfall over the Sahara Desert

December 2016 saw what was reported as the first snow in the Sahara desert for 37 years. The snowfall continued in January, completely covering some dunes and creating waist high drifts. This remarkable occurrence can be seen in this high resolution image, created using data from NASA’s Terra satellite, from over 700km above.

26 January 2017 - Chile wildfires

Drought conditions and high temperatures in Chile's central Maule region in January led to the rapid spread of wildfires, causing a state of emergency to be declared as the fires caused widespread destruction and deaths. The image above shows the extent of the fires and smoke on 26 January.

NASA's Terra satellite contains a Moderate-resolution Imaging Spectroradiometer (MODIS). This instrument measures incoming radiation from the Earth and it's atmosphere as it orbits 710 km above the surface of the Earth. Each orbit takes 99 minutes to complete. If we combine the measurements from three visible wavelengths, corresponding to red light, green light and blue light, we can create a 'true colour' image which looks like a photograph.