Absorbing Aerosol Index, Fire radiative power, True Colour RGB, Fire temperature RGB, Natural Colour RGB, Cloud Type RGB
Fire signatures and the smoke plumes from first major wildfire episodes in 2023 at high latitudes are highly visible in different satellite observations.
06 September 2023
11 May 2023
By Anu-Maija Sundström, Julia Wagemann, Julien Chimot, Federico Fierli, Mark Parrington, Jochen Kerkmann and Ivan Smiljanic
The first major wildfire episodes of the 2023 boreal zone fire season are ongoing in Alberta, Canada and Siberia. In these areas fire danger is typically high during spring, after the snow melts and before the vegetation greens up. In early May, temperatures have been much higher than normal, especially in Alberta, with soil moisture lower than normal. The high temperature combined with windy and dry conditions have made the wildfires ignite easily and spread rapidly.
The smoke plumes from the wildfires are visible in multiple satellite observations. Sentinel-3 OLCI True Colour RGB images, together with fire radiative power observations from the SLSTR instrument (Figure 1), clearly show the brown smoke plumes originating from the active fires in Alberta and Siberia on 6 May.
The extent of the smoke plumes the following day can be seen in the OLCI True Colour RGB images in Figure 2.
The plumes are also visible in the GOME-2 absorbing aerosol index (AAI), where smoke appears as positive index values. Figure 3 illustrates the transport of the smoke plumes, using GOME-2 AAI observations starting on 5 May.
The observations show that the Alberta plume reached the Arctic circle on 7 May, due to the smoke plume extending over an area of more than 3.5 million km2. Since 6 May, a plume over Siberia could also be seen in the GOME-2 observations.
Copernicus Atmosphere Monitoring Service (CAMS) forecasts of atmospheric constituents, such as aerosol optical depth (Figure 4) and carbon monoxide, agree with the distribution of the smoke transport observed by GOME-2 and OLCI. They also predict long-range transport across the North Atlantic between 12-15 May (Figure 5).
CAMS forecasts are initialised from observations, including wildfire emissions estimated from NASA's MODIS observations (Figure 6), and observations of atmospheric constituents from a number of different sensors.
On 15/16 May the smoke could still be seen in satellite imagery, spreading thousands of kilometres. Figure 7 and 8 are the GOES-16 Fire temperature and Natural Colour RGBs from overnight 15-16 May, as smoke is better seen in GOES-16 evening imagery.
Figure 8 shows an almost Haboob-like spread of smoke, against the predominant westerly flow along the (north) eastern border of British Columbia. Figure 9 shows that the model picked up this low level flow.
What is apparent in the Cloud Type RGB is the power of the NIR1.3 channel (red component) to assist the aerosol height assignment — the low(er) level smoke appeared in cyan shades (light reflected only in the green and blue component from smoke). In contrast, the high and thin smoke filaments in the south of the area appeared in red shades (vague reflection only from NIR1.3). In general, in the NIR1.3 spectral region low features are not normally seen (due to a high water vapour absorption), however, in this case they were due to that fact higher level features (like cirrus or smoke clouds) are detected even if very thin.
The extent and duration of the Canadian fires even affected the atmospheric composition over Europe, for many days. Long distance transport of smoke over the Atlantic, carried along the Rossby planetary wave, could be tracked by Meteosat-10 (Figure 10). Forward scattering from the smoke particles during sunset hours (for Europe) gives the best detection potential. This is apparent through a Figure 11, where smoke is not seen at all (or to some degree through backward scattering in the morning hours) but at the low Sun angles.