Fire-induced convection over the summer 2010 Russian wildfires.
22 October 2020
04 August 2010
Convective clouds that form in response to the intense heat from wildfires are commonly referred to as pyrocumulonimbi, or pyroCbs. During the mid- to late-summer 2010, an intense heat wave plagued western Russia, and a number of very large wildfires formed and persisted for many days during late July and early August. At least 40 pyrocumulus events were observed over these fires, including five significant pyroCbs. One of these events, which occurred on 4 August about 300 km southeast of Moscow, was particularly intense. Although on the limb of MSG, some spectacular imagery was obtained of this convective blowup.
The image below is an HRV view of the 4 August pyroCb during its mature phase from MSG-1 (Meteosat-8). Although the upper-level winds were relatively weak, enough southerly shear existed to blow the pyroCb's anvil to the north, exposing the side of the convective turret, as indicated on the image. The steep limb view from MSG-1 also assists in this three-dimensional perspective. Residual low-level smoke can be seen to the west of the pyroCb; this smoke caused significant problems for the residents of many cities in western Russia.
Additional thunderstorms are present to the south of the pyroCb, but with only the visible channel, significant differences between the pyroCb and 'regular' convection are not evident. The second image is a multi-channel RGB image from the AVHRR instrument aboard the NOAA-15 polar orbiter. This near-nadir view shows an overshooting top and a plume-like feature atop the pyroCb.
Below are a series of MSG-1 loops showing the evolution of the 4 August pyroCb, including the HRV, 3.9 µm, the HRV/IR10.8 'sandwich product' and the HRV/Convection RGB 'sandwich product' (see explanation below). Looping the visible band shows the explosive nature of the pyroCb. The 3.9 µm loop is particularly useful for two purposes: 1) identifying the hotspots associated with the fires (appearing as red and yellow flickering pixels), and 2) inferring the cloud-top microphysical structure of the storms.
During the daytime, the 3.9 µm band contains a solar reflected component, and clouds with smaller ice crystals reflect significantly more radiation at 3.9 µm than those with larger ice crystals. This is manifested in warmer (darker) brightness temperatures at 3.9 µm. Note how the anvil of the pyroCb is significantly warmer than those of the regular convective storms further south. Smoke particles from the fire serve as cloud condensation nuclei, resulting in many very small cloud droplets, and after freezing within the storm's updraft, many very small anvil ice crystals.
The HRV/IR10.8 'sandwich product' is an image combination of the HRV and color-enhanced 10.8 µm image, allowing one to spatially co-locate the storm's overshooting top (at HRV resolution) with the warm/cold spots in the infrared. The temperatute scale for the IR10.8 layer is 210 K to 250 K (not the standard interval 200 K to 240 K). Similarly, the HRV/Convection RGB 'sandwich product' (called storm sandwich product), created by Zdenek Charvat from the Czech Hydrometeorological Institute in Prague, is an image combination of the HRV channel and the Convection RGB (see recipe and examples ), allowing one to spatially co-locate the smoke, the fires (hot spots), the cloud structures and the different types of convective storms (small ice particles, large ice particles).
In this case the best product for monitoring the pyroCb is probably the storm sandwich product (see Animation (Zoom) , AVI, 08:00–16:00 UTC). One can instantly see that the cloud top of the pyroCb is dramatically different from the tops of other storms in the region (very small ice crystals). Also, one can see very well in this product the 'hot spot', the storm-feeding fire for most of the time (see red arrow in this 12:15 UTC image ).
Animations (Meteosat-8 rapid scan service, 5-minute intervals)
- Animation 1: HRV Channel (MP4, 06:00–18:00 UTC)
- Animation 2: IR3.9 Channel (AVI, 06:25–16:00 UTC)
- Animation 3: HRV - IR10.8 sandwich product (MP4, 06:00–18:00 UTC)
- Animation 4: HRV - Convection RGB sandwich product (MP4, 06:00–18:00 UTC)
- Animation 4: HRV - Convection RGB sandwich product (Zoom) (AVI, 08:00–16:00 UTC)
Meteosat-9 HRV Image
Catastrophic fires over Portugal and Spain (3 August 2003) (look at the HRV animation)
The untold story of Pyrocumulonimbus (Fromm et al, 2010)
Terra MODIS image multi-overpass composite (4 Aug 2010, source: NASA)
NOAA AVHRR Image
NOAA-15, AVHRR, 04 August 2010, 13:10 UTC
RGB Composite VIS0.6, VIS0.8, IR11.0
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