Southern Spain had muddy rain (also called red rain or rain dust) as a result of convection on 20 July.
26 September 2022
18 July 2016
By Jose Prieto (EUMETSAT)
The dust originated from one of many outbreaks in the Sahara desert a few days before. From there it travelled in the layers of the mid-atmosphere, along the western African coast, to the south-western part of the Iberian peninsula. There it became incorporated with the water and ice particles generated in updrafts, and fell to the ground as dusty rain, as can be seen on this photo of a dust-covered car in Madrid.
The dust that travelled along the coast took in contributions from the south of Mauritania and from the Moroccan bay of Agadir. The main dust contribution reaching the Iberian peninsula originated on the South of Algeria on 16 July around 19:00 UTC and travelled, moved by different synoptic systems to the north of Morocco, through a more northern route, reaching Agadir on the early hours of 19 July, as can be seen in the Dust RGB animation, 16 July 00:00 UTC–20 July 23:30 UTC
In the infrared imagery, both the animated gif (Figure 1) and the longer animation from 18 July 00:12 UTC to 20 July 12:42 UTC, the dust appears in pink hues. It shows as a softer and more of a blue colour over the seas, where the thermal contrast between the surface and the dust is not so pronounced as over land; and there is more humidity in the air.
Over the ocean, dust can be confused with low-level cloud, especially in the infrared combination.
However, the more uniform areas in the infrared composite are only dust above the ocean heading towards southwestern Europe. This is confirmed in the solar imagery, animated gif (Figure 2) and the longer animation from 18 July 06:42 UTC to 20 July 12:42 UTC.
In the afternoon hours, the reflection conditions are perfect for showing the vertical structure of the dust front — for instance around 18 July at 18:42 UTC — or the convection generating cumulonimbus (Cb) towers along a gust line. The projection of shades allows an estimate of the Cb height above the dust level. Convection occurs at areas of high humidity in the low levels, showing in blue in the infrared animation.
Next morning, the dust seems to have disappeared, but it is there, and it becomes observable again in the afternoon. Convection then occurs in the Iberian peninsula, trapping the dust in the droplets or crystals.
Finally, on 20 July in the morning the concentration of dust is so high that it can be seen even under unfavourable conditions in the solar image (Figure 3). Frontal rain left abundant precipitation in the Iberian peninsula, putting a temporary end to a heatwave.