Time-lapse photography of clouds and other phenomena in the sky

Cloud waves above Praha. Determining the height of this and subsequent waves is somewhat uncertain. According to the High Resolution Visible (HRV) channel images from Meteosat-11 (MSG-4, Meteosat Second Generation), the individual waves in the wider area over the Czech Republic seem to cast shadows on a lower, more continuous cloud layer - see this HRV image  from the beginning of the timelapse, in which the wave shown in the timelapse is marked with a green arrow, along with the location and angle of the timelapse, and the  HRV loop, in which the location of the imaging location is marked with a white cross, and its red color indicates the time of the timelapse. According to lidar observations (source: EUMETNET e-Profile) from nearby Praha-Libuš, the continuous cloud layer is at levels around 1.5 to 2 km - so the waves must be higher above it. The midday (12 UTC) atmospheric sounding (also from Praha-Libuš) indicates a possible additional cloud layer at around 4 km - which might be the level of the waves.

On that day, a narrow band of Saharan dust was passing over western and central Europe, getting here from the Atlantic - see the mosaic of Aerosol Index Product (source: Copernicus Browser), composed of several subsequent passes of the Sentinel-5P satellite. Part of the dust band (indicated by the arrow) is also visible over NW France in the RGB-24M image product from the NOAA-20 satellite, disappearing under a layer of cirrus clouds further inland above central Europe. Animations of the VIS-IR and RGB-24M images from the Rapid Scan mode of the MSG satellite show the situation over central Europe on that day, with a jet stream drifting the cirrus clouds rapidly to the east (see also the 12 UTC sounding from Praha-Libuš station).

The Saharan dust layer is very well visible in the ALC profile from Praha-Karlov station (source: EUMETNET E-PROFILE), where it is marked with the number [3]. The number [1] indicates the surface aerosol layer (of a local origin), [2] the layer in which shallow convective clouds (cumulus) were present at the time of the timelapse (indicated by vertical lines and double arrow), [4] indicates the cloud-free clear layer between the Saharan dust and the cirrus levels [5]. The NOAA-20 image at 375 m resolution shows in detail the cirrus clouds over the Czech Republic, their large horizontal variability. These cirrus clouds are both of natural origin as well as remnants of airplane condensation trails (contrails).

Now to the timelapse itself. It is a result of heavy computer processing of the original images, which themselves showed almost no detail - see the original image (as shot) and the same image after processing from a raw file in Lightroom. In the timelapse, notice especially the rapidly advancing shadows of the cirrus clouds, cast into the layer of Saharan dust. In the detailed image of the contrail shadows, numbers [1] and [2] indicate shadows cast on two nearby layers of cirrus clouds (the plane must have been flying just above these), and [3] indicates the contrail shadow cast into the Saharan dust layer. As can be seen very nicely from this slower animation of the contrail shadows, the relative position of the shadow (including its beginning) to the contrail itself depends on the actual position of the airplane and its contrail relative to the Sun and the location of the observation.

Besides the shadows, notice also the motion of larger cumulus clouds along a horizontal helix, caused by strong vertical wind shear at the cumulus levels, approximately between 2 and 3 km above the ground.

NLC (noctilucent clouds) and cirrus clouds above Prague, captured from slopes of Okrouhlík (south of Prague). The NLC begin to gradually appear in the left part of the video as the sky darkens and the Sun dips below the northwest horizon. NLC can be easily distinguished from tropospheric clouds (especially cirrus) by their gradual westward drift (toward the left), while cirrus and remnants of convection move more rapidly eastward (to the right in the image). As the Sun sinks deeper and deeper below the horizon, the apparent height of NLC above the horizon decreases (as the Earth's shadow height increases in the upper mesosphere, about 85 km above the Earth's surface, where NLC occur). See also the static image from 20:30 UTC (21:30 CEST), when the NLC were probably most prominent, and the OSWIN mesospheric radar record (source here). And one more image, from 20:45 UTC - what looks like a greenish hair here is a trail of firefly flying in front of the lens.