Objects in Clouds
Falling Rain Droplet
Virga and Praecipitatio
Falling Cloud
Tropical Rain
Tropical Rainforest
Diamond Dust


Falling Rain Droplet

The Vertical Wind Tunnel Laboratory in Mainz (MAVERT) makes it possible to levitate cloud and rain drops as well as iced hydrometeors (ice particles, snow flakes, hail and graupel) at a stationary location floating within an upwards air flow. The smallest objects which can be treated in this way have a diameter of 30 µm, the largest ones a diameter of 10 mm. This allows investigation of trace element uptake by hydrometeors, measurements of their physical properties, and investigation of mechanisms of rain formation (and so on) under laboratory conditions. The basic scheme of the wind tunnel equipment is drawn in ChannelScheme.jpg. It has a height of approximately 6 m. Details of the experimental chamber are presented in Construction.jpg. The two aluminium boxes with the turning knobs on the right side are used for the manual adjustment of the vertical air velocity. The other instruments are used for the conditioning of the air (e.g. humidity, content of trace gases etc.)

The image and the movie show a raindrop with a basal diameter of 3 mm which is levitated by the vertical flow in the experimental section. The change of the droplet shape can be clearly recognized. This shape corresponds with those of a natural raindrop falling from a cloud. Compared to droplets dropping off a water tap falling droplets are apparently not "tear-like" - as often misleadingly assumed.

The largest natural raindrops have a diameter of 8 mm. If the droplets were larger, the air flow would cause sufficient vibration to destroy them (aerodynamically induced destruction of the falling drops). For this reason water which is poured out of a bucket from a tower does not reach the ground as a compact bulk, but as a shower of droplets with diameters below 8 mm.
Raindrops with a diameter of 1 mm, 3 mm and 8 mm fall with a velocity of approximately 14 km/h, 29 km/h and 43 km/h.

Drop.jpg and Movie: R. Jaenicke, Institute for Atmospheric Physics (IPA), Johannes Gutenberg University at Mainz, 2002

Construction.jpg: S. Mitra, IPA, Johannes Gutenberg University at Mainz, 2002

ChannelScheme.jpg: N. von Blohn, IPA, Johannes Gutenberg University at Mainz, 2003