vir·ga | /ˈvər-gə/
Virga is the meteorological term for those wispy streaks of rain sometimes seen falling from the underside of clouds that don’t reach the ground. Children might know them as jellyfish clouds – the drifting streaks reminiscent of their tentacles trailing through the water. Adopted from the Latin for rod, some may wonder if the similarity of the term virga to a well-known medication is no coincidence.
Virgae are generally associated with altocumulus, altostratus, cirrocumulus, cumulus nimbostratus, and stratocumulus clouds. They occur when shafts of precipitation, often starting as ice crystals before melting into water droplets, fall from relatively cool, low-pressure air into drier, warmer air. As the rain falls, it’s heated by the friction caused by the increasing air pressure closer to the ground – a process known as compressional heating. As the heat builds, the rain evaporates – or as chemists would say, it sublimates. Virgae can be extremely dangerous for aviation, causing sudden and severe turbulence.
Extraterrestrial virgae have been observed on Venus, Mars, and even gas giants like Jupiter – which of course has no solid ground as such to fall to. On Venus, it’s sulphuric acid rain that vapourises. On Mars, it’s snow. Scientists from Nasa’s Jet Propulsion Laboratory say they’re pretty sure that actual diamonds rain on Jupiter – lightning storms carbonising methane that then hardens as it falls to form diamonds about a centimetre in diameter. With no solid ground and subject to increasing heat and pressure as they fall, the diamonds eventually sublimate. Diamond rain is also believed to fall on Saturn, Uranus, and Neptune.
Introduction Aeolian Alpenglow
Benthos Crepuscular Crispate Crown shyness
Desire lines Dreich Endragoned Edgelands
Frondescence Fumarole Gluggaveður Gossamer
Karst Komorebi Lawrence Long acre
Machair Monkey’s wedding Moonglade
Psithurism Quartz Rakuyou Roaring forties
Snag Soft estate Specular, diffuse and pellucid
Spoondrift Steam fog Swash zone Sylvan
Tellurian and thalassic Terracettes Uliginous