orographic cloud


Clouds stream over Landmannalaugar, Iceland, as the sun sets

Weather Words

accumulation advisory air air mass air pollution air pressure almanac altocumulus altostratus anemometer atmosphere atmospheric pressure aurora  autumn avalanche balmy barometer barometric pressure Beaufort  wind scale biosphere black ice blizzard blustery breeze calm cell chinook wind cirriform cirrus climate climatology cloud cloud bank cloudburst cloudy cold cold  ront cold snap cold wave compass condensation contrail convergence cumuliform cumulonimbus cumulus current cyclone cyclonic flow degree depression dew dew point disturbance doldrums downburst downdraft downpour downwind drift drifting snow drizzle drought dry dust devil duststorm earthlight easterlies eddy EF-scale El Niño emergency radio evaporation eye eye wall fair fall feeder bands firewhirl flash flood flood flood  stage flurry fog fog bank forecast freeze freezing rain front frost Fujita scale funnel cloud gale global warming graupel greenhouse effect ground fog gully  asher gust gustnado haboob hail halo haze heat heat index heat wave high humid humidity hurricane hurricane season hydrologic cycle hydrology hydrometerhydrosphere hygrometer ice ice age ice crystals ice pellets ice  storm icicle inversion isobar isotherm jet stream Kelvin knot ake effect land breeze landfall landspout leeward lightning low low clouds low pressure  system macroburst mammatus cloud meteorologist meteorology microburst mist mistral wind moisture monsoon muggy National Hurricane Center (NHC) National Weather Service (NWC) NEXRAD nimbus nimbostratus nor'easter normal nowcast orographic cloud outflow outlook overcast ozone parhelion partly cloudy permafrost pileus cloud polar polar front pollutant precipitation pressure prevailing wind radar radiation rain rainbands rainbow rain gauge rain shadow relative humidity ridge rope tornado sandstorm Santa Ana  wind scattered sea breeze shower sky sleet slush smog smoke snow snowfall snowflake snow flurry snow level snow line snow shower snowsquall snowstorm spring squall squall line stationary front steam St. Elmo’s fire storm storm surge storm tracks stratosphere stratocumulus stratus subtropical summer sun dog sun pillar sunrise sunset supercell surge swell   temperate temperature thaw thermal thermometer thunder thunderstorm tornado tornado alley trace triple point tropical tropical depression tropical disturbance tropical storm tropical wave Tropic of Cancer Tropic of  Capricorn troposphere trough turbulence twilight twister typhoon unstable updraft upwelling upwind vapor vapor trail visibility vortex wall cloud warm warningwatch water water cycle waterspout wave weather weather balloon weathering weather map weather satellite weathervane wedge westerlies whirlwind  whiteout wind wind chill wind chill factor wind shear windsock wind  vane winter zone 

alabasterskies  asked:

Can you explain the science behind the formation of undulatis asperatus?

I can try! 

I haven’t seen an acutal paper on these amazing clouds, buutttt I’ve read a few things of how they work and can lay it out for you all in my terms.

So for starters, here’s the clouds we’re talking about:

Pretty cool, right? First thing that probably comes to mind for you is “wow, those really look like waves… or water… or something”! And you’re really hitting the nail on the head by looking at this. It does look like the surface of a body of water. Water is a fluid, air is a fluid, so let’s take this analogy and run with it!

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Nice shot of Fuego (Fire) volcano, Guatemala. As wind blows over the top you can see water vapor condensing into a lenticular cloud, and then the volcano blows ash out through that cloud.


Spectacular shot of clouds pouring off the peaks in Jasper National Park, Alberta, during a storm - air rising over the peaks cools and triggers those clouds.

Liberty cap

The Royal Observatory in Greenwich, England is currently exhibiting the shortlisted entries for the Astronomy Photographer of the Year competition. This amazing picture of the Milky Way and orographic lenticular clouds hanging above Liberty Cap, a granite dome in Yosemite National Park, was taken by Rogelio Bernal Andreo.



The flat top of South Africa’s Table Mountain produces a very interesting version of a marine layer/lenticular cloud nicknamed the “Table Cloth”. Take a look.

Time-lapse video featuring Table Mountain in Cape-Town, South Africa.

The mountain has a level plateau approximately 3km from side to side. Elevation is roughly 3,563ft above sea level.

The flat top of the mountain is often covered by orographic clouds, formed when a south-easterly wind is directed up the mountain’s slopes into colder air, where the moisture condenses to form the so-called “table cloth” of cloud.

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Orographic cloud over Iceland

The melting glacial ice in the foreground provides a beautiful setting for this lovely cloud etched in glowing colours. These formations of water vapour in the atmosphere form when moist air rises above an obstruction, in this case the hills to the right, condenses its moisture, and then sinks on the far side of the topography. Streamers of water vapour indicate the wind direction in that layer of the layer of air that surrounds the thin rind of our planet.


Image credit: • Iurie Belegurschi /http://on.fb.me/1NHQ086

Mars near opposition

Tonight Mars is between opposition (April 8) and closest approach (April 14) looping through the constellation Virgo opposite the Sun in the night sky. That makes it prime season for telescopic views of the the Red Planet, like this one from April 3rd. The clear, sharp image was captured with a high-speed digital camera and 16-inch diameter telescope from Assis, Brazil, Planet Earth. Mars’ north polar cap is at the top left. Also visible are whitish orographic clouds - water vapor clouds condensing in the cold atmosphere above the peaks of Mars' towering volcanos. The exact dates of closest approach and opposition are slightly different because of the planet’s elliptical orbit. Still, get your telescope out on the night of closest approach (April 14/15) and you can view both Mars and a total eclipse of the Moon. Mars will be about 1/100th the angular size of the Moon.

Image credit & copyright: Fabio Carvalho and Gabriela Carvalho


Hubble confirms new dark spot on Neptune

New images obtained on May 16, 2016, by NASA’s Hubble Space Telescope confirm the presence of a dark vortex in the atmosphere of Neptune. Though similar features were seen during the Voyager 2 flyby of Neptune in 1989 and by the Hubble Space Telescope in 1994, this vortex is the first one observed on Neptune in the 21st century.

The discovery was announced on May 17, 2016, in a Central Bureau for Astronomical Telegrams (CBAT) electronic telegram by University of California at Berkeley research astronomer Mike Wong, who led the team that analyzed the Hubble data.

Neptune’s dark vortices are high-pressure systems and are usually accompanied by bright “companion clouds,” which are also now visible on the distant planet. The bright clouds form when the flow of ambient air is perturbed and diverted upward over the dark vortex, causing gases to likely freeze into methane ice crystals. “Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains,” Wong said. “And the companion clouds are similar to so-called orographic clouds that appear as pancake-shaped features lingering over mountains on Earth.”

Beginning in July 2015, bright clouds were again seen on Neptune by several observers, from amateurs to astronomers at the W. M. Keck Observatory in Hawaii. Astronomers suspected that these clouds might be bright companion clouds following an unseen dark vortex. Neptune’s dark vortices are typically only seen at blue wavelengths, and only Hubble has the high resolution required for seeing them on distant Neptune.
In September 2015, the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble Space Telescope project that annually captures global maps of the outer planets, revealed a dark spot close to the location of the bright clouds, which had been tracked from the ground. By viewing the vortex a second time, the new Hubble images confirm that OPAL really detected a long-lived feature. The new data enabled the team to create a higher-quality map of the vortex and its surroundings.
Neptune’s dark vortices have exhibited surprising diversity over the years, in terms of size, shape, and stability (they meander in latitude, and sometimes speed up or slow down). They also come and go on much shorter timescales compared to similar anticyclones seen on Jupiter; large storms on Jupiter evolve over decades.

Planetary astronomers hope to better understand how dark vortices originate, what controls their drifts and oscillations, how they interact with the environment, and how they eventually dissipate, according to UC Berkeley doctoral student Joshua Tollefson, who was recently awarded a prestigious NASA Earth and Space Science Fellowship to study Neptune’s atmosphere. Measuring the evolution of the new dark vortex will extend knowledge of both the dark vortices themselves, as well as the structure and dynamics of the surrounding atmosphere.

The team, led by Wong, also included the OPAL team (Wong, Amy Simon, and Glenn Orton), UC Berkeley collaborators (Imke de Pater, Joshua Tollefson, and Katherine de Kleer), Heidi Hammel (AURA), Statia Luszcz-Cook (AMNH), Ricardo Hueso and Agustin Sánchez-Lavega (Universidad del Pais Vasco), Marc Delcroix (Société Astronomique de France), Larry Sromovsky and Patrick Fry (University of Wisconsin), and Christoph Baranec (University of Hawaii).