CLOUD
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| Name | CLOUD |
| Classification | Atmospheric phenomenon |
CLOUD Clouds are visible aggregates of minute liquid droplets, frozen crystals, or mixed-phase particles suspended in a planetary atmosphere. They occur across Earth and other bodies such as Mars, Venus, Titan, and the gas giants Jupiter and Saturn and influence weather, climate, and radiation balance. Observations from platforms like Hubble Space Telescope, Landsat, and GOES satellites, together with field campaigns such as GLOBE Program and ARM, underpin modern understanding.
Etymology and definitions
The English word "cloud" derives from Old English and Proto-Germanic roots related to massed vapor and obscuration; comparable terms appear in Old Norse and Old High German lexicons. Scientific definitions differ among institutions: the World Meteorological Organization classifies clouds by altitude and form, while the International Cloud Atlas offers standardized nomenclature used by organizations including National Aeronautics and Space Administration and Met Office. Technical distinctions arise in works by researchers affiliated with NOAA and UK Met Office regarding terms such as cumuliform, stratiform, and cirriform.
Physical cloud types and classification
Cloud classification follows the scheme codified in the International Cloud Atlas, which lists genera like Cumulus, Stratus, Cirrus, Nimbostratus, and Cumulonimbus. Each genus subdivides into species and varieties; examples include Cumulus congestus and Cirrus fibratus. Special forms—such as Lenticular cloud and Mammatus—are documented in case studies by teams at University of Reading and NCAR. Altitudinal categories (low, mid, high) reference levels defined by World Meteorological Organization standards and are used in climatologies by IPCC and ECMWF.
Formation processes and atmospheric dynamics
Cloud formation arises from parcel lifting mechanisms: convection over heated surfaces described in analyses by Rayleigh–Bénard convection experiments and fieldwork near Amazon Rainforest; frontal lifting across boundaries studied in Frontal cyclone research; orographic uplift observed in the Rocky Mountains and Himalayas; and convergence zones like the Intertropical Convergence Zone. Microphysical pathways involve nucleation on aerosols, with roles for mineral dust from Sahara Desert, sea salt from Pacific Ocean, and biogenic particulates traced to environments like Amazon Basin. Dynamics of entrainment, shear, and turbulence are modeled in studies at MIT, Princeton University, and ETH Zurich, often employing theoretical frameworks from Navier–Stokes equations and mesoscale models used by NOAA.
Optical, electrical, and acoustic phenomena
Clouds produce optical phenomena including halos, coronas, and glories, investigated in imagery from Mount Washington Observatory and optical studies at University of Arizona. Ice-crystal halos correlate with hexagonal crystal habits analyzed in work by British Antarctic Survey teams. Electrification processes leading to lightning were characterized in campaigns like STEP (Stratosphere–Troposphere Experiment Project) and in studies by Benjamin Franklin’s heirs in atmospheric electricity research at Pennsylvania State University. Acoustic interactions, including thunder propagation and infrasound from convective systems, have been recorded by arrays operated by USGS and experimental groups at Scripps Institution of Oceanography.
Climate role and hydrological impacts
Clouds modulate Earth's radiative balance by scattering and absorbing shortwave and longwave radiation, central to assessments by the Intergovernmental Panel on Climate Change and climate modeling centers such as Met Office Hadley Centre and NOAA GFDL. Low stratocumulus decks over the Eastern Pacific exert cooling feedbacks examined in studies by Scripps Institution of Oceanography, while high cirrus layers influence greenhouse trapping in analyses by NASA Goddard Institute for Space Studies. Cloud-mediated precipitation processes feed continental hydrology linked to river basins like the Amazon River and Ganges River, affecting water resources documented by World Resources Institute and impacting agriculture studied at CGIAR centers.
Observation, remote sensing, and modeling
Observational platforms span in situ radiosondes from Vaisala networks, ground-based lidars at ARM Climate Research Facility sites, and satellite sensors aboard MODIS, CALIPSO, and CloudSat. Remote sensing algorithms developed at NOAA and NASA retrieve cloud top height, optical depth, and phase. Numerical cloud-resolving models are implemented in frameworks like WRF (Weather Research and Forecasting Model) and large-eddy simulations at NCAR to study convection and microphysics. Data assimilation approaches at ECMWF integrate cloud observations into global forecasts used by national services including Japan Meteorological Agency.
Cultural significance and symbolism
Clouds have rich symbolic roles across cultures: classical motifs in Chinese painting tied to the Tang dynasty, Renaissance depictions in works by Leonardo da Vinci, and Romantic-era landscapes by J.M.W. Turner. Religious texts from Bible narratives and Qur'an references use cloud imagery; myths among Maori and Navajo peoples embody meteorological symbolism. In literature, clouds figure in poetry by William Wordsworth and prose by Gabriel García Márquez, while modern visual culture employs cloud motifs in logos for corporations like IBM and Salesforce and in filmography from studios such as Studio Ghibli.
Category:Atmospheric phenomena