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Clouds and fogs Atmos 3200/Geog 3280 Mountain Weather and Climate Pilatus, Switzerland © S.W. Hoch Sebastian Hoch and C. David Whiteman Additional reading • Rangno, A. L., 2003: The Classification of Clouds. Chapter 21 in Handbook of Weather, Climate and Water: Dynamics, Climate, Physical Meteorology,Weather Systems and Measurements, Thomas D. Potter and Bradley R. Colman (Eds.), John Wiley and Sons, Inc. • You can download the Rangno article from the class website. There are some good B&W pictures of clouds in this article. Also, download the US stamps pdf and the accompanying textual explanation. • There is a good color cloud chart in the book Meteorology Today, By C. Donald Ahrens. Motivation / Definitions Why naming the animals in the zoo … ? © Burroughs et al. (2002) © Ronald G. Warfield photo, 1999, Mt. Rainier Genera, species, varieties, supplementary features, … Clouds and fogs are Hydrometeors. Oregon Dept of Forestry photo Definition: Hydrometeor (http://amsglossary.allenpress.com/glossary/) Greek: Yδωρ, hudōr, ‘Hydro’, meaning "water" Greek: meteōros, ‘meteor’ meaning “high in the air”. Any product of condensation or deposition of atmospheric water vapor, whether formed in the free atmosphere or at the earth's surface; also, any water particle blown by the wind from the earth's surface. Definition - Cloud Cloud – a visible aggregate of minute suspended particles of water droplets or ice particles, or both, in the atmosphere above the earth’s surface. Clouds form in the free atmosphere as a result of condensation of water vapor in rising currents of air, or by the evaporation of the lowest stratum of fog. For condensation to occur at a low degree of supersaturation, there must be an abundance of cloud condensation nuclei for water clouds, or ice nuclei for ice-crystal clouds, at temperatures substantially above −40°C. Definition - Cloud The size of cloud drops varies from one cloud type to another, and within any given cloud there always exists a finite range of sizes. Generally, cloud drops (droplets) range from 1–100 μm in diameter, and hence are very much smaller than raindrops. Characteristics: clouds are tenuous and transitory, most small clouds in the lower atmosphere exist for only a few minutes. Definition may depend on where you are: many high clouds consist of ice crystals or snowflakes. If encountered on Mt. Everest, we might call this a snow shower. Fog Definition Fog - “a cloud based on the ground” • Water droplets or ice particles (ice fog) suspended in the atmosphere in the vicinity of the earths surface that affect visibility. • Visibility below 1 km (0.62 miles). • Difference between clouds and fog ? • 1 m3 of fog typically contains 0.1 g of liquid water dispersed over 1-10 million droplets with diameters between 1 and 20 micrometers. Types of Fog • Radiation fog - nighttime outgoing longwave radiation cools near-surface air below its dew point temperature • • Upslope fog - moist air is cooled by lifting up terrain slopes. Advection fog - warm air flows over cold surface and cools from below until saturation is reached • Evaporation-mixing fog - water evaporates and mixes with adjacent air, raising the mixture’s dew point temperature. If sufficient moisture is present mixture becomes saturated. [steam fog, breath] • Ice fog - composed of small ice crystals. Can form in extremely cold air in areas (esp. valleys) with open sources of water vapor. Fog - cloud based at the ground Whiteman (2000) Whiteman photos Cloud Classification Genera, Species,Varieties Heights, Shapes, Composition Cloud classification depends on the Height of the cloud base Consider cloud base heights somewhat flexible. An altocumulus might be considered a stratocumulus by an observer on a nearby mountaintop. Cloud Height Category Cloud Base Height (above ground level, mid-latitudes) Low below 6,500 ft below 2,000 m Middle 6,500 - 23,000 ft 2,000 - 7,000 m High above 16,000 ft above 5,000 m Note the overlap between middle and high cloud base heights. The boundary between middle and high clouds is higher near the equator and lower in the polar regions. Cloud classification depends on the overall Shape of the cloud stratiform clouds “Stratus” – layered, large horizontal extent cumuliform clouds “Cumulus” – heaps cirriform, fibrous clouds “Cirro-” – bundle of hair, featherlike, silky Cloud classification depends on the Composition (liquid, ice, or both) Cirrus are ice clouds, altocumulus are liquid water clouds ‘undersun’ Whiteman photo Cloud classification (11 types or “genera”) Cloud Height Cloud Shape Low Middle Stratiform (strata=”layer”) Stratus (St) Altostratus (As) Cumuliform (‘piled’ or ‘heaped’) Cumulus (Cu) Altocumulus (Ac) Mixed (“layered piles”) Stratocumulus (Sc) Precipitating, without lightning Cirrostratus (Cs) Cirrocumulus (Cc) Cirrus (Ci) Fibrous Cumuliform clouds of great vertical development High Towering cumulus (Tcu) Cumulonimbus (Cb) Nimbostratus (Ns) High clouds Cirrus (Ci) © Burroughs et al. (2002) © S. W. Hoch Cirrus (Ci) © S. W. Hoch Cirrostratus (Cs) © S. W. Hoch Cirrocumulus (Cc) Cu elements less than one finger width (otherwise Ac) © Burroughs et al. (2002) Mid-Level Clouds Altostratus (As) © Burroughs et al. (2002) Altostratus (As) © S. W. Hoch Altocumulus (Ac) Cu elements more than one finger width (otherwise Cc) © Burroughs et al. (2002) Altocumulus (Ac) Mackerel sky Cu element larger than 1 finger width © Burroughs et al. (2002) Low Clouds Stratus (St) © Burroughs et al. (2002) Stratocumulus (Sc) © Burroughs et al. (2002) Cumulus (Cu) © S. W. Hoch MultiLevel Clouds Cumulonimbus (Cb) © Marc Attinasi Cumulonimbus (Cb) © Burroughs et al. (2002) Nimbostratus (Ns) © S. W. Hoch 14 Species 14 Species (1) ... fibratus – hairlike, striated, separated filaments (cirrus fibratus, cirrostratus fibratus) Cirrus fibratus © Bernhard Mühr Cirrus fibratus © Bernhard Mühr 14 Species (2) ... cirrus uncinus – no gray parts, comma-like shape topped with a un-rounded hook or tuft Cirrus uncinus © Bernhard Mühr 14 Species (3) ... cirrus spissatus – dense cirrus, grayish in color, dense enough to veil the sun, conceal its outline or even hide it. Cirrus spissatus © Gordon Richardson (http://www.capetownskies.com) 14 Species (4) ... castellanus – (‘castle’, turreted) – at least a fraction of the cloud’s upper part presents some vertically developed cumuliform proturbances (which are taller than wide) stratocumulus castellanus, altocumulus castellanus, cirrus castellanus, cirrocumulus castellanus Altocumulus castellanus © Bernhard Mühr 14 Species (5) ... floccus – each cloud element is a small tuft, the lower part is more ragged an accompanied by virga Altocumulus floccus virga © Bernhard Mühr Cirrus floccus virga © Bernhard Mühr 14 Species (6) ... stratiformis – clouds with a extensive horizontal development Cirrocumulus stratiformis © Bernhard Mühr 14 Species (7) ... nebulosus – nebulous, showing no distinct detail Cirrusstratus nebulosus Stratus nebulosus © Bernhard Mühr © Bernhard Mühr 14 Species (8) ... lenticularis – (‘lentil’-shape) – the Mountain cloud! Altocumulus lenticularis © Ronald G. Warfield photo, 1999, Mt. Rainier 14 Species (9) ... fractus – irregular small cloud elements presenting a ragged, shredded appearance Stratus fractus © C. D. Whiteman Cumulus fractus © Bernhard Mühr 14 Species (10) ... cumulus humilis – (“fair weather cloud”) a cumulus with limited vertical extent. Cumulus humilis © Bernhard Mühr 14 Species (11-12) ... Cumulus mediocris – moderate vertical development – uppermost sproutings not well marked Cumulus congestus – a strongly sprouting cumulus with generally sharp outlines and sometimes great vertical extent Cumulus mediocris Cumulus congestus © Bernhard Mühr © Bernhard Mühr 14 Species (13-14) ... Cumulonimbus calvus – Cb evolving from Cumulus congestus: the protrusions in upper portion loose their cumuliform outline (water ice). © Bernhard Mühr Cumulonimbus cappilatius – upper portion formed by cirriform parts, as an anvil or plume © Bernhard Mühr Most common cloud species and varieties CLOUD TYPE SPECIES VARIETIES Cirrus (Ci) uncinus, fibratus, spissatus, castellanus intortus, radiatus, vertebratus Cirrostratus (Cs) nebulosis, fibratus Cirrocumulus (Cc) castellanus, floccus, lenticularis undulatus Altocumulus (Ac) castellanus, floccus, lenticularis translucidus, opacus, undulatus, perlucidus Altostratus (As) - translucidus, opacus Nimbostratus (Ns) - - Stratocumulus (Sc) castellanus, lenticularis perlucidus, translucidus, opacus Stratus (St) fractus, nebulosus Cumulonimbus (Cb) calvus, capillatus Cumulus (Cu) fractus, humilis, mediocris, congestus Sources • Photographs from Ronald L. Holle, Brooks Martner, Edward Hindman III, and others are copyrighted. • A fantastic source of cloud photographs: Mühr, B., 2000: Der Karlsruher Wolkenatlas, Karlsruhe, Germany. CD ROM and web archive of cloud photographs at www.wolkenatlas.de • • http://www.capetownskies.com • Burroughs, W. J., et al., 2002: A Guide to Weather. Fog City Press, San Francisco, 288pp. Rangno, A. L., 2003: The Classification of Clouds. Chapter 21 in Handbook of Weather, Climate, Physical Meteorology, Weather Systems and Measurements. T. D. Potter and B. R. Colman (Eds.), John Wiley and Sons, Inc..
