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Clouds AOSS 102: Extreme Weather Lecture 10 30 September 2015 Temperature/ Humidity Measures Dry bulb temperature: temperature of the air Wet-­‐bulb temperature: lowest temperature that an object can reach by evaporaKng water into the air Dew point: temperature to which the ambient air must be cooled to reach 100% relaKve humidity wet sock What is Their RelaKonship? Dry bulb T ≥ Wet bulb T ≥ Dew point T All three temperatures are same if the air is saturated (100% relaKve humidity). Check out some measurements: Check the difference between the dew point and wet bulb T: hPp://www.srh.noaa.gov/epz/?n=wxcalc_rh hPp://www.eol.ucar.edu/cgi-­‐
bin/weather.cgi?
site=fl&units=english Why are there water droplets on the soda can? Short Answer
Reminder: The Five Types of Fog
(a,b,c) Created by cooling of air (c) Upslope fog (d) EvaporaKon (mixing) fog (d,e) Created by evaporaKon (e) PrecipitaKon (frontal) fog Fog: An Example
Mul?ple Choice
Annual number of days with dense fog (Visibility < 0.25 miles) Fig. 4.9, p. 101
Image Quiz
Mixing can increase the rela?ve humidity and might create clouds
T = 12°C
e = 12 mb
RH = 86%
T = 24°C
e = 27 mb
RH = 91%
Clausius-­‐Clapeyron Graph Clausius-Clapyron Graph
Mixing Increases
Relative Humidity
T = 24°C
e = 27 mb
RH = 91%
e = 19.5 mb
RH = 95%
T = 12°C
e = 12 mb
RH = 86%
Clouds cloudappreciaKonsociety.org cloudappreciaKonsociety.org Great collecKon of cloud photos: hPp://australiasevereweather.com/photographs/index.php The Four Major Cloud Groups
DisKnguished by their alKtude and verKcal evoluKon Table 4.1, p. 104
Approximate Heights of Cloud Bases
The meaning of ‘High’, ‘Middle’ and ‘Low’ depend on the laKtude Table 4.2, p. 105
Image Quiz
Cirrus Thin wispy ice clouds blown by high winds into long streamers Fig. 4.11, p. 105
Cirrocumulus Ice clouds that appear as small, rounded white puffs, might be organized in long rows Fig. 4.12, p. 106
Cirrocumulus Here: organized in one cluster, cirrocumulus only covers small porKon of the sky cloudappreciaKonsociety.org Cirrostratus •  Very thin ice cloud •  Sun or moon can shine through •  Ice crystals bend the light: halo Altocumulus •  Appear as gray, puffy masses, someKmes organized in bands cloudappreciaKonsociety.org Altostratus •  Gray cloud without structure •  Oeen covers enKre sky •  Moon or sun might be dimly visible cloudappreciaKonsociety.org Nimbostratus (Low precipitaKng cloud) •  Dark-­‐gray cloud •  ConKnuously falling rain or snow (light to moderate) •  Visibility reduced cloudappreciaKonsociety.org Stratus • 
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Uniform grayish cloud Oeen covers enKre sky Typically no precipitaKon SomeKmes light drizzle cloudappreciaKonsociety.org cloudsonline.com Stratocumulus •  Low lumpy cloud layer •  Appears in rows or patches •  Blue sky in-­‐between cloudappreciaKonsociety.org Cumulus (Clouds with verKcal development) •  Pieces of ‘floaKng coPon’ with flat base and sharp outlines •  Oeen develop on warm summer mornings, might grow verKcally cloudappreciaKonsociety.org Cumulonimbus: Thunderstorm Clouds Anvil (made of ice crystals) •  Top might extend to tropopause •  Violent up-­‐ and downdraes •  Lightning, thunder, tornadoes possible cloudappreciaKonsociety.org What type of cloud is this? Can you speculate how these clouds are generated? Short Answer
‘Man-­‐made’ Cirrus Clouds: Contrails