ATM 10 Severe and Unusual Weather Prof

Home , Convection, Mammatus cloud, Thermal

ATM 10 Severe and Unusual Weather Prof. Richard Grotjahn L 4 http://canvas.ucdavis.edu Lecture topics:

• Heat • 3 ways to transfer heat energy • Radiative energy properties • Cloud types – Four categories of common clouds – Unusual types

th References to “Ahrens” mean: ‘Meteorology Today’ by Donald Ahrens, 7 Ed. Heat – some basic concepts, part 1 • Heat is energy being transferred from one object to another • Candle illustrates 3 types heat energy transfer: • Conduction (left figure) heat flows in rod (red arrow) • Convection (middle figure) blue arrows show hot air rising • Radiation (right figure) purple arrows show light and infra red radiation (radiant energy) emitted.

Figure 2.5 (Ahrens) Heat – some basic concepts part 2

• Heat felt or measured is “sensible” heat

• Heat used to change the state of an object is “latent” heat. (Changes of state: gas – liquid - solid) Changes of State – water

G. Moore photo Figure 2.4 (Ahrens)

All 3 states of water occur in Why do the states matter? the atmosphere: Solid: ice particles, snow, hail, sleet Liquid: rain, cloud droplets Gas: water vapor Latent & Sensible Heat

Heat energy changes between vapor, liquid, and solid phases.

Gas has most molecular motion, liquid has less, solid (ice) has the least.

Since temperature constant during a change of phase we say LATENT heat energy changes to reflect the change in molecular motion.

Example: As liquid water becomes vapor (i.e. evaporation) it absorbs heat to make the liquid molecules have the more rapid motion of a gas.

Figure 1.14 Heat Transfer by Convection (no cloud)

Figure 2.6 (Ahrens) Convection: heat energy moving air from hotter to cooler areas. Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence cools. Example in figure is dry convection since no cloud is formed.

Advection is heat energy transport in the horizontal by winds. Heat Transfer by Convection (with cloud)

G. Moore photo Figure 2.4 (Ahrens)

All 3 states of water occur in Why do the states matter? Because heat is transferred when the atmosphere: Solid: ice particles, snow, hail, the state changes. Latent heat is released when water sleet Liquid: rain, cloud droplets vapor becomes billions of cloud Gas: water vapor droplets during condensation; this warms the air and encourages taller cloud growth. Heat Transfer by Radiation

All objects have T>0 K & so emit radiation. Figure 2.7 (Ahrens)

Sun’s radiation travels as waves of photons across space

Wavelength is distance between successive crests

Those photons release their energy when absorbed by the earth.

Gases, aerosols, and dust For hotter objects: 1) radiation is greater absorb sun’s rays. 2) Peak wavelength is shorter (‘yellow’ for sun, infrared for Earth) Demo: Radiometer – heat transfer by radiation

A radiometer works by light rays striking black and white panels.

White panels reflect the light; Black ones absorb it. So, black ones heat up more than white.

Tiny amount of air inside heated more near black panels. Air molecules move faster when warmer and so strike black surface harder than white surface causing pinwheel to spin.

Shows: radiation energy, temperature as molecular kinetic energy. ? ?

Will it turn if we blow ‘really hard’ on it? ? ? What if we use a hair drier instead of a light? Heat Transfer by Conduction Conduction: heat energy transferred from molecule to Figure 16.15 molecule.

Conduction: air exchanging heat with underlying surface.

Example: In Fig. 16.15 radiation cools ice. Thin layer of air (thinner than drawn) in contact with ice cap is cooled by conduction, becomes very cold. (Fig. 16.15 discussed more later) Clouds

• Clouds can be mainly composed of: – liquid water droplets or – ice particles • Formed when air becomes saturated usually when air rises. (One exception to this)

Wetterhorn from Uncompahgre Peak, CO © R Grotjah Liquid versus Ice Cloud You can tell by looking if a cloud is composed mainly of water droplets or ice particles

Florida Everglades © R. Grotjahn Photo © R. Grotjahn Liquid water clouds look ragged or hard edged. Ice clouds look fibrous. Common Cloud Categories

10 Common Cloud Types

• 10 combinations of these 5 names: • Cirrus : wispy or hair-like (often high) • Alto: middle elevation • Stratus: sheet-like or uniform layered. • Cumulus: puffy, heaped, vertical~horizontal • Nimbus: precipitating

4 Common Cloud Groups

(10,000-60,000 ft) (surface-6,500 ft) (3-18 km) (0-2 km)

(6,500-25,000 ft) (2-8 km)

Ranges overlap because a given T occurs at a lower elevation in polar regions than in tropics Hence, ice can form at a lower elevation in polar regions than in tropics. Uncommon Cloud Categories Cirrus Types

Desolation Pks, CA © R. Grotjahn Altocumulus

Mt. Rainer © R. Grotjahn Wairikori Beach New Zealand © R. Grotjahn Stratus Big Sur, CA © R. Grotjahn Altostratus & stratus Nimbostratus Paria Canyon © R. Grotjahn Wilson’s Prom, Australia © R. Grotjahn

Mt. Cook, NZ © R. Grotjahn Stratocumulus, cumulus

Photo © R. Grotjahn Cumulus congestus, cumulonimbus

Note precipitation from the anvil  Summary of major cloud types What’s most Altocumulus Common?

Catskill Creek. T. Cole Odd clouds: Human sources

U.K. © Steve F

Contrail “fumulus” from a plume Odd clouds: severe weather © G. Moore

Mammatus

Shelf cloud Roll cloud

• Only cloud that grows by downward moving air • Down motion caused by evaporation of drops that cools the air until it reaches saturation (and also sinks) Odd clouds: made by forced-uplift

Altocumulus lenticularis • Or “Wave clouds”

 from above

From below   From below

• First new type of cloud proposed in 60+ years. • Technically, ‘asperatus’ is a ‘supplementary feature’ on an existing cloud type, like ‘undulatus’.

• ‘cumulus humorus’ • OK, these aren’t really cloud types, but they are fun. – Bunny? – Fish? (over water!) – Valentine flowers? – how many? Odd Clouds: continued

• ‘cumulus humorous’ • OK, these aren’t really cloud types, but they are fun. – My point? – Clouds soar and inspire… – I hope you enjoy them a little bit more now. Cloud Development - Cap Clouds • Often associated with Strong winds

Cap clouds & wave clouds indicate a stable atmosphere.

But what does “stable atmosphere” mean? (See next lecture…) Lecture Summary: • Heat – Heat is energy being transferred from one object to another – Sensible heat is felt (seen as a temperature change) – Latent heat is what is need (absorbed or released) to have a change of state. The temperature does not change during a state change so the heating is ‘latent’. • 3 ways to transfer heat energy – conduction: transfer of molecular vibration – convection (vertical) or advection (horizontal) transport of molecules – radiation: transfer of energy by a form of light: visible light for sun; infrared (IR) for earth • Radiative energy properties – all objects with T>0o K emit radiation, amount increases rapidly as T increases – wavelength of peak in radiation decreases as T increases • Cloud basics: – Formed by saturated air – Saturation usually created by rising air. (exception: mammatus cloud) • Cloud types – 4 categories of common clouds: low, middle (alto-), high (cirr-), tall (cumul-) – altocumulus most common. – 5th category: add the prefix: ‘Nimbo’ to mean cloud is precipitating – 10 basic names: cirrus, cirrocumulus, cirrostratus, altostratus, altocumulus, stratus, stratocumulus, nimbostratus, cumulus, cumulonimbus. – Cloud appearance: ice clouds fibrous while water clouds hard-edged or ragged – Unusual types to note: altocumulus lenticularis (wave clouds), mammatus, tornado, roll cloud, shelf cloud. End of lecture 4

I hope our cloud show made you smile! Next time: stability and how a cloud forms

• Pour water in paper cup • Light candle under cup. • Watch what happens… • Why didn’t it burn? • Heat conducted through paper, then water removes it by convection. (water)

(cup)