ATMO 105 Test 2

• Understand the processes that promote the growth of cloud droplets,

Condensation: Water vapor → tiny droplets (up to ~20 μm).

Collision-coalescence: Droplets collide and merge → large raindrops (millimeters).

Ice processes: Ice crystals grow at the expense of water droplets → snow or rain after melting.

Understand the relationship between droplet size and likelihood of evaporation prior to

hitting the surface,

Small droplets → high likelihood of evaporation before reaching the surface.

Large droplets → low likelihood of evaporation, more likely to reach the surface as rain.

Understand the relationship between drop size, max velocity of droplet descent, uplift

velocity, and likelihood of droplet growing to precipitation size,

Its terminal velocity must exceed the updraft velocity to start falling.

It must collide and merge with smaller droplets efficiently during descent.

If too small, it may stay suspended or evaporate before growing.

Be able to diagnose probability of drizzle vs. rain using figure (pg. 82) and know

relationship between cloud thickness and probability of drizzle vs. rain

Drizzle: Thin clouds, small droplets, slow growth, low terminal velocity.

Rain: Thick clouds, larger droplets, efficient collision-coalescence, high terminal velocity.

Rule of thumb: The thicker the cloud, the higher the probability of rain instead of drizzle.

Supercooled water

liquid water that exists below 0 °C.

Latent Heat,

energy absorbed or released by a substance during a phase change

Collision and Coalescence,

the process by which larger cloud droplets collide with smaller droplets as they fall and merge (coalesce) into bigger droplets.

Bergeron Process,

explains how ice crystals grow at the expense of supercooled water droplets in clouds below freezing

• Understand how cloud height affects the composition of the cloud (ice vs liquid water),

Low = liquid water, middle = mixed liquid/ice, high = mostly ice.

• Understand what characteristics are used to classify clouds,

Their form and height

• Understand the relationship between pressure and temperature,

As pressure increase so does temperature

Cloud,

a visible accumulation of liquid water droplets, ice crystals, or a mixture of both suspended in Earth's atmosphere

Fog,

a visible accumulation of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface, essentially a cloud that touches the ground

Adiabatic process,

a change in an air parcel's temperature and volume without any heat exchange with its surroundings

Diabatic process,

a change in an air parcel's temperature that is caused by the exchange of heat with its surroundings, rather than by pressure-induced expansion or compression

Cloud condensation nuclei,

how atmospheric water vapor condenses onto tiny airborne particles called cloud condensation nuclei (CCNs) to form cloud droplets and, ultimately, clouds

low clouds,

clouds with bases at or below approximately 6,500 feet (2,000 meters) above the Earth's surface Stratus, Stratocumulus, Cumulus, and Cumulonimbus

middle clouds,

forming between approximately 6,500 and 23,000 feet (2,000-7,000 meters). The three main types of middle clouds are altocumulus, altostratus, and nimbostratus

high clouds,

cirrus, cirrocumulus, and cirrostratus. These clouds are found above 20,000 feet made of ice crystals

clouds of vertical development,

those that form from convection (rising air) and extend through multiple atmospheric layers, rather than being layered horizontally

• Be able to identify sources/mechanisms of air rising/lifting in the atmosphere,

Orographic lifting, frontal wedging, convergence, and localized convective lifting

• Understand why the moist adiabatic lapse rate (MALR) is less than the dry adiabatic lapse rate (DALR)

as saturated air rises and cools, the water vapor within it condenses into liquid water droplets, releasing latent heat

Air parcel -

a conceptual, imaginary pocket of air that is treated as a self-contained, uniform unit with its own temperature, pressure, and humidity

atmospheric lifting -

the upward vertical movement of air, a critical process that causes air to cool, condense its moisture into clouds, and often lead to precipitation

• Understand the relationship between stability and if a parcel will rise or sink.

An air parcel rises if it is warmer (less dense) than its surroundings and sinks if it is colder (denser) than its surroundings

• Understand under what conditions favor cloud formation/convection.

moisture, a lifting force, and atmospheric instability

Positive lapse rate

the atmospheric condition where temperature decreases as altitude increases

negative lapse rate (inversion),

occurs in a temperature inversion, where air temperature increases with height instead of decreasing, as is normal

Isothermal lapse rate,

occurs when there is no change in temperature with an increase in altitude, resulting in a lapse rate of zero

Inversions

an atmospheric condition where a layer of warm air sits above cooler air, trapping it near the ground and preventing normal air mixing

Dew point depression

the difference in between the air temperature and the dew point temperature

cloudy layer,

a continuous or fragmented horizontal sheet of clouds, all sharing the same base altitude and appearing as a distinct layer in the sky

mixing ratio

the ratio of the mass of water vapor to the mass of dry air in a given air parcel

saturation mixing ratio,

how much water vapor the air could hold if it were completely full (saturated).

dry adiabats,

describes the temperature change of an air parcel as it rises or sinks in the atmosphere without exchanging heat with its surroundings

Moist adiabats,

lines on thermodynamic diagrams (like a Skew-T Log-P chart) that show how the temperature of a saturated air parcel changes as it rises and cools

Isotherms

a line on a weather map or chart that connects points of equal temperature at a specific time or over a given period

Isobars,

a line on a weather map connecting points of equal atmospheric pressure

inversions: radiation,

occurs when the ground rapidly cools on a clear, calm night by radiating heat into space, which in turn cools the air directly above it

frontal inversion

when warm air lies above cooler air

Subsidence,

a type of temperature inversion where air sinks over a large area, warms due to adiabatic compression, and creates a layer of warmer air aloft, trapping cooler air below

Stratospheric.

occurs naturally and inherently within the stratosphere, the atmospheric layer from about 15 to 50 km (9 to 31 miles) altitude, where temperature increases with height due to the absorption of UV light by ozone

What is stability?

Condition of the environment; determined by comparing ELR to DALR & MALR.

Stability Criteria

ELR < MALR = Absolutely StableMALR < ELR < DALR = Conditionally UnstableELR > DALR = Absolutely Unstable

What is a lapse rate?

Rate of temperature change with height.

Difference between ELR, DALR, MALR?

ELR = actual atmosphere, DALR = dry parcel cools faster, MALR = saturated parcel cools slower (latent heat).

How to destabilize atmosphere?

Cooling aloft, surface heating.

How to stabilize atmosphere?

Warming aloft, cooling surface at night, cold air over warm ground.

What happens to T & Td over a mountain?

Up: T decreases, Td decreases slower. Down: T increases, Td increases slower.

Why do cumulonimbus clouds have flat tops & bottoms?

Bottom = LCL, Top = Tropopause.

What controls cumulus cloud base height?

Difference between T & Td (small = lower, large = higher).

Ordinary thunderstorm requirements?

Moist surface air, unstable atmosphere, lifting mechanism, weak shear.

What is a multicell thunderstorm?

Group of single cells with moderate vertical shear.

What is a supercell?

a large, severe thunderstorm that rotates and can produce hail, strong winds, and tornadoes.

NWS severe thunderstorm definition?

Hail > ¾ in, winds > 50 kt, or tornado.

What is a gust front?

Cool downdraft spreads out; causes wind gusts, temp drop, pressure rise, turbulence.

Watch vs. Warning?

Watch = conditions favorable; Warning = severe weather occurring.

Why do storms change with seasons?

Changes in temperature, moisture, and instability.

Severe storm modes?

Air mass, Bow echo, Squall line, Supercell, Multi-cell, Mesoscale Convective Complex.

Parts of a supercell?

Updraft, Downdraft, Mesocyclone, Anvil.

How are tornadoes classified?

Enhanced Fujita Scale (Damage)

How to use a Skew-T?

Find T & Td → DALR to LCL → MALR up → compare to ELR.

What is CAPE?

Convective Available Potential Energy - Energy: area where parcel T > environment.

What is CIN?

Inhibition below LFC.

What is LCL?

Level where T = Td.

What is LFC?

Height where parcel T > environment.

What is EL (equilibrium level)?

Height where parcel T = environment again.

Q: How does cloud height affect cloud composition?

A: Low = liquid water, middle = mixed liquid/ice, high = mostly ice.

Q: What is the Beaufort scale used for?

A: Estimating wind speed from surface observations.

Q: Why did adding smoke produce a thicker cloud in the lab?

A: Smoke provided cloud condensation nuclei (CCN) for water vapor to condense.

Q: How do you lift a parcel over a mountain?

A: Lift dry adiabatically to LCL → moist adiabatically to peak → descend dry adiabatically.

Q: Why is the leeward side of a mountain drier and warmer?

A: Descending air warms dry adiabatically (rain shadow effect).

Q: What does absolute stability mean?

A: ELR < MALR → parcels sink.

Q: What does absolute instability mean?

A: ELR > DALR → parcels rise.

Q: What is conditional instability?

A: MALR < ELR < DALR → depends if parcel is saturated.

Q: What does an inversion mean?

A: Temperature increases with height → very stable.