AOS 3 Final Flashcards
What does planetary scale circulation mostly result from?
1) The difference of temperature between the equator and the poles (PGF)
2) The rotation of the planet (Coriolis)
3) Distributions of land and water over the planet (friction)
Describe the polar front
Cold air from the pole meets warmer air from the subtropical high at the polar front
Upper winds are well-predicted within the ________ but completely off for the _________
Hadley cell, Ferrel cell
In which direction does the air in the polar jet stream
flow in the Northern Hemisphere?
From west to east
Compare the polar jet stream and subtropical jet stream.
- Polar jet is very strong (110 mph in the winter) & effects US weather development
- Subtropical jet is much weaker & brings warm moist air to the US
Describe rossby waves
- The largest of the atmospheric long waves
- three to seven Rossby waves circle the globe at any one time, and each has its own wavelength and amplitude
- Although they have preferred anchoring positions they do migrate eastward (very slowly)
What happens when rossby waves “break”?
- seen as oscillations in the polar jet stream
- By moving the jet stream around, they can affect the weather
- “Breaking” Rossby waves can be considered a source of low and high pressure centers
What happens to ice crystals in the Bergeron process
Ice crystals grow rapidly at the expense of supercooled droplets (via net deposition and net evaporation)
Describe the process of precipitation.
- Unsaturated air rises and cools by adiabatic expansion, reaching saturation
- Presence of CCN allows for condensation, leading to formation of tiny droplets
- Droplets grow by additional condensation
For it to rain, droplets need to fall ________ than the vertical velocity in the updraft
faster
Describe the terminal velocity state of equilibrium
drag force equals gravitational force
Describe Collision Coalescence
- Warm clouds grow
- cloud droplets collide and stick together
- Promoted by large collector drops, which have high terminal velocities so they fall faster and collide with smaller drops
What is riming?
liquid water freezes onto ice crystals
What is aggregation?
ice crystals collide and merge via thin coating of liquid water (ice crystals come together to form snowflakes)
What limits the growth of ice particles by the Bergeron process?
- amount of supercooled water in the cloud
- time an ice particle remains in the cloud
Describe snow crystals.
- single crystals
- depend on temperature and degree of supersaturation (for ice)
Describe snowflakes. How do they differ for warm/cold clouds?
- aggregates of snow crystals
- mostly formed by riming in warmer clouds and form dense wet snowpack (snowballs)
- formed by aggregation in colder clouds making less desne powdery snowpack (skiing)
What is lake effect snow?
- Develop as the warm lake waters evaporate into cold air
- Friction over land reduces winds and creates a lifting mechanism downwind from the lake
Compare rain in warm and cool clouds.
- Cool clouds:
Most middle-latitude precipitation starts out as snow, then melts to rain - Warm clouds:
Predominant in the tropics, starts and falls as rain
Compare graupel and hail
Graupel: Rimed ice crystal
Hail: Concentric layers of ice built around graupel (wet growth results in solid ice)
Both results from in-cloud processes!
What are possible types of precipitation that could originate from a cold cloud?
- Rain
- Snow
- Hail
- Graupel
- Freezing rain
- Sleet
Compare the different spatial scales
Global Scale
- planetary waves
- hadley cell
Synoptic scale
- extratropical cyclones
- weather systems
Mesoscale
- thunderstorms
- tornadoes
(smaller length and time scales as you move down)
Describe the single-cell model
- Simplified model of the general circulation proposed by Hadley (1735)
- Based on idealized water planet with no effects of rotation (no CF, no friction)
- Deflection by Coriolis
- One single cell in each hemisphere
- First model of a thermally driven circulation
Describe the three-cell model
- Improved model of the general circulation proposed by Ferrel (1865)
- Each hemisphere divided into three cells
- Not perfect, but more realistic thansingle-cell model
Describe surface winds
- Surface winds fairly well predicted (note that “westerlies”= from the west)
- Main differences are caused by land-water contrasts
What are air masses?
large volumes of air with “uniform” temperature and humidity
What are fronts?
boundaries between different air masses
What are source regions?
areas of the globe where air masses form
What is required for an air mass to form?
Long-term heating or cooling of large bodies of air must remain over a source region for a substantial length of time for an air mass to form (low and high latitudes)
Describe the basic characteristics of air masses and source regions
- Moisture:
* Continental (c) = dry
* Maritime (m) = humid - Temperature:
* Tropical (T) = warm
* Polar (P) = cold
* Arctic (A) = very cold
Is the position of the Polar Jet Stream more or less constant during each season?
No, rossby waves can cause the jet to meander
Describe the Maritime Polar from the Gulf of Alaska
- Cold, humid, unstable
- The main trajectory into US depends on the position of the Polar Jet Stream
- During winter, it can enter the US through California
- One of the two major sources of (winter) precipitation in California
- Already cold and humid + adiabatic expansion = precipitation
Why is California’s snowpack important?
- The snowpack is particularly important to California’s drought picture because when the snow melts, the water runs off and refills the state’s reservoirs
- provides roughly 1/3 of the state’s overall water supply
What happened in Winter of 2018 in LA?
- really dry winter for CA
- only 1 major precipitation event (jan 7-8)
- polar jet stream was basically locked in one position for all of December so there was almost no rain
- dipped to South for just a few days and there was rain
- shows jet stream position really determines if we have cold/wet or warm/dry winter
Describe the Maritime Polar Air Mass from Atlantic
- Cold, humid, unstable
- Nor’easters: usually the air mass reaches the coast when it is caught up in a strong extra-tropical cyclone
Describe the Maritime Tropical Air Masses
- develop over warm tropical waters.
- warm, moist (high dew points), and unstable near the surface
- precipitation/thunderstorm source in southeast
- only occasional precipitation during summer (bc of cold ocean current in Pacific)
What is the pineapple express (atmospheric rivers)?
- relatively long, narrow regions in the atmosphere that transport most of the water vapor outside of the tropics
- second major source of precipitation in California
What are the two main sources of precipitation in Southern California?
1) The maritime polar air mass from the Gulf of Alaska
2) Atmospheric rivers bringing moisture from the tropical Pacific Ocean
In terms of synoptic pattern development, what happens 7 to 10 days before a precipitation event?
7 to 10 days before event:
1) Heavy rain over far western pacific
2) moisture plume extends northeast
3) strong polar jet
4) strong blocking high
In terms of synoptic pattern development, what happens 3 to 5 days before a precipitation event?
3 to 5 day before event:
1) Heavy rain shifts east
2) mixture plume extends further northeast
3) split jet forms
4) block weakens and shifts westward
In terms of synoptic pattern development, what happens at the time of a precipitation event?
Precipitation event:
1) Heavy rain shifts
2) deep tropical moisture plumes
3) extend jet
4) deep low heavy rain and possible flooding
What are reservoir conditions and droughts in California like right now?
Drought:
- Bad drought last year
- basically none right now
Reservoir conditions:
- Most reservoirs in the state are above the historical average
- This is in part due to the snow from last winter
What type of clouds is Collision Coalescence most efficient in?
clouds with large distribution of droplet sizes and strong updrafts
________ occurs when a mountain range forces air to rise.
orographic lifting
What is the most common mechanism of cloud formation?
lowering the air temperature to the dew point by adiabatic cooling of rising air
You would most likely expect a rain shadow on which?
- west side of the Andes.
- west side of the Coast Range in California.
- west side of the Sierra Nevada Mountains.
- east side of the Cascade Mountains in the Pacific Northwest.
east side of the Cascade Mountains in the Pacific Northwest.
What type of air will keep rising after an initial upward push?
statically unstable air
What type of air neither rises on its own following an initial lift nor sinks back to its original level?
statically neutral air
When the ELR exceeds both the DALR and the wet adiabatic lapse rate of a parcel of air, that air parcel contains what type of air?
absolutely unstable air.
When is the lower atmosphere most likely to have the steepest ELR?
mid-day
What is the most important mechanism for stopping the rise of unstable air parcels?
encountering a layer of stable air
Clouds that are high and are always composed entirely of ice crystals are called what?
cirrus
In what region is Collision-coalescence the predominant cause of precipitation?
the tropics
What is the process by which supercooled water droplets freeze onto falling ice crystals called?
riming
The collision-coalescence process is dependent upon what?
dependent upon the different downward velocities of different-sized droplets
Aggregation is facilitated by what?
a thin coating of water on ice crystals.
Which of the following cloud constituents would have the highest terminal velocity?
- raindrops
- hailstones
- ice crystals
- condensation nuclei
hailstones
What is the most important principle underlying the Bergeron process?
For a given temperature, the saturation vapor pressure of ice is less than that for supercooled water.
Lake-effect snowfall requires what?
requires that the lake be relatively warm.
What does rain usually begin as in the midlatitudes?
snow
What are 3 processes snow results from?
- deposition.
- riming.
- aggregation.
What scale do cyclones, anticyclones, troughs, and ridges, covering hundreds or thousands of square kilometers, occur on?
Synoptic scale
Meridional flow is characterized by flow that is ________; while zonal flow is characterized by flow that is ________.
north/south; west/east
List the four scales of atmospheric motion from largest to smallest
planetary, synoptic, meso, and micro
What does the hadley cell model say happens to air and where does it say it happens?
air rises at the equator and sinks at the poles
What area does the hadley cell actually cover?
just areas near the equator
What amount of precipitation is there in areas close to the ITCZ?
they receive abundant precipitation
What are the southward bulges in the patterns called? What are the northward bulges called?
Troughs (southward) and ridges (northward)
The polar front is a region marked by _________.
a sharp change in horizontal temperature
Winds in the upper atmosphere are…
- faster in summer than in winter in both the northern and southern hemisphere.
- westerly in both the northern and southern hemisphere.
- westerly only in the southern hemisphere.
- westerly only in the northern hemisphere.
westerly in both the northern and southern hemisphere.
Westerly winds in the upper atmosphere at mid-latitudes in the Northern Hemisphere
- are stronger in summer than in winter.
- are the reason most mid-latitude storms move from west to east.
- are moving perpendicular to 500 mb contours.
- are a result of a pressure gradient that moves air from the poles toward the equator.
are the reason most mid-latitude storms move from west to east.
The Ferrel Cell is associated with the ________
mid-latitudes
What are jet streams?
bands of high-speed wind found at elevations of 9-15 km
In which direction do jet streams generally travel?
west to east
Where are the two main hemispheric jet streams located?
between 50-60 degrees latitude and at about 30 degrees latitude
What are rossby waves?
major undulations in the path of a jet stream
How can the jet stream return to normal zonal flow after Rossby waves build?
through separation of a mass of cold air from the jet stream
The Hadley model of atmospheric circulation assumes __________.
a planet covered entirely by water.
The Hadley cell…
- creates a high-pressure area at the equator.
- does not account for the formation of trade winds.
- originates with strong solar heating at the equator.
- does not explain upper air movement in the troposphere.
originates with strong solar heating at the equator.
The northeast trade winds are the result of what?
air flowing from the subtropical high to the ITCZ
Usually, the pressure gradient force would be strongest at what level?
700 mb level
Which of the following best defines an air mass?
- A large body of air containing fronts
- A large body of air with similar temperature and moisture characteristics
- A large body of air with uniform temperature and no precipitation
- A large body of air residing over a water mass
A large body of air with similar temperature and moisture characteristics
Where do maritime air masses originate?
over water?
Which air masses are cold?
polar and arctic
Which air masses are warm and humid?
tropical and maritime
Which air masses are warm and dry?
continental and tropical
Which air masses originate at high latitudes?
polar and arctic
Continental is a term referring to _______
dry air masses
The following air masses are listed in what order?
- a wintertime cP air mass
- a wintertime mP air mass,
- a wintertime mT air mass
- a summertime cT air mass
coldest to warmest
Rainstorms are generally shorter when ________ comes in quickly and collides with ________.
a cold air front, a warm air front
When warm air collides with a cold air front, its slow journey up the slope of the cold air front causes what?
longer rains
Where are air-mass source regions least likely to be found?
middle latitudes (because the weather is to variable)
Most of the air masses in the central part of the United States are either _______ or _______.
continental polar or maritime tropical
Which of the following best describes a front?
- A narrow boundary separating different air masses
- A narrow boundary between air masses where cloudiness occurs
- A narrow boundary between air masses where precipitation occurs
- A narrow boundary separating cold air from colder air
A narrow boundary separating different air masses
If you observe short, intense, scattered rainfall as a front passes, you are likely to be experiencing what?
A cold front
What do we find between a cold front and a warm front?
a warm, moist, and unstable air mass
What type of front has a mass of warm air cut off from the surface?
occluded front
Why do the sources of air masses occur only in low and high latitudes?
middle-latitude weather is too variable.
Northeasters often bring what?
heavy snowfall
Which air mass is responsible for bringing virtually all of the moisture that impacts the United States east of the Rocky Mountains?
maritime tropical
After passing over a series of mountain ranges, what happens to maritime polar air?
it becomes drier
Which of the following best describes midlatitude cyclones that move along the U.S. East Coast and bring moist maritime air towards New England, often producing cold winds and heavy snowfall in winter?
- Southeasters
- Northeasters
- Drylines
- Overrunning
Northeasters
Which front does not separate tropical from polar air masses?
occluded front
________ fronts usually have showery precipitation while ________ fronts usually have continuous precipitation.
cold, warm
What is the first type of cloud an observer will see when a warm front is approaching?
cirrus
