Final Flashcards
Three types of clouds
Stratus
Cumulus
Nimbus
Stratus characteristics
- wide flat layer of clouds
- stable ELR
- no vertical motion
Cumulus characteristics
- puffs/ piles of clouds
- unstable ELR.
- vertical motion
Nimbus characteristics
precipitating cloud (rain)
Low clouds are usually what type of cloud? What are they made of?
Stratus
- mostly liquid droplets
where are cirrus clouds located and what are they made of?
high, bases above 19,000 ft
mostly ice crystals
middle clouds are also called? What are they mostly made of
alto
- mostly liquid droplets
which clouds have violent updrafts, heavy precipitation and large temp differences?
cumulus or cumuliform
which clouds are associated with thunderstorms?
cumulonimbus
steps of precipitation (3)
- Unsaturated air rises and cools by adiabatic expansion, reaches saturation at LCL
- Presence of cloud condensation nuclei (CCN) allow for condensation, leading to water droplet formation
- Droplets grow by additional condensation
Droplets need to fall faster than the __________ in the _________.
vertical velocity, updraft
what is the equilibrium force that acts on a water droplet falling?
drag force equals gravitational force
when drag force = gravitational force, a water droplet has reached ________
terminal velocity
when a droplet is first released it has ______ velocity
zero
before raindrop reaches terminal velocity the droplet
is accelerating down because gravity is stronger than drag force (drag force proportion to velocity)
size of cloud droplet vs raindrop
500,000 cubic micrometers vs 5,000,000,000 cubic micrometers
Where do warm clouds occur? How does precipiation happen in warm clouds?
occur mostly in tropics and warm season in midlatitudes
collision- coalescence
- two droplets collide and merge
collision coalescence is promoted by large ________, which have high ___________
collector drops, terminal velocities
collision coalescence is more efficient in clouds with ______ distribution of droplet sizes and ______ updrafts
large, strong
Processes that lead to precipitation in cold clouds
- Bergeron process
- Riming
- Aggregation
stages of bergeron process
- saturation vapor pressure of ice is less than that of supercooled water (water vapor is saturated over
supercooled water, but supersaturated over ice) - water vapor molecules deposit directly onto the surface of the ice crystal, causing it to grow at the expense of nearby supercooled water droplets.
- ice crystal grows rapidly at the expense of supercooled droplets (net deposition and net evaporation)
a key aspect of the bergeron prcess is that saturation vapor pressure of ice is _____ than that of supercooled water
lower
what is riming?
liquid (supercooled) water freezing into ice
aggregation
ice crystals joining with each other (via thin coating of liquid water)
what limits the growth of ice particles by the bergeron process?
the amount of supercooled water in the cloud
the amount of time that ice particle remains in the cloud
snow crystals vs snow flakes
single crystals vs aggregates of snow crystals
what does the shape of ice crystals depend on?
temp and degree of saturation
what process causes the formation of snowflakes?
riming
What is the lake effect?
warm lake waters evaporate into cold air that comes from land, form clouds and precipitation
Warm clouds temp profile
above 0C
cool clouds temp profile
starts below 0C, precipitation starts out as snow then melts to rain, mostly middle latitude
what is graupel?
rimed ice crystals
what is hail?
concentric layers of ice built around graupel
what types of precipitation can originate from a cool cloud?
rain
snow
hail
graupel
freezing rain
sleet
top middle and bottom of cold/cool clouds, processes that cause precipitation?
top: glaciated, ice and vapor
middle: mixed ice and supercooled water droplets (bergeron process, riming and aggregation coexist)
bottom: liquid and vapor, collision coalescence
length and time scales, bigger to smaller
global
synoptic scale
mesoscale
microscale
global scale phenomena examples
- planetary waves
- hadley cell
weather at synoptic scale
- extratropical cyclones (mid latitude)
- weather systems(high & low pressure systems aka anticyclones and cyclones)
Weather at mesoscale
- thunderstorms
- tornadoes
microscale
- turbulence in clouds
- turbulence in the planetary
planetary scale circulation results mostly from (3)
difference of temp between the equator and the poles
rotation of the planet
distribution of land and water over the planet
what assumption does the single cell model make? why is the model important?
that the planet is covered in water & no deflection by coriolis
first model of a thermally driven circulation
three cell model names
hadley cell
ferrel cell
polar cell
at the equator the is a branch of _________ air. The bottom of this branch is known as the ______. It has _____ pressure and ________ precipitation
rising, Intertropical convergence zone (ITCZ)
low
heavy
between the hadley cell and the ferrel cell, there is a __________ jet accompanied by a sinking branch, at the surface under the jet there is a _______ _______. It has ________ pressure and is very ________.
subtropical
subtropical high
high
dry
between the ferrel cell and the polar cell there is the _____ jet. Under is the subpolar low. It has ______ precipiation
polar
much
True or false: surface winds are fairly well predicted by the three cell model
true
the main differences in surface winds are caused by
land-water contrasts
true or false: upper winds are well predicted in the ferrel cell but completely off for the hadley cell
False: upper winds are well predicted within the hadley cell but completely off for the ferrel
in which direction does the air in the polar jet stream flow in the northern hemisphere
from west to east
which is stronger: the polar jet stream or the tropical jet stream?
polar jet stream is much stronger, important effect in the development of weather systems in the US
Subtropical jet stream is much weaker and brings warm moist air to the US
True or false: the positition of the polar jet stream is more or less constant during each season
false. rossby waves can cause the jet to meander
what are rossby waves?
how many are there at any given time?
largest of the atmospheric long waves, in upper atmosphere, migrate eastward slowly
three to seven at any one time
rossby waves are seen as oscillations in the _______
polar jet stream
air masses are large columns of air with “uniform” ______ and _______
temperature and humidity
what is colder, polar or arctic air masses
arctic
explain the role of maritime polar air from the gulf of Alaska on weather in US
during the winter, enters the US through california and brings precipitation (cold and humid air expands adiabatically through orograhic lifting as it passes over mountain ranges)
depends on the position of the polar jet stream
How does the polar jet stream change from summer to winter?
higher in latitude in the summer
in the winter it oscillates more, dips down to form trough in the southern US
what are characteristics of the maritime polar air mass from the gulf of alaska?
Cold, humid, unstable
What causes winter precipitation in California?
Maritime polar air mass from gulf of alaska follows polar jet stream & atmospheric rivers such as the pinapple express (origins near hawaii)
Maritime polar: already cold and humid + adiabatic expansion = precipitation
- orographic lifting over the coastal
ranges, sierra nevada and rocky
mountains
Why was last winter in california very wet?
The position of the polar jet stream changed so that it brought maritime polar air from the Gulf of Alaska
what is the weather phenomenon caused by maritime polar air from the atlantic?
nor’easters: air mass reaches the coast when it is caught up in a strong extra-tropical cyclone
what are are nor’easters? how do nor’easters form?
midlatitude cyclones that form on the east coast
polar jet stream transports cold arctic air south from canada
gulf stream moves warm water from the gulf of Mexico northward
labrador current moves maritime polar air
what air mass is a major source of precipitation and thunderstorms in the southeastern US?
maritime tropical air from gulf of mexico and the atlantic
atmospheric rivers are ________ and _________ regions that transport most of the water vapor outside of the tropics
long, narrow
is california still in a drought?
No!
northern sierra snowpack vs southern sierra snowpack
southern sierra got more precipitation in 2022-2023
definition of a front
boundary between two air masses at the surface, bring changes in temp and humidity as one air mass is replaced by another
four types of fronts
cold front
warm front
stationary front
occluded front
cold fronts
air masses &
weather associated:
continental polar (cold, dry, stable), maritime tropical (warm, humid, unstable)
heavy precipitation (rain/snow)
rapid temp drop
order of cloud types as cold front approaches
cirrus
cirrostratus
cumulonimbus
where does precipitation happen in a cold front? warm fronts?
cold: at the front and directly behind
warm: ahead of the front
precipitation from cold front in more/less localized than clouds observed from satellite?
more
warm fronts
air masses &
weather associated:
maritime polar (cold, not as humid, stable)
maritime tropical (warm, humid, unstable )
slow predictable changes
light precip for days
frontal fog
warm from clouds in order of appearance
cirrus
cirrostratus
altostratus
nimbostratus
stratus
which has a larger band of clouds out in front of it, warm or cold front?
warm front, cold front has more localized bands and upward expansion instead of horizontal
stationary fronts are two _______ air masses side by side
unlike, do not have advancing air
doesnt have same north south movement
in an occluded front, the ______ front is slower than the ______ front. When the two fronts meet what happens? what remains at the surface?
warm, cold
warm air mass is displaced aloft
at the ground we have two cold air masses
what are the two types of occlusion and how do they work?
cold type occlusion and warm type occlusion
cold occlusion happens more inn the easteern part of the continent, where
a cold front (continental polar air) meets a warm front (maritime polar ahead)
cold air reaches cool air
warm occlusion happens more in western par of the country, where cold front (maritime polar) migrates to an area occupied by continental polar air
cool air reaches cold air
what is the name of the point where all three fronts meet in an occluded front?
triple point
what are drylines?
air masses:
weather associated:
boundaries between humid air and dry air, without large temp diffs
continental tropical (warm, dry, very unstable)
Maritime tropical (warm, humid, unstable)
thunderstorm development and
tornados because the combination of moisture contrast, atmospheric instability, lift mechanisms, and wind shear along drylines creates favorable conditions for the formation of thunderstorms
how does avogadro’s law apply to drylines and what we know about storm formation around drylines
tells us that dry air is more dense than sense air because water vapor molecules have less mass than oxygen and nitrogen
moist air lifts and can cause severe storms
what causes may gray and june gloom?
cool sea breeze produces moist marine layer, pushed onshore throughout may and june
moist air lifts and condenses into low clouds, causes drizzle if lifting is strong enough
clouds trapped by heat inversion
Steps of polar front theory
- Stationary polar front
- Frontal wave (cyclogenesis)
- Open wave (cyclogenesis)
- Mature cyclone
- Occlusion
- Cut off cyclone
Stationary polar front step of polar front theory
- continental polar air mass meets maritime polar air mass in the subpolar low pressure region
- air flows parallel to the front in the opposite direction
frontal wave step of polar front theory
- frontal wave forms a minor kink along the front, giving rise to a cold and a warm front
- low pressure center begins to form at the junction between two fronts
open wave step in polar front theory (cyclogenesis)
an open wave forms and low pressure
precipitation along both frontal boundaries
winds spiral inward and toward the low (friction)
mature cyclone step in polar font theory
low pressure center deepens (lower pressure at center, upper level divergence)
entire system moves toward east-northeast
cold front moves faster than the warm front, reducing the size of the warm sector
occlusion polar front theory
beginning of occlusion marks peak in cyclone intensity and wind speeds
fronts begin to occlude and cyclone intensity starts to decrease
cut off cyclone step in polar front theory
original front gradually disappears
new stationary front forms, leaving a cut-off weakened low pressure center
where does precipitation happen in the mature phase of a mid latitude cyclone
light precip in front of the warm front
havy precip behind the cold front
heavy precip near the low pressure center
what is vorticity?
spinning motion of air parcels, useful to describe the amount of rotation in the wind
what is relative vorticity?
relative vorticity is positive when the direction of rotation is the same as the plate’s (counterclockwise) and negtive if its clockwise
in a rossby wave, where is vorticity negative and positive?
bottom of trough is positive
top of a ridge is negative vorticity
_________ plays a key role in connecting rossby waves aloft to __________ at the surface
voritcity
cyclone patterns
where does convergence and divergence happen in a trough?
convergence in upper altitudes on the left and to the right there is divergence. This corresponds to vorticity increasing and then decreasing
difference between zonal height patterns and meridional height patterns
zonal height patterns prevent development of intense cyclones and promote mild atmospheric conditions at the surface
meridional height patterns support cyclone development as vorticity changes between troughs and ridges
(steering midlatitude cyclones)
upper level winds are about ___ as strong in the ______ than ________
2x, winter, summer
what are the two common paths that steer midlatitude cyclones across North America?
what jet stream do they follow
Alberta clippers (zonal flow and light precip, summer midlatitude jet stream)
Colorado lows (stronger storms and heavy precip, winter midlatitude jet stream)
how long is a mid latitude cyclone lifetime?
a few days
as the midlatitude cyclone gets closer to the top of the ridge , what happens?
weakening low due to lack of divergence aloft
what happens if anticyclones linger over a region for long periods of time?
drought
what weather phenomena is responsible for the santa ana wind conditions?
anticyclones
what are the 4 main types of lightning?
cloud to ground, cloud to air, intra-cloud, spider lightning
Steps of lightning formation
- Charge separation
- Stepped leader
- Ground spark
- Return stroke
what happens during the charge separation (lightning formation)?
positive and negative charges separate into different regions of the cloud
(usually, positive charges are at the top and negative at the bottom)
likely produced by interaction between ice crystals and hail
describe the stepped leader of lightning formation
rapid and staggered advance of a shaft of negatively charged air
usually not visible
what is the ground spark? (lightning)
as leader approaches the ground a spark is created
what is the return stroke of lightning?
when the leader and the spark connect a flow of electrons illuminates the cloud by strokes, or return strokes
stroke propagates upward
dart leader follows, producing other strokes
(lightning flash is the combination of strokes)
what is thunder?
air expands violently
- caused by sudden increase in pressure and temp
- lag in lightning strike and thunder due to the sound traveling slower than light
are negative lightning strokes stronger or weaker than positive?
negative are weaker
What are the key processes in the development of a thunderstorm?
- Source of moisture
- Unstable atmosphere
- Lifting mechanism to initiate updraft
- Vertical shear in wind
Key features of a thunderstorm:
warm updraft separated from cold downdraft (with heavy rain dragging air downward)
cool pool at of cold air that accumulates near surface
what does severe mean according to US nat weather service?
potential to threaten lives and property
contains:
hail with diameter of one inch or larger
winds in excess of 93km/h
tornadoes
characteristics of a single cell thunderstorm (7)
- most common and least destructive thunderstorm
- relatively small, localized, and short lived
lifetime of about one hour - not classified as severe
- form in the absence of wind shear, with weak. winds aloft
- form away from frontal systems, 6. triggered by surface heating or orographic lifting
- symmetric anvil
What scale do thunderstorms and tornadoes occur at?
mesoscale
What are mesoscale convective systems?
what are the two types?
organized clusters of thunderstorms
Mesoscale convective complexes (MCCs)
squall lines- linear bands of thunderstorms
severe thunderstorms with lifespan of 12 hours or more
what is a derecho and what causes them? How long do they last?
large scale horizontal winds
produced by strong downdrafts associated with MCCs
can last several hours, winds generally exceed hurricane force
wind shear is a key factor of MCSs. Why?
strong winds aloft push updraft preventing the downdraft from suppressing updraft- moisture source is not cut off
where do frontal squall lines usually form?
in the warm section of midlatitude cyclone, just ahead of cold front
sometimes in front of drylines
structure is similar to MCS squall lines , except they are usually hundreds of kilometers long
what is a vortex?
region in a fluid where air (wind) or water rotates around an axis line, which may. be straight or curved
what is a tornado?
a rapidly rotating column of air that is in contact with the surface and a cumulonimbus cloud
- visible in the form of a condensation funnel with a cloud of rotating debris and dust beneath it
how long does a tornado last
usually only a few minutes
types of tornados (2)
supercell and non-supercell
name and scale for tornado strength measurement
Enhanced fujita scale
0-5
category 4&5 tornados make up only ___% of all tornados but cause ___% of the deaths
1%
70%
do tornados have high or low pressure at the center?
very low pressure center
True or false: Most tornadoes occur in the US than anywhere else in the world
true
Why does tornado valley exist?
- large land mass with cold continental air meeting moist warm air
- large flat region with no mountain ranges allow strong collision of air masses
- warm dry air (continental tropical) also plays a role (drylines)
what is the cloud wall and how is it formed?
area at the top of a tornado, formed by stretching of mesocyclone
what is a funnel cloud?
narrow rapid rotating vortex part of a tornado
when is a tornado considered a tornado?
when the funnel cloud touches the ground lifting up dust
rope life formation of a tornado
can lead to dissipation
when is a tornado at its mature stage?
when it is nearly vertical, this is when it is at its most intense
steps of tornado formation
Formation of a Supercell: Tornadoes are most commonly associated with supercell thunderstorms, which have a persistent rotating updraft known as a mesocyclone. The rotation in supercells is often initiated by wind shear, where winds change speed and/or direction with height in the atmosphere.
Tilt of the Updraft: As the supercell thunderstorm develops, the rotating updraft, or mesocyclone, can become tilted vertically by environmental wind shear. This tilting separates the updraft and downdraft portions of the storm and can enhance the storm’s organization and longevity.
Development of a Wall Cloud: Within the supercell, a lowered cloud base known as a wall cloud may form beneath the mesocyclone. Wall clouds are often associated with strong updrafts and are a common precursor to tornado formation.
Formation of a Funnel Cloud: Under the right conditions, the rotation within the wall cloud can intensify, leading to the development of a funnel cloud extending downward from the cloud base. A funnel cloud is a rotating column of air that has not yet made contact with the ground.
Tornado Touchdown: If the rotation within the funnel cloud strengthens further, it can extend all the way to the ground, forming a tornado. Once a tornado makes contact with the ground, it becomes a tornado, and it can cause significant damage as it moves across the landscape.
where do tornados form in the supercell structure?
on the left side, left of the precipitation
2011 tornado outbreak
362 tornados in 3 days
multiple tornados spawned by the same synoptic scale weather system
How can weather forecasters predict tornados?
try to identify existing mesocyclones (ie storm rotation) as seen on doppler radars
examples of other vortices?
waterspouts
dust devils
what are waterspouts?
intense vortices that occur over warm water bodies (weaker than supercell tornados)
what are dust devils and how are they formed?
type of vortex that lifts dust and sand
formed from the bottom up by convection
- last seconds to minutes
- peak at 10-20 mph
two main factors for development of tropical cyclone
sea temp
coriolis
differences between extra tropical and tropical cyclones
- cold and warm air vs warm air masses
- fronts vs no fronts
- driven by horizontal temp gradient vs warm oceans
- diameter 4000km vs 1000km
- 6 days vs 4 days
- max winds near tropopause vs max winds near surface
similarities b/w extra tropical and tropical cyclones
low pressure center
counter clockwise
coriolis
heavy precip
