A&O Sci 3 Final

Terminal velocity

Terminal velocity

The constant speed an object reaches when the force of gravity is balanced by the drag force of the medium through which it is falling.

Cold Clouds

Not much growth, ice and vapor

Cold Clouds

Below 0 degrees, all 3 phases coexists

1. Bergeron process

2. Riming

3. Aggregation

Riming

The process where supercooled water droplets freeze upon contact with ice particles, leading to the accumulation of ice on the particle.

Aggregating

The process where ice crystals collide and stick together via thin coating of liquid water, forming larger snowflakes or ice particles.

Bergeron process

A process that describes how ice crystals grow in cold clouds by extracting moisture from supercooled water droplets, resulting in precipitation.

Warm Cloud

Above 0 degrees, contains liquid and vapor, collision coalescence

Collision coalescence

A process in warm clouds where larger droplets collide with smaller droplets, causing them to merge and grow larger, leading to precipitation.

Global scale

Refers to atmospheric phenomena or processes that occur over large distances, typically involving the entire planet or significant portions of it. Planetary waves and Hadley cell

Synoptic scale

Refers to atmospheric phenomena that occur over intermediate distances, typically ranging from a few hundred to a few thousand kilometers, often associated with weather systems like fronts and cyclones.

Mesoscale

Refers to atmospheric phenomena occurring over distances of a few kilometers to several hundred kilometers, often associated with localized weather events such as thunderstorms and planetary boundary layer.

Microscale

Refers to atmospheric phenomena occurring over very short distances, typically less than a few kilometers, often associated with small-scale weather events like individual clouds and turbulence.

Planetary scale circulation mostly from

Difference of temperature between equator and poles, rotation of the planet, Distribution of land and water over the planet

Single Cell Model

• Simplified model of the general circulation proposed by Hadley

  • Based on idealized water planet with no effect of rotation (no Coriolis force)

  • Deflection by Coriolis

  • One cell in each hemisphere

  • First model of a thermally driven circulation

Three Cell Model

• Improved model of the general circulation proposed by Ferrel

  • Hemisphere divided into 3 cells

  • Not perfect but more realistic and capable of explaining many of the observed features of the real circulation, surface winds are fairly well predicted by the 3 cell model, the main differences are caused by land water contrasts, Hadley pretty well predicted but not Ferrel

  • Wind speeds increase with altitudes as isobars slope more steeply with height due to latitudinal thermal differences, causing trade wind, westerlies

Trade winds

Winds blowing east to west in subtropical highs due to Coriolis force

Westerlies winds

Winds blowing west to east in subpolar lows due to Coriolis force

Polar front

Cold air from the pole meets warmer air from the subtropical high at the polar front (warm air from ferrel cell and cold air from polar cell)

• Causes high PGF at higher altitudes near the tropopause this is called the Polar Jet Stream

• Polar jet stream forms from west to east in the Northern Hemisphere

• The same concept applies but with Hadley cell and Ferrel cell, this makes the subtropical jet

Polar jet

Very strong and it has important effect in the development of weather systems in the US

Subtropical jet

Much weaker and it brings warm moist air to the US

Rossby Waves

•  largest atmospheric long waves, 3-7 circle the globe at any one time and each has its own wavelength and amplitude

  • Although they have preferred anchoring positions, they migrate eastward really slowly

  • Oscillations in the polar jet stream

  • By moving the jet stream around, they can have a profound effect on the weather

  • Rossby waves breaking can be considered a source of low and high pressure centers

Air masses

Large volumes of air with uniform temperature and humidity

Fronts

Boundaries between different air masses

Source regions

Areas of the globe where air masses 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

Continental

Dry

Maritime

Humid

Tropical

Warm

Polar

Cold

Arctic

Very cold

mP from Gulf of Mexico:

• Cold humid unstable

• Main trajectory into the US depends on the position of Polar Jet Stream

  • Winter based on the jet stream it may dip lower from like washington to like florida but in summer it stays very north and lower winds

• During the each season Rossby waves can cause the jet to meander

mP from Gulf of Alaska:

• During winter, air mass can enter the US through California

• This is one of the 2 major sources of precipitation in California

• Uses orographic lifting to cause precipitation so cold+humid air + adiabatic expansion = precipitation

mP from Atlantic

• Northeasters: usually the air mass reaches the coast when it is caught up in a strong extratropical cyclone

• The cyclone brings the cold arctic air southward from Canada

mT air masses

• Major source of precipitation and thunderstorm in southeastern US as masses from Atlantic and Gulf of Mexico are warm and humid

• Cold ocean current in the Pacific limit temperatures and humidity in this air mass, so only occasional precipitation during the summer

Atmospheric Rivers

2nd major source of precipitation in California, relatively long, narrow regions in the atmosphere that transport most of the water vapor outside of the tropics

Cold fronts

• mass of cold air advancing towards warm air

  • cP (cold, dry, stable) and mT (warm, humid, unstable)

  • Associated w/ heavy precipitation and rapid temperature drops

Warm fronts

• mass of warm air advancing towards cold air

  • mP (cold, not as humid, stable) and mT (warm, humid, unstable)

  • Associated with slow predictable changes and light precipitation for days, frontal fog

Stationary fronts

Fronts that do not move or move very slowly, two unlike air masses side by side

Occluded fronts

• warm front is slower than cold front, both fronts meet and the warm air mass between them is displaced aloft, at the ground is 2 cold air masses

Cold type occlusion

Usually occurs in the eastern half of the continent where a cold front associated with cP air meets a warm front with mP air ahead

Warm type occlusion

Usually occurs in the western edge of the continents where the cold front associated with mP air migrates to an area that is occupied by cP air

Drylines

• Boundaries between humid air and dry air, without large temperature differences

  • cT (warm dry very unstable) and mT (warm humid unstable)

  • Associated with thunderstorm development and tornado outbreaks

  • Dry air is more dense than moist air so when moist air is lifted, potential for severe storms

Steps of Polar front theory (Cyclogenesis)

1. Stationary polar front

2. Frontal wave (cyclogenesis)

3. Open wave (cyclogenesis)

4. Mature cyclone

5. Occlusion

6. Cut off cyclone

Stationary polar front PFT

1. cP air mass meets maritime polar air mass in the subpolar low pressure region

   1. Air flows parallel to the front in opposite directions

Frontal wave (cyclogenesis)

1. frontal wave forms a minor kink which gives a rise to a cold and a warm front

   1. Low pressure center begins to form at the junction between two fronts

Open wave (cyclogenesis)

1. An open wave forms around low pressure center, precipitation along both frontal boundaries, winds spiral inward and towards the low (friction at surface atmosphere)

Mature cyclone

1. low pressure deepens and the entire system moves towards east-northeast

   1. Cold front moves faster than warm front reducing the size of the warm sector

Occlusion

1. beginning of occlusion marks peak in cyclone intensity and wind speeds

   1. Fronts begin to occlude and cyclone intensity starts to decrease

Cut off cyclone

1. Cut off cyclone: Original front gradually disappears

   1. New stationary front forms, leaving a cut off weakened low pressure center

Vorticity

• spinning motion of air parcels, and it is useful to describe the amount of Rotation in the wind

Planetary vorticity

• vorticity due to the rotation of the planet

  • Any object that is sitting on top of the planet have vertical vorticity, since they are rotating w/ the planet, only exception is for objects at the equator

Relative vorticity

• Wind is such that it causes air parcels to rotate

  • Right hand rule

Predominantly zonal height patterns

Prevent development of intense cyclones and usually mild atmospheric conditions at the surface

Predominantly meridional height patterns

Support cyclone development as vorticity changes between troughs and ridges

Conveyor belt model

Connects upper level circulation with the surface cyclone system, a good 3D representation of mature cyclone

Steps in lightning formation

1. Charged Separation

2. Stepped Leader

3. Ground spark

4. Return stroke

Charge separation

1. Separation of positive and negative charges into different regions of the clouds

2. Positive charge on top and negative charge on bottom of cloud

3. Likely produced by interaction between ice crystals and hail

Stepped leader

1. Rapid staggered advance of a shaft of negatively charged air

2. 50 m in 1 microsecond

3. In between pauses of about 50 microseconds for electrons to pile up at the tip

4. Usually not visible

Ground spark

1. As the leader approaches the ground, a spark is created

Return stroke

1. When the leader and the spark connect, a flow of electrons illuminates the cloud by strokes, or return strokes

2. Return stroke propagates upward and heat the air up to 30,000K

3. Dart leader follows producing other strokes

Thunder

• A sudden increase in pressure and temperature causes surrounding air to expand violently at a rate faster than the speed of sound, similar to a sonic boom

• Shock wave extends outward for first 30 ft

• A lag in lightning strike and thunder occurs due to sound traveling slower than light

Positive lightning stroke

positive charges at the top of the cloud can result in lightning strikes that shoot positive charges to the surface, ahead of the storm. These r stronger than negative strokes

Main types of lightning

Cloud to ground

Cloud to air

Intra cloud

Spider lightning

Key processes in development & evolution of thunderstorms

• Source of moisture, Unstable atmosphere, Lifting mechanism to initiate updraft, Vertical shear in wind

• Warm updraft and cold downdraft

• Cumulonimbus cloud

Severe thunderstorms

Hail w/ diameter of one inch or larger, winds in excess of 68mph, tornadoes

Single cell thunderstorm

• Most common, least destructive, not severe

• Small, localized, ~1 hour

• For in the absence of wind shear, w/ weak winds aloft

• Form away from frontal systems, triggered by surface heating or orgraphic lifting

Life cycle for single cell thunderstorm

• Developing stage:

  • Large updraft velocities, cumulus cloud grows up the troposphere w/ the anvil, moist within the cloud, formation of ice crystals that grow via Bergeron process

• Mature stage

  • Precipitation particles fall dragging the air, creating a downdraft

  • The air is further cooled by evaporation of droplets into dry air entrained, ultimately enhancing the downdraft

  • Downdraft slow displaces updraft

• Dissipative stage

  • Downdraft suppresses updraft, eventually cutting off source of water moisture

  • Outflow of cool air produces a gust front or outflow boundary

  • Gust front propagates lifting warm air, possibly seeding a new thunderstorm

Mesoscale convective systems

• Thunderstorms can develop into organized clusters, severe thunderstorms w/ lifespan of 12 hours or more

• Key factor is the wind shear: strong winds aloft push updraft ahead preventing the downdraft from suppressing the updraft so the moisture source is not cut off

• Derechos: Large scale horizontal winds produced by strong downdrafts associated with MCCs

  • Long lived, straight line winds generally exceed hurricane force

Mesoscale convective complexes

Circular clusters of thunderstorms

Squall lines

Linear bands of thunderstorms

Frontal squall lines

• Usually form in the warm section of a midlatitude cyclones, just ahead of the cold front

  • Sometimes form in front of drylines

  • Structure is similar to MCS squall lines except they are usually hundreds of km long

  • Lifting associated with the gust front usually produces shelf clouds and roll clouds

Supercell thunderstorms

• Contain a single updraft zone and are more severe and powerful

• Characterized by the presence of a deep persistently rotating updraft called mesocyclone

• Found in the warm sector of a low pressure system propagating generally in a north easterly direction in line with a cold front of the low pressure system

• Can last for a few hours and spin up large tornadoes

• Rotation in mesocyclone comes from the vorticity that exists in the environment (by wind shear)

Tornadoes Alley

• Large land mass with encounters of cold (cP) air masses with moist warm (mT) air masses

• Large flat region with no mountain ranges in the east/west direction allow strong collision of air masses

• Warm dry air dry lines also contribute

Tornado life cycle

1. Mesocyclone (rotating updraft), Wall cloud is formed by the stretching of the mesocyclone, then funnel cloud where narrow rapid rotating vortex

2. Tornado: when the funnel cloud touches the ground lifting up dust

3. Rope like formation: can lead to dissipation

Tornado formation

• Warm moist air rises rapidly within a thunderstorm creating a rotating updraft that tilts vertically due to wind shear

• Usually occurs in supercell

• Tornado forms in relatively warm downdraft and strong suction

Enhanced Fujita Scale

• from 4-5 is 1% of all tornadoes but cause 70% of the deaths

Similarities between Midlatitude and Tropical cyclones

• Both low pressure center

• Both have counterclockwise rotation

• Both are strongly influenced by Coriolis force

• Both cause heavy precipitation

Differences between Midlatitude and Tropical Cyclones

• Midlatitude:

  • Cold and warm air masses (fronts)

  • Driven by horizontal temperature gradients

  • Diameter ~ 4000km

  • Lifetime ~ 6days

  • Minimum sfc pressure 1000-970mb

  • Maximum winds near tropopause

• Hurricane:

  • Warm air masses

  • Driven by warm oceans

  • Diameter ~ 1000km

  • Lifetime ~ 4 days (Storm ~ 2weeks)

  • Minimum sfc pressure 1000-880 mb

  • Maximum winds near surface

Hurricane Formation

• Ocean surface temp 81F, as result of latent heat release

• Late summer and early fall

• Do not form between 0-5 latitude, instead 5-20 latitude

• Unstable atmospheric conditions must be present and strong vertical shear must be absent for hurrican formation

• Self generating but may be limited by supply of latent heat from warm ocean waters

Hurricane Lifecycle

1. Tropical disturbances: disorganized cluster of thunderstorms w/ weak pgf and no rotation that form in the easterly waves over west Africa

2. Tropical depression: organized w/ cyclonic rotation and at least one closed isobar and sustained wind speeds below 39 mph

3. Tropical storms: tropical depressions that intensify to sustani winds of at least 39 mph

4. Hurricanes: if further intensification to 74 mph

Hurricane Dissipation

1. Hurricane moves over land: loss moisture and latent heat and friction deflect

2. Hurricane moves further poleward: too cold

3. Hurricane reaches a location where flow aloft is unfavorable (counteracting hurricane movement)