Meteorology Test 1

4 levels of the atmosphere

• Troposphere

• Stratosphere

• Mesosphere

• Thermosphere

troposphere

• The lowest layer of the atmosphere near the earth's surface

• Closest to the surface of the earth

• Typically around 12km deep

• Weather occurs in this layer

• 90% of the atmospheric mass is contained in this layer (gravity pulls the molecules down into this layer)

stratosphere

• The second layer of the atmosphere

• Separated from the troposphere by the tropopause

• Contains Ozone layer

• Not necessarily as important to weather as the troposphere but it is important to life on earth

mesosphere

• Meso = in between

• Midway through the atmosphere

thermosphere

top of atmosphere

meteorology

the study of the physics, chemistry, and dynamics of the Earth’s atmosphere

atmosphere

the layer of air extending from the Earth’s surface to a height of a few hundred kilometers

Atmosphere Made up of two main gases

Nitrogen (N2) 78% of the mass

Oxygen (O2) 21% of the mass

Remaining 1% of the atmosphere’s mass is made up by many other gases

Argon (Ar)

Carbon dioxide (CO2)

Ozone (O3)

Hydrocarbons (methane (CH4), butane(C4H10)

Water vapor (H2O)

4 properties of the atmosphere

• Temperature

• Pressure

• Moisture

• Wind

Temperature

measurement of the average speed of molecules in a substance

temperature scales

Celsius

Fahrenheit

temperature conversions

F = 9/5 (C) + 32

C = 5/9 (F-32)

commonpoint: - 40

K = C + 273

Pressure

measure of the force applied by the air per unit area

why does density change with pressure

Density increases when pressure increases and decreases when pressure decreases. As pressure increases, the molecules of a substance come closer resulting in a higher density. On the other hand, when pressure decreases, the molecules become distant. Due to this, the density reduces.

why does density change with temperature

Density is affected by temperature because as temperature increases so does the kinetic energy of the particles. The more kinetic energy a substance has, the warmer it will be and the faster particles will be moving, which reduces the density of the substance.

How does pressure change with height

Pressure decreases rapidly as height increases

Atmosphere has less weight present above you (fewer molecules)

pressure scales

Typically millibars (mb) or Pascals (Pa) when discussing pressure

1mb = 100 Pa

how does pressure change horizontally

Pressure changes very slowly in the horizontal dimension, especially when compared to how quickly pressure changes in the vertical dimension

Moisture

The amount of water vapor molecules present in the air

Wind

Movement of the air

Where are official wind measurements made

10 meters above ground level

How is wind measured

anemometer

Units: knots (kts) nautical miles per hour

1kt = 1.15 mph = 0.514 m/s

How is wind reported

Wind direction is reported at the direction the wind is blowing from (not blowing to)

Wind blowing from north to south is a north wind

Temperatures patterns of the atmosphere

• Troposphere

  • temperature generally decreases with height

  • as we move up vertically we are displaced further and further from the heat source: the earth’s surface

  • Earth emits heat throughout the entire day

• Stratosphere

  • Temperature increases with height

  • Stratosphere is close to another heat source the stratospheric ozone layer

• Mesosphere

  • temperature decreases with height

  • Now we’re getting farther away from the heat source: stratospheric ozone layer

• Thermosphere

  • Temperature increases with height

  • Few molecules exist in this layer (minimal mass), those that do move very rapidly

Mean sea level pressure

pressure at a given location corrected to sea level

Pressure and density with height

Pressure decreases rapidly as height increases

Atmosphere has less weight present above you (fewer molecules)

pressure decreases 500mb (half the surface value) at around 5,5 km above the ground (Half of the atmosphere is below you at this point and half is above)

Density (mass per unit volume) also decreases as you go up in the atmosphere

Pressure changes a LOT more in the vertical dimension than inthe horizontal dimension

higher elevataions = lower pressure

pressure is measured with

Typically millibars (mb) or Pascals (Pa) when

Water vapor

an invisible gas composed of individual water vapor molecules

The amount of water vapor the air is able to hold is determined by

temperature

warmer temperatures = air that can hold more water vapor = higher water vaper pressures

Vapor pressure (VP)

the force per unit area applied only by the water vapor molecules

Saturation vapor pressure (SVP)

the vapor pressure at which the atmosphere becomes saturated

This is the maximum amount of water vapor the air can hold before it starts to condense is directly related to

temperature

Higher temperature = higher SVP

Relative humidity

the ratio of vapor pressure to saturation vapor pressure\

RH = VP/SVP x 100%

Saturated air means that VP = SVP and RH = 100%

RH depends on two quantities

Absolute amount of moisture in the air

The temperature of the air

Dewpoint Temperature (T_d)

the temperature at which water vapor will condense into liquid water

Determined by cooling the air until water begins to condense out of it.

Dewpoint Temperature and saturation

• Subsaturated: T > T_d and RH < 100%.

  • No condensation.

• Saturated: T = T_d and RH = 100%.

  • Air cannot hold more water vapor.

• Supersaturated: T < T_d and RH > 100%. 

  • Water will actively condense from the air.

  • (vapor → liquid or ice)

  • does not occur often in nature

  • Will never go much higher than 100% (usually 101% or 102%)

Dewpoint temperature is a measure of water content

Higher dewpoint = higher water vapor pressure

what goes on at a molecular level water becomes a gas

the intermolecular forces between the water molecules are decreasing. The heat is providing enough energy for the water molecules to overcome these attractive forces

how does density change when water changes phases

the density of a substance typically changes as it changes phase due to the change in volume. In general, solids have the highest density, liquids have lower density, and gases have the lowest density

How does energy move around in relation to water phase changes

Water must release energy to move from a higher to lower energy phase, i.e., from gas (water) vapor to liquid during condensation and from liquid to solid (ice) during freezing. In each case, the energy released by the water results in a change in the internal molecular bonding structure

Latent heat

heat absorbed or released during phase change (important for transferring heat in the atmosphere)

latitude

lines that circle the Earth horizontally, segmenting it in the North-South dimension

Equator is the baseline of this segmentation, has latitude of 0°

Usually written as °N or °S (or positive values for N lat.; negative values for S lat.)

Minimum value of 0° at the equator; maximum of 90° at the poles

measures north and south

latter up and down

longitude

Lines that circle the Earth vertically, segmenting it in the East-West dimension

The Prime Meridian is the baseline (reference) longitude; Longitude: 0°

Typically written in °E and °W (sometimes

positive values for E, and negative values

for W)

Minimum of 0° at the prime meridian, maximum of 180° (international date line)

measures east west

long chicken left right

two characteristics of the wind

speed

direction

Weather

The given state of the atmosphere at a single point in time

climate

the state of the atmosphere averaged over a long period of time

global climate

average conditions around the entire globe or large portions of it (such as low latitudes)

earths properties that affect climate

Sphericity

Tilt

Orbit

Rotation

Sphericity

Because the Earth is a sphere, the radiation hits the Earth unevenly

Most direct at the Equator, least direct at the poles

tilt and rotation

together, the Earth’s tilt and orbit are responsible for creating our seasons

polar cells

Hadley cells

Caused by rising warm air at the Equator

Thermally direct

Located in the low latitudes

polar cells

Caused by sinking cold air at the poles

Thermally direct

Located in the high latitudes

Ferrel cells

Caused by mixing air between the Polar and Hadley cells

Thermally indirect

The most variable weather happens here!

Located in the middle latitudes

Between the Hadley cells at the Equator

the Intertropical Convergence Zone (ITCZ)

the interface between the

northern and southern Hadley Cell

Between the Hadley and Ferrel Cells

The Horse Latitudes

Between the Ferrel and Polar Cells

The Polar Front

global atmospheric circulation

the result of the atmosphere’s attempt to

establish thermal equilibrium via the

movement of air (i.e., wind)

why does the earth never reach thermal equilibrium

the temperature of the

circulating air changes within each

circulation cell due to a change in the

amount of direct solar radiation, thermal

equilibrium is never achieved

Coriolis effect

Causes fluid to curve as it travels

does not create wind or change wind speed but is affected by wind speed (stronger speed = stronger Coriolis effect)

the Coriolis force is strongest at the poles and 0 at the Equator

The Coriolis Effect deflects fluids/objects in the Northern Hemisphere to the

right of their original motion

causes Counter-clockwise spin

air traveling to the north will deflect to

the east; air traveling to the south will

deflect to the west

The Coriolis Effect deflects fluids/objects in the Southern Hemisphere to the

to the left of their original motion

causes clockwise spin

air traveling to the

north will deflect to the west, while air

traveling southward will deflect to the east

energy

a property of a substance that allows for activity

heat

energy that is in the process of moving from a warmer to a colder substance

Heat transfer mechanisms

Physical processes that redistribute energy from regions of higher temperatures to regions of lower temperatures

radiation

conduction

convection

radiation

Heat transfer accomplished by electromagnetic radiation

Ex: The earth s warmed by radiation from the sun

conduction

Heat transfer accomplished via direct contact between a warmer substance and a colder substance.

Ex: A pan on an electric stove

convection

Heat transfer accomplished by the movement of warmer fluid into a colder fluid (most relevant to weather systems)

Ex: steam from a coffee cup, thunderstorms

Humidity

concentration of water vapor present in the air

regional climate

the average conditions observed in a

location/region over a long period of time.

◦ Typically exhibit larger variability than the global patterns

o Compared to the global climate, the distribution of land and water have

considerable effects on a region’s climate patterns.

how does the presence of moisture affect

temperatures/their rate of change?

The temperature of water (and water

vapor) changes much more slowly

than that of dry air

Air over the oceans changes

temperature much more slowly than

air over land

◦ Because air above the oceans is moist, and

air over land is dry

relationship between water temperature and air masses

Evaporation of water into the air from bodies of water, along with the typical temperature

characteristics of the low (warm), middle (cool), and high latitudes (cold), form air masses

air mass

a large body of air having similar temperature and moisture characteristics at a constant altitude across a large horizontal area

Air mass source regions shared characteristics

They are large regions with similar geographic features (all land or water)

They have mainly flat topography

They allow air to remain in place for many days (stagnant)

airmass moisture description

Air masses above land and ice are dry (continental)

Air masses above water are moist (maritime)

air mass temperature description

Air masse over the low latitudes are warm (tropical) or very warm (equatorial

Air masses over the middle latitudes are cool (polar) or cold (also polar)

Air masses over the high latitudes are cold (polar) or very cold (arctic and Antarctic depending on the hemisphere)

continental

developed over land (dry)

maritime

developed over water (moist)

polar

Cool or cold from having developed over subpolar source regions

tropical

Warm from having developed over subtropical source regions

cT

cP

mT

mP

air parcel

an independent bubble of air in the atmosphere

What happens when these parcels rise?

air pressure decreases with height in the

Earth’s atmosphere

As parcel rises (into a lower pressure

environment), it will expand

As the parcel expands, its molecules

spread apart and become less active, and

temperature decreases

nucleation

The process in which water molecules attach to the surface of a nucleation agent,

such as a CCN or INP.

cloud condensation nuclei (CCN)

the starting point for cloud formation to occur

Formed from: smoke particles, ash, dust,

clay, soil, ocean spray, pollutants

1000x larger than water molecules

how do CCNs grow

CCN serve as surfaces that water

molecules can condense onto

The adhesion properties of water, allows water droplets (or ice) to form and grow on CCNs, until gravity is strong enough for droplets to fall as rain or snow

No droplet formation

If air cools down enough...

◦ Evaporation rate = condensation rate

◦ Air is saturated

◦ Still no droplet formation

If air cools down even more...

◦ Evaporation rate < condensation rate

◦ Air is supersaturated

◦ Droplet formation! Cloud formation!

To keep drops from evaporating and cloud

from disappearing, rate of condensation

must be ≥ rate of evaporation

◦ By definition, saturation is when rate of

condensation = rate of evaporation

◦ So, to maintain a cloud, the air must be

either saturated or supersaturated

◦ “At least saturated”

what is fog

◦ Fog forms when the air near the ground

becomes at least saturated

◦ Just a cloud forming near the ground

For water vapor to condense onto CCN as liquid water, the air must first reach

saturation

◦ Condensation rate = evaporation rate

◦ VP = SVP

◦ RH = 100%

◦ T = Td

o Any cooling past T = Td will cause some of the water vapor in the air to

condense onto CCN as liquid cloud droplets

◦ Places the air into a slightly supersaturated condition, where active condensation of water

from vapor to liquid drops is occurs.

why is rising motion necessary for cloud formation

◦ Allows air parcels to enter environments of lower

pressure

◦ Leads to cooling, cooling to Td (saturation),

cooling past Td (supersaturation, cloud)

cloud formation parcel theory

Sun heats ground via radiation

Ground heats air parcels via

conduction

Air parcels rise via convection

Air parcels expand and cool as they

rise

Air parcels cool to and past Td

Cloud forms

How do we get from cloud drops to precipitation

Constant rising motion of air parcels, called

the updraft, keeps the cloud droplets aloft

o If cloud keeps growing, droplets can get

too heavy to be suspended in the air by

the updraft

◦ Falls as precipitation

Warm cloud process (warm rain)

Temperature of the cloud is entirely above freezing (technically above -10)

Cloud contains only liquid water

Cold cloud process (cold rain, consecutive rain, snow/frozen hyrdometers)

Temperature of the cloud is not entirely above freezing

Can be entirely below freezing or have regions of both above freezing and below freezing air

Cloud contains either entirely ice or both ice and liquid water

warm rain process

Cloud droplets form and grow in a supersaturated environment

Cloud droplets grow more slowly as they get larger

Cloud droplets continue to grow by colliding with one another (collision-coalescence growth)

Once they get sufficiently large the drops will fall our as precipitation (rain)