The Final Flashcards
Weather
The state of the atmosphere at a given time and place.
Climate
The sum of all statistical information about weather in a place or region.
Climatology
Allows for the study of atmospheric processes and their impact beyond present-day weather.
Three properties of climatology
Extremes, normal, and frequencies.
Vertical structure of the atmosphere
spheres are separated by pauses marked by a change in the vertical gradient of temperature, either causing a reversal of cooling or warming with height.
Modern Composition of Atmosphere
78% Nitrogen (N), 21% Oxygen (O), 1% Argon (A)
Constant Gases
relatively long residence times in the atmosphere. Includes Nitrogen, Oxygen, Argon, and Helium
Variable Gases
Changes in quantity from place to place and over time. The most common are water vapor, carbon dioxide, and Ozone.
The Atmosphere (general)
Made up of thin gaseous veil surrounding Earth.
Held down by the force of gravity.
Includes essential gases needed for life.
Hydrosphere
Where all of Earth’s water flows and is stored
Water in this sphere exists in three states: gas, liquid and solid.
Lithosphere
Earth’s crust and portion of the upper mantle directly below the crust form this sphere.
Biosphere
The living portion of Earth’s surface
Aka “ecosphere” exists wherever life is sustained.
Two protective layers of atmosphere
Ionosphere - Extends through the thermosphere, absorbing gamma rays and x-rays, changes ions to atoms, where the Northern Lights are.
Ozonosphere - portion of the stratosphere that contains increased levels of ozone. Ozone absorbs certain wavelengths of ultraviolet radiation.
Troposphere
Lower portion
Temperature decreases with height.
75% of atmospheric mass
Nearly all water vapor and aerosols
Deeper in tropics: Shallow at poles
All-important weather phenomena
Thickest around equator
Stratosphere
Above the troposphere
properties of air are independent of turbulence
concentration of ozone
ozone absorption of UV radiation heats the stratosphere
higher temperature results
Mesosphere
Coldest
Thermosphere
High temps but very low pressure
O2 and N2 absorb solar shortwave energy.
So little atmosphere that you do not feel heat, low heat content.
Atmospheric Conditions
Air is a mixture of discrete gases.
O2 and N2 make up 99% of atmosphere - largely irrelevant to weather conditions.
CO2 present in minute amounts
CH4 present in even more minute amounts.
Both CO2 and CH4 concentrations have risen in recent centuries.
Rising Greenhouse gases
CO2 is 1.21 times more abundant than in the 1960s.
CH4 is 1.5 times higher than in 1750 from 700 to 1745 ppb. CH4 rise has recently slowed: 200 ppbv/decade in 70s, 0-130 ppbv/decade now.
Still, CH4 is more potent than GHG, 20x the CO2 effect.
Warming from a 20% rise in CO2 is like a 1% rise in CH4.
Water Vapor
Near 0-4% by volume
Source of all clouds and precipitation
Hugely important for heating the atmosphere.
Its change of phase from solid to liquid to gas or releases heat without temperature change.
The latent is moved with water and is a critical energy source that drives storms.
Aerosols
Ejected and suspended particles, transported by atmospheric motions and kept aloft.
Insolation and Heating
More than 99.9% of the energy that heats Earth’s surface comes from solar radiation
Not evenly distributed, varies with latitude, time of day, and season of year.
Unequal heating of Earth results in winds, and ocean currents which in turn moves heat from the tropics to the poles.
Energy
Capacity to do work.
Kinetic - motion
Potential - stored kinetic
Temperature
how warm to a relative standard
formally: the average kinetic energy of the molecules of some object
When an object gains energy, molecules speed up.
temperature either rises or there is a change in state.
Heat
transfer of energy into or out of an object because of the temperature difference between an object and its surroundings
Flows from high to low until equal
heated objects take on internal energy, typically as molecules increase.
Mechanisms of heat transfer
Conduction
Convection
Radiation
Conduction
Direct transfers between molecules in contact
Objects can be good or bad conductors’ metals and stones are good: wood and air are poor.
Here, only active for contact of Earth’s surface and air just above
Convection
transfer involving the movement or circulation of a substance.
fluids flow and carry heat with their motions.
convection cells in boiling water
thermals used by hawks, vultures, and hang-gliders
Radiation
emission and propagation of energy in the forms of waves or particles and through some material or space
does not require medium to travel
spread across a wide range of electromagnetic spectrum, waves of different sizes
short waves are more energetic and potentially damaging, solar radiation is a shortwave radiation
Laws of radiation
- All objects emit unless at absolute zero
- hotter objects emit more energy
- hotter objects emit in shorter wavelengths
- good absorbers are good emitters
Planck’s Law
all objects above absolute zero emit radiation over various wavelengths
spectrum of radiation depends on temperature.
Stefan-Boltzmann Law
Intensity of radiation increases with temperature.
What happens to incoming solar radiation?
- Absorbed: molecules vibrates faster, temp. increases
- Transmitted: passes through the object
- Redirected: reflection or scattering
Reflection is bouncing back at the same angle and intensity.
Scattering weakens the rays in different directions.
Albedo
The fraction of radiation that is reflected off an object.
Varies in wavelength.
Total planetary albedo in the shortwave portion of the spectrum includes reflection from the surface of the Earth plus reflection off clouds and the atmosphere itself.
Varies widely for different surfaces.
What happens to sunlight when it strikes Earth?
some are absorbed by the outer atmosphere.
some make it through the troposphere.
parts bounce back to space.
part is absorbed by the atmosphere and clouds.
part heats the surface.
Earth-sun Relations
Sun angle varies by latitude because Earth is spherical
The larger the solar angle, the more intense the insolation
Motions causing variations in solar radiation
rotation - Earth spinning about its axis, causes the daily cycle
revolution - movement along an orbital path around the sun - causes seasons
tilt - seasonal variations of heating
Solstices
When earth’s axis tilts towards or away from the sun
Equinoxes
When earth’s axis tilts neither toward nor away from the sun
Elliptical orbit
Sun is not centered
plane of elliptical: flat plane on which the Earth travel as it revolves around the sun.
Aphelion
July 4th - Earth is the farthest distance from the sun
perihelion
January 3rd - Earth is the closest distance from the sun
Solar noon
the time of the day when the sun is at its highest position in the sky
Isotherm
a line that connects points on a graph that have the same temperature
Isotherm Contour Map show:
- temperature in space
- temperature gradient in space or how temperature changes with distance and direction
Controls on temperature
- Latitude
- Differential heating of land and water
- Ocean currents
- Elevation
- Geographic position
- Clouds and albedo
Latitude
variation in sun angle
variation in length of daylight
Differential heating of land and water
What is a fluid and convection redistribute heating from solar radiation
Water, being more transparent, distributes heat vertically
Specific heat is three times higher for water than land
evaporation of water carries away heat from wet surfaces
Ocean currents
responsible for about 1/4 of latitudinal redistribution of heat, wind is responsible for the other 3/4
Warm currents keeps temperatures relatively moderate at unexpected latitudes
Cold currents moderate tropic heat
Elevation
Temperature drops about 6.5 C per km rise in the troposphere
Air is thinner - atmosphere loses the ability to absorb and radiate - resulting in rapid heating and cooling
Geographic position
difference in temperature because of prevailing winds
Land receiving wind from ocean tend to have milder temperatures
Land sending wind to sea receive more extreme temperatures
Mountain ranges also affect temperature
Cloud cover and albedo
cloud cover associated with seasonal rains prevent solar radiation from reaching the surface
clouds also keep it warm from absorbing and reradiating longwave radiation emissions from Earth’s surface
Water and temperature
maritime - moderate temperatures
high specific heat
radiation penetrates
Mixing
high evaporation (cooling)
Land and temperature
continental - extreme temperatures
Low specific heat
opaque surfaces
no mixing of land
low evaporation
Specific Heat
amount of heat needed to raise the temperature of 1 gram of substance by 1 degree Celsius
water has uncommonly high specific heat
takes more energy to warm water than warm rocks, soil, plant biomass, roads, etc.
The Global Water Cycle
powered by energy from the sun
drives evaporation into the atmosphere
moisture and associated energy are carried by winds
precipitation and dew return it to oceans and land
some of this ends up as runoff, meaning leaving continental surfaces via rivers
Water molecules
water molecules consist of two hydrogen and one oxygen
Oxygen is a negative charge
Hydrogen is a positive charge
attraction between water molecules is called hydrogen bonding
Ice has the strongest bond, molecules firmly bonded in a hexagonal form
Energy absorbed in a change of state
melting
evaporation
sublimination
Energy released in a change of state
Freezing
condensation
deposition
latent heat
term for how much energy is required or released by a change in phase
associated with a change in state, not a change in temperature
stored energy
Mixing ratio
mass of water vapor/mass of air in total
Absolute humidity
mass of water vapor/volume of air in total
specific humidity
mass of water vapor/mass of water vapor or mass of total air
Vapor pressure
another measure of water vapor in air is the pressure it exerts on the air
parcels with water vapor exert higher water vapor pressures on the air
Saturation
the amount of water that can be held by air is controlled by the temperature
Saturation is when a parcel of air cannot hold anymore water
Saturation Vapor pressure
the vapor pressure exerted by water molecules for air in a saturated state
relative humidity
actual vapor pressure/saturated vapor pressure
changes in two ways
1. add or subtract moisture (changes in numerator)
2. changing the temperature (changes in denominator)
approaches to saturation
- addition of water vapor by evaporation
- cooling to the dew point temperature
Dew-point temperature
temperature to which a parcel would need to be cooled to become a saturated parcel
determined by the air parcel’s absolute water content (aka mixing ratio)
Adiabatic temperature changes
results from expansion and compression of air
expansion = cooling
compression = warming
Dry adiabatic rate
10 C per 1km
air parcel rising upward
experiences successfully lower pressure
cools and expands adiabatically
Wet adiabatic rate
5 C per 1km
If it’s cooled to its dewpoint
condensation begins
this releases the heat from gas to a liquid changing of phase
slows the rate of cooling with continued rise
What causes air parcels to rise upward
- Orographic lifting
- Frontal wedging
- Convergence
- Localized Convective lifting
Orographic lifting
air is forced to rise over a topographic barrier
Frontal wedging
warmer, less dense air forced over cooler, denser air
Convergence
horizontal airflow piles up and is forced upward
Localized convective lifting
unequal surface heating causes local pockets of hot air that then rises
Stability
air’s tendency to rise, sink, or stay where it is, controlled by the parcel’s temperature compared to its surroundings
If the parcel is cooler than the surrounding air it sinks and is called stable.
Stability enhanced when
the Earth’s surface is radiatively cooled after sunset
an air mass is cooled from below when passing over a cold surface and there is subsidence within an air column
Instability
If the parcel of air is warmer than the surrounding air it rises
Instability is enhanced when
solar heating is intense
an air mass is heated from below when passing over a warm surface
lifting mechanisms are activated
cloud tops are radiative cooled
Clouds
visible aggregate of minute droplets of water, tiny crystals of ice, mixture of both
Necessary conditions for clouds
- Saturation
- surface for condensation
High clouds
low temperature, small water vapor source, thin, white, icy
cirrus - high (> 6km), white, or thin - separated or detached - delicate veil-like patches or wispy fiber, often feather
Middle clouds
Prefix is alto, typically water droplets
cumulus (2-6km) globular individual cloud masses - flat bases and rising domes or towers - cauliflower like
Low clouds
stratus - (<2km) sheets or layers covering much or all of the sky
stratocumulus - 3km or below
Cirrus and its effects
highly transparent to shortwave radiation, reflecting little sunlight - low albedo effect
high altitude and thus very cold cloud tops with lower radiative emissions to space - high greenhouse effect
readily absorbs outgoing longwave radiation trapping radiation from below - high greenhouse effect
Net warming effect
Stratus and its effects
thick, reflective, and opaque to shortwave radiation, reflecting sunlight - high albedo effect
Close to surface temperature, thus similar longwave emissions - low greenhouse effect
Net cooling effect
Cumulonimbus
storm clouds
common source of heavy precipitation, lightning, thunder and hail
Cloud’s role in earth’s energy budget: its direct effects
reflection, absorption, or transmission
properties differ for longwave and shortwave
Radiation energy balance must include SW and LW
Cloud’s role in earth’s energy budget: its indirect effects
Heat fluxes
lateral and vertical redistributions of energy/heat
Cloud albedo forcing
Clouds usually have higher albedo than surfaces underneath
they tend to reflect more shortwave radiation out to space than the surface would by itself
results in negative forcing or cooling effect on the atmosphere
Cloud albedo effect outweighs the greenhouse warming effect
cloud greenhouse forcing
clouds are usually colder than the underlying surface
they tend to reduce longwave emission back to space
results in a positive force or warming effect on the atmosphere or surface
Fog
a cloud with its base at or near the ground, that differs in place and method of formation
Methods of formation
- by cooling to saturation
(radiation, advection, upslope types) - by addition of water vapor
(steam, frontal types)
Radiation Fog
from radiative cooling of the ground and adjacent air, requires clear skies and high relative humidity
cold, dense air sinks into landscape lows
thick in valleys, dissipates in evaporation, not actually through physical “lifting”
Advection fog
warm, moist air blown over a cold surface, then chilled by contact to dew point
often thick and persistent
Upslope fog
adiabatic cooling of moist air to its dew point from winds carrying it upslope
Steam fog
cool air over warm water
evaporation from the water surface saturates the air just above
shallow fog
evaporates with mixing
Frontal fog
occurs after rain from frontal wedging falls where surface air is cold and nearly saturated
Evaporation of rainwater saturates the air and creates clouds at the surface
Dew
condensation of water vapor onto objects that are radiatively cooled below its dew point temperature
sometimes grass transpires locally creating pockets of high humidity
Frost
Not frozen dew
direct deposition
gas to solid
dew point of air is below freezing
Conditions needed for precipitation
- Saturation
- Condensation
- Accumulation to precipitable size
Crystal Growth
Aka the Bergeron process
Water in three different states at once (ice crystals, supercooled water droplets, water vapor)
Ice has a stronger affinity for gaseous water vapor than liquid droplets do, thus ice attracts and accumulates water from surrounding objects
Collision Coalescence
Large cloud droplets fall, collide with smaller ones, grow, flatten from friction, split, and they fall
Radar
Radio waves sent
Wavelengths determine what is sensed
penetrate cloud droplets
reflect off larger droplets, ice crystals and hail
intensity of echo = precipitation intensity
Thermal
Cold cloud tops indicate deep cloud development
temperatures and arrangement relate to precipitation
Rainshadow Effect
the upwind side of mountains is typically humid and wet with more precipitation compared to the downwind side of mountains
Two reasons for rainshadow effect
- The mountains lift air approaching the mountains causing saturation from adiabatic cooling
then cloud formation and precipitation ringing out most of the moisture in the air as it travels over the mountains. - air descending on the downward side of the mountain is heated adiabatically causing it to be further from saturation and thus inhibiting clouds and precipitation.
Air pressure and winds
Variations in pressure drive winds, which influences temperature and moisture
Highs v lows: horizontal pressure differences
Wind is nature’s attempt to balance inequalities in air pressure
Unequal heating of the Earth’s surface generates the pressure differences
Why does air pressure vary?
altitude
temperature
humidity
airflow
altitude influence on pressure
pressure decreases with an increase in altitude
Temperature influence on pressure
Heated surface - causes molecules to scatter - rise, density decreases - low pressure
Cooled surface - molecules sink, density increases - high pressure
Humidity influence on pressure
The more moisture, density decreases, lower pressure
airflow influence on pressure
Convergence is a net flow of air into a region (air piles up, creating a taller column, this increases the weight of the air column’s weight, thus its pressure increases)
temperature/density/pressure
Cold = High density = high pressure
warm = low density = low pressure
more water = lower density = lower pressure
Three main forces govern winds
- pressure-gradient
- Coriolis force
- Friction
pressure-gradient
greater pressure on one side of air than another
force imbalances cause movement in the direction from high to low pressure
magnitude of force depends on magnitude of the difference in space, horizontal pressure-gradient
If only PG then air winds would only act to balance inequalities, other forces prevent this
Coriolis force
Winds often deviate from high to low path due to Earth’s rotation
right in the north, left in the south
Strength increases with latitude (o at equator, heavy at poles)
always at 90-degree angle
Friction
- slows wind
- is a surface feature
- acts opposite to airflow direction
- thus, it reduces coriolis effect that depends on wind speed
Geostrophic winds
idealized upper-level wind around curved
starts stationary
accelerates in direction of pressure gradient force
as velocity increases, Coriolis force increases
until forces are balanced
results in flow horizontal to the gradient
Gradient winds
idealized upper-level wind around curved
concentric circle isobars around a high or low pressure system
involves a balance between pressure gradients and coriolis force causing wind to flow perpendicular
inward pointing force is stronger to overcome additional outward force in which is centripetal acceleration
isobars
lines of equal pressure
spacing indicates the steepness of the pressure gradient, so wind speed
winds flow from high to low but note deflection to the right
anticyclonic vs cyclonic
anticyclonic = high pressure
cyclonic = low pressure
Friction (anticyclonic and cyclonic)
Net inflow (convergence) around cyclones (low-pressure systems)
New outflow (divergence) around anticyclones (high pressure)
Convergence/divergence aloft
airflows together or spreads out in the upper atmosphere
cyclones and anticyclones would not be sustained for very long without them
Surface convergence
Low pressure
maintained by divergence (spreading out) aloft with corresponding upward motion
Surface divergence
High pressure
maintained by convergence aloft with corresponding downward motion
Convection
vertical mixing of air or water
Advection
horizontal movement of air or water
Circulation of the atmosphere
a series of deep rivers of air
embedded in the main current are vortices (hurricanes, tornadoes, cyclones)
Macroscale winds
planetary: westerlies and trade winds
synoptic: cyclones and anticyclones, hurricanes
Mesoscale winds
thunderstorm, tornadoes, etc
part of a larger macroscale wind systems
Microscale winds
chaotic motions including gusts and dust devils
small, very localized breezes
Eddy
Whirl of wind
comes in different sizes
small volume of air that behaves differently from the large flow in which it resides
caused by heating or encountering an obstacle (downwind from obstacle)
flow composed largely of eddies is called turbulent
Sea breeze
land is more intensely heated than water. cooler air over the water moves onto land
Land breeze
land cools more rapidly than the sea, causing a land breeze
Chinook
warm dry air moving down the leeward slopes of mountains, in the Alps, Foehn
Santa Ana winds and fires
strong anticyclones over the Great Basin, direct desert air over CA coast range
Valley breeze
air along mountain slopes is heated more intensely than air at the same elevation over the valley floor causing upslope flow from valley to mountain
Mountain breeze
rapid radiation heat loss along the mountain slopes cools the air, which drains below into the valley
Katabatic winds
ice sheet/snow surface cools adjacent air relative to air over the ocean. Cold, dense air sinks with gravity and flows over the water
Haboobs
Giant dust storms: 50mph, 3,000ft high
caused by outflow air from a thunderstorm
whirling winds of debris
dense dark clouds can engulf desert towns, and deposit enormous amounts of sediment
Dust devils
rotating column of air
pick up dust
look like tornadoes (smaller, short lived)
forms on clear skies (not associated with storms)
heating creates low pressure, air rises, air flows into lows, and circulation speeds up
Easterlies (trade winds and polar)
each involves pressure-gradients pointing from the pole towards the equator
deflected by CF right in north, left in south causing east to west flow
Westerlies (midlatitude)
pressure gradient pointing from subtropical high-pressure band toward the polar front
deflection from the CF causing west to east flow
Inter-Tropical Convergence Zone
zone of low pressure where converging surface winds near the equator contribute to lifting, clouds and precipitation
this marks the lifting of side of the Hadley cell
it shifts seasonally, drifting toward the tropic of cancer or capricorn during their respective summer seasons.
subtropical high
- radiative cooling of upper-level air
- Coriolis force increases deflection to being nearly east to west
- air piles up (converges) aloft, causing subsidence
Subtropical highs and deserts
adiabatically heating with subsidence lowers the relative humidity
water has rained out over equator
Monsoons
wind systems with a pronounced seasonal reversal in direction
winter cold continents, dry continental air blows offshore
summer warm continents, moist maritime air blows landward
Jet streams
narrow ribbons of high-speed winds that meander for thousands of kilometers
mechanisms: strong temperature gradient at the surface, generate steep pressure gradients aloft, hence fast upper air winds
seasonal variations in strength, stronger in winter when the PGF is greater.
Hadley Original model
one large convection cell in each hemisphere
air rises at the equator, travel poleward, and subsides around 20-35 latitude
Rising equatorial air reaches tropopause and travels poleward
cooling and sinking in polar areas
as cold approaches the equator, re-heats, and rises again
Doesn’t take earth’s rotation into consideration
3-cell model
accounts for earth’s rotation
each cell is in a Hadley
Polar cell
60-90 N and S
subsidence at poles
surface flows moves equatorward, deflected by coriolis force: polar easterlies
as cold moves toward the equator, it meets warmer westerly airflow.
Westerly and heat flow
general west to east flow
shear generates a meander
southward excursion of cold air creates a steep temperature gradient and strong flow aloft and…
steep pressure gradient which can organize rotating cyclonic storm
these rotating systems transfer heat
eventually, they weaken the temperature gradient causing the system to dissipate
Cycles last 1 to 6 weeks
pressure zones
idealized pressure zones from equator to pole
Includes: equatorial low, subtropical high, subpolar low, polar front, polar high
Pressure zones influenced by
both differential heating and wind way flow
deflection arising from the CF
polar front where polar easterlies and mid-latitude westerlies collide
real pressure zones
influence of continents that heat and cool more and thus break up the idealized zonal bands
Ocean currents
follow the winds: westerlies and trade winds, similarly deflected by CF
deflection when they meet a continent
Upwelling
offshore winds promote the rising of cold, nutrient-rich water up to the surface
Cold currents
also creates stable conditions over adjacent land masses, sometimes creating fog and cool air conditions over a desert environment
Normal
cold peruvian current and easterlies prevail
westward ocean current (along with tradewinds/easterlies)
warm, wet low pressure in Australia
cold, dry high pressure off western South America
El Nino
strong counter current, weak peruvian current and tradewinds
associated with excursion of jets
bring abnormally warm, wet low pressures to Ecuador
cooler and dryer off Indonesia
La Nina
an exaggerated version of Normal
Southern Oscillation
measures El Nino, La nina or normal conditions
pressures drop over the Southeastern pacific
pressures rise over the western pacific
Air masses
a large body of air characterized by homogeneous physical properties
large meaning 1000 miles (1600km) across several km thick
physical properties mainly include temperature and moisture
Temperature and air masses
tropical = warm (T)
polar = cold (P)
Artic = coldest (A)
Humidity and air masses
maritime = wet (m)
Continental = dry (c)
Migration and air masses
k = colder than the underlying surface
w = warmer than the underlying surface
Migration and different surface characteristics
modifies the conditions of the new region
air modifies itself
source region
stagnant, uniform region, air mass comes into equilibrium with the surface conditions
Koppen-Geiger Classification
A - humid tropical, monthly T > 18 C, winterless
B - dry, potential evaporation > prec.
C - humid middle-latitude, mild winters, monthly T of coldest month < 18 C but > - 3C
D- humid middle-latitude, severe winter, monthly T of coldest month <18 C but < -3
E- polar, month max < 10 C, summerless
Defining “dry”
water deficiency is the key
annual precipitation < annual potential water loss to evaporation (often represented by temperature)
hot, low humidity = high demand for water mainly driven by solar radiation
We define the Bs, - A, C, or D boundary based on
- annual precipitation
- annual temperature
- their seasonality… wet, warm different from the wet, cold season, precipitation is more effective at supporting humid (wet) climate conditions
Seasonal shift
In latitudinal heating and pressure belts contribute to seasonal variation in precipitation, temperature, and potential evaporation
Humid Tropical (A)
wet tropics (Af, Am)
tropical wet, dry (Aw)
Wet tropics
Af, Am
consistently intense solar radiation
seasonal differences often induced more by clouds than sun angle variation
max temperatures similar or even lower than those experienced in middle latitudes and little temperature variation year-round
Tropical wet, dry
Aw
transitional between rainy tropics and subtropical high deserts
rainforest gives away to woodland and savanna or tropical grasslands with scattered deciduous trees
larger annual temperature range than other A types
pronounced seasonal variation in humidity and cloudiness
markedly seasonal precipitation with wet summers and dry winters clearly attributable to seasonal variations in the ITCZ + hadley cell migration induced by shift in the vertical rays of the sun
Dry (B)
Steppe (BS)
Arid (BW)
Steppe
BS
water deficiency is prevalent
hot and dry but not as severely so compared to desert BW type
Tend to be located within subtropical High-pressure belts because of their prevalent condition of descending, dry air that inhibits condensation and precipitation and can have a warm year round (h) or cold water (k) designation
Arid
BW
same as steppe but dryer still
West coast subtropical deserts
within the subtropical high-pressure belt and adjacent to the cold ocean currents, air close to the saturation and fog can be common
the still stable atmospheric conditions inhibit precipitation thus keeping these areas very dry
Humid Midlatitude Mild winter (C)
Dry summer subtropics (Csa, Csb)
Humid Subtropical (Cfa)
Marine West Coast climate (Cfb)
Dry Summer subtropics
(Csa, Csb)
west sides of continents equatorward of the Cfb and poleward of subtropical steppes
summer dry winter wet climate (Mediterranean) is found
Seasonal migration of the subtropical high-pressure systems
poleward in summer and equatorward in the winter
brings this zone into its influence in summer and out of its influence in winter
corresponding migration of the polar front (moist, unstable) brings this zone into its influence in winter and out of its influence in summer
Humid subtropical
(Cfa)
eastern side of the continents in 25 to 40 latitude
hot, humid summer, wetter part of the year but mostly uniform
mT airmasses from western portion of subtropical anticyclones are lifted from continental heating and generate thunderstorms
cool winters can have frost, some frozen precipitation
Marine West Coast Climate
Cfb
western, windward side of continents about 40 - 65 degrees latitude
mountains restricted to coast, not extending inland
reduced precipitation in summer linked to poleward migration of the oceanic
High pressure; still wet though
Humid Midlatitude Severe Winter (D)
Humid Continental Warm Summer or cool summer (Dfa, Dfb)
Subarctic (dfc, Dfd)
Highland (H)
Humid Continental warm summer or cool summer
Dfa, Dfb
land controlled middle latitudes central around 40-50 degrees latitude
missing from southern hemisphere
extends to east side of continents because of westerlies
severe summer and winter
winter has a steep latitudinal temperature gradient
Subarctic
Dfc, Dfd
north of humid continental, south of polar tundra
corresponds to taiga forest distribution
similar seasonality but a deeper drop in winter, long cold season
cP air masses provide limited precipitation year-round
greatest annual temperature ranges on earth
Highland
H
variation with latitude, cooler with increasing elevation
promote precipitation on windward sides and rain shadows on opposite
Polar (E)
Tundra (ET)
Ice cap (EF)
Tundra
ET
cold year-round except for short, cool growing season
permafrost common
little precipitation partly because of the limited capacity of cold air to hold water vapor
deep cold in winter
Ice cap
EF
same as ET just without vegetation
Fronts
boundary surfaces that separate air masses of different densities
Typically, one is warm and has more moisture
air masses can move together
often of different speeds and thus they clash
there is little mixing when they clash, meaning they retain their character
displacement occurs when cold, more dense air displaces warm, less dense air
overrunning: warm air gliding over a cold air mass
5 types of fronts
- warm front
- cold front
- Stationary front
- Occluded front
- Dryline
Warm front
redline, semicircles protruding into colder air
mT gulf air meets receding cooler air
warm air wedged (overruns) over cold
surface friction slows advance of cold relative to warm air
gradual sloping surface of about 1:2000
Cirrus clouds foretell approaching front
as front approaches, clouds get closer to surface and denser
low to moderate precipitation unless warm air is conditionally stable
Cold front
cold cP advances into region occupied by warmer air
steeper slope of the surface, 1:100, is again linked to surface friction
more violent with airlifted faster, thus towering clouds develop, dark bands
cumulonimbus clouds, heavy downpour, vigorous winds
cold fronts generally move faster than warm fronts, important for mid-latitude cyclones
Mid-latitude cyclones (L): warm and cold fronts meet
warm sector mT air overruns cP or mP air
cP air pushes up mT at the cold front
Occluded front
fast cold front overtakes a warm front
warm air is wedged between two cold air masses
complex precipitation
purple line and alternating triangles and semicircles pointing in the direction of motion
Stationary front
airflow parallel to line of front
blue triangle points on one side, red semicircles on the other
can involve the stalling of a cyclone or storm and hence threat of flooding
often linked to polar easterlies on one side, westerlies on the other
Midlatitude cyclones
a low pressure system involving a clash of maritime tropical and continental polar air masses giving rise to a warm front matched with a cold front located in the counterclockwise direction
warm sector lies between these two front and helps fuel low pressure system
cold front often catches up to and meets warm front creating an occluded front
Cyclogenesis
stationary fronts
wave develops, warm invades cold, cold invades warm
creates low pressure and cyclonic, counterclockwise flow
convergence, lifting, overrunning, clouds
occlusion: beginning of an end, storm may intensify but PG weakens as the horizontal temperature difference at surface is eliminated
Dryline fronts
generated by a density gradient from humidity
wet = lower density
just like a cold front but hot dry (cT air) meets hot wet (mT air)
mT air is lifted vigorously, generating intense weather, squall lines, and tornadoes
Air mass type thunderstorm
lifting by unequal heating, commonly a mT air becomes unstable when heated from below often in mid-afternoon, when surface temperatures are highest
3 stages of development - air mass type thunderstorms
- cumulus
- mature
- dissipate = where dissipation occurs because the cool, moist downdraft and heated surface air, cutting off fuel for the cloud and storm
severe type of thunderstorms
unequal heating plus frontal or mountain lifting
involves strong vertical winds shear that tilt the updraft portion
strong vertical wind shear from changes in wind direction or speed with height
tilts updraft so they do not extinguish themselves and allows the storm to be sustained
Supercell thunderstorms
single, very powerful cell up to 20km
persists for many hours
have rotating updrafts and can produce tornadoes
requires huge quantities of latent heat
Mesoscale convective complexes
cluster of individual thunderstorms
afternoon air-mass thunderstorm decays
transform into complexes with continued inflow of very warm and moist air
Microbursts
concentrated bursts of wind in a downdraft
accelerated by lots of evaporative cooling and associated rapid change in density
high surface winds
hazard of aircraft takeoff/landing, boats, and tree blow downs
Lightning
electrical discharge carrying the negative flow of current from region of excess negative charge to region of excess positive charge
80% cloud-cloud, not cloud to ground
air is poor conductor, so charge builds
charge separation in clouds with positive cluster at top, negative cluster at bottom with positive induced in ground
Thunder
lightning superheats air immediately around lightning channel generating a supersonic shock wave that gives off an acoustic wave
light travels instantaneously but sound is slower and thus arrives later to an observer
Tornadoes
violent winds spinning in a vortex; low pressure inside; winds up to 300mph
form in cold front supercells, squall lines, or tropical cyclones
wind shear creates rolling which gets lifted by an updraft and is vertically stretched to tighten it up into tornado feature
intensity measured by devastation
