Geog 2015N Lecture notes
jan 13 2009
climate is a long term statistical analysis of what is normal or expected
weather is individual events or conditions at a specific time
atmosphere 78% nitrogen 21% oxygen and other trace gases
temp decreases with altitude b/c air pressure drops
the stratosphere warms up from the tropopause b/c ozone absorbs UV light
all solar radiation is either absorbed, reflected or transmitted.
albedo changes with surface types
snow reflects 40-95% of solar energy
forests and oceans absorb more than dry land
oceans transmit solar energy and have high heat capacity
radiation - energy due to rapid oscillations of electromagnetic fields, transfered by
photons
Stefan-Boltzmann Law - as the temp of an object increases the more energy it
releases
Jan 20 2009
winds blow clockwise out of high pressures and CCW into low pressures
- conduction - the transfer of heat from molecule to molecule w/i a substance
convection - hot air rising off the surface and cool air falling to replace it. the
transfer of heat by the mass movement of a substance. rising air expands and
cools sinking air is compressed and heats
Latent heat - THERE IS NO IMMEDIATE TEMP CHANGE WHEN LATENT
HEAT IS RELEASED. it is heat added to water in the air that will be released
later when clouds are formed. the heat energy required to change a
substance from one state to another
melting and evaporation - heat is taken from the environment
freezing and condensation - heat is released to environment
heat capacity - the amount of heat energy absorbed/released by unit volume of a
substance for a corresponding temp rise/fall of 1 degree Celsius
specific heat - the amount of heat energy absorbed/released by unit mass of a
substance for a corresponding temp rise/fall of 1 degree Celsius
sensible heat - heat energy that we can feel and sense w/ a thermometer
seasons change b/c of the tilt of the earth in relation to the sun. the angle of the
earth never changes
on avg the equator receives 37 C surplus of radiant energy that it disperses
towards the poles
clouds cause white light (all light) to be scattered some light however makes it
through the clouds and it is also scattered in all directions
A sunset is red b/c the blue light is scattered (this is why the sky is blue) very
efficiently and has been diffused out and all that is left for us to see is the
incoming red light.
light bends upon entering our atmosphere and thus we can see the sun before it
has risen above the horizon
there are 1.36 billion cubic kms of water on earth but less that .001% of it is
atmospheric water
water vapour is the most variable component of our atmosphere
absolute humidity - mass of water in a volume of air
specific humidity - mass of water in a mass of air
mixing ratio = mass of water vapour/total mass of dry air
vapour pressure - the portion of atmospheric pressure that is made up from the
water in the air
vapour pressure changes exponentially with temp.
Jan 27 2009
summer humidity - hot humid air with a high dew point and high relative humidity
comes up out of the gulf of mexico and blows north. Hot dry air with a low dew
point and low relative humidity blows east out of the pacific and over the
mountains
humidex = T+(.55 x air pressure - 10)
frost is due when the temp is below freezing
the best due formations occur on clear night with a wind speed b/w 2 and 6 kms
Hoar frost - frost forming on frost but only on the side facing the wind
black frost - the temperature goes below zero but not low enough to hit the due
point
condensation nuclei - a surface is required for water to condense on and the
condensation nuclei is what the water condense onto. there are b/w 10 and
10,000 large nuclei per cm cubed although there can be more over land and the
lower troposphere
there are hydroscopic(water attracting) and hydrophobic(repels water) nuclei
dry haze - dust in the atmosphere appears blue
wet haze - condensation occurring on hydroscopic nuclei when humidity is below
100%
radiation fog - cold air near the ground causes fog to form
valley fog - radiation fog and cool air that pools in the valley
advection fog (cold water) - cold water gathers near the coast b/c cold deep
water has been forced up and along the coast. very humid air from the ocean
flows over the cold water and and it cools. because the dew point is so high fog
forms very quickly and then dissipates once it gets over land
advection fog (warm water) - very cold air hits warm water and fog rises off the
water like steam b/c right above the warm water there is warm moist air that
mixes w/ the cold air and fog forms
Dry adiabatic lapse rate - with increases in altitude the temp decreases due to
dropping pressure -9.8 degrees per km
moist adiabatic lapse rate- the same as dry but the temp changes slower b/c
saturated air condenses and releases heat as it rises. -6 degrees per km
both adiabatics rates are only theories.
absolute stability - the environmental lapse rate is lower than the adiabatic lapse
rate. (the environmental lapse rate is the actual lapse rate and the adiabatic
lapse rate is a theory)
the temp changes more slowly with altitude than the adiabatic rate. when
graphed if the environmental lapse rate is to the right of both the adiabatic lapse
rates then it is absolutely stable
absolute instability - means that the environmental lapse rate changes temp
faster than both adiabatic lapse rate. when graphed the environmental rate is to
the left of both lapse rates
conditional instability - the environmental lapse rate is slower than the dry
adiabatic lapse rate but faster than the moist adiabatic lapse. when graphed the
environmental lapse rate is to the right of the dry lapse rate and to the left of the
moist lapse rate. Thus if it is a dry day it is stable and if it is moist day it is
unstable.
First test to here
Feb 3 2009
instability is caused by anything that causes the air by the ground to
become hot and the air aloft to remain cold
solar heating of the earths surface
warm air advection at surface
air moving over a warm surface
Aloft - cold advection and radiational cooling of clouds
As an entire air mass moves the top part is able to rise more and cool more
than the bottom part resulting in instability
A stable layer of air (the top of the troposphere) caps the rise of air in
unstable conditions and thus clouds stop growing
cloud formation
convection - warm air rises off the ground - cools and expands, when
the dew point is reached vapour condenses out and clouds form
topographic (orographic) - air is forced up by a landmass - cools and
condenses
convergence - air blows into a low pressure trough and is forced
upwards - cools and condenses
lifting along weather fronts - dense cold air moves along the ground
forces warm air up very quickly. often results in short but intense storms.
Warm fronts meet a cold stable front and have difficulty pushing it away
thus the lighter warm air rises on top of the cool air resulting in long lasting
rainy days.
condensation nuclei - .2 micrometers
typical cloud droplet - 20 micrometers
typical raindrop - 2000 micrometers
once a raindrop starts falling it increases in size by colliding and absorbing cloud
droplets along its leading edge
feb 10 2009
smaller water droplets have such a tight curvature that it is very difficult for
them to freeze
there is roughly 1 ice nuclei per 100,000 water nuclei
ice droplets grow at the expense of water droplets
riming causes snow pellets - supercooled droplets that freeze on contact
with falling ice
snowflakes form through aggregation
high altitude clouds can seed lower level clouds by providing the required
ice nuclei and the lower level clouds can then precipitate
virga - precipitation that falls but never reaches the ground b/c the
precipitation is evaporating in the atmosphere
rain often starts as snow and upon reaching the melting points becomes rain
sleet is when snow melts but the the temp drops as the rain falls and the
rain re-freezes forming sleet or ice pellets. the cold layer near the surface
must be thick for this to happen
when the cold layer near the surface is thin freezing rain events happen
and as the rain hits the ground it freezes on contact
hail stones are the largest when they travel horizontally through a cloud.
warm air’s pressure decrease slower with altitude than does cold air’s
pressure.
wind flows from the equator to the poles on avg b/c there is high pressure at the
equator and low pressure at the poles b/c of the above point.
there is a sudden transition from warm to cold air thus a sudden change in
the pressures from high to low b/c of the polar fronts and subtropical air
creating a jet stream
the jet stream in the northern hemisphere moves from west to east. this is
because of the coriolis effect.
geo-potential heights - the height you have to go to to reach half of sea
level pressure. geo-potential height lines show us the direction of the wind
and if they are getting closer together they are converging and if they are
getting farther apart they are diverging.
fast moving air that is diverging up high air is sucked up off the surface creating a
low pressure underneath the fast moving air. As long as the air above continues
to diverge air will keep getting sucked up off the surface. this is why some low
pressure systems die quickly and others don’t.
convergence aloft promotes high pressure below. divergence aloft promote
low pressures below.
Feb 24, 2009
wind barbs point in the direction that the wind is traveling and the barbs
indicate the speed of the wind.
wind speeds are highest over the shortest pressure differences (lines are very
close together on a pressure gradient map)
at the surface winds blow CW out of a high and CCW into a low but high up b/c
of the coriolis effect and the lack of friction the winds follow (run parallel) to
pressure lines.
when pressure lines converge up high it forces the air down as it cannot go
up (top of the troposphere) and this causes high pressures to form at the
surface. and when pressure diverges up high it sucks air up off the surface
and creates a low pressure
when upper air converges it forces the air to speed up like a river as it narrows
geostrophic wind is the theoretical wind that would result from an exact
balance between the Coriolis effect and the pressure gradient force. The
geostrophic wind is directed parallel to isobars (lines of constant pressure
at a given height)
in the southern hemisphere winds blow CCW out of a high and CW into a low.
winds can occur in systems from a few meters across and lasting from seconds
to minutes to huge systems that cover the globe and last days to weeks.
when talking about wind you describe them as where they come from not where
it is going to
sonic anemometer - sound waves determine wind speed and direction both
horizontally and vertically. also tells you the temp as well.
wind under stable conditions is almost always horizontal but wind under
unstable conditions averages 0 degrees but can be up to 15 degrees up or
down.
weak wind in stable air will have very small eddies but strong winds under
unstable conditions will have large eddies with strong wind gusts.
snow drifts form in eddies where the wind is not as strong - it is behind an
obstruction the forces the wind to eddy.
tornadoes almost always spin in a CCW rotation. the reason is b/ they are
associated with the larger spin of a thunder storm.
for the coriolis force to have an effect there must be a large area for a the system
to work over and thus when a wind goes past a relatively small obstruction like a
mountain or something the winds can spin or eddy either direction
wind speeds can be high all the way to the surface of the prairie's b/c there
is very little surface friction, but over a forest or city there is more friction
and thus the air slows down near the obstruction. that air slows down the
air above it and that air slows down the air above it.
thus there are higher wind speeds closer to the ground over flat clear
ground than over hilly or obstructed land like forests and cities.
depth of mixing depends on
surface heating
wind speed
topography
and surface elements
readings for test - pg 112-135, 142-165, 170-wherever we just got to.
lenticular clouds form as air moves over a mountain and the air roles up
and over it. ripples of air form in the turbulence of the mountain and it
makes lines of clouds running parallel to the mountain range that extend
off behind the mountains for hundreds of kms
shelter belts lower wind speed near the surface, capture snow and reduce soil
erosion
wind shear’s can happen without a change in wind direction
wave height, if you have deep enough water is a function of wind speed and
fetch and the length of time wind blows along the surface of the water. and this
accentuates the wave
fetch - the max length of open water over which wind can blow
as land heats up by the sun the land heats faster than the ocean and thus
the air over the land rises faster over the land than the water creating a low
over the land and a high over the water and wind blows from the ocean to
the land. as the air over land rises more and more then a high pressure is
created high in the atmosphere over the land and the wind blows back to
over the ocean at altitude.
land breezes are the opposite
when land is sided by two bodies of water like florida it gets water induced
convergence as sea breezes meet over the land and there are many many
thunderstorms
the reduction of friction as wind blows over the water causes the wind to speed
up and for the coriolis force to have an effect on the wind which causes it to
bend.
monsoon seasons - during the winter solar radiation is weak and a high
pressure forms over eurasia and all low pressure systems move south
following the greatest energy of the sun. thus winds blow from the north
and starts as very dry cold air and it has to go over the worlds highest
mountain range thus India, Bangladesh, Sri Lanka and other nations get
very very very little moisture.
During the summer the inter-tropical convergence zone (low pressure)
parks itself over India and solar heating is very strong and as warm moist
air blows over the land and rains a lot then the air is forced up against the
Himalayans and rains even more, thus Cherrapunji India is the wettest
place on earth.
Santa Ana winds - a high pressure sits over the desert states of the US and
then blows over California and as the air drops it rises at the dry adiabatic
lapse rates and is very hot and very dry.
Katabatic wind - occur where there is a big plateau that is allowed to cool.
as cold air pools on the plateau and then blasts down off the plateau and is
very cold even though it warms as it falls, it is so cold with such high wind
speeds that there can be dangerous wind chills.
haboob - a sand storm combines with a rain storm resulting in very muddy
water falling.
a given wind speed can pickup varying size of particles depending on what
the particle is made of. Clay can be held up with virtually no wind but sand
needs a very high wind speed to stay suspended.
where the sun is most intense there is a band of convection and precipitation
around the center of the earth. this is the inter-tropical convergence zone. it
moves south during the winter and north during the summer and causes two
rainy seasons around the equator (on each side) a year.
low pressure forms along the jet stream and high pressures form in the tropics
and this causes the prevailing westerlies in the mid latitudes. The pressure tends
to be higher at the poles than at the mid latitudes which causes polar easterlies
the Hadley cell form b/w the equator and the midlatitudes the Ferrel cell b/w the
midlatitudes and the polar front and the polar cell above the polar front.
ITCZ equatorial lows => subtropical highs => sub-polar lows => polar highs
2nd test comes to here
Mar 3, 2009
the eastern seaboard sees even rain fall events that happen all year and the
west coast sees rainfall during the winter but gets hardly any during the summer
there is a huge difference in the hight of the air column that it takes to
reach half sea level pressure (500mlb)
in the summer in the northern hemisphere you must go much higer to reach the
500mlb level than in the winter
the jet stream is much stronger in the winter than in the summer b/c there
is a stronger gradient of pressure b/w the equator and the poles.
in the summer the jet stream almost breaks down b/c there is such a small temp
difference with latitude
jet stream - a ribbon of fast flowing air at the top of the troposphere b/w the
subtropical and polar air masses
it is a self perpetuating system b/c it causes low pressure below it and
causes a strong division of temps and thus it can feed itself b/c the division
of air temp is what causes the jet stream.
warm subtropical air is held to the south and cold polar air is held to the north of
the jet stream
there is a very strong pressure gradient around the jet stream b/c pressure
drops more slowly in warm air and thus when the air temps are thinly but
quickly divided so is the air pressure.
b/c there is no friction, unlike at the earths surface, the coriolis force is the
only thing that acts on the air in the jet stream which flows from the west to
the east around the globe.
the polar jet stream vary b/w 30 and 70 degrees north.
oceans are large enough that they have their own coriolis effect but they are
effected more by air flow
air masses can be classified by their location, either continental or
maritime, and where they are coming from, either polar or tropical.
maritime air masses have very little temperature change from winter to summer
while continental air masses can have extreme temperature differences. areas of
siberia can see a 90 degree change from winter to summer
polar air masses also see more temperature variation than do tropical air
masses.
Mar 10, 2009
when a cold front moves through and forces warm air out then precip is
virtually instant and can be very intense and happens right at the front.
when a warm front is moving over a cold air mass precip is usually light
but long lasting and can happen hundreds of kms in front of the front line.
high pressure systems often form over the center of continents. They
usually follow a pattern in their movements.
if a high pressure system moves over the Arctic and down the western side of
north america it will stay along the western side of the continent and extremely
cold temps will be felt. if the system moves down over the center of the continent
it will move off to the east coast over the great lakes and it won’t be as cold here
in leth.
Rossby Waves - the wave like pattern of the isobars around the north pole.
they are in long wave patterns and short waves move through these long
wave troughs and exaggerate the trough which enhances the wind speeds
aloft and the divergence aloft on the other side of the trough
Baroclinic Wave Theory - differential temps cause advection to intensify as
a short wave moves through and exaggerate the trough. cold air is pushed
into warm air and vice versus. high wind speeds form and a circulation is
started and more condensation may release more heat energy for the
storm.
two things can happen - the flow is cut off and a cold air is stuck in a
small low aloft but there is no advection and the low at the surface dies.
- the cold front catches up to the warm front and
there is no longer any mixing
a Baroclinic is caused by a short Rossby wave moving through an area
along the lines of long Rossby waves.
in the northern hemisphere there is CCW vorticity which is the same direction as
a low pressure system.
as the air moves through the rossby waves trough the air gains cyclonic
relative vorticity b/c it is flowing in the same direction as the air is already
moving
as the air moves through a rossby waves ridge the air is flowing CW and
the air gains anti-cyclonic relative vorticiy as the air is rotating in the
opposite direction of a high pressure system
a low pressure system would form easiest just downstream from a zone of
maximum cyclonic vorticity
on the down flow from a ridge to a trough is the region of upper-level
convergence and the up flow from a trough to a ridge is a region of upper-level
divergence.
vort-max - area of maximum vorticity. occurs where the rossby waves
bend. this happens in the mid latitudes where objects are moving with a
cyclonic motion as the earth spins.
Mar 17, 2009
thunderstorms have requirements to form
conditional instability - a shallow stable layer sits above a layer of
unstable warm moist air near the ground. eventually the warm unstable
layer erodes the stable air. once it has punched through the stable layer it
is into the cold air aloft. the lower air rises and condenses. where ever the
stable air is eroded first that is where the warm moist air rushes up into
and causes a thunderstorm
trigger mechanisms - could be fronts, sea-breeze front, mountains, localized
zones of excess surface heating, shallow boundaries of converging surface
winds.
thunderstorm development
heating w/i boundary layer - air trapped here due to stable air aloft
increasing heat/moisture w/i the boundary Layer (BL)
external trigger mechanism - forces parcel to rise to the lifted condensation
level (LCL) clouds form and the temp follows MALR
Parcel may reach level of free convection (LCF) - parcel accelerates under
own buoyancy because it is warmer than its surroundings which leads to
explosive updrafts
saturated parcel continues to rise until it eventually reaches a level of
stable air which it is unable to erode
Types of thunderstorms
ordinary cell thunderstorm
limited wind shear
often form along shallow boundaries of converging surface winds
- cumulus stage - sun heats land, warm humid air rises, condensation
points is reached producing cumulus cloud, grows quickly b/c of release of
latent heat, updrafts suspend droplets, towering cumulus or cumulus
congestus clouds form
- Mature stage - droplets are large enough to overcome updraft
(rain/hail), entrainment (drier air is drawn in), air descends in downdraft
(due to evaporative cooling and falling more rain/hail), anvil head when
stable layer is reached (cloud follows horizontal wind), strongest stage with
lightning and thunder
- Dissipating stage- updrafts weaken as the gust front moves away
from the storm, downdrafts cut off the storms “fuel supply”, anvil head
sometimes remains afterward, ordinary cell thunderstorms may pass pass
through all three stages in about 60 minutes.
supercell thunderstorms
precipitation does not fall into the updraft
cluster of cells at various developmental stages due to cold outflow
undercutting updraft
the downdraft does not kill the updraft by mixing as they stay
separate.
defined by mid-level rotation (mesocyclone) highest vorticity is near
the updraft core
the severe storm environment:
high surface dew point
cold air aloft - increases conditional instability
statically-stable layer - capping the boundary layer
strong winds aloft - aids tornado development
wind shear in low levels - allows for long lasting storms
dry air at mid levels - increases downdraft velocities
tornados are often in the southwest corner of a large storm. around a tornado
there is often no rain as the updraft is so strong.
tornados start as a shaft of high speed horizontally rotating air that is
forced vertical by a strong updraft.
toradogenesis
mesocyclone 5-20 km wide develops
vortex stretching: lower portion of mesocyclone narrows in strong
updrafts
wind speed increases here due to conservation of angular momentum
narrow funnel develops: visible due to adiabatic cooling associated w/
pressure drops
Test comes to here
Mar 31, 2009
the only part of smog that we can see are the nitrogen compounds which means
that the majority of pollution is invisible
smog can form in areas of stable inversions formed by adiabatic warming
due to subsidence and inversions formed in the lee of mountains
potential temperature - temp that has been corrected to sea level.
unstable conditions result in looping plume patters - it is well mixed in the
atmosphere
neutral conditions result in cloning plume patterns. - doesn’t mix very well
but it eventually spreads out up and down
very stable conditions result in fanning plume patterns - the plume travels
horizontally but doesn’t mix at all
stable air near the ground and unstable above will result in lofting plume
patterns - means that the pollution doesn’t drop down to the ground it
spreads up into the unstable air
unstable air near the ground and stable air above results in a fumigation
plume pattern - the pollution mixes down to the ground but is trapped near
the ground and cannot mix upwards.
climate change
there have always been climate fluctuations and these can be for any number of
reasons.
there have been times that are warmer than currently but not many and the rate
of current warming is very fast.
large composite volcanoes can effect global avg temps but it is temporary
April 7, 2009
lifespan of sulfates is much shorter than the lifespan of CO2 or Methane and the
likes.
there are many different models on climate change and temperature and
precipitation increases. we know things are getting warmer but we don’t know
really anything other than that.