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.