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Science of Storms Cheat Sheet .docx

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McGill University
Atmospheric & Oceanic Sciences
ATOC 184
Imad Mansour

EXAM REVIEW SHEET PROPERTIES Temperature  temp= average speed of molecule movement in a substance ( and dependent on property of material you are dealing with) eg: stove (movement in vibrates for solid things)  temp of air= energy of all air molecules that surround us.  Movement= faster for higher temperatures  Absolute zero= zero kelvin where molecules stop moving  Celcius= linked with water (vs human comfort) 100 celcius= water boils  Where is warmest temperaturs on planet? At equator  Warmest and coldest temps= over land because water heats up and cools more slowly than land does (so water= larger heat capacity because it takes more energy to heat up water)  If we had more land= rate of global warming would be higher  Energy source= the sun (tilt of earth). How much heat we get is related to amount of photons that hit an area. When the sun is directly overhead, spot there receives more photons and is thus hotter aka the equator.  Angle and tilt and distance(diming further away)= are the things that determine how warm or how cold areas of the planet get  Seasons= axis of rotation. Season variations at equator= much less (more constant temps). Canada= huge temp variations.  When air is warm= molecules become more energetic, move faster and collide more Pressure  Fx=mx (mass times acceleration = force)  Pressure= force atmosphere is applying on ground  Atmospheric pressure: measuring force of air in column above us.  When pressure is higher= more mass above us  Pressure drops rather quickly when you go up in height (9km-> 66% drop of pressure)  Fewer oxygen molecules higher up you go(ex: mountain climbing)  The higher the pressure is, the more the molecules per square inch. Therefore, the molecules get more sparse as you go aloft since pressure decreases.  Pressure change more vertically than horizontally ex: CN tower vs NYC and Boston  MAP: where values are high= pressure is high  Highs= rising up of air  Low= sinking down of air  Gravity pulls molecules towards surface( more molecules at surface than aloft)  Air molecules= in motion and colliding. Number of collisions= determines pressure (more collisions= higher pressure).  As # of molecules decrease with height= pressure decreases. When we have a lot of molecules, pressure= high.  If the pressure remains the same but temp increases, volume must increase (due to than spacing out more because there is no boundary to collide to walls unlike containers). Cold temp= molecules pack down.  Molecules travel from areas of high concentration to areas of low concentration.= pressure gradient (change of pressure across distance)  Regions that are warm= thickness is larger  WIND= motion of air molecules from regions of high to low concentrations  When pressure isn’t uniform: air molecules try to balance out (from high to low pressure via force). Atmosphere tends to exhibit a balance between vertical pressure gradient going upwards and gravity . So wind doesn't blow much up or down due to this balance.  Layers of atmosphere: o Troposphere (temp decreases as we go up) Ozone= reason why weather is confined to troposphere. (stratosphere= lighter and hotter EX: OIL AND WATER) o Stratosphere (temp goes up because ozone absorbs radiation of the sun) o Mesosphere o Thermosphere   Tropopause: line between troposphere and stratosphere o Takes up more place at equator than north pole because warm air takes up more space than cold air. Jet Stream  Wind= movement of air  Regions where wind is blowing faster than everywhere else (wind blows as result of diff. in pressure from one location to the next)  Strong difference in temp= strong difference in pressure (warm air takes up more space than cold air) which leads to creation of jet stream  Jet stream= demarcates where cold cold air masses and warm air masses will be  North of jet= cold & south of jet= hot (divider between relatively warm air and cool air)  Expect storms to follow stream. Jet stream moves due to temperature gradient.  Wind= direction FROM PLOTTING WIND: WATER  Water in all 3 forms: liquid, gas, ice  Water vapour on earth= concentrated in specific areas (usually where storms are occurring and mostly located in clouds)  Water vapour= 0-6% of actual atmosphere  Force exerted by water vapour= vapour pressure. In cold atmosphere, pressure is near zero and can go up to 60mb. [vapour pressure= can separate pressure for each gas in atmosphere]  IMAGE: areas that are bright= moist  GET Water vapour through the evaporation of water  Dewpoint= temp at which condensation starts to occur.  If dewpoint and temp is the same= then you are in a cloud  Dewpoint can’t be higher than air temp because liquid falls out from the sky and there is a removal of moisture from atmosphere at that point  More water vapour in summer (cant hold water when really cold) o because it is easier to evaporate water than ice and the sun is hotter so we have more energy as well. o The warmer the atmosphere= higher the capacity for water vapour is because warmer temp increases speed of molecules and since they are more energetic it is harder for than to bond together into liquid molecules o Capacity for water vapour= saturation vapour pressure  Vapour pressure= amount of pressure associated with water molecules  When capacity for air to hold Water Vapour increases, the relative humidity drops  Saturation vapour pressure= largert amount of pressure that we have have in atmosphere at given time (how much atmosphere can hold)  Relative humidity= vapour pressure/ saturation vapour pressure  Dewpoint gives actual vapour pressure  Actual temp gives saturation vapour pressure  Relative humidity goes up and night and down during day. Temp at night= cooler. Capacity for air to hold WV decreases so RH rises. MEASUREMENTS  Synoptic measurements=take measurements simultaneously across the globe in Greenwhich meantime  Weather station: temp sensors, instruments to measure height of clouds etc, measurements provided by instrument= recorded every hour (or every minute when weather is interesting)   Stations across N.A= density of stations= where population is and near water bodies  5 centers in Canada, 300 approx in USA  How important is # of station? Weather can change a lot across short distance ex: jet stream  Meteogram: trace of temp, dewpoint and weather and recreates time traces of weather for any station READ CONIDTIONS  Weather buoys (reading over water and measure wave height)  Rawinsodes= weather balloons (with instrument package and launched 2 times a day. GPS = get idea of wind. Also measures pressure. 75 stations o Allows us to get readings from higher up in atmosphere and at surface as well  Radar: transmits microwave energy o Sends a signal o How heavy precip= how much is reflected back (large reflectivity= heavy precip)  Need targets for radar beam to hit  Once radar beam bounces off of something, can tell through frequency and if thing is moving away or towards radar and how fast  Doppler Radar: (tells us about precip and wind through reflectivity o Doppler effect= car goes by (at rate which sounds waves reach air, high pitch vs low pitch) The rate at which sound wave is hiting ear as it gets closer gets quicker and increases in pitch.  Satellite images o A) Infrared  Brightest= high clouds aka colder clouds & cold surface  Darkest= low clouds= warm clouds & warm surface  Times wont be able to tell if there is cloud or not due to little diff. of temp of cloud and ground.  As cloud grows= temp at top of cloud gets colder and colder  Water vapour= regions bight= moist and dark= dry  Hurricane= concentration of WV o B) Visible satellite images (what you could see if you were looking at earth)  Cant use at night  Brightest= thick clouds and snow (hard to tell diff.)  Darkest= water and forests  What we see on visible satellite is dependant on albedo of thing (aka how much sunlight something reflects). Snow and clouds don't have much of a different in albedo) o C) Satellites for NA= GOES W and GOES E= don't move  Aircraft reports, better when going up or down in altitude because then we can have a good picture of atmosphere wheres if not, just measures at one point in altitude  Lightening Detection: crackling in radio signal due to energy wave wend out by lighteing that causes interference EX: lightening, many stations close by will receive signal so sensors can determine location and strength of lightening TEMP AND THICKNESS  Temp is dropping, atmosphere takes up less space.   Temp is rising, and pressure is lowering, we have to travel more distance in atmosphere to get same pressure aka expanding  Pressure decreases as we go up because gravity is pulling more molecules towards the surface WEATHER MAPS  Weather map= gives us summary of weather at given time o Surface maps reveals what is happening and other maps reveal why  When wind comes from north= cold temps, and south winds= warm temps  Isobars= contours of pressure o Tells a lot about wind where are usually parallel to bars (but friction sometimes prevents it from being that way) o Isobars connect points on weather map where pressure= same o Pressure of weather readings:  042 translates to 1004.2 mb  996 translates to 999.6 mb  pressure generally ranges from 970-1040 mb  if you see # with 7, 8. 9 , preceding #= 9  if you see # with 1,2,3 precding #= 10 o on maps:  low pressure= red  high pressure= blue o cold front: cold air is displacing warm air (because temp goes down) o warm from: warm air moving into region that used to be cold because temp goes up  fronts on map tells us if we expect temp to go up or down  wind blows= counterclockwise around low pressure system  clockwise around high pressure systems  closer isobars= STRONGER winds  if BACK TO WIND LOW PRESSURE WILL BE ON YOUR LEFT (low left, wind back)  west side of LOW pressure= winds are coming from north and generally cold  UPPER AIR MAPS: not dewpoint but rather dewpoint depression o If dewpoint depression 3+ = no clouds form o Dewpoint of 2 or less= probably clouds  Mountains cause winds to not blow parallel to isobars  As you go higher and higher in atmosphere, pressure systems are less circular and more wave like PREDICTIONS  Numerical Weather Predictions: use computer model o A) can do a forecast vs what actually happened for PREDICTION o B)Comp simulations for UNDERSTANDING  Run comp simulation of event to understand what is going on ex: thunderstorms since they are hard to observed and measure  We gather data from radars, satellite images, upper air observations..etc  Put that in comp model and we let do it’s thing and the output= helps ppl forecast the weather  Dots= grid points where there is data in model  The smaller the area we are concerned= better the resolution and distance between 2 points  Need certain resolution to set the details of forecast correctly  Lower resolution: can still get general idea sometimes but lose details  Need resolutions that depict mountains etc  Vertical resolution: different data distructions (more towards surface where ppl live)  Map through mountain= fictional data but new models work around that (called signma coordinate system)    Take all observations that we have at surface and turn it tinto map and that’s what we give the comp model  We have to give data to model by creating analysis  Models we use across globe o Only 4 good ones: 2 usa, one from Canada and one from Europe  LIMITATIONS OF MODELS: o Inexact equations: no physical law or understanding of certain processes thus we need to use imperial relationships (if this goes down than the other one does too) through correlation and observations o Parameterization= imperial relationships  Ex: what goes on in a cloud, radiation from sun (how much gets absorbed etc) o Sensitivity to Initial conditions: if you make a small change in one location, creates a huge change elsewhere down the line o Chaos theory: extreme sensitivity to initial conditions o Small changes in data can totally change path of weather and thus there are forecast that are going to be either sunny & hot or raining because small changes can change that down the line o But not every weather condition is sensitive to initial conditions ex: huge storm that going to occur regardless of errors in initial conditions o Problem with initial conditions= human error and huge areas we
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