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Lecture 8 and 9

by: Cora Man

Lecture 8 and 9 ATM 102

Cora Man
Stony Brook U
GPA 3.92

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Lecture 8 & 9
Introduction to Weather and Climate
Professor Mak
Class Notes
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This 6 page Class Notes was uploaded by Cora Man on Monday February 15, 2016. The Class Notes belongs to ATM 102 at Stony Brook University taught by Professor Mak in Winter 2016. Since its upload, it has received 21 views. For similar materials see Introduction to Weather and Climate in Physical Science at Stony Brook University.

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Date Created: 02/15/16
Lecture 8 – Tuesday, September 25, 2012 1. which force is a static force? a. Coriolis  b. Friction c. Pressure gradient (acts upon stationary objects, that don’t move) 2. Is the Earth’s atmosphere headed evenly, solarly?  - No, we live on a sphere.  o Solar radiation – solar altitude increases to 90 degrees – solar input  increases, solar altitude decreases – solar input decreases, strength of sun  is proportional to the sin(solar altitude in degrees)  o Solar altitude of 90degrees = solar zenith angle of 0degrees  o Net loss at high altitudes  o Net gain at low altitudes (circulation of atmosphere = fast and circulation  of ocean =slow)  o Amount of energy needed to boil water > amount of energy  o Heat released from atmosphere – convection – vertical  o advection – horizontal 3. What causes seasons? - Earth’s axial tilt (winter in northern hemisphere, summer in southern  hemisphere)  - Distance between Earth and Sun (seasons would be the same time everywhere)  o Axial tilt o Variation in solar input causes changes in length of day, which leads to  seasons o 23.5degrees off normal, top half of planet will be in sunlight for more than half the day and solar altitude will increase = length of day and solar  altitude = axial tilt is greater with respect to the sun  o circle of illumination to be 66.6 degrees must be facing the sun = summer  sollistice = longest day – june 21,june22  o axis of rotation is rotated to the same plane as the sun = September 21 – go through north pole (straight up and down) – equinox – 12 hour day  everywhere  - know how to draw: o pressure gradient force o Coriolis force o Friction o Centripetal forces o Gradient wind o Geostrophic wind  Chapter 8 What forces control the speed and direction of the wind? - Forces      Pressure Gradient Force  Strength = difference in pressure   Air moves from high pressure to low pressure o Bigger difference, bigger force   Strength is dependent on the distance between the points of  different pressure  P2−¿P 1  PGF between point 1 and 2 is proportional to  D 2D 1 ¿  Pressure = Force / Area   Pressure is measured by how much matter is on top of you o The deeper down you are in the ocean, the more  pressure there is on your body because there is more water above you.       Coriolis Force  Always points toward the center of rotation   Force is causing the curve  o Deviation to the right in the Northern Hemisphere  (NH)  Direction of Coriolis force always points 90  degrees to the right of motion (direction of  motion) o Deviation to the left in the Southern Hemisphere  (SH)  Direction of the Coriolis force always points 90 degrees to the left of motion (direction of motion)       No Coriolis force at the Equator       Maximum force at the North and South Poles  o Needs velocity (speed and direction)       Centripetal force  Any time you have curvature (not straight motion), the centripetal  force is present.      The centripetal force always points toward the center of a  curved path.       Friction force  Resistance between two objects  Friction acts on two interacting bodies with or without motion.   Friction force will always act in the opposite direction of motion  force.  1. Slower wind speed 2. Reduced Coriolis Force  Coriolis Force = 2  2Ωvsinθ 3. Wind direction changes and shifts toward Pressure Gradient  Force 4. Coriolis Force shifts   ***Friction is always the opposite of the direction of travel.       Gravity  Attractive force between two bodies  - Interacting forces – forces describe interact to control the vertical and horizontal  motion of air (what is happening at the surface)  o Hydrostatic equilibrium – balance of gravity and the vertical pressure  gradient   Air parcel – a pocket of air with boundaries  o Geostrophic wind – balance of the following two forces:  1 .     Pressure gradient force  2 .     Coriolis force   Isobar – lines of constant/same pressure   Force balance – pressure gradient force is balancing the  Coriolis force   Geostrophic wind is parallel to isobars (on a weather map)   Pressure gradient force is perpendicular to the isobars.  ***Wind direction follows isobars (Geostrophic Flow – always in a straight  line) o Gradient wind – an “imbalance” of the following three forces causing  (curved) circular motion:  1 .     Pressure Gradient Force  2 .     Coriolis force  3 .     Centripetal force   Gradient wind points parallel to isobars  Newton’s Second Law – Force = mass x acceleration  o Geostrophic and gradient wind are frictionless. How to  maintain balance or equilibrium with friction?   The frictional force acts against motion, but we  still need to balance.   Ageostrophic – with friction   Continuity of Wind   We can have convergence of and  divergence of wind. Remember that  what comes in has to come out.   This is accomplished through  vertical  motions.  - Vertical motion (gravity is involved)  o Surface winds and friction o Convergence and divergence     Scales of motion o Planetary o Synoptic o musicale o Mesoscale Lecture 9 – Thursday, September 27, 2012  Wps.prenhall. - northern hemisphere summer is closer to the sun than the southern hemisphere  summer  - equinox – 12 hours of day/night  o everyone has a 12 hour day during vernal equinox (03/21) and autumn  equinox (09/23)  - altitutde changes 47degrees  - 23.5degrrres = most northern position in the sky  - as you go from the summer to the fall, the latitude is lower, every day the sun is  going to get a little bit lower  - tropic of cancer –  - tropic of Capricorn –  - tropics – The area equatorward od the most poleward latitude where the sun  reaches zenith (SZA=0), solar alititude=90,  o never cold because of intense heat  o weather pattersn will change due to the precipitation (monsoons), wet  seasons  - North pole – sun will not set for 6 months  - Seasons  o Caused by the length of exposure (axial tilt, position of aaxial tilt relevant  to the sun) and intensity of exposure to sunglight (how high the sun is off  the horizon)  o Shorter the day, the lower the sun is off the horizon o Sun goes lower, the solar intensity is lower  - Artic circle  o Lowest altitude where there is a polar day and a polar night  o One 23hour day per year and one 24 hour night per year o Polar circle latitude =90degrees – 23.5degrees (axial tilt) = 66.5degrees  latitude (one day where the sun does not set for 24 hours)  - Anarctic circle  o Winter solistice – the sun will never be above the horizon  -  Wnter time – release heat from water= colder  - summer – absorb heat from water = hotter ‘ - what is the maximum solar altitude at stony brook (lattidude =40.3degrees) - 40 – most northern position of sun = axial tilt (23.5) = 16.5 degrees  - subtact  90­ 16.5 degress = 73.5 degrees  - when is it? = summer socilitce june 21  - what is the maximum solar altitude at north pole (lat. =40)? - 90­23.5 = 66.5  - 90 – 66.5 = 23.5 = axial tilt  - what about interannual variations in temperature? (global/regional? What’s the  difference?)  o solar exposure  - how does the air near the ground heat up?  1 .     radiation 2. convection – much more of a good  source – heating up a liquid and the liquid can mix, can diffuse its heat  3. conduction  ­ air itself is a good insulator


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