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Introduction to Weather and Climate Laboratory

by: Kayli Reichel

Introduction to Weather and Climate Laboratory ATS 351

Marketplace > Colorado State University > Atmospheric Science > ATS 351 > Introduction to Weather and Climate Laboratory
Kayli Reichel
GPA 3.83


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This 54 page Class Notes was uploaded by Kayli Reichel on Tuesday September 22, 2015. The Class Notes belongs to ATS 351 at Colorado State University taught by Staff in Fall. Since its upload, it has received 99 views. For similar materials see /class/210246/ats-351-colorado-state-university in Atmospheric Science at Colorado State University.

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Date Created: 09/22/15
Water is very important Hydrologc Cycle Properties of Water Physical States quotW mass Gas Water v r Molecules move fleely and mix wellwith othel molecules Liquid quotquot Molecules are close together nunml and constantly bump one ano he39 lceMnlecule Solid In ice mo ecules are anarged a I in a hexagonal crystal D Only natural slbstance that occurs naturallyin all three RV states on Earth s surface Wquot m Phases of Water Condensation A smrrrmrruarr s e afiee imn airahave and dilecllyinln are vapnl phase a to v 8 n pnlmnlecu P crystaland charges in he Evaporation Wake has a very high surface tensi 7 Take enefgyto break the surface in order to evapofate from the surface ofwater 7 Men temperatures are increases r and can b reak are surfaee lensin rr mn re easrly 7 Wind alm enhanmsevapnlalinn Condensation Deane arremearm e n mama arry area as am quotea mammanem min 7 We call these 1mm rrr arr Cnndensillnn me a nu uahnmhervamdu ar Iswanu and ale mave fasrwarer vapnl may f we When a r Is mld and maeeu es mave n s lywalelvapmismmelikelyln iek r quotus shawSr aearrr in mm ymale mwelllely er rrr are raw mm rrr aarr rrarre mare wit nu Ilhanlnm Saturation lfwe evaporate water in a closed container eventually the evaporated water vapor will oondense back into The air above the water is said to be saturated withwater vapor when the evaporation and condensation rates reach equilibrium With the same number orwater vapor molecules in the air saturation is more likely to occur in cool air than warm air So we have all this really important water vapor in the air all of the time It would be really helpful if we could keep track of it Let s review how we measure water vapor in the atmosphere Absolute Humidity Absolute humidity tells us the mass of water vapor in a fixed volume of air or 391 water vapor densr y Absolute lmdry Mm 01W 39 When avolume of air uctuates the absolute humiditychanges even though the vapor content has remained constant Therefore absolute humidity is not commonly used in atmospheric studies Speci c Humidity q When the mass of the water vapor in the parcel is compared with the mass of all air in the parcel vapor included This measurement does not change as a parcel rises and descend Zonally Averaged Specific ml y new sariw snhy Mixing Ratio Compares the mass ofthe water vapor in the parcel to the mass of the remaining dry air Mm Ra 5 mass of dry air Very similar to speci c humidity 7 Uses only dry air where speci c humidity uses the dry air PLUS the water vapor itself Mixing ratio and specific humidity stay constant as long as water v r is not o or removed from the parcel Vapor Pressure e The 39r 39 39 by measuring the pressure exerted by the water vapor intne air s aw a The lnlal pressure exerted bythe gasesina mixture is equal in the slm rrnhe parlialpressur suieaeh 39 39 errmprrrrem in gas mixune mb rriair e7 mh zin mh 1 quot20quot 1n Inhmgt sauairporprasure 7 Mine air mnre press re a Higher vapnl pressure e Larger nlwaler vapnl mnlecules Saturation Vapor Pressure es Recall when evaporation and condensation are in equilibrium the air is saturated w39 apor Saturation vapor pressure describes how much water vapor is necessary to make the air saturated at any given temperature It is the pressure that that amount of vapor would exert Saturation vapor w pressure epends primarily on the air temperature s a s When water and ice both exist below freezing at the same temperature the saturation a vapor pressurejust above water is a greater than the saturation vapor pres ur 39 Vr n vwaoreurrarr r Relative Humidity RH dicate the actual amount of the air but instead tells us RH does not water vapor how close the a RH water vapor comm water vapor capacity e I RH 100 is saturate I RH gt 100 is supersaturated air XII WX mw mamam m m Changing Relative Humidity I How do we alter a location s relative Id t 7 a Change the water vapor oonten Irrerease wv muterrt raise actual vapnl pressure relatrve humidilyincmases a Change the air temperature Irrerease temperature irrerease saturatiurr vapnl pressure relative himidily deere es arru las12mnlecu es less likely tu mndense a IRH u Remmder Relative Humidity I Since water vupul quot oes not vary much during an entire day changing air temperature primarily regulates the daily variation Y in relative humidit Dew Point Temperature to which air would have to be cooled for saturation to occur with respect to water Icator of air s actual water vapor content 7 Higher dew point higher water vapor content 7 Adding w v to the air incieases the dew point Frost por when dew point is determined with respect to a flat surface of ice Dew Point amp RH Rel ve humidity can be misleadingin indicating areas with high water vapor content 39 important to look at along th RH order to determine the water vapor content of a location One location has a RH 100 and adew p int of UT while a second location has a RH of only 35 but a dew point of 4w 7 W ich location has mole watel vapol in the ail7 Dryaircan have high relative hlmidily July Dew Point Averages Skew T Diagrams Since the advent of rawinsonde observations thennodynamic diagrams have been used to plot sound ng data and to assess atmospheric stab ty Despite numerous advancements in technology and forecast techniques the thermodynamic diagram remains an essential tool of today39s weather orecaster Skew T Diagrams Why are skew T diagrams useful Forecasting applications Temperature and dew point pro le 0 atmosphere Daily maximum temperature Levelol cloud lormation Stable vs unstable air Precipitation type lining lorecastingj Leveloltropopau e CAPE convective Available Potential Energy asti Microburst lorec And many more n m 2n 3 4n universnyotwyommu m m 72 on as Feb acne Isobars pressure Isotherms temperature Isomyms K Q Saturation Adiabats Saturation Adiahas mm 4a 4a 4 n n m m m m Saturation Mixing Ratio sammuon Mlxlug Rana Lines What Makes the Wind Blow ATS 351 Lecture 9 March 25 8c 26 2009 Outline Atmospheric pressure Measurement ofpressure Forces that affect the wind per Coriolis Centripetal Friction Vertical Motion Atmospheric Pressure I Ideal Gas Law I prRT p pressurep densityj cunstant 2871kgK T e temperamr Hold pressure constant what is the relationship between temperature and olensit 7 Hold temperature constant what is the Atmospheric Pressure It takes a shorter column ofdense cold airto exert ssure as a taller column ofless dense arm a Warm air alo is normally associated wrch high acmospherr39e pressure V r M than culd ar hrgher pressure horizontal variations in pressure chat causes due air to ove creates wrnd Measuring Atmospheric Pressure Barometer harorhehie pressure eter rhehes ufmercury m H9 mm 725 W a quot Pressure Readings A I Baro particularloc station pressure meter reading at a adon Must adjust pressure at higher altitudes to sea level sealevel pressure Add l mb ufpressure r l I Elm ab uve fu ry sealevel Surface and UpperLevel Charts Sealevel pressure chart constanthei ht Upper level or isobaric Chan constant pressure surface Le 500mb Cold air alo low helghts orlow pressure Warm air alo high heights or high pressures Rldge where isobarsbulgehorthward Trough where lsobarsbulge southwarol In Northern Hemisphere High pressure anticyclohe winds blow clockwise and outward from center Low pressure mldrlatlmde cyclone winds blow counter clockwise and lnward towards center Newton s 2nd Law of Motion I 2nd Law I F ma r mm m carriage column At a constant mass the force acting on the object is The object accelerates in the direction ofthe net force acting on it Therefore to identify which way the wind will blow we must identify all the forces that affect the movement of air Forces that Affect Wind pressure gradient force PGF Coriolis force Centripetal force Friction Pressure Gradient Force Pressure gradient Apd Ap differen em pressure a distance PGF has direction amp ma 39tude Dxremun duected sum hxgh m luwpressure atnght anglestu xsubars Magutude directly related m pressure gadxent TxgmthnzsmmngPGF 2 mugquot We I PGFis the force that causes the wind to blow mm mzu PGF FGF MAPVIEW Mant WA H t par a 20000000 PG ttt1 PGF some my FFFI HFFFFFFFFIW d 1 P Stronger wind greater de ection l Coriolis 2mm No Codolis effect atthe equator greatest at p0 es Only in uence direction not Speed Geostrophic Winds When the farce ufFGF and Cunulxs arebalanced Travelparalleltmsubars eta mm speed m1 atmusphere but class enuugh m understand was aim1 spacmg ufxsubars indicates speed mm W Clasef55L fpxead Hut slww t Gradient Winds amp Centripetal Force level of frictional in uence winds alott An object accelerates when it is changing speed andor 39rection Therefore gadlentwmd bluwmg aruund aluw pressure eenter is eunstsntly aeeeleraung Centripetal acceleration directed atngnt angles to the wind inward toward center oflow Centripetal force inwarddirech force andtne FGF wiumi now Amlmclv c mm emrn s in MM new ins mine in in tin prismmu indium iuli Cyclonic ow PGFgt CF Anticyclonic ow PGFlt CF Z onal amp Meridional Winds Zonal winds oriented in the WE direction parallel to latitude Moves clouds storms surface anticyclones rapidly from west to east Meridional winds oriented in ms major storm systems Surface and UpperLevel Winds Winds on Upperlevel Charts wlnuls parallel tu euntuur lines and Claw west tu east llelghts decrease 39nm nu uuth I Surface Winds wlnuls nurrnslly eruss lsubars and bluwmure sluwly than wrnuls pneuun reneestn wind sneeuwnenrnurn nirvana the Canal set Fncumlayex snrueetn unuutluuuntzzuurt wlnuls eruss Lhelsubars at about no lntu luwpressure and nut ufhlgh pressure ff l9 e16 I PGF a1 sulface is balanced by the sum of friction and Coriolis force I Surface winds mm low and uutward from Winds amp Vertical Motions Since surfaee winds blow into the center of alow they are converging and that airh to go somewhere 2 slowly rises su aee and dzvergence aloft and a surfaee hlgh has the opposite Therefore a surface low has Cunvergence at Convergence Dlvergencs Hydrostatic Balance There is always a strong PGF directed upward Gravity balances the upwardPGF When they are equal hydmstau eqmllbnum exists Good appmxlmau39on for almosth walla slow vertical movements Is not valid for violent thunderstorms and tornadoes What is energy a The ability to do work Energy is always conserved a Potential Energy a R epresentstne peienirai tn ge Wurk51ured a PE mgn u Kinetic Energy B Energy aeeeeraiegwnn mutiun KE in my a u Tne temperat energy er it is a measure onne average speed onne atoms and molecules u Internal Energy a Sum eraii stared energy rn muiecuies Potential vs Kinetic Energy At any mamem rn its new ine ball nae exadlytne me enereyri nag at ine Stan energy rmi ismnserved neenerey is kinetic buttne Mal energy staystne same What do we mean by heat in Heat is energy in the process of being transferred from one object to ano er because of the temperature difference between them in The transfer of energy goes from higher temperatures to lower temperatures in In the atmosphere heat is transferred by conduction convection an radiation Transfer of Energy in Conduction u Molecules transfer energy to other molecules they come in contact with 1 Ex The Lll l warms the ground and this heats a thin layer ofalrabovethe surface in Convection u Energy transfer by the motion ofmatterfrom one location to ano er 1 Ex Warm less dense parcel of airrisihg ii Radiation u Energy transfer not requiring contact between bodies or a uid between them The Sul i warms the earth from 9i million miles away Sensible amp Latent Heat in Latent Heat the heat energy required to cha e a substance such as water from one state to another a Latent heat is released to environment during condensation 39eezing and deposition warming recess a Latent heat takes energy from the environment durin evaporation melting and sublimation cooling process in Sensible Heat the heat we can feel sense and measure with a thermometer a When the vapor condenses back into liquid water Latent Heat Radiation n Ramatpntravetstntheturrn uteteetrurnagnette Waves that retease Energy when they are absurbed byan abject n Achmgs nu rnatterh uvv ptg ur smaH Ermt ramatmn u The waveteng hs ernttteu depend pnmamy an the abject s temperature a htgherternpe amvea tasterwhrahen u122mvunsgt sh m r enerwavetengthsetern 2d ramahen As the temperature ufan abjectm ease ramatmn S Emmed eaeh secund Stefane mtzmann Law EaT smu re tuta Electromagnetic Spectru mwvvvm W Shunvvave sutar ramatpn A lt4 prn Lungwave terresttat ramatmn A a 4 prn m Solar vs Terrestrial Radiation Wien s Displacement Law a The wavelength ofmaximum emission from an object is related to the temperature by a simple expression Am 7 2897m K1 7 T a Sun km 05 pm a Earth 9 10 um What happens to radiation in the atmosphere u Reflemiun u Albedu is a percentage utineieent Yadlatlun that is immediately retlected hack a Absorption u Everythingthat Emits Yadlatlun alsu absurhs Yadlatlun u Sumethings aie hetterat absurbing than uthers u Scattering u EM waves can be scattered utlin all directiunswhen they came in cuntact with particles in the atrnusphere u The reasun Whythe skyis blue and sunsets are red u Transmission u Waves alsu may simply pass directlythruugh an uhiect The Energy Budget EARTH39S ENERGY BUDGET mm m Reilczml Rellnzrm lmm mam w mm mm smut a ms 6 Why is the sky blue and why are sunsets red towards the observer so the sky appears blue Red Sunsets When the Sun is reacht eobs Ner Greenhouse Effect u Greenhouse gas molecules and clouds absorb outgoing infrared radiation keeping the Earth from cooling without end a Greenhouse gases are carbon dioxide water apor me u These same absorbers radiate as well slightly less though since they are a lower temperature than the surface a Water vapor and CO2 absorb and radiate IR energy and act as an insulating layer around the earth 2 net effect is warming ofthe earth Greenhouse Effect a V 7 gt Wm 7 ti Surface Analysis Contouring u tsotherms contour hnes connectmg tocattons otequat temperature Remtnder temperature ts the top tett numberon a statton ptot I Be sure to tapet taotherm tmes thh a temperature a m ctass examp e n Reminders Please put the last 4 digits of your CSU ID on your homework so we can post scores online Please show your work on problems with calculations Thanksllll ATS 351 Lecture 2 Atmospheric Structure and Composition amp Energy Chemical Gas Composition NI 0 Oxygen 02 2095 cm aloxlde 002 Mon cm 390 Ar nvsa Mathn t 17 Na moms Nllmu nxl e N20 in 0 H2 mom Helium moon 3 0 on a Hydrogen H2 000005 puncluwusuuohIa o onnnm xanen Xe nmoonn ChlarolluummrbnnCFC0110000002 am Table 11 Campasilinn a m almasphzre newline emus sumac 39 om 1 H Chemical Gas Composition Each constituent has a Source Production Sink Destruction eg Plant photosynthesis decay See Ahrens Gas Characteristics Expand or compress due to pressure containers etc Easily mixed Individual molecules far apart Individual molecules have distinct mass Most common measurements temperature pressure and volume Atmospheric Pressure pressure forcearea Measure ofthe weight of air above you Force push or pull especially on other air molecules Compressibl More air mass above means more compression Air closer to the surface more dens e because compressed bythe weightquotofthe air above it Pressure decreases with height exponentially 5 mm mm Ntnu e ikml Hydrostatic Balance We tend to make the assumption that the atmosphere is in Hydrostatic Balance Hydrostatic Balance is when the net upward force on a slab of air equals the net downward force Volume of Gas Temperature and Density Temp is the measure of 7 tne kinetic energy at rneieeuies speed V Warmer air is less dense 7 Cunsiderthe ideal gas lavv wear 7 lfvve cunsidermnstant pressure then PR er Or Censtant eT e ean see then ifthetemperature increases density must decrease It follows Colder air is more dense gum mun i 5 lLilt i m 4mm i ii mm mm v Atmospheric Temperature Complicated vertical pro le Can depend on atmospherlc composltlorr 39 current condltlons lapse rate the rate at which the air temperature decreases with height Layers of the Atmosphere mmml l Layers of the Atmosphere De ned by changes in temperature with height Troposphere 7 Sun warms surface surface radlates Stratosphere 7 Zone absorbs solar radlatlorl Warmlrlg results Mesosphere e No ozone molecules lose more energy than they absorb Thermosphere e 02 absorbs solar radlatlorl Energy Conduction Energy transfer by molecular collisions warms the ground and this heats a thin layer of air above the surface In general airis a poor conductor Convection energy transfer by the motion of matterfrom one location to another Ex parcel of air rising Important in our atmosphere Radiation transfer of energy not requiring contact between bodies or a fluid between them Ex the sun warms the surface ofthe earth 13 Surface Analysis Variables of interest Temperature Cloud Cover Wind direction and speed Weather occurring Wind Wind direction is named for where the wind is coming from Expressed in either cardinal directions N S E W NW SE etc or degrees from north an E Mathematical Meteurulugical Station Plot Temperature BF G23 Station Pressure 72 998 Visibility quot miIes 9 V 16 3 hour pressure 45 change Current PM 09 Weather 3 hour DEWPOInt precipitation 0F Sky bration Cover ID is G23 Station Pressure 72 998 Sealevel pressure is plotted in tenths of 9 V 46 millibars mb with the leading 10 or 9 omitted For reference 1013 mb is 45 09 equivalent to 2992 inches of mercury FNL 39 Below are some sample conversions between plotted and complete sealevel pressure values 410 10410 mb 103 10103 mb 987 9987 mb 872 9872 mb i7 0 haze drizzle rein snnw x W smote slight mudevate heavy Wquot du ulssnd mm imermMen 39 E my continuous 5 O 9 W Preciuimiun rain v Showers 15kt 0 A 5i K rhunueisiorm 25 O r Wemhus ymhnls o 39 3 6 g amissm winmsea u heewuiiitingsnow iow l rw 9 Sandstorm 1 drillingsnowihigh e severesanumim gig heavydli inginuw hlgii f dustdevils unneiciaud i elionln i 39 Whale di smtromstaiion IV 5mm 0 mummy in 5mm Snow Deciphering Station Plot Tlaplcsl Depression below 33 n will lhlckenlng Tmplcal Storm 33m A 1 6 Huvnc na above 50 H a in SW dxscemihle Maximumwnd 5pm in patchy mg patthv shallow mg Fug Trnnicnl 51mm mums mm Cumulitmm Cwmmm 1 7 51 m a Cu 22 a CiUilamemS 2 FS 11 a cumming 23 J Cidense 3 v SI 12 A Cbnm lacimed 26 ClUmme a 0 same 13 5 Ch 25 7 Cimaak spveadlng 5 4 A m oquot 25 2 cl SKA aw i ayes 7 A Cspamalmmmcv15 Ac hickemng a A Cs 174 W my a L CsandCi ma cum 3 m Mme 2n M Annunets 21 AD ch 9 l9 Clmm mm Station Plots Vl nd Barbs vm um Marlin m mkmhm yhrn in claim 115 mph Surface Analysis One ofthe earliest maps produced from measurements Each point contains data taken from speci c surface station Designed to relay maximum data Next Time Energy Radiation Sample Station Data cs 5 Precipitation and Intro to Rada aATS 351 Lecture 8 March 118121 2009 Droplet Formation Recall the two types of nucleation Homogeneous Nucleation Water molecules come together to form a cloud droplet Heterogeneous Nucleation Requires a cloud condensation Nuclei CON Hygmsxutv xiiJ Minimum mum Heterogeneous Nucleation uml grams and xholawcv m m A l data aim Droplet Growth Once a cloud droplet torm s there are 2 ways it can grow into precipitation Growth by condensation Growth by Collision and Coalescence Growth by condensation Very slow process Growth by Collision and Coalescence More realistic mechanism Collision and Coalescence oalescen ce occurs in clouds With tops warm er than 5 F 45 C The greater the speed ol thelalling droplet the more air molecules the drop encounters lmportantlactorslordropletgrowth 7 High liquid water contentWithin the cloud 7 Strong and consistent updralts 7 Large range of cloud droplet sizes 7 Vertically thick cloud 7 Terminal yelocit 7 Droplet electric charge and cloud electriclield Collision and Coalescence iii iiii a 392 39 39 quotililliiig quot i 39 1 I39t quot ice only glaiialed Horn ogeneous nucleation of ice Freezing of pure water Enough molecules in the droplet must join together in a rigid pattern to form an i ryo The smaller the amount of pure water the lower the temperature at which water freezes Supercooled droplets Water droplets existing at temperatures 1 ice crystal to to6 liquid droplets at 10 Homogeneous nucleation freezing occurs at temperatures of 40 C Vapor deposition From vapor to solid Not likely to be sufficient in our atmosphere below freezing C Ice nuclei Ice cry calle Ice nuclei are rare only 1 out of 10 million aerosolsis an effective ice nuclei Fewer sourcesthan CON 7 Desert and arid regions silicate particle dominant 7 Clay particles for temperatures between 710 and 720 C 7 Volcanic emissions 7 Combustion products 7 Bacteria Oceans are NOT good sources of IN stals IN form in subfreezing air on particles 39ce nuclei IN requirements lnsolubility 7 If soluble cannot maintain molecular structure requirement for ice Size 7 Must be comparable or larger than that of a critical ice embryo typically 01 microns Chemical bond 7 Must have similar hydrogen bonds to that of ice available at its sur ace Crystallographic 7 Similar lattice structure to that of ice hexagonal Active Site 7 Pits and steps in their surfaces Growth m ech anism s Vapor deposition Saturation vapor pressure over water greater than over ice Temperature affects saturation vapor pressure over ice the same way that it affects saturation vapor pressure over liquid When ice and liquid coexist in cloud water vapor evaporates from drop and flows toward ice to maintain equilibrium Ice crystals continuously grow at the water droplets expense The process of precipitation formation in cold parts of clouds by ice crystal diffusional growth at the expense of liquid water droplets is known as Bergeron process H Saturation Vapor pressure Vs Temperature s saturation vapor pressure tha 245 Temperature lKeivml Growth m eohanisms 39 Diffusional growth alone not sufficient for precipitation formation 39 AccretionRiming ice crystals collide with supercooled droplets which freeze upon impact Forms graupel snow pellets May fracture or split as falls producing more ice crystals a Graupel from Accretion Equot g r Growth m echanisms Aggregation Collision of ice crystals with each other and sticking together Clump of ice crystals referred to as a snowflake Common in temperatures near freezing where there may be some liquid water on the surface of the crystal Differing temperatures can cause aggregates to grow into different shapes Precipitation Types Rain drop greater than 05 mm Rarely larger than mm because collisions break them up What is the shape of a raindrop Drizzle lt 05 mm Usually from stratus Snow small ice of many form Fallstreaks like virga but from cirrus Flurries no accumulation Snow 5 ua lls Blizzard winds gt 30 kts Precipitation Types Sleet tiny ice pellets form ed from refreezing of rain drops Translucent unlike graupel lt 5 mm Freezing raindrizzle freezes upon contact with the surface Can be extremely damaging Knocks out power Pulls down tree branches Both are common along warm fronts Damage from freezing rain Precipitation Types Virga any precipitation that evaporates before hitting the surface Graupel Ice crystals falls through cloud accumulating supercooled water droplets that freeze upon impact Thus graupel is an example of growth by accretionriming Creates many tiny air spaces These air bubbles act to keep the density low and scatter light making the particle opaque When ice particle accumulates heavy coating of rime it s called graupel Hail An extreme example of growth by accretion Hailstones form when either graupel particles or large frozen drops grow by collecting copious amounts of supercooled water Graupel and hail stones carried upward in cloud by strong updrafts and fall back downward on outer edge of cloud where updraft is weaker Hail continues to grow through updrafts until it s so large that it eventually falls out bottom of cloud Hangowth As hailstone collects supercooled drops which freeze on surface latent heat released warming the surface of the hailstone Dry Growth At low growth rates caused by lower liquid water contents this heat dissipates into surrounding air keeping surface of stone well below freezing and all accreted water is rozen Wet Growth If a hailstone collects supercooled drops beyond a critical rate or if the cloud water content is greater than a certain value latent heat release will warm surface to 0 C Prevents all accreted water from freezin Surface of hailstone covered by layer of liquid water HaHlayers Alternating dark and light layers Wet growth solubility of air increases with decreas39n temperature so little air dissolved in ice during wet grow Ice appears clear Dry growth Hailstone temperature closeto environmental temperature so at cold temperatures large ount of air dissolved Ice appears opaque Hail Descriptors RADAR 39 RAdio Detection And Ranging 39 Transmits a microwave into the atmosphere and measures the return power 10 5 3 cm typical 39 Size chosen depends on use Radar Parts How does radar work g Pulse of microwave energy sent out emitted from antenna to parabolic dish reflector dish focuses energy into beam Beam travelsthrough atmosphere lf the beam hits an object then some of the energy is reflected bacllt to he ra ar turn power measured Data processed to a VlSUal display Energy Return Radar measuresthe intensity of the returned signal the frequency of the returned signal and the elapsed time from the transmission of the pulse Energy beam travels at the speed of light Knowledge of the elapsed time allows the computation of the distance from the radar site Fremiencv uses donnler shift to Return Power Only a fraction of the emitted energy gets returned from reflection amplified and measured in decibels dbz Reflectivity r ldbz 10 logp2p 7 p2 power received at radar varies 39 Reflectivity is dependent upon the size of the ob39ect 39 In meteorology the objects are precipitation particles A plotted region of high reflectivity is called an echo Reflectivity Dependence 39 The return power reflected beam is dependent on the number of particles present and the size of the particles 39 Particle diameterquot 6 dependence 39 Numberquot 1 dependence 39 Larger drops lead to larger reflectivities echoes 39 Reflectivity mostly based on partic e size General Reflectivities 39 Drizzle 20 25 de 39 Light rain 25 35 de 39 Heavy Rain 35 50 de 39 Thunderstorm Heaviest Rainfall 50 de 39 Light Snowfall 15 25 de 39 Heavy Snowfall 25 35 de Rainfall Rates How much rain falls to the surface in a given hour R incheshour z aR a and b are constants Higher reflectivity generally corresponds to higher rainfall rates Saturday s Snow Severe Weather ATS 351 Lecture 11 15 amp 16 Apr 2009 Outline Prevequisiiesi vseveveweaihev Huwcundiiiuns EYE assessed Wim respect 1n seveveweaihev Types miseveve Weather 7 swmemunrceu munuevsmvms S s Types of Severe Weather Thunderstorms Hail Lightning Flood Tornado Severe Wind StraightLine Winds Thunderstorm Distribution Favorable Conditions Instability Shear Initial Li Fuel Restricting Cap Instability Steep lapse rate s warm moist air near the surface Colder air above it Needs to be calculated from a sounding Updrafts and Downdrafts Degree of instability and updraft and downdr s Sources of Lift Convective Ii ing Boundaries ronts Orogra hic Convergence Shear Because of the way a thunderstorm works it needs to be tilted to remain strong Therefore winds need to change with height Two kinds of shear S eed Shear Wind is faster as you go up Directional Shear Wind changes direction with height Vertical Wind Shear Change ofwind speed andor direction with eight Weak vertical wind s ear shortlived since rainy downdraft quickly undercuts and chokes offthe updr ft ed environments are associated with organized convection Vertical Wind Shear r r r l Fuel Just like any other weather phenomenon a storm needs fuel to sustain itself The fuel for a storm 39 39 39 what starte it The storm needs to remain in areas ofw rm moist air If storm moves into a colder region it will die Restricting Cap lfthe atmosphere i get a constan upd It is more effective wh and released all at on e ans ean nappen by having a sta surraee that suppresses eenvem As gro heats during the day energy builds up until it can break the c quot e Aise referred in as a eapprng inversiun e RErnErnberCiN s unstable all the way up you rafl en the energy is held back ce ble iayernearthe inn Back to the SkewT Meteorologists have formulated various ear 7 Ora urnbinatiun er buth CAPE Convective Available Potential Energy 7 Huvv unstable atrnusphere is Ll Lifted Index normally at 500mb levle e L T envnannrent 7 Tvavcel Types of Thunderstorms Thunderstorms eurne lrl many varieties Likelihuud er severity prupumunai m sturrn lifetime NW5 definitiun er severe une ur rnere er the fuiiuvving elements 7 weriargererameiernari e an kt 58 mph ur greaterwinds e turnadues


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