GPH 212, Week 4 Notres
GPH 212, Week 4 Notres GPH 212
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This 8 page Class Notes was uploaded by Sheridan Smede on Thursday September 15, 2016. The Class Notes belongs to GPH 212 at Arizona State University taught by Matei Georgescu in Fall 2016. Since its upload, it has received 9 views. For similar materials see Introduction to Meteorology in Physical Geography at Arizona State University.
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Date Created: 09/15/16
Important Dates ● Exam 1 September 21st ● Friday September 16th forecasting contest ○ Find daytime max and min for KSAT location (San Antonio, TX) ○ ASU vs. UTSA Temperature Scales ● Gabriel Fahrenheit ○ 212 degrees F = boiling point ○ 32 degrees F = freezing point ● Anders Celsius ○ 100 degrees C = boiling point ○ 0 degrees C = reezing point ○ Celsius > Fahrenheit ○ F only used in America ● F = 9/5 C +32 ● C = 5/9(F32) ● To overcome shortcoming of negative values, the Kelvin scale was introduced ● Didn’t make sense that temperature could have a negative value ○ K = C +273.15 ○ 373.15 K = boiling point ○ 273.15 K = freezing point ○ An increment of Kelvin change is identical to an increment of Celsius change ● Absolute zero ○ 460 F ○ 273 C ○ 0 K ● Celsius degree is 1.8 more than Fahrenheit degree ● 0 Kelvin = all motions stop (absolute zero) ● Adding 10 degrees Celsius = adding 18 degrees Fahrenheit ○ 104 F = 40 C ○ 86 F = 30 C Meteorological History ● When were these scales developed? ● Galileo Galilei (1593) first thermometer prototype (thermoscope) ○ Lacked a numerical value to indicate temperature ● Evangelista Torricelli (1643) invented device to measure air pressure (barometer) ● Joseph Louis GayLussac (French chemist/physicist) ○ GayLussac Law advanced our understanding of gases and atoms ○ Traveled several thousand feet in a hot air balloon; collected air to analyze ○ Went on a solo flight 40k feet in the air ○ Expansion and contraction of our atmosphere GayLussac Law ● When you add heat, air expands ○ After air expands, pressure is lost ○ Air molecules will begin to leave vessel they are in ○ Eventually, vessel will reach equilibrium ○ Higher pressure = outside the vessel ○ Lower pressure = inside the vessel, compared to outside the vessel ● Air moves in response to pressure imbalances ● Air will move from high to low pressures History Cont. ● Joseph Henry helped purchase meteorological instrumentation to establish an observational network ○ “Programme of Organization” ○ Goal was to solve problem of American storms ○ Around the same time, telegraph was invented Is it possible a librarian will discover a temperature record going back to the middle ages? ● No, they did not have a way to measure temperature back then Energy ● Defined as anything that has the ability to do work ○ Agent capable of setting an object in motion ○ Agent capable of warming a teapot ○ SI unit of energy Joule [kg*m^2/s^2] ● Simplest of activities require a transfer of energy (for example, looking at and writing these words) ● One two billionth of the energy emitted by the sun is transferred to earth as electromagnetic radiation ○ Some ER is absorbed by atmosphere and some by the earth’s surface ● Kinds of energy ○ Kinetic ■ Energy in use or in motion ■ Ex: light, radiation, heat, motion, electrical power ○ Potential ■ Energy in reserve or stored ■ Ex: reservoir behind dam, high pressure ■ Chemical potential energy ● Ex: battery, gasoline, explosives, firewood, food ● Food ○ Process of metabolism is used to convert potential energy stored within food to kinetic energy ● Gravitational potential energy ○ Object’s placement ○ A falling raindrop has both kinetic and potential energy Model output statistics (MOS) ● A technique that interprets numerical weather prediction (NWP) output to produce sitespecific guidance (weather information the public depends on for daily activities) ○ 9 million regression equations ○ 75 million forecasts per day ○ 1200 products sent daily ○ 400k lines of cost (mostly FORTRAN) ○ Millions of hours of supercomputer time ● MOS involves historically tracking how a forecast model performs compared to real observed records ● Used to improve forecast accuracy ● Cooling leads to contraction ● Heating leads to expansion ● Add value to NWP model to quantify uncertainty MOS ● Advantages: ○ Reliable probabilities ○ Removal of some systematic model bias ○ Specific element and site forecasts ● Disadvantages: ○ Changing NWP models (ex: numerical models themselves are always modified) ○ Availability and quality of observations MOS What is needed? ● Historical weather output ● Observations ○ Compare data to what actually happened Reading a MOS message (interpretation goes from top to bottom of message) ● Starts with identifier of location ○ Always 4 letters, starts with K (ex: KDEN, KSEA, KPHX) ● GFS a numerical weather prediction model ● MOS guidance the title ○ Guidance = prediction ○ Because meteorology is an inexact science ● Valid date for forecast ● 1200 UTC coordination of time globally ○ Greenwich where we base time globally ● DT the date ○ A short term prediction, not more than four days ● Values by hour ○ Every three hours ○ Some metrics provided every 6 hours ○ Once you reach 00 (midnight) the day changes ● N/X ○ Nighttime minimum temperature ○ Daytime maximum temperature ● TMP temperature at designated hour ● DPT dew point at designated hour ○ Dew point = the temperature current temp needs to d saturation to occur ○ Dew point cannot be higher than actual temperature ● CLD cloud conditions; coverage ○ OV overcast ○ BK broken ○ Clear ○ SC scattered clouds ● WDR wind direction (in tens of degrees) ○ Ex: 19 = 190 degrees ○ 180 degrees = wind is coming from the south ○ 90 degrees = coming from the east ○ 270 degrees = coming from the west ● WSP wind speed, given in units of knots ● P06 probability of precipitation for 6 hours previous ● P12 probability of precipitation for 12 hours previous Characteristics of Radiation ● Intensity and wavelengths of emitted radiation ○ Categorized into a few individual “bands” along the electromagnetic spectrum ● Electromagnetic radiation ○ Visible light (VIS) is a narrow band bound by infrared (IR) and ultraviolet (UV) ○ Xray radiation has very short wavelengths and can penetrate soft tissues ○ Wavelengths typically specified in micrometers ○ From short to long wavelengths: ■ Gamma rays > xrays > ultraviolet > visible light > Infrared > Radio waves ■ Longer wavelengths = less harmless to humans ■ Wave lense distance between peaks of waves ● All matter radiates energy over a wide range of electromagnetic wavelengths ● Physical laws defining amount and wavelength of emitted energy apply to hypothetical perfect emitters of radiation known as blackbodies ○ The earth and sun are similar to blackbodies ○ Absorbs and emits maximum amounts of radiation ● Energy radiated by substances occurs over a wide range of wavelengths ● Shape of curve of intensity of emitted radiation is similar ● Peak of the curve (for earth) corresponds to a longer wavelength StefanBoltzmann Law ● Single most important factor that determines how much energy a blackbody radiates is its temperature ● The intensity of radiation depends on the temperature raised to the fourth power ○ StefanBoltzmann law: ● Surface of sun is 5800 K (5500 C or 9900 F) and emits about 64 million watts per square meter ● Surface of earth is 288K ● StefanBoltzmann constant (5.67E8Wm^2K^4) Emissivity ● Percentage of energy radiated by a substance relative to that of a blackbody ● Radiation intensity in real objects (not blackbodies) is a function of both emissivity and temperature ● The graybody version of StefanBoltzmann law Shortwave/Longwave radiation ● For any radiating body, the wavelength of peak emission is given by Wien’s law ○ Lambda (Greek) used as constant 2898/T ● Warmer objects radiate energy at shorter wavelengths than do cooler bodies ● Wavelengths less than 4 micrometers are considered shortwave radiation ● Wavelengths more than 4 micrometers are considered longwave radiation ● Warmer bodies radiate more energy than do cooler bodies at all wavelengths Questions for upcoming exam: ● What are the two measures of pressure? ○ ● What is the Wien’s law equation? ○ Lambda = 2898/T ● T/F the earth is a perfect blackbody? ○ False ● Where does most weather occur in the atmosphere? ● What is the most common gas in our atmosphere? ● Where is the ozone located in our atmosphere?
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