Atmospheric Phenomenon (Weather)

1. Atmospheric Phenomenon(Weather) Thunderstorms, hurricanes, tornados, blizzards, heat-waves and drought

2. Energy • Fundamental to understanding weather • Force • Acts on physical materials • Is not seen, but rather felt • 3 types : Tension, compression, shear • Newtons (N) = force necessary to move 1 kg 1m / sec • Work • Done by the expenditure of energy • Joules = 1 newton over 1m • 10 trillion joules / average thunderstorm • 100,000 x that for average hurricane • Power • Rate at which work is done • Power = joules/sec • 1 joules/sec = 1 W • Global solar flux = 120,000 TW • Global energy consumption = 13 TW (TerraWatts) • The amount of energy reaching the surface of the Earth every hour is greater than the amount of energy used by the Earth's population over an entire year

3. Types of Energy • Potential • Stored energy potentially available • Rock on a cliff contains potential energy • Kinetic • Energy of motion • Rock falls, gains kinetic E and loses potential E • Thermal • Heat or random motion of atoms and molecules • Transferred from one body to another by delta temperature • Sensible • Heat felt by senses • Measured by thermometer • Latent • Result of phase change • Liquid H2O to vapor absorbs heat (latent heat of vaporization) • Conversely, vapor to liquid drop releases heat (condensation)

4. Heat Transfer • Conduction • Transfer of heat through atomic or molecular interactions • Thermal energy moves from area of higher temp to area of lower temp • Coffee to spoon • Convection • Transfer of heat through mass movement of fluid • Convection cells • Hot fluids rise, cool fluids sink • Radiation • Electromagnetic energy transferred through wave emission • Oscillations in magnetic and electrical fields • Transfers through vacuum (e.g. space) • Red light emitted by glowing ember • Sun’s light and/or heat

5. Earth’s Energy Balance • Electromagnetic energy • Travels in waves @ 186,000mi/sec • Infrared • Involved with global warming • Ultraviolet • Increases with depletion of the ozone • Radiation • All matter radiates energy except @ absolute zero temperature • Radiation increases to the 4th power as temp increases • Absorption • Related to temp • Cooler object absorbs until a balance is achieved with radiation • Earths energy balance is changing • Reflectivity • Varies with color • Clouds reflect 30-90% • 30-40% grasslands • 10-15% coniferous forests • Temperature • Hotter objects emit more energy at shorter wavelengths • Sun emits mostly gamma, x-rays, visible and ultraviolet light • Earth emits mostly infrared radiation

6. Electromagnetic Spectrum

7. Earths Atmosphere • Composition • Stable or permanent gases • 77% nitrogen • 21% oxygen • Variable gases • 2% other ( Argon, H2O vapor, CO2)

8. Earths Atmosphere • Structure • No well-defined upper limit • Mostly below ~100km • 5 major layers • Exosphere • Free-roaming ions that may migrate in and out of the solar wind • Very thin • Thermosphere • Mesosphere • Meteors burn up • Stratosphere • Ozone layer • Troposphere • Where we live • Significant < in temp • H2O content

9. Earths atmospherictemperature profile • Atmospheric temp fluctuates w/altitude • Hottest where Suns solar energy is not attenuated by denser atmosphere

10. Weather Processes • Atmospheric pressure (barometric pressure) • Weight of column of air • Air rises in areas of low atmospheric press • Cools and condenses H2O vapor creating clouds and precipitation • Air descends in high press areas • Drier air results in clear atmospheric conditions • Unstable air • When lighter, warm air is overlain by denser, cool air • Vertical adjustments occur • Conditions for thunderstorms • Coriolis effect • Deflection of air currents caused by rotation of the Earth • Right in northern hemi/left in southern hemi • Fronts • Boundary between cooler and warmer air masses • Cold • Warm

11. Coriolis Effect and Winds Patterns • Winds are simply moving molecules of air • Subject to Coriolis forces • Deflects to the right in the Northern hemisphere and to the left in the Southern hemisphere • when viewed along the line of motion • Wind patterns driven mostly by Solar heating

12. Coriolis Effect and Winds Patterns • Solar heating on the Earth produces 3 major convection zones in each hemisphere • If solar heating were the only thing influencing the weather, the prevailing winds along the Earth's surface would either be from the North or the South, depending on the latitude • Coriolis force deflects these wind flows • Strongest at poles weakest at equator

13. Cyclone and anticyclone wind patterns • The wind flow around high pressure (anticyclonic) systems is clockwise in the Northern hemisphere and counterclockwise in the Southern hemisphere • The corresponding flow around low pressure (cyclonic) systems is counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere • This is a consequence of the Coriolis force

14. Atmospheric Pressure • 1yd3 of air at MSL pressure & a temperature of 70 F weighs almost exactly 2 pounds • The air in a room 12 ft x 14 ft with an 8-foot ceiling weighs almost exactly 100 pounds • The average air pressure at sea level is about 14.7 psi • A column of air 1cm2 , from sea level to the top of the atmosphere, has a mass ~1kg and a weight of 2.2 lbs • A column 1in2 in cross-section would weigh about 14.7 lb • Ave sea-level pressure is : 1Bar or 1,013.25 mbar, or 29.92 in of mercury (inHg) • The > barometric press ever recorded on Earth was 32.06 inHg measured in Tonsontsengel, Mongolia on 2001/12/19 • The < non-tornadicatmos press ever measured was 25.69 inHg, set on 1979/10/12, during Typhoon Tip in the W Pacific Ocean

15. This image from September 4, 2003 shows a beautifully-formed low-pressure system swirling off the SE coast of Greenland, (Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC) Low-Pressure System

16. Hazardous Weather • Thunderstorms • Hurricanes • Tornados • Blizzards and Ice Storms • Drought • Dust and Sand Storms • Heat waves

17. Thunderstorms • Thunderstorms • Lower H2O-laden air mass • Temp gradient between overlying cooler, dryer air & underlying warmer, moist air • Updrafts • Exist during periods where updrafts and downdrafts produce convective cells • Warm air has > moisture capacity than cold air

18. Ocean Currents • Oceans act as weather modulators due to role • as heat sinks • Water temp plays a key role in amount • of moisture in the air • Continents: • E coasts have warm water current • W coasts have cool water currents

19. ThunderstormsAverage number of thunderstorm days per year in the US(Source: Oklahoma Climatological Survey) • Greatest incidence in SE and parts of Co, Az, & NM • Spatial distribution suggests extreme solar heating is NOT only requirement for thunderstorm formation • Other critical factor availability of warm moist air • Gulf of Mexico supplies moist maritime tropical air masses • Relatively unstable • Quickly form cumulonimbus clouds

20. ThunderstormsAverage number of thunderstorm days per year in the US(Source: Oklahoma Climatological Survey) • In Co, Az, & NM leeward side of Rocky Mountain slopes face Sun & absorb more direct solar energy • become relatively warmer creating strong updrafts that form into cumulus clouds • Few thunderstorms occur along the west coast of US • dominated by cool maritime polar air masses which suppress convectional uplift over land

21. Thunderstormsmajor features and circulation patterns • Form when moist, unstable air is lifted vertically into the atmosphere • Lifting results in condensation and the release of latent heat • Lifting occurs by: • Unequal warming of the surface of the Earth • Orographic lifting due to topographic obstruction of air flow • Dynamic lifting because of the presence of a frontal zone

22. Severe thunderstorms • MCC (Mesoscale Convective Complexes) • Most common & self perpetuating • Squall lines • Average 500km long • Develop parallel to cold fronts • Supercells (single, large updraft area) • Smallest of three • Spawn most tornados • High wind shear and downdrafts • Much damage in short time duration

23. Thunderstormsdevelopment of a common air-mass stormCumulus Stage • Normally develop in late afternoon • Surface heating produces the max number of convection currents • Flagstaffs summer “monsoon” season • Three stage life cycle • The first stage is called the Cumulus Stage • Oceanic (usually) evaporation creates air mass with high humidity • Parcels of warm, humid air rise and cool to form clusters of puffy white cumulus clouds • Cloud formation due to condensation • Formation releases large quantities of latent heat • Added heat energy keeps air inside cloud warmer than air around it • Cloud continues to develop as more humid air is added from below • Updrafts dominate the circulation within the cloud

24. ThunderstormsMature Stage • When the updrafts reach max alt ~12-14 kms, change direction 180° becoming downdrafts • Storm is in its Mature Stage • Downdrafts = precipitation through collision and coalescence • At its most intense stage of development • Now a cumulonimbus cloud • Top of cloud takes on familiar anvil shape • Strong stratospheric winds spread ice crystals in the top of the cloud horizontally • Several kms in diam @ base • Mature T-storm contains heavy rain, thunder, lightning, and wind gusts at the surface

25. ThunderstormsDissipating Stage • Mature T-storms decrease in intensity entering the Dissipating Stage • After ~1/2 hr • Air currents dominated by downdrafts • Supply of warm, moist air from lower atmos is depleted • Within ~ 1 hr storm is finished and precipitation stops

26. Tropical Cyclones • Characterized by low pressure center & numerous T-storms that produce strong winds, flooding rain, and storm surges • Fueled by different heat mechanism than other cyclonic windstorms: nor'easters, European windstorms, and polar lows • Classified as "warm core" storm systems • "tropical" refers to geographic origin & their formation in Maritime Tropical air masses • "cyclone" refers to CCW rotation in the N Hemi and CW rotation in the S Hemi • Depending on their location and strength can be referred to as hurricane, typhoon, tropical storm, cyclonic storm, tropical depression and simply cyclone

27. Hurricanes • Created by complexes of T-storms • Evolve into hurricane strength w/the aid of the ocean and atmos • Water must be warm enough to provide energy usually > 75 degrees F • Warm water provides heat & moisture which provides energy • Why hurricanes quickly weaken when they travel over land or colder ocean waters • High humidity in the mid & lower troposphere assist in development • Reduce amt of evap in clouds & max the latent heat released due to increased precip • Concentration of latent heat is essential to the system • Vertical wind shear, the amount of change in the winds direction or speed as alt > • Wind shear weak • Storms grow vert as latent heat from condensation is released above storm • The stronger the wind shear the more slanted the storm & more latent heat is released and dispersed over a larger area

28. Tropical CycloneMajor Components • Spiral Bands - Localized areas of tall/deep clouds, heavy rain, and high winds may extend a few hundred kms outward from the center of a hurricane • Eyewall – area just outside eye, usually formed by sheer wall of clouds • Most intense precipitation • Most intense winds • Eye – calmest part ofstorm • Hi press near top of hurricane causes the air in the eye to sink • Why the weather is nice in the eye • In contrast, surface press near eye is very low • < barometric press > storm

29. Hurricanes • 5 categories • Saffir-Simpson Scale (at right) • Damages • Storm surge • Coastal erosion • Wind • Doubling speed = 8X increase in power • Rain driven floods The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being precisely equal to 101.325 kPa. The following non-standard units are equivalent: 760 mmHg (torr), 29.92 inHg, 14.696 PSI, 1013.25 millibars.

30. Development/stages of a Tropical Storm System • From right to left in order of increasing energy: Tropical Disturbance, - Depression, - Storm, - Hurricane • Most hurricanes that impact the U.S. develop off the west coast of Africa in the mid-Atlantic

31. 150yrs of typhoon storm tracks • Follow warm ocean currents • Coriolis effect • Weakest at equator keeps rotational storms from forming • S. Amer. Typhoon gap • Catarina

32. Atlantic hurricane storm tracks

33. The Eye of the Storm

34. Hurricane Asymmetry • The "right side of the storm" is defined with respect to the storm's motion: • if the hurricane is moving to the west, the right side would be to the north of the storm; if the hurricane is moving to the north, the right side would be to the east of the storm, etc. • In general, this is because the motion of the hurricane also contributes to its swirling winds • A hurricane with a 90 mph winds while stationary would have winds up to 100 mph on the right side and only 80 mph on the left side if it began moving (any direction) at 10 mph • Note : forecasting agencies take this asymmetry into account when stating wind speeds

35. Hurricanes(Katrina) • Destructive tropical cyclone that forms in the western Atlantic Ocean • Winds > 75 mph • Usually accompanied by electrical storms • Typically occur during summer & early autumn • In a day can release the amount of energy to satisfy the electrical needs of the entire US for ~6 months

36. 2004 Gulf Coast Hurricane Season • 15 named storms • 3,132 deaths (Haiti) • >$59B in damages

37. Hurricanes • Form over warm, tropical waters (>80F) • Lose strength 3 ways • Remain stationary and siphon off warm waters • Move over cooler waters to the north • Move over ground mass • Must have sustained winds of > 74mi/hr • Rotating winds around a calm eye begin by Coriolis Effect • Cover extensive area

38. Storm Surge • Offshore rise of water associated with low pressure weather systems • Caused primarily by high winds pushing on the ocean's surface • Causes water to pile up higher than ordinary sea level • Low pressure at center of system also has a small secondary effect, as can the bathymetry of the water body Images from Gulf Coast area during Gustav Sept. 2008

39. Storm Surge • It is the combined effect of low pressure and persistent wind over a shallow water body which is the most common cause of storm surge flooding problems • In areas where there is a significant difference between low tide and high tide, storm surges are particularly damaging when they occur at the time of a high tide

40. Current 2009 North Atlantic storms

41. Hurricane Sandylate Oct. 2012 • 10th hurricane of the 2012 Atlantic season • Category 2 at peak • Largest Atlantic hurricane on record (as measured by diameter) spanning 1,100mi • Preliminary est. of losses $65.6 billion • Costliest Atlantic hurricane (only Katrina >) • At least 253 people killed in seven countries

42. Climate change component? • Jet Stream’s prevailing winds typically blow Atlantic hurricanes E & out to sea • This typical pattern was blocked by a ridge of high pressure over Greenland forming a kink in the jet stream, causing it to double back on itself off the East Coast • Sandy was caught up in this northwesterly flow • The blocking pattern over Greenland also stalled an arctic front which combined with the cyclone creating “The Perfect Storm” • Scientists suggest the jet stream's unusual shape was caused by the melting of Arctic ice • MSL at NY & along the New Jersey coast has increased by 1ft over the last 100yrs • Harvard geologist Daniel P. Schrag called Sandy's 13ft storm surge an example of what will be, by mid-century, the "new norm on the Eastern seaboard"

43. 2009 North Atlantic storms

44. Used to be named with by lat/ long • 1953 the National Hurricane Center began giving women's names to tropical storms originating in the Atlantic Ocean • 1979 a new naming method began with men's and women's names being alternated • Six different lists of names are now used • Recycled every six years • One exception - if a storm is especially deadly or costly then that name is retired from the list and a new name is selected to replace it Hurricane Names

45. Tornados • Tornados • From 1992-2002 killed aver. of 57 people/yr • Form under large barometric pressure gradients • Increased danger because of material inside spinning vortex • Funnel clouds vs tornado (vortex must touch ground) • Fujita or F-scale classification system • Based on post storm damage survey • Central U.S. has more than anywhere else

46. Tornados • A violent rotating column of air in contact with the ground and a cumliform cloud • Condensation funnel • Family • Multiple events from same storm • Outbreak • No break in activity • Types • Multiple vortex • Satellite • Waterspout • Landspout

47. Supercell Relationship • Tornadoes often develop from a class of thunderstorms known as supercells • Supercells contain mesocyclones • An area of organized rotation a few miles up in the atmosphere, usually 1–6 miles (2–10 km) across • Most tornadoes from supercells follow a recognizable life cycle • Formation • Maturity • Dissapating • Dissapation begins when > rainfall drags an area of quickly descending air known as the rear flank downdraft (RFD) • RFD completely wraps around and chokes off the tornado's air supply • Vortex weakens • Becomes thin and rope-like • During this stage the shape of the tornado becomes highly influenced by the winds of the parent storm, and can be blown into fantastic patterns.

48. Multiple Vortex TornadoDallas, Texas, 1957 • Tornado in which two or more columns of spinning air rotate around a common center • Very often observed in intense tornadoes • Satellite tornado is a weaker tornado which forms very near a large, strong tornado contained within the same mesocyclone • The satellite tornado may appear to "orbit" the larger tornado

49. Funnel Clouds • Tornados are not necessarily visible • Intense low pressure caused by high wind speeds & rapid rotation usually causes water vapor in the air to become visible as a funnel cloud or condensation funnel • Most tornadoes produce strong winds at the surface while the visible funnel is still above the ground • It can be difficult to discern the difference between a funnel cloud and a tornado from a distance

50. Tornados • Usually travel NE • Most have wind speeds between 40 mph & 110 mph • ~ 250 ft across • Travel a few mi before dissipating • Few attain wind speeds of more than 300 mph • More than a mile across • Travel more than 10’s/100’s of mi • Observed on every continent except Antarctica