CHAPTER 1 THE TURBULENT ATMOSPHERE

1. CHAPTER 1 THE TURBULENT ATMOSPHERE

2. THREATS FROM THE SKY • “Extreme and unusual weather” are the focus of public fears, and are often the impetus behind our quest for knowledge about the atmosphere • In the United States, the risk of death due to a weather event is relatively small when compared to other risks • About two in one million

3. Table 1.1, p. 5

4. THREATS FROM THE SKY • Weather-related events cause an estimated $10 billion in property damage annually • Virtually no part of the globe is free of the threat of extreme weather

5. The total number of billion dollar weather and climate disasters from 1980 through 2004. Fig. 1.2, p. 5

6. Weather-related Deaths Note! Represents Percentages in One Year Only: 2000 Fig. 1.3, p. 5

7. REASONS FOR CONCERN • There are a number of concerns about the atmosphere that are not related to isolated extreme weather events • Global warming • Toxic chemicals • A basic understanding of the atmosphere is required for understanding the acute impacts caused by extreme and unusual weather

8. Fig. 1.4, p. 7

9. Table 1.2, p. 6

10. THE EARTH’S ATMOSPHERE • Our atmosphere is a thin, delicate life-giving blanket ofair that surrounds the earth • Warmth for our planet is provided primarily by the sun’s energy • Radiant energy drives the atmosphere into the patterns of everyday wind and weather, and allows life to flourish • Mean sfc temp is 59F (15C), but can be much more extreme

11. Composition of Earth’s atmosphere • 99% of the atmosphere is within 20 miles of the Earth’s surface • N2 78% and O2 21% • The percentages represent a constant amount of gas but cycles of destruction and production are constantly maintaining this amount

13. Composition of the atmosphere • Water is a variable, but very important gas • The hydrologic cycle: evaporation, precipitation, runoff, etc. • Carbon dioxide concentrations have risen in recent years • CO2 is an important greenhouse gas, though not the only one • Ozone: “Good up high, bad nearby”

14. CO2 concentrations from Mauna Loa, Hawaii • Lower in summer when plants are active and absorb CO2 • Has risen more than 20% since 1958

15. Stepped Art Fig. 1-4, p. 7

17. Ozone • “Good up high, bad nearby” • Near the ground, ozone is the main ingredient in smog, which irritates the eyes and throat and damages plants • In the stratosphere, ozone provides a protective shield from ultraviolet radiation • This protective shield erodes over Antarctica in their winter, causing a stratospheric “ozone hole” Low concentrations of ozone over Antarctica, September 2004

18. Weather and climate • Weather: short term air temperature, air pressure, humidity, clouds, precipitation, visibility, and wind • Climate: long term patterns and average weather; not just magnitude but also frequency. • But climate is not just the average, it also describes the range of possibilities

19. The Primary Variables • Atmospheric Pressure • Temperature • Moisture • Water vapor in the air • Precipitation • Wind • Direction • Speed

20. Air pressure • Atmospheric Pressure is the force per unit area of a column of air above you (extending all the way to the “top” of the atmosphere) • In other words, pressure is the weight of the column of air above you - a measure of how hard this column of air is pushing down • More fundamentally - atmospheric pressure arises from gravity acting on a column of air

21. Pressure • Molecules bumping into an object create a force on that object • Pressure is the force applied per unit area • P = F/A • Which box below is exerting the greatest pressure upon the ground? 1 kg 1 kg Force = mass x gravity

22. Why pressure? • Pressure is one of the most fundamental forces which produces weather and makes our atmosphere move – the wind! • Pressure defines many of our most important weather patterns: midlatitude cyclones, hurricanes, anticyclones • Pressure is usually in units of millibars (mb), though sometimes in inches of Mercury (in Hg) • Barometers with mercury in them can be used to measure pressure • Typical pressure at sea level is 1013.25 mb, or 29.92 in Hg

23. Density • Density = mass / volume • Denser air displaces less dense air - just like water displaces air • Lower-density air rises when it is surrounded by denser air - one of the primary forces which produces vertical motions in the atmosphere • Think of a ping-pong ball submerged under water. What happens when you release it? Which box is more dense? 1 kg 1 kg

24. Change in pressure and density with height

25. Most of the air is near the ground • At an altitude of 5.5 km (about 18000 ft), you are above 50% of the air in the atmosphere. At 50000 ft, you are above 90% of the air!

26. Fig. 1.16, p. 19

27. Temperature • Temperature is a measure of the kinetic (motion) energy of air molecules • K.E. = ½ mv2 m = mass, v = velocity • So…temperature is a measure of air molecule speed • The sensation of warmth is created by air molecules striking and bouncing off your skin surface • The warmer it is, the faster molecules move in a random fashion and the more collisions with your skin per unit time

28. Temperature scales What is 25° in F?

30. Vertical structure of the atmosphere • Layers of the Atmosphere • Troposphere: Where weather happens and where we live! • Stratosphere: temperature increases with height, contains lots of ozone • Mesosphere: temperature decreases with height again • Thermosphere: hot! Very little air • At the top of each layer is a “pause”: the tropopause is at the top of the troposphere, etc.

31. Stepped Art Fig. 1-11, p. 13

32. Red line shows temperature • Temperature decreases with height in troposphere and mesosphere; increases with height in thermosphere

33. Lapse rate • The change in temperature with height is called the lapse rate • In the troposphere, on average, the temperature decreases 6.5° Celsius for every kilometer that you go up • Sometimes, though, it’s the opposite: when temperature increases with height, it is called an inversion • If temperature is constant with height: isothermal (iso=same, thermal=temperature)

34. Wind • Moving air – determines many aspects of the weather • Wind is the atmosphere’s response to pressure differences • We care about both the wind speed and direction • Units: • Meters per second (m/s) • Miles per hour (mph) • Nautical miles per hour (knots) • 1 meter/second = 2.24 miles/hour = 1.94 knots • A hurricane has sustained winds greater than 74 mph, or 64 knots, or 33 m/s

35. Wind Direction • In meteorology, we describe the wind in terms of where it is coming from • So, a “west wind” blows from west to east N 0o or 360o 315o 45o W 270o E 90o 135o 225o S 180o

36. Scales of Motion Examples Most meteorologists refer to this as the synoptic scale. Or, the size of a large thunderstorm or cluster of storms. Fig. 1.17, p. 20

37. PROPERTIES OF THE ATMOSPHERE • Moisture • Clouds and precipitation are associated with surface low pressure; clear skies with surface high pressure. • Relative humidity does not tell us how much water vapor is actually in the air; rather, it tells us how close the air is to being saturated. • The dew point temperature is the temperature to which air would have to be cooled in order for saturation to occur.

38. Fig. 1.20, p. 21

39. Fig. 1.21, p. 22

40. Fig. 1.22, p. 22

41. Fig. 1.23, p. 24

42. Airflow over a mountain • As a parcel of air (think of a large balloon) is lifted up a mountain, the pressure surrounding it decreases – it must expand • The energy that goes into the expansion is lost, and the parcel cools • As it sinks, the pressure outside the parcel increases – it is compressed • As it compresses, the molecules inside move faster, leading to a higher temperature • Rising air expands and cools, sinking air compresses and warms

43. What if parcel cools below dew point? • Rising air causes clouds • Air parcel • Air that rises expands and cools • Dew point • Air that sinks compresses and warms

45. Appetite Whetting: EXTREMES OF WEATHER AND CLIMATE • Wind chill • Drought • Heat waves • Tornadoes (cyclones, twisters) • Thunderstorms (lightning, flash floods, downburst) • Mid-latitude cyclones • Hurricanes

46. Fig. 1.24, p. 26

47. Fig. 1.25, p. 27

48. Fig. 1.26, p. 28

49. Fig. 1.27, p. 29

50. Fig. 1.28, p. 29