Weather and the Atmosphere. RAP Short Course

Transcription

1 Weather and the Atmosphere RAP Short Course

2 Syllabus 1) Vertical structure and composition of the atmosphere, basic weather variables 2) Warming Earth and its atmosphere the diurnal and seasonal cycles 3) Humidity, condensation, clouds, fog 4) Cloud development and precpitation 5) Large-scale processes upper-air winds, mid-latitude cyclones, fronts

3 Syllabus continued 6) Mesoscale processes mountain-valley breezes, sea breezes 7) Severe weather hurricanes, thunderstorms, tornadoes 8) Global climate and climate change 9) Atmospheric optics mirages, rainbows, etc. 10) The weather-forecast process

4 More about the course Selected topics and lectures from a CU course ATOC 1050 (45, 50-min. classes). The course is aimed at non-science as well as science majors so no math and physics beyond high school are assumed. No meteorologists allowed in class. Text available from NCAR bookstore, but not required Essentials of Meteorology, by Ahrens

5 Please interrupt with short questions when necessary. If the answer is not also short, I may ask you to see me after class. No exams No homework Course web site with notes at

6 Class dates all 1:30-2:20 1) 6 March, Thur 2) 13 March, Thur 3) 20 March, Thur 4) 27 March, Thur 5) 3 April, Thur 6) 10 April, Thur 7) 29 April, Tues 8) 1 May, Thur 9) 8 May, Thur 10) 15 May, Thur

7 Composition of the Atmosphere

8 The atmosphere A molecular cocktail

9 COMPOSITION OF THE ATMOSPHERE NEAR EARTH S SURFACE Permanent gases (percent is the same everywhere) Nitrogen 78 % Oxygen 21 % Hydrogen % Others (less than 1 %) ozone, methane, helium, etc. Variable gases (amount depends on place and time) Water vapor 0-44 % Carbon dioxide about.037 %

10 CO 2 varies with time Upward trend from , plus seasonal variational Not zero

11 Why the variation with time? Overall upward trend carbon dioxide from combustion by industry, autos, etc. Sawtooth pattern seasonal variation. Q: What would cause winter-summer oscillation? A: Vegetation is active in warm season, consuming carbon dioxide Q: But shouldn t two hemispheres balance? A: More land and vegetation in Northern Hemisphere

12 Seasonal Variation in Vegetation Equator

13 Equator Distribution of forests

14 Water-vapor Content

15 Content of the atmosphere in addition to gases Mineral particles dust from ground, man-made made pollution Water droplets clouds, fog Water drops rain Ice small crystals, snow flakes, hail

16 Structure of the atmosphere Varies depending on the meteorological conditions But we can talk about average conditions - horizontal structure (as shown on a weather map) - vertical structure

17 Vertical structure of the atmosphere First how deep is it? White line is the thickness of the atmosphere (99% of molecules) Earth

18

19

20 Within this thin atmosphere, there are three ways of defining layers How temperature changes with height (increase versus decrease with height) Composition (mixture of gases) Electrical structure

21 Different Layers of the Atmosphere

22 A Glossary of Weather Variables Air temperature Air pressure Humidity amount of water vapor Clouds Precipitation rain, snow, hail, etc. Wind direction and speed Visibility

23 Air Temperature

24 Temperature Related to rate of motion of molecules: The warmer the air, the more rapidly the molecules move. Primary temperature scales Fahrenheit (F): freezing point of water = 32 F, boiling point = 212 F Celsius (C): freezing = 0 C, boiling =100 C Absolute (A) or Kelvin (K): absolute zero = 0 A = C (all molecular motion stops) Temperature observations near the surface (2m) are reported in degrees F, and above that are reported in degrees C.

25 The temperature scales, A

26 Vertical Temperature Structure of the Atmosphere Commercial Aircraft All the Weather

27 Denver temperature profile at 5:00 AM 28 Feb 03 Stratosphere Tropopause Troposphere Temp Up

28 Experiences that confirm that temperature decreases with height It is colder on the tops of mountains Some of the hottest places in the world are below sea level Death Valley, the Dead Sea Commercial aircraft need to be heated

29 Air Pressure

30 Why do we care about pressure?

31 Air Pressure - Definition Pressure = force/area (e.g., pounds per square inch) 1) Hydrostatic pressure weight of the atmosphere above the surface 2) Dynamic pressure force of the wind (e.g., against a door)

32 Air Pressure - Units In this course, pressure is expressed in millibars (mb) average sea-level pressure = 1013 mb Sometimes (e.g., in weather forecasts) it is given in inches of mercury average = in. mercury Surface pressure values are adjusted to sea level, so that values show high and low pressure patterns rather than the elevation of the observation

33 How is sea-level pressure estimated for plotting on weather maps?

34 Vertical Pressure Variation in the Atmosphere

35 Experiences that confirm that pressure decrease with height Ears pop in elevator or driving up mountain Commercial airplanes need to be pressurized - pain in ears when landing Analogy with water ears sometimes hurt as you dive deeply

36 Air Density

37 General definition of density - Mass per unit volume Air density Mass (e.g., kilograms) of air molecules per unit volume (cubic meter) More dense Less Dense *********** *********** *********** *********** * * * * * * * * * * * * * * * * * * * *

38 Density Variation With Height

39 Sea level

40 6-77 km, 450 mb,, 4 mi ASL 50 % reduction

41 20 km, 50 mb,, 12 mi ASL 90 % reduction

42 Personal experience showing that air density decreases with height It is more difficult to breath at higher elevations fewer oxygen molecules

43 Humidity A measure of the amount of water vapor in the air There are many different measures of humidity, and a few used in this class are Relative humidity Vapor pressure Dew point temperature

44 Clouds Percent of sky covered by clouds Types of clouds Cumulus Cirrus Stratus, etc.

45

46

47

48

49

50

51

52 Wind Speed miles per hour or knots (nautical miles per hour), meters per second Direction - Given in terms of the direction from which the wind is blowing. A northwesterly wind is blowing from the northwest. Horizontal wind is measured, but vertical wind is also very important

53 Visibility The maximum distance at which an observer can distinguish an object against the sky as a background May be limited by fog, air pollution, etc.

54 Precipitation Type of precipitation - rain, snow, sleet, hail, etc. Rate at which it is falling (inches/hour)

55 Scales of atmospheric motion - Storms of all sizes Mid-latitude cyclones mile Hurricanes 500+ miles Thunderstorms miles Tornadoes few hundred yards Turbulence centimeters-meters

56

57 Measuring the atmosphere Weather balloons, or radiosondes make upper-air measurements of horizontal wind, temperature and humidity.

58 Radiosonde helium balloon with measurement instruments

59 Measuring the atmosphere Weather balloons, or radiosondes make upper-air measurements of horizontal wind, temperature and humidity. Surface weather stations (land and seas) measure horizontal wind, temperature, humidity, cloud cover Satellites can estimate winds, temperature and humidity

60 Radiosonde launch locations

61 Surface observations - NWS

62 Zooming in to see even more Northern Utah