1. MADISON’S CURRENT WEATHER
Madison Weather at AM CDT 10 JUL 2002
Updated twice an hour at :05 and :25
Sky/Weather: CLOUDY
Temperature: 70 F (21 C)
Dew Point: 62 F (16 C)
Relative Humidity: 76%
Wind: E10 MPH
Barometer: 30.20R ( mb)

2.                                                                                                                                                                     
                                                                                                                                                                    
Last 24 hrs in Madison

3.
CURRENT VISIBLE

4.
CURRENT IR

5.
CURRENT WATER VAPOR

6. Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar

7. Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H

8. Current Temperatures (°F) & Isotherms (“iso” = equal +”therm” = temperature)

9. Current Temperatures (oF) – 24 Hrs Ago
Cold Advection + Drier Air

10. Current Dewpoints (oF)

11. Current Apparent Temperatures (oF)

12. Tomorrow AM Forecast Map

13. Announcements Please pick up Exams and homeworks!
If you have ??, please see me.

14. ATM OCN 100 - Summer 2002 LECTURE 10 (con’t.)
WATER & THE HYDROLOGIC CYCLE
Introduction
Importance of the Hydrologic Cycle
Assessing the Hydrologic Cycle
Water: A Wonder

15. C. ASSESSING THE HYDROLOGIC CYCLE
Mass Budgets
Total Water Budget of Planet Earth
Measurement Techniques
Precipitation = Evaporation + Storage (change in water level)

16. “Rain Sensor” for NWS Automatic Weather Station

17. Evaporation Pan From J.M. Moran & WES Project of AMS

18. Evapotranspiration
Combination of:
Transpiration
Evaporation

19. D. WATER - A WONDER
Background
Molecular Structure of Water (H2O) A “dipole”

20. Molecular Structure of H2O Chemical Properties of H2O
D. WATER - A WONDER
Molecular Structure of H2O
Chemical Properties of H2O
Physical Properties of H2O

21. D. WATER - A WONDER (con’t)
Physical Properties of H2O
Three Phases & High Latent heats
High Specific heat
Anomalous Density & temperature relationship
Heat conductivity
An excellent absorber/emitter of IR radiation where...

22. PHYSICAL PHASES of H2O
Solid (Ice) – “Low Energy” -- Note Hexagonal (6 sided) Structure

23. PHYSICAL PHASES of H2O
Liquid “Medium Energy”

24. PHYSICAL PHASES of H2O
Vapor “High Energy”

25. Physical Phase Changes of H2O See Fig 4.2 Moran & Morgan (1997)

26. Distinguishing Sensible & Latent Heats See Fig 4
Distinguishing Sensible & Latent Heats See Fig 4.3 Moran & Morgan (1997)

27. Implications
Large amounts of latent heat are utilized to transfer surplus energy from earth’s surface to the atmosphere.
Maritime vs. Continental Climate

29. At Southern Lake Michigan Buoy

30.                                                                                                                                                                     
                                                                                                                                                                    
Last 24 hrs in Madison

31. SPECIFIC HEAT Recall Sensible Heat
Specific Heat Quantity of heat required to change temperature of a unit mass of substance by 1 Celsius degree.

32. SPECIFIC HEATS Water has a high specific heat [Table 3. 2, pg
SPECIFIC HEATS Water has a high specific heat [Table 3.2, pg. 76 Moran & Morgan, 1997]

33. TEMPERATURE RESPONSE for substances with differing specific heats See Table 3.2, Moran & Morgan (1997)

34. Implications
For the same amount of heat energy added, Water takes longer to heat.
Maritime vs. Continental Climate

35. DENSITY OF LIQUID WATER

36. Implications Ice expands when water freezes; Ice floats;
Lakes freeze from top down.

37. Freezing cycle of lakes

38. Madison skyline from frozen Lake Monona

39. HEAT CONDUCTIVITY [Table 3.1, pg. 74 Moran & Morgan, 1997]

40. Implications Water is efficient at conducting heat.
Humans can suffer hypothermia when immersed in cold water:
Survival time in 32.5° F water is 15 to 45 minutes!

41. IR Absorption/Emission Properties of H2O
Water molecules are great absorbers (& emitters) of IR radiation
Consequences
Water vapor is the most dominant “Greenhouse Gas”
Clouds (liquid & ice) elevate nighttime temperatures
Snow surfaces are great emitters

42. Humidity (Atmospheric vapor) Considerations
E. WATER VAPOR
Properties
A colorless gas
Found in many locations
Humidity (Atmospheric vapor) Considerations

43. E. WATER VAPOR
Concept of Saturation
A dynamic equilibrium between Evaporation & Condensation;
Depends upon temperature of system.

44. E. WATER VAPOR (con’t.) SPECIFICATION OF WATER VAPOR @ SATURATION
Consider Saturation vapor pressure.
Recall concept of Dalton’s Law of Partial Pressure: PTotal = p(N2) + p(O2) + p(Ar) + e + … where e = (partial water) vapor pressure.
Now consider values of e at saturation conditions, defined as es(T)

45. SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg
SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg Moran & Morgan, 1997

46. E. WATER VAPOR (con’t.)
What is Boiling?
Boiling point depends on air pressure;
Variation of boiling point with altitude;
Pressure cookers
Vacuum evaporators

47. SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg
SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg Moran & Morgan, 1997
Sea Level: Tbp = 100°C = 212°F
5000 ft: Tbp = 95°C = 203°F
10,000 ft: Tbp = 90°C = 194°F
From p6 Reifsnyder (1980) See bp-z.xls

48. E. WATER VAPOR (con’t.)
Humidity Measurement & Instruments
hair hygrometer
dewpoint hygrometer
sling psychrometer
hygristor where...

49. HUMIDITY INSTRUMENTS
HAIR HYGROMETER
Measure how length of hair varies with relative humidity changes.

50. HUMIDITY INSTRUMENTS (con’t.)
DEWPOINT HYGROMETER
Cool surface and measure temperature at which water vapor condenses (i.e., forms dew).

51. Hygrometer & Thermal Sensor at ASOS

52. HUMIDITY INSTRUMENTS (con’t.)
SLING PSYCHROMETER
Measure temperature when evaporation causes cooling of a moist surface by ventilation to point where no additional evaporation takes place.

53. Sling Psychrometer (con’t.)

54. Sling Psychrometer (con’t.)

55. Inside an Instrument Shelter

56. HUMIDITY INSTRUMENTS (con’t.)
HYGRISTOR
Measure electrical resistance of a substance which varies with relative humidity.

57. Hygristor on a Radiosonde

58. WATER VAPOR (con’t.) Water Vapor Variables vapor pressure mixing ratio
dewpoint (& frostpoint)
wet-bulb temperature
relative humidity
apparent temperature/heat index
defined as....

59. WATER VAPOR (con’t.)
(Water) Vapor Pressure
Partial pressure exerted by water vapor molecules;
Range: 0 mb to 40 mb under normal conditions;
Determined indirectly.

60. WATER VAPOR (con’t.) Dewpoint temperature
Temperature to which air is cooled at constant pressure & without change in vapor content to reach saturation;
Obtained from dewpoint hygrometer;
Typically less than air temperature, except for saturation or supersaturation;
When Tdew > 65oF, human discomfort increases.

61. WATER VAPOR (con’t.)
Frostpoint temperature
Saturation point at temperatures below freezing point (T < 0oC) when “frost” could be formed.
Frost forms directly through deposition.

62. WATER VAPOR (con’t.)
Wet-bulb temperature
Temperature resulting when air is cooled to saturation by evaporation of water;
Cooling produced by latent heat of evaporation;
Measured by a sling psychrometer;
Lower atmospheric vapor content produces lower Twet-bulb.

63. WATER VAPOR (con’t.)
Wet-bulb temperature
Used to obtained other moisture variables such as dewpoint & relative humidity;
Requires dry bulb, wet-bulb readings & determination of wet-bulb depression;
Read Tdew or RH from psychometric tables.

64. Psychrometric Tables Table A: Relative Humidity [%] Inside cover, Moran and Morgan (1997)

65. Psychrometric Tables Table B: Dewpoint Temperature (C) Inside cover, Moran and Morgan (1997)

66. WATER VAPOR (con’t.) Water Vapor Variables vapor pressure mixing ratio
dewpoint (& frostpoint)
wet-bulb temperature
relative humidity
apparent temperature/heat index
defined as....

67. WATER VAPOR (con’t.) Relative Humidity
A measure of the relative closeness to saturation conditions;
Requires specification of air temperature;
RH = 100% at saturation (i.e., dewpoint).

68. SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg
SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg Moran & Morgan, 1997

69. WATER VAPOR (con’t.)

70. WATER VAPOR (con’t.)

71. Diurnal Variation in Relative Humidity See Fig. 6
Diurnal Variation in Relative Humidity See Fig. 6.5 Moran & Morgan (1997)
NOTE: Dewpoint ranged between 8° to 9° C during day

72. WATER VAPOR (con’t.)
Apparent Temperature/Heat Index
An index based upon heat loss from human body;
Incorporates role of evaporative cooling by perspiration (sweating);
Used for high temperatures & high relative humidities;
Human comfort/safety: Heat Stress.

73. Apparent Temperature (°F) – Heat Index From NWS

74. Late Sunday Afternoon Temperatures (oF)

75. Late Sunday Afternoon Dewpoints (oF)

76. Late Sunday Afternoon Apparent Temperatures/Heat Indices (oF)

77. Announcements
Homework #3 is returned today Answer Key is posted at
Homework #4 is due Thurs.
2nd Hour Exam is scheduled for Thurs.
Study sheet is posted at:
If you have ??, please see me.

78. WATER VAPOR (con’t.)
Climatology of Atmospheric Humidity
tropical vs. polar
maritime vs. continental

79. Rule of thumb
When:
Air temperature falls to within 2 to 3 Fahrenheit degrees of dewpoint and
Winds are light
Then:
Fog often forms.