View
67
Download
3
Category
Tags:
Preview:
DESCRIPTION
Class #3: Humidity, condensation, and clouds. Chapters 4 and 5. Atmospheric Humidity. Chapter 4. Circulation of Water in the Atmosphere. A general definition of humidity is the amount of water vapor in the air. - PowerPoint PPT Presentation
Citation preview
Class #3 July 9, 2010 1
Class #3: Humidity, condensation, and clouds
Chapters 4 and 5
Class #3 July 9, 2010 2
Atmospheric Humidity
Chapter 4
Class #3 July 9, 2010 3
Circulation of Water in the Atmosphere
• A general definition of humidity is the amount of water vapor in the air.
• Remember, humidity is not constant through time or space, there is constant circulation of water through the hydrologic cycle.
Class #3 July 9, 2010 4
Class #3 July 9, 2010 5Stepped Art
Fig. 4-1, p. 90
Class #3 July 9, 2010 6Fig. 4-2, p. 91
Class #3 July 9, 2010 7
The Many Phases of Water
• Phase is related to molecular motion, an increase or decrease in motion creates a phase change.
• Ice is the coolest/slowest phase• Water vapor is the warmest/fastest phase
Class #3 July 9, 2010 8
Class #3 July 9, 2010 9
Evaporation, Condensation, & Saturation
• Evaporation is the change of liquid into a gas a requires heat.
• Condensation is the change of a gas into a liquid and releases heat.– Condensation nuclei
• Saturation is an equilibrium condition in which for each molecule that evaporates, one condenses.
Class #3 July 9, 2010 10
Class #3 July 9, 2010 11
Class #3 July 9, 2010 12
Humidity
• Any of a number of ways of specifying the amount of water vapor in the air.
• Absolute humidity: mass of water vapor/volume of air– Water vapor density– Not commonly used due to frequent change of
volume
Class #3 July 9, 2010 13
Class #3 July 9, 2010 14
Class #3 July 9, 2010 15
Humidity
• Specific Humidity: mass of water vapor/mass of air
• Mixing ratio: mass of water vapor/mass of dry air
• Neither measurement changes with volume, must add or subtract water vapor.
Class #3 July 9, 2010 16
Class #3 July 9, 2010 17
Class #3 July 9, 2010 18
Humidity
• Vapor pressure: the pressure exerted by water vapor molecules in an air parcel (Dalton’s Law of Partial Pressure)– Fraction of total vapor pressure (1% or so)– More water molecules = high vapor pressure
• Saturation vapor pressure: the vapor pressure at which an air parcel will be saturated, changes with temperature
Class #3 July 9, 2010 19
Class #3 July 9, 2010 20
Humidity
• Special Topic: Vapor Pressure & Boiling– Once water boils it requires more energy to
increase temperature.– Water boils at a low temperature in the mountains
and thus needs more energy and time to cook items as compared to sea level.
Class #3 July 9, 2010 21
Humidity
• Relative Humidity: (actual water vapor/saturation water vapor)*100– RH can be changed two ways:• Change vapor content• Change saturation
– Decrease temperature causes an increase in relative humidity (inverse relationship).
Class #3 July 9, 2010 22
Class #3 July 9, 2010 23
Humidity
• Relative Humidity and Dew Point– Dew point is the temperature at which saturation
occurs– Cool air parcel to dew point and liquid water
condenses– A good measure of actual water vapor content– Relative humidity indicates how close to
saturation, dew point indicates the amount of water vapor
Class #3 July 9, 2010 24
Class #3 July 9, 2010 25Fig. 4-13, p. 98
Class #3 July 9, 2010 26Fig. 4-13, p. 98
Class #3 July 9, 2010 27Fig. 4-13, p. 98
Class #3 July 9, 2010 28Fig. 4-13, p. 98
Class #3 July 9, 2010 29
Class #3 July 9, 2010 30
Class #3 July 9, 2010 31
Class #3 July 9, 2010 32
Class #3 July 9, 2010 33Fig. 4-15a, p. 100
Class #3 July 9, 2010 34Fig. 4-15b, p. 100
Class #3 July 9, 2010 35
Humidity
• Relative Humidity in the Home– Due to an increase in temperature in a heated
home there is a decrease in relative humidity, causing more evaporation from body, plants, etc• Humidifier, chapped lips
– Swamp cooler
Class #3 July 9, 2010 36
Class #3 July 9, 2010 37
Humidity
• Relative humidity & human comfort– “It’s not the heat, it’s the humidity.”– High relative humidity equates to less evaporative
cooling.– Sweat cannot evaporate and cool the body– Wet bulb temperature– Heat Index
Class #3 July 9, 2010 38
Class #3 July 9, 2010 39
Humidity
• Special Topic: Heavier humid air– Due to the molecular weight of water as
compared to nitrogen, humid air is lighter than dry air.
– Baseball announcers are incorrect.
Class #3 July 9, 2010 40
Humidity
• Measuring humidity– Sling psychrometer– Hygrometer
Class #3 July 9, 2010 41
Class #3 July 9, 2010 42
Condensation: DEW, Fog, & clouds
Chapter 5
Class #3 July 9, 2010 43
The Formation of Dew & Frost
• Dew forms on objects near the ground surface when they cool below the dew point temperature.– More likely on clear nights due to increased
radiative cooling• White frost forms when temperature cools
below the dew point and the dew point is below 0°C
Class #3 July 9, 2010 44
Class #3 July 9, 2010 45
Class #3 July 9, 2010 46
Condensation Nuclei
• Particles suspended in the air that around which water condenses or freezes.– Hydrophobic/hygroscopic
Class #3 July 9, 2010 47Table 5-1, p. 113
Class #3 July 9, 2010 48
Class #3 July 9, 2010 49
Class #3 July 9, 2010 50
Haze
• Dry condensation nuclei (above dew point) reflect and scatter sunlight creating blueish haze.
• Wet condensation nuclei (75% relative humidity) reflect and scatter sunlight creating grayish or white haze.
Class #3 July 9, 2010 51Fig. 5-4, p. 114
Class #3 July 9, 2010 52
Fog
• Saturation reached condensation forms a cloud near the ground
• Radiation fog: ground cools through conduction and radiation; ground fog– Valley fog created by cold air drainage– High inversion fog
Class #3 July 9, 2010 53
Class #3 July 9, 2010 54
Class #3 July 9, 2010 55
Fog
• Advection Fog: warm moist fog moves horizontally (advects) over a cool surface.– Summer fog on the Pacific coast
• Observation: Headlands– Air converges and rises over headlands forming
fog as compared to lower elevation beaches.
Class #3 July 9, 2010 56
Class #3 July 9, 2010 57
Class #3 July 9, 2010 58
Fog
• Upslope Fog: moist air flows up an orographic barrier– East side of the Rockies
• Evaporation Fog:– Warm moist surface provides enough moisture to
saturate a dry air parcel; short lived• Steam fog• Breath in winter
Class #3 July 9, 2010 59
Class #3 July 9, 2010 60
Class #3 July 9, 2010 61
Foggy Weather
• In general fog not common for most location in the US. However several areas do exist with a high frequency of fog. Two causes:– Elevation– Ocean currents
Class #3 July 9, 2010 62
Class #3 July 9, 2010 63
Foggy Weather
• Environmental Issue: Fog dispersal– Mix air with air craft or fans– Introduce large particle into air to reduce total
number of cloud droplets.– Use dry ice to lower temperature below freezing.
Class #3 July 9, 2010 64
Clouds
• Classification of clouds: use Latin words to describe height and appearance.
• Factors described– Height: low, mid, high, vertical– Appearance: shape, density, color
Class #3 July 9, 2010 65
Class #3 July 9, 2010 66
Class #3 July 9, 2010 67
Class #3 July 9, 2010 68
Class #3 July 9, 2010 69
Class #3 July 9, 2010 70
Class #3 July 9, 2010 71
Class #3 July 9, 2010 72
Class #3 July 9, 2010 73
Class #3 July 9, 2010 74
Class #3 July 9, 2010 75
Class #3 July 9, 2010 76
Class #3 July 9, 2010 77
Class #3 July 9, 2010 78
Class #3 July 9, 2010 79
Some Unusual Clouds
• Not all clouds can be placed into the ten basic cloud forms.
• Unique atmospheric processes and environmental conditions create dramatic and exotic clouds.
• Unusual clouds and weather balloons often cause of UFO reports.
Class #3 July 9, 2010 80
Class #3 July 9, 2010 81
Class #3 July 9, 2010 82Fig. 5-26, p. 130
Class #3 July 9, 2010 83Fig. 5-27, p. 130
Class #3 July 9, 2010 84Fig. 5-28, p. 130
Class #3 July 9, 2010 85Fig. 5-29, p. 130
Class #3 July 9, 2010 86Fig. 5-30, p. 131
Class #3 July 9, 2010 87Fig. 5-31, p. 131
Class #3 July 9, 2010 88
Cloud Observations
• Sky conditions: cloud coverage divided into eighths and each amount associated with term such as scattered clouds.
• Observations: cloud ceilings– Ceilometer used at airports to determine height
from clouds by light or laser striking clouds and then amount and speed of reflected light recorded.
Class #3 July 9, 2010 89Fig. 5, p. 132
Class #3 July 9, 2010 90
Class #3 July 9, 2010 91
Cloud Observations
• Satellite Observations– Geostationary, polar orbiting– Visible light provides a black and white picture of
clouds– Infrared approximates cloud temperature which
infers height– Satellites measure many other variables: sea
surface temperatures, ozone, upper level features, snow cover, land cover
Class #3 July 9, 2010 92
Class #3 July 9, 2010 93
Class #3 July 9, 2010 94
Recommended