EXAM ONE CH 1 2 3 4 10 16 2012 Moisture and Wind Q Is the change over the annual cycle in the Northern Hemisphere larger or smaller then the annual cycle in the Southern Hemisphere A Northern because there is more land mass which absorbs more heat quickly Properties of the Atmosphere Temperature Pressure Moisture Wind Atmosphere is a thin layer of air extending from the surface to 100 km 90 of mass is below 12km Weather occurs 2 5k 78 nitrogen 21 oxygen 00001 water vapor Temperature the average speed of molecules When object of different temperature come into contact the object with more heat shares with object of lesser heat 2nd law of thermodynamics Absolute zero no molecule movement 459 67 degrees F 273 15 degrees C If the temperature on the Fahrenheit scale is 100 degrees then the corresponding temperature on the Celsius scale is greater than 100 degrees FALSE How does moisture exist in the atmosphere Solid ice crystals Liquid cloud droplets fog rain Gas water vapor In clouds it exists as Liquid water Ice crystals Seasons Why does the temperature change during the year and why is this change larger in middle and high latitudes than in the tropics How does the tilt of the earth cause seasons Length of daylight Amount of sunlight able to pass through the atmosphere Area illuminated by the sun Air Pressure the force applied by air to a unit area of surface P force area The air pressure at a given point is equal to the weight of all of the air above that point Pressure decreases with altitude 870 typical pressure in Boulder Pressure at sea level in different units 10 tons per square meter 14 7 psi pounds per square inch 29 92 inches of mercury 760 millimeters of mercury meteorologists use 1013 25 millibars or hPa Station pressure the air pressure measured at a surface weather station this is also called surface pressure Mean sea level pressure the pressure that would be measured if the weather station were located at sea level SUMMARY Why does temperature change during the year Tilt of the Earth and Earth rotating around the Sun How are the different layers of the atmosphere defined Name the layers and describe how and why temperature changes Role of troposphere and tropopause and how tropopause height changes with latitude What is the difference between station and sea level pressure What are typical pressure readings at sea level and in Boulder What is the typical range of sea level pressure Why do we use sea level pressure in weather maps The Vapor Pressure is a measure of how much water vapor is in the atmosphere Vapor pressure increases as the amount of water in the atmosphere increases the force per unit area applied by only the water vapor molecules vapor pressure at normal atmospheric temperature ranges form 0 mb in a dry cold atmosphere to 60 mb in a humid tropical atmosphere Vapor pressure is an absolute measure of the amount of water in the atmosphere o Doesn t depend on anything else Vapor pressure varies with season and weather system Where is the vapor pressure low and high Higher vapor pressure more water in atmosphere How does the vapor pressure change from Winter to Summer More evaporation in summer water vapor increases The dew point temperature is another measure of absolute amount of water in the atmosphere Saturated Invisible vapor condenses into visible cloud droplets When the atmosphere can not contain any more water vapor without condensing into cloud droplets is it saturated When air is near saturation our bodies cool inefficiently because water has difficulty evaporating The limit of how much water vapor can be in the air is determined by the saturation or equilibrium vapor pressure Water is continually condensing while liquid water is continually evaporating When the rate of condensation equals the rate of evaporation the situation is in a state of equilibrium The atmosphere is saturated when it cannot contain any more water vapor without having cloud droplets Saturation Vapor Pressure is the vapor pressure at which at atmosphere become saturated Only factor for saturation is the temperature Saturation vapor pressure increases as temperature increases Little capacity for moisture in cold The Leaky Bucket Analogy Level of balance is determined only by rate of inflow of evaporation which depends on temperature The saturation vapor pressure always increases as the air temperature increases Relative Humidity The amount of water vapor in the atmosphere relative to the atmosphere s capacity for moisture at a given temperature Relative humidity vapor pressure saturation vapor pressure x 100 Depends on two quantities 1 the absolute amount of moisture in the air vapor pressure 2 the amount of moisture the air can contain when it is saturated saturation vapor pressure When the air is saturated the relative humidity 100 Can be roughly estimated by comparing dew point temperature and the actual temperature o Ex If the temperature is 70 and the dew point in 69 air only needs to cool 1 for saturation to occur Relative humidity fluctuates and it can be approximated by comparing temperature to dew point temperature Location Vapor pressure Temp Saturation Vapor Pressure Relative Humidity SW Desert in Summer 8mb 35 C 60 mb 13 Northern Plaines in winter 2 mb 0C 6mb 33 Which Location has higher absolute humidity SW Desert Vapor pressure is the variable you look at to determine humidity At which location is the air closer to being saturated NW in winter look at relative humidity to determine this The Dew Point Temperature is the temperature to which air must be cooled at constant pressure to just become saturated dew forms Td increases as the amount of water vapor in the atmosphere increases Td is an absolute measure of water vapor in the atmosphere Maps often express Td as a dew point depression or T Td 1 The relative humidity is high when the different between the temperature and the dew point temperature is small 2 The relative humidity is low when the different between the temperature and dew point temperature are large Which one of the following weather observations would tell you how close the atmosphere is to being saturated Temperature Dew Point Temperature Relative humidity Saturation vapor pressure Which one of the following weather observations would tell you the actual amount of water vapor in the atmosphere Temperature Dew Point Temperature Relative humidity Saturation vapor pressure Latent heat is critical for weather The energy associated with the phase