Humidity and precip

Water and Atmospheric Moisture : 

Water and Atmospheric Moisture

Hydrologic Cycle : 

Hydrologic Cycle

Moisture, Clouds, and Precipitation : 

Moisture, Clouds, and Precipitation Humidity Global Precipitation Lifting Mechanisms Precipitation Processes Big Question: What Causes Air to Precipitate?

Global Precipitation : 

Global Precipitation

U.S. Current Relative Humidity[click on map] : 

U.S. Current Relative Humidity[click on map]

Slide 8: 

ABSOLUTE HUMIDITY: Absolute humidity (expressed as grams of water vapor per cubic meter volume of air) is a measure of the actual amount of water vapor (moisture) in the air, regardless of the air's temperature. The higher the amount of water vapor, the higher the absolute humidity. RELATIVE HUMIDITY: Relative humidity (RH) (expressed as a percent) also measures water vapor, but RELATIVE to the temperature of the air. In other words, it is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that can exist in the air at its current temperature. Warm air can hold more water vapor than cold air, so with the same amount of absolute/specific humidity, cooler air will have a HIGHER relative humidity, and warmer air a LOWER relative humidity.

Humidity : 

Humidity Capacity of air is primarily a function of temperature Relative Humidity (RH) = (actual water vapor content) x 100 (max. water vapor capacity of the air) Heated air becomes lower in RH because denominator gets larger Cooled air becomes higher in RH

Saturation vsAir Temperature : 

Saturation vsAir Temperature The actual amount of Water air can hold changes With air temperature Air at 104 F can hold 3 times As much water as 68 F air ! (47 grams vs only 15 grams) Air at 68 F can hold 4 times As much water as air at 0 F (15 grams vs only 4 grams) 32 F 68 F 104 F 4 grams 15 grams 47 grams

Saturation and Dew Point : 

Saturation and Dew Point Saturated v. unsaturated air Dew-point temperature temperature to which air must be cooled to reach saturation (100% RH) water on outside of drinking glass ice on your car window dew and fog

Adiabatic Cooling: Clouds and Lifting Condensation Level (LCL) : 

Adiabatic Cooling: Clouds and Lifting Condensation Level (LCL) LCL / Cloud base = dew point altitude

Relative Humidity and Temp. : 

Relative Humidity and Temp. RH fluctuates over a day or season.

Measuring Relative Humidity : 

Measuring Relative Humidity Sling psychrometer Hair hygrometer

After Saturation Occurs the AirMust Release Extra Water as Fluid : 

After Saturation Occurs the AirMust Release Extra Water as Fluid Water forms on the outside of a cold glass as the cold Air surrounding the glass chills the air to the Dew Point Temperature The resulting water is not from the glass, the water is from condensation of moisture in the air around the glass

In Nature Extra Moisture isTransformed to Water Droplets : 

In Nature Extra Moisture isTransformed to Water Droplets Cold air next to the rain-soaked cliff is chilled To The Dew Point Temperature & creates a Misty Cloud along a Rocky Mountain slope Air near the Slope is 100% Saturated

Slide 18: 

Fog by the Golden Gate

Temperature Inversions : 

Temperature Inversions Common Summer Inversion in Los Angeles

Slide 20: 

Yakima River, Washington Which of the four types is this?

Fog: A Cloud on the Ground : 

This April fog occurred in the San Fernando Valley after a clear, cold April night. It evaporated by noon. Fog: A Cloud on the Ground Fog in Glendale

Temperature Inversions : 

Temperature Inversions When warmer air overlies cooler air, pollutants and fog are trapped beneath the inversion. Common Winter Radiation Inversion in Valleys

Slide 23: 

Which of the four types is this?

Slide 24: 

Valley Fog in the Valleys of the Appalachian Mountains Which of the four types is this?

Slide 25: 

An often Very dense Type of Valley Fog Called Tule Fog in the Central Valley of California Pacific Ocean

Atmospheric Lifting Mechanisms : 

Atmospheric Lifting Mechanisms Air Lifting processes create clouds & precipitation Are the only means of precipitation on Earth Four types of lifting are recognized: Convectional Lifting Convergence Orographic Lifting Frontal Lifting

Convectional Lifting of Air : 

Convectional Lifting of Air Convergence occurs When Air masses meet & are forced To rise vertically This process is best seen at The Equator where the Trades Winds Meet & rise to form towering Clouds & heavy Precipitation

Convectional Lifting & Global Precipitation Patterns : 

Convectional Lifting & Global Precipitation Patterns Convergence and Convection provide the greatest amount of Precipitation On Earth

Convectional Lifting : 

Convectional Lifting Anywhere the land is very warm, Air will rise In this example A plowed field Creates warmer Air temperatures Than nearby Green cropland & Local air rises

Convectional Lifting Over Florida : 

Convectional Lifting Over Florida Warmer temperatures over the peninsula of Florida, which is land, cause air to rise compared to the cooler oceans nearby Rising air in this Shuttle Picture is Shown by a Cloud pattern which generally follows the shape of the southern Florida peninsula

Convectional Lifting in the Desert : 

Convectional Lifting in the Desert Extremely high afternoon temperatures in late summer often leads to thunderstorms throughout the world’s arid regions. The Grand Canyon in August Mojave Desert

Orographic Lifting of Air : 

Orographic Lifting of Air When air moving Horizontally Encounters a Mountain it must Rise over the crest As it rises, it cools To create clouds, And most often precipitation Moist Air Moisture Lost Dry Air Run off NO Run off

Frontal Lifting of Air : 

Frontal Lifting of Air Although not a mountain range, masses of moving air Create the same effect – Unlike mountains air masses Can provide lifting in many different locations Fronts can lift air Which is stable, Creating clouds & large amounts Of precipitation As rain, snow, Sleet or hail

Precipitation Types / Properties : 

Precipitation Types / Properties

Snowflakes and Temperature : 

Snowflakes and Temperature Snow crystal images from an electron microscope

Seasonal and Global Variation in Lifting Mechanisms and Precipitation : 

Convective – ITCZ; increases when insolation is most intense and when marine air moves over land masses; common also in deserts, with their intense heating Orographic – requires elevation change Frontal – Midlatitudes only Seasonal and Global Variation in Lifting Mechanisms and Precipitation

Summary : 

Humidity Relative Humidity Relationship to Temperature Dew Point LCL Precipitation (Rain, Snow, Sleet, Hail) When air is dramatically cooled below the dew point, large droplets form and fall. Lifting Mechanisms Convective, Orographic, Frontal, Convergence Summary