weather. hydrologic cycle saturation and dew point saturated verses unsaturated air at the dew-point...
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WEATHER
Hydrologic Cycle
Saturation and Dew Point• Saturated verses
unsaturated air• At the dew-point
temperature, air reaches saturation– temperature to
which air must be cooled to (100% RH)• water on outside of
drinking glass• ice on your car
window• dew and fog
After Saturation Occurs the AirMust Release Extra Water as FluidWater 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
Lifting Condensation Level (LCL)The altitude where the dew point is reached
and clouds form
• LCL / Cloud base = dew point altitude
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 RockyMountain slope
Air near theSlope is 100%Saturated
Measuring Relative Humidity
Sling psychrometer
Hair hygrometer
There are a number of ways in which clouds can form
ConvergenceConvergence occurs when large air masses meet & are forced to rise vertically by crowding of molecules.
This process is best seen at the ITCZ where the Trades Winds meet & rise to form towering clouds & heavy precipitation
Convectional LiftingAnywhere air is warmer than its surrounding air, it will rise.
In this example an island heats more than the surrounding water and causes a massive cumulus cloud to form.
Convectional Lifting Over FloridaWarmer temperatures over the peninsula of
Florida, which is land, cause air to rise compared to the cooler oceans nearby
Rising air in thisShuttle Picture isShown by a Cloud patternwhich generallyfollows the shape of the southern Florida peninsula
Convectional Lifting in the DesertExtremely 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 AirWhen air movingHorizontally Encounters aMountain it mustRise over the crest
As it rises, it coolsTo create clouds,And most oftenprecipitation
MoistAir
MoistureLost
DryAir
Run off NO Run off
WHY SO MUCH SEVERE WEATHER OCCURS IN THE MIDWEST
CHANGES IN LATITUDE: WESTERLY WINDS WHERE WE LIVE; FLORIDA AND SOUTH TOEQUATOR ARE THE TRADE WINDS FROM THE EAST. THE TRADE WINDS FROM NORTH AND SOUTH OF THE EQUATOR MEET AND CAUSE UPLIFT. THE WEATHER NEAR THEEQUATOR: LOTS OF RAIN AND NO WINDS.
• Air Mass – an extremely large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any given latitude.
• Source Regions – are regions where air masses originate. In order for a huge air mass to develop uniform characteristics, its source region should be generally flat and of uniform composition with light surface winds.
Classification
• Air masses are grouped into four general categories according to their source region– Polar (P) are air masses that originate in
polar latitudes– Tropical (T) are air masses that form in warm
tropical regions– Maritime (m) are air masses that originate
over water (moist in the lower layers)– Continental (c) are air masses with a source
region over land (dry)
Air mass source regions and their paths.
Fronts
• A front is a transition zone between two air masses of different densities. Since density differences are most often caused by temperature differences, fronts usually separate air masses with contrasting temperatures. Often they will also have contrasting humidities as well.
Cold Front
• Represents a zone where cold, dry stable polar air is replacing warm moist unstable tropical air.
• Drawn as solid blue line with the triangles along the front showing its direction of movement.
In the case of a cold front, a colder, denser air mass lifts the warm, moist air ahead of it. As the air rises, it cools and its moisture condenses to produce clouds and precipitation. Due to the steep slope of a cold front, vigorous rising motion is often produced, leading to the development of showers and occasionally severe thunderstorms.
COLD FRONT
Cold front
Warm Fronts
• A warm front is a front that moves in such a way that warm air replaces cold air
In the case of a warm front, the warm, less dense air rises up and over the colder air ahead of the front. Again, the air cools as it rises and its moisture condenses to produce clouds and precipitation. Warm fronts have a gentler slope and generally move more slowly than cold fronts, so the rising motion along warm fronts is much more gradual. Precipitation that develops in advance of a surface warm front is typically steady and more widespread than precipitation associated with a cold front.
WARM FRONT
Warm Front
Frontal Lifting of AirAlthough not a mountain range, masses of moving airCreate the same effect – Unlike mountains air massesCan provide lifting in many different locations
Fronts can lift air Which is stable,Creating clouds& large amountsOf precipitationAs rain, snow,Sleet or hail