Transcript Weatherx - rgreenbergscience

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 Air
Water forms on the outside of a cold glass as the cold
Must
Release
Extra
Water
as
Fluid
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 is
Transformed 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
Measuring Relative Humidity
Sling psychrometer
Hair hygrometer
There are a number of ways in which clouds can form
Convergence
Convergence 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 Lifting
Anywhere 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 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
Extremely high afternoon temperatures in late
summer often leads to thunderstorms
throughout the world’s arid regions.
Mojave Desert
The Grand Canyon in August
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
Moisture
Lost
Moist
Air
Run off
Dry
Air
NO Run off
WHY SO MUCH SEVERE WEATHER
OCCURS IN THE MIDWEST
CHANGES IN LATITUDE: WESTERLY WINDS WHERE WE LIVE; FLORIDA AND SOUTH TO
EQUATOR ARE THE TRADE WINDS FROM THE EAST. THE TRADE WINDS FROM NORTH
AND SOUTH OF THE EQUATOR MEET AND CAUSE UPLIFT. THE WEATHER NEAR THE
EQUATOR: 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.
COLD FRONT
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
Warm Fronts
• A warm front is a front that moves in such a way
that warm air replaces cold air
WARM FRONT
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
Although not a mountain range, masses of moving air
Create the same effect – Unlike mountains air masses
Can provide lifting in many different locations
Frontal Lifting of Air
Fronts can lift air
Which is stable,
Creating clouds
& large amounts
Of precipitation
As rain, snow,
Sleet or hail