Transcript Weather Part 2

WEATHER PART 2
Water Vapor enters the atmosphere in 3 ways:
1.
2.
3.
Evaporation – the change of phase from liquid to vapor
Transpiration – plants releasing water vapor to the air (plant sweat)
Evapotranspiration - a combo of evaporation and transpiration
Factors that effect the rate at which water vapor enters the air:
1. Air Temperature – as air temp. increases, evapotranspiration
increases
2. Surface Area (how spread out something is)– as surface area
increases, evapotranpiration increases
3. Air Circulation (wind) – the more air circulates, the more
evapotranspiration occurs.
4. Moisture Content of the Air – moist air already had a lot of water
in it, so it does not want any more. Water will evaporate more
easily off of surfaces when is air is dry.
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Atmospheric Moisture
Saturation – when the air is holding all of the water vapor that it
can. There is no more room. The air becomes saturated when it is
cooled to and reaches it’s Dewpoint Temperature.
Relative Humidity – how much water vapor is in the air compared
to how much it can hold (which is 100%). If the Relative Humidity is
70%, that means it can still hold 30% more before it reaches it’s Dewpoint
Temperature and becomes saturated.
Cloud – a collection of tiny liquid water droplets which remain in
suspension (floating because they are too light and little). Some
very high clouds are made of ice crystals (Cirrus – looks like feathers).
Clouds are not made of water vapor. They are either liquid or ice. Each
cloud droplet, raindrop, and snowflake form around a tiny piece of
dirt, dust, sand, pollen, or salt. This tiny piece of dirt in the center is called
the condensation nuclei. Water needs something to cling onto. Do not eat
snow or drink rain water. It is dirty.
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How a cloud forms:
1. Air rises, expands, and cools to it’s Dewpoint Temperature.
2. When air reaches it’s Dewpoint Temperature, a few other things
automatically happen:
a) the air is SATURATED
b) the RELATIVE HUMIDITY is 100%
c) CONDENSATION OCCURRS
Condensation makes a cloud. The water vapor turns to liquid,
because heat was released. Clouds are liquid water droplets.
Precipitation does not come out of every cloud. The
cloud droplets are too light and too tiny to fall. As
condensation continues, the droplets begin to grow in
size. Once they are heavy and big enough, they fall. That
is precipitation.
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Types of Precipitation
1.
2.
3.
4.
Rain – this happens when the air temperature reaches it’s dewpoint temperature
(condensation), and that is above 0º C. This simply liquid water with a
condensation nuclei in the center. Cloud droplets are also liquid water. When
the cloud droplets reach a certain size, they start to fall as rain.
Snow – this happens when the air temperature reaches it’s dewpoint temperature,
and that is below freezing. This is not condensation, it is SUBLIMATION.
Sleet – this is when the droplets begin to fall out of clouds as rain in the upper
atmosphere, but the air temperature down here is below freezing, and the
droplets turn into ice pellets before they reach the ground.
Hail – this occurs from large thunderstorms. The droplets begin to fall as rain.
These droplets are whisked back up very high into the storm clouds by the severe
wind, and they freeze. Then, as they fall again and begin to melt, they are
whisked back up into the storm and freeze again. Hail can have many layers.
Freezing Rain is when the air temperature is higher than the ground
temperature. Liquid rain droplets freeze when they hit the ground.
Dew, Fog, and Frost are not forms of precipitation!!!!
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Dry Bulb Temperature = Air
Temperature
A sling psychrometer measures the
wet-bulb and dry bulb temps.
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The Wet-Bulb Depression is the difference between the wet-bulb and dry-bulb
temperatures. You do not have to subtract if you are given the Wet-Bulb Depression.
The chart looks like and works like the Dewpoint chart. Do not confuse
them.
Air temp.
and
Relative
Humidity
are
inverse.
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The R.H.
is high in
the
morning
and
night,
and
lowest
during
mid-day.
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Air Masses – there are two basic types of air masses
High Pressure – Anticyclone
Low Pressure - Cyclones
1.
1.
2.
3.
4.
Winds blow clockwise away
from the center.
Divergent air mass
In the center, the air is dry, cool,
clear, and windy.
Higher density air.
2.
3.
4.
Winds blow counter-clockwise
towards the center.
Convergent air mass
In the center, air is moist, cloudy,
warmer.
Lower density air
H
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Source Regions – areas on the Earth’s surface where air masses
form and acquire their characteristics.
The diagram above shows the source regions that create air masses effecting the
United States.
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Cold Front – an anti-cyclone overtaking a cyclone. The cold air in
the anti-cyclone moves in and pushes the warm cyclone out
of the way. Cold fronts have cooler, clear weather behind
them. Cold fronts travel the fastest.
Warm Front – a cyclone overtaking an anti-cyclone. The warm air
in the cyclone moves in and pushes the cooler air out of the
way. Warm fronts have warmer, cloudy, moister air behind
them.
Occluded Fronts
Results by warmer air being pushed above the surface of Earth
by cooler air closing in from both sides.
Associated with large areas of rainy, unsettled weather.
Stationary Front
Boundaries between air masses that are not moving.
Winds are blowing in opposite directions along a boundary
between warm and cold air masses.
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It always precipitates
on the cold front.
High-Pressure
Systems are behind a
cold front. Cold
fronts have brief,
heavy storms on
them.
It always precipitates
ahead of the warm
front.
Low-Pressure systems
are behind a warm
front. Steady
precipitation is ahead
of these.
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Forecasting and reading weather maps:
Synoptic Weather Map
As a class, we are going to write some weather forecasts below:
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Thunderstorm
Thunderstorms can occur anywhere in the world and at any time of the day. All
thunderstorms produce lightning and thunder. Some have the potential to produce
damaging straight-line winds, large hail, heavy rain, flooding, and tornadoes.
A thunderstorm is classified as severe when it contains one or more of the following
phenomena:
•Hail 3/4" or greater
•Winds gusting in excess of 50 knots (57.5 mph)
•A Tornado
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Lightning
A moving thunderstorm gathers a pool of positively charged
particles along the ground that travel with the storm. As the
differences in charges continue to increase, positively charged
particles rise up taller objects such as trees, houses, and
telephone poles. The negatively charged area in the storm will
send out a charge toward the ground called a stepped leader.
It is invisible to the human eye, and moves in steps in less
than a second toward the ground. When it gets close to the
ground, it is attracted by all these positively charged objects,
and a channel develops. You see the electrical transfer in this
channel as lightning. There may be several return strokes of
electricity within the established channel that you will see as
flickering lightning.
Thunder
The lightning channel heats rapidly to 30,000 °C. The rapid
expansion of heated air causes the thunder. Since light travels
faster than sound in the atmosphere, the sound will be heard
after the lightning. If you see lightning and hear thunder at the
same time, that lightning is in your neighborhood!
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Tornado
Warm, humid conditions are very favorable for thunderstorm development as
strong updrafts feed warm, moist air into thunderstorms. If the air is very
unstable, severe thunderstorms with damaging winds, large hail, and
sometimes tornadoes erupt.
A tornado is a violently rotating column of air which is in contact with both a
cumulonimbus (or, in rare cases, a cumulus) cloud base and the surface of the
earth. Tornadoes come in many sizes, but are typically in the form of a visible
condensation funnel, whose narrow end touches the earth and is often encircled
by a cloud of debris. They are measured on the Fujita scale (1-5), which is now
changed to the EF scale because of a few modifications.
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Category
Description
Level Of Damage
F-0
Gale Tornado
40 - 72 MPH
Chimneys damaged; branches broken off trees; shallow-rooted
trees uprooted; sign boards damaged.
F-1
Moderate
Tornado
73 - 112 MPH
Roof surfaces peeled off; mobile homes pushed off foundations
or overturned; moving autos pushed off roads.
F-2
Significant
Tornado
113 - 157 MPH
Roofs torn off frame houses; mobile homes demolished; box cars
pushed over; large trees snapped or uprooted; light-object
projectiles generated.
F-3
Severe Tornado
158 - 206 MPH
Roofs and some walls torn off well-constructed houses; trains
overturned; most trees in forest uprooted; heavy cars lifted off the
ground and thrown.
F-4
Devastating
Tornado
207 - 260 MPH
Well-constructed houses leveled; structures with weak
foundations relocated; cars thrown and large projectiles
generated.
F-5
Incredible
Tornado
261 - 318 MPH
Strong frame houses lifted off foundations and carried
considerable distance to disintegrate; automobile-sized projectiles
hurtle through the air in excess of 100 yards
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Hurricane
Hurricanes start out as Tropical Depressions (mT, Low-Pressure) in the Atlantic
Ocean surrounding the Equator, off the coast of Africa. Hurricane season begins
at the end of summer and runs into late October. They form because the
abundance of summer heat evaporates large amounts of ocean water putting it
into the atmosphere. Once storm winds reach 75 miles/hour, it is classified as a
hurricane. Hurricanes loose their energy after they hit land, because the
evaporation of ocean water is their fuel. Hurricanes are measured by The Saffir
Simpson Scale of 1-5.
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1
Wind Speed: 74 95 MPH
Storm Surge: 4 - 5
Feet Above Normal
Primary damaged to unanchored mobile homes,
shrubbery, and trees. Some coastal road flooding and
minor pier damage. Little damage to building structures.
2
Wind Speed: 96 110 MPH
Storm Surge: 6 - 8
Feet Above Normal
Considerable damage to mobile homes, piers, and
vegetation. Coastal and low-lying escape routes flood 2
- 4 hours before arrival of hurricane center. Buildings
sustain roofing material, door, and window damage.
Small craft in unprotected moorings break moorings.
3
Wind Speed: 111 130 MPH
Storm Surge: 9 12 Feet Above
Normal
Mobile homes destroyed. Some structural damage to
small homes and utility buildings. Flooding near coast
destroys smaller structures; larger structures damaged
by floating debris. Terrain continuously lower than 5 feet.
ASL may be flooded up to 6 miles inland.
4
Wind Speed: 131 155 MPH
Storm Surge: 13 18 Feet Above
Normal
Extensive curtain wall failures with some complete roof
structure faiture on small residences. Major erosion of
beaches. Major damage to lower floors of structures
near the shore. Terrain continuously lower than 10 feet.
ASL may flood (and require mass evacuations) up to 6
miles inland.
5
Wind Speed: Over
155 MPH
Storm Surge: Over 18
Feet Above Normal
Complete road failure on many homes and industrial buildings.
Some complete building failures. Major damage to lower floors
of all structures located less than 15 feet ASL and within 500
yards of the shoreline. Massive evacuation of low ground
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residential
areas may be required.