Transcript Cold Fronts - Crowley AP Environmental Science

Chapter 5 Weather
What is weather?
What makes weather change?
Solar Radiation
• Temperature Changes with Latitude
Like equator
Like at poles
Seasonal Changes
• Temperature Changes with Season
The Atmosphere
• Nitrogen 78%
• Oxygen 21%
• CO2
.038%
Carbon dioxide
Argon
Water vapor
Pollutants
Helium
Etc.
1%
The Atmosphere
Atmospheric Circulation
• Atmospheric
Circulation
Circulation
spawned
by heating
/ cooling
Prevailing
winds:
Generated by
pressure
differences
and Coriolis
effect
Coriolis Effect
Southern Hemisphere
Coriolis Effect
Gaspard de Coriolis (1792-1843)
• Size of deflection is directly related to both the speed at which the air
is moving and its latitude.
• The Coriolis force is zero right at the equator.
• The Coriolis force only acts on large objects like air masses moving
considerable distances. Small objects, for example ships at sea, are
too small to experience significant deflections.
Trade Winds
Horse Latitudes
30 degrees north
(Horse latitudes)
&
30 degrees south
(Horse Latitudes)
&
Equator
(Doldrums)
Fronts
What is a front?
Fronts
Fronts
1. A front is defined by temperature, relative humidity, and air pressure:
1. Temperature = the kinetic energy of a substance
2. Relative Humidity = is a function of temperature and water content
3. Air pressure = the weight of the atmosphere
Warm Fronts
1. Retreating Cold fronts under advancing warm fronts are drawn out in a triangular
fashion due to friction with the ground causing a triangular shape to the advancing
warm front.
2. Warm fronts move towards the northeast
3. Warm fronts usually travel at about 15mph
Cold Fronts
1. Cold fronts become rounded due to friction with the ground as they advance on
warm fronts.
2. Cold fronts tend to move towards the east or southeast
3. Cold fronts usually advance at speeds of 20mph
4. Cold fronts may produce violent weather depending on their speed and air
stability.
5. Faster moving cold fronts produce “squall Lines” Where high upper level winds
stop a warm front from lifting up but whip up warm air ahead of the storm producing
violent weather.
Air Movement
Pressure Systems (in the north)
1. Low Pressure systems rotate counter clockwise
2. High pressure systems rotate clockwise
Jet Streams
1. Tend to follow the borders between warm and cold air
2. In the summer they are located further north and in the winter further south
3. Jet streams blow west to east in the northern and southern hemispheres
4. How are airline flights impacted by jet streams (speed and turbulence)
Wind Shear
1. Is any sudden change in wind speed or direction causing, turbulence.
Turbulence
Micro-Burst
Micro-Burst
Wind
What is wind and what makes wind?
Beach Winds
Hanging at the beach
Day time Vs. Night time breezes
Sea breezes
Micro-Climate & Turbulence
Wind
Tornados
Tornados
Katabatic Winds
Katabatic winds exist in many parts of the World and are winds that flow from the high
elevations of mountains, plateaus, and hills down their slopes to the valleys or planes
below. There are many diffent names for katabatic winds depending where they are
located - Santa Anna (funneled & dry), and Chinook (dry).
Chinook Winds Over Rockies
Weather and Climate
• Rain shadows
Insert Fig 5.19 b
Santa Ana Winds
N
O
R
’
E
A
S
T
E
R
Adiabatic Problems
1.
2.
3.
4.
5.
A 10k foot mountain
Air temperature at mountains base is 60 degrees
Clouds form at 4k and extend to the mountain top
What is the temperature of the valley floor (leeward side)
How does humidity and temperature change from winward to leeward?
Problem 2
A 14k peak with a valley temperature of 70
Cloud formation begins at 7k and ends at 10k
(5.5 and 3.2 = temperature changes for every thousand feet)
1.
2.
3.
4.
What is the temperature at 7K?
What is the temperature at 10K?
What is the temperature at 14K?
What is the temperature in the leeward valley?
Is there compression of the air as in refrigeration or a decompression?
Adiabatic Temperature Change & Condensation
Adiabatic heating and cooling is a temperature change within a gas
due to compression (resulting in heating) and expansion
(resulting in cooling); no heat is added to, or removed from the
gas.
Why rising air cools and Rain Shadows
1. Decreased pressure
2. For every 1k/feet air rises it cools 5.5 farenheight due to lowering gas
pressures and heats the same going down (adiabatic cooling & heating)
3. Air that rises and condenses at the same time only cools 3.2F for every 1k it
rises due to the “heat of condensation”
4. Air moving up western slopes can come down warmer on the other side.
Creating cool moist western slopes and warm dry eastern slopes.
The Global Ocean
• Patterns of Circulation in the Ocean
Influenced by:
1. Coriolis Effect 2. Winds
3. Land Masses
4. Water Density
The Global Ocean
• Patterns of Circulation in the Ocean
The Global Ocean
• Vertical Mixing of Ocean Water
2005 Hurricane tracks
Hurricanes
•
•
•
•
•
Severe weather events:
Tropical cyclones
Atlantic Ocean = hurricanes
Pacific Ocean = typhoons
Indian Ocean = cyclones
Category One Hurricane: Winds 74-95 mph
Category Two Hurricane: Winds 96-110 mph - Storm surge generally 6-8
feet above normal
Category Three Hurricane: Winds 111-130 mph - Some structural damage to
small residences
Category Four Hurricane: Winds 131-155 mph - Complete destruction of
mobile homes
Category Five Hurricane: Winds greater than 155 mph - Storm surge
generally greater than 18 ft above normal and framed homes destroyed
Hurricanes
1. Hurricanes are powered by the energy released during condensation
2. Hurricanes are steered by prevailing wind patterns and wind sheer will
destroy a hurricane.
3. What are positive and what are negative feed-back-loops for hurricanes
4. When winds reach 74mph a tropical storm becomes a hurricane
5. Why is the eye clear? Air coming in from the eye wall is coming inward
towards the center from all directions. This convergence causes the air to
sink in the eye. This sinking creates a warmer environment and the clouds
evaporate leaving a clear area in the center.
Katrina
Katrina
El Niño/Southern Oscillation (ENSO)
• Chicken and Egg scenario – ocean
temperatures or trade winds?
This decreases
during El Niño
Increases
during La Niña
http://esminfo.prenhall.com/
science/geoanimations/ani
mations/26_NinoNina.html
El Niño/Southern Oscillation (ENSO)
1. Heavier rainfall over coastal equatorial South America
2. Drought in Western Pacific (Indonesia & Australia)
3. Increased transmission of disease – mosquitoes and stagnant
water – Les or More water and heat
4. Migration of fish species (North or South – Inshore or Out)
5. Death of seals and sea birds due to changing fisheries
6. Heavier rains in the southwestern deserts of United States
7. Fewer hurricanes in the Atlantic
8. Changes in disease due to shifts in temperature and moisture
2010-2011 Australia has record flooding?
• La Nina or El Nino
• Weak or Strong
El Nino
La Nina
Lightning
What do you know about lightning
Lightning
Thunder and Lightning
1. Sound travels about one mile every 5 seconds
So if you count to ten the storm is 2 miles away
2. Thunder rumbles because the sound from different points on the bolt
reaches our ears at different times
3. Thunder, is produced by the heating (expansion) and cooling (contraction) of
the air around a lightning strike.
4. Lightning forms from negative charges at the bottom of the cloud that meet
with positive charges from the ground. A stepped leader from the cloud
meets a streamer from the ground. Visible light moves up and charge flows
down. Individual charges are drained separately causing lightening to flash
and strike multiple times in one location.