Natural Disasters Week 2
Types of energy.
Energy is the ability to do work. Kinetic energy is the energy of motion while potential energy is the energy granted by Energy that can be transferred, but it cannot be destroyed.
Some of the energy of our planet is derived from the energy inside the Earth. Much of this energy comes from the radioactive decay of heavy elements that are more concentrated in the depths of the earth. Some of the heat is left over from the formation of the earth.
The sun is the primary source of energy for the Earth. Energy is released from the sun via convection and radiation in the form of visible light and infrared energy (electromagnetic radiation).
Solar radiation.
Vast amounts of energy hit the atmosphere from the sun. The sunlight is the strongest where the sunlight hits the planet’s surface perpendicular to the surface. Solar radiation is generally strongest at the equator and lowest at the poles.
Albedo.
Albedo is a measure of how much solar radiation is reflected by the earth. In general light and white surfaces have high albedo and reflect sunlight while dark and black surfaces have low albedo and very little sunlight is reflected.
polls ice reflects 90% of the solar radiation
oceans absorb 90% of solar radiation
albedo decreases with the melting of ice, leading to higher absorption of solar radiation
The Equator receives roughly 2.4X the energy as the polar regions of the planet.
Air
is a mixture of gases that make up the Earth’s Atmosphere.
The atmosphere provides us with oxygen as a vital part of being alive.
Stores carbon dioxide necessary for photosynthesis (and our existence).
Absorbs solar radiation and moderates the climate (keeps the difference between day and night much less extreme.
Protects the surface from incoming meteors.
Troposphere
The troposphere is the part of the atmosphere that is most important for us.
The troposphere is warmer at the base and cooler at the top Atmospheric composition.
Has been largely stable for millions of years.
Primarily made of Nitrogen and Oxygen with Argon being (generally) the next most concentrated gas.
Nitrogen is largely inert, but extremely reactive when put in unstable atoms.
Oxygen is produced by plants.
Water vapor, carbon dioxide and methane are all potent greenhouse gases that trap heat in the atmosphere.
Nitrous Oxide and sulfur dioxide are often byproducts of industrial processes and “pollution.”
Ozone helps block UV
contains weather, the air we breathe, ¾ of the atmospheres mass, heated by the earth”s surface
CFC’s - chlorofluorocarbons (the hairspray ruining the ozone layer) they don’t decay in the atmosphere (now banned)
Weather vs Climate.
Weather is the specific conditions found outdoors at a given time and place.
Climate: is the average, range, and seasonality of weather conditions that occur over the course of decades or longer in a region.
When discussing the weather, temperature, pressure, water vapor, and air density become important parts of the story.
Air temperature is a measure of the average kinetic energy of the particles
of a substance (how energetic each particle is).
Heat represents the transfer of energy.
Most of the air in the troposphere is heated on the bounce. Short-wave energy comes in from the sun, hits the surface, and loses some energy to become long-wave energy.
Greenhouse gases – Work like a blanket and keep the heat in. The thicker the blanket the more heat is kept in.
Pressure – The weight of the column of air above you pushing down on you.
Density – the amount of mass per unit volume. Less dense materials rise while more dense materials sink.
Combine density with pressure and you get mass air movements.
Pressure and density together. The weight of air above squeezes the air together so there is more dense
air near the Earth’s surface (generally).
Density and Temp. Heating something causes it to expand. Cooling it causes it to contract. Cold objects
are denser and hot objects are less dense.
Convection cells occur when you have a hot area and a cold area in proximity to each other. The hot object causes hot air to rise while the cold object causes the air to cool and sink.
Hydrosphere is all of the Earth’s water. The cryosphere is all of the Earth’s ice (and is part of the Hydrosphere).
97% of the Earth’s surface water is in the oceans.
Hydrologic cycle – Radiant energy from the sun heats water which evaportates. Water vapor rises intothe atmosphere where it cools down. The vapor condenses as precipitation.
Water vapor in the atmosphere varies greatly from 0% to 4% of the atmosphere. It is in all three phases in the atmosphere.
Water vapor and density. Cold air can’t hold much water vapor.
Relative humidity is the ratio of water vapor in the air to the amount of water vapor the air COULD
contain at that temperature.
Lecture 14: Air Continued
Wind
The atmosphere is in constant motion because air flows due to pressure, moisture, and
temperature differences. Wind moves and mixes water as well as nutrients. This constant motion
also brings precipitation and storms.
Wind Direction
With no spin, wind would flow directly towards the lowest pressure, converge, and rise. With
spin, The Coriolis Force deflects wind to the right , producing an overall counter-clockwise
rotation of the wind. But with friction slowing the flow, which diminishes the Coriolis Effect,
wind actually spirals towards the center and up. System is reverse for high pressure.
Three forces act to influence the direction and speed of the wind at a location:
1) Pressure gradient: variations in temperature and water content of air over the Earth’s
surface result in variation of air density and pressure.
o Fluids move from high pressure to low pressure
o Velocity depends on the size of difference: larger difference = faster movement
2) Frictional force: Air feels friction as a volume of faster air shears past a slower volume
of air OR as it flows over the Earth’s surface.
o Air is denser at the Earth’s surface
o More stuff at the surface to flow over and around.
o This boundary layer, where air feels more friction, varies from 200m over the
ocean to around 2,500m over cities and mountains.
3) Coriolis force: the apparent east-west deflection of air currents of the convective cells
o As Earth rotates, equatorial regions spin faster resulting in:
▪ Divergence being to the right in the Northern Hemisphere
▪ Divergence being to the left in the Southern Hemisphere
Geostrophic Wind
The Coriolis force and pressure gradient force become equal and the wind flows along lines of
equal pressure rather than perpendicular to them (geostrophic).
• The Coriolis Effect, and resulting deflection, increase as air volume accelerates
• The pressure gradient force decreases once you leave the boundary layer
• Common above the boundary layer over much of Earth
o When we deviate from geostrophic we get big storms
Convective Circulation
Less dense, warmer air rises, creating vertical currents
• Air rises because it is warm and lower density (expands)
• Once it is away from the surface, it cools, and increases density
• Precipitation makes cooler dry air that sinks
• It then warms and rises again, continuing the process
Global Circulation
1) Vertical and north-south circulation in the hemispheres
2) Hadley Cells
o Equator gets the most solar radiation
o Heated, warm air rises over equator and cools
o Water vapor condenses, precipitates and dries
o Air moves away from the convergence
o Descends again as dry, cold air near 30 degrees latitude
Global circulation patterns create rain forests at the equator where warm, wet, rising air
produces a lot of rain. These patterns also create deserts at 30 degrees where cold, dry, falling air
flows back towards the equator.
These patterns repeat twice more further north and south
• Wetter, warmer, (OK, snowier) Taiga forests (Ferrel cell)
• Cold, dry polar regions (Polar Cell)
Global Winds
At the equator where there is little wind is a region know as the doldrums. Curving global wind
patterns from the Coriolis Effect cause the trade winds between the equator and 30 latitude,
and the westerlies between 30 and 60. These wind patterns facilitated ocean travel by wind-
powered sailing ships.
These global winds are historically important because they aided in global “trade”:
• North America exported sugar, tobacco, and cotton to Europe
• Europe exported textiles, rum, and manufactured goods to Africa
• Slaves taken from Africa and brought to America
Southern Oscillation and El Nino
Walker Circulation patterns are east-west air movements related to ocean temps:
• Flow of air pulls warmer water towards New Zealand and Australia
• Cold water rises to replace it enforcing the circulation
• When Walker Circulation weakens, wind and upwelling cease and warm water pours
back towards Peru
• Trade winds weaken or reverse and storms shift east
The east-west seesaw in surface air pressure across equatorial Pacific accompanies changes in
Walker Circulation in called El Nino – Southern Oscillation (ENSO). These changes in the
Pacific Walker Circulation patterns impact the globe:
• El Nino: drought and fires in Australia and Indonesia, flooding in Peru, California floods,
and Midwest blizzards and droughts
o El Nino in 1983 was catastrophic: droughts, dust storms, brush fires, encephalitis
outbreak from an increased population of mosquitoes, bubonic plague in New
Mexico, etc.
• La Nina: drought in Somalia, wildfires in the Rockies, floods in SE Asia, weakened
India monsoons
Monsoons
Monsoons are a seasonal change in air circulation directions over a region that results in
seasonal changes in rainfall. Usually, produced by summer winds blowing off a body of water
(typically the ocean) and winter winds blowing from land to sea.
In the summer, the land heats faster than the sea. Warmer land heats the air causing lift, and
cooler, wet sea air comes to replace it. Water laden air heats and rises producing rain.
In the winter, the land cools more than the sea. Warmer air rises over the sea and colder air flows
off the land to replace it. Colder, drier air produces clear skies and dry weather.
Mid-Latitude Weather
Mid-latitudes are the battleground between cold polar air and warm equatorial air. This battle is
between air masses along fronts. An air mass is a broad body of air where temperature and
humidity are relatively uniform. Incoming air either absorbs heat from the warm surface
(and takes on water) or incoming air loses heat to the colder surfaces.
Where cold, the air sinks and semi-permanent high pressure systems dominate. High pressure
usually involves sinking, cooler air, producing clear skies. Where warm and/or wet, the air rises
and semi-permanent low pressure systems dominate.
Fronts
1) Cold front: boundary where faster moving cold air lifts warm air in front of it
o Warm air cools and precipitation occurs
2) Warm front: boundary where cold air retreats and warm air advances to fill the space
o Warm air cools and precipitation occurs
o Less severe storms, but big storms can develop
o Ice and blizzards
3) Occluded front: boundary where faster moving cold air overtakes and lifts warm air
between fronts
o Heavy rain and blizzards
4) Stationary front: boundary where adjacent air masses aren’t moving
o Warm air cools over the cooler mass
o Can bring rain for days
o Heavy snow, floods over time
5) Polar front: divides warm air originating in the Tropics and polar air originating in the
Arctic and Subarctic
Jet Streams
Jet streams are formed when large temperature changes occur over relatively short distances
across the front, producing steep pressure gradients. Large pressure gradients induce high
velocity geostrophic winds at altitude. This pattern forms jet streams.
Jet streams are typically wavey depending on the air mass position and speed. This forms ridges
of warm air and troughs of cold air which strongly influence the weather.
Cyclones
Cyclones are broad areas of precipitation and strong winds due to rising warm air and steep
pressure gradients. The head of the storm is an occluded front and warm front that can
produce blizzards and ice storms, or long lasting rain. The tail of the storm is the cold front
producing a line of precipitating clouds that can produce thunderstorms, tornadoes, and
windstorms.
Steps to forming a cyclone:
1) Warm air flows upward over the front
2) Cold air rapidly comes in to replace warm air
o Storms along this front
3) Warm air continues to pass over the cold front and cold air continues to pass under the
warm air
o Everything begins to speed up
4) Eventually, the cold front catches the warm front, forming an occluded front
o Cooler air over cold air which is capped by warm air
Mid-latitude cyclones (what the Midwest experiences) formation:
1) Air deficit at divergence zones (air thins where it speeds up) creating a low pressure
center
2) Air rises in the low pressure area and is replaced by lower level air
3) The whole thing feeds itself as it spins, often creating heavy storms or multiple storms
over a period of days
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EES:1400 – Natural Disasters
Lecture 14: Air Continued
Wind
The atmosphere is in constant motion because air flows due to pressure, moisture, and
temperature differences. Wind moves and mixes water as well as nutrients. This constant motion
also brings precipitation and storms.
Wind Direction
With no spin, wind would flow directly towards the lowest pressure, converge, and rise. With
spin, The Coriolis Force deflects wind to the right , producing an overall counter-clockwise
rotation of the wind. But with friction slowing the flow, which diminishes the Coriolis Effect,
wind actually spirals towards the center and up. System is reverse for high pressure.
Three forces act to influence the direction and speed of the wind at a location:
1) Pressure gradient: variations in temperature and water content of air over the Earth’s
surface result in variation of air density and pressure.
o Fluids move from high pressure to low pressure
o Velocity depends on the size of difference: larger difference = faster movement
2) Frictional force: Air feels friction as a volume of faster air shears past a slower volume
of air OR as it flows over the Earth’s surface.
o Air is denser at the Earth’s surface
o More stuff at the surface to flow over and around.
o This boundary layer, where air feels more friction, varies from 200m over the
ocean to around 2,500m over cities and mountains.
3) Coriolis force: the apparent east-west deflection of air currents of the convective cells
o As Earth rotates, equatorial regions spin faster resulting in:
▪ Divergence being to the right in the Northern Hemisphere
▪ Divergence being to the left in the Southern Hemisphere
Geostrophic Wind
The Coriolis force and pressure gradient force become equal and the wind flows along lines of
equal pressure rather than perpendicular to them (geostrophic).
• The Coriolis Effect, and resulting deflection, increase as air volume accelerates
• The pressure gradient force decreases once you leave the boundary layer
• Common above the boundary layer over much of Earth
o When we deviate from geostrophic we get big storms
Convective Circulation
Less dense, warmer air rises, creating vertical currents
• Air rises because it is warm and lower density (expands)
• Once it is away from the surface, it cools, and increases density
• Precipitation makes cooler dry air that sinks
• It then warms and rises again, continuing the process
Global Circulation
1) Vertical and north-south circulation in the hemispheres
2) Hadley Cells
o Equator gets the most solar radiation
o Heated, warm air rises over equator and cools
o Water vapor condenses, precipitates and dries
o Air moves away from the convergence
o Descends again as dry, cold air near 30 degrees latitude
Global circulation patterns create rain forests at the equator where warm, wet, rising air
produces a lot of rain. These patterns also create deserts at 30 degrees where cold, dry, falling air
flows back towards the equator.
These patterns repeat twice more further north and south
• Wetter, warmer, (OK, snowier) Taiga forests (Ferrel cell)
• Cold, dry polar regions (Polar Cell)
Global Winds
At the equator where there is little wind is a region know as the doldrums. Curving global wind
patterns from the Coriolis Effect cause the trade winds between the equator and 30 latitude,
and the westerlies between 30 and 60. These wind patterns facilitated ocean travel by wind-
powered sailing ships.
These global winds are historically important because they aided in global “trade”:
• North America exported sugar, tobacco, and cotton to Europe
• Europe exported textiles, rum, and manufactured goods to Africa
• Slaves taken from Africa and brought to America
Southern Oscillation and El Nino
Walker Circulation patterns are east-west air movements related to ocean temps:
• Flow of air pulls warmer water towards New Zealand and Australia
• Cold water rises to replace it enforcing the circulation
• When Walker Circulation weakens, wind and upwelling cease and warm water pours
back towards Peru
• Trade winds weaken or reverse and storms shift east
The east-west seesaw in surface air pressure across equatorial Pacific accompanies changes in
Walker Circulation in called El Nino – Southern Oscillation (ENSO). These changes in the
Pacific Walker Circulation patterns impact the globe:
• El Nino: drought and fires in Australia and Indonesia, flooding in Peru, California floods,
and Midwest blizzards and droughts
o El Nino in 1983 was catastrophic: droughts, dust storms, brush fires, encephalitis
outbreak from an increased population of mosquitoes, bubonic plague in New
Mexico, etc.
• La Nina: drought in Somalia, wildfires in the Rockies, floods in SE Asia, weakened
India monsoons
Monsoons
Monsoons are a seasonal change in air circulation directions over a region that results in
seasonal changes in rainfall. Usually, produced by summer winds blowing off a body of water
(typically the ocean) and winter winds blowing from land to sea.
In the summer, the land heats faster than the sea. Warmer land heats the air causing lift, and
cooler, wet sea air comes to replace it. Water laden air heats and rises producing rain.
In the winter, the land cools more than the sea. Warmer air rises over the sea and colder air flows
off the land to replace it. Colder, drier air produces clear skies and dry weather.
Mid-Latitude Weather
Mid-latitudes are the battleground between cold polar air and warm equatorial air. This battle is
between air masses along fronts. An air mass is a broad body of air where temperature and
humidity are relatively uniform. Incoming air either absorbs heat from the warm surface
(and takes on water) or incoming air loses heat to the colder surfaces.
Where cold, the air sinks and semi-permanent high pressure systems dominate. High pressure
usually involves sinking, cooler air, producing clear skies. Where warm and/or wet, the air rises
and semi-permanent low pressure systems dominate.
Study Guide Questions
1) What three forces that influence the direction and speed of the wind? Explain each.
2) What is geostrophic wind and how does it form?
3) Understand the convective circulation nature of warm and cool air.
4) What are the three different kinds of circulation cells and how do they affect the Earth’s
climate?
5) What are the three kinds of global winds and where are they located?
6) What are Walker Circulation patterns? What are they related to?
7) What is El Nino – Southern Oscillation and what affects does it have on the weather?
8) What are monsoons? How are they different in the summer and winter?
9) Understand mid-latitude weather and how high/low pressure systems occur.