AIR MASSES/ FRONTS NOTES
- Air masses have different temperatures and amounts of moisture because of the uneven heating of earths surface
- heat: transfer of thermal energy from a warmer material to a cooler material
- meteorology is the study of atmospheric phenomena
- The root word of meteorology is the Greek word which means "high in the air"
- Short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth are called weather.
- Climate is the long-term average of variations in weather for a particular area
- imbalanced heating
- one reason that temperatures may vary from location to location at a certain time of year is that Earth’s axis of rotation is tilted relative to the plane of Earth’s orbit.
- imbalanced heating due to earths tilt
- Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area.
- Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area.
- thermal energy redistribution
- The constant movement of air and water redistributes thermal energy around the world.
- Weather—from thunderstorms to large-scale weather systems—is part of the constant redistribution of Earth’s thermal energy.
- The constant movement of air and water redistributes thermal energy around the world.
- An air mass is a large volume of air that has the same characteristics, such as humidity and temperature, as its source region
- A source region is the area over which an air mass forms
- Types of air masses
- the origins of maritime tropical air are tropical bodies of water: moist warm air mass
- the southwestern US and Mexico are the source regions of continental tropical air, which is hot and dry, especially in summer
- Maritime polar air masses form over the cold water of the North Atlantic and North Pacific: cooler moist air mass
- Continental polar air masses from the interior of Canada and Alaska, and carry frigid air southward in the winter: Cool dry air masses
- Earths ice- and snow covered surfaces above 60 N latitude in Siberia and the Artic Basin are the source regions of arctic air masses
- Air mass modification
- When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification.
- As the cold, continental polar air moves over the warmer Great Lakes, the air gains thermal energy and moisture. This modified air cools as it is uplifted and produces lake-effect snows.
- When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification.
WIND, PRESSURE, WEATHER WEB QUEST
systems
- Weather results when air masses with different pressures and temperatures move, change, and collide.
- convection:the transfer of thermal energy by the flow of a heated substance
- The directions of earths winds are influenced by earths rotation
- This Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line
- The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur.
- Global wind system- 3 systems
- polar easterlies: are the wind zones between 60 N latitude and teh north pole, and 60S latitude and the south pole, east to west
- prevailing westerlies: are the wind systems on earth located between latitudes 30 N and 60 N and 30 S and 60 S, west to east
- trade winds: between latitudes 30° N and the equator is a circulation belt of wind known as the trade winds
- A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams.
- A jet stream is a narrow band of fast, high-altitude, westerly wind.
- Weather in the middle latitudes ( our area)is strongly influenced by fast-moving, high-altitude jet streams.
- Two type sof jet streams
- polar jet streams separate the polar easterlies from the prevailing westerlies
- subtropical jet streams. They occur where the trade winds meet the prevailing westerlies.
- A collision of two air masses forms a front—a narrow region between two air masses of different densities.
- Cold front: When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. This type of collision is called a cold front.
- Intense precipitation and sometimes thunderstorms.
- widespread light precipitation
- sometimes light winds and precipitation
- strong winds and heavy precipitation
- Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high and low systems in the atmosphere
- 2 types
- low pressure systems: in surface low pressure systems, air rises. When air from outside the system replaces the rising air, this air spirals inward toward the center and then upward
- clouds and precipitation
- high pressure systems: in a surface high pressure system, sinking air moves away from the systems center when it reaches earths surface
- clear skies and fair weather
- low pressure systems: in surface low pressure systems, air rises. When air from outside the system replaces the rising air, this air spirals inward toward the center and then upward
- in the northern hemisphere, winds move counterclockwise around a low- pressure center, and clockwise around a high pressure center
- Weather results when air masses with different pressures and temperatures move, change, and collide.
- The three major wind systems are the polar easterlies, the prevailing westerlies, and the trade winds.
- Fast-moving, high-altitude jet streams greatly influence weather in the middle latitudes.
- The four types of fronts are cold fronts, warm fronts, occluded fronts, and stationary fronts.
- Air moves in a generally circular motion around either a high- or low-pressure center.
- Data from earths surface
- two important factors in weather forecasting are the accuracy of the data and the amount of availablle data
- thermometer measures temperature using either the F or C scale
- a barometer measures air pressure
- a anemometer measure wind speed
- a hygrometer measure relative humidity
- Automated surface observing system
- The Automated Surface Observing System (ASOS) gathers data in a consistent manner, 24 hours a day, every day. It provides essential weather data for aviation, weather forecasting, and weather-related research.
- Data from the upper atmosphere
- The instrument used for gathering upper-atmosphere data is a radiosonde.
- A radiosondes sensors measure the airs temperature, pressure, and humidity
- Also wind speed and direction (by its movement)
- Doppler
- Analysis of Doppler radar data can be used to determine the speed at which precipitation moves toward or away from a radar station.
- Station model is a record of weather data for a particular site at a particular time
- Meteorological symbols are used to represent weather data in a station model. Advantages: universal language, more info in less space.
- plotting station model data
- to plot data nationwide and globally meteorologists use lines that connect points of equal or constant values
severe weather notes
THUNDERSTORMS
•Other factors also play a role in causing some storms to be more severe than others.
•Cold fronts are usually accompanied by upper-level, low-pressure systems that are marked by pools of cold air, which cause the air to become more unstable.
•When the strength of the storm’s updrafts and downdrafts intensifies, the storm is considered to be severe.
Stages of Tropical Cyclones
–Tropical cyclones usually begin as disturbances that originate either from the or as weak, low-pressure systems called tropical waves.
–Only a small percentage these ever develop into hurricanes because conditions throughout the atmosphere must allow rising air to be dispersed into
the upper atmosphere.
–When a disturbance over a tropical ocean acquires a cyclonic circulation around a center of low pressure, it is known as a tropical depression.
–When wind speeds around the low-pressure center of
a tropical depression exceed 65 km/h, the system is called a tropical storm.
–If air pressure continues to fall and winds around the center reach at least 120 km/h, the storm is officially classified as a hurricane.
- at any given moment, nearly 2000 thunderstorms are occurring around the world
- Some are capable of producing hail the size of baseballs, swirling tornadoes, and surface winds of more than 160 km/h
- All thunderstorms, regardless of intensity, have certain characteristics in common
- for a thunderstorm to form, three condition must exist
- there must be an abundant source of moisture in the lower levels of the atmosphere
- some mechanism must lift the air so that the moisture can condense and release latent heat
- The portion of the atmosphere through which clouds must be unstable
- Limits to Growth
- the air in a thunderstorm will keep rising until:
- it meets a layer of stable air that it cannot overcome
- the rate of condensation, which diminishes with height, is sufficient to generate enough latent heat to keep the cloud warmer than the surrounding air
- typical thunderstorms last only about 30 minutes and individual storms are only about 24 km in diameter
- a thunderstorm usually has three stages: the cumulus stage, the mature stage, and the dissipation stage
- The stages are classified according to the direction in which the air is moving
- Cumulus Stage
- in the cumulus stage air states to rise nearly vertically upward
- transported moisture condenses into a visible cloud and releases latent heat
- As the cloud droplets coalesce, they form larger droplets, which eventually fall to Earth as precipitation
- Mature Stage
- As precipitation falls, it cools the air around it which becomes more dense than the surrounding air, so it sinks creating downdrafts.
- The updrafts and downdrafts form a convection cell.
- In the mature stage, nearly equal amounts of updrafts and downdrafts exist side by side in the cumulonimbus cloud.
- Dissipation stage
- The supply of warm, moist air runs out because the cool downdrafts cool the area from which the storm draws energy.
- Without the warm air, the updrafts cease and precipitation can no longer form.
- The dissipation stage is characterized primarily by lingering downdrafts.
•Other factors also play a role in causing some storms to be more severe than others.
•Cold fronts are usually accompanied by upper-level, low-pressure systems that are marked by pools of cold air, which cause the air to become more unstable.
•When the strength of the storm’s updrafts and downdrafts intensifies, the storm is considered to be severe.
- Super cells are self sustaining extremely powerful severe thunderstorms which are characterized by intense, rotating updrafts
- only 10 % of the roughly 100000 thunderstorms that occur each year in the US are considered to be severe; even fewer become super cells
- instead of dispersing over a large area underneath a storm, downdrafts sometimes become concentrated in a local area
- Down bursts are violent downdrafts that are concentrated in a local area and can contain wind speeds of more than 160 km/h
- macro bursts can have wind speeds of more than 200 km/h can last up to 30 minutes
- a tornado is a violent, whirling column of air in contact with the ground
- before a tornado reaches the ground it is called a funnel cloud
- tornadoes are often associated with super cells
- the air in a tornado is made visible by dust and debris drawn into a swirling column or by the condensation of water vapor into a visible cloud
- A tornado forms when wind speed and direction change suddenly with height, a phenomenon known as wind shear.
- Under the right conditions, this can produce a horizontal rotation near Earth’s surface.
- A thunderstorm’s updrafts can tilt the twisting column of wind from a horizontal to a vertical position.
- Air pressure in the center drops as the rotation accelerates.
- The extreme pressure gradient between the center and the outer portion of the tornado produces the violent winds associated with tornadoes
- Tornado classification
- The Fujita tornado intensity scale classifies tornadoes according to their path of destruction, wind speed, and duration.
- The scale ranges from F0, which is characterized by winds of up to 118 km/h, to the violent F5, which can pack winds of more than 500 km/h.
- Most tornadoes do not exceed the F1 category.
- Only about one percent ever reach the violent categories of F4 and F5.
- The Fujita tornado intensity scale classifies tornadoes according to their path of destruction, wind speed, and duration.
- Tornado distribution
- while tornadoes can occurs at any time or place, some places are more conductive to their formation
- most tornadoes form in spring during the late afternoon and evening,when the temperature contrasts between polar air and tropical are the greatest
- tornadoes occur most frequently in a region called "Tornado Alley" which extends from northern Texas through Oklahoma, Kansas, and Missouri
- Tropical Storms
- Tropical cyclones are large, rotating, low-pressure storms that form over water during summer and fall in the tropics.
- The strongest of these cyclonic storms are known in the United States and other parts of the Atlantic Ocean as hurricanes.
- Tropical cyclones thrive on the tremendous amount of energy in warm, tropical oceans.
- This latent heat from water that has evaporated from the ocean is released when the air begins to rise and water vapor condenses.
- Rising air creates an area of low pressure at the ocean surface.
- The cyclonic rotation of a tropical cyclone begins as warm air moves toward the low-pressure center to replace the air that has risen.
- As the moving air approaches the center of the growing storm, it rises, rotating faster and faster as more energy is released through condensation.
- Air pressure in the center of the system continues to decrease, while surface wind speeds increase—sometimes in excess of 240 km/h.
- As long as atmospheric conditions allow warm air to be fed into the system at the surface and to be removed from the system in the upper atmosphere the process will continue.
- Formation of cyclones
- –Tropical cyclones require two basic conditions to form:
- An abundant supply of very warm ocean water
- Some sort of disturbance to lift warm air and
keep it rising
- –Tropical cyclones require two basic conditions to form:
- These conditions exist in all tropical oceans except the South Atlantic Ocean and the Pacific Ocean west of the South American Coast.
- They occur most frequently in the late summer and early fall, when Earth’s oceans contain their greatest amount of stored heat energy.
Stages of Tropical Cyclones
–Tropical cyclones usually begin as disturbances that originate either from the or as weak, low-pressure systems called tropical waves.
–Only a small percentage these ever develop into hurricanes because conditions throughout the atmosphere must allow rising air to be dispersed into
the upper atmosphere.
–When a disturbance over a tropical ocean acquires a cyclonic circulation around a center of low pressure, it is known as a tropical depression.
–When wind speeds around the low-pressure center of
a tropical depression exceed 65 km/h, the system is called a tropical storm.
–If air pressure continues to fall and winds around the center reach at least 120 km/h, the storm is officially classified as a hurricane.
- Classifying Hurricanes
- The Saffir-Simpson hurricane scale classifies hurricanes according to wind speed, air pressure in the center, and potential for property damage.
- The Saffir-Simpson hurricane scale ranges from Category 1 hurricanes to Category 5 storms, which can have winds in excess of 155 mph.
- Most of the deadliest hurricanes that strike the United States were classified as major hurricanes.
HURRICANE /TORNADO BIO
The Tri-State Tornado
The Tri- State tornado was the worst tornado is United States history. It came through eastern Missouri, southern Illinois, and southern Indiana on March 18th 1925. It killed 695 people ad injuring another 13,000 people. It causes 17 million dollars in property damage. The hardest hit was in southern Illinois, more than 500 of the 695 people who died those 500 were killed in southern Illinois. 9 schools were affected by this tornado, killing 69 students. The tornado traveled 219 miles and was on the ground for more than 3 hours. It destroyed 164 square miles and had a diameter of more than a mile and traveled 70 miles per hour. It was a F5 on the Fujita scale. There is still a question that if this was a single tornado or a series of tornadoes that caused the damage.
The Tri- State tornado was the worst tornado is United States history. It came through eastern Missouri, southern Illinois, and southern Indiana on March 18th 1925. It killed 695 people ad injuring another 13,000 people. It causes 17 million dollars in property damage. The hardest hit was in southern Illinois, more than 500 of the 695 people who died those 500 were killed in southern Illinois. 9 schools were affected by this tornado, killing 69 students. The tornado traveled 219 miles and was on the ground for more than 3 hours. It destroyed 164 square miles and had a diameter of more than a mile and traveled 70 miles per hour. It was a F5 on the Fujita scale. There is still a question that if this was a single tornado or a series of tornadoes that caused the damage.