Meteorology
Imbalanced heating
1. Polar Easterlies
• A collision of two air masses forms a front—a narrow region between two air masses of different densities.
Data from Earth’s Surface
Weather Radar
Plotting station model data
Digital Forecasts
- Meteorology is the study of atmospheric phenomena.
- The root word of meteorology is the Greek word meteoros, 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.
- 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.
- 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.
- 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.
- The origins of maritime tropical air are tropical bodies of water.
- The southwestern United States 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 waters of the North Atlantic and North Pacific.
- Continental polar air masses form over the interior of Canada and Alaska, and carry frigid air southward in the winter.
- Earth’s ice- and snow-covered surfaces above 60*N latitude in Siberia and the Arctic Basin are the source regions of arctic air masses.
- 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.
- The directions of Earth’s winds are influenced by Earth’s 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.
1. Polar Easterlies
- The polar easterlies are the wind zones between 60* N latitude and the north pole, and 60* S latitude and the south pole.
- The prevailing westerlies are the wind systems on Earth located between latitudes 30* N and 60* N, and 30* S and 60* S
- Between latitudes 30* N and the equator is a circulation belt of wind known as the trade winds.
- Near latitudes 30* N the sinking air creates an area of high pressure. This results in a belt of weak surface winds called the horse latitudes.
- Trade winds from the North and the South meet and join near the equator. The air is forced upward, which creates an area of low pressure
- called the intertropical convergence zone (ITCZ).
- 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.
- The major jet streams, called the 1.polar jet streams, separate the polar easterlies from the prevailing westerlies.
- The minor jet streams are the 2.subtropical jet streams. They occur where the trade winds meet the prevailing westerlies.
- Storms form along jet streams and can generate large-scale weather systems.
- Jet streams affect the intensity of weather systems by moving air of different temperatures from one region of Earth to another.
• 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.
- Warm Front- Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope. Widespread light precipitation.
- Stationary Front- When two air masses meet but neither advances, the boundary between them stalls. This stationary front frequently occurs between two modified air masses that have small temperature and pressure gradients between them. Sometimes light winds and precipitation
- Occluded Front- Sometimes, a cold air mass moves so rapidly that it overtakes a warm front and forces the warm air upward. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front. A warm air mass is squeezed upward between two cold air masses. Strong winds and heavy precipitation.
- Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere.
- 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
- In a surface high-pressure system, sinking air moves away from the system’s center when it reaches Earth’s surface.
- Clear skies and fair weather.
Data from Earth’s Surface
- Two important factors in weather forecasting are the accuracy of the data and the amount of available data.
- A thermometer measures temperature using either the Fahrenheit or Celsius scale.
- A barometer measures air pressure
- An anemometer measures wind speed.
- A hygrometer measures relative humidity
- 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.
- The instrument used for gathering upper-atmosphere data is a radiosonde.
- A radiosonde’s sensors measure the air’s temperature, pressure, and humidity.
- Also wind speed and direction( by its movement)
Weather Radar
- A weather radar system detects specific locations of precipitation.
- The Doppler effect is the change in pitch or frequency that occurs due to the relative motion of a wave, such as sound or light, as it comes toward or goes away from an observer.
- Analysis of Doppler radar data can be used to determine the speed at which precipitation moves toward or away from a radar station.
- Radar- detects specific locations of precipitation.
- Doppler radar- speed at which precipitation moves toward or away from a radar station.
Plotting station model data
- To plot data nationwide and globally, meteorologists use lines that connect points of equal or constant values.
- Lines of equal pressure are called isobars.
- Lines of equal temperature are called isotherms
- Using isobars, isotherms, and station model data, meteorologists can analyze current weather conditions for a particular location.
Digital Forecasts
- A digital forecast is created by applying physical principles and mathematics to atmospheric variables and then making a prediction about how these variables will change over time.
- An analog forecast is based on a comparison of current weather patterns to similar weather patterns from the past.
- Digital- by analyzing current weather data
- Analog- by comparing weather patterns with similar patterns from the past
- The most accurate and detailed forecasts are short term because weather systems change directions, speeds, and intensities over time.
- Because it is impossible for computers to model every variable that affects the weather at a given time and place, all long-term forecasts are less reliable than short-term forecasts.
- Short term forecasts are more reliable.