What direction do high and low pressure systems spin What direction do high and low pressure systems spin? Do Now: What causes air to deflect to the right in the northern hemisphere? HW: Weather castle learning  

The directions of Earth’s winds are influenced by Earth’s rotation. Global Wind Systems 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. Copyright © McGraw-Hill Education Weather Systems

Visualizing the Coriolis Effect The Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line. Global Wind Systems The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur. Weather Systems Copyright © McGraw-Hill Education

Global Wind Systems 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. Prevailing westerlies The prevailing westerlies are the wind systems on Earth located between latitudes 30° N and 60° N, and 30° S and 60° S. Weather Systems Copyright © McGraw-Hill Education

Global Wind Systems Trade winds Between latitudes 30° N and 30° S are two circulation belts of wind known as the trade winds. Near latitudes 30° N and 30° S, the sinking air associated with the trade winds 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. This process, called convergence, can occur on a small or large scale. Near the equator, it occurs over a large area called the intertropical convergence zone (ITCZ). Weather Systems Copyright © McGraw-Hill Education

A jet stream is a narrow band of fast, high-altitude, westerly wind. Jet Streams 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 is strongly influenced by fast-moving, high-altitude jet streams. Weather Systems Copyright © McGraw-Hill Education

Jet Streams Types of jet streams The major jet streams, called the polar jet streams, separate the polar easterlies from the prevailing westerlies. The minor jet streams are the 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. Weather Systems Copyright © McGraw-Hill Education

Fronts 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. Warm front Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope. Weather Systems Copyright © McGraw-Hill Education

Fronts 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. 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 another cold air mass that was in front of the warm air. This is called an occluded front. Weather Systems Copyright © McGraw-Hill Education

High-pressure systems Pressure Systems Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere. 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. High-pressure systems In a surface high-pressure system, sinking air moves away from the system’s center when it reaches Earth’s surface. Weather Systems Copyright © McGraw-Hill Education

Pressure Systems In the northern hemisphere, winds move counterclockwise around a low-pressure center, and clockwise around a high-pressure center. Low-pressure center High-pressure center Copyright © McGraw-Hill Education Weather Systems

Data from Earth’s Surface Temperature and air pressure A thermometer measures temperature using either the Fahrenheit or Celsius scale. A barometer measures air pressure. Wind speed and relative humidity An anemometer measures wind speed. A hygrometer measures relative humidity. Gathering Weather Data

Data from Earth’s Surface 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 radiosonde’s sensors measure the air’s temperature, pressure, and humidity. Gathering Weather Data Copyright © McGraw-Hill Education

Weather Observation Systems Weather radar A weather radar system detects specific locations of precipitation. Doppler effect -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. Gathering Weather Data Copyright © McGraw-Hill Education

Weather Observation Systems Weather satellites Some weather satellites use infrared imagery to make observations at night. Objects radiate thermal energy at slightly different frequencies. Infrared imagery detects these different frequencies, which enables meteorologists to map either cloud cover or surface temperatures. Another type of satellite imagery that is useful in weather analysis and forecasting is called water-vapor imagery which shows moisture in the atmosphere, not just cloud patterns. Gathering Weather Data Copyright © McGraw-Hill Education

Surface Weather Analysis Station models A 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. Copyright © McGraw-Hill Education Weather Analysis and Prediction

Surface Weather Analysis 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. Weather Analysis and Prediction Copyright © McGraw-Hill Education

Surface Weather Analysis Interpreting station model data The weather map shows isobars and air pressure data for the continental United States. Using isobars, isotherms, and station model data, meteorologists can analyze current weather conditions for a particular location. Weather Analysis and Prediction Copyright © McGraw-Hill Education

Types of Forecasts 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. Analog forecasts An analog forecast is based on a comparison of current weather patterns to similar weather patterns from the past. Weather Analysis and Prediction Copyright © McGraw-Hill Education