THE CAUSES OF WEATHER Section 12.1

Meteorology Is the study of atmospheric phenomena Root word (Greek – meteoros) means high in the air. A meteor is anything that is high in the sky DIFFERENT TYPES OF METEORS hydrometeors – cloud droplets and precipitation lithometeors – smoke, haze, dust, other particles electrometeors – thunder and lightening

Weather versus climate Weather- Short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth. Climate- The long term average of variations in weather for a particular area. Know the difference “Beautiful climate we’re having today Bob.” WRONG

Heating Earth’s Surface Sunlight, a part of solar radiation, is always heating some portion of the Earth’s surface. The amount of thermal energy that the Earth receives is the same amount that the Earth radiates back to space. Imbalanced heating The Earth’s axis of rotation is tilted. The number of hours of daylight and amount of solar radiation is greater in some places. The Earth is a sphere

Thermal energy redistribution The constant movement of air and water among the Earth’s surface help areas around Earth to maintain about the same average temperature over time. This movement redistributes thermal energy around the world. Weather is part of the ongoing redistribution of Earths thermal energy.

Air Masses Air mass- Large volume of air that has the same characteristics (humidity and temperature) of the area over which it forms. Source region- The area over which the air mass forms. Modification – when an air mass exchanges thermal energy and/or moisture with the surface over which it travels

Types of air masses Maritime (over water) or Continental (over land) Tropical air masses - form over warm bodies of water (Gulf of Mexico, Caribbean sea…) or warm land masses (southwest United States, Mexico) Summer time brings hot, humid weather to two thirds of North America. Polar air masses - form over cold bodies of water (North Atlantic, North Pacific) or cold land masses (Interior of Canada and Alaska). The air masses that affect weather in the United States. Arctic (extremely cold/frigid) Continental polar Continental tropical Maritime polar Maritime tropical

Weather Systems Section 12.2

Coriolis Effect Objects move in apparent curved path Northern Hemisphere – curve to right Southern Hemisphere – curve to left This creates global wind systems; help to equalize thermal energy on earth

Coriolis Effect Animation

Coriolis Effect Activity Find a partner. One person cuts out a large circle from a piece of white paper. One person rotates the circle while the other person attempts to draw a straight line from the center outward. What is happening?

3 basic wind systems Polar easterlies Prevailing westerlies Trade winds

Polar Easterlies Location: Dense polar air sinks 60°N latitude and North Pole 60°S and South Pole Dense polar air sinks Earth spins, air deflected as it moves away from poles Cold, weak winds

Prevailing Westerlies Location: 30°N - 60°N 30°S - 60°S Originate from the WEST Steady winds Move much of weather across US and Canada

Trade Winds 30°N - 30°S Air sinks, warms, and moves toward equator At equator: rises and moves back towards 30° N and 30° S

RECALL FROM CH. 11… Warmer air has _________ pressure than colder air. HIGHER What causes wind? Movement of air from higher to lower pressure.

Jet Streams Larger temperature gradient + Coriolis effect = strong westerly winds (jet stream) Speed varies with temperature differences Position varies with season Located in area of strongest temperature differences

Partner activity How might jet streams have an effect on the aviation industry?

Jet Streams & Weather Storms form along them Large-scale weather systems are generated Weather systems follow the path of jet streams

Fronts and Pressure Systems Fill out Table

Gathering Weather Data Section 12.3

There are four different atmospheric conditions that meteorologists measure These are: Temperature Air pressure Wind speed Relative humidity The accuracy and amount of data available are two important factors when forecasting weather.

Temperature and Air Pressure Thermometer - measures temperature using Fahrenheit or Celsius scale Barometer - measures air pressure

Wind Speed and Relative Humidity Anemometer - instrument that measures wind speed Hygrometer - instrument that measures humidity

Automated Surface Observing System A system that gathers data in a consistent manner in different locations Provides essential weather data for: Aviation Weather forecasting Weather related research

Data from the Upper Atmosphere Surface weather data is important but is largely the result of changes that take place in the troposphere Data must be gathered at high altitudes Up to 30,000 meters Radiosond - Instrument used for gathering upper atmosphere data i.e. air temperature, air pressure, and humidity

Weather Observation Systems Weather radar system detects specific locations of precipitation Doppler weather radar Doppler effect - change in pitch or frequency that occurs due to relative motion of a wave, (i.e. sound or light) as it comes toward or goes away from an observer Weather Satellites orbit earth to observe weather These satellites use infrared imagery to make observations at night Visible light imagery - satellites that require visible light in order to help determine cloud coverage Water-vapor imagery - shows moisture in the atmosphere and helps meteorologists monitor storm systems even when clouds aren’t present

High and Low Pressure Systems