BioEd Online

The Role of Energy in Weather and Climate

The teacher understands the role of energy in weather and climate.

“The difference between weather and climate is a measure of time.” The reference below is an excellent starting place for understanding weather and climate. As it points out, the difference between the two is time. Weather is what is happening outside now. Climate is the average of the daily changes of weather over a long period of time in a particular location. Summer in Houston is hot. Winter in Houston is rainy. These two statements relate to the Houston climate. Day-to-day weather, however, may be very different. A day in summer could be cool and rainy, and a single day in winter might be warm and dry. When day-to-day weather is the same for long stretches (e.g., no rain for months), a climate change may be taking place. The climate concern regarding global warming is based, in part, on extensive daily weather records that show a worldwide warming trend.

What’s the Difference Between Weather and Climate?: NASA

Subtopics:

• Weather Properties and their Measurement
• Weather and Climate
• Monitoring and Predicting Weather
• Energy Transfer
• Effects of the Geosphere on Weather

Weather Properties and their Measurement

The beginning teacher understands the elements of weather (e.g., humidity, wind speed, pressure, temperature) and how they are measured.

Key Concepts:

• Weather often is described in general terms, such as warm and sunny or windy and cold, but these terms are based on measurable observations of weather conditions.
• Humidity is a measure of the amount of moisture in the air. Relative humidity is a measure of the actual amount of moisture in the air compared to how much moisture the air could hold based on its temperature. Warm air is able to hold more moisture than cold air. Relative humidity is measured as a percentage of the total amount of water the air can hold.
• Air pressure is a measure of the force exerted at Earth’s surface by the weight of air above.  Because air is a gas, its volume and density can change. High-pressure air is air that is compressed. Low-pressure air is expanded (less compressed). Earth’s surface is covered with areas, referred to as cells, of alternating high and low pressures. These are due to variations of solar heating across the surface. The cells move across Earth’s surface and bring variations of the weather with them.
• Air pressure is measured with a device called a barometer. Pressure is measured in bars. One bar is roughly equivalent to the pressure at sea level. Changes in pressure, which indicate a change in the weather, are measured in millibars (1 millibar is equal to about 100 pascals). Air pressure is also measured as pounds per square inch. At sea level, the pressure is 14.7 psi. Air pressure drops with increasing elevation.
• Wind speed is measured with an anemometer, which is an instrument made of a propeller or cups at the ends of rods that spin horizontally about a pivot. Wind speed usually is reported in miles per hour. Along with wind speed, wind direction is measured. The device for measuring direction is a weather vane. Winds are named for the direction from which they come.
• Temperature is measured in degrees Fahrenheit or Celsius with a thermometer.
• Changes in pressure, temperature, wind speed, and humidity indicate an impending change in the weather.

Resources:

The National Snow and Ice Data Center offers a detailed glossary of meteorological terms.

The US Search and Rescue Task Force offers basic information about predicting weather and the instruments that are used for this purpose.

Weather and Climate

The beginning teacher compares and contrasts weather and climate.

Key Concepts:

• Weather is the condition of the atmosphere at a specific location and a specific time.
• Climate is the average weather (e.g., temperature, humidity, cloud cover, etc.) over long periods of time (e.g., seasonal or annual) in a particular geographic location. Climatological studies of Earth’s past can span thousands of years.
• The same units of measure apply for both weather and climate. The difference is the time period covered.

Resources:

The difference between weather and climate is explained along with several other features that offer insights into weather and climate by the National Center for Atmopheric Research and UCAR.

What’s the Difference Between Weather and Climate? is explained by NASA.

Monitoring and Predicting Weather

The beginning teacher analyzes weather charts and data to make weather predictions.

Key Concepts:

• Weather charts are used to track and compare the weather in different locations. Charts may just show daily temperatures, rainfall, cloud cover, or pressure or they may combine several weather properties, such as wind speed and direction, and temperature. Weather charts may feature lines showing areas of equal temperatures or pressure. Called isoclines, the lines are similar to contour lines on a topographic map.
• The purpose of weather charts is to enable predictions of what the weather will be like in a few hours to several days, and to be able to document weather trends or changes over time.
• Satellite views of Earth’s clouds, temperatures, etc. provide weather forecasters with wide-scale view of current weather conditions. Images and data collected over several hours can be assembled into animated weather charts showing the direction and speed with which weather systems are moving.
• Weather systems, such as cold or warm fronts, tend to move west to east across the US, but they can also move south to north or north to south depending upon specific circumstances and the location where weather is being monitored. Cold air masses in Canada in winter tend to spread southward. Moist air masses from the Gulf of Mexico tend to move towards the northeast. Tropical storms and hurricanes work their way from the east Atlantic Ocean to the Eastern U.S.

Resources:

The National Weather Service explaces how to view and interpret weather maps.

Current weather maps, satellite images, video loops, warnings, data, etc. are available from this extensive site from the National Weather Service.

Energy Transfer

The beginning teacher applies knowledge of how transfers of energy among earth systems affect weather and climate.

Key Concepts:

• The Sun’s energy is the primary driver of Earth’s weather and climate systems.
• Unequal heating of Earth’s surface produces large regions of rising and falling air, which trigger horizontal wind flow across Earth’s surface and in the upper zone of the troposphere.
• Day/night changes in temperature, wind, and precipitation are strongly influenced by stored solar energy. A desert, for example, becomes very hot during the day, but yields up its heat very quickly at night. The absence of insulating cloud cover permits daytime heating and nighttime loss of heat. The balance between incoming solar energy and outgoing solar energy is called Earth’s Energy Budget.
• The greenhouse effect is one of the major processes of energy transfer within the atmosphere. Clouds and gases, such as CO2, trap solar energy and cause global heating and climatic changes. Global warming refers to increased heating through the greenhouse effect. However, without the normal amounts of heat trapping gases in Earth’s atmosphere, Earth would be too cold for most living organisms.
• Seasonal changes are affected by land and water. Earth’s oceans are solar heat reservoirs. The winter temperatures of northern coastal areas are moderated by heat yielded by the oceans. Along with heat, moisture is added to the air, which becomes snow that falls over the continents. During summer, continental regions become heat reservoirs for solar energy. Rising and falling air currents generate winds.

Resources:

The Windows to the Universe site has an excellent description of Earth’s atmosphere and how the Sun’s energy drives its system. The site contains several detailed charts depicting atmospheric layers, the energy budget, clouds, etc.

Effects of the Geosphere on Weather

The beginning teacher analyzes how Earth’s position, orientation and surface features affect weather and climate.

Key Concepts:

• The inclination of Earth’s axis and the parallelism of the axis during its year-long orbit around the Sun produces Earth’s seasons.
• Earth’s seasons are characterized by climatic and daily weather variations.
• Earth’s seasons are not due to the small variations in the distance of Earth to the Sun during its orbit.
• Variations in the topography of Earth’s solid surface can control weather and climate patterns. For example, warm air, which can hold considerable amounts of water vapor, cools as it rises to cross mountain ranges. As it cools, it loses some of its ability to hold moisture, which is released as rain or snow. This is called the orographic effect.
• Adjacent land and water bodies tend to affect local weather patterns. In the summer, the dark land surface heats rapidly while bodies of water, such as lakes or oceans, remain relatively cool. Warm air currents rise over the land and cool currents fall over the oceans. A circular pattern forms as cool ocean breezes move on to the land to replace rising air that has been warmed over the land. In winter, this pattern is reversed with the land being cold and the water relatively warmer.
• Oceans tend to reduce extremes of weather around islands, such as the Hawaiian chain, producing “perfect climates,” with less seasonal variation than other locations at similar latitudes.

Resources:

The seasonal effect of Earth’s axial tilt to the plane of the ecliptic is explained on this site provided by NASA.

Orographics is the effect of Earth’s terrain on weather. When clouds rise to clear the tops of mountains, they drop moisture because of cooling. Consequently, the opposite sides of mountains have significantly less rain. This is called the rain shadow. The satellite image below shows the rain shadow of the Kilauea Volcano of Hawaii.