LESSON 5 - ACTIVITY 4 - HIGH AND LOW PRESSURE SYSTEMS
Materials
Background Information
Key Questions
Vocabulary
Procedure
Evaluation
Objectives:
- Identify high pressure systems
- Identify low pressure systems
- Draw isobars
Materials:
- weather map transparency
(Print in landscape mode)
Background Information:
Low pressure systems usually produce cloudy, stormy weather. An easy way to remember this is L = Low = Lousy. When a low pressure system is situated over a region, the air begins to rise into the atmosphere. When air rises, it cools down and condenses into precipitation and clouds. This is why an approaching low pressure system means an increased chance for clouds, rain, or snow. It is called "low pressure" because as air rises, the air pressure is lower at the surface. Air flows in a counterclockwise direction with a low pressure system in the Northern Hemisphere.
A steady snow or rain can fall north of a warm front where moist warm southern air moves up & over cold air that is in front of a warm front. Thunderstorms and showers often form ahead of a cold front in warm, unstable air. The thunderstorms & showers that form ahead of a cold front are generally shorter in duration than precipitation that forms in front of a warm front. Because of the counterclockwise rotation of a low-pressure system in the northern hemisphere, cold air will usually be located north & west of a low-pressure area and warm air is usually found south & east of a low-pressure area.
High pressure systems usually produce fair weather. An easy way to remember this is H = High = Happy. It is called "high pressure" because air sinks around areas of high-pressure, which prevents cloud formation and precipitation. For this reason, high-pressure systems bring sunny days and calm weather. Locations east of an area experiencing high-pressure will experience northerly winds which bring in cooler air whereas areas to the west will experience southerly winds which bring in warmer air.
This activity will focus on identifying high or low pressure areas and the weather associated with each.
In this activity students will also learn about isobars which are lines that connect areas that have the same barometric pressure.
Key Questions:
- What symbol is used to identify high pressure systems on a weather map?
- What symbol is used to identify low pressure systems on a weather map?
- What are isobars and how are they plotted on a weather map?
Vocabulary:
- high pressure systems
- low pressure systems
- isobars
Procedure:
1. On the chalkboard, draw a capital "L" and "H". Ask your students to give you examples of weather that is generally associated with each system. Remember, low pressure systems produce cloudy, stormy weather and high pressure systems produce fair, sunny weather.
2. Explain to your students that a red "L" is used to represent areas of low pressure and a blue "H" is used to represent areas of high pressure.
3. Explain to your students what isobars are and how they are used on a weather map. Make an overhead transparency of the following weather map to illustrate the concept of isobars. Have your students locate the areas on the transparency which have the same pressure.
4. Allow your students sufficient time to access the internet to collect data for High pressure systems, Low pressure systems, and isobar information for the 13 weather stations. They should become more familiar with the internet site the more times they access it, resulting in less time spent collecting data.
5. Students will use the appropriate symbol to denote high and low pressure areas for the thirteen weather stations on their weather maps and also enter this information into their spreadsheet.
6. Assist your students in drawing isobar lines to correctly connect weather stations that are reporting the same barometric pressure readings.
Evaluation:
Students will be able to appropriately determine where areas of high and low pressure exist based on what they have learned in this lesson. Students will also be able to properly use isobars to denote areas of high and low pressure.
