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Graphing and Comparing Climates

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Weather refers to the current conditions of the atmosphere. In contrast, the term climate refers to an area’s typical weather. It can be defined as the average pattern of weather for an area. Weather data over a span of many years is used to compute these averages.

A good picture of a location’s climate can be obtained by examining its pattern of temperature and precipitation. The data used in this activity are monthly means for these two measures. The mean temperature is determined by averaging the mean high and low temperature for every day of the month. Data for every year available is used to compute the mean.

The mean precipitation is determined by finding the average total precipitation for each month using weather record for as far back as they are available. The total annual precipitation and the mean yearly temperature are provided for comparison.

Climate graphs provide a useful tool for examining and comparing climates. Students can easily see monthly levels of temperature and precipitation and well as the seasonal variation. Temperature is displayed as a line graph connecting points for each month. Precipitation is represented as monthly bar graphs.

Depending on the source, data may be given in degrees Fahrenheit of Celsius for temperature and in inches or centimeters (or millimeters) for precipitation. Some students may find it easier to relate to temperatures expressed in Fahrenheit. The following formulas can be used to convert data from one scale to the other.

°C x 9/5 + 32 = °F            cm x 0.39 = in.
(°F – 32) x 5/9 = °C            in. x 2.54 = cm

Climate is determined by a variety of factors. Latitude has a strong influence on temperature due to the varying angle of the incoming solar radiation. It also affects the magnitude of the seasonal variation and the length of day. The prevailing wind direction (e.g. the Westerlies for most of the U.S.) determines the path of weather across an area. Proximity to bodies of water and/or mountains couples with the prevailing wind direction will influence precipitation as well as temperature. Elevation and local topography can also have an effect on climate.

The climate of Antarctica is one of extremes. It is the coldest place on Earth. Consistent low temperatures occur during winter, which stretches from March through September. Most of Antarctica receives little or no sunlight during this period. The sun is up for much of the brief summer but it remains low in the sky.

The continent is covered with a thick ice sheet. The ice reflects about 90% of the incoming solar radiation. The average elevation of the polar plateau is over one mile above sea level, which contributes to its low temperature. The ocean moderates the temperature somewhat along the edges of the continent, but this effect is mitigated by sea ice, which can stretch far out into the ocean.

Most of the continent receives very little precipitation. This is mainly due to the low moisture holding capacity of very cold air. The plateau, which covers the majority of Antarctica, receives only a few inches of precipitation annually. It can come in the form of light snow or more often as tiny ice crystals known as “diamond dust.” Strong winds and drifting snow make precipitation measurements very difficult. 8 to 16 inches a year is typical for the edge of the continent. Greater amounts fall along the west side of the Antarctic Peninsula due to the eastward progression of storm systems.

Temperature and precipitation data from a variety of locations are provided. You may want students to collect their own data using websites listed in the resources. Data for your individual area should be available at one of the websites or in the reference section of the local library. Climate graphs in both inches/Fahrenheit and centimeters/Celsius are also included.

Resources and Reference Materials

GLACIER website
An excellent resource for a variety of information about Antarctica.

Local/US Climate Data
Monthly temperature and precipitation means for US cities.

USA Today
Mean high and low temperature and precipitation for US cities.

World Climate Data
USA Today
Mean high and low temperature and precipitation for cities worldwide.

Antarctic Climate Data
Cooperative Research Centre for Antarctica and the Southern Ocean
Mean monthly temperature data in Celsius for all Antarctic stations.

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