Page 176 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

aQuantitativeSOlUTiOn Humidex
Humidex, a calculated parameter that is based on temperature and humidity, can be easily calculated to determine the comfort level of the air at a specific temperature and humidity. It gives a measure of the amount of discomfort felt by the combined effect of the two elements. Humidex is calculated using the following formula:
Then use the vapour pressure value in the Humidex equation:
5 Humidex=T+q ×(e−10)r
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where e is the vapour pressure (in mb, e = 6.112 ×
10(7.5 × T/(237.7 + T)) × H/100)), T = air temperature (°C), and H = relative humidity (%).
For example, given a temperature of 25°C with relative humidity of 82%, first determine the vapour pressure, e:
e = 6.112 × 10 (7.5 × T/(237.7 + T)) × H/100) = 6.112 × 10(7.5 × 25/ (237.7 + 25)) × 82/100)
= 6.112 × 100.5852683 = 23.52078 mb
So, on a day with a temperature of 25°C, the high humidity makes it feel much warmer, 33°C.
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9 = 33°C
5 Humidex=T+q ×(e−10)r
= 25 + q
= 25 + 7.5115444
× (23.52078 − 10)r = 32.5115444
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concepts review
key learning
■ Define the concept of temperature, and distinguish between Kelvin, Celsius, and Fahrenheit temperature scales and how they are measured.
Temperature is a measure of the average kinetic energy, or molecular motion, of individual molecules in matter. Heat transfer occurs from object to object when there is a temperature difference between them. The wind-chill factor indicates the enhanced rate at which body heat is lost to the air under conditions of cold temperatures and wind. As wind speeds increase, heat loss from the skin increases, decreasing the apparent temperature, or the temperature that we perceive.
Temperature scales include
• Kelvin scale: 100 units between the melting point of ice (273 K) and the boiling point of water (373 K).
• Celsius scale: 100 degrees between the melting point of ice (0°C) and the boiling point of water (100°C).
• Fahrenheit scale: 180 degrees between the melting point of ice (32°F) and the boiling point of water (212°F).
Scientists use the Kelvin scale because temperature readings on that scale start at absolute zero and thus are proportional to the actual kinetic energy in a material.
temperature (p. 119)
1. What is the difference between temperature and heat?
2. What is the wind-chill temperature on a day with
an air temperature of –12°C and a wind speed of
32 km·h−1?
3. Compare the three scales that express temperature.
Find “normal” human body temperature on each
scale and record the three values in your notes.
4. What is your source of daily temperature informa- tion? Describe the highest temperature and the
lowest temperature you have experienced. From what we discussed in this chapter, can you identify the factors that contributed to these temperatures?
■ Explain the effects of latitude, altitude and elevation, and cloud cover on global temperature patterns.
Principal controls and influences on temperature patterns include latitude (the distance north or south of the equa- tor), altitude and elevation, and cloud cover (reflection, absorption, and radiation of energy). Altitude describes the height of an object above Earth’s surface, whereas elevation relates to a position on Earth’s surface relative to sea level. Latitude and elevation work in combination to determine temperature patterns in a given location.
5. Explain the effects of altitude and elevation on air temperature. Why is air at higher altitude lower in temperature? Why does it feel cooler standing in shadows at higher elevation than at lower elevation?
6. What noticeable effect does air density have on the absorption and radiation of energy? What role does elevation play in that process?
7. Why is it possible to grow moderate-climate-type crops such as wheat, barley, and potatoes at an elevation of 4103 m near La Paz, Bolivia?
8. DescribetheeffectofcloudcoverwithregardtoEarth’s temperature patterns. From the last chapter, review
the effects of different cloud types on temperature, and relate the concepts with a simple sketch.
■ Review the differences in heating of land versus water that produce continental effects and marine effects on temperatures, and utilize a pair of cities to illustrate these differences.
Differences in the physical characteristics of land (rock and soil) compared to water (oceans, seas, and lakes) lead to land–water heating differences that have an impor- tant effect on temperatures. These physical differences, related to evaporation, transparency, specific heat, and movement, cause land surfaces to heat and cool faster than water surfaces.
Because of water’s transparency, light passes through it to an average depth of 60 m in the ocean. This pen- etration distributes available heat energy through a much greater volume than is possible through land, which is opaque. At the same time, water has a higher specific heat,
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