Introduction to Temperature
Temperature is one of the most basic elements of weather and climate.
The daily mean temperature can be determined by averaging the 24 hourly readings or by adding the maximum and minimum temperatures for a 24-hour period and dividing by two.
The daily temperature range is the difference between the maximum and minimum temperatures.
Monthly Mean Temperature
The sum of the daily mean temperatures divided by the number of days in the month.Annual Mean Temperature
The average of the 12 monthly mean temperatures.Annual Temperature Range
The difference between the warmest and coldest monthly mean temperatures.Daily Temperature Range
The difference between the day's maximum and minimum temperatures.Controls of Temperature
The controls of temperature are the factors that cause temperature to vary from place to place.
Differential Heating
of Land & Water
Ocean Currents
Altitude
Geographic Position
Cloud Cover
Albedo
Ocean Temperatures
Click the image for a larger view.
View Global Ocean Temperatures →
Ocean Currents
Global Temperature Patterns
On maps showing the world distribution of temperature, isotherms are lines connecting points having the same temperature.
Isotherms generally trend east and west and show decreasing temperatures toward the poles. They also reveal the effects of the seasonal migration of the Sun's vertical rays and the influence of ocean currents.
The north-south migration of isotherms is generally more pronounced over continents because land experiences greater temperature changes than water.
Seasonal Lag
The warmest and coldest months do not occur exactly when incoming solar radiation reaches its maximum and minimum.
In the Northern Hemisphere, the greatest solar intensity occurs around the summer solstice, but July and August are generally warmer. Likewise, minimum solar energy occurs around the winter solstice, but January and February are usually colder.
Measuring Temperature
Thermometers measure temperature mechanically or electrically.
Liquid-in-Glass Thermometer
Uses the expansion and contraction of a liquid as temperature changes.Maximum Thermometer
Traditionally designed to record the highest temperature reached during a period.Minimum Thermometer
Records the lowest temperature reached during a period.Thermistor
An electrical thermal resistor used to measure temperature.A bimetal strip mechanical thermometer can be used in a thermograph, an instrument that continuously records temperature.
Temperature Scales
Steam point: 212°F
Steam point: 100°C
Ice point approximately: 273 K
Temperature Conversion Formulas
Practice Temperature Conversions
Example: Celsius to Fahrenheit
16°C:
Temperature Conversion Videos
Degree Days
Three common applications of temperature data are heating degree days, cooling degree days and growing degree days.
Heating Degree Days
Each degree that the daily mean temperature is below 65°F contributes to heating degree days.Cooling Degree Days
Determined from how far the daily mean temperature is above 65°F.Growing Degree Days
Determined from the difference between the daily mean temperature and the base temperature required for a crop to grow.Heat Index & Wind Chill
Heat Index
The heat index combines air temperature and humidity to describe how hot conditions feel to the human body.
National Weather Service Heat Index Information →
Wind Chill
Wind chill combines air temperature and wind speed to describe how cold conditions feel to exposed skin.
Isopleths & Isotherms
An isopleth is a line connecting points having an equal value of a particular quantity.
Analysis charts may show isotherms in 2-, 4-, 5- or 10-degree increments.
Meteorologists use isotherms to help identify temperature gradients, fronts, warm-air advection, cold-air advection and other important atmospheric features.
What You Need to Know for Test 2
Chapters 3, 4 and 5
- Read textbook Chapter 3.
- Know how to convert temperature scales.
- Know the Fahrenheit and Celsius conversion formulas.
- Understand what temperature is and how it is measured.
- Know the different types of thermometers.
- Understand daily mean temperature and daily temperature range.
- Know what controls temperature.
- Understand why land and water heat and cool differently.
- Understand the influence of ocean currents.
- Know what an isotherm is.
- Know what heating degree days and cooling degree days are.
- Remember the base temperature of 65°F.
- Understand heat index and wind chill.