1.2 Units of Measure Used in Atmospheric Science
This submodule reviews the units of measure that will be used in this course. Most scientific fields use the metric system and atmospheric science is not an exception. However, the United States uses some English system units when measuring surface parameters. These exceptions are noted below.
The information in Module 1.2 does not need to be memorized, rather it is presented as an introduction to the notation and terms used throughout the course.
Scientific Notation
| Long-form | Scientific notation | Name | Symbol | |
|---|---|---|---|---|
| 1,000,000,000 | = | 109 | giga | G |
| 1,000,000 | = | 106 | mega | M |
| 1000 | = | 103 | kilo | k |
| 100 | = | 102 | hecto | h |
| 10 | = | 101 | deka | da |
| 1 | = | 100 | ||
| 0.1 | = | 10-1 | deci | d |
| 0.01 | = | 10-2 | centi | c |
| 0.001 | = | 10-3 | milli | m |
| 0.000001 | = | 10-6 | micro | µ |
Video: Express a small number in scientific notation| Khan Academy (4:11 min.)
This short video provides a review of using scientific notation.
Units of Length
| Unit | Symbol | Relationship | English System |
|---|---|---|---|
| micron | µ | 106 µ = 1 m | |
| millimeter | mm | 1000 mm = 1 m | 1 mm = 0.03937 in |
| meter | m | 1 m = 1.0936 yd | |
| kilometer | km | 1 km = 1000m | 1 km = 0.6214 mi |
Units of Mass
| Unit | Symbol | Relationship | English System |
|---|---|---|---|
| gram | g | 1 g = 0.03527 oz | |
| kilogram | kg | 1 kg = 1000 g | 1 kg = 2.2046 lb |
Temperature
| Unit | Symbol | Conversion equation |
|---|---|---|
| degree Celsius | oC | 1oC = 5/9 (oF – 32) |
| degree Fahrenheit | oF | 1oF = 9/5 (oC) + 32 |
In the United States surface temperatures are reported in Fahrenheit, and everything aloft is reported in Celsius. Most other countries report all temperatures in Celsius.
Speed
| Unit | Symbol | Relationship | English System |
|---|---|---|---|
| meters/second | m/s | 1 m/s = 2.24 mph | |
| kilometers/hour | kph | 1 km/hr = 0.278 m/s | 1 km/hr = 0.6214 mph |
| knots | kn | 1 kn = 0.514 m/s | 1 kn = 1.151 mph |
A knot is a nautical mile per hour and is not part of the metric system. Traditionally all wind speeds were reported in knots. With the advent of computers, wind speeds at the surface frequently are given in miles per hour (mph). Winds aloft are always reported in knots in the United States.
Pressure
| Unit | Symbol | Relationship | English System |
|---|---|---|---|
| atmosphere | atm | 1 atm = 1013.2 mb | 1 atm = 14.7 lb/in2 |
| kilometers/hour | mb | 1 mb = 0.6895 lb/in2 | |
| kilopascal | kPa | 1 kPa = 10 mb | 1 kPa = 6.895 lb/in2 |
Most of the world, including the United States, uses millibar (mb) as the atmospheric pressure measurement. Some countries use kilopascal (kPa), which is essentially the same as millibar with the decimal moved one place to the left.
Energy
| Unit | Symbol | Relationship |
|---|---|---|
| joule (Newton meter) | J (N m) | 1 J = 0.239 calorie |
| watt | W | 1 W = 1 J/sec |
Most energy measurements are based on the metric system. The defining unit of energy is the calorie. One calorie is the amount of energy required to raise 1 gram of water 1 degree Celsius. Food nutritional labels use the calorie as an indication of how much energy a person will get from this product. The watt is commonly used as a measurement when dealing with electricity. Light bulbs post their energy consumption in watts.
