What is a diurnal temperature range?

As one might guess from the term, diurnal temperature range means the variation between the lowest and highest temperatures during a given day at a certain location. This can vary widely, depending on the season and place. For example, the climate on the Front Range of the Rocky Mountains in North America has been known to change by as much as 100 degrees within a 24-hour period, while in the tropics temperatures tend to remain more stable, changing by, perhaps, 10 degrees or so within a specific day.

What is a temperature inversion?

Simply put, this is when temperatures in the troposphere (lowest layer of the atmosphere) are colder at lower altitudes than at higher altitudes, which is just the opposite of what normally occurs. Inversions can occur as the result of weather fronts moving through an area, or because of winds blowing over ground that is frozen over with ice or snow, or because of frigid lake or ocean conditions. When an inversion occurs it prevents air from circulating vertically, which can result in pollutants being trapped at low altitudes. Inversions also disrupt radio and radar transmissions.

What are the wet bulb and dry bulb temperatures?

Taking a reading of the wet bulb temperature is a way of measuring humidity. It is the temperature of a volume of air that has been cooled adiabatically until the humidity is at 100 percent and then compressed to the original pressure of the system prior to cooling. Using a wet bulb thermometer provides one reading, while a dry bulb thermometer is used for the second reading. The greater the difference between the temperatures read on the two thermometers, the less humid the air is. Using the two in conjunction is a single device called a psychrometer. The psychrometer measures the difference between the wet and dry bulb, and then, using established tables, the humidity of the air can be calculated.

How is a wet bulb thermometer constructed?

The basic design of a wet bulb thermometer is to insert a thermometer into a reservoir of pure, distilled water. Wrapped around the thermometer is a piece of cloth (usually muslin) that acts as a wick, drawing water up through the reservoir via capillary action. As the moisture in the cloth above the surface of the water evaporates, it draws heat from the thermometer, thus lowering the temperature until the surrounding air reaches a point of saturation. A dry bulb thermometer is simply a regular thermometer that is not dipped into the water reservoir or wrapped in cloth.

What types of psychrometers are there?

Old-style sling psychrometers are made from two thermometers secured to metal that is allowed to hang for a number of minutes until the wet bulb begins to cool. More modern psychrometers use a variety of sensors, including the use of chemicals that change their electrical conductivity due to humidity levels.

What are cooling degree days and heating degree days and what do they have to do with air conditioning?

Utility companies in the United States use the term "cooling degree days" to refer to the number of days when it is likely that air conditioners will be turned on, and "heating degree days" to determine when furnaces are likely to run. Because it would be impractical to visit every home and business to see whether the air conditioner or furnace was running, utility companies assume that customers are most comfortable when the temperature is 65°F (18.3°C) and that they will run their air systems accordingly. A "degree day" is not actually a 24-hour period. Rather, it is a measurement of the difference between the optimum of 65°F (Fahrenheit is used as the standard because it is a U.S. system)

Utility companies use a measurement called

Utility companies use a measurement called "cooling degree days," which estimates how many days people are likely to run their air conditioners yearly.

and the mean (average) temperature of a particular day. So, for example, if the mean temperature in Dallas, Texas, on a warm July day is 85°F, the utility companies will count that as 20 cooling degree days (85°F - 65°F = 20 cooling days). The states with the most annual cooling days on average are Florida, Texas, Arizona, California, and other southern states that, on average, rack up about 4,000 cooling days annually. Heating degree days use the same concept to calculate furnace use. As one might imagine, northern states log more heating degree days than southern states.

What month is known for the most extreme changes in temperature?

July holds the honor for most extreme variations of temperature globally. Record extremes on the planet occurred when measuring the temperature in Libya versus the temperature at the South Pole. The difference between the two was 265°F (129.4°C).

What is the "120 Club"?

Any U.S. state that has recorded a temperature at or above 120°F (48.9°C) is a member of the "120 Club." Nine states have met this dubious requirement:

• California: 134°F/56.7°C

• Arizona: 128°F/53.3°C

• Nevada: 125°F/51.7°C

• New Mexico: 122°F/50°C

• Kansas: 121°F/49.4°C

• North Dakota: 121°F/49.4°C

• Oklahoma: 120°F/48.9°C

• Arkansas: 120°F/48.9°C

• South Dakota: 120°F/48.9°C

• Texas: 120°F/48.9°C

What is the "60 Below Club"?

Given the above answer, this is pretty easy to guess. States that have recorded temperatures of -60°F (-51°C) or below belong to this chillin' club.

• Alaska: -80°F/-62.2°C

• Montana: -70°F/-56.6°C

• Utah: -69°F/-56°C

• Wyoming: -63°F/-54.4°C

• Colorado: -61°F/-51.6°C

• Idaho: -60°F/-51°C

• Minnesota: -60°F/-51°C

• North Dakota: -60°F/-51°C

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