Temperature conversions of special types

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I'll start with the most familiar temperature measurements.  Here are two simple temperature conversions for you.

Fahrenheit scale

Start with Celsius.  Take 40 and add it.  Multiply by 9.  Divide by 5.  Subtract 40 from that.  Now you've got it in Fahrenheit.

Now the other way:  Start with your Fahrenheit.  Just add 40.  Take that number and multiply it by 5.  Then divide by 9.  Subtract 40 from the result.  Easy peasy.

The Fahrenheit scale is mainly used in the United States and a few other countries.  Water's freezing point is 32°F, and its boiling point is 212°F.  -459.67°F is absolute zero, the lowest temperature possible.

The Celsius scale is the most widely used temperature scale worldwide.  It's common in science and everyday life.  The freezing point of water is 0°C, and the boiling point is 100°C.  The absolute zero temperature is -273.15°C.

Kelvin (K): This is an absolute temperature scale that's used in science and thermodynamics.  Temperature differences and energy calculations are common uses for it.  Kelvin scale starts at absolute zero, where 0 K represents no thermal energy.  A Kelvin increment is the same size as a Celsius degree increment, so an increase of 1 Kelvin is the same as an increase of 1 Celsius.

Rankine is another temperature scale used in some engineering applications, especially in the US.  With absolute zero being 0 Rankine (R), the Rankine scale is based on the Fahrenheit scale.  Rankine scale increments are the same size as Fahrenheit degrees.  Although Rankine isn't as common as Celsius, Fahrenheit, or Kelvin, it's still used in specific engineering and scientific contexts, especially in the US.

Absolute zero is the lowest temperature on any scale.  All molecular motion stops at absolute zero, and substances reach their lowest possible energy state.  The point where no heat can be extracted from a system is the point of minimum thermal energy.  In scientific and thermodynamic calculations, absolute zero serves as the starting point for measuring temperature.

Special Temperature conversions used in meteorology

Weather forecasters use conversions to find the average temperature of any upper layer.  They convert an individual temperature profile into a typical value for that atmospheric layer.

You can do this with a tephigram or skew-t chart.  You can use layer averaging or other things like mixing ratios. But why?  Check out these examples.

1) The type of precipitation is determined by the average temperature.  It could be rain, snow, hail, or something else.

2) One can estimate atmospheric turbulence near the ground by averaging potential temperatures.  That's especially true if it's sunny!

3) Check out one of these charts for the dewpoint curve.  At low elevations, it shows that the air mixes well in this layer if it slopes up to the right.  Warmer air moves up and cooler air moves down because of this mixing. As a result, the temperature in different layers of the atmosphere stays the same and vapour in the air are dispersed.  This is a handy tool for forecasting convection, turbulence and storms.

4) Let's go back to the good old wet-bulb potential temperature.  Here's another temperature conversion.  It's great for finding temperatures after rain or downbursts.  We can also figure out what type of air mass it is.

Here is how you can do it

Firstly, by eyeball.  This is a quick, crude way to convert temperatures.  The person needs to have enough skill to average this way.

Here's the formal method.  Decide what layer you need an average for.  Decide what parameter (isotherm, temperature, etc) you need to average.  Find a value for that parameter, by trial and error if necessary, that meets this condition:

From the top of your chosen layer to the bottom, draw a single line or curve so that one side of the radiosonde curve has about the same area as the other side.  Take a look at this American example...

Analyzing Skew-T Log-P charts

Here's an equal area technique.  The black area above the red line is roughly equal to the grey area below.  With it, we figure the average temperature between 550 millibars and 650 millibars (3774 meters above sea level and 5076 meters above sea level) was -5 degrees Celsius.  Our average temperature value is halfway between 0 and -10, as you can see from the straight yellow isotherms sloping down to the left.

Besides the temperature conversions, notice the hockey sticks on the right in this sample drawing.  These are in a lot of plots.  Wind speed and direction are displayed at corresponding heights.  We get this data from the balloon's trajectory, not stationary wind meters.

A long spike means 10 knots, which is about 11 mph or 19 km/h, a half spike means 5 and a black flag (pennant-shaped, not shown in this example) means 50.  In addition, the shaft angle shows the upwind direction, with most of these in the picture above showing westerly or northwest winds near the surface.

Go back from Temperature Conversions to the Chasing Storms webpage. If you have anything to add, please leave your comment right here.

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Thank you to my research and writing assistants, ChatGPT and WordTune, as well as Wombo and others for the images.

GPT-4, OpenAI's large-scale language generation model (and others provided by Google and Meta), helped generate this text.  As soon as draft language is generated, the author reviews, edits, and revises it to their own liking and is responsible for the content.