Special temperature conversions

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Here are two simple temperature conversions for you.

Start with a Celsius temperature. Add 40. Divide by 5. Multiply by 9. Subtract 40. You now have it in Fahrenheit.

To go the other way, start with your Fahrenheit. Add 40. Multiply by 5. Divide by 9. Subtract 40. Piece of cake.

Even simpler, look at the picture. Fahrenheit numbers are on the left and Celsius temperatures are on the right. These might be different than you have used before, but they give the same result, and should be easier to remember.

What kind of temperature conversions do professional meteorologists do on the job? Here's a rather complicated example.

Temperature conversions in meteorology

Weather forecasters use a system of conversions to find the average temperature of an upper layer of any thickness. In this way they convert from an individual temperature profile to a typical value for that atmospheric layer.

You can do this on a chart such as a tephigram or skew-t. And you can use layer averaging for the conversions you need or other things such as mixing ratio. But why? Here are some examples of this idea in action.

1) Meteorologists find average temperature to determine the type of precipitation. They may predict rain, snow, hail or other types.

2) Averaging potential temperature enables one to estimate the capacity for atmospheric turbulence near the ground. Especially if it is sunny!

3) Look at the dewpoint curve on one of these charts. If it slopes up to the right, parallel to the mixing ratio lines, at low elevations, it shows that the air mixes well in this layer. A handy idea for forecasting convection and its resulting turbulence or storms.

4) Once again we go back to the good old wet-bulb potential temperature. Yet another one of our temperature conversions. It helps us find temperatures after events such as rain and downbursts. We can also determine what type of air mass the layer belongs to.

How to do it

First of all, by eyeball. This is a quick, crude technique for temperature conversions. Averaging this way can be effective if the person has sufficient skill.

The formal method goes more like this. Determine what layer you need an average for. Determine what parameter (isotherm for temperature etc) you need to average. Find a value for that parameter, by trial and error if necessary, that satisfies this condition:

You draw a single line or curve along your chosen isopleth from the top of your chosen layer to the bottom, so that the area of the "triangle" on one side of the radiosonde curve is about equal to the area on the other side. Have a look at this American example...

You can see the equal area technique here. It has the black area above the red line roughly equal to the grey area below. With it we determine that the average temperature between 550 millibars and 650 mbar (3774 metres above sea level and 5076m) was about -5 degrees Celsius. Follow the straight yellow isotherms sloping down to the left, parallel to the black arrow, and note that our average temperature value is halfway between 0 and -10.

As an aside from our temperature conversions instance, notice in this sample drawing the hockey sticks on the right. Many plots have these. They display the wind speeds and directions at the corresponding heights. The balloon's trajectory, rather than wind meters, gives us this data.

Each long spike means a speed of 10 knots, which is about 11 mph or 19 km/h, while a half spike means 5 and a flag means 50.

Additionally, the angle of the shaft shows the directions, with most of these in the picture above displaying westerly or northwest winds with southwest 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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