Temperature trace F 160

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The temperature trace looks complicated.

Let’s look at what all the lines are. The pink lines are lines of constant temperature. 0 Degrees

Lines of constant pressure As a guide 100 mb per 3000 ft

The graph does not use °C The graph uses mill bars On this basis we can see the pressure at sea level.

Why do constant temperature lines not go vertical. Because this reduces the amount of paper that the graph takes up. The next diagram will explain this.

Dry Adiabat This is the rate that a bubble of air cools if raised through the atmosphere.

Air cools at 3° -per 1000 ft If the dry lines of constant temperature were vertical the dry adiabat lines would be very laid back and consume a lot of paper.

Saturated Adiabat Saturated Adiabat. The rate of cooling for a bubble of saturated air. About 1.1°C per 1000 ft

Mixing Lines These lines indicate how the moisture in a bubble of air changes as it mixes with the surrounding air as it rises

Let’s look at some traces

There are two red lines and generally 2 blue lines. The red lines are the last trace. The right line indicates the air temperature with height. The left line indicates the due point. What can we see from this trace.

The height that the balloon has been released The air is moist were the due point comes close to the temperature trace. Indicating there may be upper level cloud We are interested in the lower levels

There are 3 Grey lines drawn by the met office that help us The lower right line shows what would happen to a bubble of air that is heated to the maximum temp for the day. 25°C in this case. All things being normal it would rise till it met the inversion at 800mb (6000ft)

On this day the grey line on the left, running parallel with the mixing lines, meets the grey line on the right running parallel with the dry adiabat. They meet to the right of the temperature trace. At the point these meet the humidity will reach 100% and thus cloud will form.

Now we have a cloud the cooling rate follows the saturated adiabat. Until it reaches the inversion. You can see the thickness of the cloud about 2000ft The top of the thermal 6000ft If the temperature rose you could see that the cloud base will rise. But the cloud will get thinner.

Let’s look at another day

You can see the morning inversion Thermals will top 3000ft until the temperature gets to about 30°

With 38 degrees thermals will go to about 10,000 ft but because the mixing lines meet the dry adiabat to the left of the temperature there will not be cloud. What if the temperature were to be a few degrees hotter.

We have assumed that the temperatures we take are from the point where the balloon is released 32° in this case If we were at a higher altitude say 700ft We would only need to get a temperature of 28° on the assumption that the inversion is no different from the trace inland.

What happens here?

Wind I have not shown on this chart the wind. This is shown by bars up the side of the chart indicating wind direction and strength with height they are quite self explanatory

So what can we see from the chart? The shape of the inversion and thus the amount of heating requited for it to be broken. The depth of the inversion, can we go cross country before it is broken. The temperature that the inversion will be broken. The height that the thermals will reach If cloud will form The base and depth of cloud if it were to form

For an article you can download Go to the gliding links and articles

To get the temp trace Click Aviation Users Sport Aviation Vertical temperature and wind profiles User name bomw0007 Password aviation Click on the area on the map