MetLink Activity 21 (age 16+)

Please see the note at the end about application of this activity to world areas other than the UK.

Anticyclones and temperature inversion – a case study:

This activity is designed for use with students aged 16+ years. In England and Wales, these are AS and A2 Level students; in Scotland they are young people studying for Higher Grades.

It can be used as a supplementary to Activity 14, or as a stand-alone exercise.

The aims of this activity are:
+ to use ICT skills in finding information, particularly the selection and extraction of data appropriate to a specific task
+ to describe spatial distribution and temporal change in pressure systems
+ to describe how weather conditions change with time and in different locations
+ to interrelate and attempt to explain some of the weather associated with anticyclones and temperature inversions
+ to begin to learn the skills needed to interpret Skew T – Log P diagrams.

The Activity:

Throughout the period Sunday 22 January to Monday 6 February, the weather over much of the British Isles has been dominated by an anticyclone (area of high pressure). This period therefore includes the whole of the first week and the start of the second week of the current active phase of the MetLink project.

To see the anticyclonic conditions on the weather maps of Europe, please click on the following links:
Monday 30 January
Tuesday 31 January
Wednesday 1 February
Thursday 2 February
Friday 3 February
Monday 6 February

With the aid of the maps, describe the anticyclone affecting the British Isles over this period. Describe pressure values, the area covered, and how the winds circulating around the anticyclone affected Britain (remembering that winds move clockwise round an anticyclone in the northern hemisphere and slightly outward at a very oblique angle to the isobars). You should also comment on the relationship between the anticyclone over the UK and neighbouring anticyclones. For example, how was the anticyclone over the British Isles related to high pressure over continental Europe?
To do this, it is suggested that you firstly write a paragraph using this guide to describe the situation on Monday 30 January. Then follow this with an account of how, if at all, the situation changed on subsequent days through to Monday 6 February.

A temperature inversion sometimes forms within approximately 1000 metres of the surface in an anticyclone.
+Through research, describe what a temperature inversion is.
+ Explain how these temperature inversions are formed in winter anticyclones.

The vertical temperature changes through the atmosphere at any time can be shown by the use of a special type of graph called a Skew T – Log P diagram. This type of graph is similar to a tephigram, of which you may have heard. On a Skew T – Log P diagram, the temperature (T) and pressure (P) lines are straight and the others curved. On a tephigram, the temperature (T) and dry-adiabatic (Φ = phi) lines are straight and the others curved.

Click here to see the Skew T – Log P diagram for Nottingham at 12:00UTC on Thursday 2 February. Here is an explanation of the main elements of the graph:
+ The vertical axis (y) shows pressure and altitude and has a logarithmic scale, hence the name Log P.
+ The horizontal axis (x) shows temperature and has an arithmetic scale.
+ There are two lines in bold black running upwards through the graph.
+ The right line shows the variation of the environmental temperature with height.
+ The left line shows the variation of the dew-point temperature (DPT) with height. If the DPT is fairly close to the environmental temperature, then the air will be of high relative humidity, possibly approaching saturation; if the difference between the environment temperature and the DPT is large, the air will be of low relative humidity and therefore dry.
+ There are two fine sets of lines running from bottom right to top left. The green lines show the dry-adiabatic lapse rate (DALR) temperatures and the purple ones show the saturated adiabatic lapse rate (SALR) temperatures.
+ The lines running from bottom left to top right can be disregarded for the purposes of this activity.

Consider the following questions, with reference to the Skew T – Log P diagram:
1. At lowest altitude, how is the environmental temperature changing with increasing height?
2. What happens to the change of environmental air temperature with height at approx 800 metres?
3. At lowest altitude, how is the DPT changing with increased altitude, and so how is the relative humidity of the air changing?
4. What happens to the DPT and therefore to the air at approximately 300m, and so what would have formed at this level?
5. What happens to the DPT at approx 800 metres and therefore to the air?
6. In physical terms, what would have been found at this level?
7. What happens to the environmental temperature of the air from approximately 1,500 metres to approx 10,500 metres?
8. What term is given the temperature feature that occurs between 800 metres and 1500 metres?
9. What happens to the environmental temperature above 10,500 metres?
10. Around the 10,500 metre level, there is a major division in the atmosphere. What is this called?

Study the satellite images for the UK on Thursday 2 February by clicking on these links:
For the visible image, click here.
For the infra red image, click here.
Describe what you observe, especially in the area of the East Midlands where Nottingham is located.

What weather was observed near Nottingham on Thursday 2 February?
Go to the MetLink Homepage and follow these links:
Data Central è Search observations data è Set: Country – UK; Dates 2 February to 2 February and Search now è Scroll through the data to find Eastwood, Nottinghamshire (the observation was made at 16:00 Local Time). How does this relate to what you have already found out?
Look at some other observations of MetLink participants in the Midlands and East Anglia that you can easily identify. How consistent are their observations with Eastwood’s?
The weather that you have been discovering in this case study, and that many MetLink participants in the UK have been experiencing during the period Monday 30 January to Monday 6 February, is sometimes described by meteorologist and weather forecasters as Anticyclonic Gloom.

Further investigations:

Some further Skew T – Log P diagrams, illustrating different conditions, may be studied by clicking on these links:

Skew T – log P Jokioinen Finland 12:00UTC 2 February

Skew T – log P Fort Dauphin Madagascar 12:00UTC 2 February

Skew T – log P Meiningen Germany 12:00UTC 3 February

Skew T – log P Trappes France 12:00UTC 3 February

Try to describe what is happening in some or all of these other cases.

Adaptation for use in other areas of the world:

This study format can be applied to areas of the world other than the UK as follows:
Skew T – Log P diagrams can be obtained for the area of the world you wish to study by clicking here.

During the MetLink project’s active phase, satellite images and weather charts can be obtained via the MetLink Homepage, Resources, Daily images, and weather observations by MetLink participants via Data Central, Search observations. The MetLink resources will remain available indefinitely. The Skew T – Log P data source is live and continually updated but has an archive extending back over several years. Use the Region, Type of plot, Year, Month, From and To drop-downs to find what you want.