MetLink Activity 34

MetLink Activity 34 (ages 14+)

MetLink in Africa

During the January/February 2006 active phase of the MetLink project, there have been several participants in Africa actively participating and logging their observations. Most of them have logged observations for most or all of the period from Monday 30 January to Thursday 9 February (the time of writing). Their locations are:
KE Kenya 1
MU Mauritius 1
NG Nigeria 1
ZA Republic of South Africa 4
ZM Zambia 1

The aims of the activities on this sheet are:
+ to use ICT skills in finding and extracting information
+ to use mapping and graphical skills in presenting information and making use of standard weather mapping symbols
+ to describe how weather conditions change with time and in different locations.

Needed for the activities: An atlas, large map of Africa or computer-based map (for example from MS Encarta), and large outline maps of Africa.

The Activity:

1. Locating and mapping the participants’ observations:
The suggested days to be selected are:
Monday 30 January
Thursday 2 February
Monday 6 February
Thursday 9 February
It is also suggested that the class divides and that different individuals, pairs or small groups deals with one day each.
Searching for, collecting and using the observational data:
Go to the MetLink database of observations by using the MetLink Home page (click here). Then, by working from the Home page:.
+ Click on Data central
+ Click on Search observations
+ Click on the Country drop-down menu and select each of the countries listed above in turn
+ Set the dates as From 30 January To 09 February
+ Click on Search now
This shows you all of the observations made by MetLink participants in that country during that period.
For each participant in that country:
+ Find their location and mark it on your Africa outline map. Use the Details page for the participant to find this by clicking on their name on the observations sheet.
+ Present their observations on the map using the following methods:
Write the temperatures in a horizontal rectangle divided into 3 vertical sections. Show current temperature (at time of observation) in black, maximum in red and minimum in blue, thus:

5.1

9.1

4.4

Write the rainfall amount inside a blue circle.
Show the relative humidity percentage written in blue and in brackets.
Show the air pressure written in black.
Use the Met Office weather key to show the other observations, including current precipitation.
To see this key, please click here.
Click here to see an example of this type of presentation.
As an optional extra, the cloud types could also be shown by using the standard letter key:
Ci cirrus; Cc cirrocumulus; Cs cirrostratus;
Ac altocumulus; As altostratus;
Cu cumulus; Sc stratocumulus; St stratus;
Cb cumulonimbus; Ns nimbostratus.
The end product should be four maps, one for each of the dates, and each showing the observations for up to eight locations.

Using the maps describe:
+ Differences in the weather of the different locations.
+ How the weather in each place has changed over the 11-day period shown.

2. Graphing each participant’s weather observations:
Of course, it needs to be remembered that a sampling technique has been used in Question 1 in order to save on time and to make the information more easy to handle. The problem, as with any sampling technique, is that it may miss out some very important events. A way to overcome this would be to graph the complete set of data for each participant. This could be done in a basic manner, just showing maximum and minimum temperature and rainfall on a single graph. One graph for each participant’s data. Temperature values shown on the left vertical axis with a red line for maximum temperature and a blue line for minimum temperature. Rainfall values shown on the right vertical axis and the rainfall amounts for each day shown by vertical shaded columns. If the task of drawing the graphs is shared round the class, each person can describe the main things their graph shows and this can then be discussed in groups or as a whole class, comparing the observations for different locations.
Alternatively, more complex pictographs could be drawn. An example can be seen by clicking here. This example is a five-day version and for the purposes of this work it would be extended to the appropriate number of days for the data available.

3. What the satellite images show:
Study the satellite images for the four selected days by clicking on each of these links:
For 30 January infra-red image at 12:00UTC, click here.
For 30 January visible image at 12:00UTC, click here.
For 2 February infra-red image at 12:00UTC, click here.
For 2 February visible image at 12:00UTC, click here.
For 6 February infra-red image at 12:00UTC, click here.
For 6 February visible image at 12:00UTC, click here.
For 9 February infra-red image at 12:00UTC, click here.
For 9 February visible image at 12:00UTC, click here.
Using the images:
+ Describe the distribution of cloud, including the main cloud masses and areas of clear sky.
+ Explain the types and origins of the cloud masses and also the reasons for the areas of clear sky.
+ Describe the changes which can be seen to have occurred over the period of study.

4. Pressure maps:
Study the weather charts for South Africa and the surrounding oceans for the four selected days by clicking on each of these links:
For 30 January at 06:00UTC, click here.
For 2 February at 06:00UTC, click here.
For 6 February at 06:00UTC, click here.
For 9 February at 06:00UTC, click here.
Describe the main features shown by each of the maps.
Describe the changes which occur over the 11-day period.
Relate what the weather maps show, as far as possible, to the weather conditions observed by the MetLink participants in the area.
Also attempt to explain the rainfall in Southern Africa as shown by the Southern Africa rainfall map (24 hours to 06:00UTC on 9 February) – click here by reference to the pressure chart for 9 February and the previous day (click here).

5. Advanced study: The South Atlantic Subtropical Anticyclone:
The centre of the anticyclone was to the south of St Helena today, as the 06:00UTC weather chart from the South African Weather Service shows. Research the topic of anticyclones and this specific anticyclone.
As with any weather system, vertical changes within the atmosphere are very important. 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.
Click here to see the Skew T – Log P diagram for St Helena based on the upper air sounding made there at 12:00UTC today. 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-hand line shows the variation of the environmental temperature with height.
+ The left-hand line shows the variation of the dew-point temperature (DPT) with height. If the DPT is relatively close to the environmental temperature, then the air will be of high relative humidity, possibly approaching saturation. If the DPT is considerably less than the environmental temperature, 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) and the blue ones show the saturated adiabatic lapse rate (SALR).
+ The lines running from bottom left to top right for the purposes of this activity can be disregarded.

A temperature inversion sometimes forms within an anticyclone..
+Through research, describe what a temperature inversion is.
Now, describe the changes that were taking place vertically in the atmosphere today above St Helena, starting from the surface. In particular, did a temperature inversion exist and at what level? What effects would this have had on the weather?