We know that this weather map (Figure 13.16) is showing a low- pressure system or depression because the lowest number is in the middle circle over Ireland.
Ascending air typically results in low atmospheric pressure, a lot of cloud and precipitation, and strong winds. As air ascends, it cools and loses its ability to hold moisture, which results in the formation of clouds and rain.
The isobars are close together which means that winds are strong. Winds in low-pressure systems blow in an anti- clockwise direction.
Anticyclone
• Descending air and temperatures rise • High atmospheric pressure • Winds blow in a clockwise direction • Isobars are well spaced indicating light winds • Clear skies and cold nights in winter • Dry weather
• Ascending air and temperatures fall • Low atmospheric pressure • Winds blow in an anti-clockwise direction • Isobars are close together indicating strong winds
• Cloudy skies • Wet weather
: Figure 13.17 Satellite image of an anticyclone
: Figure 13.18 Satellite image of a depression
(i) List two characteristics of an air mass. (ii) Name two air masses that Ireland experiences. (iii) Explain what a front is. Name the three types of front. (iv) Describe the main differences between an anticyclone and a depression.
/ I understand air masses and how they form fronts.
/ I can explain the different fronts that are formed and I can identify them on weather maps.
