Isobars Isobars are lines on a weather map which join together places of equal atmospheric pressure. In Figure 13.10 the isobar north of Ireland marked 962 represents an area of low pressure, while the isobar marked 1022 west of Italy represents an area of high pressure.
While examining isobars on this weather map of Ireland, note the following points:
• Isobars show areas of equal atmospheric pressure.
• Atmospheric pressure is measured in millibars. • Isobars are usually drawn at intervals of four or eight millibars.
• The closer together the isobars are, the stronger the wind will be.
Fronts
Fronts occur where two different air masses meet.
The three different types of front are shown in Figure 13.11. These are a warm front, a cold front and an occluded front.
Warm fronts are formed when warm air rises over a mass of cold air. As the warm air lifts into areas of lower pressure, it expands, cools and condenses the water vapour as wide, flat sheets of cloud. These clouds bring gentle rain.
A warm front is shown on a weather map as a solid red line with red semicircles.
Warm Cold : Figure 13.12 The formation of a warm front
