Factors influencing air temperature

Overview

Main factors that determine the air temperature of a place, how latitude influences air temperature and why air temperature falls with altitude.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What are the main factors that determine the air temperature of a place?

   Model answer

   Latitude, distance from the sea or continentality, altitude, the ocean currents washing nearby coasts, and seasonality. Latitude sets the broad level of energy received, continentality and ocean currents modify it according to the surrounding surface, altitude reduces it with height, and seasonality accounts for how it varies through the year.

2. 2

   Explain how latitude influences air temperature.

   Model answer

   Latitude controls the angle at which solar radiation strikes the surface. Near the equator the sun is high in the sky, so a beam of given width is concentrated on a small area and heating is intense. At high latitudes the same beam strikes obliquely and is spread over a much larger area, so heating per square metre is weaker. The oblique beam also passes through a much greater thickness of atmosphere, so more energy is scattered, reflected and absorbed before it arrives. Mean temperature therefore falls steadily from the equator towards each pole.

3. 3

   Why does land heat up and cool down faster than the sea?

   Model answer

   There are four reasons. Land has a much lower specific heat capacity, so a given amount of energy raises its temperature far more. Land is opaque, so heating is confined to a thin surface layer, while water is transparent and the energy is spread through many metres. Water is mobile and mixes by currents and waves, distributing heat downwards, whereas rock and soil cannot circulate. Finally, a good part of the energy reaching water is used in evaporation rather than in raising temperature. The same reasons in reverse mean the sea also loses heat far more slowly.

4. 4

   What is continentality and what effect does it have on the annual temperature range?

   Model answer

   Continentality is the effect of being distant from the moderating influence of the sea. Places deep inside a continent experience hot summers and cold winters because the surrounding land heats and cools rapidly, so their annual temperature range is large, often over 30 degrees Celsius and in eastern Siberia over 50. Coastal or maritime places have cool summers and mild winters because the sea warms and cools slowly and the air passing over it takes on those properties, so their annual range is small, often under 10 degrees Celsius in the west of Ireland.

5. 5

   Two European cities lie at similar latitudes, one on the Atlantic coast and one far inland in eastern Europe. Describe how their temperature regimes would differ and why.

   Model answer

   The Atlantic coastal city would have a mild winter, with monthly means staying above about 5 degrees Celsius, a cool summer of perhaps 15 degrees, and a small annual range, because onshore winds crossing water that has stored summer heat keep winter mild and water that has stayed cool keeps summer moderate. The inland city would have a cold winter, with means well below freezing, and a warm summer of perhaps 20 degrees, giving a much larger annual range, because the surrounding land radiates its heat away rapidly in winter and heats intensely in summer, and no maritime air reaches it. The maritime station would also have its warmest and coldest months arriving later in the year because of the lag in the sea's response.

6. 6

   Explain why air temperature falls with altitude, and at what average rate.

   Model answer

   The air is heated from below by long-wave radiation from the ground, so the further above the surface you go the less of that heat reaches you. Air at height is also less dense, with fewer molecules of water vapour, carbon dioxide and dust to absorb and retain energy, and it is under less pressure, so a rising parcel expands and cools. The average rate of decrease in still air is about 6.5 degrees Celsius for every 1000 metres of ascent, known as the environmental lapse rate. It is an average and can be reversed near the ground when an inversion forms.

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