The following are the factors that affect and control the annual range of temperature

The following are the factors that affect and control the annual range of temperature in the same way as they do the horizontal distribution of temperature: latitude; height above the mean sea level; ocean currents; prevailing winds; precipitation and cloudiness; local relief; and distance from the sea.

Latitude:

The height of mid-day sun is never less than at the equator. Twice in a year the sun’s rays are vertical at the equator. Thus, the temperature is uniformly high in the equatorial region, and the annual range of temperature is negligible.

But from the equator pole-ward, there is a progressive decrease in temperature. It results in greater annual range of temperature. In the Polar Regions, where the length of day and night is 6 months, one should expect the highest annual range of temperature.

But the fact is otherwise, because the low angle of incidence in the sun’s rays does not allow the temperatures to rise to higher values. Besides, a larger part of insolation received in the Polar Regions is expended in melting the ground snow.

This factor also checks any substantial rise in the temperature in those regions. Therefore the mid-latitude regions, where the seasonal variation in temperature is greatest, record the highest annual range of temperature.

Thus, it is evident that the effect of latitude on the distribution of temperature is modified to a great extent by other factors discussed below.

Height above mean sea level:

The annual range of temperature at a particular place is largely controlled by the height at which the place is situated. At high elevations, the rarity of the air, larger amount of precipitation and cloudiness combine together to lower down the average temperature even during the warmer months of the year.

But the mean values of temperature for the colder part of the year are not affected by these factors to the same degree. Thus, places situated at higher elevations have lower annual ranges of temperature.

Ocean currents:

The effects of ocean currents upon the temperature of adjacent land areas are variable, depending on the direction of prevailing winds. Where the prevailing winds are onshore, they carry the moderating effect far inland.

Under these conditions, the warm ocean currents help to raise the temperatures of the adjoining regions. For example, the prevailing westerly’s keep the winter time temperatures in Great Britain and much of the western Europe warmer for the latitude, because of the presence of the North Atlantic Drift, a warm ocean current, in the nearby ocean.

The effect of the warm ocean currents is more pronounced in winter. Hence the annual range of temperature is relatively smaller. Another example is offered by the cold ocean current of California because of which summer temperatures in the subtropical coastal Southern California are lower by 6° Celsius.

Thus, the difference between the average winter and summer time temperatures in the coastal regions of California is never large resulting in the small annual range of temperature.

Prevailing winds:

Among the factors that have controlling influence over the annual range of temperature, the prevailing winds are the most important.

Off-shore winds bring about an increase in the annual range of temperature of the adjacent land, while the on-shore winds carry the moderating influence of the oceans far inland and impose a restriction on the annual range.

The effect of ocean currents is largely determined by the direction of the prevailing winds. On­shore winds carry their influence to the coastal regions, while the off-shore winds deprive them of the warming or cooling effects of ocean currents.

Precipitation and cloudiness:

In those regions where the rains are falling or where the skies are covered with clouds, the summer temperatures are relatively lower. But during the winter, the clouds check the loss of heat by terrestrial radiation.

Thus, in cloudy regions the winter time temperatures are not allowed to fall much. Therefore in such regions the annual range of temperature is relatively smaller than those regions where the weather is clear and dry.

Local relief:

Slope is one of the potent factors which affect the temperature of a place. The slopes facing the sun have higher temperatures during summer months, and the slopes protected from the sun have much lower temperatures during winter. Thus, this local factor also affects the annual range of temperature.

Distance from the sea:

Water is heated or cooled in a longer period of time than land. Because of this peculiar characteristic of water, the coastal areas enjoy a moderate climate, and the difference in temperature of the warmest and the coldest months is not very large.

On the contrary, the interior locations have extremely hot summers and cold winters. Thus, with increasing distance from the sea-coast, there is a corresponding increase in the seasonal variation of temperatures.

However, in the vicinity of the equator the effect of distance from the sea on the annual range of temperature is quite negligible. Its effect is more marked in the temperate regions.

It may be pointed out that since the coastal locations have larger amount of clouds and the resultant precipitation, the diurnal range of temperature is also very small.