Weather is a highly complex and dynamic, energy charged process that is powered by the sun and linked with the earth’s hydrologic (water) cycle.

water cycle
Image source:  United States Geological Survey – Public Domain

The weather is subject to numerous factors that operate and interplay both on a ‘macro’ and ‘micro’ level and this makes forecasting it accurately such a challenge.

Macro Factors Affecting Weather

The tilt of the earth (23.5º from the perpendicular) significantly affects the weather for the following reasons:

  • The Equator receives more concentrated solar energy than the poles. As one moves from the equator towards the poles, the angle of the sun becomes lower meaning less solar energy is received for a given area. In addition, ice and snow at the poles reflect a lot of energy.

solar energy distribution
Image source modified: Earth Image by Nasa – Public Domain

  • Earths seasons. During the earth’s one year cycle around the Sun, those locations tilted towards the Sun experience summer whilst those tilted away winter.

earths axis, rotation and seasons
Image source modified: astronomyonline.org – Creative Commons

Therefore, areas of air with non-uniform depth are produced by the combined effect of:

  • The earth’s rotation on its tilted axis.
  • The surface being heated unevenly by the sun.

Where air ‘piles up’ ( ‘mountain’ of air) the weight of air and the pressure it exerts on the ground will be greater than the average i.e. a high pressure area or high pressure ridge. Therefore, high pressure areas have more atmospheric mass above their location. The opposite occurs where the air is less deep (‘valley’ of air) i.e. a low pressure area or low pressure trough. Hence , low pressure areas have less atmospheric mass above their location.

This system is dynamic and in a process of constant change. There is a tendency for air to flow (wind) from a region of high pressure to low pressure, which due to the earth’s rotation causes the air to circulate:

  • Northern Hemisphere – clockwise motion around high pressure with a small component directed outwards and towards a low pressure region, where the air flows in a counter-clockwise pattern.
  • Southern Hemisphere – opposite to northern hemisphere.

earths atmospheric circulation
Image source modified: astronomyonline.org – Creative Commons

The equator tends to produce masses of warm and moist air and the polar regions masses of cold and dry air.

The placement of the continents and oceans are of significant importance in determining the world’s weather patterns due to the way in which they react to solar radiation:

  • Land reacts quickly therefore it becomes warm in the summer and cold in winter.
  • Oceans react slower and tend to be cooler in the summer and warmer in the winter than adjoining land.

Micro Factors Affecting Weather

On a micro level, the weather can be influenced by numerous factor such as:

  • Contour of land and proximity to hills or mountains.
  • Proximity to large lakes.
  • Living in a city. Sometimes referred to as urban heat which is the ‘characteristic warmth of both the atmosphere and surfaces in a city (urban area) compared to its (non-urbanized) surroundings’. In major cities 1-2C is a common differential but under ‘optimum’ conditions there can be a difference of up to 4-6C.