Factors that influence climate
FOCUS QUESTION:
What are the factors that influence climate?
ELEMENTS OF CLIMATE
Solar radiation (sunlight) is all the light and energy that comes from the sun.
First and foremost, it heats the Earth’s surface which, in turn, determines the temperature of the air above.
It drives evaporation, so long as there is water available. The heating of the air determines its stability, which affects cloud development and precipitation.
It creates pressure gradients through unequal heating of the Earth’s surface that results in wind.
Air masses are large volumes of air in the atmosphere that are mostly uniform in temperature and moisture.
They form over large surfaces with uniform temperatures and humidity, called source regions.
Low wind speeds let air remain stationary long enough to take on the features of the source region, such as heat or cold.
When winds move air masses, they carry their weather conditions (heat or cold, dry or moist) from the source region to a new region.
When the air masses reache a new region, they may clash with another air mass that has a different temperature and humidity.
This can create a severe storm. Earth. Meteorologists identify air masses where they form over the
There are four categories for air masses: arctic, tropical, polar and equatorial.
However, for our study, we will focus on tropical and equatorial.
PRESSURE SYSTEMS (AND CYCLONE BELTS)
We live at the bottom of the atmosphere and the weight of all the air above us is called air pressure.
Air pressure is the atoms and molecules that make up the various layers in the atmosphere and are constantly moving in random directions. Despite their tiny size, when they strike a surface, they exert a force on that surface in what we observe as pressure. What causes high and low pressure? The Earth’s atmosphere exerts a pressure on the surface. Pressure is measured in hectoPascals (hPa), also called millibars.
Standard pressure at sea level is defined as 1013hPa, but we can see large areas of either high or low pressure.
These areas are all relative to each other – so what defines a high will change depending on the area around it.
Areas of high and low pressure are caused by ascending and descending air.
As air warms, it ascends, leading to low pressure at the surface.
As air cools, it descends leading to high pressure at the surface.
This is illustrated in the diagram below.
A LOW-PRESSURE SYSTEM
Has lower pressure at its centre than the areas around it. Winds blow towards the low pressure, and the air rises in the atmosphere where they meet.
As the air rises, the water vapour within it condenses, forming clouds and often precipitation, too.
Because of Earth’s spin and the Coriolis effect (shift in wind direction due to Earth’s rotation), winds of a low-pressure system swirl counterclockwise north of the equator and clockwise south of the equator. This is called cyclonic flow.
On weather maps, a low-pressure system is labelled with a red ‘L’.
Please take note.
A HIGH-PRESSURE SYSTEM
Has higher pressure at its centre than the areas around it. Wind blows away from high pressure. Winds of a high-pressure system swirl in the opposite direction as a low-pressure system – clockwise north of the equator and counterclockwise south of the equator. This is called anticyclonic flow. Air from higher in the atmosphere sinks down to fill the space left as air blew outward.
On a weather map, the location of a high-pressure system is labelled with a blue ‘H’.
Please study the diagram below; they should give you a better understanding of the concept. In the next lesson, we will continue to talk about the factors that influence weather and climate.