The physical factors which play a major role in everyday weather are temperature, air pressure, wind and humidity.
Energy radiated by the sun is absorbed by the earth's surface as heat energy. The amount of energy reaching the earth's surface determines the temperature. If there are a lot of clouds present in the morning, it is difficult for the sun's rays to heat the earth and the temperature will be cooler. The heat in the earth's surface is transferred to the adjacent layer of the atmosphere - called the tropopause. From the tropopause the heat is transferred to the next layer, the stratopause, then the mesopause, then the thermopause and finally the exosphere. Less and less heat energy is transferred to the different layers of the atmosphere, and that is why the temperature decreases as the altitude increases. If many clouds are present in the afternoon, they prevent the heat energy from reaching higher atmospheric layers. Instead they cause the energy to return to the earth, which can make the temperature slightly higher.
Temperature is measured in degrees Fahrenheit or degrees Celsius, with a thermometer.
Air exerts pressure on everything around it. Pressure on a point on the ground, is the weight of the column of air above that point. Therefore, because mountain peak has a higher altitude, the column of air above it would not be as great as the column of air above a point at sea level (a lower altitude). Therefore the weight of the air on the mountain peak is less than that at sea level, which means that a lower pressure will be exerted on the mountain peak. Therefore, we can say that pressure also decreases with altitude. The differing pressures at different altitudes can have an affect on people, especially athletes. This is because at an area of lower pressure (high altitude), the air will contain less oxygen, and breathing will therefore be more difficult.
Air pressure can also indicate certain weather conditions because of the convergence or divergence of air on a global scale. Where air converges, the mass will be greater and the pressure will be high - a high pressure. Where air diverges, the mass will be small and the pressure will be low - a low pressure. Different weather conditions are associated with the different pressures. These pressures do not remain constant for very long, because nature always needs to be balanced.
Pressure is measured in millibars or pascals with a barometer.
Wind is actually the movement of air particles from a high pressure to a low pressure in order for the atmospheric conditions to be balanced. The greater the difference in pressure between the two areas, the stronger the wind. Wind closer to the ground is slower than wind higher up, because wind along the ground is slowed by friction. Wind direction is measured by means of a wind vane and the wind is named after the direction from which it originates. An anemometer is used to measure wind speed in knots.
At different temperatures the air can contain different amounts of water vapour. Warm air can hold more water vapour than cooler air. If at a certain temperature, the air contains the maximum amount of water vapour it can hold at that temperature, the air is said to be saturated. If the temperature then drops (the air rises, etc.), the amount of water vapour it can hold will decrease as the temperature decreases. Because it still contains the same amount of water vapour it did originally, but at a new, lower temperature, there is too much water vapour for the air to hold. The excess water vapour then condenses to form clouds and falls to the earth as rain.
Relative humidity is the amount of water vapour in a column of air, expressed as a percentage of the total amount of water vapour the air can hold at that temperature. For example, if the air is saturated (holding the maximum it can hold) then the relative humidity is 100%.
The amount of water vapour in the air is measured with a dry bulb thermometer in grams per cubic metre.