Wind

Wind is the movement of air. 

Wind occurs when air moves from an area of high pressure to an area of low pressure

Pressure gradient is the difference in air pressure between two locations. The greater the pressure gradient, the faster the wind speed

Wind is measured by its speed, direction and frequency

Wind speed is the rate of movement of air measured in km/h(kilometer per hour) using an anemometer 

Wind direction is the direction from which the wind blow measured using a wind vane. The wind vane points to the direction from which the wind is blowing 

Wind frequency is the percentage of time where a wind blows from one particular direction. The direction where the wind blows the most frequent is known as the prevailing wind.

Wind direction and frequency is recorded in a wind rose.

Sea Breeze

In the day, the land is warmer than the sea, since the land conducts heat faster than the sea. This results in a low pressure at the land and high pressure at the sea

Land Breeze

At night, the sea is warmer than the land, since the sea loses heat slower than the land. This results in a lower pressure at the sea and a higher pressure at the land

Monsoon Winds

Monsoon winds are regional wind patterns that reverse direction seasonally. There is the southwest monsoon and the northeast monsoon

Southwest monsoon*

Take place from June to September.

Northeast Monsoon*

Take place from October to February

*This is the name of the winds only at the Northern hemisphere!

The monsoon wind doesn't blow in a straight direction due to the Coriolis effect. The Coriolis effect is a force produced by the rotation of the earth. This force change the direction of winds. Therefore, monsoon winds doesn't blow in a straight direction and will change i's direction when it crosses the equator.

Coriolis Effect

Air Pressure

Air pressure is the force exerted on a unit area of the Earth's surface by the mass of air above it.

Air pressure is measured using a barometer, measured in millibars (mb).

Air pressure is considered high if it is more than 1013 mb and considered low if it is less than 1013 mb

The measurement of air pressure can be used to produce a weather map or a synoptic chart.

Factors Affecting Air Pressure

Altitude

The higher the altitude, the lower the air pressure

At a higher altitude, there is a smaller mass of air above compared to the mass of air at a lower altitude. Therefore, the air is less dense so the air pressure is lower



Rainfall

Precipitation is the fall of water, in any form, from the atmosphere to the surface of the earth. There are 4 types of precipitation-hail, snow, sleet and rain
Rain is the most common rainfall in the tropics. Areas with an annual rainfall of above 1500mm are classified as having high rainfall; areas with an annual rainfall of below 250mm are classified as having low rainfall.
Rainfall is measured in millimetres using a rain gauge
There are 2 types of rainfall

Conventional Rainfall

Conventional rainfall occurs when the earth's surface is intensely heated up. This rainfall is common in the tropics as it receive a great amount of sunlight. Conventional rainfall often have thunder and lightning, last for a short time and rains intensely

 

Relief Rainfall

Relief Rainfall occurs when moist air is forced to rise over high landforms. This rainfall is common at places with high landforms with a large water body next to it.

 

 

Cloud

Clouds are visible mass of water droplets or ice crystals suspended in the atmosphere. Clouds are formed when evaporation takes place, causing water to evaporate and rise up. As the air rises up, it starts to cool. When the water vapour rise up to the air at the dew point temperature, the water vapour will condense on tiny particles, known as condensation nuclei. The condensed water droplets will bump into each other and become larger in a process known as coalescence, which forms clouds.

Relative Humidity

Relative humidity is the ratio of the actual amount of water vapour in the air to the maximum amount of water vapour the air can hold;

Relative humidity(%)= Actual Amount of water vapour in the air(g/m³)/Maximum amount of water vapour the air can hold(g/m³) × 100

Relative humidity is measured using a sling psychrometer

When the air holds the maximum amount of water vapour the air can hold, the relative humidity is 100% and the air becomes saturated. The temperature at which saturation occurs is known as the dew point temperature. Condensation will occur at the dew point temperature.

 

Factors Affecting Relative Humidity

Amount of Water Vapour in the air

The more the amount of water vapour in the air, the higher the relative humidity

Since relative humidity is the amount of water vapour in the air divided by the maximum amount of water the air can hold, then it would be more humid if the amount of water vapour in the air increases. 

Example, if the air can hold a maximum of 10g/m³ of water vapour, and that the air has 5g/m³ of water, the relative humidity would be 50%. If there is more water vapour in the air, example, the amount of water vapour in the air becomes 7.5g/m³, and that the maximum amount of water vapour the air can hold remains the same, then the relative humidity becomes 75%.  

 

Temperature

The lower the temperature, the higher the relative humidity

 Example, the amount of water vapour in the air is 15g/m³ and at a temperature of 35°C, the maximum amount of water vapour the air can hold is 30g/m³. Therefore, the relative humidity would be 50%. If the temperature drops to 15°C, and that the maximum amount of water vapour the air can hold drops to 20g/m³, then the relative humidity would increase to 75% 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Temperature

Temperature is the degree of hotness or coldness of a place, determined by the amount of energy from the sun that reaches the Earth. Energy from the sun travels through the atmosphere and the earth surface absorb the energy and warm up, in turn heats the atmosphere. In the study of weather, 20°C and above is considered high temperature; 10°C and below is considered low temperature. A temperature range of more than 15°C is considered a large temperature range while a  temperature range of less than 10°C is considered a small temperature range
Mean daily temperature is the sum of total hourly temperature divided by 24
Diurnal temperature range is the difference between the maximum and minimum temperatures recorded in a day
Mean monthly temperature is the sum of total daily temperature divided by the number of days in the month
Mean annual temperature  is the sum of total monthly temperature divided by 12
Annual temperature range is the difference between the maximum mean monthly temperature and the minimum mean monthly temperature in the year

Factors Affecting Temperature

 

Latitude→

Example, in Singapore(With a latitude of 1°N), the temperature range from 24°C to 34°C
In South Korea(With a latitude of between 33°N and 39°N), the temperature range from -20°C to more than 30°C
In Antarctic(With a latitude of between 63.5°S and 90°S), the temperature range from less than -80°C to more than 5°C
 

Altitude→
Temperature decreases with increasing altitude

Generally, every increase in 1000 m of altitude results in the temperature to decrease by 6.5°C

Explanation 1

Explanation 2

Longwave radiation emitted by the Earth's surface is being absorbed by greenhouse gases. When greenhouse gases absorb the heat emitted, the heat is trapped and this warms the atmosphere. There is more greenhouse gas near the Earth's surface as they are denser than air, so there is more heat absorbed by the greenhouse gases near the Earth's surface. Therefore, it is warmer at lower altitude

Explanation 3



The air is less dense at higher altitudes. Less dense air absorbs lesser heat emitted from the Earth's surface through Longwave radiation compared to dense air. Therefore, at higher altitude, where the air is less dense, lesser heat is absorbed, so it is cooler at higher altitude

Example, at the base of Mount Kilimanjaro, the temperature is around 19.5°C. However, at it's peak, 5895m high, the temperature is around -18.8°C

Distance from the sea→

Example, in Anchorage, Alaska(A city at the coastal area of Alaska), the temperature ranges from 14°C to -9°C
In Fairbanks, Alaska(A city at the inland area of Alaska), the temperature ranges from 16°C to -24°C

 

Cloud Cover→

Example, in Singapore(With a cloud cover of 90%), the daily temperature range is from 24°C to 34°C
In the Atacama Desert(With a cloud cover of nearly 0%), the daily temperature range is from -0.5°C to 47°C