Geography - Weather & Climate (EQ1) Flashcards
What is absolute humidity?
Amount of water vapour in the air.
What is relative humidity, its percentages and measuring instrument?
The proportion of water vapour present in the air, in relation to the maximum amount the air can hold at a particular temperature. 100% is saturation point; dew point. Humidity can be measured by the difference in temperature in the psychrometer and a conversion table. The greater the difference, the lower the relative humidity.
What is the formula for relative humidity?
RH = actual amount/max capacity x 100%
What are factors affecting relative humidity?
Availability of water bodies
→ vapour comes from evaporation of water bodies
Availability of vegetation
→ transpiration process + evaporation of moisture from the soil = evapo-transpiration
Temperature
–> The warmer the air, the greater its capacity to hold water vapour, therefore it is less humid. Vice versa.
Higher temperature → higher evaporation of water bodies –> higher RH
How does RH differ from day to night?
During the day, temperature is higher → higher capacity → RH is lower
During the night, temperature is lower → lower capacity → RH is higher
However, high RH can be attained during the day as a result of high rates of evaporation.
How is convectional rain caused?
- Ground heats up
- Surrounding air closest to the ground is heated by conduction
- Being lighter than the surrounding air, the parcel of warm air rises and expands, RH increases
- Air cools as it rises and reaches dew point due to condensation
- Cumulonimbus clouds formed
- Further condensation and water droplets become too heavy
- Rain falls
It is often accompanied by lightning and thunder, has intense rainfalls and for a short duration.
What are the conditions & characteristics of relief rain?
It requires warm, moist air coming from the sea (onshore winds)
and the presence of highland (mountains).
Relief rain only falls on the side it went up the mountain; windward side. There is rain shadow on the other side of the mountain, as well as cold descending dry air.
How is relief rain formed?
- Warm moist air comes in from the sea carried by onshore winds
- Winds are forced to rise up the highland
- Warm air cools, RH increases
- Air reaches dew point and condenses to form clouds
- Condensation continues, water droplets become too heavy
- Rain falls
What is air pressure and its characteristics?
Air pressure: Weight of the air exerted on any exposed surface
Air nearest the ground has the highest pressure due to the weight of the overlying air
Low temperature → high pressure
There is less overlying air near the top of the atmosphere, so air pressure decreases with increasing height
Air will move if there are differences in air pressure from high pressure to low pressure.
The bigger the difference in air pressure (causes air to move), the faster the air moves → stronger wind
What is an isobar?
Line on a map connecting points of similar atmospheric pressure.
How is a sea breeze formed?
Formed during the day.
- Land heats up faster than the sea
- Air above land is warmer, air above sea is cooler
- Air pressure above land is lower (LP) and warm air rises, air pressure above sea is higher (HP)
- Air moves from sea toward land as sea breeze
How is a land breeze formed?
Formed during the night.
- Sea retains heat, land loses heat faster
- Air above sea is warmer, air above land is cooler
- Air pressure above sea is lower (LP), air pressure above land is higher (HP)
- Air moves toward the sea as land breeze
How does wind travel regionally?
Winds do not travel in a straight path, due to the rotation of the earth, leading to the Coriolis effect.
→ Wind in northern hemisphere is deflected to the right
→ Wind in southern hemisphere is deflected to the left
