Physical Geography

What is high and low pressure?

low pressure - seen on isobars with a low centre with pressure increasing outwards, the isobars are closely spaced 

- the ground warms up during the day which heats the air above it, warm air rises, creating low pressure, the air continues to rise, expand and cool (ELR) until it reaches dew point, assuming hydroscopic nuclei are present, condensation occurs and water droplets form clouds

high pressure - high centre point on isographs where pressure decreases outwards (usually starting above 1000) and isobars are further apart 

- after moisture has condensed, air is cooler and denser so sinks back to the surface, near the surface it compresses, heating slightly and any remaining moisture evaporates, the warm air is now extremely dry so no or few clouds can form 

wind - is the movement of air from high to low pressure, air moves out of high pressure in a clockwise direction and due to the coriolis effect, high pressure turns wind to the right as it enters low pressure 

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What is humidity, dew point and relative humidity?

humidity - the amount (in weight) of water vapour per unit of air (specific humidity) 

dew point - when air cools, theres a temperature below which water vapour condenses to water droplets (clouds), that temperature is DEW POINT and usually occurs when air reaches saturation 

relative humidity - warm air can 'hold' more water vapour than cold air, as air cools, relative humidity increases 

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What factors affect the temperature and climate?

temperature depends on the altitude and composition of each layer of the atmosphere

factors affecting climate:

1. latitude (main factor) - due to the earths curviture the equator gets more solar radiation and at the poles the sun is lower in the sky and there is a bigger surface area so it is colder 

2. altitude - the atmosphere is heated through conduction so the ELR occurs, with altitude air pressure decreases and so there are less particles to heat, making it cooler

3. continentality - sea water has a higher specific heat capacity than land so it takes longer to heat up and cool down, affecting the climates near the coasts 

4. ocean currents - Britain has a maritime climate thanks to the Gulf Stream which brings warm and wet weather 

5. prevailing winds (most frequent wind direction) - winds are named after where they come from , southerly winds bring heat and northely winds bring cold, if winds travel over seas it can bring rain fall as they pick up moisture and can create deserts if they travel over lands 

6. albedo - the proportion of solar radiation reflected by a surface, ice and snow create higher albedo 

7. aspect - the compass direction which a slope faces

*aspect and albedo are local factors 

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What is weather, climate, the ELR and the atmosphe

weather - the short term environmental conditions 

climate - the long term environmental conditions 

ELR (environmental lapse rate) - temperatures decrease by 6.5 degrees per km, radiation from the earths surface heats up the lower parts, heating the air which expands and rises, losing energy and cooling 

atmospheric heat budget - light from the sun is shortwave solar radiation, this is absorbed by the ground and coverted to heat energy, this heats the air above, warm, less dense air rises and loses energy as it expands and cools, the atmosphere traps and reflects heat back creating the greenhouse effect 

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What are the 4 layers of the atmosphere?

1. troposphere (0-12km) - temperatures decrease with altitude due to heat from the Earth's surface, there are lots of turbulence (warm air rising and sinking) and clouds (water vapour evaporating from the Earth) 

2. stratosphere (12-50km) - the ozone layer is in the bottom half of the statosphere, it absorbs UV radiation which warms the upper layer so increasing altitude creates increasing temperature

3. mesosphere (50 - 80km) - heated by the stratosphere so increasing altitude creates decreasing temperature

4. thermosphere (80-120km) - temperatures increases with altitude, small amounts of oxygen absorb the UV rays heating this layer up

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