# Basic Geography/Weather

What is weather? I'm sure your mum always complains about the weather! But weather is more than an excuse to moan. Weather affects our health, culture and evolution. I'm sure you've heard about thunderstorms, rain, sun etc., but how do they form? This page tells you all you must know about weather.

## Atmosphere

The atmosphere is anything between 'the ground' and 'space'. The atmosphere is the driving force of the weather, and is vital for the well-being of all life on Earth. But why?

### Layers

The atmosphere is sectioned into different layers. Each layer does different things.

#### Troposphere

The first layer. It extends to 6 miles, slightly higher than Everest. This layer holds the Oxygen we need to breathe and this is the place weather forms. Without weather, we would have no rain, how could we live without rain?

#### Stratosphere

The second layer. Extends from 6-30 miles above us. The Stratosphere is important because The Ozone layer lies in this zone. The Ozone layer protects us from the harmful rays the sun produces.

#### Mesosphere

Not just the layer with a catchy name! This layer extends from 30-50 miles. It doesn't really have any specific importance, but without it, our atmosphere would be a lot thinner, meaning less protection from dangers in space.

#### Thermosphere

This is the last layer of the atmosphere. It extends from 50-310 miles and is the first line of protection against hazards such as meteorites ('space rocks'). There is lots of friction here, which makes it hot enough to burn up most dangers. Temperatures in some areas may be 1000 °c, or even hotter! Past the Thermosphere is 'space'.

## The engine behind weather

What is the engine behind weather? There are three important engines: the sun, convection, and pressure.

### The Sun

The sun is the main reason why some places are hotter than each other. Death Valley, Nevada, experienced the hottest recorded temperature on Earth, at a scorching 57°c- that's nearly as hot as your hot tap. The world's coldest recorded temperature was at Vostock station, Antarctica, which recorded a temperature of -89- colder than your average day on Mars. Death Valley is near the equator, and Vostock is in Antarctica- so the sun must be a big contributor to heat. Earth, although tilted, has a sort of bulge, the equator being at the centre of this 'bulge'. The Arctic diameter is much less than the equator's. So in fact, the equator is closer to the sun than Earth. Another common factor that changes temperature is altitude (how high you are)

### Convection

Warm air is much less dense (the particles are much more spread out) than cold air. In other words, warm air is lighter than cold air. Because warm air is light, it rises, and because cold air is heavy, it falls. The warm air rises to a certain height and becomes cold again (it gets colder the higher into the atmosphere you go); it may condense (turn into liquid) and become rain. Once the cold air warms up by being close to the surface, it starts rising, completing the cycle. Convection is a great engine of weather.

### Air Pressure

Air pressure greatly affects what kind of weather we experience. There are two types of air pressure: high pressure and low pressure.

#### Low Pressure

This is the type of weather that usually means stormy weather. Warm air is much less dense than cold air, so it rises. As it rises, the air cools, condensing to form clouds. Water vapour condenses in the clouds to form rain.

#### High Pressure

Although high pressure usually means calm, settled weather, high pressure is usually cooler than low pressure. Cold air is much denser than warm air, so it sinks. You end up with settled, but cool, weather- shame you can't get the best of both!

## Types of weather

There are many types of weather that we experience in our daily lives: you sunbathe when it is hot and sunny; and you put your coat on when it rains and becomes cold, we all have a pretty good general idea of weather- but you may not know how they form. We are going to look at the effect of features on local weather.

### Wind

We all experience wind. Wind is basically the movement of air- but how are some winds different to others?

#### Sea Breezes

The sea takes longer to heat up than land. This makes the air over the land warmer. The warmer land air rises over the sea, and the air above gets replaced by the cooler sea air, creating sea breezes. Land breezes are the reverse, and happen because the sea also takes longer to cool.

#### Valley and Mountain Winds

The sun heats up the air over Valley Slopes, making the warm air rise, and have a lower pressure than the air at the same level over the valley, creating the breeze. Mountain winds are simply the reverse of Valley Winds.

### Precipitation

There are a number of types of precipitation. Although sometimes we moan about it, it's a very important part of life of about every life form. The types:

#### Rain

This forms from layered clouds. Clouds, caused by condensation of water in the air, hold small ice droplets, caused by condensed water vapour. When the ice droplets fall through the cloud to a layer above 0°c, the droplets melt into drizzle or rain.

#### Drizzle

Simply rain, but with smaller water droplets.

#### Hail

In thunderclouds, ice droplets falling may be caught in strong updrafts, they collide with many other ice droplets, growing larger and larger. Some hailstones may be bigger than golfballs and may damage cars.

#### Snow

If it is really cold, the ice droplets may not melt as they fall through the clouds, so they land as snow. The temperature effects what the snow is like: the shape and hardness.

#### Sleet

Sleet are small drops of snow like drizzle is small drops of rain. This is when rain falls through cold cloud (below 0°c), sleet is kind of between rain and snow.

#### Frost

Frost is the cold white sheets on grass, and gives a beautiful crispy texture. There are two types of frost:

##### Hoar Frost

This is the most common type of frost and forms in two ways:
1. Dew freezes on grass and other surfaces
2. Water vapour freezes before turning into Dew.

##### Rime Frost

Less common. This is when liquid water below freezing point (0°c) in fog touch a surface below freezing point and finally freezes into ice.

### Thunderstorms

There is something about a Thunderstorm that fascinates; perhaps the boom of a thundercloud, or maybe the danger of a lightning strike.

#### Which comes first

A good way of remembering the speed of light and sound is to remember the famous phrase: 'which came first: the thunder or the lightning?'

##### How far away...

Light travels at an astonishing 186,282 miles per second! So we see lightning almost as it happens. But sound travels much slower (but it's still very fast). To estimate how far away lightning is, count the number of seconds between seeing the lightning and hearing the thunder. Divide by 5 to discover the distance by miles (or by 3 for km).

#### How they are formed

The stages of a thunderstorm.
1. A Cumulus cloud grows. Updrafts develop, preventing precipitation from falling.
2. Downdrafts develop, precipitation forms. Wind, thunder, and lightning occur.
3. Downdrafts cut off updrafts. Cloud begins to collapse. Precipitation stops. Other clouds may form over the shrinking cloud.

### Fog

Fog is formed when the air becomes saturated. Water vapour comes in contact with the ground, condensing to form fog.
NOTE: Mist is light fog

#### Types of fog

There are a number of types of fog. These include Advection fog. This is when warm ocean air is blown across a colder landmass, the vapour falls onto the land. (see convection) Dew is the moisture that can be seen on grass or other surfaces on those cold mornings. Like fog, it forms within contact with the ground, direct contact in this case.

### Rainbows

Rainbows are present when the sun is out and it is raining at the same time. The science of a rainbow is quite complicated: put simply, sunlight rebounds of the raindrops, extracting all the sunlight's colours, forming the famous bow.

## Quiz

* What part of the map do the storm warnings seem to be centred?
* In which direction is the Hurricane moving in?
* Using the scale, how far does the storm seem to be moving in a day;
* What does this mean about the speed?

## Answers

* The coast/ beach
* North
* 250 miles
* Roughly 10mph

## References

Weather, Reader's Digest

## External Links

Weather extremes and useful info