The what, where and whys of weather

I know this sounds like a silly question, we all know what weather is don’t we? But I want to use this space to separate weather from climate, something which not everyone knows or has thought about. I will also look, very briefly, at how weather comes to be.

What?

Weather is the day to day conditions of a particular place eg it is dry and cloudy in York today.

Climate is the average weather conditions over a long period of time, say 30 years. So the climate in the desert can be dry and hot but that does not mean you won’t get a wet day. This is why climate change deniers are wrong when they cite weather as proving climate isn’t changing.

The most common types of weather on earth are wind, cloud, rain and other precipitation. There are also less common events which have a much greater impact, that is natural disasters such as hurricanes.

Where?

Well, a more detailed definition is that weather is the state of the atmosphere, primarily the lowest level that is the troposphere. Weather fluctuates and is hard to predict because small changes make huge differences.

So weather is the effects of atmospheric activities.

Why and how?

This is where we’re getting a bit more technical and I’m testing my understanding of weather!

To start with, we need to understand the global circulation system. We all know the sun warms the earth and that the sun’s energy is concentrated on the equator and most dispersed at the north and south poles. With me so far? Good.

What you might not know (I’m assuming I have a range of readers here and you aren’t all experts!) is that nature likes things in balance and acts to rebalance them if they aren’t in equilibrium. So nature tries to make the poles warmer and the equator cooler. This, plus the earth’s rotation, creates six (three per hemisphere) circulation cells a closed loop in which air circulates. This is the global circulation system.

As well as moving heat, these create areas of semi-permanent high and low pressure. This is because air rising creates an area of low pressure and air sinking creates high pressure.

Hopefully you’ve got the idea. Warm air moves towards the cold air and as it does so the cold air moves to the warm air and thus we have wind!

Wind and pressure are important as they move and create other weather. That’s why the weather report is always talking about high pressure and low fronts and the like!

In brief, high pressure suppresses weather development so you get weather which is a bit more stable and tends to be calm, clear or sunny. There can also be cloud and fog which are trapped in the weather system and because it’s steady, don’t leave. Low pressure is more volatile and is when clouds are formed and comes with rain and storms. The interaction of high and low pressure also affects our weather.

One example I found helpful was that of the breeze you find on the coast. Land warms more quickly that the sea so we get an area of lower pressure on land than at sea. Where the two meet, on the coastline, the air from the higher pressure area moves into the lower pressure area, that is from sea to land (remember nature likes balance).

I think most of us have had to study the water cycle at some point in our education so I’m not going to look at how clouds and precipitation is formed, although I will return to clouds and snow later this month. And the other main part of weather, heat, is obviously partly down to the sun and cloud cover and factors like cold winds.

Of course there are other factors which influence things such as the earth turning and the sun hitting earth with different intensities depending on the season but I hope this has given a basic idea.

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