How it blows

Hi,
tommorow I am writing test on geography, it will be on pedosphere, hydrosphere and atmosphere and since I forgot to learn atmosphere I decided that I will make post about winds and how air circulates on Earth so I can remember it.


The most important thing is that air wants to go from area of high pressure to area with low pressure, this is practicly the key thing in weather forecast because wind also takes rainfall with it and it is key when forming storms.

So it is important to know where are those areas of high and low pressure.

Low pressure areas create when there is warm air which expands thus lowering the pressure and then it rises. This of course happens on equator so there is low pressure always moving just a little bit north and south during year as the angle towards Sun changes.

On poles on the other side is high pressure because cold air falls down and its density increases because it is heavy.

Whole process is not so simple there is no gradient between equator and poles because there are lot other things that change this.

Key picture of winds on Earth

The picture above shows how air travels on Earth, I will start with the area of equator. So there is low pressure because of hot air. It raises and as anti trade wind (in Czech we call it anti-pasát) it goes north or south because the air is pushed by the new air coming. At about 40° the air loses all its humidity and temperature so it goes down. Because it is so dry at those areas deserts tend to create. This is area of high pressure compared to equator so the air goes south as trade wind. It is called like this because it helped sailors when they wanted to trade something. Around equator those winds are weaker and weaker and the air goes up because it is warmer. This area is called doldrums. It is famous for leaving boats powered by wind for weeks on same place, sometimes even killing whole crews since they can not move without wind.

This process described above is called Hadley cell.

Same thing happens around poles except the high pressure area is around poles so winds blow from there. This for example creates what is called tornado valley which is area in USA where hot air from south and cold air from Canada meet to create winds moving spiraly on small area: tornadoes.

It gets much more complicated on what is called Ferrel’s cell which is area between Hadley and Polar cell. Here lot of difference is also made by area above oceans and above land.

Because of Coriolis effect (Earth rotating), trade winds are turned towards west because of their inertia, Earth rotates from west to east.

Dragallur

Check out those two video for coriolis effect and how water turns in toilet:

 

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Leap seconds

Hi,
I was just reading post by Science Geek and then I realized that I was learning some stuff for school on similar topic so I decided to make a short post about it.
Today I will write about leap seconds.


Look at the picture on the left. Now look at it again if you did not find the strange thing there. Unless you have some kind of strange clock you should not see 60 seconds normally but you should see instead one more minute and 00 seconds.

So lets take a look on what exactly happened here.

So this picture is picture of time when leap second was added to our time because our day was shifting with actual solar day which corresponds to our position with Sun (this gets messier when you see that on this also our orbit and axis have effect).

The problem here is that the rotation of Earth for longer term is unpredictable, of course we are talking about very small amount of time. The thing is that lot of stuff can change the Earth`s rotation: earthquakes, crust moving relatively to core, slowing of the rotation because of friction from tides (about 2ms per century) and many others, actually anything that happens here is slowing Earth rotation down.

There are of course two types of leap seconds but only positive ones were added for now, actually 26 of them and last one on June 30, 2015. This makes some problems in computing because of course all-time running programs with lot of data are not very well prepared to just add one second. This is also why those seconds are always allowed to be inserted two times per year.

On the graph you can see how the time changes (y-axis) through years (x-axis). Those fastest vertical changes are leap seconds. As you can find on Wikipedia on the table with leap seconds, around the year 2006 there were none needed.

Dragallur

Both pictures are from wiki article about leap seconds

How to! 1) Using stars to navigate

Hi,
here it goes, here it comes. Just because of random I just made another series which may not continue anymore but I don`t care I made it just for fun and today I will write about really practical skill if you dont know where the hell you are. You just have to know couple of things.


So I will start with the easiest skill which you probably already know.
It is always crucial to know the constant direction in which you want to walk. If you have compass it should not be a problem unless when you are in the mountains there may appear bubble because of different pressure and it wont disappear again so watch out for this because then it wont be so accurate.

So the easiest thing is to find Polaris or North Star on the northern hemisphere. It is one of the most bright stars and and also Polaris is exactly at the point around which whole sky is rotating so it will always be on the same spot as you can see on the picture with high exposure.


You can find it when extending the big dipper, which is very bright constellation, 5 times.

Polaris will always point to the north and it should rise as you go north and set while you go south. This concept is very useful when measuring your latitude.

For this you need something to measure degrees. I heard that your fist on the length of your arm is about 10° or you can use watch that are not digital because the difference Image titled Navigate by the Stars Step 4between two numbers should be 30°. If you are PRO then you will have sextant of course :D. You should measure 90° on poles and zero on equator.

To know your longitude it is a bit more complicated. You need clockwatch which has some time like Greenwich, just that you know where this time is. Then during day you will measure when the Sun is highest which can be almost anytime since your watch are not on the time zone where you are.

Then because there is 24 time zones you know that for one time zone there is 15° of longitude + you will add half hours or whatever you measured when was the Sun highest. Then you will know how much you moved to west or east. With the method of sextant you can easily measure where is your place on the Earth. I will make sure to try it when it will be clean sky to see how accurate it is. Anyway if you want this to be useful you have to check the map to see the coordinates of some cities.

But you can use any star to orient yourself!
Put two tall things about meter apart. Than line up the tops of the things with any star and wait to what direction it moves.

  • If the star rose, you’re facing east.
  • If the star sank, you’re facing west.
  • If the star moved to the left, you’re facing north.
  • If the star moved to the right, you’re facing south

Btw. for this last one thanks to wikihow article, I did not know that.Image titled Navigate by the Stars Step 8

Also on south to know south, use South cross. Line up the two stars that
are making the T and they should point Alpha Centauri, the closest star and Alpha Centauri points to south.
Dragallur

Polaris photo 1st and 2nd
Sextant photo and South cross photo