# Atmospheric Pressure

By: trHUrrIXC5MMX , 6:38 PM GMT on March 14, 2013

I'll be working on some weather topics every once in a while, as trying to explain some things which help me out in my career....

By dictionary definition, pressure is the physical force applied against or onto an object, as being stressful or crushing in many cases.

In the atmosphere air determines the pressure, the exact weight of the air concentrated above a certain point tells what the pressure is.
Air has density, believe it or not, therefore it has pressure, just like water.

There are different levels of stress in different altitudes in the atmosphere, in general as you go ascend the pressure decreases.

There are different ways on measuring pressure, mmHg (inches of mercury, as when you see it in weather.com), psi (pounds per square inch), pascals and bars (e.g. 100 bar).

1 bar (it's really 1.01325 bars) equals to the mean sea level pressure (or surface pressure)
So where does the "milibars" come into play? Well, a milli-bar is a 1000th of a bar (bar /1000), so our surface pressure in millibars is 1013.25 mb which equals to 29.918" (inches of mercury, mmHg)
Of note: millibars=hPa
^ It might sound confusing to you, but that's what it is

High pressure systems and low pressure systems are called so because of their air weight pressure.
Low pressure systems are so because they have a lower pressure than the surrounding areas at the surface. The lower pressure, the less crushing the force is. In hurricanes, by getting deeper into the topic, the pressure becomes a serious matter.

Image 1: Powerful Major Hurricane Wilma as being the strongest hurricane ever in the Atlantic Ocean. The NHC did not believe the storm had attained a pressure of 882mb after the Hurricane Hunters reported, it had to be calibrated first...

"BASED ON DROPSONDE AND FLIGHT-LEVEL DATA FROM AN AIR FORCE PLANE
JUST RETURNING FROM ITS MISSION IN WILMA...THE MINIMUM CENTRAL
PRESSURE IS ESTIMATED TO BE 882 MB...26.05 INCHES. THIS IS THE
LOWEST PRESSURE ON RECORD FOR A HURRICANE IN THE ATLANTIC BASIN"

A pressure of 882 mb (-131.25mb from the mean surface pressure) has been the lowest pressure ever recorded in a low pressure system.
Remember that low pressure systems full everything in towards them, that's what causes the low pressure values. Think of a vacuum cleaner.

That's still far from the all time's pressure record set by Typhoon Tip in 1979 of 870 mb.

In the other hand, high pressure systems, expand the air away from them, "cleaning the area" what's why in most cases is clear and sunny outside, however, it could be warm or cold. High pressures cover a wider area than a low pressure. The flow from a high pressure is much denser and heavier which allows to pull anything away.

If you were to place a 1070mb high pressure system over you, it would equal to 2,235,000 pounds of weight per foot. Which would crush you to nothing, killing you :(. Yes that is how much weight the air can hold, even more. No doubt that density can clear away any clouds or thunderstorms.

As I mentioned before, the higher you go up into the atmosphere the lesser amounts of pressure there are. That is called Pressure Altitude

Let's start below sea level (thousands of feet below)

Image 2:Mariana Trench.

The Mariana Trench is so deep, over 36,000 feet (6.8 miles), that it's very difficult to explore... Why? The pressures in the deepest areas are so high: over 1,086,000 mb! Which can totally dissolve anything in a matter os seconds. The pressure there is extremely high and highly lethal to any living organism. Anything there must be strong enough to support the heaviest weights of the water and gravity.

Image 3: Surface

At the surface, the pressure is much lower than that at the Mariana Trench.
1013.25 mb or hPa. This is the sea level pressure.

Image 4: Burj Khalifa... the tallest man-made building in the world. 2,722 feet!

Going a little higher. The Burj Khalifa is nearly 3,000' above sea level, the pressure is less than that at the surface. Over 900 hPa or mb the pressure would be.
I want to go there one day...acrophobia is not a problem for me..

Image 5: Mount Rainier seen over Tacoma, WA.

A jump to nearly 15,000 feet would take you over the summit of Mt. Rainier. The pressure there is nearly 570 mb, and decreasing with more height.

Image 6: Mt. McKinley

At 20,000ft you'll be over the tallest mountain in North America. Pressure near 465 mb.

Image 7: Mount Everest. The highest peak on earth.

A big jump to nearly 30,000ft (5.68 miles up) would take up to the top of the Himalayas. The pressure there is very low, 300 mb.

Anything above this is much below 230 mb.

If you want to find an additional pressure value not listed here or making a conversion you can go here to find out yourself.

Pressure is key to determine how strong a cyclone or anticlone is.

For tropical cyclones, pressure can depend heavily on the size of a storm and how strong it is. In recent years it was proven that larger cyclones have lower than normal pressure. By lower than normal I mean pressures that stronger storm usually have.

Hurricane Ike, Alex, Irene, Isaac, and Sandy were examples of large storms which had lower than normal pressures to what their wind intensity was originally. That is why the SSHS is only now for measuring winds, not pressure or surge. We now very well what happened with Ike and the SSHS surge.

Just remember that low pressure systems are "suckers" and high pressure "snow plowers".

___________________________________

Hurricane Season 2013
By the way...I'll be still updating my chart every once in a while, please keep sending me your thoughts about this season if you haven't yet, you don't have to do it now if you want until May or June.

My 2013 Hurricane Season Outlook

MaxWeather
Tropical Awareness

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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5:17 AM GMT on March 16, 2013
 trHUrrIXC5MMX has created a new entry.
##### 23. trHUrrIXC5MMX
2:36 AM GMT on March 16, 2013
 Northern US Snow.... mainly a trace to 3" across the Great Lakes... over 3" from Twin Cities and west as well as portions of Northern New EnglandThe shade for NYC and Mid Atlantic represents the potential for a storm next weekclick for larger size.
Member Since: December 31, 1969 Posts: Comments:
##### 22. trHUrrIXC5MMX
4:36 PM GMT on March 15, 2013
 thanks TA...yes it's much better...forget imgur...lol
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##### 21. TropicalAnalystwx13
4:21 PM GMT on March 15, 2013
 Max, if you've never used imageshack, I recommend making an account (there's a free version) and using it. The uploads come out a lot cleaner.For example...w/ imgur:w/ imageshack:
Member Since: December 31, 1969 Posts: Comments:
##### 20. trHUrrIXC5MMX
4:12 PM GMT on March 15, 2013
 since today is my day off...making another update to my chart...Grothar is alongside Ped.fun fact: originally this picture is about 65"x 70", a very big size image to store. I just shrink it to 15x20" to be able to upload.Also, all my maps are about the same original size, over 50". In some computers of yours the image could cover the whole screen while looking at it. I don't save this stuff I do in photoshop in my computer, it'll slow it down. I bought a 1 TB external storage long ago, everything is stored there. click image for larger size
Member Since: December 31, 1969 Posts: Comments:
##### 19. trHUrrIXC5MMX
3:30 PM GMT on March 15, 2013
 Quoting TropicalAnalystwx13:Perhaps you could get rid of the UK then since they're the only TSR.We don't go around saying USA National Hurricane Center. :Pok, I'll do that... k, not too many would know where TSR is from though. imo
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##### 18. TropicalAnalystwx13
3:28 PM GMT on March 15, 2013
 Quoting trHUrrIXC5MMX:actually Im aware of that...but as you see if I place the O there... RISK is going to move down to a second line (it won't fit all in one).Perhaps you could get rid of the UK then since they're the only TSR.We don't go around saying USA National Hurricane Center. :P
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##### 17. trHUrrIXC5MMX
3:24 PM GMT on March 15, 2013
 Quoting TropicalAnalystwx13:Just make sure you change "UK TRPICAL STORM RISK" to "UK TROPICAL STORM RISK" ;-)actually Im aware of that...but as you see if I place the O there... RISK is going to move down to a second line (it won't fit all in one).
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##### 16. TropicalAnalystwx13
3:21 PM GMT on March 15, 2013
 Quoting trHUrrIXC5MMX:thanks...i'll add you inJust make sure you change "UK TRPICAL STORM RISK" to "UK TROPICAL STORM RISK" ;-)
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##### 15. trHUrrIXC5MMX
2:12 PM GMT on March 15, 2013
 Quoting Grothar:Really nice blog, Max.18 - 6 - 3thanks...i'll add you in
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##### 14. Grothar
2:11 PM GMT on March 15, 2013
 Really nice blog, Max.18 - 6 - 3
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##### 13. trHUrrIXC5MMX
2:05 PM GMT on March 15, 2013
 Quoting originalLT:Nice discussion Max. One sentence I'm not sure I understand. It is in the paragraph right above the first picture you show, the hurricane photo. . You state, "The lower the pressure, the more crushing the force is". I think it would be the opposite. Lower pressure allows the air to rise, forming clouds and precipitation, not crushing it down. Maybe I read this wrong?yep you are correct, I sometimes get confused with that too... high and low
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##### 12. originalLT
2:02 PM GMT on March 15, 2013
 Nice discussion Max. One sentence I'm not sure I understand. It is in the paragraph right above the first picture you show, the hurricane photo. . You state, "The lower the pressure, the more crushing the force is". I think it would be the opposite. Lower pressure allows the air to rise, forming clouds and precipitation, not crushing it down. Maybe I read this wrong?
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##### 11. trHUrrIXC5MMX
1:59 PM GMT on March 15, 2013
 my updated list of the 30 people who have contributed...click image for larger view... link should work
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##### 10. trHUrrIXC5MMX
1:48 PM GMT on March 15, 2013
 Quoting pcola57:Wow!!Great explanation of pressure..Some of those facts I didn't know..Very well done my friend.. :)yep, thanks for stopping by, reading it and for showing interest my friend!:) I'll be doing some of these, I plan on doing one about winds and the SSHS this weekend
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##### 9. pcola57
1:46 PM GMT on March 15, 2013
 Wow Max!!Great explanation of pressure..Some of those facts I didn't know..Very well done my friend.. :)
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##### 8. trHUrrIXC5MMX
2:57 AM GMT on March 15, 2013
 Alright...I'll have my chart updated tomorrow. got some mail from some others to be included to. Still wanting some more to join.
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##### 7. trHUrrIXC5MMX
10:57 PM GMT on March 14, 2013
 that does not make sense to me... the track is going to eventually make the storm just go backwards the same path it took going forward?
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##### 6. TropicalAnalystwx13
9:16 PM GMT on March 14, 2013
 JFV wanted me to relay his numbers to you...16-8-4.
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##### 5. trHUrrIXC5MMX
7:28 PM GMT on March 14, 2013
 Quoting MAweatherboy1:Thanx Max! Euro is showing a real messy storm for the NE early/mid next week. Looks like snow to start, possibly a period of ice and sleet, and likely rain to finish. Blah.GFS is more just rain.yeah, I saw something about that. Yesterday night TWC was calling for snow across the area next week from a storm...
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##### 4. MAweatherboy1
7:13 PM GMT on March 14, 2013
 Thanx Max! Euro is showing a real messy storm for the NE early/mid next week. Looks like snow to start, possibly a period of ice and sleet, and likely rain to finish. Blah.GFS is more just rain.
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##### 3. trHUrrIXC5MMX
7:07 PM GMT on March 14, 2013
 Thanks WuGirl, Hydrus :)
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##### 2. hydrus
7:06 PM GMT on March 14, 2013
 Cool stuff..Great Pictures.:)
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##### 1. WunderGirl12
6:48 PM GMT on March 14, 2013
 Thanks Max for the updated blog!! :) Can you check out my new blog post?? Thanks!
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