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I Atmospheric pressure vs elevation understanding problem

  1. Apr 27, 2017 #1
    My wife has a medical condition where her symptoms are reduced at a higher elevation. I have done some study about the relationship between elevation and atmospheric pressure. My understanding is that the higher the elevation, the lower the atmospheric pressure.

    Looking at a graph of elevation vs pressure, or a chart, it seems to me that at sea level the pressure would be 14.7psi and at say 7000 ft., such as Santa Fe, NM., the pressure would be 11.3psi. Or if in.Hg. it would be 29.9 vs 23.1.

    Now for the problem that I am having trouble understanding. If I check the weather channel say now, it shows the barometric pressure in Panama City Beach, Fl. is 29.87 in. At the same time the pressure in 29.56 in.

    Why are they so close when it seems that they shouldn't be? I know that if my wife was to go to Panama City Beach or for that matter anywhere that the elevation is close to sea level she sometimes passes out. And in Santa Fe when we were on vacation recently she is much better. By that I mean she can function and do some things but still very limited. But that is a whole different conversation.

    I am desperately looking for understanding of why these posted barometric pressures are not what I expect to see.

    I currently live in NC at an elevation of about 2700'.

    Thank you for your time.
     
  2. jcsd
  3. Apr 27, 2017 #2

    Mark44

    Staff: Mentor

    Generally speaking, with everything else being equal, this is true, but see below.
    What you're missing is that atmospheric pressure isn't constant. Weather systems contain air that is at different pressures. "Highs" are regions with higher air pressure, and "lows" are regions of lower air pressure. As these systems move around, the air pressure changes.
    Apparently, there is a high pressure region over Panama City, and a relatively lower one over Santa Fe. This is not unusual.
     
  4. Apr 27, 2017 #3

    boneh3ad

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    Science Advisor
    Gold Member

    In weather reports, the barometric pressure is typically reported as an equivalent sea level pressure. In other words, they are not reporting the true, current atmospheric pressure, but the sea level equivalent of it.
     
  5. Apr 27, 2017 #4
    Ok, that makes sense. Would you venture to explain why the elevation would make a difference the way it does for her. I don't mean explain her medical condition, but more like in terms of a bike rider or mountain climber. The elevation affects their blood pressure correct? That seems to be what helps my wife. The elevation effect on her blood pressure. Do the weather patterns not make a difference in those scenarios? Would blood pressure not be pushed up as elevation increases no matter the weather? I know this is seeming more of a medical question but I am trying to stay focuses on the pressure issue. Thanks
     
  6. Apr 27, 2017 #5
    not really understanding the weather reports part that boneh3ad is talking about. So is the pressure that is posted on the weather channel app not really the atmospheric pressure in that location?
     
  7. Apr 27, 2017 #6
    As I give it more thought, maybe I am looking at this from the wrong point of view. Let's try this. Take a closed loop system such as a persons circulatory system. Closed loop that blood is pumped around in. An increase in elevation increases blood pressure correct? If that is correct, then does elevation effect blood pressure and say spinal fluid pressure reguardless of what the weather system is?
     
  8. Apr 27, 2017 #7

    boneh3ad

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    Science Advisor
    Gold Member

    Correct, the pressure in the Weather Channel app is not the actual barometric pressure. Weather services use what is called a standard atmosphere. Basically, at a given altitude, what is the average barometric pressure expected there. They then take the difference between that pressure and the average sea level pressure to come up with the average pressure difference between a given altitude and sea level. Then, when doing the weather report, they are reporting the actual pressure plus that pressure difference between the average pressures.

    Basically, the only trend that is important to the weather is the departure of barometric pressure from average, so they are just adjusting the measured pressure so that it looks like a departure from sea level pressure rather than from the actual pressure.
     
  9. Apr 28, 2017 #8
    Blood pressure is usually meant to be the difference between the absolute pressure of the blood versus the absolute atmospheric pressure.
    A change in elevation should not directly affect the blood pressure reading. At least, I see no reason for a direct effect just based on pressure differences.

    The body itself can be responsible blood pressure changes, such as when checking blood pressure after exercise.
    Physiological affects can not be reasoned out by air pressure changes, and there may be an inverse relationship between blood pressure and absolute atmospheric pressure, due to for example, less oxygen absorption into the blood at higher elevations, the body then asking the heart to pump more blood thus increasing the blood pressure. An indirect effect if that is the case.
     
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