Hectopascal (hPa) as seen in weather related reports - info, please!?

Question

I have lived in the relatively non-humid north-western part of South Africa for many years. The heat was terrible, but it was a dry heat that I learned to cope with.

Now, I live in Taiwan - which is extremely humid. Now my question is how does the hPa differ between these two countries? Does the humidity affects the hPa? What is a "normal" hPa for a hot summers day?

In short, I would like more information on how hPa differs in different countries, humidity's affect on hPa, and anything else you could tell me.

But please, don't be too technical - I'm not very scientific orientated.

Thanks!

Answer 1

Cyswxman gave you the correct and full answer. But - just for fun - here are some details.

If you try to measure the pressure of the air, you would see that it is about one kilo per square centimeter. To do that you would need to fill a ten meter long tube with water then close the upper end and bend the other end upward. The water will not come out because it would create vacuum at the closed end. The tube is in equilibrium between the air pressure on one side and vacuum on the other.

That is the reason you can't pump water more than ten meters high with a suction pump.

But a ten meter high instrument to read the air pressure is not practical. So we use mercury that is  also liquid but much heavier. A column of mercury would then be 760 mm high, which is 29.9 inches and what American barometers are graduated in.

The atmospheric pressure has been called one bar. But, after worldwide measurements, it turns out that the actual average is 1.01325 bar. It is then said that the average pressure on earth is 1,013.25 millibars (mb). But then, not so long ago, the Metric system decided to call a millibar for a hectoPascal (hPa), the Pascal being the metric unit of force and the bar not being used anymore except maybe to measure tyre pressure.

So ... hPa is only the pressure and 1,013 hPa is the worldwide average. Anything under that is a low pressure (rain and wind) and anything above that is a high pressure (sun and calm).

Answer 2

There is no difference, in that a hectopascal is the same as a millibar, a unit of pressure.  Air pressure varies across an area, and that variance is what causes wind.  More humid air tends to be less dense, thus the air pressure is typically a little lower.  There is not a "normal" pressure, and it is not unique to any country.