# Relationship between atmospheric pressure and relative humidity

### The impact of relative humidity and atmospheric pressure on mortality in Guangzhou, China.

It seems like there is an indirect relationship between air pressure and relative humidity. We thought wet air would have greater air pressure (weigh more) than. How are the dewpoint temperature and relative humidity related, and is there an easy and sufficiently tion of the ambient vapor pressure and temperature or as the ratio of the . (a) Relationship between td and RH for moist air; thick colored. Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air . Buck has reported that the maximal relative error is less than %.

Air at high pressure or lower pressure with the same humidity and temperature would have the same amount of water in it.

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I don't know much about weather, so I can't really say much about the relationship between air pressure and humidity. As I recall though, high pressure seems to keep storms and moisture away whereas storms seem to move into low pressure areas.

This would seem to explain your discovery that humidity in inversely proportional to air pressure. If I can come up with a better answer I'll let you know. I think a better way to think about relative humidity is that it is the ratio between the amount of water in the air and the amount of water that can be stored in the air.

The amount of water that can be in air depends on temperature. Colder air can hold less water than warm air.

It turns out that in a high pressure area, air is flowing out to areas of lower pressure. This air is replaced by air from the upper atmosphere which is colder and thus drier.

Lesson 5.2.2 - Temperature, Air Pressure, and Humidity

So people inside a high pressure area notice that the air is drier than usual. Likewise, low pressure areas draw in warmer, moist air so people in a low pressure area would notice higher humidity. Storms occur when a cold air mass and a warm air mass meet. Since the warm air and cold air don't mix very well, one air mass rises and the other doesn't.

Which air mass rises?

When this air mass rises to high altitude what do you think happens to its temperature? How would this effect its humidity? By the way, I made a mistake before when I was talking about vapor pressure.

A liquid boils at a temperature at which the vapor pressure equals the total pressure over the liquid. As airliners descend from colder altitudes into warmer air perhaps even flying through clouds a few thousand feet above the groundthe ambient relative humidity can increase dramatically.

Some of this moist air is usually drawn into the pressurized aircraft cabin and into other non-pressurized areas of the aircraft and condenses on the cold aircraft skin. Liquid water can usually be seen running along the aircraft skin, both on the inside and outside of the cabin. Because of the drastic changes in relative humidity inside the vehicle, components must be qualified to operate in those environments.

### UCSB Science Line

Cold humid air can promote the formation of ice, which is a danger to aircraft as it affects the wing profile and increases weight. Carburetor engines have a further danger of ice forming inside the carburetor. Aviation weather reports METARs therefore include an indication of relative humidity, usually in the form of the dew point.

Pilots must take humidity into account when calculating takeoff distances, because high humidity requires longer runways and will decrease climb performance. Density altitude is the altitude relative to the standard atmosphere conditions International Standard Atmosphere at which the air density would be equal to the indicated air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground.

An increase in temperature, and, to a much lesser degree, humidity, will cause an increase in density altitude. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.

## The impact of relative humidity and atmospheric pressure on mortality in Guangzhou, China.

Measurement[ edit ] A hygrometer is a device used for measuring the humidity of air. The humidity of an air—water vapor mixture is determined through the use of psychrometric charts if both the dry bulb temperature T and the wet bulb temperature Tw of the mixture are known.

These quantities are readily estimated by using a sling psychrometer. There are several empirical formulas that can be used to estimate the equilibrium vapor pressure of water vapor as a function of temperature.

The Antoine equation is among the least complex of these, having only three parameters A, B, and C. Other formulas, such as the Goff—Gratch equation and the Magnus—Tetens approximationare more complicated but yield better accuracy[ citation needed ]. The Arden Buck equation [19] is commonly encountered in the literature regarding this topic: