How Does Altitude Affect Humidity Sensor Readings?

In summary, the conversation discusses obtaining the absolute humidity profile by correcting the output of a humidity sensor on a weather balloon. The equations for relative humidity and absolute humidity are mentioned, as well as the concern for accounting for the changing density and atmospheric pressure with altitude. The question of whether atmospheric pressure/vapor pressure is a constant is raised, and the importance of accurately measuring atmospheric pressure is emphasized. The conversation also touches on the relationship between vapor pressure and temperature.
  • #1
oobgular
8
0

Homework Statement


So I sent a humidity sensor up in a weather balloon, which gave a reading for relative humidity. I eventually want an absolute humidity, but I am unsure whether I need to correct the output based on the changing density and atmospheric pressure with altitude.

Homework Equations


As I understand it:
RH = (% volume of water) * atmospheric pressure / vapor pressure.
AH = mass of water / volume of air.

The Attempt at a Solution


I want to obtain the %volume of water, and multiply by the density profile of air to obtain the absolute humidity profile.

The vapor pressure changes with height (I think) since the temperature and density changes, moving you to a different spot on the vapor dome. The atmospheric pressure also changes. So is atmospheric pressure / vapor pressure a constant? If not, how can I account for that to get the % volume of water?

Thanks!
 
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  • #2
Do you know how to get the atmospheric pressure as a function of altitude?
 
  • #3
Yes, I can just assume the exponential atmosphere. It's the vapor pressure I'm confused about-- doesn't it change with temperature and density as well?
 
  • #4
oobgular said:
Yes, I can just assume the exponential atmosphere. It's the vapor pressure I'm confused about-- doesn't it change with temperature and density as well?
It changes with temperature only.
 
  • #5
You can get a more accurate pressure profile by measuring it directly, or by knowing the temperature profile and applying the barotropic equation.
 

FAQ: How Does Altitude Affect Humidity Sensor Readings?

1. How does humidity change with altitude?

The amount of water vapor in the air decreases as altitude increases. This is because colder air at higher altitudes can hold less moisture than warmer air at lower altitudes. As the air rises, it cools and the water vapor condenses into clouds and precipitation, resulting in lower humidity levels.

2. What is the relationship between humidity and altitude?

The relationship between humidity and altitude is inverse. As altitude increases, humidity decreases, and vice versa. This is due to the changing temperature and pressure of the air as it moves up and down the atmosphere.

3. Why does humidity decrease with altitude?

Humidity decreases with altitude because of the decrease in air temperature and pressure. As the air rises, it expands and cools, causing the water vapor molecules to condense and form clouds. This process leads to a decrease in the amount of water vapor in the air and a decrease in humidity levels.

4. How does change in humidity with altitude impact weather patterns?

The change in humidity with altitude plays a crucial role in the formation of weather patterns. As air rises and cools, it can reach its dew point, causing water vapor to condense and form clouds. These clouds can lead to precipitation, such as rain or snow, which can influence weather patterns and climate in a specific region.

5. Is there a specific rate at which humidity changes with altitude?

There is no specific rate at which humidity changes with altitude, as it can vary depending on different factors such as temperature, pressure, and wind patterns. However, in general, humidity decreases by about 3% for every 1000 feet increase in altitude.

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