What is relative humidity and how is it related to dew point?

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Multiple Choice

What is relative humidity and how is it related to dew point?

Relative humidity shows how close the air is to being saturated at the current temperature. It’s the ratio of the actual water vapor pressure to the saturation water vapor pressure at that temperature, expressed as a percent. The dew point is a temperature: the temperature at which the air would become saturated (condense) if cooled further without losing moisture. Since saturation depends on temperature, the actual amount of moisture fixes both, so the dew point is the temperature corresponding to that moisture content. When the air temperature falls toward the dew point, the relative humidity moves toward 100%. So the best way to picture it: the dew point reflects how much moisture is present, while relative humidity tells you how close you are to saturation at the current temperature. If there’s a lot of moisture, the dew point is high and RH can be high even at warm temperatures; if there’s little moisture, the dew point is low and RH is lower for the same air temperature.

Relative humidity shows how close the air is to being saturated at the current temperature. It’s the ratio of the actual water vapor pressure to the saturation water vapor pressure at that temperature, expressed as a percent. The dew point is a temperature: the temperature at which the air would become saturated (condense) if cooled further without losing moisture. Since saturation depends on temperature, the actual amount of moisture fixes both, so the dew point is the temperature corresponding to that moisture content. When the air temperature falls toward the dew point, the relative humidity moves toward 100%.

So the best way to picture it: the dew point reflects how much moisture is present, while relative humidity tells you how close you are to saturation at the current temperature. If there’s a lot of moisture, the dew point is high and RH can be high even at warm temperatures; if there’s little moisture, the dew point is low and RH is lower for the same air temperature.

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