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River Science: Relative Humidity

Mouse over to use the sling psychrometer.
Andrew uses a sling psychrometer.

Relative humidity levels represent the amount of water vapor circulating in the air. (In a sense, relative humidity is the mirror opposite of dissolved oxygen levels in the water.)

Unlike some weather phenomena, humidity has little effect on the Half Moon itself, but the same cannot be said of its crew -- particularly when high humidity tips over into precipitation.

To study humidity levels, we use a sling psychrometer (pictured) and/or a whirling hydrometer. The sling psychrometer contains both wet and dry bulb thermometers. By twirling the psychrometer around for 60 seconds, its user induces evaporation from the wet bulb, cooling it. The resulting temperature differential between the wet and dry bulbs can be used to measure humidity -- the drier the air, the cooler the wet bulb becomes. The whirling hydrometer uses a similar method, but utilizes a wind-up motor to automate the process.

Mouse over to put Peter to work.
Peter uses a sling psychrometer.

Combining relative humidity and barometric changes allows us to accurately predict coming weather fronts, the frequent bearer of stormy weather conditions.

On this Voyage of Discovery, Luke and Peter opted to study relative humidity for their student presentation; we also collected humidity data for the Deck Log.

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