Define absolute humidity, specific humidity, and mixing ratio.

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Multiple Choice

Define absolute humidity, specific humidity, and mixing ratio.

Absolute humidity measures how much water vapor is in a given volume of air, expressed as the mass of water vapor per unit volume (for example, grams per cubic meter). It changes with air density, so warm, less dense air can hold the same amount of water vapor in a larger volume, leading to lower absolute humidity even if the water amount hasn’t changed. Specific humidity is the ratio of the water vapor mass to the total mass of moist air (the water plus the air itself). It’s a mass-based fraction that remains meaningful as the air parcel expands or compresses, since the denominator is the entire moist air mass. Mixing ratio is the ratio of the water vapor mass to the mass of dry air (water-free air). This excludes the water vapor from the air mass in the denominator and is convenient in many thermodynamic equations because it is more directly related to the amount of moisture carried by the air. So the best description is: absolute humidity = mass of water vapor per volume of air; specific humidity = mass of water vapor per total moist-air mass; mixing ratio = mass of water vapor per mass of dry air. For example, a small amount of water vapor in a large volume yields low absolute humidity, while the same vapor adds to the specific humidity and mixing ratio relative to the total or dry-air masses.

Absolute humidity measures how much water vapor is in a given volume of air, expressed as the mass of water vapor per unit volume (for example, grams per cubic meter). It changes with air density, so warm, less dense air can hold the same amount of water vapor in a larger volume, leading to lower absolute humidity even if the water amount hasn’t changed.

Specific humidity is the ratio of the water vapor mass to the total mass of moist air (the water plus the air itself). It’s a mass-based fraction that remains meaningful as the air parcel expands or compresses, since the denominator is the entire moist air mass.

Mixing ratio is the ratio of the water vapor mass to the mass of dry air (water-free air). This excludes the water vapor from the air mass in the denominator and is convenient in many thermodynamic equations because it is more directly related to the amount of moisture carried by the air.

So the best description is: absolute humidity = mass of water vapor per volume of air; specific humidity = mass of water vapor per total moist-air mass; mixing ratio = mass of water vapor per mass of dry air. For example, a small amount of water vapor in a large volume yields low absolute humidity, while the same vapor adds to the specific humidity and mixing ratio relative to the total or dry-air masses.

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