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Earth and Space Sciences · 术语表

什么是 Vapour pressure; mixing ratio; specific humidity？

又称： vapour pressure · mixing ratio · specific humidity

Definition 21.1 University Earth and Space Sciences — Year 2 · 第 21 章 — Atmospheric Thermodynamics

The vapour pressure $e$ of moist air is the partial pressure of its water vapour. Its mixing ratio is $r = m_v/m_d$ , the mass of water vapour per unit mass of dry air in the same volume, and its specific humidity is $q = m_v/(m_d + m_v)$ , the mass of vapour per unit mass of moist air. Both are usually given in grams per kilogram.

示例

Example 21.4 (The air at Norman)

At the ground the sounding gives $p = 971.1\,\mathrm{hPa}$ , $T = 19.0\,{}^{\circ}\mathrm{C}$ and a dew point of $18.5\,{}^{\circ}\mathrm{C}$ . The vapour pressure is the saturation vapour pressure at the dew point, $e = e_s(18.5\,{}^{\circ}\mathrm{C}) = 21.5\,\mathrm{hPa}$ (Proposition 21.5 below). Then $r = 0.622 \times 21.5/(971.1 - 21.5) = 14.1\,\mathrm{g}/\mathrm{kg}$ , $q = 13.9\,\mathrm{g}/\mathrm{kg}$ , and $T_v - T = 0.61 \times 0.0141 \times 292.15\,\mathrm{K} = 2.5\,\mathrm{K}$ : this air is as light as dry air two and a half degrees warmer.

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