Moist convection

Convection in a column of a compressible gas is more complicated than it was in our nice simple pan of incompressible water, but I hope it helped to think about the incompressible water case first. To get to convection in the real atmosphere, though, we need to add one more ingredient, and that is latent heat from water vapor. Imagine a source of water vapor at the Earth's surface, so that the air above the ground has a relative humidity of 100%. If we raise this air parcel aloft, it will decompress and cool. The saturation water vapor pressure decreases with temperature (Fig. 5.6), and so the air parcel becomes supersaturated, carrying more water than it wants for equilibrium. The excess water condenses into cloud droplets or perhaps rain. As the water condenses, it releases its latent heat, just as the steam from the teapot burns your skin by releasing latent heat. The effect of the latent heat is to warm the air parcel up a bit in the face of its decompression cooling (Fig. 5.9). We distinguish between the dry and the wet cases by referring to a dry adiabat or a moist adiabat. One more definition: the decrease in

Condensation releases latent heat

Condensation

Condensation e d

Risi adiabat exp

Condensation releases latent heat

Temperature

Rising and expansion

Temperature

Fig. 5.9 The effect of water on the temperature profile in the atmosphere. Air cools as it rises, as in Fig. 5.8. The cooling drives water vapor to condense into droplets, releasing its latent heat to the air. The moist adiabat therefore cools less with altitude than does the dry adiabat.

temperature with altitude in the atmosphere is called the lapse rate. The lapse rate of a dry convective atmosphere would be about 10 K/km of altitude, whereas the lapse rate of a wet atmosphere is only about 6 K/km.

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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