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Section 3.1 Modes of energy transfer

Energy is the capacity to do work (when a force acting on an object causes it to move), and can be further divided into kinetic and potential energy.

Considering a parcel of air in the atmosphere, its temperature would describe the average kinetic energy of its atoms and molecules. The higher the temperature of a gas, the fast its atoms and molecules are traveling through three-dimensional space. Temperature is typically expressed in F, C, or K:

Table 3.1.1. Temperature unit conversions
Unit Conversion
Celsius \(^\circ\textrm{C}=\frac{5}{9}((^\circ\textrm{F})-32)\)
Fahrenheit \(^\circ\textrm{F}=\frac{9}{5}(^\circ\textrm{C})+32\)
Kevlin \(\textrm{K}=(^\circ\textrm{C})+273.15\)

Heat refers to the transfer of energy from warmer objects to colder objects and represents the total thermal energy of a system. It is distinct from temperature!

The amount of heat depends upon (\(q=mC_s\Delta T\)):

  • the total amount of the the material in the system

  • the thermal properties of the material

In atmospheric systems, energy is transferred by

  • radiation (emission and absorption of radiation)

  • conduction (contact between substances)

  • convection (vertical movement of air parcels)

  • advection (horizontal movement of air masses)

  • latent heating (energy released by phase changes of water)

Latent heat effects can be found in two common atmospheric processes:

  • ice \(\rightarrow\) liquid water \(\rightarrow\) water vapor (absorbs heat)

  • water vapor \(\rightarrow\) liquid water \(\rightarrow\) ice (releases heat)

Cloud formation (for example) will release heat to the surrounding atmosphere. This slows the rate of cooling with altitude (i.e., the lapse rate decreases).