Published online by Cambridge University Press: 05 June 2012
Under radiative equilibrium, the First Law reduces to a balance between radiative transfers of energy. This simple energy balance determines the radiative-equilibrium thermal structure. It is valid for a resting atmosphere. However, radiative equilibrium breaks down for an atmosphere in motion. Heat is then also transferred mechanically, by air motion. The radiative-equilibrium thermal structure (Fig. 8.21) differs conspicuously from the observed global-mean temperature (Fig. 1.2). Under radiative equilibrium, temperature is much too warm at the surface. It decreases upward too steeply. The discrepancy from observed temperature points to the importance of mechanical heat transfer. Under radiative-convective equilibrium, mechanical heat transfer is accounted for – by convection. It reconciles the equilibrium thermal structure with that observed, but only vertical structure that is characteristic of the global-mean.
Horizontal thermal structure differs significantly from that observed (Fig. 10.1). Under radiative-convective equilibrium (Fig. 10.1a), temperature decreases poleweard at all latitudes, from ∼315 K over the equator to colder than 180 K over the winter pole. Observed zonal-mean temperature (Fig. 10.1b) decreases poleward more gradually. It is some 20 K cooler over the equator and 40 K warmer over the winter pole. By comparison, radiative-convective equilibrium produces a meridional temperature gradient that is too steep. It accounts for mechanical transfer of heat, but only in the vertical.
At observed temperatures, individual latitudes are not in radiative equilibrium, not even in radiative-convective equilibrium. According to the distribution of net radiation (Fig. 1.34c), low latitudes experience radiative heating.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.