Latitude energy transport

The transport of heat between latitude bands is assumed to be diffusive and is proportional to the temperature difference divided by the distance between the midpoints of each latitude band. This is the temperature gradient. In this simulation all these distances are equal, so the distance need not appear explicitly. The temperature gradient is multiplied by a transport coefficient here called diffc, the effective diffusion coefficient. The product of the diffusion coefficient and the temperature gradient gives the energy flux between latitude zones. To find the total energy transport, we must multiply by the length of the boundary between the latitude zones. In... 

Atmospheric circulation transports heat from areas of positive radiation balance to areas where there is an energy deficit. A significant characteristic of this circulation is that a portion of the heat is transported in latent form, which means that the heat is delivered by the condensation of water vapour in the moving air. It is estimated that about one-third of the energy crossing latitude of 30° of both hemispheres is in the form of latent heat. Another one-third of the energy transport takes place in the ocean. Thus only 30 % of the heat is transported directly by the atmosphere. 

Latent heat is the energy associated with phase changes. Evaporation of water requires an energy input of 2.5 x 10 J per kilogram of water at 0°C, almost 600 times the specific heat. When water vapor is transported via atmospheric circulation and recondensed, latent heat energy is released at the new location. Atmospheric transport of water vapor thus transfers both latent and sensible heat from low to high latitudes. 

The lapse rate in the PBL is imstable and vertical motion leads to the transport of significant amounts of energy upward, due to the buoyancy of air that has been in contact with the surface. A mixed layer forms up to a height where static stability of the air forms a barrier to thermally induced upward motion. This extreme occurs practically daily over the arid areas of the world and the barrier to upward mixing is often the tropopause itself. On the average in mid-latitudes, the imstable or mixed PBL is typically 1-2 km deep. 

Significant economies of computation are possible in systems that consist of a one-dimensional chain of identical reservoirs. Chapter 7 describes such a system in which there is just one dependent variable. An illustrative example is the climate system and the calculation of zonally averaged temperature as a function of latitude in an energy balance climate model. In such a model, the surface temperature depends on the balance among solar radiation absorbed, planetary radiation emitted to space, and the transport of energy between latitudes. I present routines that calculate the absorption and reflection of incident solar radiation and the emission of long-wave planetary radiation. I show how much of the computational work can be avoided in a system like this because each reservoir is coupled only to its adjacent reservoirs. I use the simulation to explore the sensitivity of seasonally varying temperatures to such aspects of the climate system as snow and ice cover, cloud cover, amount of carbon dioxide in the atmosphere, and land distribution. 

Figure 7-6 are plotted in Figure 7-7. The absorbed energy falls off more rapidly with latitude than does the long-wave flux. Transport in this climate system carries excess energy away from the tropics to higher latitudes where there is a deficit in the energy budget.

I also applied the revised computational method to calculate zonally averaged temperature as a function of latitude. I introduced an energy balance climate model, which calculates surface temperature for absorbed solar energy, emitted planetary radiation, and the transport of heat between... 

The presence of water on our planet regulates the climate and is essential for life. Oceans store heat and release it slowly. Wind currents distribute heat in the latent energy of water vapor. In the tropics warm, humid air rises and is transported to cooler latitudes. 

The constant k parameterizes all atmospheric dynamics. It can be estimated by taking approximate values for the other quantities in (2). Taking 02=100 Wnr, Nakamura and Oort, 1988, g2 = 0.05, and AT = 30 K, leads to k=l/6 Wmr K" . Notice that Di is only about 5 Wm". The poleward heat transport is a large term in the energy balance for the polar cell, but a small term for the low latitude cell. It is positive in the pole cell, thus warming the atmosphere, which radiates half of that heat down to the surface, and half to space. In the low latitude cell, D is negative, so the downward radiation at the surface, and the radiation at the top of the atmosphere are bodi reduced by Di /2. 

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