On the bottom of page 11 in the notes, ΔFa is positive in the tropics and negative near the poles. State what this means physically in terms of energy transport, and explain why these oppositely-signed results occur in terms of the other quantities in the atmospheric energy balance model (notes, top of page 11).
To understand the physical meaning of ΔFa being positive in the tropics and negative near the poles, we need to consider the concept of energy transport in the Earth's atmosphere.
In the atmospheric energy balance model, we have several key components that contribute to the net radiation flux (ΔFa) at different latitudes. These components include incoming solar radiation (S), outgoing longwave radiation (LW), and the energy transport by latent heat (LE) and sensible heat (H) fluxes.
In the tropics, where ΔFa is positive, this means that there is a net energy gain in that region. More energy is being absorbed from the Sun (S) than being lost through outgoing longwave radiation (LW), latent heat (LE), and sensible heat (H) fluxes. This positive net radiation flux indicates an energy surplus in the tropics. The surplus energy is responsible for heating the atmosphere, leading to warm temperatures.
Near the poles, where ΔFa is negative, there is a net energy loss. More energy is being lost through outgoing longwave radiation (LW), latent heat (LE), and sensible heat (H) fluxes than being absorbed from the Sun (S). This negative net radiation flux indicates an energy deficit in the polar regions. The deficit energy results in cooling of the atmosphere, leading to cold temperatures.
The opposite-signed results of ΔFa in the tropics and near the poles can be explained by the balance between different energy components. In the tropics, there is high incoming solar radiation (S) and significant cloud cover, which reduces the outgoing longwave radiation (LW), creating a positive ΔFa. Additionally, strong convective activity and moisture in the tropics contribute to higher latent heat (LE) and sensible heat (H) fluxes, further increasing ΔFa.
Near the poles, there is lower solar radiation (S) due to oblique sunlight angles and longer nights. Also, the polar regions often have low cloud cover, allowing more outgoing longwave radiation (LW). The cold polar atmosphere holds less moisture, resulting in lower latent heat (LE) and sensible heat (H) fluxes, which contribute to a negative ΔFa.
In summary, the positive ΔFa in the tropics signifies a net energy gain, leading to warm temperatures, while the negative ΔFa near the poles indicates a net energy loss, resulting in cold temperatures. The difference in ΔFa between these regions is attributed to variations in solar radiation, cloud cover, and heat fluxes, which play crucial roles in the atmospheric energy balance model.