The surface radiation budget of a region is strongly tied to its climate. Previous work using the 8-year climatology of the Surface Radiation Budget and the yearly cycles of net longwave and shortwave fluxes have established a set of parameters that distinguish climate classes. This paper will build on that previous work but examine the annual cycle of only the upward and downward longwave radiation.

Radiation hodographs were plotted as the annual cycle of surface downward longwave flux as a function of surface upward longwave. These plots were separated into different climate classes based on previous work. The plots for land sites looked much different than those for ocean. Over ocean regions, there is very little annual cycle in the longwave flux. This is the result of the strong coupling between the ocean surface and the atmosphere. Most land regions have a larger annual cycle and tend to be linear. The exception is the region of the Sahel. As the Sahel changes from dry to wet during the year, its hodograph shows movement from the radiation space of the deserts to that of rain forest.