An Interactive Tool for Incoming Solar Radiation Demonstrations

The Earth's seasons are controlled by the changes in intensity and duration of incoming solar radiation (insolation). Although this seems like a simple concept, in large lecture based courses filled with slides containing snapshots of planets and angles of incidence the concept can quickly become lost in a sea of arrows and numbers. In smaller lectures or laboratory sessions, the use of exercises and examples often use enough trigonometry to cause students to become more focused on the procedure of getting the right answer than what that answer actually means. Because the point of the assignments is understanding the concept, not doing the math, we decided to develop a tool that would allow insolation at the top of the atmosphere for any latitude to be calculated and displayed graphically, thereby performing the calculations for the user. The program we created calculates values on 3 axes representing the hours of the day (x), days of the year (y) and the insolation that occurs at any [x,y] time (z). The program is fully interactive and requires only that the user enter the desired latitude, desired declination of the Sun and the number of times to solve the equation during a 24 hour period. This program is currently being utilized in an undergraduate paleoclimate course that allows students to alter the declination in accordance with Milankovitch cycles if desired, but we expect this program to be useful in other educational settings and applications as well.