Use of the Clark Atlanta University Energy Balance Module in a Freshman Earth System Science Course

The Earth System Science Program (ESSP) at Clark Atlanta University is developing an instructional module to study energy balance at the air/land and air/sea interfaces. A graphical user interface (GUI) has been developed which is used to model each of the components (net radiation, sensible and latent heat fluxes, ground heat flux, storage, anthropomorphic, and residual) involved in the partitioning of energy at the air/land and air/water interfaces. The GUI consists of a graphical model in the form of an energy balance diagram. The energy balance diagram is composed of sky elements (sun, moon, clouds), a line representing the air/land or water/land interface, and arrows which indicate magnitude and direction of each of the energy fluxes. The storage component is represented as a box when present. Fig. 1 illustrates an example of the energy balance for an ideal surface, such as moist, bare soil. In Fig. 1 Q* signifies the net radiation flux, HS the sensible heat flux, HL the latent heat flux, and HG the ground heat flux.

The energy balance model is applied to numerous (33 at present) scenarios which vary by (1) climate or microclimate, (2) day and night, (2) cloudiness and sunshine, (3) windy and calm, (4) land or water surface, and (5) freezing and non-freezing temperatures. The model is currently available in a semi-quantitative form. Fixed arrow lengths (e.g., zero, 1/4, 1/2, 3/4, 1) are used to express flux magnitude and direction. An advanced version of the module is also under development. This version will require the user to calculate arrow magnitudes and directions from diffusion, evaporation, radiative transfer, and energy storage equations.

The module was tested in a project assigned in the Physics 104 "Introduction to Earth System Science" and Physics 106 "Introduction to Earth System Science II" courses during the Spring semester 2005. The first part of the project used one year of archived data from the Georgia Automated Environmental Monitoring Network (AEMN) to illustrate how variations in solar zenith angle influence air temperature, the soil temperature profile, and evapotranspiration. In the second part of the project the students were to use daytime and nighttime 15-minute averaged surface weather data to infer the directions of net radiation and sensible, latent and ground heat fluxes for clear-sky, ideal land-surface conditions. Ideal land-surface conditions are approximated at most of the AEMN sites by either bare soil or short grass canopies on relatively flat ground. A link to Unisys weather was provided to aid in identification of days with clear-sky conditions.

The majority of the 96 students enrolled in the courses consisted of liberal arts and education majors. Students who attempted to complete the project without recourse to the energy balance module did poorly, whereas those who used the energy balance module to complete the project did well and came away with a greater understanding of energy partitioning at the earth's surface.

The module was in a stage of intermediate development in the Spring semester. This required the instructor to run the GUI model for the students both in class and in study sessions outside of class, a cumbersome and time-consuming procedure. In order to avoid this happening again, development of the elementary version of the module will be completed early in the Fall semester 2005. The students will learn in a laboratory assignment how to use the module to calculate energy balance at the land surface and will apply this knowledge to completion of the energy balance project. Results from both semesters will be presented in the poster.