Final answer:
Changes in the reflectivity of Earth's atmosphere and surface, as well as variations in the sun's energy reaching Earth, are two causes for the trend in worldwide Total Electron Reflection (TER).
Step-by-step explanation:
One of the causes for the trend in the worldwide Total Electron Reflection (TER) is changes in the reflectivity of Earth's atmosphere and surface. When the reflectivity of Earth's atmosphere and surface changes, it affects the amount of electron reflection that occurs. For example, if there is an increase in the presence of particles or pollutants in the atmosphere, it can lead to a decrease in electron reflection.
Another cause for the trend in TER is variations in the sun's energy reaching Earth. The amount of solar energy that reaches Earth can vary due to factors such as solar activity, the Earth's position in its orbit, and atmospheric conditions. These variations in solar energy can impact the electron reflection process and ultimately contribute to the trend in TER.