Introduction to Physical Geography
... natural systems are grey box systems. The energy entering and leaving the Earth system is determined by; 1. the characteristics of electromagnetic radiation 2. the intensity and duration of solar radiation 3. the nature of the atmosphere through which it passes (in and out) 4. the nature of the objects on which it impinges (absorption, reflection, etc…) Types of systems; Systems with inputs and outputs are open systems. Self-contained systems (with no transfers across boundaries) are closed. The Earth is an open system in terms of energy, but is essentially closed in terms of matter. Most systems maintain basic structure and function through time and are said to be in equilibrium. However, there are several types of equilibrium; a. steady state equilibrium occurs when rates of input and output are equal and the processing of energy and matter in the system are fairly constant. b. systems may change gradually and progressively through time, i.e. they show trends. Such systems are said to be in dynamic equilibrium. c. some systems show marked rapid and irreversible changes that through them out of one equilibrium state into another. This is termed metastable equilibrium. Feedback; Systems are regulated by feedback by which information produced by the system determines its persistence and stability. Negative feedback tends to maintain balance in systems, while positive feedback will cause a change in system behaviour. Principles of Radiation 1. all materials with temperature above absolute zero (-273oC) emit radiation 2. the wavelength of radiation is temperature dependent – the higher the temperature of the emitter, the shorter the wavelength. 3. the amount received at a surface is inversely proportional to the distance from the source. 4. some materials absorb and emit at selected wavelengths (e.g. the green house gases). The radiation from the sun is received unevenly at the Earth’s surface. One aspect of that unevenness is variation in the du...