The electromagnetic Spectrum
Figure: Illustration of the different wavelengths of the electromagnetic spectrum.
What is light? Some say it's made of waves, others say it's made of particles, and still others say that it's both, just depends on how you look at it. Let's take the classical wave view, light is a part of a wide spectrum of electromagnetic radiation ranging from wavelength (L) on the order of nucleons to the size of skyscrapers. The speed of any electromagnetic wave in vacuum is c = 299,792,458 m/s. Amazingly, it is constant, no matter how fast you move relative to it. For each wavelength, there is a corresponding frequency (f = c / L) and a temperature.
Figure: The effect of atmosphere on electromagnetic radiation transmission.
Mechanisms that drive the transfer of energy on Earth surface
Shortwave Radiation (Q_SW):
Electromagnetic radiation in the UV (10 - 400 nm), visible (400 - 700 nm), and near-infrared (700 - 2500 nm) range. Majority of sun's radiation reaching the surface of Earth is shortwave radiation. To calculate the amount of radiation reaching the surface of Earth from the Sun, we apply the Stefan-Boltzmann Law: 𝜎T^4 = j = energy flux, where 𝜎 = 5.670367×10^−8 W⋅m^−2⋅K^−4 and T is the black body temperature of Sun's surface. Assuming that the surface of the sun is 5,780 Kelvin, what is the energy flux at the top of Earth's atmosphere?
Figure: Shortwave radiation Q_SW reaching the surface of Earth. Positive numbers indicate energy gain.
Long wave radiation (Q_LW):
This is infrared radiation with wavelength of 4 to 100 microns (10^-6 m). This is what we normally consider as 'heat'. If we calculate the wavelength of black body radiation from Earth, it would fall into the long wave radiation range. Green house gases in Earth atmosphere partly blocks long wave radiation from both entering and leaving Earth. That is why cloudy days can feel warmer than clear days because the long wave radiation back to the surface from the cloud.
Figure: Average long wave radiation (Q_LW) at the surface of Earth. Negative numbers indicate heat loss.
Latent Heat (Q_L):
This is the heat associated with phase change of materials, mainly water in the geophysical context.