how the atmosphere works

• the atmosphere is composed primarily of 3 gases:

  • the molecular form of nitrogen (78%)
  • molecular state of oxygen (21%)
  • argon (1%)
• carbon dioxide is a minor constituent of the atmosphere by is important and now presently running over 400ppm which was exceeded in 2015
• the atmosphere contains variable components of and water vapour which have variable percentages anywhere from near zero percent in the driest environment
• the ozone layer makes up to 4% of the earth's atmosphere in very humid tropical environments. the ozone varies with altitude:

  • we expect around 0.01ppm at the surface, even in urban environments
  • around 10ppm in highest places
• at a height of around 25km, the atmosphere has solid and liquid constituents. there are water droplets and ice that will comprise the clouds and precipitation. then there is also dust and salt particles which are called aerosols.
• the structure of the atmosphere is regarded by pressure, temperature, and height:

  • pressure and height profile are linked exponentially as pressure decreases with increasing height
  • the value of pressure averaged across the earth is 1013 millibars
  • pressure is the weight of the atmosphere pressing down on us
  • around 75% of the earth's weight lies below 10km
• the lowest layer of the atmosphere is called the troposphere:

  • this is where almost all of the weather that we experience on a day-to-day basis is generated
  • in this layer, temperature decreases with height
• after the troposphere, we reach the stratosphere:

  • in this region, temperature begins to increase with height
  • the stratosphere is a region that is very stable and we also expect to find a lot of ozone in this layer
• at some point we reach a temperature about freezing and then the temperature decreases above about 50km - this layer is called the mesosphere
• as we go up higher to about 85km, the temperature reaches another minimum and that it will rise again above that. we call this layer the thermosphere.

  the thermosphere is a result of the intense radiation coming down into this layer, breaking up the constituent atoms into ions causing heating.
• relatively warm air is located at the bottom of the troposphere. the temperature decreases with height until we get to the top of the troposphere. this heating comes from the greenhouse effect as solar radiation comes down and is absorbed by the ground. the ground having a high temperature then emits infrared radiation into the lower part of the atmosphere which the atmosphere absorbs.
• above the tropopause, there is no more convection so there is no mixing between layers. this means that the gases can be transported around without being mixed together. this is why we have different chemical composition in different parts of the atmosphere.
• the upper regions of the atmosphere are much thinner than the lower ones. this makes them easier to escape from gravity and they do not contribute significantly to the mass of the atmosphere.
• there are two main types of atmospheric circulation: horizontal (wind) and vertical (convection)
• it is warm between the boundary of the stratosphere and the mesosphere due to the presence of ozone. we have ultraviolet radiation that's coming down from the sun. it encounters the ozone and breaks it apart into molecular oxygen plus atomic oxygen. breaking the bonds that construct the ozone leads to the release of heat. although the ozone is concentrated mostly in the stratosphere, this ultraviolet radiation encounters it in the upper part of the stratosphere and the lower part of the mesosphere.
• it is warm in the thermosphere as more reactions take place here. where we get up high in the atmosphere, we start to encounter more intense radiation coming from the sun. we have x-rays and extreme short-wave ultraviolet radiation (which would be damaging to cells if it make it to the ground).

  both oxygen and nitrogen absorb this radiation and it causes them to break apart their atomic components oxygen and nitrogen. then, this radiation interacts with oxygen and nitrogen and its atomic state and kicks out electrons from these atoms, leaving ions (ionisation of gases).
• the thermosphere may also be referred to as the ionosphere. this is where the aurora occurs
• the 3 radiation laws:

  1. Planck's law
  2. Stefan-Boltzmann law
  3. Wiens displacement law
• Planck's law says that all objects emit radiation at a specific frequency.
• the Stefan-Boltzmann law states that the temperature of an object is directly proportional to the fourth power of the absolute temperature of the object. this means that hotter objects emit more radiation than cooler objects
• Wiens displacement law says that hotter objects emit their peak radiation at shorter wavelengths. this is due to shorter wavelength radiation having more energy
• how do the 3 radiation laws apply to the earth's climate system?

  the sun has a surface temperature of 6000K and the earth has a surface temperature of about 300K.

  use the laws to see the sun emits more radiation at all wavelengths.

  when we say that the sun emits primarily in the visible spectrum, that doesn't mean that it's not emitting infrared radiation as well. it means that the peak wavelength the radiation lies in is visible.
• input from the sun of 1362 w/m^2 at the top of the earth's atmosphere. this energy gets absorbed unevenly around the earth. the earth is in thermal equilibrium (temperature is neither decreasing or rising).

  if the earth is in thermal equilibrium, then the amount of energy emitted must be equal to the incoming solar radiation.