From time to time we see fog and mist in Tamborine Mountain and surrounding areas.
Fog and mist are dense clouds of water droplets suspended in air close to the ground. Fog is denser than mist; fog reduces visibility by more than 1 km while mist reduces visibility by less than 1 km.
The formation of fog and mist is a result of the processes of condensation and evaporation.
Water molecules (H2O) in the atmosphere can be gaseous (water vapour) or liquid (water droplets) or solid (ice). The atmospheric temperature affects the state of the water molecules. High temperatures provide energy for the water molecules bound together as liquid water droplets, to split away and become gaseous water vapour in a process called evaporation. Cold temperatures reduce energy available for the gaseous water vapour molecules, they slow and clump together to form liquid water droplets in a process called condensation.
As a result of the interaction of evaporation and condensation changes in the atmospheric temperature also change the capacity of air to hold moisture i.e. the number of water molecules. Warm air can hold more moisture than cold air because the water molecules are spread out as a gas.
Dew point is the temperature at which the air cannot continue hold its water molecules as water vapour and condensation becomes the dominant process. Dew point is always less than or equal to atmospheric temperature. When the dew point equals atmospheric temperature because the dew point rises to the atmospheric temperature, or the atmospheric temperature falls to dew point, then fog, dew and clouds begin to form.
There are a variety of conditions which cause dew point and produce fog.
Radiation fog occurs when the land surface cools, usually overnight when there is a clear sky. The air close to the ground cools causing condensation to occur and fog to form. This type of fog usually dissipates by mid morning when warmed by the sun and broken up by wind.
Valley fog occurs when a temperature inversion traps heavy cold air below a layer of warm air.
Hill fog occurs when wind lifts moist air up a slope, as the air rises its temperature drops causing condensation and producing fogs on the windward side of hills and mountains.
Advection fog occurs when air flows over a surface with a different temperature producing contact cooling. This may be warm air flowing over a cold surface or cold air flowing over a warm surface.
Fog and mist, like clouds, appear white and opaque because of the effect of light. Sunlight appears as white light but it is made up of the seven principle colours of the spectrum. Fog and mist contain an immense number of water droplets which reflect and scatter the different wavelengths of visible light producing intact reflected white sunlight.