Now for something completely different.. Why are some stretches of roads particularly susceptible to fog?
How does it form, what sort of local topography “encourages” fog?
party_pants said:
Now for something completely different.. Why are some stretches of roads particularly susceptible to fog?How does it form, what sort of local topography “encourages” fog?
low ground with water.
AwesomeO said:
party_pants said:
Now for something completely different.. Why are some stretches of roads particularly susceptible to fog?How does it form, what sort of local topography “encourages” fog?
low ground with water.
Places that mirages appear in summer.
https://en.wikipedia.org/wiki/Fog
Fog forms when the difference between air temperature and dew point is generally less than 2.5 °C or 4 °F.
Fog begins to form when water vapor condenses into tiny liquid water droplets suspended in the air. The main ways water vapor is added to the air: wind convergence into areas of upward motion; precipitation or virga falling from above; daytime heating evaporating water from the surface of oceans, water bodies, or wet land; transpiration from plants; cool or dry air moving over warmer water; and lifting air over mountains. Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds.
Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.
Fog normally occurs at a relative humidity near 100%. This occurs from either added moisture in the air, or falling ambient air temperature. However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.
Fog can form suddenly and can dissipate just as rapidly. The sudden formation of fog is known as “flash fog”.
Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets. This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.
The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fogbank it may contain, will be “squashed” when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.
http://www.britannica.com/science/fog
http://www.universetoday.com/85349/how-does-fog-form/
party_pants said:
Now for something completely different.. Why are some stretches of roads particularly susceptible to fog?How does it form, what sort of local topography “encourages” fog?
The “ground fog” only forms in slight valleys, dips.
It seems to form by radiation to the sky from the ground. ie. the “sky” at night in the radiation equation has a temperature many degrees below that of the air near the ground, this results in radiation from the ground at night, “undercooling” the ground. If the temperature of the ground is less than the dewpoint of the adjacent air you get ground fog. OK, so the ground cools the adjacent air below the dewpoint which creates fog. Because this near-ground air is cold it sinks slowly towards the dips and valleys, taking the fog with it.
So, to summarise in three points:
1. Radiation to the night sky cools the ground.
2. The ground cools the near-ground air below dewpoint creating fog.
3. The cold air containing the fog settles in dips and valleys.
When there’s a significant wind, the wind turbulently stirs the air making the temperature more uniform and dissipating the fog.
Now if somebody will just give me an explanation of why fog rises in the morning to form clouds?
mollwollfumble said:
party_pants said:
Now for something completely different.. Why are some stretches of roads particularly susceptible to fog?How does it form, what sort of local topography “encourages” fog?
I’ve noticed this on the road from Caboolture to Bribie Island.The “ground fog” only forms in slight valleys, dips.
It seems to form by radiation to the sky from the ground. ie. the “sky” at night in the radiation equation has a temperature many degrees below that of the air near the ground, this results in radiation from the ground at night, “undercooling” the ground. If the temperature of the ground is less than the dewpoint of the adjacent air you get ground fog. OK, so the ground cools the adjacent air below the dewpoint which creates fog. Because this near-ground air is cold it sinks slowly towards the dips and valleys, taking the fog with it.
So, to summarise in three points:
1. Radiation to the night sky cools the ground.
2. The ground cools the near-ground air below dewpoint creating fog.
3. The cold air containing the fog settles in dips and valleys.When there’s a significant wind, the wind turbulently stirs the air making the temperature more uniform and dissipating the fog.
Now if somebody will just give me an explanation of why fog rises in the morning to form clouds?
Is the fog hotter (relatively speaking) than the air above it.
Cymek said:
Is the fog hotter (relatively speaking) than the air above it.