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Weather: Difference between revisions
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+ wikipedia template (I love it :D)
m (more updates from http://forum.flightgear.org/viewtopic.php?f=69&t=23214&p=211785#p211785) |
(+ wikipedia template (I love it :D)) |
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[[File:Windboundaries.png|thumb|250px|A drawing giving an idea of what's the boundary/aloft layer separation (drawn in red)]] | [[File:Windboundaries.png|thumb|250px|A drawing giving an idea of what's the boundary/aloft layer separation (drawn in red)]] | ||
[[File:ASW-20 landing configuration.png|thumb|350px|Advanced Weather can simulate the conditions for [[soaring]]]] | [[File:ASW-20 landing configuration.png|thumb|350px|Advanced Weather can simulate the conditions for [[soaring]]]] | ||
Weather is the state of the atmosphere, especially the | Weather is the state of the atmosphere, especially the {{wikipedia|troposphere}}, at a given time for a given place. Calculating the complete atmosphere or even a small part of it is extremely demanding in computing power. Hence, FlightGear calculates the state of the atmosphere only for a vertical line beginning at earth's center straight through your aircraft up to an appropriate altitude. For every point along this line, the following fundamental parameters are calculated: | ||
* '''temperature''': usually in °C. | * '''temperature''': usually in °C. | ||
* ''' | * '''{{wikipedia|dew point}}''': indicating at what temperature the air in that point would become a "cloud". It gives an indication of the {{wikipedia|relative humidity}}. | ||
* '''pressure''': in inches of mercury (inHg) or hectopascals (hPa) | * '''pressure''': in inches of mercury (inHg) or hectopascals (hPa) | ||
* '''density''': this affects the behaviour of the aircraft. | * '''density''': this affects the behaviour of the aircraft. | ||
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=== Atmosphere layers === | === Atmosphere layers === | ||
Like the real atmosphere, the simulated one is divided in layers. For what concerns flight, a first distinction is made with the ''boundary layer'' and the ''aloft layer''. The | Like the real atmosphere, the simulated one is divided in layers. For what concerns flight, a first distinction is made with the ''boundary layer'' and the ''aloft layer''. The {{wikipedia|Planetary boundary layer|boundary layer}} is the thin one close to ground, where the atmosphere, mainly the wind, is affected by the earth's surface. Its thickness may vary depending on how rough the ground is (e.g. sea as opposed to Alps), but in general it's less than 600 ft AGL. The aloft layer is immediately above the boundary one, and is by definition not affected by ground, i.e. there is free to flow air. | ||
Within these layers, there are other sub-layers that can be defined, because the atmosphere still changes a lot, especially in the aloft layer. These sub-layers in FlightGear define the state of the fundamental parameters above, and can specifically define the presence of clouds. For the points in between, the values are calculated by interpolation, e.g. if you're halfway between two, the values will be set to the average. | Within these layers, there are other sub-layers that can be defined, because the atmosphere still changes a lot, especially in the aloft layer. These sub-layers in FlightGear define the state of the fundamental parameters above, and can specifically define the presence of clouds. For the points in between, the values are calculated by interpolation, e.g. if you're halfway between two, the values will be set to the average. | ||
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== Basic Weather == | == Basic Weather == | ||
[[File:Basic weather selected.png|thumb|350px|Basic Weather selected in the main Weather dialog]] | [[File:Basic weather selected.png|thumb|350px|Basic Weather selected in the main Weather dialog]] | ||
In Basic Weather most calculations are based on the | In Basic Weather most calculations are based on the {{wikipedia|International Standard Atmosphere}}. The default weather definition is: | ||
* Boundary layer, 0ft, wind 270° at 3 kt, visib. 10SM, 29.92inHG (1013hPa), temp. 15°C, dewpoint 5°C | * Boundary layer, 0ft, wind 270° at 3 kt, visib. 10SM, 29.92inHG (1013hPa), temp. 15°C, dewpoint 5°C | ||
* Boundary layer, 500ft, wind 280° at 6 kt | * Boundary layer, 500ft, wind 280° at 6 kt | ||
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* Warm sector | * Warm sector | ||
These correspond to some '' | These correspond to some ''{{wikipedia|Air mass|airmasses}}'' which are well defined areas of a map (see the picture) that simulate a classic patterns of {{wikipedia|Extratropical cyclone|cyclones}} and {{wikipedia|Anticyclone|anticyclones}}, as we often see them in the weather forecast maps of mid-latitude areas. So, for example, if you start flying in a low pressure region and keep flying towards E-N-E, you will eventually see how the weather changes while you move to higher pressure regions. Being a large scale phenomenon, this of course requires mid or long range flights. | ||
Tropical areas currently have a ''weather tile'' definition but it's not used by any scenario. Also, at the moment there's no definition for polar areas. | Tropical areas currently have a ''weather tile'' definition but it's not used by any scenario. Also, at the moment there's no definition for polar areas. | ||