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Sunday, April 15, 2012
Monday, April 9, 2012
Why is temperature dewpoint important
As a pilot you are responsible for planning and acquiring all information related to the trip. One of the critical information you need to be aware of is temperature dewpoint spread. Let's discuss it in detail:
What is temperature dewpoint -- Simply put it nothing but a temperature, at which the moisture i.e. water vapor in air (or humidity in a volume of air) condenses and appears as liquid, in other words forms cloud. So this parcel of air will need to be cooled to this temperature to form a cloud.
Hence when you gather weather reports, you not only need to know the current prevailing temperature at the airport but also temperature dew point.
The difference between temperature and dew point is known as "temperature dew point spread".
Why we need this information -- This will help pilot get an idea of where the cloud bases are i.e. how high the clouds are possible. Also gives an idea of the likelihood of carburetor ice.
Let's take an example:
Say the temperature at the surface of airport = 14° celsius.
Temperature dewpoint = 5° celsius
Over here what are trying to find out at what altitude is this temperature available so that any water in the air will condense will form cloud.
The formula to be used:
Cloud base in feet = [(temperature in °F - dew point in °F) * 1000]
4.4
hence putting the numbers above:
cloud base in feet = [(57.2 - 41) * 1000)/4.4 = 3681 feet above the surface of airport (add airport elevation to get MSL figures).
What is temperature dewpoint -- Simply put it nothing but a temperature, at which the moisture i.e. water vapor in air (or humidity in a volume of air) condenses and appears as liquid, in other words forms cloud. So this parcel of air will need to be cooled to this temperature to form a cloud.
Hence when you gather weather reports, you not only need to know the current prevailing temperature at the airport but also temperature dew point.
The difference between temperature and dew point is known as "temperature dew point spread".
Why we need this information -- This will help pilot get an idea of where the cloud bases are i.e. how high the clouds are possible. Also gives an idea of the likelihood of carburetor ice.
Let's take an example:
Say the temperature at the surface of airport = 14° celsius.
Temperature dewpoint = 5° celsius
Over here what are trying to find out at what altitude is this temperature available so that any water in the air will condense will form cloud.
The formula to be used:
Cloud base in feet = [(temperature in °F - dew point in °F) * 1000]
4.4
hence putting the numbers above:
cloud base in feet = [(57.2 - 41) * 1000)/4.4 = 3681 feet above the surface of airport (add airport elevation to get MSL figures).
What does it mean, if there is enough humidity or moisture in air then expect clouds to form at that that height. This is considering a standard lapse rate. However you should look out for an altitude where this temperature i.e. 5°C is prevailing and will give an idea of cloud base.
Couple of things it helps us identify:
- The ceiling at the airport i.e. if you are planning a flight and need to know how high the clouds are.
- carburetor ice, so expect to have the possibility of carb ice at that altitude and above. Keep an eye on RPM to see a drop.
Hope this explanation helped.
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