Meteorolgy Flashcards
What is a Barograph?
This is an instrument used to show the change in pressure over time.
It is scaled in hectopascals in periods of 2 hours for 7 days
It’s turned by either clockwork or an electrical mechanism, which must be checked daily and weekly.
The barograph is not accurate however it allows us to read trends to give indications of depressions and storms.
What is a Barometer and how does it work?
Inside the barometer there is a small vacuum box.
As the air pressure rises the box is compressed.
As the air pressure falls the box expands.
Read the reading nearest to the hectopascal (the scale shown on the barometer) by gently tapping the instrument.
Where should the Barometer be fixed?
Must be in a place easy to read on the ship’s centre line.
Out of direct sunlight.
And where there is no significant change in temperature.
What are the corrections which need to be applied to the barometer?
Height above mean sea level.
Index error.
What is a Stevenson Screen?
Most vessels are equipped with two Stevenson’s Screens, one on each side of the bridge wing, protecting the Mason’s Hygrometer found inside.
The Windward instrument should be used.
Within the Stevenson’s Screen, there is an Mason’s Hygrometer which is used to determine humidity and dew point.
How does a Stevenson screen work/is used?
There are two thermometers, a wet and dry thermometer.
Around the wet thermometer is wrapped a single layer of Muslin, tied to a cotton wick which hangs below the thermometer with the lower end of the wick dipped into distilled water.
Capillary action draws the water up the wick, keeping the wet bulb wet.
If there is evaporation the wet bulb will cool.
Both thermometer temperatures are read.
The difference between the two temperatures is recorded and specialist tables are used to work out the relative humidity and dewpoint.
* The onset of fog may be predicted by calculating the dew point.
What is a Cold Front?
- The leading edge of an advancing colder air mass.
- This is marked by cloud and precipitation, followed by a drop in temperature and/or humidity.
What is a Warm Front?
- The leading edge of an advancing warmer air mass.
- This brings cloud and precipitation followed by increasing temperature and /or humidity.
What is an Occluded front?
- Generated when the cold front of a depression catches up with the warm front.
- Lifts warm air between the fronts into narrow wedge above the surface.
- Brings cloud and precipitation.
What is a developing cold/warm front (frontogenesis)?
This represents a front that is forming due to increase in temperature gradient at the surface.
What is a weakening cold/warm front (frontolysis)
This represents a front that is losing its identify, usually due to rising pressure. Cloud and precipitation becomes increasingly fragmented.
What is the Upper cold/warm front?
This represents the boundaries between air masses at levels above the surface.
What is a Quasi-stationary Front?
A stationary or slow-moving boundary between two air masses. Cloud and precipitation are usually associated.
What is a Trough?
- Elongated area of relatively low surface pressure.
- They may also represent an area of low thickness or a deviation in the upper troposphere.
- All are associated with increasing cloud and precipitation.
What are the warning signs of a TRS?
o Increase in Swell.
o Increase in Wind.
o Decrease in Pressure.
o Gloomy Sky.
o Increase in Clouds.
o Increase in Humidity.
What are in the category of high latitude clouds.
- Cirrus, wispy clouds.
- Cirrostratus, halo around sun.
- Cirrocumulus, (Mackerel sky).
- Anvil top.
What are in the category of middle latitude clouds.
- Altostratus, (sun dimly visible).
- Altocumulus.
- Cumulonimbus.
What are in the category of low latitude clouds.
- Nimbostratus, (steady precipitation).
- Cumulus, (showery precipitation).
- Stratocumulus.
