GSK - Meteorology Flashcards
Items of Meteorological Information found on Routing charts
-ocean current - set/ rate/ drift
-wind direction and force of weather rose
-mean air temperature
-mean air pressure
-hurricane forecasting
-fog percentage
-low visibility percentage
-TRS winds
-Shipping Routes
-Limits of ice
Synoptic Chart
The synoptic chart shows pressure systems (High and Low), isobars and weather fronts (Warm & Cold) at a given level over a large area at a given date and time
Its used for weather forecasting and the weather to be expected
Warm Front
- cirrus, altostratus, Cumulus, Stratus Clouds
- light to moderate prolonged rain ahed of front, patchy behind
- moderate or poor visibility in Fog
- Wind increases and backs
- pressure drops
- temperature rises
Occluded Front
- happens when either warm or cold front is suspended due to one catching up with the other and so no longer reaches sea level
- the depression is filling and so no more pressure starts to rise
-persistant rain and showers with moderate visibility - light winds as the system is decaying and slowly advancing
- increased amount of mid-level clouds conditions like those in warm sector
Cold Front
-brief Period of clear skys ahead of front
- Cumulonimbus clouds
- heavy rain and thunder at the front,
- very poor visibility at the front, excellent after
- wind decreases and veers
- conditions rapidly improving after
- pressure rapidly increases after
- temperature falls
Factors determining strength and direction of wind
- geographical location
- proximity of High and Low pressure systems
- pressure gradient between High and Low pressure systems
- proximity of land
Meteorological indications of approaching TRS (Tropical revolving storm)
-Falling Pressure 3mb below normal
-long low swell from direction of TRS
-appreciable change in wind strength and direction
-extensive cirrus clouds followed by altostratus
-good visibility
Karabatic Winds
Dangers…
- Occurs when there is intense radiation on a clear night
- this causes cooling over sloping ground
- cold dense air ´falls´down the mountain slope when the air below is less dense under the influence of
gravity - producing the Katabatic wind.
Dangers: strong offshore wind arriving without warning
Mistral wind is example
Barometer
barometer
records pressure at a given time
by using fixed pointer from a previous reading the change over a period of time can be observed.
Barograph
barograph
gives a continual readout on graduated paper by use of a pen and revolving drum thus provides for the yachtsman the ‘trend/tendency’.
Land Fog
Land (Radiation)
- forms over low-lying land on clear nights, when conditions are ideal for maximum radiative cooling, especially during the winter months
- Radiation Fog forming over land is cool and so the air is denser and will flow downhill.
- Occasionally it drifts out to
sea, but it is found no farther than fifteen miles offshore, as the relatively
- high sea surface temperature causes the fog to disperse
Sea Fog
When warm moist air flows over a cold sea surface and cools it to its dew point (vapor condenses)
Sea (advection) fog is formed.
- main type of fog experienced at sea
- may form and persist with moderate or even strong winds
Most common in: - Polar regions
- Grand Banks of Newfoundtland (Canada)
- near cold ocean currents, California, Chile Peru
- SW approaches to English channel
- north west Pacific Ocean
Effect of Land masses on the general direction of winds
land masses disturbs the ideal distribution
- due to local heating and cooling, pressure systems move
Weather in ITCZ
- variable light winds
- squalls and thunder storms clouds
- very hot and humid
Weather in Variables
/ Subtropical Anticyclone (STACs)
- fairly nice weather
- small amounts rain and clouds
Buys Ballots Law
in the northern Hemisphere when standing with your back to the wind, Low Pressure will. be on your left
Land Breeze
- land cools at night faster than at sea
- Cool air is denser and falls creating a H Pressure
- Sea cools more slowly creating a relatively Low Pressure
- Wind blows offshore from H to L
Name 6 Air Masses UK experiences
- Arctic Maritime (very cold, moist)
- Polar Continental (cold and dry)
- Tropical Continental (hot and dry)
- Tropical Maritime (hot and moist)
- Returning Polar Maritime (cold, very moist)
- Polar maritime (cold, moist)
ITCZ
Inter Tropical Convergence Zone)
How do clouds form
form as result of condensation of water vapor in the atmosphere
- Ascent in convention currents
- Uplifting at a front
- air being forced over higher grounds (mountains)
- radiation cooling
Trade Winds Weather
- persistent strong winds
- fair and small cumulus clouds
- generally nice weather
Warm Sector Weather
- Stratus clouds
- light to moderate showers
- moderate to poor visibility
- steady wind
- steady low pressure
- steady warm Temperature
Sea Breeze
- Land heats faster than sea during the day
- Sea warms more slowly creating a relatively Low Pressure
- warm air rises creating Low pressure at surface and H pressure is formed aloft
-pressure aloft is higher then same level at sea and so High Pressure moves towards the Low Pressure above the sea to equal out - cooler air falls, creating High Pressure at sea surface
- sea breeze results blowing onshore
Hygrometer
- Obtain a range of readings of the dry and wet bulb Maisons Hygrometer.
- Take the difference between the two (depression) and enter Mariner’s Handbook Dewpoint Table
- Plot graph with time against temperature
- At the same time obtain regular readings of the sea surface temperature.
- where 2 lines cross, Fog is present
- Start of Advection fog is likely when the Dew Point of the air is within 5° C of the sea surface temperature
Where can we source Weather Forecast ?
- local Forecast from VHF
- Navtex
- Sat C
- Weatherfax
- Weather Routing charts
- Television
- Internet
Dew Point
temperature below which air becomes saturated and water droplets begin to condense and dew forms
Relative Humidity
amount of water vapour present in air expressed as a % of the amount needed for saturation at the same temperature
Published Sources of Weather information
- Mariners Hanbomok
- Routing Charts
- Admiralty Sailing Directions
- Ocean Passages of the world
- A.R.L.S Volumer 3
If an unsaturated parcel of air is cooled beyond its dew point, what will happen?
It will become saturated and some of the water vapour will condense out, forming clouds.
What is the difference between absolute and relative humidity?
Absolute humidity is the quantity of water in the air, expressed in grams per cubic metre. Relative humidity is absolute humidity in relation to the quantity required for the air to be saturated, expressed as a percentage.
What is the troposphere?
The troposphere is the lowest layer of the atmosphere. It is the layer which contains almost all of the water and most of what we think of as
‘weather’
Complete the sentence:
When air rises, it…
cools, due to expansion.
What type of atmospheric stability results in clear skies?
Absolute stability, where the parcel of air is always cooler than the surrounding air and therefore wants to sink back down to its original altitude.
What does SALR stand for?
Saturated Adiabatic Lapse
Rate.
What is it called when air is forced to rise because of two or more air flows meeting?
Convergence.
What is it called when air is forced to rise due to land?
Orographic uplift.
What is a fluffy cloud at low altitude called?
Cumulus.
What does a nimbostratus cloud look like?
nimbostratus cloud is a flat layer of cloud at low altitude which brings rain.
How might clouds change when a depression is approaching?
As a depression approaches, high cloud will appear and it will thicken and lower as the depression gets closer.
What are squalls?
A squall is a sudden and dramatic increase in the wind speed, which lasts longer and is more significant than a regular gust. It can also cause a significant shift in the wind direction.
Which air mass forms over
Northern Canada and
Greenland, and moves directly across the North Atlantic to the UK?
Polar Maritime.
How is an air mass which originates over land termed?
Continental.
What are the characteristics of maritime air?
Maritime air masses are more humid (contain more water) than continental air masses.
What are the expected weather conditions when the
UK is under the influence of a tropical maritime air mass?
This air mass is warm and moist. As it moves towards the UK and cools a little, it will become stable and saturated.
When it reaches the UK, it will cause low cloud and drizzle, and perhaps some fog.
What are the expected weather conditions when the
UK is under the influence of a tropical continental air mass?
tropical continental air mass brings warm, dry weather and clear skies because it
originates in a warm place and doesn’t carry much moisture with which to form clouds or rain.
Which type of breeze occurs because land absorbs heat more quickly than water?
Sea Breeze
What causes a land/offshore breeze?
At night, the land cools more quickly than the sea. The air over the land is cooled and sinks, creating a high pressure, in contrast to the lower pressure over the sea. This creates a pressure gradient which results in the land/offshore breeze.