Meterology Flashcards
Veering wind changes n which direction
Clockwise
Backing wind changes in which direction
Anti clockwise
Buys ballots law
Back to the wind inn the northern hemisphere low on the left
What is anabatic wind?
Wind traveling up a valley during the day
The three cells
Hadley Ferrel Polar
What is katabatic wind
Strong wind traveling down a valley. On a clear night Wind subsides down a valley but the surrounding cold landmass cools the air faster than the a adiabatic lapse rate and sinks very quickly.
What and how does advection fog form
Advection fog is formed when warm air moves over cold sea. It may persist in wind. Also know as sea fog
What is sea smoke
Type of fog that forms when cold air moves over warmer sea. Will disappear in wind and sun.
What is frontal fog
Air masses involved in a frontal system are forced to mix.
Radiation fog
On calm cloudless nights Land looses heat and cools down. The cold land now cools the air and fog is formed. Does not occur at sea but may be blown on to the sea surface by land breeze.
What is a lapse rate
The lapse rate is the rate at which air cools while it rises. 1*c per 100m
What is a aneroid barameter
Measures atmospheric pressure. Partially exhausted/vacuumed compressible box which is connected to a spring. Air pressure distorts the box and and moves a needle which is preset. No correction at sea level
What is a Barograph
A barograph is a barometer which is connected to a recording device. It makes tracking changes in barometric pressure easier
What is a wet and dry bulb hygrometer and how does it work
It is used to measure realtime humidity. Two Mercury filled thermometers. One has muslin cloth wrapped around the bulb and is dampened by water, the other is exposed. Evaporation causes the wet bulb to be cooler than the exposed bulb. The depression between the two and the air temp compared in psychometric tables. The hygrometer is usually housed in a Stevenson screen.
Where can you get met information while under way/on passage?
MSI (navtex, Inmarsat)
Own ship oservations
VHF, MF, HF radio listing to coast stations for weather broadcasts. ALRS vol 3 (To obtain weather report broadcast times from coast stations)
Weather routing services
Weather fax
Internet - Government Met offices (NOAA, UK MET Office)
Local radio
Harbour master
What is a whirling phsycrometer
Spinning wet and dry bulb hygrometer.
Requirements for a TRS to form
Warm Air Mass, Warm air contains more moisture, Warm air rises cools condenses and sinks creating vertical circulation.
Low upper atmospheric winds, If high upper atmospheric winds exist they will essentially decapitate the top section of the vertical circulation required for TRS formation.
Warm seas, Ocean temp above 27 Celsius through at least 50m water coloumn. Warm seas increases water vapour absorption encourage vertical circulation.
Strong Coriolis effect. Sufficient coriolis effect only exitsts from more than 5-10 Degrees North or south of the equator. (5 and 25 degrees northern hemisphere 10 and 20 degrees Southern Hemisphere).
Avoiding a TRS
If wind veers (northern hemisphere) them in dangerous semi circle. Proceed with wind on starboard bow as close as is safe. If wind back. (Northern hemisphere) then in navigable semi circle. Proceed with wind on starboard quarter Opposite for Southern Hemisphere. Wind on port how or port quarter
Precursors condition of TRS
- Long large swell from direction of Centre of low..
- When between 500 and 100 miles extensive cirrus cloud followed by altostratus, nimbostratus and strato cumulos
- Atm pressure change of 3mb below average for time of year. When corrected (height of eye and diurnal variation(sailing directions))drop is more than 5 mb then it must be assumed that storm exists.
- Appreciable change in wind direction
- Radar may show the leading edge, but by this time the weather would already be severe.
How to report TRS or any unpredicted severe weather.
SOLAS requires all vessels to report the presence of a TRS. To vessels in the vicinity and to a coats station. Information required: - position course and speed of vessel - position of the storm at UTC and date - current barometric pressure, not corrected for diurnal variation. - The change in barometric pressure form the past 3 hours - true direction and force of wind - Sea state - height of swell and direction Security message must be sent every three hours
Where can you find psychometric tables and what are they used for
In the Mariners handbook. Used to determine due point
How to determine if fog will develop
When Air temp approached or matches dew point temp fog will most likely form. Viz is likely to start hazing with in about 2 - 5 degrees difference. To determine, Due point and air temp must be checked every 10minutes and the dew point and air temp plotted against time. average line can be extended and when the two meet fog is likely to develop, there fore it is possible to predict the development of fog by the graphs
What is an anamometer
Relative wind speed
What is the Mean atmospheric pressure at mean sea level?
1013 mb
What are the expected meteorological conditions as a frontals system passes over, including warm front, warm sector and cold front.
What are land and sea breezes?
Seabreeze - Wind from sea, during day hot land air rise cool air form sea replace
Land breeze - Wind from land, Night air cools over land pushed out over sea.
What is Orographic Wind?
Air being forced up by a land mass(mountain range) forcing to cool, condense and rain
Name 5 ways in which an air parcel can be cooled.
Radiation: Water vapour radiates heat and cools the layer with out upward movement.
Thermal Convection: Air is heated by direct contact with earths surface forcing to rise, as it rises it cools. Likely to condense and form Cumulos or Cumulo nimbus clouds
Frontal: Cooler air mass forces a warmer air mass to rise
Orographic: Land mass forces a parcel of air to rise.
Turbulence:Moist air being carried up by turbulence caused by unevenness in earths surface.
What is Relative humidity?
It is the description of how much water vapour is contained with in an airmass compared to the maximum quantity it can hold at that temperature.
Sources of met Info for Passage planning
Routing charts
Sailing Directions
Np 100
Ocean Passages of the world
ALRS VOL3 (Weather reporting times and stations)
Stages of development of TRS.
Tropical Wave
Tropical disturbance
Tropical depression
Tropical storm
Tropical revolving storm.
Where to find barometric height of eye and temp correction tables.
Nautical almanac.
Info found on routing chart
- Wind roses - wind force and direction percentage for that month, number of observations, days of calms,
- Ice limits and iceberg sightings
- Ocean current - Direction and consistency
- Load line limits
- Shipping routes
- TSS tracks
- Winds force 7 and above.
- Atmospheric pressure aver
Wet and Dry Bulb Hygrometer and determining dew point
Mercury filled thermometer x 2
1 wrapped in muslin cloth and dipped in water
difference in temp due to evaporation of water out of cloth
Input difference into psychometric table to work out due point.
Maletmi Wind
Strong N
Aegean sea
Summer
Balken High pressure ridge
Anatolian low pressure
Mistral Winds
Strong NW
France
Winter and early spring
HP over bay of Biscaye
Low pressure in gulf of Genoa
Prep for operations in ICE
Clothing
Footwear
Sunglasses
Food
Vitamins
Medical supplies
Fuel
Batteries
Antifreezee
Survival kits
When reporting Barametric pressure what must be done to it
Corrected to mean sea level, using the height of eye correction table.
How do you read a tidal diamond?
1) Find a tidal diamond close to the area where you will be boating
2) Locate the tidal diamond data on the chart
3) Here you will also find the directions on what each column means, the information at the top of the column gives you the geographical location in Lat & Long
1st column = Direction of the stream in degrees (True bearing)
2nd Column = Rate (speed) in Knots during a Spring Tide
3rd Column = Rate (speed) in Knots during a Neap Tide
4th Column = Hours of the Tide, 0 = HW time (found in a tide table)
Passage of a Low.
Ahead of the Warm Front
Passage of a Low.
In the Warm sector
Passage of a Low.
Approaching Cold Front
Passage of a Low.
At the Cold Front
