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MWOC Study > Changing Nav / Met > Flashcards

Changing Nav / Met Flashcards

1
Q

Define Moonrise / Moonset

A

True - When the moons centre appears practically on the Visible Horizon

Visible - When the Upper Limb appears above or disappears below the observers Visible Horizon

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2
Q

Define sunrise / sunset

A

The time of true rising and setting occurs when the centre of a heavenly body is on the observers Celestial Horizon

True - When the suns centre lies on the celestial horizon, the suns lower limbs appears one semi-diameter above the Visible Horizon

Visible - When the upper limb of a heavenly body is just appearing above or disappearing below the observers Visible Horizon

True and Visible must not be confused.

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3
Q

Define Celestial Horizon

A

The great circle on the celestial sphere midway between the observer’s zenith and nadir

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4
Q

Define Visible Horizon

A

The line at which the sky and Earth appear to meet

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5
Q

List the seven surface currents around Australia

A
  • South Equatorial current
  • West Australian current
  • Leeuwin current
  • East Australian current
  • Tasman front
  • Zeehan current
  • Antarctic Circumpolar current
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6
Q

List the factors determining the growth of sea and swell

A
  • Wind strength
  • Wind duration
  • Fetch
  • Distance (for swell)
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7
Q

Depending on the factors determining the growth of sea and swell, the sea is categorised by what three names

A
  • Duration limited
  • Fetch limited
  • Fully developed
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8
Q

Sea states according to the Beaufort Scale

A 
0 = calm - 0m
1 = rippled - 0.1m
2 = smooth - 0.1-0.5m
3 = gentle breeze/slight - 0.5-1.25m
4 = moderate - 1.25-2.5m
5 = rough - 2.5-4m
6 = very rough - 4-6m
7 = high - 6-9m
8 = very high - 9-14m
9 = phenomenal - >14m
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9
Q

Describe the basic weather conditions associated with Ridges

A
  • An extension from an anticyclone / High
  • Marked by ‘U’ shaped isobars
  • Light winds
  • Winds move anticlockwise
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10
Q

Define Meridian

A

A meridian is a semi-Great circle on the Earth’s surface which passes through both poles

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11
Q

Define civil twilight

A

Nautical Almanac calculated as the moment when the sun’s centre is 6 degrees below the celestial horizon.

  • Morning: Roughly when the horizon becomes clear (Dawn)
  • Evening: Roughly when the horizon becomes in distinct (Dusk)
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12
Q

Define Nautical and Astronomical Twilight

A

Nautical - The suns centre is 12 degrees below the celestial horizon

Astronomical - The suns centre is 18 degrees below the celestial horizon

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13
Q

Define total darkness

A

After Astronomical Twilight, with no moon present (more than 18 degrees below the celestial horizon)

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14
Q

Define tides

A

Tides are the Periodic Vertical Reversing movements of the water on the Earth’s surface, caused by the Tides Raising forces of the moon and sun.

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15
Q

Define Perigee and its relation to tides

A

When the moon is closer to the Earth. There are greater tidal ranges.

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16
Q

Define Apogee and its relation to tides

A

The moon is further away from the Earth. There are lesser tidal ranges

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17
Q

Define Perihelion and its relation to tides

A

The sun is closer to the Earth. There are greater tidal forces

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18
Q

Define Aphelion and its relation to tides

A

The sun is further away from the Earth. There is less effect on tidal forces

19
Q

Procedure for weather observing and reporting at sea IAW AFGO’s

A

Rough log:

  • compiled by the QM
  • Observations every woman’s

Ships log:

  • compiled by the OOW
  • entered every 6 hours
  • entered at the end of every watch

Observations are reported as:

  • routine reports
  • non-routine reports
20
Q

Parts of a wave: Define height

A

The difference between a crest and trough

21
Q

Parts of a wave: Define amplitude

A

The difference between the still water line and the crest/trough

22
Q

Parts of a wave: Define Period

A

The time difference between successive points for a stationary observer.

  • For ocean waves, a 100m wavelength = 10sec period
23
Q

Parts of a wave: Define wave length

A

The difference between successive points on a wave. Eg. crest to crest, or trough to trough

24
Q

Describe tropical cyclones and the hazards associated with them, as well as duration of Australian cyclone season

A
  • Synoptic scale, intense, low pressure systems
  • Behind tornadoes, one of the most dangerous weather phenomena
  • Only occurs in tropical latitudes

Duration: 01 Nov to 01 May

25
Q

Define Solar Day

A

Interval that elapses between two successive transits of a heavenly body across the same meridian

26
Q

State the difference between rain and showers

A

Rain:
- Falls from Stratiform clouds, Widespread and continuous rain fall

Showers:
- Falls from Cumuliform clouds, Isolated and intermittent rain fall

27
Q

Definition of atmosphere

A

The atmosphere is the gaseous envelope surrounding the earth.
No recognised upper limit to the atmosphere.
The atmosphere is retained around the earth by gravitational forces.

28
Q

What is the seasonal movement of the general circulation?

A

Winter solstice - Sun over the Tropic of Cancer Circulation shifts North

Summer solstice - Sun over the Tropic of Capricorn Circulation shifts South

29
Q

List the 5 formation requirements for a tropical cyclone

A
  1. A pre existing area of low pressure
  2. Sea Surface Temp (SST) at least 26 degrees
  3. Latitude minimum of 5 degrees N/S
  4. Upper level divergence
  5. Little or no Vertical Wind Shear
30
Q

How does the balance of Pressure Gradient Forces (PGF) and Coriolis cause geostrophic wind to flow parallel to isobars?

A

PGF and Coriolis forces act in opposite directions to produce geostrophic wind to flow parallel to isobars.

31
Q

Describe the basic weather conditions associated with Depressions/Lows

A
  • Wind circulates clockwise
  • Winds strongest near the centre
  • Winds generally strong
  • Air converges at low levels and diverges at high levels
32
Q

State the composition of the atmosphere and the names of the two main categories

A

Atmosphere id composed of a mixture of gases but also contains solid and liquid particles. Two main categories:

  • Non-variable constituents - nitrogen, oxygen, inert gases
  • Variable constituents - carbon dioxide, water, dust, salt, smoke, volcanic ash
33
Q

State the vertical layers and boundaries throughout the atmosphere

A 
Thermosphere - layer, closest to sun
Mesopause - boundary
Mesosphere - layer
Stratopause - boundary
Stratosphere - layer
Tropopause - boundary 
Troposphere - layer, closest to earth
34
Q

Describe the basic weather conditions associated with Troughs

A
  • An extension from a depression/low
  • ‘U’ shaped isobars (the stronger the U the worse the weather)
  • Strong winds
  • Wind moves clockwise
  • Marked by - - - - - - - -
35
Q

State the four trigger mechanisms associated with the formation of a cloud

A
  • Convection: occurs when air heated at the earths surface rises in the form of a thermal current or bubbles
  • Turbulence: when airflow moves over a trough surface, causing eddies
  • Orographic ascent: air is forced upwards by a barrier of maintains or hills
  • Widespread ascent: movement of cold air mass forcing warm air to rise before it
36
Q

List the 3 requirements for a thunderstorm

A
  • Instability
  • Moisture
  • Trigger: convection, orographic uplift, mass (frontal) ascent
37
Q

Definition of convection

A

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, while colder, denser material to sink under the influence of gravity which consequently results in the transfer of heat.

38
Q

Describe thunderstorms and the hazards associated with them

A
  • Most severe type of small-scale weather feature
  • Consists of a cumulonimbus cloud (reaches up to tropopause, produces heavy rain, hail, lightning and thunder
  • Lightning produced
  • Reduced visibility
  • Squalls - strong gusty winds
  • Turbulence
  • Icing
  • Hail
39
Q

List the types of logs available

A
  • Electromagnetic speed log
  • Doppler speed log
  • Sonar speed log
  • Sonar correlation speed log
  • Dutchman’s log
40
Q

What are speed logs used for?

A

Record ships speed and distance run

41
Q

What is LRG ‘Lock in’ error

A

At low rotation rates the LRG contra rotating beams can lock in

42
Q

Define Orthomorphism or Conformal

A

A chart projection of the earth is correctly presented including shape and scale, and bearing. At the expense of some area properties.

43
Q

What are the equipment requirements of having and using AIS

A

Mandatory to be carried on all vessels

AIS station consists of:

  • One VHF transmitter
  • Two VHF receivers
  • One VHF DSC receiver
  • A standard marine electronic comms link and sensor system
44
Q

What are the 3 different modes of AIS

A

Static mode - MMSI, Identity, Size, Type, NAVaid location

Dynamic mode - Position, time stamp, COG, SMG, Direction, Turn

Voyage Related mode - Draught, cargo, NAVplan, short text messages

MWOC Study (3 decks)

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