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Linglis OOW Module study > Meteorology > Flashcards

Meteorology Flashcards

1
Q

Define Barometric pressure

A

The amount of air pressure exerted by a column of air above the measuring point

Surface pressure varies with temparature

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2
Q

What is the mean atmospheric pressure?

A

1013 hPa (millibars)

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3
Q

Define Stable air

A

An air parcel that is cooler than the surrounding atmosphere will sink as the cool air is less dense than the warm air

This creates a stable air parcle as it does not continue to rise and create precipitation etc

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4
Q

Define Un stable air

A

An air parcel that is warmer than the surrounding atmosphere will continue to rise as cold air is denser than warm air

This produces clouds and rain

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5
Q

Explain the Coriolis effect

A

The speed of the Earths rotation is seen to be faster at the equator than at higher latitudes, due to the Earths circumference.

As the Earth rotates in an E’ly direction, Air masses moving towards the poles are seen to be deflected to the Right in the Northern Hemisphere, and the Left in the Southern Hemisphere, seemingly overtaking the Earths surface

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6
Q

Backing

A

When winds are deflected in an anti clockwise direction they are described as backing

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7
Q

Veering

A

When winds are deflected in a clockwise direction they are described to be Veering

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8
Q

Northern hemisphere direction of wind rotation in pressure systems

A

Low pressure systems rotate in an anti clockwise direction

High pressure in a clockwise direction

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9
Q

Southern Hemisphere direction of wind rotation in pressure systems

A

Low pressure systems rotate in a clockwise direction

High pressure in an anti clock wise direction

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10
Q

What are the four factors that help to determine local wind strength and direction

A
  1. Geographical Location
  2. Proximity of areas of high and low pressure systems
  3. Pressure Force Gradient between areas of high and low pressure systems
  4. The proximity of land masses
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11
Q

Clouds form due to these four factors

A
  1. Ascent in convection currents
  2. Uplifting at a front
  3. Air being forced over high ground (ornographic Cloud formation)
  4. Radiation cooling
  5. Turbulence Mixing
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12
Q

Define Dew Point

A

The atmospheric temperature (varying with pressure and Humidity) below which the air becomes saturated, water droplets begin to condense and Water droplets that we can see (clouds), and dew begins to form

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13
Q

Define Relative Humidity

A

The amount of water vapour present in the air expressed as a % of the amount needed for saturation at the same temperature

(the amount of water vapour an air parcel can hold)

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14
Q

Relative Humidity Formula

A

Actual vapour density / Saturation vapour density x 100

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15
Q

How is Advection fog Formed

A

Warm moist air being transported over cold Sea surface or ocean currents

Most commonly in spring and early summer when the ocean temperatures are at their lowest

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16
Q

Where is Advection fog most commonly found

A

In areas where the prevailing winds transport warm moist air over areas of cold water or over the major cold ocean currents

Polar regions in summer

Grand banks of Newfoundland (Labrador current)

NW Pacific Ocean (Kamchatka current)

Cold ocean currents off the Western seaboards of continents lying within the trade wind belts (California, Chile, Peru, SW Africa, Morocco)

British isles

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17
Q

What does Buys ballot Law state (N hemisphere)

A

If you stand with your back to the surface wind in the N hemisphere:

The centre of the LP system will be to your left and slightly forward
The centre of the HP system will be to your right and slightly backwards

18
Q

What does Buys ballot Law state (S Hemisphere)

A

If you stand with your back to the surface wind in the S hemisphere:

The centre of the LP system will be to your right and slightly forward
The centre of the HP will be to your left and slightly back

19
Q

How does Frontal Fog Form?

A

Forms due to the mixing of cold and warm air on two sides of a passing (warm) frontal system.

Rain ahead of the front may help to raise the relative humidity and aid the formation of fog

Usually confined to a narrow belt in front of the fog, however Advection fog can form in the warm moist air behind the front.

20
Q

How does Radiation fog form

A

Due to radiation cooling of the Earth

Forms over low-lying land, valleys, water and damp vegetation

Ground cools, damp moist air flows upwards, creating low lying fog

Usually late at night and early hours of the morning

21
Q

Published sources of Weather Information

A

Mariners Handbook (NP100)

Admiralty Sailing directions (pilot books)
Commercial nautical almanacs

Admiralty Routeing charts

Ocean passages for the World

ALRS Vol 3 (Maritime Weather Services. Safety Information broadcasts. Worldwide NAVTEX and SafetyNET information)

22
Q

Function of a barograph

A

Allows the reader to follow trends in a barometer

Records changes in Barometric pressure via a lever and pen, recording variations of pressure on a chart attached to a revolving drum. This coincides with a Barometer

Drum makes one revolution in 7 days

Should be secured in a position where least likely to be affected by vessel movement

23
Q

Hygrometer

A

Two thermometers, one with a dry bulb, one with a wet bulb covered in muslin, kept damn with fresh water

Stored inside a wooden box painted white with louvered sides (Stevensons screen)

The wet muslin allows the air to be fully saturated around the bulb

The difference in temperatures between the two Thermometers (wet bulb depression) is the measurement used to measure the relative humidity and dew point of the ambient air

This is done via the Dew point tables in the Mariners handbook

24
Q

Areas where advection fog may occur

A

North Sea

North West Atlantic (Newfoundland)

North West Africa

Polar regions in Summer

North West Pacific Ocean (Kamchatka Current)

British Isles

25
Q

Some items found on an Admiralty Routeing chart

A

General weather conditions for the year, based on previous observations

Ice limits

Shipping routes

Ocean currents

Wind Roses

Mean Sea temp

Mean Dew point temp

Load Line Limits

26
Q

Define the Inter Tropical Convergence Zone (ITCZ)

And its weather patterns

A

The equatorial Trough

Considered to be the Earths thermal equator.

Moves North and South with the declination of the sun and change of seasons.

Weather will usually be fair, with variable or light winds, alternating with squalls and thundery showers.

Conditions are generally worst when the trade winds are strongest

27
Q

Mistral Wind

A

Cold Northerly Catabatic wind on the Southern French Coast

28
Q

Sirocco Wind

A

Warm Dry continental wind from Africa over Europe

29
Q

Levante

A

Strong wind of a convergence zone running between the semi permanent LP of the Med, and the semi permanent HP of western Europe

Causes strong easterlies down through the Gibraltar straights

30
Q

Geostrophic wind deflection over land vs sea:
Speed and direction

A

Speed: 40% less over land, 25% less over sea

Direction: 30 degrees over land, 15 degrees over sea

31
Q

Define Gradient wind

A

The simple wind direction from a H to L pressure system

32
Q

Define Geostrophic wind

A

Gradient wind effected by the Coriolis effect

33
Q

Define Surface wind

A

Geostrophic wind after friction / deflection from land and sea masses,

34
Q

Define Saturation Point

A

The state of the atmosphere in which an air parcel is at the maximum amount of water vapour it can hold, at a specific temperature

35
Q

What is a precision aneroid barometer

A

What it says on the tin. Reads, very precisely, the atmospheric pressure at a specific height

Usually found on MET reporting ships
Must be corrected for temp and height above sea level according to the included calibration card

36
Q

Use of a Masons Hygrometer

A
  1. Obtain the Dry bulb reading and the wet bulb depression from the hygrometer
  2. With these readings, pull the Dew point from the Dew point table in NP100
  3. Create a graph, with the x axis labeled ‘temperature’, and the y axis labeled ‘time’
  4. Plot measurement, continue to plot and draw a LOBF
  5. Meanwhile, take recordings of the Sea level temp, and plot. Also Draw a LOBF
  6. Where the two lines intersect is the Dew point
  7. The point at which the two lines are 5 degrees apart is considered the ‘warning of approaching dew point’
37
Q

What are the 6 Air masses surrounding the UK

A

Arctic Maritime
Polar Continental
Tropical Continental
Tropical Maritime
Returning Polar Maritime
Polar Maritime

38
Q

What is a ‘mid latitude depression’

A

Essentially a LP system and frontal system, with a warm and cold front.
Moves NE towards the UK

39
Q

How to interpret a wind rose on an Admiralty Routeing chart

A
40
Q

Define an Isobar

A

A line of Equal Pressure

Linglis OOW Module study (43 decks)

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