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MasterYachts_JP > Master Yachts | Meteorology > Flashcards

Master Yachts | Meteorology Flashcards

1
Q

The atmosphere is divided vertically into Troposphere and Stratosphere, where does the weather we experience on earth generated from?

A

The Troposphere.

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2
Q

When air is forced to rise, it will…

A

…cool.

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3
Q

Gases forming in the atmosphere have a physical weight which produces an average pressure at sea level, what is it?

A

1013 millibars (mb), 1013 hectopascals (hPa)

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4
Q

What is the Dry Adiabatic Rate (DALR) for rising, cool, unsaturated air?

A

1 degree per 100 metres.

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5
Q

Saturated air forced to rise will cool at a variable Saturated Adiabatic Lapse Rate (SALR), what is the average rate?

A

0.5 degrees per 100 metres.

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6
Q

Normally wind will move at right angles to isobars, but what force is present that causes it to be defected to the right in the Northern hemisphere, and to the left in the Southern Hemisphere?

A

The Coriolis Effect.

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7
Q

What are the regions between 30 and 40 degrees called, and what weather is associated with these regions?

A
  • Horse latitudes or Variables
  • Light variable winds, fine weather associated with sub-tropical ant-cyclones, high pressure areas.
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8
Q

The surface outflow from the sub-tropical anti-cyclones produce trade winds with mean speed of 14 kts, what latitudes do these occur in?

A

Located 25 to 30 degrees N/S of the equator.

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9
Q

What is Buys Ballots Law? And where does this law not apply?

A
  • In the Northern Hemisphere, if you face the wind, the low pressure centre will be about 90 to 135 degrees on your right hand
  • In the Southern Hemisphere, if you face the wind, the low pressure centre will be about 90 to 135 degrees on your left hand
  • Within 5 degrees of the equator as there is no apparent Coriolis force
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10
Q

What is a Monsoon area?

A

An area that experiences a marked seasonal change of prevailing wind direction, and a marked change in precipitation with the wind change producing wet and dry seasons.

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11
Q

When does the SW Monsoon of the North Indian Ocean occur?

A

From June to September.

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12
Q

When does the NE Monsoon of the North Indian Ocean occur?

A

October to March

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13
Q

The amount of water vapour that an air mass can contain depends on temperature - the higher…

A

…the air temperature, the greater the quantity of water vapour that the air can hold

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14
Q

What is saturated air and what occurs when it is cooled and becomes unsaturated?

A
  • Saturated air contains the maximum amount of water vapour at its present temperature.
  • If cooled the excess water will form as water droplets, in the form of dew, clouds, mist, fog, drizzle or rain
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15
Q

What is relative humidity?

A

This is the ratio of the amount of water vapour actually present to the maximum amount possible at the same temperature expressed as a percentage (%).

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16
Q

What are the 3 types of fog?

A
  1. Advection fog (sea fog)
  2. Frontal fog
  3. Radiation fog (land fog)
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17
Q

Describe the Polar Maritime Air mass.

A
  • cold, moist, stable air
  • moves over relatively warm sea
  • destabilises and forms cumulus cloud
  • creates showery weather, often good visibility
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18
Q

Describe the Polar and Arctic Continental Air mass.

A
  • very cold air originating from cold land mass
  • has low moisture content
  • often clear skies
  • after passing may become unstable, form cumulus cloud and result in showers
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19
Q

Describe the Arctic Maritime Air mass.

A
  • very cold originating from above very cold sea
  • stable
  • low temperature means low moisture content
  • may pick up moisture as it passes over warmer sea, becomes unstable, cumulus cloud and rain or hail squalls
20
Q

Describe Tropical Maritime Air mass.

A
  • warm
  • very moist, unstable air originating from warm sea
  • cooled from below
  • forms Stratus cloud
  • drizzle
  • possible advection fog
21
Q

Describe Tropical Continental Air mass.

A
  • warn dry unstable air originating from over very dry land
  • cools as it moves north
  • usually clear skies, warm dry weather in summer
  • may sometimes carry dust or sand, creating haze
22
Q

What group of clouds form 6000m (high clouds) upwards?

A
  • Cirrus, cirrostratus and cirrocumulus
  • note: Ci, Cs and Cc
23
Q

What group of clouds form between 2000m to 6000m (medium clouds)?

A
  • Altocumulus and altostratus
  • note: Ac and As
24
Q

Which group of clouds form below 2000m (low clouds)?

A
  • Stratocumulus, nimbostratus, stratus, fractostratus
  • note: Sc, Ns, St and Fs
25
Q

What is the vertifical extent of Cumulus (Cu) and Cumulonimbus (Cb)?

A
  • Cu - 2000m to 4000m
  • Cb - 2000m to 6000m
26
Q

What cloud type is necessary for the formation of hail and thunder?

A

Cb - Cumulonimbus

27
Q

What are some important elements to Tropical Storms?

A
  • Originate in the tropics - 8 to 20 degrees N/S
  • Pressure gradient steep
  • Isobars being close to circular, no fronts
28
Q

What wind strengths do the following exhibit?
* tropical depression
* moderate tropical storm
* severe tropical storm
* hurricane

A
  • Tropical depression - force 7 or less
  • Moderate tropical storm - force 8 and 9
  • Severe tropical storm - force 10 and 11
  • Hurricane - force 12
29
Q

The size of a Tropical storm can vary, what may be experienced when encountering a tropical storm?

A
  • Force 12 may be encountered 25 to 150 miles from the centre
  • Storm width may exceed 300 miles in diameter
  • The eye may be 10 to 30 miles in diameter
30
Q

What conditions must exist for the formation of a Tropical Storm?

A
  1. Sea temperature greater than 26 degrees C, and humidity in the air above
  2. Latitude greater then 5 degrees
  3. Low wind shear (change of wind speed with height)
  4. Divergency of rising air at altitude, reducing pressure
  5. Tropical stimulus to initiate the process (minor low pressure or heavy cloud formation)
31
Q

When generally do Tropical storms occur?

A

They are most frequent late summer and early autumn.

32
Q

What are the precursory signs of a Tropical Storm?

A
  • Barometer reading 3 hPa or more below mean for time of year as shown on weather routeing charts. If 5 hPa below normal, the storm may be within 200nm.
  • Long low swell from unusual direction
  • High cirrus clouds
  • Wind may change direction from normal
  • Sunrise or sunset may exhibit lurid clour clouds
  • Visiblity becomes exceptionally poor as it approaches
33
Q

What is diurnal variation in relation to pressure?

A

This is the variation in pressure at a location due to heating and cooling of the air from the sun - found in the Sailing Directions

34
Q

What does the term Pressure Gradient mean?

A

The Pressure Gradient is the rate of change of pressure with distance, measured at right-angles to the isobars.

35
Q

What does the term Pressure Tendency mean?

A

The Pressure Tendency is the rate of change of atmospheric pressure with time, the standard time being over 3 hours.

36
Q

What are the regions to a storm termed?

A
  • Dangerous semi-circle
  • Navigable semi-circle
  • Dangerous quadrant
  • Eye
37
Q

What is the World Meteorological Organisation (WMO)?

A

Its purpose is to foster international co-operation in the collection and dissemination of meteorological information. Responsible for establising international standards in forecasting.

38
Q

What are some sources of weather information?

A
  • Mariners handbook
  • Admirlaty sailing directions
  • Admilraty list of radio signals, VIII
  • Admiralty ocean passages of the world
  • Admiralty and Imray routeing charts
  • US hydrographic office monthly pilot charts
39
Q

What information does a roueting chart contain?

A
  • Prevailing winds
  • Ocean currents
  • Ice limits
  • Tropical storm tracks
  • Frequency of winds over Force 6
  • Dew point temperatures
  • Mean sea temperatures
  • Mean air temperatures
  • Mean air pressure
  • Fog frequency
  • Low visibility
40
Q

What sources transmit weather information?

A
  • NAVTEX
  • Fax
  • Satellite
  • Coastguard stations
  • Port radio stations, VTS
41
Q

What does a Surface or Synoptic chart show?

A
  • Observed general surface pressure over a large area for a certain date/time.
42
Q

What does a Forecast or Prognostic chart show?

A
  • General surface pressure situation over a large area for a certain date/time, in the future.
43
Q

Winds blow from high to low pressure, which way are they deflected due to the Coriolis effect, in both hemispheres?

A
  • In the northern hemisphere, deflected to the right
  • In the southern hemisphere, defected to the left
44
Q

What do the terms ‘gale’ and ‘imminent’ mean in weather forecasting?

A

Winds of at least force 8 (34 - 40kts), expected within 6 hours at time of issue.

45
Q

What do the terms ‘very poor’ and ‘slowly’ mean in weather forecasting?

A

Visibility less then 1000m, and moving at less than 15kts.

46
Q

What do the terms ‘rising or falling’ and ‘veering’ mean in weather forecasting?

A

Pressure change of 1.6 to 3.5 hPa in preceding 3 hours, and change of wind direction clockwise.

47
Q

What do the terms ‘slight’ and ‘very rough’ mean in weather forecasting?

A

Wave height of 0.5 to 1.25m, and wave height of 4 to 6m

MasterYachts_JP (18 decks)

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