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Chief Mate / Master Unlimited > Meteorology > Flashcards

Meteorology Flashcards

1
Q

What to do before reading a barometer?

A

gently tap the glass

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2
Q

What is the purpose of the 2nd pointer on a barometer

A

Adjusted manually to current pressure, can see later if rising or falling

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3
Q

Difference between barograph and barometer
How do they work?

A

Barograph draws a graph!
shows readings/ Trend for 7 days
Aneroid cell - Thin metal cylinder, partly exhausted of air and sealed. sensitive to the slightest changes in pressure, and connected to a pointer to magnify the movement

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4
Q

Why is there a daily range of pressure shown on the barograph?

A

The Diurnal Range
Atmospheric pressure waves, period of nearly 12 hrs
caused by daily heating and cooling
sweep around the earth from East to west
Max in tropics of 3mb, decreasing north and south

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5
Q

What is a Psychrometer

A

Wet and dry bulb thermometer
Known as Masons Hygrometer (Stevensons Screen - the box)

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6
Q

How does a stevensons screen work

A

White box to shade thermometers from radiation heat, giving only air temp
2 thermometers, 1 regular, giving air temp,
1 kept wet by muslin dipped in a reservoir of distilled water, to give humidity. As the water evaporates, it loses heat, so the wet bulb is a lower temperature

The difference between the thermometers indicates the relative humidity.
Very little difference - 100% humidity
Large difference - low humidity

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7
Q

How do you use a Masons hygrometer to predict fog

A

Use the table in the Mariners Handbook
Dry bulb temp down the side/ depression of the wet bulb along the top
Read off the dew point
If Dew point is within 5ºC of the Sea temp, fog may form
Frequent observations allow you to graph dew point and sea temp to predict fog ahead of time

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8
Q

What is the Whirling Psychrometer?

A

Another hygrometer - wet and dry bulb thermometer
Both thermometers side by side, 1 wrapped in wet cloth
Whirl that MoFo around for 1 minute
Repeat several times until bored or lowest Wet bulb Temp obtained

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9
Q

What is Relative Humidity

A

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

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10
Q

What causes fog?

A

The cooling of air, so that it becomes fully saturated by the water vapour in it, called its Dewpoint

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11
Q

Sea or advection Fog
What causes it?
characteristics?
Location and time of year?

A

Warm moist air flows over a relatively cool sea
Main type of fog experienced at sea,
Will persist until conditions change
Often shallow, so mastheads may protrude above it
Sometime the base sits above sea level, clear low level
In temperate and high latitudes, most common in spring and early summer, when the sea temp is lowest
Prevelant in certain areas, where prevailing winds transport warm moist air over cold ocean current.
Incuding British isles and english channel,

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12
Q

Radiation fog
Causes?

A

Low lying land on clear nights
land radiates heat and cools down, cooling the air
Forming fog, this can occasionally drift out to sea but no more than 10-15 miles

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13
Q

Frontal Fog?
which Fronts?
Causes?

A

Warm or Occluded Front
Common if the Air temp ahead of the front is very low
Caused by mixing of warm and cold air at the front
Rain ahead of the front may help to raise humidty
Usually confined to a narrow belt at the front, but Sea fog may develop after.

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14
Q

Katabatic wind

A

Prevelant in high coastal areas
Land/Air cooling on high ground, cold dense air
Wind runs down hills/cliffs, accelerating with gravity
Can give little warning and be very powerful

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15
Q

The Mistral?

A

A violent, cold, North or NW wind that accelerates through France into the Med
Caused by a high pressure in Biscay, and a Low pressure in Genoa, funneling Cold Northerly winds through

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16
Q

Stratus/strato:
Cumulus/cumulo
Cirrus/cirro:
Alto:
Nimbus/Nimbo

A

Stratus/strato: flat/layered and smooth
Cumulus/cumulo: heaped up/puffy, like cauliflower
Cirrus/cirro: high up/wispy
Alto: medium level
Nimbus/Nimbo: rain-bearing cloud

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17
Q

Sources of weather forecasts?

A

Own ships instruments
VHF
SafetyNET info via Inmarsat
MSI Via Navtex
Weather Routing
SatC
WeatherFax
Internet
TimeZero

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18
Q

Publications with weather info?

A

Mariners Handbook
ALRS 3,4
Admiralty Routing Charts
Admiralty Sailing Directions
Admiralty Ocean Passages of the World

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19
Q

Mariners handbook for weather?

A

TRS - Causes and avoidance
Formation of Fronts and depressions
Fog
Ice
Heavy weather handling

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20
Q

ALRS for Weather?

A

Vol 3 frequencies for radio weather services and MSI
Vol 4 list of Met observational stations

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21
Q

Admiralty routing charts for weather?

A

All major oceans for each month of the year
Display average conditions for that month
Wind roses
currents
sea temps
fog and ice
tracks of TRS

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22
Q

Admiralty sailing directions for weather?

A

details of coastal areas, safe anchorages, nav hazards
prevailing conditions
Gives some average pressures for certain areas

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23
Q

Ocean passages of the world for weather

A

wealth of info on ocean voyage planning
for each of the worlds oceans
notes on weather, currents, swell and Ice for common routes

24
Q

What is a TRS

A

A tropical Revolving Storm
a Fecking hurricane, typhoon, cyclone

25
Causes and characteristics of a TRS?
Sea surface temps of at least 26ºC Latitudes between 8-15ºN or S Generally form at the east end of Oceans and track West May re-curve upon reaching 20ºN/S and hitting the westerly trade winds
26
Hurricane seasons? in the Caribbean?
At the end of the local summer, when sea temps are highest Caribbean June - October
27
Signs of an approaching TRS?
Barometer drops 3mb below average (within 5 hrs) Significant change in wind direction or strength Long low swell from approximate centre of storm Heavy rain High cirrus cloud followed by broken cumulous
28
Imminent? Soon? Later?
Imminent: within 6 hrs Soon: within 6-12 hrs Later: more than 12 hrs From time of issue
29
Average speed of a weather system?
20 knots, Steadily = 15-25 knots
30
Gale and Hurricane force winds?
Gale = Bf 8 - 34-40 Kn Hurricane Bf 12 - 64Kn or More
31
Visbility? Very Poor Poor Moderate Good
Very Poor = less than 1000m Poor = 1000m - 2M Moderate = 2-5M Good = 5M +
32
Wind Becoming Cyclonic Veering Backing
Becoming Cyclonic = considerable change in wind direction across the path of a depression within the forecast area. Veering = Clockwise - SW to W Backing = Anitclockwise - SW to S
33
Sea State: Smooth Slight Moderate Rough Very Rough High Very High Phenomenal
Smooth Wave height less than 0.5 m. Slight Wave height of 0.5 to 1.25 m. Moderate Wave height of 1.25 to 2.5 m. Rough Wave height of 2.5 to 4.0 m. Very Rough Wave height of 4.0 to 6.0 m. High Wave height of 6.0 to 9.0 m. Very High Wave height of 9.0 to 14.0. Phenomenal 14+
34
Passage of a low Conditions of an approaching Warm Front
Wind Backs and increase Cloud Thickens into lowering layers Weather Increasing rain Pressure Decreasing Temperature Increasing Visability Decreases in rain
35
Passage of a low Conditions in the Warm Sector
Wind Veers and increases Cloud Low level layers Weather drizzle and maybe fog Pressure rate of fall slows and steadies Temperature increasess ad steadies Visability Mod or poor
36
Passage of a low Conditions of an approaching Cold Front
Wind Backs and increases Cloud Increasing mid/high clouds (maybe Large Cumulonimbus) Weather Rain recommences Pressure Decreasing Temperature steady Visability Moderate
37
Passage of a low Conditions at the cold Front
Wind Veers and increases Cloud Cumulonimbus, breaks as front clears Weather heavy rain / squalls Pressure sharp increase Temperature sharp decrease Visability Sharp increase after squalls
38
Wind at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Backs and increases Warm Sector Veers and increases Approaching cold front Backs and increases Cold Front Veers and increases
39
Cloud at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Thickening into lower layers Warm Sector Low level layers Approaching cold front Increasing mid/High cloud Cold Front Cumulonimbus
40
Weather at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Increasing rain Warm Sector Drizzle, potentially fog Approaching cold front Precipitation restarts Cold Front Squalls and heavy showers
41
Pressure at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Decreasing Warm Sector Decreasing and steadying Approaching cold front Decreasing Cold Front Sharp increase
42
Temperature at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Increasing Warm Sector Increasing and then Steady Approaching cold front Steady Cold Front Sharp decrease
43
Visability at: Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Decreasing in rain Warm Sector Mod or Poor Approaching cold front Mod Cold Front Poor in squall, improving after
44
Dew point at Approaching warm Front Warm Sector Approaching cold front Cold Front
Approaching warm Front Increasing Warm Sector Increasing Approaching cold front Steady Cold Front Sharp fall
45
What info do we need to easure wind speed on a synoptic chart?
Our latitude Measure the distance between the isobars at the location Then compare to the scale to get the geostrophic wind speed Wind at sea level is 70% the geostrophic wind speed
46
How high are geostrophic winds?
600m
47
What is the ITCZ? What effect does it have
Intertropical Convergence Zone/ Equatorial Trough Thermal equator, As it moves N/S with the season, has a marked changed on weather conditions It pulls pushes the Cells as it moves
48
What effect does land and sea friction have on the wind?
Reduces the coriolis Force Cause wind to back in Northern hemisphere deflected 15º and slowed 25% over sea Deflected 30º and slowed 50% over Land
49
When does wind Convergence occur in the Northen hemisphere
When the wind is behind you and Land is on you right
50
What Is buys Ballot Law?
In the Northern Hemisphere, with the wind on your back the lower pressure is on your left side
51
Where are the Trade winds? what direction to they blow? Where are the westerlies?
up to 30º N/S NE in the N hemisphere 40-60º N/S
52
Where are the Horse latitudes?
30-40º N. Light and variable winds
53
Average pressure at sea level? WHat is key for using pressure for forcasting
1013 mb The Trend, one measurement is useless The barometer does not even need to be calibrated correctly, just need to know if it is going up or down
54
How can you tell which side of a trs you are? Which is the navigable side?
If the Wind is Veering, you are north of it NE to E Backing, you are south of it NW to W Steady, you are right in front of it! Northerly The south side, in the Northern hemisphere, system moves east but wind is from west, so relatively safe Also, South side the wind will push you away
55
How to use a precision barometer
adjust the dial until the light breaks on/off Read off the pressure Correct to sea level via table
56
What is a trough
Black line on a synoptic chart Show an area of relatively low pressure
57
How can you tell if a front is building or fading?
Building/frontogenesis - Dots in the line Fading/frontolysis - Hashes accross the line

Chief Mate / Master Unlimited (34 decks)

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