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NP100 > CH05 Meteorology > Flashcards

CH05 Meteorology Flashcards

1
Q

What is the unit of pressure on a synoptic chart?

A

hectopascals. Although millibar represents the same value.

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2
Q

What forces affect the direction of wind flow?

A

Pressure Gradient Force - movement from high to low.
Coriolis Force - deflection due to earth’s rotation.
Friction - tbc.

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3
Q

What is Buys Ballot’s Law?

A

Face the wind and Low is on your right in the NH (LHS in the SH).

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4
Q

Describe the idealised Earth?

A 
N (H)
Polar Easterlies
60 (L)
Westerlies
30 (H)
NE Trades
0/ITCZ (L)
SE Trades
30 (H)
Westerlies
60 (L)
Polar Easterlies
S (H)
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5
Q

What effect does the annual cycle in the sun’s declination have on the idealiesd Earth?

A

There is a corresponding movement of the pressure belts and winds. Generally there is 5-8° change in lat some 6-8 weeks behind the sun.

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6
Q

What weather do you expect in the ITCZ?

A

Light or calm winds. Alternating with squalls and thundery showers. Massive cumulonimbus are common.

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7
Q

Where would you expect to sea trade winds?

A

In all major oceans except N Indian and China Seas (where monsoons predominate).

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8
Q

When are trades at their stronges?

A

Spring.

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9
Q

What weather do you expect in the trade wind zones?

A

Generally fair with some broken cumulus clouds. Winds averaging force 3-4 generally from N/S E.

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10
Q

What weather do you expect in the Westerlies zones?

A

Continual passage or depressions from W to E. Wind varying greatly in both direction and strength. Roaring forties in SH. In NH fog common in W parts of oceans in summer.

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11
Q

What weather do you expect in the Polar regions?

A

Often unnavigale due to ice. E winds prevail and gales are common in winter. Usually cloudy and fog is frequent in summer.

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12
Q

What are monsoons?

A

These deviate from the idealised earth due to large land masses developing significantly H or L pressures as the land heats/cools seasonally.

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13
Q

What weather would a monsoon bring in winter?

A

Typically NE-N moderate to fresh winds (may surge). Generally cool, fair with broken cloud. Coastal areas may see extensive low cloud and drizzle.

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14
Q

What weather would a summer monsoon bring?

A

Typically SW-S fresh to strong with considerable seas. Warm humid air gives cloud and rain on windward coasts.

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15
Q

Daily cycle of land/sea breezes?

A

Day - sea breeze.

Night - land breeze.

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16
Q

What are katabatic winds and where are they found?

A 
Accumulation of cool air on/near sloping ground. Further light may displace. Give strong winds, up to gale/storm force in extreme cases. Wind may extend several miles offshore. 
Commonly found:
Greenland
Norway
N Adriatic Sea
E Black Sea 
Antarctica
17
Q

What causes a cold occlusion?

A

Cold front moving faster than warm front and subsequently displacing the warm sector and front upward.

18
Q

What causes a warm occlusion?

A

Cold air in the cold sector being less dense than the air ahead of the warm front displacing the warm sector and cold front upward.

19
Q

What is a veering wind?

A

A wind which changes direction in a clockwise fashion with height.

20
Q

What is a backing wind?

A

A wind which changes direction in an anticlockwise fashion with height.

21
Q

What weather would you expect approaching a warm front?

A

Winds backing in NH and veering in SH.
Clouds thicken and lower, sun obscured.
Intermittent light precipitation increases to moderate to heavy just ahead of front.
Pressure falls fater.
Very slow increase in temperature.
Steady reduction in visibility in increasing precipitation.

22
Q

What weather would you expect in a warm sector?

A 
Winds veers in NH and backs SH.
Medium and high-level cloud breaks up. Typically, lower level cloud remains.
Precipitation eases to drizzle.
Fog banks may develop.
Pressure stabilises.
Sharp increase in temperature.
Visibility is moderate to poor.
23
Q

What weather would you expect when approaching cold front?

A

Winds back and freshen in NH and veer and abate in SH.
Increase in medium and high cloud, often obscured by thickening of low cloud.
Precipitation recommences.
Pressure falls.
Temperature steady.
Dewpoint steady.
Visibility moderate.

24
Q

What weather would you expect when at the cold front?

A

Winds veers markedly in NH and backs in SH.
Thank banks of cloud break up as front clears.
Precipitation moderate to heavy then clearing as front passes. Showers may develop.
Pressures sees sharp rise.
Temperature falls sharply.
Dewpoint falls sharply.
Visibility improves sharply.

25
Q

What weather would you expect in an occluded front?

A

Winds backing in NH and veering in SH.
Sky completely overcast.
Precipitation moderate to heavy.
Other characteristics of both warm and cold front develop but depend on the combination of factors.

26
Q

What weather would you expect if a frontal system was passing between you and the farthest pole?

A

Winds backing in the NH and veering in the SH.
Ahead of system skies begin to cloud over.
Showers become more frequent.
Pressure fall increases.
As system passes long periods of precipitation and low cloud with poor visibility experienced.
Pressure drops suddenly.
Behind system precipitation breaks into showers and visibility improves.
Pressure gradually increases.

27
Q

What weather would you expect within a TRS?

A

Winds of +34kts in lats

28
Q

What are the classifications of TRS?

A

Tropical Depression (7 or less).
Tropical Storm (8/9).
Severe Tropical Storm (11/12).
typhoon, Hurricane, Cyclone (12 or more).

29
Q

What are the signs a TRS is in your vicinity?

A

A long low swell from the direction of the storm.
Barometric pressure (corrected) 3hPa below the mean for the time of year and diurnal variation. 5hPa is extremely clear indication.
Appreciable change in direction and strength of wind.
Extensive cirrus cloud, followed by altostratus and then broken cumulus.
High seas.
Gale force winds.

30
Q

What actions can be taken to avoid a TRS?

A

If the TRS is between you and the equator (NH), put the wind on your starboard bow/quarter and keep it there.
If the TRS is between you and the equator (SH), put the wind on your port bow/quarter and keep it there.
If the TRS is farther from the equator (NH) than you then put the wind on your starboard quarter and turn to port as the wind comes onto your port quarter.
If the TRS is farther from the equator (SH) than you then put the wind on your port quarter and turn to starboard as the wind comes onto your starboard quarter.

31
Q

How can you determine where a TRS is and it’s potential path(S)?

A

Hourly pressure (corrected) readings in TRS regions.
Monitor storm warnings.
Buys Ballot’s Law give general bearing. Two such bearings (R) 2-3 hrs apart will give approx. path.
Assume TRS is moving away from equator.
Assume W’ly element to direction.
Remember after passing lat 20° the path usually recurves and heads E’ly.

32
Q

Action to take when a TRS approaches a harbour/anchorage?

A

Put to sea.

Heave to with wind on starboard bow (NH) or port bow (SH).

33
Q

What are the reporting requirements for a TRS?

A

SOLAS requires that when a ship suspects the existence of or is in the vicinity of a tropical storm the Master must communicate the information by all means at his disposal to ships in the vicinity and to the nearest maritime ration station or signal station with which he can communicate.

34
Q

What weather would you expect in an area of high pressure?

A 
In summer
Winds slight to moderate.
Weather fine or partly cloudy
In winter
Overcast.
Drizzle.
35
Q

What causes fog?

A

Cooling of air to the dewpoint temperature.

36
Q

What is sea/advection fog?

A

When warm moist air flows over a relatively cold sea surface and cools to its dewpoint (typical fog at sea).
Can be predicted by monitoring the air and sea surface temperatures (using windward Stevenson screen and dewpoint table in norries).
Prevalent in:
Polar regions in summer
Grand Banks of Newfoundland
NW Pacific Ocean
West coast of African and American continents
British Isles

37
Q

What is frontal fog?

A

A narrow belt of fog just ahead of a warm fronts boundary.

Occurs where the temperature of the air in advance of the front is very low.

38
Q

What is arctic sea fog/smoke?

A

Occurs in high latitudes.
When very cold air moves over a relatively warm sea surface.
Sea surface evaporates but cold air is unable to hold the moisture and it therefore re-condense and forms fog on the surface.

39
Q

What is radiation fog?

A

Forms over low-lying land on clear nights when maximum radiative cooling can occur.

NP100 (10 decks)

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