CH05 Meteorology

Question 1

What is the unit of pressure on a synoptic chart?

Answer 1

hectopascals. Although millibar represents the same value.

Question 2

What forces affect the direction of wind flow?

Answer 2

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

Question 3

What is Buys Ballot’s Law?

Answer 3

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

Question 4

Describe the idealised Earth?

Answer 4

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)

Question 5

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

Answer 5

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.

Question 6

What weather do you expect in the ITCZ?

Answer 6

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

Question 7

Where would you expect to sea trade winds?

Answer 7

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

Question 8

When are trades at their stronges?

Answer 8

Spring.

Question 9

What weather do you expect in the trade wind zones?

Answer 9

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

Question 10

What weather do you expect in the Westerlies zones?

Answer 10

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.

Question 11

What weather do you expect in the Polar regions?

Answer 11

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

Question 12

What are monsoons?

Answer 12

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

Question 13

What weather would a monsoon bring in winter?

Answer 13

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

Question 14

What weather would a summer monsoon bring?

Answer 14

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

Question 15

Daily cycle of land/sea breezes?

Answer 15

Day - sea breeze.

Night - land breeze.

Question 16

What are katabatic winds and where are they found?

Answer 16

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

Question 17

What causes a cold occlusion?

Answer 17

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

Question 18

What causes a warm occlusion?

Answer 18

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.

Question 19

What is a veering wind?

Answer 19

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

Question 20

What is a backing wind?

Answer 20

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

Question 21

What weather would you expect approaching a warm front?

Answer 21

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.

Question 22

What weather would you expect in a warm sector?

Answer 22

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.

Question 23

What weather would you expect when approaching cold front?

Answer 23

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.

Question 24

What weather would you expect when at the cold front?

Answer 24

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.

Question 25

What weather would you expect in an occluded front?

Answer 25

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.

Question 26

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

Answer 26

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.

Question 27

What weather would you expect within a TRS?

Answer 27

Winds of +34kts in lats

Question 28

What are the classifications of TRS?

Answer 28

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

Question 29

What are the signs a TRS is in your vicinity?

Answer 29

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.

Question 30

What actions can be taken to avoid a TRS?

Answer 30

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.

Question 31

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

Answer 31

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.

Question 32

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

Answer 32

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

Question 33

What are the reporting requirements for a TRS?

Answer 33

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.

Question 34

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

Answer 34

``` In summer Winds slight to moderate. Weather fine or partly cloudy In winter Overcast. Drizzle. ```

Question 35

What causes fog?

Answer 35

Cooling of air to the dewpoint temperature.

Question 36

What is sea/advection fog?

Answer 36

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

Question 37

What is frontal fog?

Answer 37

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.

Question 38

What is arctic sea fog/smoke?

Answer 38

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.

Question 39

What is radiation fog?

Answer 39

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