Meteorology

Question 1

What is Buys ballots law?

Answer 1

Face the wind. The centre of the low will be 90 - 135 degrees on the right hand in the N Hemisphere or on the left hand in the S Hemisphere

Question 2

What are characteristics of a depression in the N hemisphere?

Answer 2

Anti clockwise air movement

Brings warm air from the South ahead of the depression generating a warm front

Brings cold air from the North behind the depression generating a cold front.

Question 3

What are the characteristics of a warm front?

Answer 3

1. Takes a long time to clear
2. Shallow gradient and covers a large area
3. High cloud at the forward edge up to 500 miles ahead of the front (Cirrus, cirrostratus)
4. Pressure falling slowly
5. Thickening and lower cloud
6. Wind backing to SW or S
7. Persistent rain
8. warmer air and cloudy after the rain

Question 4

What are the characteristics of a cold front?

Answer 4

1. Steep gradient and quick to clear
2. Tall cumulonimbus clouds
3. Heavy rain
4. Cooler air after the rain
5. Sharp rise in pressure after the front
6. Sky clears
7. Wind veers W or NW and eases

Question 5

What are the characteristics of an occluded front?

Answer 5

The cold front has caught up with the warm front and pushes the warm air up.
The warm air doesn’t reach the surface so cool air remains.
Cold front weather dominates with heavy rain preceded by thick medium cloud from the warm front

Question 6

What are the 10 main cloud types?

Answer 6

High - Cirrus, cirrostratus and cirro cumulus

Medium - Alto stratus, alto cumulus, nimbo stratus

Low - Stratus, stratocumulus, cumulus, cumulonimbus

Question 7

What latitudes do TRS typically form?

Answer 7

Between 5 degrees and 30 degrees

Question 8

What speeds do TRS move at?

Answer 8

Between 10-15 kn before recurving

Between 20-25 kn after recurving

Can move at up to 40Kn

Question 9

How can I receive storm warnings to warn of a TRS?

Answer 9

1. VHF from the coast station
2. EGC message
3. NAVTEX
4. Meteorological websites

Question 10

What evidence can I see of a TRS in the area?

Answer 10

1. Barometric pressure 3hpa or more below mean for the time of year. If 5hpa or more below, it is certain.

Take hourly pressure readings

2. Appreciable change in strength or direction of the wind
3. Long low swell from the direction of the storm
4. Extensive cirrus cloud, followed by altostratus then broken cumulus

Question 11

How big is a TRS?

Answer 11

400-500 NM wide typically

Question 12

How do you find the centre of a TRS?

Answer 12

Facing the wind, the centre will be 100-125 degrees on the right in the N Hemisphere and on the left in the S Hemisphere when the storm is 200Nm away

The closer the observer is to the centre, the closer it will be to 90 degrees

The TRS path can be approximated by taking 2 bearings 2-3 hours apart

Question 13

What is the dangerous semicircle of a TRS?

Answer 13

The North side of the TRS in the North hemisphere and the South side of a TRS in the southern hemisphere.

It is dangerous because the wind direction pushes the ship into the path of the storm

Question 14

What is the navigable semicircle in a TRS?

Answer 14

The South side of the TRS in N Hemisphere and North side of the TRS in the S Hemisphere

The wind direction pushes the ship away from and behind the storm

Question 15

How far from a TRS should a ship pass to be safe?

Answer 15

Always more than 80Nm but ideally more than 250 NM

Question 16

In the Northern hemisphere, what action should you take if the pressure is falling and the wind is veering?

Answer 16

I am in the dangerous semicircle so i will put the wind on the starboard bow and keep altering to starboard as the wind veers

Question 17

In the Northern hemisphere, what action should you take if the pressure is falling and the wind is steady?

Answer 17

I am in the track ahead of the storm. I should put the wind on the starboard quarter with best speed.

Question 18

In the Northern hemisphere, what action should you take if the pressure is falling and the wind is backing?

Answer 18

I would put the wind on the starboard quarter with best speed and keep altering to port as the wind backs.

Question 19

What should you do if your vessel is in port and there is a TRS warning approaching?

Answer 19

Vessel should go to sea if the storm is approaching within 80Nm

Question 20

What is the difference between the wind in the N Hemisphere TRS and the wind in the S Hemisphere TRS?

Answer 20

The wind veering in the North is dangerous.

The wind veering in the South is safe.

Question 21

What are the two main types of fog?

Answer 21

Advection fog where warm moist air blows over cold sea

Radiation fog where fog forms over cold lay and drifts over sea

Question 22

In what conditions does fog form?

Answer 22

When the air dew point is lower than that of the sea temperature.

When the dew point is within 5 degrees of the sea temperature, fog is likely.