Meteorology

Question 1

Explain a sea breeze

Answer 1

As land is heated during daytime the air over it is heated by conduction. This heating causes a reduction in density and thus a pressure decrease over the land.

The sea temperature remains more or less constant and the pressure over it is relatively high compared with the land and a pressure gradient is formed.

The difference in pressure creates an airflow from high to low - from the sea to the land

Question 2

Explain katabatic winds

Answer 2

Occurs when there is intense radiation on a clear night. This causes cooling over sloping ground. The colder and denser air adjacent to the slope will now flow down the slope under the influence of gravity producing the katabatic wind

Question 3

State at least 5 items of meteorological info to be found on a admiralty routeing chart

Answer 3

Ocean current - set and rate

Mean sea temperature chartlet

Wind direction and force - weather rose

Dew point chartlet

Mean air temperature

Fog chartlet

Mean air pressure

Low visibility chartlet

hurricane forecasting and track

Question 4

Define the term synoptic chart and its use for weather forecasting

Answer 4

The synoptic chart shows pressure systems, isobars and weather fronts,
At a given level over a large area at a given date and time.

To indicate the weather to be expected

Question 5

Describe and compare the information obtained from a barometer and barograph and explain their use in weather forecasting

Answer 5

Barometer - records pressure at a given time by using fixed pointer from a previous reading the change over a period of time can be observed

Barograph - gives a continual readout on graduated paper boy use of pen and revolving drum thus provides for the yachtsman the trend/tendency

Both used to obtain the atmospheric pressure and trend and to predict future weather. From the pressure trend, a mariner can determine the likely weather to be experienced, in simple terms ie- rising pressure indicated improving weather and the opposite with decreasing pressure.

Question 6

Define the term prognostic chart

Answer 6

Is a weather chart forecasting the state of the atmosphere over a large area at a given level and at a future time

Question 7

List four factors which determine the strength and direction of winds

Answer 7

Geographical location

Proximity of areas of high and low pressure systems

Pressure gradient between areas of high and low pressure systems

Proximity of land

Question 8

Describe the weather conditions expected whilst navigating in the ‘variables’

Answer 8

Winds are light and variable and the weather is generally fair with small amounts of cloud and rain

Question 9

Describe trade winds, their location and how they migrate with seasons

Answer 9

Are air streams originating in the sub tropical oceanic high pressure areas of the N. & S. Hemisphere blowing on the E. And equatorial sides of the areas of high pressure towards the equator.

The general direction is NE in the N. HemiS

And SE in the S. HemiS

They are encountered and blow with remarkable persistence over all major oceans
EXCEPT the N. Indian Ocean and China seas

The zones migrate seasonally and in each hemisphere extend to about 30* N and S latitude in the respective summers

And 25* N and S in winter

Question 10

State five meteorological publications consulted when planning a passage

Answer 10

The mariners handbook

Admiralty list of radio signals VOL3

Admiralty routing charts

Admiralty sailing directions (pilot books)

Weather forecast source

Commercial sailing directions / Pilot Books e.g : Adlard Coles

Commercial routing charts e.g. Imray

US Hydrographic office monthly pilot charts

Question 11

Explain the terms ‘synoptic’ and ‘prognostic’ chart used in weather forecasting

Answer 11

The synoptic chart shows pressure systems (highs and lows), isobars and weather front (warm and cold), at a given level over a large area at a given date and time

Question 12

Describe a weather routing service AND explain the advantages of using this service

Answer 12

A weather service is a commercial service provided by a meteorological organization, details of whom can be foi8nd in ALRS VOL3, specifying and updating an individual recommended route for a specific voyage by means of the following:

Makes use of actual weather (as opposed to expected climatic conditions)

Provided by highly trained an experience teams for forecasters and mariners

Route constantly reviewed and modified if required according to the actual and predicted weather conditions

Route “Optimized” to achieve a specified aim such as least time, minimum storm damage, etc..

Question 13

List SIX publications that may be available onboard to help the OOW assess weather information

Answer 13

Admiralty list of radio signals

Mariners handbook

AdmiraSailing directions/ Pilot books

Routing charts

Marine observation handbook

Yachtsman’s handbooks/almanacs

Question 14

State the months that hurricanes are generally expected in the Caribbean Sea

Answer 14

1st of June to 30th of November

Question 15

Describe the advantages of using a weather routing service

Answer 15

Makes use of actual weather/sea conditions (as opposed to expected climatic conditions)

It’s provided by highly trained and experienced teams of forecasters and mariners.

Route constantly reviewed and modified according to actual & predicted conditions

Route optimized to achieve specified aim:
Least time, minimum storm damage, safest passage, reduce fuel costs, ETA,

Potential reduction on wear and tear

Critical information received in time to take avoiding action around danger areas

Insurance companies may insist on their use

Reduced insurance costs overall

Question 16

Describe a whirling psychrometer and how and what it is used for

Answer 16

Consists of a wet and dry bulb thermometer, is similar to a football rattle and is rotated as per instructions by hand. The values of wet and dry temperatures are the read, the difference (depression) is then used to enter the appropriate tables along with the dry temperature to obtain.

Practical use: to obtain either the dew point temperature or the relative humidity of air (depending on tables used)
This can then aid the forecast of sea fog in conjunction with sea temp

Question 17

Describe how katabatic winds can occur

Answer 17

On clear nights the slope of mountains radiate out their heat and the temperature falls.

The air in contact with the ground becomes heavier and rolls down the slope.

Normally as it descends it would warm at the adiabatic rate lapse rate (variation of air temperature with height), but because it is still in contact with the cold ground this effect is reduced and the air increases its flow down the slope.

These winds can reach high speeds and are often funneled down water-courses

Question 18

Describe the formation of land and sea breezes

Answer 18

The land is heated by the sun during the day and loses heat at night relatively quickly and therefore the adjacent surface air changes temperature accordingly.

Hot air rises and therefore the pressure drops, similarly cold air falls and the pressure increases.

The sea temperature however changes very little and will therefore throughout a 24-hour period will be relatively hotter or colder than the adjacent land.

The change of pressure over the land causes on - and off shore winds to blow.

Sea breezes may reach force 5 in places, but land breezes are normally not as strong

Question 19

Define the ITCZ

Answer 19

Intertropical convergence zone

High temperatures at the solar equator create the low surface pressure where the trade winds converge.

In this equatorial trough (or tropical low) lies a zone of calm and weak winds of no prevailing direction. Here the air, which is very moist and heated by the sun, tends to expand and rise, maintaining the low pressure of the area.

These winds, which are roughly between 5N and 5S, are generally known as the doldrums.

This area is called the ITCZ or the equatorial belt of variable winds and calms. Because of the converging moist air and high potential for rainfall in the doldrums this region coincides with the worlds latitudinal belt of heaviest precipitation and most persistent cloud cover

Question 20

State the months when TRS would expected in the Caribbean

Answer 20

Tropical Revolving Storms

1st June - 30th November

Question 21

List 4 broadcast and 5 published sources of weather information

Answer 21

Broadcasts:

Radio weather forecasts for shipping
Radio navigation warnings
Navtex
Internet

Published sources:

Admiralty sailing directions
Routing charts
Ocean passages of the world
Mariners handbook
Admiralty list of radio signals - vol 3/4

Question 22

Describe buy ballots law for both hemispheres

Answer 22

N Hemisphere - with ones back to the the TRUE wind, the low pressure will be on the left hand side

S Hemisphere - with ones back to the true wind, the low pressure will be on the right hand side.

Question 23

Define dew point

Answer 23

Is the temperature at which water vapor in the air condenses into liquid water, such as in the form of dew, fog, or possibly rain

Question 24

Define relative humidity

Answer 24

Relative humidity is the ratio between the current amount of water vapor in the air at a given temperature to the maximum amount of water vapor possible in the air at that temperature.

Measured as a percentage %

Use of a marine hygrometer will give you this.

Question 25

What is a surface analysis chart

Answer 25

Is a chart showing a summary of the general synoptic situation in the area concerned and with an indication o the movement of the pressure systems. It provides a view of weather conditions over a geographical area at a specified time

Question 26

What 5 items of information that may be obtained from a surface analysis chart

Answer 26

Pressure pattern
Movement of the pressure systems
Highs
Lows
Fronts
Wind direction
Speed.

Question 27

State where frontal fog may occur

Answer 27

Often occurs over widespread areas ahead of warm fronts.

Whenever the rain temperature exceeds the wet-bulb temperatures of the cold air, fog or stratus form.

Fog usually dissipates after frontal passage due to increasing temperatures and surface winds

Question 28

How does radiation fog occur

Answer 28

Is formed by the cooling of land after sunset by thermal radiation on calm conditions with clear sky. The warm ground produces condensation in the nearby air by heat conduction.

In perfect cal the fog layer can be less than a meter deep but turbulence can remote a thicker layer.

Radiation fogs occur at night, usually do not last long after sunrise.

Question 29

List 5 major ocean currents

Answer 29

North Equatorial 
South Equatorial 
Equatorial counter
North and South Pacific 
N & S Atlantic 
N & S Indian 
E & W Australia 
\+more!

Question 30

Weather experienced in the trade winds?

Answer 30

generally……

Sky -
Clear to fair

Wind/Sea
3/4 Beaufort

NE northern hemisphere
SE Southern Hemisphere

Question 31

Conditions in the ITCZ

Answer 31

Generally ….

Sky
Cloudy

Wind/Sea
Light to moderate
2/4 Beaufort

Question 32

Sea breeze -
Time of day?
Time of year?
Type of weather?
Type of land?
Research to find out if location has them?
Pressure gradient wind?

Answer 32

About midday (time for sun to heat land)

Late spring/early summer (cool seas)

High pressure/ anti cyclonic

Dry rocky or sand coast (clear skies)

Sailing directions / pilot books

Will + or - total breeze noticed

Question 33

Land breeze
Time of day?
Time of year?
Type of weather?
Type of land?
Research to find out if location has them?
Pressure gradient wind?

Answer 33

After sunset + all night (land cools)

Late spring/early summer (cold land at night)

High pressure/ anti cyclonic (clear skies)

Dry rocky or sand coast (cools quickly)

Sailing directions / pilot books

Will + or - total breeze noticed

Question 34

Katabatic wind
Time of day?
Time of year?
Type of weather?
Type of land?
Research to find out if location has them?
Pressure gradient wind?

Answer 34

Normally at night - possible at day time
High pressure/anti cyclonic (clear skies)
Sailing direction/ pilot books
Will + or - total breeze noticed

Question 35

Use of a barometer

Answer 35

Reads atmospheric pressure

Needs to be recorded in an hourly log

Use of a second needle with a time when changed can give you the idea of pressure change

The reading can be adjusted with the help of an adjustment card

Needs to be sent away for error correction

Question 36

Use of a barograph

Answer 36

Operates in the same manner as a barometer

Provides a continuous record in the form of an ink trace of the pressure experienced

Paper needs to be changed weekly

Marine barographs are oil filled to reduce vibration

Very easy to interpret visually

Question 37

What is a hygrometer

Describe parts and uses

Answer 37

Two identical thermometers, one dry and one wet

The wet one has a muslin and wick attached which needs to be changed regularly and is placed in a small container of distilled water

Both are placed in a STEVENSONS SCREEN/marine screen

The screen must be hung windward and clear of exhausts

Take the reading of the two thermometers, the difference between the two is know as the depression. Dry is always more.. rarely the same.

The depression is that used with tables to find the Dew point or relative humidity using different tables

Question 38

Advection fog. Causes and where its found?

Answer 38

Caused by relatively warm moist air flowing over a cooler sea surface.

If SEA temperature is below or near the DEW POINT of the air, the air adjacent to the sea surface will be cooled toward its saturation point and food will result.

Offered occurs off the Grand Bank (canada)