Meteorology

Question 1

Explain the difference between a barograph and a barometer

Answer 1

barometer: instrument used to measure atmospheric pressure

barograph: an aneroid barometer with a lever and pen attached to a revolving drum. This records variations of pressure on a chart, over a 7 day period.
-Must take into account effect of diurnal variation.

Question 2

Whats a hygrometer and how can you use it to predict fog?

Answer 2

wet and dry bulb thermometers in a Stevensons screen

wet: muslin, distilled water.
depression indicates relative humidity.
dry: air temp
»>
-used to find dew point from table.

measure sea surface temp.
»>
plot on a graph: dew point v sea surface temp.
if curves converge, fog may be expected.

Question 3

Whats a precision aneroid barometer?

Answer 3

a non-liquid barometer measuring absolute atmospheric pressure.
Reading is correct when the thread of light breaks. Must be corrected to sea level using the instrument’s manual.

Question 4

What types of fog are there?

Answer 4

1. Sea or Advection Fog
2. Radiation Fog
3. Frontal Fog
4. Artic Smoke

Question 5

Sea Fog (advection)

Answer 5

when warm, moist air moves over a relatively colder surface and its temperate drops below its dew point- fog forms.

Question 6

Land fog (radiation)

Answer 6

over low lying land on clear nights
heat radiating from the surface at night, cools the bottom air until it reaches saturation. fog forms first at the surface, thickening as cooling continues.

Question 7

Name sources of weather info
(list 6)

Answer 7

1. Own Ship
2. VHF
3. MSI via NAVTEX
4. SafetyNET via Inmarsat C
5. Local or national forecasts in marina
6. Internet

Question 8

Tell me how you would react in a TRS?
In the Northern Hemisphere

Answer 8

Am I in the dangerous or navigable semi circle?

NH:
Dang SC: Wind on STBD bow, alter course to stbd as wind veers.
Nav SC: Wind on STBD qtr, alter course to port as wind backs.

heavy weather checklist!

Question 9

Tell me how you would react in a TRS?
In the Southern Hemisphere

Answer 9

Am I in the dangerous or navigable semi circle?

Dang SC: Wind on port bow, alter course to port as wind backs
Nav SC: Wind on port qtr. alter course to stbd as wind veers.

HEAVY WEATHER CHECKLIST

Question 10

Are you on which side of a TRS

Answer 10

buy ballots law

NH: back to wind, low is on left.

SH: back to wind, low is on right.

Question 11

Describe a synoptic weather chart

Answer 11

surface analysis chart showing current observed atmospheric conditions.

Question 12

Describe a prognostic weather chart

Answer 12

surface analysis chart showing forecast atmospheric conditions.

Question 13

Wind, Cloud, Weather, Barometric pressure, temp, vis

1. Passage of a low: As the warm front approaches (N Hemisphere)

Answer 13

-as the warm front approaches
-the pressure would fall
-the wind direction would be steady
-the wind force would be increasing
-Temperature steady
-Cloud would be high cirrus and cumulus, then cirro stratus and finally nimbostratus
-Light rain increasing to moderate.
-Visibility deteriorating

Question 14

2. Passage of a low: In the Warm Sector (behind warm front) - N hemisphere

Answer 14

-in the warm sector now
-the pressure would be steady
-wind direction begins to veer
-the wind force would be steady
-Temperature rises
-Cloud would be nimbostratus, then stratus
-Rain would stop, or ease to drizzle.

Question 15

3. Passage of a low: At the cold front - N hemisphere

Answer 15

As the cold front begins to pass:
-the pressure started to rise
-The wind veers
-the wind force increases
-Temperature falls (northerly!)
-Cloud : cumulonimbus
-Heavy rain, possibly hail and thunderstorms.
-Visibility poor (due to heavy rain)

Question 16

4. Passage of a low: After a Cold front - N hemisphere

Answer 16

Behind the cold front:
-Wind direction steady
-Wind force decreasing
-Temperature steady
-Cloud: cumulus
-Possible showers, clearing
-Visibility clearing

Question 17

Local weather to your area of cruising, e.g the mistral
(4 points)

Answer 17

1. The Mistral forms as a katabatic wind, blowing down from the highlands of southern France into the Gulf of Lion.
2. it’s a strong, dry, cold, NW’ly wind
   often exceeding force 8.
3. usually accompanied by clear fresh weather.
4. takes place when there is a High in the Bay of Biscay and a Low around the Gulf of Genoa.

Question 18

The Layers of the Atmosphere

Answer 18

The Silly Monkeys Twirled Endlessly

Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere

Question 19

define relative humidity

Answer 19

a measure of
the actual amount of water vapour in the air
compared to
the total amount of vapour
that can exist in the air at its current temperature

Question 20

Diurnal variation

Answer 20

A result from atmospheric pressure waves which sweep around the Earth (E to W) every 12hrs.
They are at a maximum in the tropics of about
3mb.