Meteorology Flashcards
Explain the difference between a barograph and a barometer
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.
Whats a hygrometer and how can you use it to predict fog?
wet and dry bulb thermometers in a Stevensons screen
wet: muslin, distilled water.
depression indicates relative humidity.
dry: air temp
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-used to find dew point from table.
measure sea surface temp.
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plot on a graph: dew point v sea surface temp.
if curves converge, fog may be expected.
Whats a precision aneroid barometer?
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.
What types of fog are there?
- Sea or Advection Fog
- Radiation Fog
- Frontal Fog
- Artic Smoke
Sea Fog (advection)
when warm, moist air moves over a relatively colder surface and its temperate drops below its dew point- fog forms.
Land fog (radiation)
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.
Name sources of weather info
(list 6)
- Own Ship
- VHF
- MSI via NAVTEX
- SafetyNET via Inmarsat C
- Local or national forecasts in marina
- Internet
Tell me how you would react in a TRS?
In the Northern Hemisphere
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!
Tell me how you would react in a TRS?
In the Southern Hemisphere
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
Are you on which side of a TRS
buy ballots law
NH: back to wind, low is on left.
SH: back to wind, low is on right.
Describe a synoptic weather chart
surface analysis chart showing current observed atmospheric conditions.
Describe a prognostic weather chart
surface analysis chart showing forecast atmospheric conditions.
Wind, Cloud, Weather, Barometric pressure, temp, vis
- Passage of a low: As the warm front approaches (N Hemisphere)
-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
- Passage of a low: In the Warm Sector (behind warm front) - N hemisphere
-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.
- Passage of a low: At the cold front - N hemisphere
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)
- Passage of a low: After a Cold front - N hemisphere
Behind the cold front:
-Wind direction steady
-Wind force decreasing
-Temperature steady
-Cloud: cumulus
-Possible showers, clearing
-Visibility clearing
Local weather to your area of cruising, e.g the mistral
(4 points)
- The Mistral forms as a katabatic wind, blowing down from the highlands of southern France into the Gulf of Lion.
- it’s a strong, dry, cold, NW’ly wind
often exceeding force 8. - usually accompanied by clear fresh weather.
- takes place when there is a High in the Bay of Biscay and a Low around the Gulf of Genoa.
The Layers of the Atmosphere
The Silly Monkeys Twirled Endlessly
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
define relative humidity
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
Diurnal variation
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.
