Meteorology Flashcards
Explain the difference between a barograph and a barometer
barometer: instrument used to measure atmospheric pressure
barograph: am aneroid barometer with a lever and pen, which record variations of pressure on a chart, attached to a revolving drum.
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 water vapour content of air.
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 consisting of a circular metal capsule. measures absolute atmospheric pressure. reading is correct when the thread of light breaks.
What types of fog are there?
- Sea or Advection Fog
- Radiation Fog
- Frontal Fog
Sea Fog (advection)
warmer, moist air moves over a colder surface and its temperate drops below its dew point- fog forms.
Land fog (radiation)
over low lying land on clear nights
heat radiating form 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
Own Ship
VHF
SafetyNET via Inmarsat and MSI via NAVTEX
Local or national forecasts in marina
Sat C
Internet
Tell me how you would react in a TRS?
establish vessels location. Am i in the dangerous or navigable semi circle?
Northern / Southern Hemisphere?
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:
Are you on which side of a TRS
buy ballots law
NH: back to wind, low is on left.
Describe a synoptic weather chart
surface analysis chart used to predict future weather patterns and conditions.
shows :
Cold , Warm + Occluded fronts
pressure systems (H&Ls)
troughs
- Passage of a low: Approaching warm front - N Hemisphere
Wind: backs and freshens
Cloud: thickens and lowers
Weather: light rain increases to moderate to heavy
Barometric pressure: increase rate of fall
Temp: Very slow increase
Vis: Steady reduction in increasing rain
- Passage of a low: Warm Sector (behind warm front) - N hemisphere
Wind: veers and may freshen
Cloud: medium and high level cloud breaks up. Nimbostratus remains.
Weather: rain eases, drizzle. fog banks maybe
Barometric pressure: rate of fall slows
Temp: Sharp increase
Vis: Moderate or poor
- Passage of a low: Approaching Cold front - N hemisphere
Wind: backs slightly and freshens
Cloud: Increase in medium and high level cloud (cumulonimbus)
Weather: Rain recommences
Barometric pressure: fall
Temp: Steady
Vis: Moderate
- Passage of a low: At Cold front - N hemisphere
Wind: veers. maybe sudden squalls.
Cloud: Cloud breaks up
Weather: Moderate or heavy rain followed by clear conditions
Barometric pressure: Sharp rise
Temp: Sharp decrease
Vis: Sharp increase
Local weather to your area of cruising, e.g the mistral
the mistral: a strong, cold, north westerly wind that blows from southern France into the Gulf of Lion in the northern med, with sustained winds often exceeding force 8.
usually accompanied by clear fresh weather.
takes place when there is an anti cyclone (high) in the bay of biscay an low pressure around the gulf of Genoa.
