Meteorology Flashcards
Explain a sea breeze
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
Explain katabatic winds
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
State at least 5 items of meteorological info to be found on a admiralty routeing chart
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
Define the term synoptic chart and its use for weather forecasting
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
Describe and compare the information obtained from a barometer and barograph and explain their use in weather forecasting
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.
Explain the term ‘selected ship’
Commonly known as a Met observation vessel
Is a vessel that has been selected to report meteorological observations in it’s area of operations to its national meteorological centre
Define the term prognostic chart
Is a weather chart forecasting the state of the atmosphere over a large area at a given level and at a future time
List four factors which determine the strength and direction of winds
Geographical location
Proximity of areas of high and low pressure systems
Pressure gradient between areas of high and low pressure systems
Proximity of land
Describe the weather conditions expected whilst navigating in the ‘variables’
Winds are light and variable and the weather is generally fair with small amounts of cloud and rain
Describe trade winds, their location and how they migrate with seasons
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
Define the term ‘surface analysis chart’
Is a weather char reflecting ther state of the atmosphere over a large area at a given level and moment in time
Describe the advantages a barograph has as a weather-recording instrument in comparison to a barometer
Provides a continuous record of
barometric pressure
Records pressure tendency
State five meteorological publications consulted when planning a passage
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
Explain the terms ‘synoptic’ and ‘prognostic’ chart used in weather forecasting
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
Describe a weather routing service AND explain the advantages of using this service
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..
List SIX publications that may be available onboard to help the OOW assess weather information
Admiralty list of radio signals
Mariners handbook
Pilot books/sailing directions
Routing charts
Marine observation handbook
Yachtsman’s handbooks/almanacs