Meteorology Flashcards
(48 cards)
List 5 published sources of weather information
- Admiralty Sailing Directions
- Admiralty list of Radio Signals
- Ocean Passages of the World
- Routing charts
- Mariners Handbook
Explain Anabatic and Katabatic Winds
On clear nights the slope of a mountain radiates out their heat and the temperature falls. The air in contact with the slope becomes heavier and rolls down the slope. These Katabatic winds can reach high speeds and are often funnelled down water-courses.
Anabatic winds are the relatively mild uphill reverse of Katabatic winds. As the sun heats up a side of a slope the air in contact with the slope heats up and rises up the slope.
Describe the air movement and associated weather for a stationary front
Two air masses meet. Neither advances to the others territory- Extensive cloudiness & precipitation
What are the four main factors that drive the Earths weather?
- Hot air rises, cool air falls. Hot air being light, and cool air being heavy. This causes low pressures and high pressures respectively.
- Pressures try to equalise.
- Latent heat contained in evaporation and condensation.
- Coriolis effect
How is wind caused?
Wind is caused by air flowing from a high pressure area to a low pressure area.
Explain pressure gradient
Is the force driving the air towards the lower pressure, and acts perpendicular to the isobars.
Explain the Coriolis Effect
Due to the rotation of the Earth, the Coriolis force deflects the direction of the wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This causes wind-flow around high and low pressure systems to circulate in opposing directions in each hemisphere. Coriolis force is one of the main factors affecting wind direction.
What is an isobar
Isobar is a line on a meteorological chart joining places of equal pressure. These are plotted at 4 millibar/hPa intervals.
What terms will be used to describe changes in wind direction?
If wind direction changes clockwise it is said to “veer”. If it changes anti-clockwise it is said to “back”.
What are the forces influencing the Gradient wind?
- Pressure Gradient
- Coriolis Force
- Centrifugal Force
What effect does the friction of the Earth’s surface have on wind?
It modifies the direction and strength of the wind and will back and veer according to what angle it strikes a land mass.
What relationship does the distance between isobars have with wind speed?
Wind speed is inversely proportional to the distance between the isobars
Explain Buys Ballots’ Law
In the Northern Hemisphere with one’s back to the true wind, the low pressure will be on the left-hand side.
In the Southern Hemisphere with ones back to the true wind, the low pressure will be on the right-hand side.
Summarise how planetary wind belts are formed
The suns radiated energy is greatest at the equator, where the sun’s rays are most direct. This causes the earth’s surface to be very hot at the equator, causing the air in that region to heat up through conduction, causing a low pressure area, due to air rising to great heights, eventually this air cools and falls back to earth at roughly 30°. Cooler air on the earths surface will fill in to replace the air at the low pressure area’s. At 30° latitude there will be a relatively high pressure, from the sinking cooler air.
The air at the poles will be cold and heavy resulting in the creation of high pressure at both poles. Between the high of 30˚and the polar high, a region partially heated by the sun at about 60˚, an area of relatively low pressure will be created. Warm rising air, upper level winds, falling cool air and surface level winds to replace the air at low pressure areas cause convection cells between these significant latitudes.
What is another name for the Inter-Tropical Convergence Zone, and what wind conditions can be expected here?
The Doldrums- Light and variable winds
What direction do the trade winds blow in each hemisphere?
NE in Northern Hemisphere, SE in Southern Hemisphere
What wind conditions can be expected in the Horse latitudes?
Light, calm and variable
Explain land and sea breezes
The land is heated during the day and cools at night. Sea temperature changes very little and therefore in a 24 hour period will be relatively hotter or colder than the adjacent land. When the land is heated during the day the hot air rises causing a relative low pressure on the land compared to the sea, causing on-shore winds to blow. This is a sea breeze
At night the air over the land cools and falls, and air pressure increases. This causes a relative high pressure on the land compared to the sea, causing off-shore winds to blow. This is a land breeze
How does advection fog occur?
Warm moist air passes over a cool surface by advection (wind) and is then cooled. It is most common at sea when moist air passes encounters cooler waters, including areas of cold water upwelling.
How does radiation fog occur?
Radiation fog occurs at night in clear conditions, where heat radiates from the land and escapes into the atmosphere, which cools the air close to the surface to the dew point, causing fog.
How does frontal fog occur?
Different air masses in a frontal system are forced to mix, the temperature of the warm moisture laden air may drop to below dew point, causing fog.
What is the difference between mist and fog?
Mist has a visibility of more than 1000 metres, fog has a visibility reduced to less than 1000 metres.
What is lapse rate?
Reduction of temperature of the air as it rises, averages 1°C per 100 metres.
What is Adiabatic lapse rate?
The rate at which atmospheric temperature decreases with increasing altitude in conditions of thermal equilibrium.
