Meteorology Flashcards
What are the units and tools of measurement for: Wind direction Wind speed Pressure Air density Temperature Relative humidity Precipitation Cloud amount Cloud base Visibility
Wind direction - degrees from North
Wind speed - knots (anemometer)
Pressure - hectopascal (barometer/altimeter)
Air density - kg/m^3
Temperature - °C
Relative humidity - % of saturation (hydrometer)
Precipitation - mm (rain gauge)
Cloud amount - oktas
Cloud base - feet (ceilometer/cloud base recorder)
Visibility - km/m (transmissometer/radar/satellite)
What are the constituents of the atmosphere ?
Nitrogen - 78% Oxygen - 21% Argon - 1% Carbon dioxide - 0.03% Water vapour - 0% to 4%
ISA figures?
Pressure - 1013.25hPA
Temperature - 15°C
Density - 1.225kg/m^3
Lapse rate - 1.98°C per 1000ft
Define specific heat capacity
The amount of energy needed to raise 1kg body by 1°C
What is an Adiabatic Process?
A process in which heat is neither added nor lost from a system.
List the sections of the atmosphere and their qualities:
The troposphere - 16km/8km from the surface, contains 99% of the weather. Temperature and pressure decreases with height.
The stratosphere - from tropopause to 50km. Temperature increases from -51°C to surface values.
The mesosphere - from stratopause up to 90km
The ionosphere - from mesopause up to 350km, ionised particles interfere with radio communication.
Define latent heat
The heat absorbed or released during the change in the state of a substance that does not change the temperature.
What are the dry and saturated Adiabatic lapse rates?
Dry - 3°C per 1000ft
Saturared - 1.5°C per 1000ft
List the methods of cloud formation:
Convection - warm air raising in columns
Mass ascent - warm air raising over mass of cold air
Turbulence - sudden changes in air speed and height
Orographic - air forced to rise over a topographic feature
Categorise cloud types by height:
High clouds - cirrus, cirrocumulus, cirostratus.
Medium clouds - altocumulus, altostratus, altocumulus lenticularis, towering cumulus.
Low clouds - nimbostratus, cumulus, cumulonimbus, stratus, stratocumulus.
Cloud a mount in oktas:
SKC - sky clear - 0 FEW - few - 1 to 2 SCT - scattered - 3 to 4 BKN - broken - 5 to 7 OVC - overcast - 8 NSC - no significant cloud - nothing below 5000ft or CB or TCu
What is the bergeron process?
Deposition and sublimation occurring simultaneously in vertical low temperature clouds causing the rapid growth of ice crystal.
What is Buys Ballot’s Law?
In the northern hemisphere with the wind to one’s back the low pressure area is to the left.
List the Visibility increments:
50m up to 800m
100m up to 5000m
1000m up to 9km
9999 when 10km+
When is visibility reported?
Prevailing visibility is stable.
The lowest visibility is less than 1500m or 50% of the PV and less than 5000m.
If prevailing visibility is not stable then the lowest visibility is reported.
RVR when is visibility is less than 1500m
What conditions are required for CAVOK?
Visibility is 10km or more.
Lowest visibility is 5km or more
No cloud below 5000ft, no CB or TCU
How does radiation fog form?
Clear sky to allow heat to radiate, cool land surface to allow conduction, moist air for vapoir to form, light wind, amplified by a long night.
Under what conditions does advection fog form?
When there is warm moist air over an area of land or sea that is warmer than an adjacent surface.
The cold surface must also have a temperature low enough to cause the moist air to reach it’s due point.
What is the coriolis affect?
The apparent change in wind direction caused by the Earth’s rotation. Curves to the right in the northern hemisphere.
Define geostrophic wind
Wind that is travelling parallel to the isobars.
What are the affects of surfaces on wind?
Over Ground speed reduced to 40% and backs 20°
Over Sea speed reduced by 80% and backs 10°
What is a katabatic wind?
A downhill wind caused by cooling at higher altitude, typically during the night.
What is an anabatic wind?
Uphill wind caused by heating at lower altitudes, typically during the day.
What is a fohn wind?
A dry wind that blows down the leeside of a mountain due to SALR on the windward side and DALR on the leeside.
