Exam 2 Flashcards
Clouds consist of
Liquid or solid water droplets suspended in the atmosphere
Cloud formation requires..
Condensation nucleii, most are between 2 and 10 micrometers.
Hygroscopic nucleii…
Are charged particles. They attract water
Cloud classification is based on..
Appearance
Altitude
Temperature
Composition
Cold clouds and warm clouds- temperature
Lower than 0 degrees Celsius are cold clouds
Above 0 degrees Celsius is a warm cloud.
Curriform clouds (appearance)
Wispy & fibrous
Stratiform clouds (appearance)
Thick and layered
Cumuliform clouds (appearance)
Heaped or puffy
Altocumulus lenticularis cloud
Most common down wind of mountain ranges. Looks like a flat oval in the sky.
Noctilucent clouds
In the upper mesopheric clouds when water freezes on meteoric particles. Kind of look like northern lights.
Fog is…
A cloud in contact with the ground. Condensation of atmospheric water vapor at low altitudes.
Types of fog..
Radiation
Advection
Steam
Upslope
Radiation fog..
Most common over saturated ground on clear nights
Ground radiates heat rapidly, cools overlying air to saturation point.
Also common in valleys due to cold air drainage.
Advection fog…
Surfaces can modify air traveling over the surface
Warm moist air moving over colder surface can cool to dew point and form fog.
Golden Gate Bridge/ San Fran Cisco is the most famous form of this.
Steam fog…
Cold dry air moves over water body.
Water body humidifies air until saturated.
Upslope fog…
Air moving upslope cools and condenses
Precipitation formation
It has to grow to form, and as it becomes heavy it will fall out.
A raindrop is 1 million times the volume of water of a typical cloud droplet.
The Bergeron Process
Typical of cold clouds in middle altitude.
Water is given up by water droplets and condenses onto the ice crystals (where relative humidity exceeds 100%)
The ice crystals will become heavy and fall out of the sky
Collision-Coalescence Process
Typical of warm clouds
Large hygroscopic condensation nucleii cause heavy water droplets to form. These droplets are running into each other and get broken up
Most efficient over tropical oceans
Forms of precipitation
Rain Drizzle Hail Ice pellets Snow
Rain
0.5 to 6 mm in diameters. The size depends on coalescence
Drizzle
0.2-0.5 mm in diameters
Limited coalescence and size equals low terminal velocity.
This is the same as rain but smaller and falls slower.
Snow
Agglomerations of ice crystals that form flakes.
They get bigger the closer you get to the freezing point.
Ice Pellets ( sleet)
Irregularly shaped particles of ice 0.5 mm or less in diameter.
Snowflakes that partially or completely melt falling through warm air, then referee into ice in a cold layer before hitting the ground.
Hail
Lumps of ice that have concentric layering.
Requires a strong updraft and a lot of energy to create this.
World record- soccer ball size
Air pressure
Air exerts force on the surface of all objects it contacts.
The air molecules collide with a surface area in contact with air.
The force of these collisions per unit are is pressure
Air pressure can be thought of as
The weight of overlying air acting on a unit area.
Average air pressure at sea level.
760 mm
The world wide standard of measuring air pressure, metric scale.
Pascal
At sea level 101,325 pascals
1013.25 hectopascals
101.325 kilo pascals
How the US measure air pressure
Bars.
A bar is 29.53 inches of mercury
The standard used to measure air pressure on weather maps
Millibar. Meaning 1/1000 of a bar
Global average of millibars at Sea level pressure.
1013 mb
Usual worldwide range of pressures found at any given time through out.
970mb- 1040 mb
Lowest ever was 870 mb
Highest ever was 1083.8 mb
As you go up in the atmosphere the pressure goes
Down.
Cold air is more dense because…
There is less spacing between the molecules and they pack together.
Warm air is less dense because…
There is more spacing between the particles and they are moving around.
On a high humid day, the pressure is
Lower
Low humidity has ——- pressure
Higher
Horizontal pressures tell us
How hard the air is pushing down in different locations.
The air pressure will ALWAYS be higher in Wilmington than in Denver.
The two ways that air pressure can be formed.
Thermal ( temperature) or Dynamic (airflow)
Thermal high pressure
= cold surface and high air density
Thermal low
= warm surface and low air density.
Dynamic high
When air is being forced down towards the surface ( piling up)
Dynamic low
When air is being forced upwards in the atmosphere ( decreasing the pile)
Measuring wind
Winds are described by speed and direction
Direction of wind
Wind is always named for the direction that the wind is coming FROM.
westerly wind is coming from the west.
What wind is
Wind is the atmosphere trying to level itself out
Prevailing wind in North America are westerly winds coming FROM the west.
Prevailing Winds
When winds often come from a predictable / reoccurring direction
How wind is measured
Measured at the surface using a cup anemometer or aerovane.
3 forces that govern the wind
1) pressure gradient force
2) Coriolis Effect
3) friction
Isobars on a map
When isobars on a map are close together that means there are higher winds.
Air flows from high pressure to low pressure.
Main force that effects the wind
Pressure gradient force
Flow is high to low and perpendicular to isobars.
Isobars tell you the speed of the wind.
How to tell if a map is showing low pressure.
When the L is a number (988) and all the numbers around it are higher. This is what makes that the low pressure.
Hw to tell if a map is showing a high pressure
The H on the map will be the highest number making it the high pressure.
Number 2 impact on wind direction
Coriolis effect
Coriolis Effect
An apparent deflection of a path related to the fact that the Earth is a curved surface.
The rotational velocity of any one point on earth is directly related to
Latitude
Coriolis effect in the Northern and Southern Hemispheres
Northern Hemisphere-deflection to the right
Southern Hemisphere- deflection to the left.
The direction is all relevant to the object in motion.
Coriolis gets stronger at
Higher locations
Coriolis is weakest at
Low latitudes
There is NO Coriolis at
The equator
Friction
Is the resistance to movement
Most friction occurs
At the surface, air running into trees, mountains, buildings, etc.
When we are in higher the atmosphere friction is not really a factor.
At high altitudes the absence of friction means that only —— and ——- are impacting airflow.
Pressure gradient and Coriolis.
When Coriolis is equal and opposite of pressure gradient force, this is called
Geostrophic winds which is high altitude, high elevation winds.
In high altitudes winds are parallel to isobars on
Isomeric maps
Cyclonic and Anticyclonic flows in the Northern Hemisphere
Cyclonic- counter clockwise
Anticyclonic- clockwise
Cyclonic and Anticyclonic flows In the Southern Hemisphere
Southern Hemisphere
Cyclonic- clockwise
Anticyclonic- counter clockwise
Geostrophic winds
Up in the atmosphere. Pressure gradient and Coriolis are factors. These winds flow parallel with isobars.
At the surface, Friction decreases
The Coriolis impact
Surface winds
Are the the lower atmosphere where friction plays a much bigger role by decreasing the Coriolis effect.
Horizontal convergence
When the air flows towards a low pressure center and will ‘pile up’ at the surface.
This air has to go somewhere so we get air rising and then DIVERGING at high altitudes.
When air goes up in the atmosphere it runs into the tropopause and
Spreads out
Air flowing away from a high pressure center will cause air flow to subside from high altitudes in the atmosphere and
Spread out at the surface
Converging airflow
The ‘removal’ of air particles at high altitudes that creates low pressure center aloft.
