Exam 3 (Lessons 7-9) Flashcards
How are clouds classified?
1) General appearance (texture) as observed from ground
2) Altitude of cloud base
3) Temperature
4) Composition
Characteristics of high clouds
Bases above 16,000ft
Average temperature below -25 degrees Celsius
Composed of ice crystals, have fibrous appearance
Include the prefix cirro
What are the 3 types of high clouds?
Cirrus (Ci) clouds
Cirrostratus (Cs) clouds
Cirrocumulus (Cc) Clouds
Characteristics of middle clouds
Bases between 6,600 and 16,000ft
Average temperature between 0 and -25 degrees Celsius
Composed of supercooled water droplets or a mixture of droplets and ice crystals
Include the prefix alto
What are the 2 types of middle clouds?
Altostratus (As) clouds
Altocumulus (Ac) clouds
Characteristics of low clouds
Bases from Earth’s surface (fog) to 6,600ft
Average temperature above -5 degrees Celsius
Composed of water droplets
What are the 3 types of low clouds?
Stratocumulus (Sc) clouds
Stratus (St) clouds
Nimbostratus (Ns) clouds
What clouds have vertical development?
Cumulus clouds
Where do clouds that have vertical development form?
In updrafts of convection currents
When does fog form?
When the air is saturated by radiational cooling, advective cooling, addition of water vapor, or expansional cooling
What are the different types of fog?
Radiation Fog
Advection Fog
Upslope Fog
What are the two basic methods for cloud particle growth?
Collision-Coalescence (warm clouds)
Combination of Bergeron-Findeisen process and collision-coalescence (cold clouds)
What is Collision-Coalescence process?
Droplets grow by colliding and merging (coalescing); only coalesce if droplets are of significantly different size
Eventually droplet grow large enough and terminal velocity overcomes updraft and precipitation occurs
What are the forces that act on the wind?
Air Pressure Gradient
Centripetal Force
Coriolis Effect
Friction Gravity
When does an air pressure gradient exist?
Whenever air pressure varies from place to place
What is a horizontal pressure gradient?
When air pressure varies along a surface of constant altitude
What is a vertical pressure gradient?
Air pressure changes above Earth’s surface
How does air pressure gradient cause water or air to move?
It causes it to move from areas of high pressure to areas of low pressure
What is the Coriolis Effect?
Earth’s rotation causes fluids to be deflected away from a straight path; strongest at the poles and decreases moving away from the poles and is 0 at the equator
The Coriolis Effect causes fluids to deflect ____ in the Northern hemisphere and ____ in the souther hemisphere
Right… Left
How does the Second Law of Thermodynamics relate to pressure gradient?
When a horizontal pressure gradient develops, air flows in a direction to eliminate the pressure gradient (Second Law of Thermodynamics)
What are the 4 interaction of forces that effect wind?
Hydrostatic Equilibrium
Geostrophic Wind
Gradient Wind
Surface and Horizontal Winds
What is hydrostatic equilibrium?
Balance between vertical air pressure gradient and gravity
What is geostrophic wind and what causes it?
Un-accelerated, horizontal movement of air that follows a straight path at altitudes above the atmospheric boundary layer
Caused by a balance between the horizontal air pressure gradient force and Coriolis Effect
What is gradient wind?
Large-scale, horizontal, frictionless wind that blows parallel to the isobars; similar to geostrophic winds but has a curved path
How does air in anticyclones move?
Clockwise and parallel to isobars
How does air in cyclones move?
Counterclockwise and parallel to isobars
How does air move in an anticyclone when affected by friction and the Coriolis Effect?
Surface winds blow clockwise and outward; opposite wind directions in the southern hemisphere
How does air move in a cyclone when affected by friction and the Coriolis Effect?
Surface winds blow counterclockwise and inward;
opposite wind directions in the southern hemisphere
Why do cyclones favor cloud development over anticyclones?
In cyclones rising air cools due to expansional cooling causing relative humidity to rise and as it nears 100% saturation will be reached and condensation will occur causing cloud formation
In anticyclones sinking air warms due to compressional warming causing relative humidity to decrease resulting in the suppression of cloud formation
What are the 4 levels of atmospheric circulation?
Planetary-Scale Systems
Synoptic-Scale Systems
Mesoscale-Scale Systems
Microscale Systems
What are planetary-scale systems?
large-scale wind belts encircling the planet
What are synoptic-scale systems?
continental or oceanic in scale
What are mesoscale-scale systems?
circulation systems that influence weather in part of a large city or county
What are microscale systems
weather systems covering a very small area such as several blocks
What areas of the globe have persistent highs and what type of weather is found there?
At the poles and 30 degree N and S latitude; weather is generally fair and desert climates often form
What areas of the globe have persistent lows and what type of weather is found here?
Around the equator and 60 degree N and S latitude; rainy climates usually occupy these areas
What are the 4 semi-permanent pressure systems?
Subtropical anticyclones
Intertropical convergence zone (ITCZ)
Subpolar lows
Polar highs
How does the intertropical convergence zone (ITCZ) shift?
It follows the sun; Furthest North in July and furthest South in January
In flowing into a trough westerlies ____ and induces speed ____ aloft.
Slow… Convergence
When flowing into a ridge westerlies ____ and induces speed ____ aloft.
Accelerate… Divergence
El Nino is a ____ phase and La Nina is a ____ phase.
Warm… Cold
What happens during an El Nino?
Air pressure falls over Eastern tropical Pacific and rises over Western Pacific
Pressure gradient and trade winds weaken
SST drops in Western tropical Pacific and rises in Eastern tropical Pacific
What happens during a La NIna
Trade winds are stronger in the tropical Pacific
SST is lower in Central and Eastern tropical Pacific
What winds does the North Atlantic Oscillation (NAO) impact?
Governs the strength of westerly winds, mid-latitude jet stream, and North Atlantic storm tracks
