Midterm II Flashcards
study for the second midterm (slides 9 & 10)
4 Major Cloud Groups?
Cirrus, Stratus, Cumulus, & Nimbus
10 Basic Cloud Groups?
Cirrus, Cirrostratus, Cirrocumulus
Stratus, Stratocumulus, Nimbostratus
Altostratus, Altocumulus,
Cumulus, Cumulonimbus
Symbols for the four different fronts on a typical surface weather map?
Cold front: blue triangles pointing the direction of movement
Warm front: red half circles pointing the direction of movement
Stationary front: alternating blue triangles & red half circles on opposite sides
Occluded front: purple alternating triangles & half circles in the direction of movement
Three names for synoptic-scale cyclones that affect north of the tropics?
- Wave Cyclones
- Mid-latitudes Cyclones
- Extratropical Cyclones
Wavenumber = 5 in the NH indicates what about the upper-level wind pattern?
Means there are five large scale ridges/troughs in the upper-level flow
Considered a high wavenumber, Low height gradient, Slower upper-level winds
What time of year is the wavenumber small or large? Why?
Small wavenumber: winter & associated with stronger winds
Large wavenumber: summer & associated with weaker winds
With a fast upper-level flow will the wavenumber be small or large?
the wavenumber will smaller, faster upper-level winds leads to fewer-larger waves
Vorticity?
measure of spin/rotation of air parcels in the atmosphere
Earth Vorticity? (Ve)
When/Where is it Positive or Negative?
The spin of air due to the earth’s rotation (Coriolis effect)
Positive vorticity in the NH (counterclockwise) - most positive at the North Pole
Negative vorticity in the Nh (clockwise) - most negative at the North Pole
No spin at the Equator
In the NH, is a cyclonic/anticyclonic flow associated with positive or negative vorticity?
Cyclonic flow is associated with positive vorticity
Anticyclonic flow is associated with negative vorticity
Shear Vorticity? (Vs)
Identify/Sketch wind pattern producing positive/negative shear vorticity in the NH?
The spin associated with the change in windspeed horizontally
Positive shear vorticity when South - North the speed slows
Negative shear vorticity when South - North the speed increases
Curvature Vorticity? (Vk)
Identify/Sketch wind pattern producing positive/negative curvature vorticity in the NH?
The spin associated with the change in wind direction horizontally (curvature vorticity is greater when the curvature is strong (small radius)
Positive curvature vorticity when the wind direction turns northern
Negative curvature vorticity when the wind direction turns southern
Relative Vorticity? (Vr)
Identify/Sketch wind pattern producing positive/negative relative vorticity in the NH?
The spin relative to the Earth’s surface
- made up of shear vorticity and curvature vorticity
Positive relative vorticity coming out of a trough (pva)
Negative relative vorticity coming out of a ridge (nva)
Absolute Vorticity?
Earth Vorticity + Relative Vorticity (Shear Vorticity + Curvature Vorticity)
vorticity tends to be conserved, one component is altered the others will compensate
Difference between Diffluent and Confluent wind pattern?
Diffluence is when the air spreads apart
Confluence is when the air comes together
Explain how the Longwaves (Rossby waves) in the NH midlatitude atmospheric flow (ex.) are promoted by the conservation of absolute vorticity
The air moves North/South, as it moves the Earth’s Vorticity changes, and to conserve the Absolute Vorticity the Relative Vorticity will be altered.
When the air moves South, the Earth’s Vorticity weakens, so the Relative Vorticity increases, increasing cyclonical spin, creating a trough.
When the air moves North, the Earth’s Vorticity strengthens, so the Relative Vorticity decreases, increasing the anticyclonically spin, creating a ridge.
These changes balance each other out and create a self-sustaining wave form
What is Rossby’s Circulation Theorem?
- write it out in full (5 variables)
- explain its importance in determining where cyclones/anticyclones form at the surface
Is that the waves are a closed system, where the vorticity remains constant
(Ve + Vs + Vk) x Area = Constant
If one variable (area or vorticity) changes then one of the other variable must change to compensate to maintain the constant
Map of upper-level ridge/trough wind pattern with a uniform windspeed indicate:
- most negative vorticity
- most positive vorticity
- negative vorticity advection
- positive vorticity advection
- horizontal convergence (aloft)
- horizontal divergence (aloft)
- horizontal convergence (surface)
- horizontal divergence (surface)
- cyclone formation at the surface
- anticyclone formation at the surface
- most negative vorticity: trough
- most positive vorticity: ridge
- negative vorticity advection: downstream of ridge
- positive vorticity advection: downstream of trough
- horizontal convergence (aloft): before trough
- horizontal divergence (aloft): after trough
- horizontal convergence (surface): below upper divergence
- horizontal divergence (surface): below upper convergence
- cyclone formation at the surface: upper divergence/surface convergence
- anticyclone formation at the surface: upper convergence/ surface divergence
Upper-level ridge/trough wind pattern, how does change in Curvature and Rossby’s Circulation Theorem explains where horizontal divergence & convergence occurs?
(Vk x Area = constant)
increasing curvature vorticity: area of the air must decrease, converge in the upper atmosphere, sinking air, divergence at surface = high pressure system
aka negative vorticity advection
decreasing curvature vorticity: area of the air must increase, diverge in the upper atmosphere, rising air, convergence at surface = low pressure system
aka positive vorticity advection
Why do cyclones form beneath areas of upper-level divergence?
Upper level divergence > raises air > surface level convergence horizontally > expands vertically > low pressure system > cyclone formation
Why do anticyclones form beneath areas of upper-level convergence?
Upper level convergence > sinks air > surface level divergence horizontally > shrinks vertically > high pressure system > anticyclone formation
What is the difference between Barotropic atmosphere and Baroclinic atmosphere?
Barotropic Atmosphere: isotherms & isohypses of an upper level chart are generally parallel (do not cross), meaning there are no fronts, common in tropics
- no temperature gradient
Baroclinic Atmosphere: isotherms & isohypses cross on an upper level chart, causing cold and warm advection and forms fronts, occurring in vicinity of short waves
- temperature gradient
Upper-level jet straight (non-curved) jet streak, how does change in Windspeed and Rossby’s Circulation Theorem explains where horizontal divergence & convergence occurs?
(Vs x Area = constant)
Entrance Region: Convergence
air entering increases speed, to conserve absolute vorticity the horizontal area must decrease, upper-level convergence
below the entrance > sinking air > divergence at surface > high pressure system > anticyclone formation
Exit Region: Divergence
air exiting decreases speed, to conserve absolute vorticity the horizontal area must increase, upper-level divergence
below the exit > rising air > convergence at surface > low pressure system > cyclone formation
left is stronger than right
Why is 500 mb level called the level of non-divergence?
it is half way between the upper level and surface level convergence/divergence, aka the transition zone between upper and lower atmospheric circulations
- area where neither effect dominates
What are the 8 conditions that promote cyclogenesis?
- East of Mountain Ranges
- East of Strong Troughs
- Small Wavelengths
- Highly Amplified Troughs
- Fast Winds
- Frontal Zones or Baroclinic Regions
- Cold Air moves over Warm Air, Wet Surfaces
- locations Further from the Equator
