Final Exam Flashcards
(45 cards)
What are the forces involved in the surface wind model?
(be prepared to recognize them in a diagram)
in the Northern Hemisphere
Pressure Gradient Force:
- pushes air parcel from high to low pressure; perpendicular to isobar
Coriolis Force: (not at the equator)
- deflects air to the right in the NH
- CF vector is drawn perpendicular and to the right of the resultant wind in the NH
Turbulent Drag:
- ‘Friction’ vector is drawn in the opposite direction of the resultant wind
- By slowing down the wind, it reduces the strength of the Coriolis Force
What are the forces involved in the surface wind model?
(be prepared to recognize them in a diagram)
in the Southern Hemisphere
Pressure Gradient Force:
- Pushes air parcel from high to low pressure;
perpendicular to isobar
Coriolis Force: (not present at the equator)
- Deflects air to the left in the Southern
Hemisphere
- CF vector is drawn perpendicular and to the
left of the resultant wind in the SH
Turbulent Drag:
- ‘Friction’ vector is drawn in the opposite
direction of the resultant wind
- By slowing down the wind, it reduces the strength of the Coriolis Force
What is gradient wind?
Wind that follows curved isobars/isohypses above the planetary boundary layer
Only occurs if the two forces are unbalanced (curving)
What forces are involved in the gradient wind model?
Pressure Gradient Force
Coriolis Force
- no friction (unlike surface winds)
How do gradient winds differ from geostrophic winds?
Geostrophic Wind: balance between the PGF and CF
Parallel to straight isobars/isohypses
Gradient Wind: imbalance between the PGF and CF
Parallel to curved isobars/isohypses
What do the u and v components of a wind indicate?
magnitude (length) and direction of the wind
u: East (+) -> West (-) wind speed
v: North (+) -> South (-) wind speed
In a Northern Hemisphere upper-level cyclone with gradient winds, which is larger:
the PGF or the CF?
Does this make the wind speed supergeostrophic or subgeostrophic?
PGF is larger than the CF
Subgeostrophic because the wind is slower than geostrophic
In a Northern Hemisphere upper-level anticyclone with gradient winds, which is larger:
PGF or the CF?
Does this make the wind speed supergeostrophic or subgeostrophic?
CF is larger than the PGF
Supergeostrophic because the wind speed is faster than geostrophic
If presented with a diagram of the forces/vectors in a surface wind model, be prepared to label those forces/vectors
PGF: perpendicular to isobars (H->L)
CF: right of wind (NH) or left (SH)
Friction: opposes wind direction
What are the 8 atmospheric/geographic conditions that promote cyclogenesis in the
mid-latitudes of North America?
- East of Mountains
- East of Trough
- Small Wavelengths
- Highly Amplified Troughs
- Fast Winds
- Front Zones or Baroclinic Regions
- Cold Air moves over Warm Air, Wet Surface
- Further from the Equator
If presented with a tephigram showing the T curve, be prepared to determine whether a particular layer of air is stable, unstable, or conditionally unstable.
(Looking at the slope of the environment lapse rate in that layer compared to the dry adiabatic and moist adiabatic lapse rates in that layer)
stable: ELR < MALR < DALR
unstable: DALR < MALR < ELR
conditionally unstable: MALR < ELR < DALR
What is the difference between the dry and moist adiabatic lapse rates?
Dry: 9.8°C/km
Moist: lower than dry, varies depending on moisture and temperature
Why does the moist adiabatic lapse rate not have a single value?
The moist adiabatic lapse rate depends on the temperature and humidity
More condensation releases more latent heat, altering the cooling rate
What is the cause of the adiabatic lapse rate?
Change in air parcels, rising, expanding and cooling or sining, compressing and warming, without heat exchange
What does it mean to say that an atmosphere (or layer of the atmosphere) is ‘absolutely stable’ or ‘absolutely unstable’?
Stable: ELR<MALR
- air parcel cooler than environment -> sinks
Unstable: ELR > DALR
- air parcel warmer than environment -> rises
What does it mean to say that an atmosphere (or layer of the atmosphere) is ‘conditionally stable’?
depends on whether the air parcel is saturated
unsaturated: stable
saturated: unstable
What does it mean to say that a layer of air is being ‘stabilized’ or ‘destabilized’?
stabilized: ELR = lower value (does not support rising air)
destabilized: ELR = higher value (supports rising air)
How does horizontal divergence of a column of air result in stabilization (e.g. when a column of air moves from a rough terrain to a smoother terrain)?
horizontal divergence of a column of air stabilizes because it causes convergence (sinking) above, warming the upper atmosphere and lowering the ELR- making it harder for air to rise
What is a subsidence inversion?
air sinks (subsides) -> compresses -> the top of the layer warms more than the bottom of the layer -> suppressing vertical motion & creating stability
inversion: normally temperature decreases with height, this layer is warmer at the top
Why does subsidence of a layer of air in the upper atmosphere result in stabilization?
compression -> top warms more than the bottom -> less vertical mixing -> stability
What kind of dewpoint depression in the upper atmosphere is indicative of subsidence?
large dewpoint depression
- temperature quickly increases, while dewpoint stays relatively the same
How does horizontal convergence of a column of air result in destabilization (e.g. when a column of air moves from a smooth terrain to a rougher terrain)?
horizontal convergence of a column of air destabilizes because it causes divergence (stretching) above, cooling the upper atmosphere and increasing the ELR, making it easier for air to rise
Does heating/cooling of air near the surface generally result in stabilization or destabilization?
Why?
At the Surface
Heating: destabilization
Cooling: stabilization
Does heating/cooling of air aloft generally result in stabilization or destabilization?
Why?
Aloft
Heating: stabilization
Cooling: destabilization
