aoss 401, fall 2006 lecture 19 october 26 , 2007
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AOSS 401, Fall 2006 Lecture 19 October 26 , 2007. Richard B. Rood (Room 2525, SRB) [email protected] 734-647-3530 Derek Posselt (Room 2517D, SRB) [email protected] 734-936-0502. Class News October 26 , 2007. Homework Homework 5 posted today - PowerPoint PPT PresentationTRANSCRIPT
AOSS 401, Fall 2006Lecture 19
October 26, 2007
Richard B. Rood (Room 2525, SRB)[email protected]
734-647-3530Derek Posselt (Room 2517D, SRB)
Class NewsOctober 26, 2007
• Homework – Homework 5 posted today– Includes a programming assignment that will
be posted this afternoon/evening– Focus your attention on question 1
Today
• Bring together physical concepts and preview the rest of the course
• Material from Chapter 6 – Middle Latitude Structure– Quasi-geostrophic theory
Flow over a mountain rangeWest to East
What is happening with planetary vorticity?(In the (east-west, north-south) plane)
Dep
th,
H
Dep
th,
H +ΔH
west easts
n Dep
th,
H -ΔH
Dep
th,
H +ΔH
f is greater for deflections to north
f is less for deflections to south
f + ζ is less than earth’s vorticity and wants to turn north.
Arrives here wanting vorticity. “Overshoots”
Flow over a mountain rangeEast to West
What is happening with planetary vorticity?(In the (east-west, north-south) plane)
Dep
th,
H
Dep
th,
H +ΔH
west easts
n Dep
th,
H -ΔH
Dep
th,
H +ΔH
Flow from east planetary and relative vorticity interact together, no overshoot or undershoot.
Wind and geopotential 200 hPa
Note: Troughs associated with
mountain ranges, continents
Observations of the Atmosphere
• Vorticity– Small scale flow– Large-scale flow
• Large scale flow and the climate system– Heat transport– Jet streams– Development of mid-latitude cyclones
Vorticity on Small Scales
• From the southern California fires:
http://video.nbc11.com/player/?id=171454
• What is the cause?http://aoss-web.engin.umich.edu/class/aoss102/tools/swf/?url=class/aoss102/tools/swf/
Vorticity on Large Scales
• Remember, vorticity is caused by– Wind shear– Rotation in the flow
• Can we identify these on weather maps?
• (The following maps come from http://www.aos.wisc.edu/weather/)
300 mb Wind Speed
Where is there positive vorticity?
500 mb Vorticity
Thermal Wind
• Remember, thermal wind relates– Vertical shear of geostrophic wind– Horizontal temperature gradients
• Can we identify these on weather maps?
Where are the strongest ?T
850 mb Temperature
Convergence/Divergence
• Remember, vertical motion on large scales directly related to– Convergence/divergence of ageostrophic
wind– Curvature in the flow
• Can we identify these on weather maps?
Where are surface lows/highs?
Surface Precipitation
850 mb Temperature
Concepts
• Vorticity: shear and curvature– Why is curvature vorticity (as opposed to
shear vorticity) usually associated with developing low pressure systems?
• Divergence and convergence and location of surface high and low pressure systems
• Thermal wind—vertical shear of the horizontal wind and horizontal temperature gradients
Concepts
• Features commonly found together– Jet stream– Upper level positive vorticity– Fronts– Midlatitude cyclones (low pressure systems)
• Coincidence?
Large scale flow and the climate system
Transfer of heat north and south is an important element of the climate at the Earth’s surface.
Redistribution by atmosphere, ocean, etc.
SURFACE
Top of Atmosphere / Edge of Space
ATMOSPHERECLOUD
heat is moved to poles
cool air moved towards equator cool air moved towards equator
This is a transfer. Both ocean and atmosphere are important!
Large scale weather systems transport large quantities of thermal energy from equator toward the poles
Hurricanes and heat
Hurricanes and heat
Mid-latitude cyclones
Mid-latitude cyclones & Heat
Mid-latitude Cyclones & Jet Stream
An estimate of the January mean temperature
northwinter
southsummer
tropopause
stratopause
mesosphere
stratosphere
troposphere
note where the
horizontal temperature gradients are
large
An estimate of the January mean zonal wind
northwinter
southsummer
note the jet streams
An estimate of the July mean zonal wind
northsummer
southwinter
note the jet streams
Wind and geopotential 200 hPa
Note: Variability in east-west of the wind
field.
Note: Troughs associated with
mountain ranges, continents
Note: Time variability of the wind field.
Waves in the atmosphere
• 300 mb Jet Stream Animation
Short summary
• We have strong mean zonal winds.
• We have latitudinal and time variability of the zonal winds– Quasi-stationary long waves.
• On these quasi-stationary long waves, mid-latitude cyclones form and propagate.
Mid-latitude cyclones
• What we know:– Low pressure systems– Form through spinup of low-level positive
vorticity– Divergence/convergence is key
• This is just the beginning…– Always closely associated with fronts—why?– Sometimes develop rapidly, sometimes not at
all—why?
The mid-latitude cyclone
Mid-latitude cyclones: Norwegian Cyclone Model
Fronts and Precipitation
CloudSat Radar
Norwegian Cyclone Model
Relationship between upper troposphere and surface
note tilt with height
Idealized vertical cross section
What’s at work here?
Mid-latitude cyclone development
Mid-latitude cyclones: Norwegian Cyclone Model
• http://www.srh.weather.gov/jetstream/synoptic/cyclone.htm
Cold and warm advection
cold
warm
Lifting and sinking
Increasing the pressure gradient force
Relationship between upper troposphere and surface
divergence over low enhances surface low
//increases vorticity
Relationship between upper troposphere and surface
vertical stretching //
increases vorticity
Modern education at its best.
• http://aoss.engin.umich.edu/class/aoss102/tools/swf/
Analysis Tools
• We have used many of the concepts and tools that we have introduced and explored.– Observed characteristics of the atmosphere– Conservation principles– Scale analysis: Geostrophic and hydrostatic– Thermal wind– Divergence and convergence
• These ideas are integrated into quasi-geostrophic theory (analysis and prediction)
Programming Exercise
• Gain experience writing programs to– Read data– Analyze data– Plot data
• Tools for research/analysis
Remember the vertical structure of the atmosphere
zRT
pgp
RT
p
gz
p
Hydrostatic
Eq. of State
If we assume T is constant with height (Isothermal)
zRT
g
p
p
zRT
pgp
If we assume T varies with height (Realistic)
p
p
z
p
p
z
sfc
sfc
T
z
R
gp
T
z
R
g
p
p
zRT
g
p
p
0
0
ln
If we assume T varies linearly with height (Not a bad assumption, in general)
sfc
sfc
sfc
p
p
z
sfc
sfc
sfc
T
zT
R
g
p
p
zT
z
R
g
p
p
zT
z
R
g
p
p
zTT
sfc
lnln
0 constant,
0
If we assume T varies linearly with height (Not a bad assumption, in general)
Rg
sfcsfc
Rg
sfc
sfcsfc
sfc
sfc
sfc
T
Tpp
T
zTpp
T
zT
R
g
p
p
/
/
)(
)(
lnln
Programming Exercise
• Read in data from two sounding files– Height– Potential temperature
• Compute pressure on each level– Isothermal atmosphere– Varying temperature– Constant lapse rate
• Use this information– Geostrophic wind– Temperature gradients
Programming Exercise
• Goals: programming concepts– Reading data– Arrays– Loops– Iteration
• Materials posted to ctools this afternoon/evening– Skeleton MatLAB program– Data– Instructions
Next Week
• Programming exercise in class Monday
• Start looking at quasi-geostrophic system– Scale analysis of equations in pressure
coordinates– Quantify wave movement and development