Download Lecture #13: Lifecycle of Mid

Classic Mid-latitude Cyclones
Advanced Synoptic
M. D. Eastin
Classic Mid-Latitude Cyclones
History of Cyclone Research
Revisiting the Classic Structure
• Air flow patterns
• Moisture patterns
• Cloud patterns
Lifecycle of Classic Cyclones
• East Coast Cyclone
• Colorado Lee-side Cyclone
Anticyclones
• Climatology
• Blocking Patterns
Advanced Synoptic
M. D. Eastin
History of Cyclone Research
Early Development (pre-1900):
• Early civilizations (e.g., Egypt, Maya, Vikings, Chinese, Polynesia) were known to monitor
local weather/climate patterns and pass this information from one generation to the next
through stories, art, religion, and architecture
• Influenced agricultural (food)
• Influenced movement and migration (nautical travel)
• Influenced site selection for town/cities (access / stability)
• Aristotle (Greek – 350 BC) is considered the “founder” of meteorology
• Wrote Meteorologica where he described the hydrological cycle
• Book served as the primary reference for centuries
• Pomponius Mela (Roman – 25 AD) formalized a climate zone system
• Varahamihira (India – 500 AD) wrote Brihatsamhita - first formal description of the
seasonal cycle and the formation of clouds/rain
• Al-Dinawari (Muslim – 900 AD) wrote Book of Plants - first formal description of
the application of meteorology to agriculture
Advanced Synoptic
M. D. Eastin
History of Cyclone Research
Early Development (pre-1900):
• True scientific progress began in the 15th century and accelerated in the 17th century
• Basic instrumentation was first developed
• Standardized rain gauge (Korea – 1441 AD)
• Anemometer (Italy – 1450 AD)
• Thermometer (Italy – 1607 AD)
• Barometer (Germany – 1611 AD)
• Hygrometer (France – 1783 AD)
• Regular meteorological observation networks were developed
• Italy – 1654 AD
• United States – 1849 AD
• England – 1854 AD
• India – 1875 AD
• Scandinavia – 1881 AD
• Japan – 1883 AD
Advanced Synoptic
M. D. Eastin
History of Cyclone Research
Early Development (pre-1900):
• True scientific progress began in the 15th century and accelerated in the 17th century
• Development and application of math / physics to the atmosphere
• General circulation → Edmond Halley (1686)
→ George Hadley (1735)
→ William Ferrel (1855)
• Use of Calculus
→ Isaac Newton (1687)
→ Leonhard Euler (1755)
• Theories regarding atmospheric processes were first described
• Vertical pressure gradient
• Kinetic theory of (ideal) gases
• Oxygen discovered
• Heat capacity
• First law of thermodynamics
• Second law of thermodynamics
• Dry / moist adiabatic lapse rates
Advanced Synoptic
Pascal (1648)
Bernoulli (1738)
Lavoisier (1777)
Dalton (1808)
Clausius (1850) - credited
Carnot (1824) - credited
Espy (1841)
M. D. Eastin
History of Cyclone Research
“Bergen School” of Meteorology (1900-1920):
• Originally based in Leipzig, Germany
• Moved to Bergen, Norway to escape WW1
 Not a real school or university – it was a research center
 A “school of thought” upon which modern meteorology is based
 Developed “polar front theory”
• Started by Vilhelm Bjerknes – Norwegian physicist and mathematician
1904
Wrote a paper outlining a vision for numerical weather
prediction that included a closed set of governing equations
(the current set) and the methods needed to integrate the
equations forward in time using human “computers”
1905
Received a large grant from the Carnegie Institute to hire
numerous “computers” and pursue atmospheric research
• Tor Bergeron
• Carl-Gustav Rossby
• Sverre Petterssen
• Walfrid Ekman
Advanced Synoptic
M. D. Eastin
History of Cyclone Research
“Bergen School” of Meteorology (1900-1920):
1910 Published the book Dynamic Meteorology and
Hydrography Part 1: Statics, which included:
• Units (such as the millibar)
• Hydrostatic equation
• Concept of geopotential height
• Concept of isobaric charts
• Utility of atmospheric soundings (from kites)
1911 Published the book Dynamic Meteorology and
Hydrography Part 2: Kinematics, which included:
• Utility of streamlines
• Methods to compute vertical motion
(from the continuity equation)
• Analyses isolating regions of confluent
flow and temperature contrast (“fronts”)
• Emphasized the surface development
of cyclones
Advanced Synoptic
Surface Analysis – 5 January 1907
M. D. Eastin
History of Cyclone Research
Developments after 1920:
1928
Carl-Gustav Rossby was invited to develop the first university training program
for meteorology at the Massachusetts Institute of Technology (MIT)
1930s Jet streams and jet streaks were discovered
Development of the upper-air sounding network (weather balloons)
Recognition that upper-level waves play a critical role in cyclogenesis
1940s Development of weather radar (WWII)
Baroclinic theory of cyclogenesis developed
1950s First numerical weather models run on “modern” computers
Multiple synoptic-mesoscale observational studies of the structure and evolution
of frontal zones and jet streaks
1960s First meteorological satellites launched (Tiros-I)
Detailed cloud patterns incorporated into cyclone theory
1980s Utility of the PV framework demonstrated
Renewed appreciation for diabatic processes in synoptic cyclogenesis
Several field programs established to collected comprehensive datasets
Advanced Synoptic
M. D. Eastin
Classic Air Flow Patterns
Air Flow Patterns: System Relative
• Most cyclone systems move faster than the low-level flow (so system-relative low-level
flow approaches from the east), but slower than the upper-level flow (so system relative
upper-level flow leaves toward the east)
• As a result of the baroclinic instability process, three distinct “conveyor belts of air” develop
Advanced Synoptic
Classic Air Flow Patterns
Air Flow Patterns: System Relative
• Most cyclones move east faster than
the low-level flow, but slower than the
upper-level flow. As a result….
• Warm-moist air enters the cyclone
from the east at low-levels south of
the center in the warm sector
(called the “warm conveyor belt”)
L
• This air often rises along the cold and
warm fronts, is deflected northward
by mid-level flow, and eventually
deflected eastward by the strong
upper-level westerlies
• Finally, the air originating in the warm
conveyor often exists the system
northeast of the center
• Warm air rises and moves poleward
as expected from baroclinic instability
Advanced Synoptic
From Bluestein (1993)
M. D. Eastin
Classic Air Flow Patterns
Air Flow Patterns: System Relative
• Most cyclones move east faster than
the low-level flow, but slower than the
upper-level flow. As a result….
• Cold-moist air enters the from the east
at low-levels, but north of the cyclone
center and north of the warm front
(called the “cold conveyor belt”)
L
• A portion of this air gradually rises
through the mid-levels and advected
equatorward (around the north side)
forming the comma head & low-level
wrap-around stratus clouds
• Eventually the cold-conveyor air is
deflected eastward by the upper-level
flow and exits the system to northeast
of the center
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Classic Air Flow Patterns
Air Flow Patterns: System Relative
• Most cyclones move east faster than
the low-level flow, but slower than the
upper-level flow. As a result….
• Cold-dry air enters the from the west
at upper and middle levels, south of
the cyclone center and west of the
cold front (called the “dry tongue jet”)
L
• This air initially sinks to the middle and
lower levels (forming the dry slot and
cold front) and is deflected northward
by the flow within the mid-level trough
• A portion of this air enters the comma
head, is forced upward and deflected
eastward by mid-level flow, and exits
to the northeast
• Cold air sinks and moves equator as
expected from baroclinic instability
Advanced Synoptic
From Bluestein (1993)
M. D. Eastin
Classic Moisture Patterns
Moisture Patterns (U.S. Perspective):
• In most cases, the warm-conveyor belt
originates over the Gulf of Mexico at
low-levels, and is warm and very moist
Water-Vapor Image
(recall your thermodynamics)
• In most cases, the cold-conveyor belt
originates over the North Atlantic at
low-levels, and is cool and less moist
(compared to the warm conveyor)
• In most cases, the dry-tongue-jet
originates over Canada at upper
levels, and is cold and dry
850mb Moisture
and Winds
• Since moisture is often more important than
temperature for development of convection,
several names have been attached to this
critical “moisture conveyor belt”:
• Moisture plumes
• Atmospheric rivers
• Pineapple express (from the Pacific)
Advanced Synoptic
M. D. Eastin
Classic Cloud Patterns
Cloud Patterns:
• In the early stages (Area 1) of cyclone
development the dense cloud layer is primarily
confined to a narrow region along the cold front,
and a broad regions north of the warm front but
east of the cyclone center
L
• Often called the “baroclinic leaf”
• As the cyclone further develops (Area 2),
the warm, moist air that is ascending begins
to wrap around the poleward side (a result of
the baroclinic instability process), and the
cloud system begins to takes the shape
of a “comma”
L
• The classic “comma cloud”
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Classic Cloud Patterns
Cloud Patterns:
• At the same time the comma cloud forms, the
cold-dry air that is descending begins to wrap
around the equatorward side (again, a result
of the baroclinic instability process), producing
a cloud free region (Area 3)
L
• Often called the “dry slot” or “dry tongue”
• As the cyclone develops, some warm, moist
air originating at low-levels east of the cyclone
is often wrapped completely around to the
equatorward side, but remains below the
descending air of the dry slot, forming a
shallow layer of stratus clouds (Area 0)
L
• Often called the “wrap-around moisture”
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Classic Cloud Patterns
Cloud Patterns:
• A very nice (but large ~9 MB) infrared satellite animation of cyclone development from
the baroclinic leaf stage to a fully occluded system:
http://www.umanitoba.ca/environment/envirogeog/weather/leafanim.html
Advanced Synoptic
M. D. Eastin
Classic Air Flow, Moisture & Cloud Patterns
Air Flow, Moisture, and Cloud Patterns in the PV Perspective
• Recall the four distinct PV anomalies associated with developing cyclones…
• They are consistent with the classic airflow, moisture, and cloud patterns !!!
Advanced Synoptic
M. D. Eastin
Lifecycle of an East-Coast Cyclone
Example Case: QG Perspective
Evolution at 850 mb
Solid Contours = Heights
Dashed Contours = Thickness
(Temperature)
Note the strong WAA/CAA patterns
Note the cyclone motion
Blue box denotes period of most
rapid development
From Boyle and Bosart (1986)
Advanced Synoptic
M. D. Eastin
Lifecycle of an East-Coast Cyclone
Example Case: QG Perspective
Evolution at 300 mb
Solid Contours = Heights
Dashed Contours = Isotachs
Circles mark the 850mb cyclone center
Note the trough evolution and tilt
Blue box denotes period of most
rapid development
From Boyle and Bosart (1986)
Advanced Synoptic
M. D. Eastin
Lifecycle of an East-Coast Cyclone
Example Case: QG Perspective
• A diagnosis of the QG omega and
QG height-tendency equations were
performed to determine the relative
contributions of the vorticity and
temperature advection terms to the
total system vertical motion
• Diagnostics were performed just prior
to and during the period of most rapid
system development (blue box)
Vorticity Advection
L
L
Vorticity Advection
QG Diagnosis
Omega (ω) at 500 mb
Solid Contours = Rising motion
Dashed Contours = Sinking motion
Temperature Advection
L
Temperature Advection
L
Rising motion was due primarily to
changes in vorticity advection with
height over the surface cyclone (L)
From Boyle and Bosart (1986)
Advanced Synoptic
M. D. Eastin
Lifecycle of an East-Coast Cyclone
Example Case: QG Perspective
• A diagnosis of the QG omega and
QG height-tendency equations were
performed to determine the relative
contributions of the vorticity and
temperature advection terms to the
total system vertical motion
Vorticity Advection
Total QG estimated χ
L
L
• Diagnostics were performed just prior
to and during the period of most rapid
system development (blue box)
Temperature Advection
Observed χ
QG Diagnosis
Height Tendency (χ) at 900 mb
4 March 00Z
Solid Contours = Height falls
Dashed Contours = Height rises
L
L
Height falls resulted from roughly
equal contributions
From Boyle and Bosart (1986)
Advanced Synoptic
M. D. Eastin
Lifecycle of an East-Coast Cyclone
Example Case: QG Perspective
• A diagnosis of the QG omega and
QG height-tendency equations were
performed to determine the relative
contributions of the vorticity and
temperature advection terms to the
total system vertical motion
Vorticity Advection
Total QG estimated χ
L
L
• Diagnostics were performed just prior
to and during the period of most rapid
system development (blue box)
Temperature Advection
QG Diagnosis
Height Tendency (χ) at 900 mb
4 March 12Z
L
Observed χ
L
Solid Contours = Height falls
Dashed Contours = Height rises
Height falls resulted from primarily
vorticity advection
From Boyle and Bosart (1986)
Advanced Synoptic
M. D. Eastin
Lifecycle of a Colorado Lee-side Cyclone
Typical Cyclogenesis:
0 hours
• Form along the lee-side of the Rocky Mountains
due to a combination of downslope westerly flow
superimposed beneath the PVA region of an
upper-level short-wave trough
• Lee cyclones never develop from downslope flow
alone (i.e., without upper-level forcing)
• The cyclone initially moves southeastward due to
low-level WAA to the east, upper-level PVA to the
east, and downslope flow to the south
6 hours
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Lifecycle of a Colorado Lee-side Cyclone
Typical Cyclogenesis:
12 hours
• As the lee cyclone moves away from the mountains:
• Strong CAA develops west of the center
• The combined CAA and WAA induce the
the baroclinic instability process, and the
cyclone begins to rapidly intensify
• The downslope flow and “southern forcing”
vanishes, and the cyclone begins to
move east
• As the cyclone continues to intensify, the strong
WAA and CAA shift the warm front northeast of the
center and the cold front to the southwest
18 hours
• Storm motion begins to turn to the northeast
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Lifecycle of a Colorado Lee-side Cyclone
Typical Cyclogenesis:
• Many lee cyclones pass
over the Chicago area
(the “windy city”)
24 hours
36 hours
30 hours
42 hours
• Most have reached maturity
and have begun the
occlusion process by the
time they have reached
the Great Lakes
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Anticyclones – Climatology
Where do Surface Anticyclones Form?
• More frequent in the winter than the summer
• Occurs further south during the winter and
further north in the summer
1. In the southern Plains from Texas to Kansas
up through North Dakota
2. In the northern (Canadian) Rockies
2
1
These two locations are related to strong
cold air advection to the west of developing
Colorado leeside-lows and Alberta Clippers
(as the cyclones move east)
From Zishka and Smith (1980)
Advanced Synoptic
M. D. Eastin
Anticyclones – Climatology
Where do Surface Anticyclones Move?
• Most surface anticyclones are short waves
and move east (progress) with the mean flow
 Initial motions may be southerly (due to
topographic influences) but mature anticyclones
almost always move southeasterly
 Related to motion toward maximum surface
pressure increases (via QG theory)
• CAA maximum is often to the southeast
• An upper-level NVA maximum is often
to the southeast
From Zishka and Smith (1980)
Advanced Synoptic
M. D. Eastin
Anticyclones – Climatology
Where do Surface Anticyclones Dissipate?
1. Far off the East Coast over the subtropical
central Atlantic → merge with “Bermuda High”
Related to “occlusion” and being cut-off from
their source of cold-dry (polar) air
2. Over the central Rockies
3. Over the central and southern Appalachians
2
1
3
Both locations are related to flow over (down)
topography, since downslope flow creates
surface lows (or weakens surface highs)
From Zishka and Smith (1980)
Advanced Synoptic
M. D. Eastin
Anticyclones – Blocking Patterns
The Lack of Motion:
 Waves no longer progress (move east) through a latitude belt
 Stationary long waves dominate the hemisphere’s circulation
• Often associated with large, intense, and stationary anticyclones
• Occur year-round – most often in April – least often in September
• Pattern persists for 10 or more days
• Produce extreme weather
→ Hot and dry under anticyclones (possible drought)
→ Cool and wet under cyclones (possible flooding)
• Three Primary Types:
Split Flow Block
Omega Block
Stationary Ridge
From Bluestein (1993)
Advanced Synoptic
M. D. Eastin
Anticyclones – Blocking Patterns
Split-Flow Block
Advanced Synoptic
M. D. Eastin
Anticyclones – Blocking Patterns
Omega Block
Advanced Synoptic
M. D. Eastin
Anticyclones – Blocking Patterns
Stationary Ridge
Advanced Synoptic
M. D. Eastin
References
Bluestein, H. B, 1993: Synoptic-Dynamic Meteorology in Mid-latitudes. Volume II: Observations and Theory of Weather
Systems. Oxford University Press, New York, 594 pp.
Bosart, L. F., 1981: The Presidents Day snowstorm of 18-19 February 1979: A subsynoptic-scale event. Mon. Wea. Rev.,
109, 1542-1566.
Boyle, J. S., and L. F. Bosart: 1986: Cyclone / anticyclone couplets over North America. Part II: Analysis of major
cyclone event over the eastern United States. Mon. Wea. Rev., 114, 2432-2465.
Brennan, M. J., G. M. Lackmann, and K. A. Mahoney, 2008: Potential vorticity (PV) thinking in operations: The utility
of non-conservation. Weather and Forecasting, 23, 168-182
Browning, K. A., 1986: Conceptual Models of precipitation systems. Wea. Forecasting, 1, 23-41.
Hoskins, B. J., 1990: The theory of extra-tropical cyclones. Extra-tropical cyclones: The Erik Palmen Memorial Volume,
C. W. Newton and E. O. Holopainen, eds, American Meteorological Society, 129-153.
Hoskins B. J., and P. J. Valdes, 1990: On the existence of storm-tracks. J. Atmos. Sci., 47, 1854-1864.
Miller, J. E., 1946: Cyclogenesis in the Atlantic coastal region of the United States. J. Meteor., 3, 31-44.
Newton, C. W., 1956: Mechanism of circulation change during a lee cyclogenesis. J. Meteor., 13, 528-539.
Petterssen, S., 1956:, Weather Analysis and Forecasting 2nd, ed. McGraw-Hill, 428 pp.
Petterssen, S., and S. J. Smebye, 1971: On the development of extra-tropical cyclones. Quart J. Roy. Meteor. Soc.,
97, 457-482.
Sanders, F., 1988: Life history of mobile troughs in the upper westerlies. Mon. Wea. Rev., 116, 2629-2648.
Zishka, K. M., and P. J. Smith, 1980: the climatology of cyclones and anticyclones over North America and surrounding
oceans environs for January and July, 1950-1977. Mon. Wea. Rev., 108, 387-401.
Advanced Synoptic
M. D. Eastin