Topic 6.1.1
1. Compare and contrast the long-wave patterns for a summer and winter mean flow discussing
the role of thermal and orographic features in the maintenance of the typical long-wave
pattern.
(a) In middle and upper troposphere (500-mb)
 Winter (January) mean flow:

An intense polar vortex over the Canadian artic islands

A broad trough extends southward through Quebec and the eastern US

A broad ridge along the Canadian Rockies and over Alaska

Large height gradient over most of N. America, greater over the eastern half than
the western half
 Summer (July) mean flow:

The arctic vortex essentially vanished

Flow is weak and largely zonal

A broad trough persists in the east, a slight ridging over the Rockies

A large high pressure over the southern half of US, and a trough apparent off the
west coast
 Difference: Westerly flow is more intense and extends to lower latitudes in winter than
in summer (due to the relatively strong temperature gradient in winter)
 Common point: in both seasons a broad trough in the east and a broad right over the
Rockies. This is because the orographic forcing is more important in middle and upper
troposphere (the long-wave trough and ridge are the indicative of the Rossby wave
generated when the westerly flow passing over the Rocky mountains)
(b) In low level or near surface (1000-mb)
 Differential heating over the land and water (sea) is a major factor determining the
seasonal changes near the surface. In winter, the relatively warm oceans act as heat
sources for atmosphere, and land as heat sinks; the roles exchanged in summer (causes
of monsoon)
 In winter

lowers are evident over the northern oceans (i.e., Aleutian low over North Pacific
and Iceland low over North Atlantic), while cold high dominates the continents.

The northwesterly flow from high arctic (Arctic pipeline) advects cold and dry air
southwards over much of the areas east of the Rockies

southwesterly and southerly flow over the west coast;

Thermal trough over the Great Lakes and off the eastern seaboard
 In summer

subtropical highs are obvious and strong over the Pacific and Atlantic Oceans

A thermal low appear over the continent (centered over the deserts over the
southwestern US)

The cyclonic flow about this low combines with the anticyclonic flow around the
Atlantic high to pump warm, moist air northward from the Gulf of Mexico into
eastern Canada
2. Describe the characteristics of blocking patterns in terms of shape, scale, duration, geographic
and seasonal frequency.
 Blocking:

breakdown of the upper zonal flow, where the mean stream in mid-latitudes splits
into two branches; The northernmost branch curves to the left and follows the
western flank of an amplified ridge; developed to a closed anticyclone (typical
diameter 2000 km); The southern branch curves right and then passing south of a
series of cold lows.

The blocking anticyclone is warm and thermally symmetric near the core and is
capped by a cold high tropopause.

It moves very little and blocks the eastward progression of the following systems
which are diverted either to the north or the south of the block

Due to its persistence (8-9 days), must be considered in medium-range weather
forecast (droughts or prolonged wet spells)
 Shape:

“” shape (as described above)

Inverted “” shape (cut-off cold low)

Complex block: repetitions of the blocking development producing an extended
block (“” type) over a long sector of the hemisphere, with two bands of upper
westerly winds and a band of zonal easterlies in the middle latitudes
 Geographical distribution:

Two preferred formation regions: (1) in the Atlantic Ocean off the west coast of
Europe; (2) the Bering strait
Latitude: high frequency at 56N (at 48N and 64N less than half)
 Seasonality (frequency):
Spring > winter > summer > fall
 Duration (average in Canada):
Spring 9.7 days; winter 13.4 days; summer 11.1 days; fall 7.1 days

3. Explain how the location of the long wave influence the location and movement of cyclone
and anticyclone
 Long waves are roughly stationary (progress very slowly eastward); short waves moves
very fast eastward through long waves
 The short waves are obliged to follow the meandering of the long waves (long wave
steers the short waves)
 Short waves are commonly associated with the developing surface cyclones:
intensifying surface cyclones are usually found downstream from the short-wave
troughs; a series of surface cyclones can be superimposed on a single planetary wave;
surface cyclone families are most often found between long-wave troughs and
downstream ridges (PVA zone); surface anticyclones are intensified between long-wave
ridges and downstream troughs (NVA zone)
 Changes in the pattern of a planetary wave (e.g., zonal long wave number) usually
herald a major cyclone genesis event. A vigorous new surface cyclone usually forms
ahead of the new amplifying wave.
4. Discuss the dynamical factors that influence the formation of cyclones and anticyclones
including the characteristics of two types of dynamical secondary circulations having limited
vertical extend
 Dynamical factors influence cyclones:

Orographic forcing: lee side generally favors cyclonegensis (Alberta, Colorado)

Baroclinic instability (wind shear)

Localized thermal forcing (heating or cooling)

Coastal cyclonegenesis: land-sea contrast, sensible heating, latent heating

Upper level initiation (divergence, long-wave PVA, Jet stream )

Changes of the latitude (change in f)

Friction difference (from relatively smooth water surface to rough land)
 Dynamical factors influence anticyclones:

Upper level initiation (NVA, convergence, Jet stream)

Break up from subtropical high

Localized cooling

Break up from Artic high
 Some synoptic scale systems

Cold Arctic high

Thermal high

Stagnant dry air cooled by radiation at high lat. during long nights over snow or ice

Weakens in vertical, often replaced by a low aloft

Diurnal variation: little change

fast moving after leaving source region; steered by flow aloft

cirrus up to the ridge

Thermal low

Stagnant dry air heated by ground at low lat. during long days over sand surfaces

Weakens in vertical and disappear

Strongest during summer afternoon

Stationary over the heat source

Cu, sand whirls or dust devils

Instability trough

Strong flow of cold air heated by passing over warmer water and by latent heat

Weakens in the vertical

Little diurnal change, most frequent in winter

Stationary over the heating source until the flow changes

Sc, Cu, Cb, Cloud lines (streaks, squalls), snow flurries

Orographic trough

Strong flow of mountain, vertical stretching to the lee side produces trough (net
heating exceeds cooling due to latent heat)

Weakens with height

Little diurnal changes

Stationary with respect to mountains until air flow changes

Wave clouds, Ac, lenticular Chinook arch

Subtropical high (deep)
Hadley Cell, upper convergence, low level subsidence, high pressure belt broken up
by land-sea effects

Intensifies with height

Little diurnal change

Slow moving, south of westerlies

Middle clouds on the west side; subsidence inversion on southeast side
Cold low (deep)

Occluded low, cut-off low, concentric contours

Intensifies with height

Little diurnal change

Slow moving

Multi-layered middle cloud, Cu, Cb


5. Describe the North American monsoon (direct thermal effect of N. Amer. continent)
 Monsoon is continental secondary circulation of direct thermal origin, having profound
effect on the weather during summer and winter seasons
 Winter monsoon:

surface circulation over North America is weakly anticyclonic with ridge along the
eastern slope of the Rocky Mountains (to the west is the giant Aleutian low); at
500-mb the ridge is weakened and displayed westward to the coast, with a trough of
low pressure over the eastern side of the continent

prevailing wind over central and eastern part: strong component from N to S

frequent outbreaks of cold dry air masses from the Arctic to subtropics

An active frontal zone established off the southeast coast (between polar cold air
and warm moist northward maritime tropical air)  significantly increases the
precipitation in eastern US and Canadian maritime provinces

On the west coast, considerable northward component of the prevailing wind gives
milder and wetter climate; but whether increase in the precipitation is doubtful
 Summer monsoon:

The monsoon circulation over N. A. is weakly cyclonic; the center of this thermal
low is over the southwestern US; the Pacific subtropical high extends onto the west
coast; the Atlantic high extends westward, dominating most of eastern US

at 500-mb, the low pressure trough is weakened and displaced westward over the
west coast; the Atlantic high is strengthened and extended westward nearly to the
southern Pacific coast

light southerly winds over much of the central & eastern of the continent, wind
turns southwest and west at high latitudes  spread moisture

warm and sultry summer weather, with widespread occurrence of thunderstorms and
heavy convective rains due to continental heating  significantly increases rainfall
in east divide of the continent

On west coast, winds are commonly northwest and north, making climate cooler
and drier than it would be (if the zonal westerlies were not disturbed), decrease the
rainfall
6. Describe the thermally induced circulations, e.g., cold high, warm low, instability trough
 Warm low:

The local heating lifts the isobaric surface in the atmosphere over the heat source 
produce an upper level high and divergence  reduces the surface pressure

Inflow of air into the surface low + earth rotation + surface friction  cyclonic
circulation at the surface
 Cold high:

The isobaric surface sinks over the heat source due to local cooling  produce an
upper level low and convergence  inflow of air aloft increases the surface pressure
and outflow in lower atmos.  the gradient and equilibrium establish a cyclonic
circulation aloft and an anticyclonic circulation at the ground
 Instability trough:

When cold continental flow out from the Arctic high pass over the warm water of
Great Lakes and East US, the air is warmed from below, instability develops and get
a thermal low trough, which is called “instability trough”
7. Indicate areas in North America favored for cyclogensis and anticyclogenesis for both
summer and winter and discuss the dominate physical process in each one
 For cyclonegenesis
Location
Physical process
Colorado, Alberta
Lee-side of Rockies;
Orographic forcing
East coast or the western Atlantic
Cold air move to warm, moist surface
Strong baroclinic instability (land-sea
contrast)
The Gulf of Alaska
Combined effect of topography and
heating
The Great Lakes
Thermal forcing
winter
Location
Physical process
Alberta-Northwest territories border
Alberta-Montana-South Dakota
Orographic forcing
Along the east coats of N. America
The Gulf of Alaska
Orographic effect or
friction difference
summer

For anticyclogenesis
Location
Physical process
Northern Canada
winter
Thermal forcing (over snow and ice)
The Great Plain of US
Location
Physical process
Southwestern Canada
Subtropical high intrude
summer
8. Describe the general storm tracks over North America
 Generally, cyclones and anticyclones are more intense, numerous, and displaced farther
south in January than in July
 Cyclones form in the lee of Rocky Mountains and along the east coast of N. America,
and generally propagate to the east or northeast
 Anticyclones are generated over the snow and ice fields of Canada and just to the south
of jet stream; tend to propagate to the east and southeast
 Four preferred cyclone tracks in winter:

The first enters the northwestern boundary of N. America and terminates along the
Pacific northwest coast by the northern Rocky Mountains

The second and third originate from Alberta and Colorado, continue east-southeast
and northeast respectively and merge over the Great Lakes before taking a more
northerly track into

The fourth begins off the Virginia- North Carolina coast (some from the Gulf of
Mexico) and move parallel to the east coast toward Greenland
 Five preferred cyclone tracks in summer:

Two cross central Canada merging over the Hudson Bay

One cross northern US

The fourth along the northeast coast of N. America

The fifth in the Gulf of Alaska to west coast
Topic 6.1.2
1. Describe the “energetics” approach
 Energetics approach is a method for accessing cyclone development potential based on
the energy conservation cycle that occurs in mid-latitude cyclogenesis.
 It is a conceptual model upon which physically realistic diagnosis of the potential for
cyclone development may be made based on standard weather map
2. Define APE, ZAPE, EAPE, ZKE, EKE
 APE (available potential energy): the maximum potential energy that the atmosphere
possesses, which can be converted to kinetic energy

Modify APE:

Sensible heat transfer:
 Amount of solar radiation (latitude, cloud cover, albedo, topography)
 Surface type (land, water, snow/ice)

Latent heat transfer:
 Condensation of water vapor – enhance APE if release heat in warm air




ZAPE (zonal available potential energy): thickness and contours parallel and straight;
little advection possible
EAPE (eddy available potential energy): thickness and contours parallel and wavelike
with a meridional component; significant advection possible
ZKE (zonal kinetic energy): kinetic energy of zonal flow
EKE (eddy kinetic energy): kinetic energy of eddy flow, usually related to vertical
motion
3. Describe the mean energy cycle for the northern hemisphere
Solar radiation
Friction
ZAPE
ZKE
EAPE
EKE
Daibatic
heating
Friction
4. Using meteorological charts, describe how to assess the amount of APE (in both ZAPE and
EAPE), the processes affecting the amount of APE and the process of changing ZAPE to
EAPE
 The amount of APE (in both ZAPE and EAPE) is assessed by the strength of T or
thickness gradient displayed on upper air mass


Baroclinic zone (sfc or 850, T > 15 high; 1000-500 thickness > 30 dam, high)
Sharpness of front zone (sfc or 850)
Amplitude of thermal pattern (500 or 850, > 15 lat ?)
The processes affecting the amount of APE (changing APE)

Cold or warm air supply? 850 or SFC, yes, APE 

Latent heat release in warm (cold) air mass? SFC, Satellite or Radar

Sensible heating (cooling) in warm (cold) air mass SFC or Satellite


Solar radiation heating warm (cold) air mass APE  ()

Long wave radiation cooling warm (cold) air mass APE  ()

Mixing air mass; lower the center of mass APE 
The processes converting ZAPE to EAPE

Thermal pattern phase lag and trend (500mb)

Thermal fields distortion

cold air injection (SFC or 850mb)  by topography, vorticity; perturbation in
mean flow

TROF/RDG tilt (500 or 250mb)

TROF/RDG diffluene (500 or 250mb)


5. Using meteorological charts, describe the processes converting EAPE into EKE, and list the
factors influencing the conversion rate
 Atmosphere tries to eliminate the T gradient in ways of mixing air mass; ascent (descent)
of warm (cold) air convert EAPE to EKE
 Factors:

Vorticity advection 500mb, PVA  ascent; NVA  descent

Thickness advection 500mb, PTA  ascent; NTA  descent

Diabatic heating (sensible, latent heating) SFC, Satellite or Radar

Stability
SFC or Tephi

Openness of the wave

Location of surface low relative to upper Jet stream (right entry, left exit)

Speed and curvature of Jet Stream (approaching trough or diffluence deepen sfc low)

Changes in surface friction
6. Using meteorological charts, describe the processes converting EKE into ZKE and frictional
loss , and list the factors influencing the conversion rate
 Some of the energy is returned to the mean westerlies by converting EKE into ZKE,
through:

Northward transport of westerly momentum, i.e. positively tilted trough/ridge

Southward transport of westerly momentum, i.e. negatively tilted trough/ridge; often
forms cut-off lows

Adiabatic cooling in warm air; warming in cold air

Warm or cold air sources are cut off as wave matures
 Frictional loss: different orographic roughness of underlying surface, from land to water,
move onshore or offshore; from plain to mountains or reverse
7. Describe the potential for development of a baroclinic wave, in terms of individual processes
in the energy cycle
 Existing high APE supply

Sharp frontal zone

Strong baroclinicity

Large amplitude of thermal pattern
 Continued APE supply for cyclone development

cold air supply to the west of low

warm air supply in warm sector

latent heating in warm air mass

sensible heating in warm air mass (from land to sea)
 Strong conversion rate of ZAPE to EAPE

Distort thermal field (cold air injection triggered by topography or upper level
disturbance; TROF/RDG tilt; TROF/RDG diffluence) allows warm advection to
build strong RDG, cold advection to deepen the trough
 Strong conversion rate of EAPE to EKE

Strong upward motion to deepen the surface low

PVA and PTA promote the conversion of EAPE to EKE

Strong CYC Jet, surface low under right entrance or left exit

Weak instability
 Low conversion rate of EKE to ZKE
 Low conversion rate ZKE loss
8. Describe how satellite imagery may be used to access the energetics of a system
 The extent and intensity of clouds provide an assessment of the stability and vertical
motion (EAPE to EKE)
 The comma cloud pattern can be used to identify the location of vorticity maximum,
where vertical motion is strong (EAPE to EKE)
 Loop the satellite images, the flow can be observed as becoming more merdional from
sharpening of the ridge line, indicating ZAPE to EAPE
 The strength and curvature of upper jet stream in satellite indicate the sharpness and
depth of the baroclinic zone in low and middle level, showing existing APE supply
 The size and thickness of cloud in satellite image provide a clue of latent heat release in
warm/cold air mass (change in APE supply)
 Underlyling surface roughness can be seen in satellite, combing with location and
movement of cloud, can infer diabetic heating and sensible heating (change APE supply)
** Facts for northeasters

A name given to a strong steady wind from the northeast that is accompanied by rain
and inclement weather. It often develops when a storm system moves northeastward






along the coast of N. America. Also called Nor’ester.
Exist strong APE

Strong baroclinic zone, between by the cold air mass from the Artic and warm air
mass from the Gulf of Mexico and Atlantic Ocean

An sharp frontal zone, between the cold continental high and the Atlantic high at low
latitudes with strong wind shear and T gradient
Continued APE supply

Cold air supplied by the cold continental high in the cold air mass

Warm air supplied by the Atlantic high in the warm air mass

Moist air from Atlantic ocean provide latent heat release in the warm air mass

The warm Gulf stream provides sensible and latent heat to the warm sector
Conversion ZAPE to EAPE

Cold air injection, triggered by the Appalachian mountains

Vorticity perturbation: by existing wind shear at the surface
Conversion EAPE to EKE

In upper level (500mb), climatologically in winter there is a broad trough extending
from Quebec to Southern US (caused by the orographic forcing by Rocky
Mountains). East coast is right underneath the downstream of this long-wave trough,
the upper level divergence favors the upward motion
Sustaining the EKE

Water surface causes instability

Warm advection and PVA

Upward motion  cloud and precip.  latent heat release  more strong upward
motion
Dissipation of EKE

Water surface has less friction than land surface  last longer
Topic 6.1.3
1. Indicate the relationship of a mature baroclinic wave to the following upper fields
 500mb contour ridge and trough

500mb trough axis is to the west of surface low

500mb ridge axis is to the east of surface low

Divergence aloft favors cyclone development at surface

NTA (PTA) before (after) upper trough favors sinking (rising) motion
 Area of significant upper level divergence/convergence

Convergence over the region of cold outbreak to the west

Divergence over the center of the low
 Areas of significant low level divergence/convergence


Predominance of convergence in the central part of the low
Divergence on the outskirt
2. Sketch diagrams showing the 3-D trajectories of airflow through a mature baroclinic wave,
including the warm, cold and dry conveyor belts
 Warm conveyor belt (WCB): originates from relatively easterly flow at low lattitudes.
This air turns northward to flow approximately parallel with the cold front and ascends
while turning anticyclonically above the warm front joining the upper-level flow
northeast of the surface low near the upper-level ridge.
 Cold conveyor belt (CCB): originates in the anticyclonic low-level flow to the rear of
the surface high east of the surface low. The air approaches the low from the east and
rises rapidly as it moves toward the west from underneath the WCB belt. It continues to
rise and turn anticyclonically toward the northeast and merges with the WCB in the
upper troposphere near the ridge.
 Dry conveyor belt (DCB): originates in high troposphere or low stratospheric levels
downstream from the ridge far to the northwest of the surface low. A portion of the air
stream descends anticyclonically to the lower troposphere west of the trough stream and
east of the surface high pressure system; some of this air splits with the anticyclonic
stream, crosses the trough axis, flow parallel to the WCB within cloud-free zone, and
ascend above and also around the middle-upper cloud deck of the cold conveyor belt. A
southwesterly jet streak whose core lies long the eastern edge of the cold tongue extends
along the line of confluence between the WCB and the dry stream.
 Southerly air flowing over the warm sector at high levels above the WCB originates
at the middle and upper levels with the tropical easterlies east of the upper trough axis.
This air may be unsaturated when it reaches the warm secotor, so that it must flow over
or around the conveyor belt cloud shield.
3. Related the characteristics of the airflow to various upper and surface features, and their
influence on the large scale cloud and precipitation patterns associated with a baroclinic wave
 The clouds and precip. associated with WCB are along the cold front and north of the
warm front, forming the comma tail and body
 Clouds and precip. associated with the CCB are low and middle clouds, situated west
and north of the surface low, forming the westward extension of the comma head
 The distinctly sharp edge of the cloud pattern on the west edge of the comma tail , and
the northern and northwestern portion of the comma head, compromising
anticyclonically curved cirrus shield northeast of the low is due to the confluence of the
moist air with the dry airstream
 Southerly flow from upper-level tropica easterlies may condense to form an extensive
sharp cirrus shield over the warm sector or within a narrow cloud band along the comma
tail