Anthes, R. A., Y.-H. Kuo, and J. R. Gyakum, 1983: Numerical simulations of a case of
explosive marine cyclogenesis. Mon. Wea. Rev., 111, 1174–1188.
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EC that damaged Queen Elizabeth II dropped 60 hPa/24 h starting at 1200 UTC 9
September 1978
Simulations see why such poor forecasts were made of the storm
Baroclinic instability in the weakly stratified lower troposphere is the major
mechanism of growth of this cyclone, while latent heat release plays an important role
in the later stages of development
o Rapid cyclogenesis occurs in the model in a shallow layer of strong
baroclinicity and low static stability
Moister environment using supplementary data was more favorable for development
Latent heating produces a stronger cyclone with a warmer core
More intense storm occurs when maximum in heating is in the lower troposphere
Bosart, L. F., 1981: The President’s Day snowstorm of 18 19 February 1979: A
subsynoptic scale event. Mon. Wea. Rev., 109, 1542–1566.
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18-19 February 1979: record-breaking snowfall in the Middle Atlantic States
Cyclogenesis initiated along coastal front as the result of lower-tropospheric WAA
Coastal front steers cyclone NNE until in a favorable phase relationship with shortwave trough over the Ohio Valley
Explosive deepening between 1200 UTC and 1800 UTC 19 February with the
outbreak of deep convection near the storm center
Unlike a hurricane, convection is asymmetric about the vortex
Carolina coastal fronts are described in Bosart et al. (1972) and Bosart (1975)
Gyakum (1980) explosive deepening coincided w/ outbreak of convection near center
Sanders and Gyakum (1980) suggest that failure to account for the influence of
cumulous convection on the large-scale circulations is mostly responsible for the
more egregious under-prediction errors in storm central pressure
While is seems likely that the President’s Day cyclone originated as a baroclinic
disturbance aided in a significant way by differential diabatic heating, the possible
importance of CISK (Charney and Eliassen 1964) cannot be ruled out
Cumulous convection rapidly developed near the cyclone center preceding and
accompanying the generation of an intense vortex
Cold air is rapidly warmed and moistened by oceanic sensible and latent heat fluxes,
leading to the creation of a highly baroclinic boundary layer superimposed over a
region of strong, horizontal SST gradient
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Bosart, L. F., and S.C. Lin, 1984: A diagnostic analysis of the Presidents’ Day storm of
February 1979. Mon. Wea. Rev., 112, 2148–2177.
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18-19 February 1979: record-breaking snowfall in the Middle Atlantic States
Initial growth of lower-tropospheric cyclonic vorticity is associated with convergence
along the Carolina coastal front
Coastal frontogenesis responds to differential warming and moistening in in
conjunction with sensible heating over the ocean and the blocking of shallow cold air
by the southern Appalachian Mountains
Impact of convection is not discussed in this paper
Jet streak locations contributed to frontogenesis along the Carolina coast
Comparison of the kinematic, quasi-geostrophic, and semigeostrophic vertical
motions is presented
Kinematic method best captured vertical motions pre-cyclogenesis, flow highly
ageostrophic at that time… all come into better agreement later with semigeostrophic
being the closest to observations
Moisture flux convergence intensifies as coastal frontogenesis commences
Barotropic processes were more important in generating kinetic energy in the storm
environment, whereas baroclinic processes dominate the immediate storm area
Vertical advection of vorticity was also important from the lower troposphere up
Grams, C. M., and Coauthors, 2011: The key role of diabatic processes in modifying the
upper-tropospheric wave guide: A North Atlantic case study. Quart. J. Roy. Meteor.
Soc., 137, 2174–2193.
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Case study of wave amplification in the North Atlantic/European sector (Sept 2008)
Cross isentropic transport of low-PV air within WCB (low PV produced diab.)
Sources: 1) Diabatic heating impact on development of ECs
2) Diabatic redistribution of PV in the vertical
3) Rossby wave train (RWT)
Use equivalent potential temperature (theta-e) over potential temperature (theta) to
show fronts
Gyakum, J. G., 1983a: On the evolution of the QE II storm. I: Synoptic aspects. Mon.
Wea. Rev., 111, 1137–1155.
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Hurricane-force winds battered the liner Queen Elizabeth II on 10-11 September 1978
Originated as shallow baroclinic disturbance west of Atlantic City, NJ  60 hPa/24 h
Suggested that deep convection, like in TC formation, played a substantial role
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Surface low was “steered” by warm advection to the left of the upper-level flow, in
contrast to most surface lows
Deep convection associated with MCC responsible for rapid deepening
Development of upper-level trough after the surface low appeared, similar to
President’s Day snowstorm (Bosart 1981)
Gyakum, J. G., 1983b: On the evolution of the QE II storm. II: Dynamic and
thermodynamic structure. Mon. Wea. Rev., 111, 1156–1173.
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Assesses the importance of heating on cyclogenesis (use PV to assess)
PV generation was concurrent with explosive deepening
Relatively weak baroclinic forcing helped to organize convective bulk heating
Studied deep convection because of the hurricane-like wind and cloud field (CISK)
“Tracton (1973) has presented evidence for convective processes triggering
cyclogenesis in a series of continental cases.”
“Bosart (1981) has shown the President’s Day (February 1979) cyclone’s rapid
intensification to have been associated with deep convection near its clear, eyelike
center.”
Temperature rise in center of cyclone due to bulk heating effects
Reed, R. J., 1979: Cyclogenesis in polar air streams. Mon. Wea. Rev., 107, 38–52.
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Cyclones forming in polar air masses
Forming on the poleward side of the jet stream
CISK and diabatic heating deemed important when on the poleward side of primary
midlatitude temperature gradient
Reed, R. J., A. J. Simmons, M. D. Albright, and P. Undén, 1988: The role of latent heat
release in explosive cyclogenesis: Three examples based on ECMWF operational
forecasts. Wea. Forecasting, 3, 217–229.
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Study looks at two well-predicted North Atlantic cyclones
Danard (1964) carried out a diagnostic study that convincingly demonstrated the
importance of latent heat release in a single case
Hoskins (1980) dry forecast of a western North Pacific EC showed the importance of
latent heat release to EC deepening
“The percentage [of deepening that LHR accounts for] can vary from case to case and
with geographical region and season.”
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“Thus, we seek numbers that can be used with others to provide statistical and
climatological conclusions.”
Latent heat release was found to account for 40% to 50% of deepening
Only ¼ of the latent heating effect was attributed to convective heating??
Impact of latent heat release was largest near the storm centers
Sanders, F., and J. R. Gyakum, 1980: Synoptic-dynamic climatology of the “bomb.”
Mon. Wea. Rev., 108, 1589–1606.
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“Bombs” are a primarily maritime, cold-season, event with hurricane-like features
Typically found ~400 n mi downstream of a 500 hPa mobile trough
Explosive development occurs over a wide range of SSTs, but, preferentially, near the
strongest gradients
1979 Fastnet yacht race = summer example of a bomb (Rice 1979)
“Some physical effect other than the commonly understood large-scale baroclinic
mechanism may play an important role”
Explosive deepening is a characteristic of the vast majority of the deepest cyclones
Bergeron is adjusted for latitude (24 hPa/24 h at 45N)
Occur within or poleward of the main belt of westerlies
Development occurs in a region of upper-level diffluence
Schemm, S., H. Wernli, and L. Papritz, 2013: Warm conveyor belts in idealized moist
baroclinic wave simulations. J. Atmos. Sci., 70, 627–652.
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Idealized modeling study
WCB = cross-isentropic flow propelled by release of latent heat due to condensation
of water vapor in the lower troposphere and ice phase processes in the upper-trop.
“PV thinking” useful because of conservation property of PV for adiabatic and
frictionless flows and for invertiblity principle, which allows diagnosis of the
balanced flow field from the PV of the atmosphere and suitable boundary conditions
In the presence of diabatic effects, entropy is not conserved and PV loses its material
conservation property. These diabatic effects comprise a wide range of physical
phenomena, among which are radiation, surface fluxes, and phase transitions of water
in clouds.
Primary cyclone intensifies faster in moist simulation, mainly due to enhanced
baroclinic conversion (EKE budget)
Moist cyclone develops a more intense bent-back warm front where the largest latent
heating occurs
Direction of warm conveyor belt can vary (rWCB and fWCB)
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Schemm S, and H. Wernli, 2014. The linkage between the warm and the cold conveyor
belts in an idealized extratropical cyclone. J. Atmos. Sci., 71, 1443–1459.
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Formation of a cold conveyor belt (CCB), linkage to WCB, and their impact on the
development of a midlatitude cyclone
CCB: Weak ascent, strong increase in PV, close to surface on cold side of bent-back
warm front, PV increases below latent heat release (LHR)
o Important impact: enhanced the low-level jet along the tail of the bentback warm front
WCB: Maximum ascent, negative PV anomaly in the upper-troposphere
o Important impact: enhancement of downstream cyclogenesis due to the
perturbation of the downstream Rossby waveguide
60% of all winter cyclones in the northern hemisphere have a WCB
Tracton, M. S., 1973: The role of cumulus convection in the development of extratropical
cyclones. Mon. Wea. Rev., 105, 469–476.
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“Significant convection occurs in the center of storms generally only during the early
stages of their life history”
Convective activity away from the center appears to not be crucial
In the midlatitudes, the fundamental mechanism of cyclogenesis is the baroclinic
instability of the meandering westerlies (Charney 1947, Eady 1949).
ECs thus have as their basic source of energy the large-scale temperature contrast
between air masses
Aubert (1957) found that released latent heat tended to lower the heights of isobaric
surfaces in the lower troposphere and raise them in the upper troposphere. These
changes resulted in a deepening of the low-level cyclone and acceleration of the rate
of movement.
Danard (1964, 1966) demonstrated that the release of latent heat could contribute
significantly to the production of the storm’s available potential energy and to an
increased rate of generation of kinetic energy.
Storms considered in this study formed over the eastern two-thirds of the United
States or western Atlantic
Close proximity to warm moist air (Gulf of Mexico/Caribbean Sea) it is an area
particularly susceptible to the generation of the convective instability necessary for
the occurrence of shower activity (Fawbush et al. 1951)
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