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upper-level forcing, or different phasing between the PV anomaly and cyclone, would have produced a higher-impact flooding event across the United Kingdom or whether the verifying solution represented the highest-impact event possible for this synoptic setup. The question is answered by using piecewise PV inversion to design a suite of model simulations with the strength and position of the PV anomaly modified in the initial conditions, following a similar method to previous studies by Huo et al
upper-level forcing, or different phasing between the PV anomaly and cyclone, would have produced a higher-impact flooding event across the United Kingdom or whether the verifying solution represented the highest-impact event possible for this synoptic setup. The question is answered by using piecewise PV inversion to design a suite of model simulations with the strength and position of the PV anomaly modified in the initial conditions, following a similar method to previous studies by Huo et al
stability) and low-level lifting mechanisms is therefore a prerequisite to understanding how convection develops downstream of an upper-level trough. The primary question addressed in this paper is whether these factors are sufficient in themselves to explain the observed convective organization, or whether the upper-level PV anomaly also played a part: does the convection self-organize under synoptic forcing or does the observed organization develop in response to some preexisting susceptibility on a
stability) and low-level lifting mechanisms is therefore a prerequisite to understanding how convection develops downstream of an upper-level trough. The primary question addressed in this paper is whether these factors are sufficient in themselves to explain the observed convective organization, or whether the upper-level PV anomaly also played a part: does the convection self-organize under synoptic forcing or does the observed organization develop in response to some preexisting susceptibility on a
cyclone deepened rapidly east of Canada. Based on the operational experience at the Ocean Prediction Center, the case was typical of extratropical cyclones with strong surface winds caused by sting jets. An area of storm-force to hurricane-force sustained winds (50–64 kt, 26–33 m s −1 ) occurred within about 460 km to the east and south from the cyclone center at 0731 UTC 8 December, with a maximum of 75 kt (39 m s −1 ) ( Fig. 1 ). These 10-m ocean vector winds were derived from the National
cyclone deepened rapidly east of Canada. Based on the operational experience at the Ocean Prediction Center, the case was typical of extratropical cyclones with strong surface winds caused by sting jets. An area of storm-force to hurricane-force sustained winds (50–64 kt, 26–33 m s −1 ) occurred within about 460 km to the east and south from the cyclone center at 0731 UTC 8 December, with a maximum of 75 kt (39 m s −1 ) ( Fig. 1 ). These 10-m ocean vector winds were derived from the National
the cold point tropopause and a corresponding increase in static stability. Randel et al. (2007) proposed that the TIL is generated by a radiative forcing mechanism associated with the vertical gradients of ozone and water vapor across the tropopause. The maximum in static stability in the TIL is located in the region where the positive portion of the PV dipole forms (not shown). Randel and Wu (2010) identified a similar maximum in static stability in the polar summer tropopause inversion
the cold point tropopause and a corresponding increase in static stability. Randel et al. (2007) proposed that the TIL is generated by a radiative forcing mechanism associated with the vertical gradients of ozone and water vapor across the tropopause. The maximum in static stability in the TIL is located in the region where the positive portion of the PV dipole forms (not shown). Randel and Wu (2010) identified a similar maximum in static stability in the polar summer tropopause inversion
, doi: 10.1175/MWR-D-10-05003.1 . Keyser , D. , M. J. Reeder , and R. J. Reed , 1988 : A generalization of Petterssen’s frontogenesis function and its relation to the forcing of vertical motion . Mon. Wea. Rev. , 116 , 762 – 780 , doi: 10.1175/1520-0493(1988)116<0762:AGOPFF>2.0.CO;2 . Locatelli , J. D. , and P. V. Hobbs , 1987 : The mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones. XIII: Structure of a warm front . J. Atmos
, doi: 10.1175/MWR-D-10-05003.1 . Keyser , D. , M. J. Reeder , and R. J. Reed , 1988 : A generalization of Petterssen’s frontogenesis function and its relation to the forcing of vertical motion . Mon. Wea. Rev. , 116 , 762 – 780 , doi: 10.1175/1520-0493(1988)116<0762:AGOPFF>2.0.CO;2 . Locatelli , J. D. , and P. V. Hobbs , 1987 : The mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones. XIII: Structure of a warm front . J. Atmos
., 2013 : Atmospheric rivers as drought busters on the U.S. West Coast . J. Hydrometeor. , 14 , 1721 – 1732 , doi: 10.1175/JHM-D-13-02.1 . Gray , S. L. , and H. F. Dacre , 2006 : Classifying dynamical forcing mechanisms using a climatology of extratropical cyclones . Quart. J. Roy. Meteor. Soc. , 132 , 1119 – 1137 , doi: 10.1256/qj.05.69 . Guan , B. , N. P. Molotch , and D. E. Waliser , 2013 : The 2010/2011 snow season in California’s Sierra Nevada: Role of atmospheric rivers and
., 2013 : Atmospheric rivers as drought busters on the U.S. West Coast . J. Hydrometeor. , 14 , 1721 – 1732 , doi: 10.1175/JHM-D-13-02.1 . Gray , S. L. , and H. F. Dacre , 2006 : Classifying dynamical forcing mechanisms using a climatology of extratropical cyclones . Quart. J. Roy. Meteor. Soc. , 132 , 1119 – 1137 , doi: 10.1256/qj.05.69 . Guan , B. , N. P. Molotch , and D. E. Waliser , 2013 : The 2010/2011 snow season in California’s Sierra Nevada: Role of atmospheric rivers and
fluxes in storm-force winds and estimated peak-to-trough ocean wave heights of 6–12 m. The circuit BCDEG was designed to be closed in a frame of reference moving with features on the front, but in practice the circuit was found to be best closed by a point between E and G, labeled F in Fig. 1 (see section 3b ). Subsequently, the aircraft turned to cross the front again before ascending through the cold-sector boundary layer (1635–1705 UTC) and finally crossing the front at high altitude to produce
fluxes in storm-force winds and estimated peak-to-trough ocean wave heights of 6–12 m. The circuit BCDEG was designed to be closed in a frame of reference moving with features on the front, but in practice the circuit was found to be best closed by a point between E and G, labeled F in Fig. 1 (see section 3b ). Subsequently, the aircraft turned to cross the front again before ascending through the cold-sector boundary layer (1635–1705 UTC) and finally crossing the front at high altitude to produce
mean system motion vector. In the two cases analyzed in detail, the observed changes in postfrontal winds and the associated vorticity and stretching increases appeared to be related to the development, or movement along the front, of subtle frontal waves. An open question is whether the waves are a consequence of dynamical processes internal to the frontal rainband, or of external factors, such as a response of the wind field to dynamic forcing in the vicinity of the NCFR (e.g., Browning and
mean system motion vector. In the two cases analyzed in detail, the observed changes in postfrontal winds and the associated vorticity and stretching increases appeared to be related to the development, or movement along the front, of subtle frontal waves. An open question is whether the waves are a consequence of dynamical processes internal to the frontal rainband, or of external factors, such as a response of the wind field to dynamic forcing in the vicinity of the NCFR (e.g., Browning and
versa, except where the isentropic surface intersects orography. This property can be demonstrated as follows. In isentropic coordinates, (2) and (3) for and , respectively, take the form where is the gradient operator in isentropic coordinates and where (with components expressed in isentropic coordinates) is the nonadvective part of the PV flux associated with the material rate of change of θ , , and the frictional or other arbitrary force per unit mass exerted on the air . Using
versa, except where the isentropic surface intersects orography. This property can be demonstrated as follows. In isentropic coordinates, (2) and (3) for and , respectively, take the form where is the gradient operator in isentropic coordinates and where (with components expressed in isentropic coordinates) is the nonadvective part of the PV flux associated with the material rate of change of θ , , and the frictional or other arbitrary force per unit mass exerted on the air . Using
