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C. W. Newton

DECEMBER 1954C. W. NEWTON449FRONTOGENESIS AND FRONTOLYSIS AS ATHREE-DIMENSIONAL PROCESS By C. W. NewtonWoods Hole Oceanographic Institution 1 and University of Chicago 2.3 (Manuscript received 12 May 1954)ABSTRACTA detailed analysis is presented to show the atmospheric structure during the earlier formative stagesof a deep, upper trough. Over the western United States, a well-marked west-east frontal layer extendsthrough the whole troposphere; in upper levels, this disappears

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Andrea Buzzi

to clarify the physical differences between F 2 and F 3 . The first is significant in the context of upper-level frontogenesis, although it represents only an ideal kinematic process: a pure rotation 1 of the vector ∇ 3 θ in its vertical plane, without change of its magnitude, would not be associated with frontogenesis (or frontolysis) according to F 3 . In contrast, rotation of ∇ 3 θ in the vertical plane associated with strong horizontal gradients of vertical velocity represents the

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Michael J. Reeder
,
Thomas Spengler
, and
Clemens Spensberger

gradient (their Figs. 3a,b) is comparable to the pattern of climatological mean diabatic frontogenesis found here ( Fig. 3d ), with frontogenesis along the SST front, strong frontolysis on the southeastern side, and weak frontolysis on the northwestern side. Similar results were found in a general circulation model by Parfitt et al. (2016) . In the present study, however, most of the diabatic frontogenesis along the SST front is associated with no front conditions (cf. Fig. 3d with Fig. 3f

Open access
Mankin Mak
,
Yi Lu
, and
Yi Deng

the location of the large positive values of . The large negative values of in those figures match well with the location of weakening gradient of (i.e., a site of frontolysis). In contrast, Fig. 11a reveals that the match between the location of the ULF and the pattern of positive values of is poor, where stands for horizontal gradient. Similar results are found in the simulation with diabatic heating. Unfortunately, in the original comment, Buzzi (2016) neither comments on the logic

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Mankin Mak
,
Yi Lu
, and
Yi Deng

its long tentacles bunching up together like the isotherms along the cold front. A positive value of F 2 would mean local frontogenesis and negative value local frontolysis. Movement of a front would manifest as closely packed bands of F 2 values in alternating signs. The F 2 values in the plots quantify the local impact of the physical processes at different parts of the two fronts during their development. For example, there are several pairs of short and broad mesoscale green and red

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Jung Hoon Shin
and
Da-Lin Zhang

surface temperature (SST), and increasing vertical wind shear (VWS) and baroclinicity ( Klein et al. 2000 ; Jones et al. 2003 ). Perhaps the most prominent structural change of an ET TC is the development of an extensive coverage of clouds and precipitation associated with warm frontogenesis when it interacts with low-level baroclinicity to the north ( Harr and Elsberry 2000 ; Klein et al. 2000 ; Atallah and Bosart 2003 ; Colle 2003 ). After its warm core is replaced by a cold core, the TC may

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Raphaël Rousseau-Rizzi
and
Kerry Emanuel

Abstract

Potential intensity (PI) is an analytical bound on steady, inviscid, axisymmetric hurricane wind speed. Studies have shown that simulated hurricane azimuthal wind speed can greatly exceed a PI bound on the maximum gradient wind. This disparity is called superintensity (SI) and has been attributed to the contribution of the unbalanced flow to the azimuthal wind. The goals of this study are 1) to introduce a new surface wind PI (PI s ), based on a differential Carnot cycle and bounding the magnitude of the surface winds; 2) to evaluate SI in numerical simulations with respect to diagnostic PI bounds on gradient wind (PI g ), azimuthal wind (PI a ), and surface wind (PI s ); and 3) to evaluate the validity of each PI bound based on the SI computations. Here, we define superintensity as the normalized amount by which each version of PI is exceeded by the quantity it bounds. Axisymmetric tropical cyclone simulations are performed while varying the parameterized turbulent mixing as a way of estimating SI in the inviscid limit. As the mixing length decreases, all three bounded wind speeds increase similarly from a sub-PI state to a marginally superintense state. This shows that all three forms of PI evaluated here are good approximations to their respective metrics in numerical simulations.

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Mankin Mak
,
Yi Lu
, and
Yi Deng

transverse circulation by the geostrophic flow component in the upper-level jet streak ( Shapiro 1981 ; Shapiro et al. 1984 ). However, ULFs seem to be a part of the synoptic-scale baroclinic waves in general ( Reed 1955 ; Newton 1958 ; Nieman et al. 1998 ). A 2D semigeostrophic model was used by Hoskins (1972) to demonstrate the formation of ULFs driven by an imposed vertically uniform confluent flow. The dynamics of frontogenesis was interpreted as a feedback process in the context of a developing

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Robert Davies-Jones

fronts and jets. The exact solutions are nevertheless useful for revealing relationships between Q vectors and ageostrophic circulations in the various approximations. For example, the exact PE solution tells us which vector ( Q *, R *, or S *) ultimately points in the direction of the true low-level ageostrophic motion during frontogenesis. The other exact solutions quantify the errors of the approximate models [an approach also used by McWilliams and Gent (1980) and Allen et al. (1990) ]. 2

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Reuben Demirdjian
,
Richard Rotunno
,
Bruce D. Cornuelle
,
Carolyn A. Reynolds
, and
James D. Doyle

⁡ ( 1 ρ ∂ ψ ∂ Z ) + ∂ ∂ X ⁡ ( ρ q g f 3 θ 0 ∂ ψ ∂ X ) = − 2 Q − g ρ f 2 θ 0 ∂ S ∂ X , where ψ is the ageostrophic streamfunction, g is the gravitational acceleration, f is the Coriolis parameter, θ 0 is the base-state potential temperature, Q is geostrophic forcing of frontogenesis

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