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Sören Thomsen
,
Carsten Eden
, and
Lars Czeschel

wavelike disturbances can be seen very quickly with time scales on the order of days and along-stream wavelengths of about 30–40 km. A wave passes a particular point in the LC within about 2 days. The enhanced variance near the 2-day period, which can be found in the spectra, can be associated with these small-scale disturbances. However, a further analysis of the time-evolving flow field reveals that frontogenesis sets in rapidly leading to nonlinear characteristics of the flow. Frontal strain and

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Kaushik Srinivasan
,
Roy Barkan
, and
James C. McWilliams

scales larger than 4 km to those smaller) during the month of January. Echoing the results of Schubert et al. (2020) , we find that the flux is largest at the frontal features that can be identified as regions of strong convergence (− δ ) and buoyancy gradient |∇ b |. Furthermore, while some of the regions of strong forward transfer are clearly at fronts that lie on the edges of large mesoscale anticyclones (leading to the possibility that these are generated through strain-induced frontogenesis

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Francois Lalaurette
,
Claude Fischer
, and
Jean-Pierre Cammas

troposphere. This is shown to be related to asingular property of the 3D flow. Parcels undergoing frontogenesis in the northwesterly upper-air flow areadvected on top of those that were forced at the surface cold front in a southwesterly flow. The occurrence of afeedback process between these upper-air frontogenesis processes and the surface ones is then investigated.Stepwise vertical profiles of horizontal diffusion are used to force local frontolysis. The resulting upper-airfrontolysis, despite its

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Gandikota V. Rao

primary importance in maintaining frontogenesis in the lowest layers.This convergence is chiefly responsible for drawing moist warm air and cold air into closer contact. Thisresulted in a solenoidally direct circulation. 2) The effect of this circulation is to cause frontolysis at higher levels. However, when the release oflatent heat is taken into account frontogenesis may result, depending upon the amount and the distributionof the heat released. 3) Meteorological quantities, such as

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Johannes M. L. Dahl
and
Jannick Fischer

-Jones 2009 ). This disruption of thermal wind balance may be described in terms of the time rate of change of the horizontal (potential) temperature gradient (i.e., vector frontogenesis) following the geostrophic motion ( Hoskins et al. 1978 ). In other words, forcing for QG vertical motion is related to the reconfiguration of isotherms (or isentropes) by the geostrophic wind if diabatic effects are neglected. The Q vector conveniently points in the direction of the lower branch of the resulting

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Callum J. Shakespeare

evolution of these frontal bands are not completely understood (e.g., Houze Jr. and Hobbs 1982 ; Schultz 2005 ). In this article we investigate one potential mechanism for the formation of frontal bands: spontaneous gravity wave generation during frontogenesis and the trapping of these waves in the frontogenetic strain field. In this context, frontogenesis refers to the sharpening of surface gradients by the action of a large-scale confluent flow. A common idealized configuration for the study of

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Ryan M. Holmes
,
Leif N. Thomas
,
LuAnne Thompson
, and
David Darr

typical horizontal scales of 100 m to 10 km ( Thomas et al. 2008 ). Thus, TIVs contain a range of flow features normally associated with midlatitude submesoscale physics, such as strong fronts, vertical velocities, ageostrophic flows, and frontogenesis ( Marchesiello et al. 2011 ; Ubelmann and Fu 2011 ). In particular, they share features in common with submesoscale coherent vortices and intrathermocline eddies (ITEs), that is, lenticular coherent anticyclonic vortices that are found in the

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Roy Barkan
,
Kraig B. Winters
, and
Stefan G. Llewellyn Smith

-amplitude mixed layer eddies that can lead to intense frontogenesis, a precondition for LOB. Nevertheless, it is a balanced instability that does not lead directly to LOB ( Molemaker et al. 2005 ; Thomas et al. 2008 ); that is, additional instability mechanisms, such as the ones described above, must take place for LOB to occur. The indirect pathways to LOB due to MLI and other balanced phenomena are therefore assumed to be accounted for by the instability mechanisms i–iv above. Capet et al. (2008b) have

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Juan A. Crespo
and
Derek J. Posselt

. L. , and S. C. van den Heever , 2014 : The role of latent heating in warm frontogenesis . Quart. J. Roy. Meteor. Soc. , 140 , 139 – 150 , doi: 10.1002/qj.2118 . Joos , H. , and H. Wernli , 2012 : Influence of microphysical processes on the potential vorticity development in a warm conveyor belt: A case-study with the limited-area model COSMO . Quart. J. Roy. Meteor. Soc. , 138 , 407 – 418 , doi: 10.1002/qj.934 . Kawanishi , T. , and Coauthors , 2003 : The Advanced Microwave

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K. J. Wilson
,
S. L. Barrell
, and
R. Del Beato

ofunforecast frontogenesis or frontolysis in the threehours prior to the base 0000 UTC analysis. In preparingthe analyses, the analyst had access to conventionaldata and remote sensing products such as imagery fromthe Japanese geostationary meteorological satellite(GMS; three hourly, high resolution infrared and visibledata) which were used in part to derive geopotentialthicknesses following the technique of Guymer (1978),imagery from the NOAA polar orbiting satellites (APTmedium resolution visible and

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