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Delphine Hypolite
,
Leonel Romero
,
James C. McWilliams
, and
Daniel P. Dauhajre

from solutions with and without WEC. In section 4 we give a dynamical interpretation of WEC statistical properties by investigating the dynamical balances for vertical and horizontal enstrophy, squared horizontal buoyancy gradient, and horizontal divergence, including WEC for the first time. This analysis allows the identification of the mechanism by which waves, when big enough, reinforce submesoscale activity (frontogenesis) near the surface. Similarly, we show how wind-forced waves can produce

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David R. Novak
,
Brian A. Colle
, and
Anantha R. Aiyyer

1. Introduction Intense precipitation bands are frequently observed in the comma head of extratropical cyclones over the northeast United States ( Novak et al. 2004 , hereafter N04 ). Theoretical work by Emanuel (1985) , Thorpe and Emanuel (1985) , Xu (1989a , b) , and Xu (1992) has shown that intense single cores of ascent can form through a coupled relationship between frontogenesis and moist symmetric stability, whereby the ascending branch of a frontal circulation is

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David E. Kofron
,
Elizabeth A. Ritchie
, and
J. Scott Tyo

end of transformation stage as determined by Klein et al. (2000) using satellite imagery. In addition, the open-wave time provides an objective way to define ET time that can be viewed using gridded datasets by nonexperts. Harr and Elsberry (2000) use the 3D frontogenesis calculated by Schultz and Doswell (1999) , which was an extension of the Keyser et al. (1988) study for the 2D vector frontogenesis, to explain some of the dynamic processes associated with transitioning TCs. Their case

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Peng Wang
,
James C. McWilliams
, and
Yusuke Uchiyama

shelf break, cold fresh shelf water is separated from warm salty slope water by a shelf-break front ( Houghton et al. 1988 ; Chapman and Lentz 1994 ; Gawarkiewicz et al. 2004 ). Internal waves can create fronts parallel to wave crests, and such fronts usually move with the waves ( Shanks 1983 ; Pineda 1994 ). Surface gravity waves affect oceanic frontogenesis ( Suzuki et al. 2016 ; McWilliams 2018 ). Surface waves may sharpen or widen a front depending on the alignment between the front and

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Brian A. Colle
,
Aaron R. Naeger
, and
Andrew Molthan

within a region of midlevel frontogenesis and weak moist symmetric stability ( Emanuel 1985 ; Thorpe and Emanuel 1985 ; Xu 1989 ; Banacos 2003 ; Moore et al. 2005 ; Nicosia and Grumm 1999 ; Novak et al. 2009 ; Novak et al. 2010 ). The vertical motion and narrowing of the region of ascent with fronts has been attributed to latent heating through cloud condensation and other microphysical processes ( Thorpe and Emanuel 1985 ; Chan and Cho 1991 ; Han et al. 2007 ). In addition, the ageostrophic

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Ryusuke Masunaga
,
Hisashi Nakamura
,
Bunmei Taguchi
, and
Takafumi Miyasaka

. 10.1017/S1350482798000553 Hoskins , B. J. , 1982 : The mathematical theory of frontogenesis . Annu. Rev. Fluid Mech. , 14 , 131 – 151 , https://doi.org/10.1146/annurev.fl.14.010182.001023 . 10.1146/annurev.fl.14.010182.001023 Hotta , D. , and H. Nakamura , 2011 : On the significance of the sensible heat supply from the ocean in the maintenance of the mean baroclinicity along storm tracks . J. Climate , 24 , 3377 – 3401 , https://doi.org/10.1175/2010JCLI3910.1 . 10.1175/2010JCLI

Open access
Shawn M. Milrad
,
Eyad H. Atallah
, and
John R. Gyakum

, the orography of the SLRV contributed substantially to higher amounts of precipitation (hereafter enhanced precipitation) within the SLRV through ageostrophic frontogenesis. The SLRV is oriented southwest to northeast, from the eastern end of Lake Ontario to the Gulf of St. Lawrence ( Fig. 1a ; Google Maps 2011 ). Two major Canadian cities (Montreal and Quebec City) are located within the SLRV, which is home to the majority of the population in the province of Quebec. Several mountain chains

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David M. Schultz
and
W. James Steenburgh

southwesterlies in western and northwestern Nevada met with southerlies in southern and eastern Nevada ( Fig. 4c ) tightened the gradient of isotherms ahead of its prior location, as evidenced by calculations of lower-tropospheric Petterssen (1936) frontogenesis from the Rapid Update Cycle 2 (RUC2; not shown). At this time, the precipitation band, as inferred from radar reflectivity, was strongest from approximately Reno to Winnemucca, Nevada (WMC), but weakened farther north, and the strongest wind gusts

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Yi-Hsuan Lin
and
Chun-Chieh Wu

advected northward by TC circulation would converge with dry and cold monsoonal northeasterlies. The confluence of two air masses of different characteristics is associated with frontogenesis, resulting in lifting and thus triggering heavy rainfall in the vicinity of northeastern Taiwan ( Wu et al. 2009 ; Chen et al. 2013 ; Chen and Wu 2016 ). Based on the different controlling factors, Wu et al. (2009) categorized the remote rainfall events in Taiwan during the late TC season (e.g., October and

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Loren D. White

(hPa)] at (a) 0000 UTC 11 Jan, (b) 1200 UTC 11 Jan, (c) 1800 UTC 11 Jan, and (d) 0000 UTC 12 Jan 2013. In summary, the upper-level baroclinic Rossby wave forcing quickly exits the south-central states during this 2-day period, leaving behind a lower-tropospheric thermal contrast that experiences almost complete frontolysis. However, the lower-tropospheric dewpoint gradient in the lower Mississippi River valley intensifies in the southerly flow. This intensification is greater than would be expected

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