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David M. Schultz
and
Joseph M. Sienkiewicz

divergence: where E is the resultant deformation and β is the local angle between an isentrope and the axis of dilatation. Positive regions of frontogenesis indicate where isentropes are instantaneously being brought together by the horizontal flow, thereby increasing the horizontal potential temperature gradient. Negative regions of frontogenesis (or frontolysis) indicate where isentropes are instantaneously being spread apart by the horizontal flow, thereby weakening the horizontal potential

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Shawn M. Milrad
,
John R. Gyakum
,
Kelly Lombardo
, and
Eyad H. Atallah

back to the Q vector and thus QG vertical motion using where Q is the Q vector, p is the pressure, p o is some reference pressure, R is the gas constant for dry air, and κ is R divided by c p , the specific heat at constant pressure. Frontogenesis and frontolysis are indicated when Q points to warmer and colder air, respectively (e.g., Sanders and Hoskins 1990 ). Figure 4 shows that CSB1 occurs in the left-exit region of a straight northwest–southeast-upper-tropospheric jet

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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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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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B. N. Hanstrum
,
K. J. Wilson
, and
S. L. Barrell

frontogenesis within a surface prefrontal trough over southern Australia is presented. Thetrough developed ahead of a surface cold front and, over a period of approximately 24 h, intensified into amature summertime frontal system while the original front underwent total frontolysis. Two-hourly rawinsondeascents at three locations were used to examine the structure of the trough both before and after frontogenesis.Diagnosis of the frontogenetic tendencies showed that horizontal deformation of the potential

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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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David J. Nicosia
and
Richard H. Grumm

function from Petterssen (1956) . This frontogenetic function is defined as the Lagrangian rate change of the magnitude of the horizontal potential temperature gradient due to the horizontal wind. When the potential temperature gradient increases, frontogenesis is implied; when the gradient decreases, frontolysis is implied. The frontogenetic function defined in (1) is based on shearing and stretching deformation of the horizontal wind field and its action on the horizontal potential

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Qian Wang
,
Qingqing Li
, and
Gang Fu

. The low-resolution data (i.e., JRA-25 and FNL) show similar patterns; however, the frontolysis in the northwestern quadrant and frontogenesis in the northeastern quadrant from FNL are both more striking than those from JRA-25 ( Figs. 5a, 5b, 5e, and 5f ). RSM-20km also suggests the presence of significant frontogenesis in the mid- and upper layers in its northeastern quadrant ( Fig. 5j ), but the frontogenesis features in other quadrants are different from those found with the JRA-25 and FNL data

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Paul J. Roebber
,
John R. Gyakum
, and
Diep N. Trat

frontolysis reMARCH 1994 ROEBBER ET AL. 435-1--15, 0 5 10 15 20 25 30 35 40 Hours FIG. 24. As in Fig. 16 but for RFE model frontogenesis at a grid point withinthe coastal front (40.9-N, 71.6-W). The data are from the model run initializedat 0000 UTC 13 December.suits from strong north-northwest ageostrophic windsin the

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