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Robert G. Fovell, Yizhe Peggy Bu, Kristen L. Corbosiero, Wen-wen Tung, Yang Cao, Hung-Chi Kuo, Li-huan Hsu, and Hui Su

) demonstrated that storm track and structure are both sensitive to the manner of TC initialization, and Hsu et al. (2013 , hereinafter P6) showed how diabatic heating forced by flow over topography could explain speed variations of typhoons approaching and crossing an island like Taiwan. P4 ’s explanation for outer region convective activity was finally assessed in Bu et al. (2014 , hereinafter P7) and was determined to be insufficient to explain why CRF results in wider tropical cyclones. Their

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Lance F. Bosart and, Alicia C. Wasula, Walter H. Drag, and Keith W. Meier

Abstract

This paper begins with a review of basic surface frontogenesis concepts with an emphasis on fronts located over sloping terrain adjacent to mountain barriers and fronts located in large-scale baroclinic zones close to coastlines. The impact of cold-air damming and differential diabatic heating and cooling on frontogenesis is considered through two detailed case studies of intense surface fronts. The first case, from 17 to 18 April 2002, featured the westward passage of a cold (side-door) front across coastal eastern New England in which 15°–20°C temperature decreases were observed in less than one hour. The second case, from 28 February to 4 March 1972, featured a long-lived front that affected most of the United States from the Rockies to the Atlantic coast and was noteworthy for a 50°C temperature contrast between Kansas and southern Manitoba, Canada.

In the April 2002 case most of New England was initially covered by an unusually warm, dry air mass. Dynamical anticyclogenesis over eastern Canada set the stage for a favorable pressure gradient to allow chilly marine air to approach coastal New England from the east. Diabatic cooling over the chilly (5°–8°C) waters of the Gulf of Maine allowed surface pressures to remain relatively high offshore while diabatic heating over the land (31°–33°C temperatures) enabled surface pressures to fall relative to over the ocean. The resulting higher pressures offshore resulted in an onshore cold push. Frontal intensity was likely enhanced prior to leaf out and grass green-up as virtually all of the available insolation went into sensible heating.

The large-scale environment in the February–March 1972 case favored the accumulation of bitterly cold arctic air in Canada. Frontal formation occurred over northern Montana and North Dakota as the arctic air moved slowly southward in conjunction with surface pressure rises east of the Canadian Rockies. The arctic air accelerated southward subsequent to lee cyclogenesis–induced pressure falls ahead of an upstream trough that crossed the Rockies. The southward acceleration of the arctic air was also facilitated by dynamic anticyclogenesis in southern Canada beneath a poleward jet-entrance region. Frontal intensity varied diurnally in response to differential diabatic heating. Three types of cyclogenesis events were observed over the lifetime of the event: 1) low-amplitude frontal waves with no upper-level support, 2) low-amplitude frontal waves that formed in a jet-entrance region, and 3) cyclones that formed ahead of advancing upper-level troughs. All cyclones were either nondeveloping or weak developments despite extreme baroclinicity, likely the result of large atmospheric static stability in the arctic frontal zone and unfavorable alongfront stretching deformation. Significant frontal–mountain interactions were observed over the Rockies and the Appalachians.

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W.-K. Tao, Y. N. Takayabu, S. Lang, S. Shige, W. Olson, A. Hou, G. Skofronick-Jackson, X. Jiang, C. Zhang, W. Lau, T. Krishnamurti, D. Waliser, M. Grecu, P. E. Ciesielski, R. H. Johnson, R. Houze, R. Kakar, K. Nakamura, S. Braun, S. Hagos, R. Oki, and A. Bhardwaj

for scientific research and applications [see a review by Tao et al. (2006) and the papers published in the Journal of Climate special collection on TRMM diabatic heating]. Such products enable new insights and investigations into the complexities of convective system life cycles, diabatic heating controls and feedbacks related to mesoscale and synoptic-scale circulations and their prediction, the relationship of tropical patterns of LH to the global circulation and climate, and strategies for

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Guoxiong Wu and Yimin Liu

regional as well as global climate. Some of the results are summarized in this study, and can be considered as a complement to the review of Yanai and Wu (2006) . Both the diagnosis and numerical experiments are used to get new insights into our understanding. The remainder of this chapter is organized as follows. In section 2 , there is an analysis of the relative importance of mechanical and thermal forcing induced by large-scale mountains. The diabatic heating characteristics of atmosphere over TP

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Sally A. McFarlane, James H. Mather, and Eli J. Mlawer

were remarkably similar. These studies indicated that if the frequency of different cloud types across a region were known from another source, such as satellite measurements, the cloud and heating rate profiles derived from the ARM data for each cloud type could be applied to estimate the vertical structure of cloud and heating rates over a larger area. Another important question is the relative contribution of radiative heating to the total diabatic heating profile. Jensen and Del Genio (2003

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Eric D. Maloney and Chidong Zhang

of h , respectively. Yanai et al. (1973) and Yanai and Johnson (1993) noted that (4-3) is able to provide profound insight into diabatic heating processes in the tropics, and can be used to check the accuracy of tropospheric budgets given surface flux information. Far-reaching implications of (4-3) for the MJO may not have come until much later, however. Neelin and Held (1987) used (4-3) to develop a model for tropical upper-tropospheric divergence as a proxy for deep convection

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David M. Schultz, Lance F. Bosart, Brian A. Colle, Huw C. Davies, Christopher Dearden, Daniel Keyser, Olivia Martius, Paul J. Roebber, W. James Steenburgh, Hans Volkert, and Andrew C. Winters

Atlantic coastal cyclones. He showed that coastal fronts served as a locus of surface frontogenesis and cyclonic vorticity generation and that northeastward-propagating coastal cyclones tended to track along a preexisting coastal front. Coastal fronts served as boundaries between frozen and unfrozen precipitation with the heaviest precipitation falling along and on the cold side of the boundary. The impact of enhanced diabatic heating due to precipitation along and toward the cold side of coastal

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Robert A. Houze Jr.

atmosphere is in a constant state of adjustment to the potential vorticity (PV) field. When diabatic processes occur, potential vorticity is not conserved, but rather it is affected by spatial gradients of the heating. In particular, the time rate of change of potential vorticity is directly proportional to the vertical gradient of heating. Thus, as can be inferred from Fig. 17-24 , the more top-heavy the MCS heating profile, the stronger the feedback to the large-scale. This feedback is sometimes felt

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Isaac M. Held

ways, encompassing nonlinearity and interactions with transient eddies and diabatic processes. The importance of nonlinearity is illustrated by the problem of the extratropical response to ENSO variability. ENSO modifies the distribution of convective heating in the tropics, generating external Rossby waves that propagate into midlatitudes. After the initial linear studies with zonally symmetric background states, it became clear from linear studies with asymmetric backgrounds and from GCMs

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Yukari N. Takayabu, George N. Kiladis, and Victor Magaña

implications for the role of convection: “It is very interesting that the two diagrams are nearly identical, that is, at all frequency ranges the EAPE is generated by diabatic heating and is immediately converted into the EKE [eddy kinetic energy]” ( Yanai 1971a , p. 10). In another prescient statement, Yanai and Murakami (1970a) saw the need for more detailed space–time spectral analysis techniques, which were then in fact being developed by Michio’s student Yoshikazu Hayashi ( Hayashi 1971 ). They

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