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Marie-Dominique Leroux, Matthieu Plu, and Frank Roux

their Fig. 9). Because it affects multiple environmental parameters, upper-level trough forcing, in particular, remains one of the strongest challenges of operational forecasting, as already recognized by the IWTC-6 ( WMO 2007 ). Upper-level troughs or cutoff lows that interact with tropical cyclones usually result from the breaking of a planetary Rossby wave train originating from the midlatitudes that propagates equatorward into the subtropical latitudes. Such events are associated with an Ertel

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Daniel Keyser, Michael J. Reeder, and Richard J. Reed

?62 MONTHLY WEATHER REVIEW VOLt,roll6A Generalization of Petterssen's Frontogenesis Function and Its Relation to the Forcing of Vertical Motion DANIEL KEYSER*Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, Maryland MICHAEL J. REEDERGeneral Sciences Corporation, Laurel, Maryland and Laboratory for Atmospheres, NA

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Philippe Lucas-Picher, Daniel Caya, Sébastien Biner, and René Laprise

predictability period in a GCM simulation is limited to about two weeks. This means that two GCM simulations started with small differences in their initial condition will become totally uncorrelated after about two weeks. In an RCM, two simulations started with different initial conditions will also diverge with time and evolve differently from one another. However, these simulations will keep a certain level of correlation throughout the simulation because they share the lateral boundary forcing. For this

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Angeline G. Pendergrass and Hugh E. Willoughby

rising motion through the locus of the heat source, but also the flow updraft that maintains mass continuity around the heat source. Similarly, cyclonic torques force both radial outflow through the locus of forcing and surrounding, mass-conserving return flow. Although the SEQ is a diagnostic equation, it is not steady state. Substitution of the velocity components deduced from ψ into the thermodynamic and tangential momentum equations allows calculation of the gradual vortex evolution. In

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Joseph A. Grim, Robert M. Rauber, Greg M. McFarquhar, Brian F. Jewett, and David P. Jorgensen

; Weisman 1992 , 1993 ), and the dynamic irrotational pressure gradient [what Weisman (1993) refers to as fluid extension and shear]. The RIJ in turn supplies cool, dry midlevel air to aid in the production of the convective- and system-scale downdrafts (e.g., Smull and Houze 1987a ). This study examines the structure, evolution, and horizontal forcing of the RIJ during the formation, development, and decay of a small, short-lived (2 h) bow-shaped squall line over north-central Kansas on 29 June

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-statemodel in which the zonal current is perturbed by the lower boundary topography and by a distribution of heat sourcesand sinks. All the perturbations are assumed to have a single meridional wavelength and the dissipation is consideredto take place in the surface boundary layer using, as a first approach, a horizontally uniform drag coefficient. After investigating some basic properties of the model atmosphere, some computations are made to determineits response to t,he combined forcing by topography

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Chih-hua Tsou, Phillip J. Smith, and Patricia M. Pauley

APRIL 1987 TSOU, SMITH AND PAULEY 763A Comparison of Adiabatic and Diabatic Forcing in an Intense Extratropical Cyclone SystemCHIH-HUA TSOU, PHILLIP J. SMITH AND PATRICIA M. PAULEY*Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907(Manuscript received 13 February 1986, in final form 2 October 1986) ABSTRACT The primary

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Raul A. Valenzuela and David E. Kingsmill

-to-southeast orientation. Such a topographic characteristic allows the typical AR to impact the mountains with a near-perpendicular orientation, favoring the cross-barrier ascent of moist, statically neutral air ( Neiman et al. 2002 ; Ralph et al. 2005 ). However, this relatively simple orographic precipitation forcing can become more complicated when a low-level terrain-trapped airflow exists. A terrain-trapped airflow (TTA) is defined as a relatively narrow air mass consistently flowing in close proximity and

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James T. Moore and Pamela D. Blakley

NOVEMBER 1988 JAMES T. MOORE AND PAMELA D. BLAKLEY 2155The Role of Frontogenetical Forcing and Conditional Symmetric Instability in the Midwest Snowstorm of 30-31 January 1982 JAMES T. MOORE AND PAMELA D. BLAKLEYDepartment of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, Missouri(Manuscript received 21 December 1987, in final form 18 March 1988)ABSTRACT On 30

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Melanie R. Fewings

initiated by the synoptic-scale forcing ( Mass and Bond 1996 ). Together, the composite averages of HEOF 1 over the wind relaxations identified in Melton et al. (2009) ( Figs. 12a,d ) indicate that positive fluctuations in the poleward and equatorward ends of the wind quasi dipole (HEOF 1) can be interpreted as stage 1, the wind relaxation/reversal off Oregon, and stage 3, the wind relaxation off central California that follows. The stage 3 wind anomalies are known to propagate poleward over the south

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