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Anthony G. Barnston and Robert E. Livezey

temporal correlations ina meteorological parameter between one given geographical location and all others in the domain. Thisexercise is repeated using every possible point as thebase point. The locations producing the highest amplitude, best defined versions of uniquely configuredcorrelation fields (called teleconnection patterns) areaccepted as the "centers of action" of the low frequencyvariability. A teleconnection pattern typically includestwo to four main centers of action (including that ofthe

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Zhaoxia Zeng, Sandra E. Yuter, Robert A. Houze Jr., and David E. Kingsmill

cloud water is available at lower concentrations in the weakly buoyant to negatively buoyant environment. The formation of hail represents an extreme of accretion and hence convective microphysical growth. The hail embryo can be either graupel or frozen drops and some storms exhibit both types ( Browning et al. 1976 ). The relative dominance of each apparently depends on storm intensity and geographic location. Hail embryos of graupel dominate in high plains storms ( Dye et al. 1974 ), while frozen

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Ngar-Cheung Lau and Mary Jo Nath

the WTP in certain geographical regions suggests that the zonally asymmetric nature of the background circulation is an important consideration in understanding this phenomenon. In particular, the behavior of the WTP could be strongly influenced by the configuration of the stationary wave field and the location of the jet streams, and by the occurrence of eddy–mean flow interactions in specific regions. Recently, the barotropic vorticity equation has been used by Anderson (1991) , Branstator and

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K. I. Hodges

tessellating the sphere has been considered for various spherical problems, such as finite elements ( Baumgardner and Frederickson 1985 ; Stuhne and Peltier 1996 ), global geographical information systems (GIS; Fekete 1990 ), astronomical information systems ( Fekete et al. 2003 ; Tegmark 1996 ), and spherical wavelets ( Schröder and Sweldens 1995 ). The organization of the spherical triangles into a tree structure linking different levels of the decomposition forms a hierarchical spatial data structure

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Christopher A. Davis and Lance F. Bosart

assimilation as the simulation progressed. The track of the simulated storm appears to agree less well with observations early in the development. Part of this error is due to the fact that the low-level cyclonic circulation was broad and weak. Bosart and Bartlo (1991) show a well-defined low center at 0000 UTC 8 September, but given the distribution of observations and the elongated nature of the pressure trough, there is some uncertainty as to the location and intensity of the incipient cyclone. More

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Craig S. Schwartz, John S. Kain, Steven J. Weiss, Ming Xue, David R. Bright, Fanyou Kong, Kevin W. Thomas, Jason J. Levit, and Michael C. Coniglio

1. Introduction Convection-allowing numerical weather prediction (NWP) efforts in the United States began in the early to mid-1990s, when experimental model predictions with horizontal grid spacing as fine as 3 km were initialized with real data ( Droegemeier et al. 1996a , b ; Xue et al. 1996a , b ). Although these forecasts focused on relatively small geographic domains and limited time scales, they demonstrated the potential value of convection-allowing model forecasts for the short

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John M. Wallace and David S. Gutzler

/ororographic forcing (Hoskins and Karoly, 1981).The observed patterns are characterized by anequivalent barotropic vertical structure. Their horizontal structure at mid-tropospheric levels tends tobe wavelike with multiple centers of action, whereasthe corresponding patterns of the earth's surfacetend to be more localized; in these respectsthe observed patterns also resemble the linear solutions obtained by Hoskins and Karoly. The geographical location of the patterns, depicted in Fig.26, appears to bear some

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Daniel J. Cecil, Edward J. Zipser, and Stephen W. Nesbitt

found at the boundary of the vortex core and the environmental envelope. The Rossby number is of order unity in this location, which places the SBC near the center of weak hurricanes and farther away in strong hurricanes. The SBC has three components, although all three are not always present: the principal band, the connecting band, and the secondary bands. The SBC may coexist with the eyewall or with concentric eyewalls. The categorizations used in this study are motivated by the three distinct

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VINCENT E. JAKL

be noted that by this time the Lake HIGH was merging into the Atlantic HIGH. The inference is optional, ac-cording to the theory one is inclined to favor, as to whether the SW. to NE. drift was incidental to the Atlantic HIGH and the process of its increment by the Lake HIGH, or that the 3W. to NE. drift was an entity,levels and at the surface wou F d depend on other modifyingdated it. on t R e weather map dissipat,ing in its ad-west that have no pronounce : LOW in their front, to beallel to a

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Caren Marzban, Scott Sandgathe, and Hilary Lyons

forecast). Cluster analysis ( Everitt 1980 ) refers to a set of statistical techniques designed to identify structures in data. The generality of the methodology allows for the objects to be not only two-dimensional (as in a gridded field), but also multidimensional entities that include spatial information as well as other dimensions, including the intensity of the field, or the time at which it is recorded. As such, the verification procedure based on cluster analysis has three desirable features: It

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