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Ian M. Ferguson, John A. Dracup, Philip B. Duffy, Philip Pegion, and Siegfried Schubert

persistence of extreme events such as droughts and heat waves ( Hong and Kalnay 2000 ; Schubert et al. 2004a ; Fischer et al. 2007 ; Pegion and Kumar 2008 ). Despite numerous studies on the relative contributions of ocean–atmosphere forcing and land–atmosphere feedbacks to the duration and magnitude of individual drought events, the influence of ocean–atmosphere forcing on the long-term stochastic characteristics of precipitation anomalies and drought—as opposed to individual drought events—has not

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Ulrike Romatschke and Robert A. Houze Jr.

cooling over the continent. The spreading over the ocean at night could also be a gravity wave response to the daytime heating over the high coastal terrain ( Mapes et al. 2003 ), but the amplitude of the daytime peak in medium system occurrence is so slight that this possibility seems unlikely. Large systems in the BOB region have a strong diurnal cycle ( Figs. 13e and 16 ). A clear minimum of occurrence of large systems occurs over BOB during the evening and the maximum is reached midday. A

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Courtenay Strong and Jessica Liptak

in the context of large-scale standing-wave teleconnections typically resolved via empirical orthogonal function (EOF) analysis (e.g., Small et al. 2010 ). The positive phase of the Pacific–North American pattern (PNA) depicts a wave train consisting of an anomalously strong Aleutian low, positive height anomalies over the western United States, and negative height anomalies over the southeastern United States ( Wallace and Gutzler 1981 ). Rodionov (1994) found that composites of 700-hPa

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Nicholas Siler, Gerard Roe, and Dale Durran

both T and R . Atmospheric circulation patterns associated with T and R How does the large-scale atmospheric circulation contribute to fluctuations in T and R ? We first present covariance maps of the DJF 500-hPa height anomalies with the time series of T and R ( Figs. 2a,b ). For reference, we also include a map of the mean DJF 500-hPa heights between 1982 and 2010 ( Fig. 2c ), which shows a stationary wave pattern characterized by low-pressure troughs in the storm track regions of the

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Sergey Y. Matrosov

1. Introduction For a number of years, the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL), in collaboration with other laboratories and agencies, has been conducting Hydrometeorological Test Bed (HMT) studies in California and the Pacific Northwest. These studies include detailed observations of precipitating systems, which move from the Pacific Ocean inland and impact the West Coast of the United States. The observations are conducted using a

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David Small, Shafiqul Islam, and Mathew Barlow

indicates a tendency for wet conditions in the central United States to occur during dry periods along the Gulf of Alaska and eastern Canada. The spatial pattern of the leading mode of fall precipitation variability in North America is tripolar, with the precipitation anomalies in the central United States having a sign opposite those along the eastern and western coasts of Canada. The correlation between PC1 and the 300-hPa streamfunction indicates the presence of a wave pattern that appears to

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Roni Avissar and David Werth

also indicate that the basin deforestation has no detectable, significant impact on the global hydroclimate. However, it is well known that El Niño has a major impact on the hydroclimate of many regions very far away from the eastern Pacific Ocean (e.g., Shabbar et al. 1997 ). With a relatively warm ocean surface, atmospheric moisture and instability above it are relatively high, providing appropriate conditions for the enhancement of thunderstorm activity. Thunderstorms are the conduit to

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Bradford S. Barrett, Dominique Bastine Krieger, and Caroline P. Barlow

, the heaviest precipitation region was collocated here in time and space. We believe that these surface data complete the conceptual model, providing additional evidence of forcing for precipitation in central Chile. Our model, therefore, is as follows: a midlevel wave and associated surface low and cold front progress eastward toward central Chile, bringing a region of light–moderate precipitation over the open ocean. As this weather system approaches the coast, about 24 h before onset of

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Michael L. Kaplan, Ramesh K. Vellore, Phillip J. Marzette, and John M. Lewis

sequence of 4–5 cyclone-scale waves crossed the entire Pacific Ocean basin (cf. Kaplan et al. 2009 , their Figs. 5 and 6). The trough and ridge patterns of each wave took approximately 4–5 days to cross the Pacific Ocean. The heaviest precipitation occurred when the final trough became embedded in the exit region of a zonal polar jet streak that spanned most of the Pacific Ocean basin. As the exit region of this polar jet approached the Pacific coast, plumes of midlevel moisture, generated by

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Barbara Turato, Oreste Reale, and Franco Siccardi

. The Piedmont 2000 event In this work the flood that occurred over Piedmont between 13 and 16 October 2000 is investigated. Between the end of September and the first 10 days of November 2000, the northern Atlantic Ocean was characterized by a sequence of deep and rapidly moving cyclones affecting the northwestern European coasts. Several flash floods and major rainfall events occurred over many European and Mediterranean regions (i.e., 11 October, southeastern England; 13–16 October, northwestern

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