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Stephen Baxter and Sumant Nigam

America. Better understanding of the development of PNA patterns can have a positive impact on intraseasonal climate prediction where current prediction is relatively weak. Currently, we are afforded reasonable forecast skill out to two weeks or so from traditionally numerical weather prediction. Longer-lead climate forecasts are made possible because of slowly varying boundary conditions (e.g., ENSO). However, the subseasonal time frame that exists between the two (weeks 3–5) remains a difficult

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T. J. Ansell, P. D. Jones, R. J. Allan, D. Lister, D. E. Parker, M. Brunet, A. Moberg, J. Jacobeit, P. Brohan, N. A. Rayner, E. Aguilar, H. Alexandersson, M. Barriendos, T. Brandsma, N. J. Cox, P. M. Della-Marta, A. Drebs, D. Founda, F. Gerstengarbe, K. Hickey, T. Jónsson, J. Luterbacher, Ø. Nordli, H. Oesterle, M. Petrakis, A. Philipp, M. J. Rodwell, O. Saladie, J. Sigro, V. Slonosky, L. Srnec, V. Swail, A. M. García-Suárez, H. Tuomenvirta, X. Wang, H. Wanner, P. Werner, D. Wheeler, and E. Xoplaki

1. Introduction The European Community (EC)-funded European and North Atlantic Daily to Multidecadal Climate Variability Project (EMULATE) began in November 2002. An initial aim of EMULATE was to define characteristic atmospheric circulation patterns over the European and North Atlantic region. Changes in mean amplitudes, variability, persistence, and transition regimes of these dominant patterns over a 154-yr period would then be assessed with both traditional and new statistical techniques

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Jared H. Bowden, Tanya L. Otte, Christopher G. Nolte, and Martin J. Otte

–aerosol–cloud–radiation feedbacks is an area of needed research for climate change ( Kucharski et al. 2010 ). To address that need, the U.S. Environmental Protection Agency (EPA) is developing a capability to downscale global climate modeling results, with particular interest in understanding those feedbacks on the regional scale using the coupled Weather Research and Forecasting (WRF)/Community Multiscale Air Quality (CMAQ) model ( Pleim et al. 2008 ). However, techniques that the EPA has applied for retrospective

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Blanca Ayarzagüena and Encarna Serrano

in the middle-tropospheric circulation in each spring month between years with a very early or very late breakup of the polar vortex. Lastly, section 4 presents the main conclusions. 2. Data and method a. Database The atmospheric data used in this study have been taken from the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40; Uppala et al. 2005 ), with a horizontal resolution of 2.5° latitude by 2.5° longitude covering the Northern Hemisphere for the period of 1958

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Xueke Wu, Xiushu Qie, Tie Yuan, and Jinliang Li

versus from the Arabian Sea for forming intense convective systems (ICSs) over the concave indentation region is still not clear. To better understand the physical processes that determine the occurrence of intense convection along the SHF, this study investigates the meteorological regimes for the onset of intense convection along the SHF using 16 years of TRMM observational data and the NCEP Climate Forecast System (CFS) Reanalysis data. Data and methods are described first, and then the temporal

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Isabel F. Trigo, Trevor D. Davies, and Grant R. Bigg

the Mediterranean area, such as HMSO (1962) , Radinovic (1987) , and Flocas (1988) presented cyclone climatologies based on the analysis of pressure charts while, more recently, Alpert et al. (1990a) introduced objective methods to detect and track Mediterranean cyclones for a 5-yr climatology. The 18-yr European Centre for Medium-Range Weather Forecasts (ECMWF) dataset employed in the present paper allows a different approach, in particular (a) the cyclone detection and tracking schemes

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J. C. Pérez, J. P. Díaz, A. González, J. Expósito, F. Rivera-López, and D. Taima

methods work by mapping one or more large-scale fields from a reanalysis project to the simultaneous records of finescale observations. They are relatively simple to implement and are computationally cheap. However, statistical downscaling is limited by the assumption of stationarity in the empirical relationships, and results for the present climate do not necessarily translate to forecasts of future climate. On the other hand, the dynamical downscaling techniques are an appropriate alternative to

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Mark R. Jury, Beenay Pathack, and Bhawoodien Parker

waves play a secondary role in the SWIO. The Indian Satellite (INSAT) imagery Hovmöller analyses occasionally reveal successive easterly waves in the 10°–18°S band to the east of Madagascar ( Jury et al. 1991 ). However, increases in the frequency of easterly waves in 1976 and 1988 coincide with summers with below normal TC days. NOAA OLR and European Centre for Medium-Range Forecasts (ECMWF) precipitable water anomaly Hovmöller analyses over the SWIO illustrate eastward-moving intraseasonal

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David J. Stensrud, Robert L. Gall, Steven L. Mullen, and Kenneth W. Howard

accountsfor over 40% of the total annual rainfall. Deep convection during the monsoon season produces frequentdamaging surface winds, flash flooding, and hail and is a difficult forecast problem. Past numerical simulationsfrequently have been unable to reproduce the widespread, heavy rains over Mexico and the southwestern UnitedStates associated with the monsoon. The Pennsylvania State University/National Center for Atmospheric Research mesoscale model is used tosimulate 32 successive 24-h periods

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Basivi Radhakrishna, Frédéric Fabry, John J. Braun, and Teresa Van Hove

1. Introduction Dense and frequent sampling of atmospheric water vapor is of great importance in both climatological research and especially in operational forecasting because water vapor fuels storms. Observations of atmospheric water vapor are primarily made through radiosondes and ground- or space-based radiometers. Though radiosondes measure atmospheric water vapor profiles with good accuracy, these measurements are limited in space and time ( Wang et al. 2000 ). Thus, radiosonde

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