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Andrea Schneidereit
,
Silke Schubert
,
Pavel Vargin
,
Frank Lunkeit
,
Xiuhua Zhu
,
Dieter H. W. Peters
, and
Klaus Fraedrich

) pattern appears with a negative anomaly over the Rocky Mountains and positive anomalies south of the Aleutians representing a weaker North American high/Aleutian low, related with a positive temperature anomaly across the eastern United States. Although the PNA is a mode of natural variability, its phase is argued to be influenced by ENSO forcing a quasi-stationary Rossby wave train emanating from the subtropics (near the Niño-3.4 region), which forms one part of the PNA dipole ( Horel and Wallace

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Yannick Barton
,
Paraskevi Giannakaki
,
Harald von Waldow
,
Clément Chevalier
,
Stephan Pfahl
, and
Olivia Martius

extreme precipitation events (i.e., which factors led to the repeated occurrence of extreme precipitation on time periods of 10–20 days). To this end, we focus on processes with time scales comparable to the length of a clustering period. Here, blocking, tropical forcing, and oceanic forcing are discussed. 1) Role of SST anomalies First, the oceanic surface conditions are discussed. The occurrence of subseasonal clustering of extreme precipitation events in southern Switzerland requires sufficient

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Martin Weissmann
,
Florian Harnisch
,
Chun-Chieh Wu
,
Po-Hsiung Lin
,
Yoichiro Ohta
,
Koji Yamashita
,
Yeon-Hee Kim
,
Eun-Hee Jeon
,
Tetsuo Nakazawa
, and
Sim Aberson

connected to two other projects that coordinated their observations: the operational DOTSTAR program enhanced its flight activity and the U.S. Navy conducted the Tropical Cyclone Structure Experiment (TCS-08). Altogether, up to four aircraft were simultaneously available in a two month period: One U.S. Air Force WC-130 aircraft, which could penetrate into the eye of TCs; one U.S. Navy P-3 aircraft, which focused on rainbands and the structure of convection; the Falcon 20 aircraft of the Deutsches

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Florian Harnisch
and
Martin Weissmann

research aircraft [e.g., the U.S. Air Force WC-130, the Naval Research Laboratory (NRL) P-3, and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Falcon 20] in combination with driftsonde gondolas, research vessels, and extra satellite observations was operated. Systematic observations targeted around tropical cyclones during the full life cycle of a storm from the genesis in tropical waters throughout the northwestward movement, recurvature, and extratropical transition were conducted. In

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Paraskevi Giannakaki
and
Olivia Martius

(1 Jan–31 Dec 2008) for the verification domain over the Northern Hemisphere. The year 2008 is chosen because it is included in the Year of Tropical Convection (YOTC) period. YOTC data explicitly contain diabatic forcing terms ( Waliser and Moncrieff 2008 ), and follow-up studies that focus in more detail on the physical processes responsible for the forecast errors are possible. A 1-yr forecast error climatology was produced by comparing output from the IFS model at five different forecast lead

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The Key Role of Diabatic Outflow in Amplifying the Midlatitude Flow: A Representative Case Study of Weather Systems Surrounding Western North Pacific Extratropical Transition

Christian M. Grams
and
Heather M. Archambault

enhanced poleward moisture transport that occurs often on the eastern side of a transitioning TC. When this moisture impinges on a midlatitude baroclinic zone in a region of upper-level forcing for ascent [e.g., near the equatorward entrance region of an upper-level jet streak; Uccellini and Johnson (1979) ] several days prior to ET, heavy precipitation and flooding may occur as a result of quasi-stationary convection in that region (e.g., Wang et al. 2009 ; Galarneau et al. 2010 ; Byun and Lee

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Jana Čampa
and
Heini Wernli

these cyclones. However, these explosive cyclones reach their maximum intensity earlier at the surface than at 500 hPa, which highlights the importance of surface fluxes, diabatically produced positive PV anomalies, and reduced static stability for the rapid development. Deveson et al. (2002) classified 16 cyclones from the Fronts and Atlantic Storm Track Experiment (FASTEX) according to the contributions of the forcing from upper and lower levels to the vertical motion ( U / L ratio) and their

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Andreas Schäfler
,
Andreas Dörnbrack
,
Christoph Kiemle
,
Stephan Rahm
, and
Martin Wirth

improvements in NWP, the quantitative precipitation forecast (QPF) skill has not changed significantly in recent years. Thus, improving the QPF is one of the main research interests in numerical weather prediction ( Fritsch and Carbone 2004 ; Rotunno and Houze 2007 ; Richard et al. 2007 ; Wulfmeyer et al. 2008 ). The interaction between various synoptic-scale and mesoscale processes, such as large-scale forcing ( Massacand et al. 2001 ; Hoinka and Davies 2007 ), orographic lifting ( Reeves and Rotunno

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Hilke S. Lentink
,
Christian M. Grams
,
Michael Riemer
, and
Sarah C. Jones

Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC). Measurements from three aircrafts provide a unique dataset for detailed analysis of structural development during ET. Between 0100 and 0600 UTC 19 September and between 0500 and 0900 UTC 20 September, the research aircrafts Naval Research Laboratory P-3 and the U.S. Air Force WC-130 flew through the central region to obtain measurements of the eyewall. The DLR-Falcon was operating in the environment northeast of

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Volkmar Wirth
,
Michael Riemer
,
Edmund K. M. Chang
, and
Olivia Martius

and E have been created during that time. c. Different types of RWPs and their propagation There are different types of RWPs associated with different temporal and spatial scales, different types of forcing, and specific properties of the background flow. Sometimes an RWP is little more than an individual trough or ridge ( Sanders 1988 ); sometimes an RWP may span a substantial part of the globe ( Branstator 2002 ). Some RWPs propagate along great circles, while others are ducted in the zonal

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