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Gloria L. Manney and Michaela I. Hegglin

1. Introduction The upper-tropospheric (UT) jet streams are a key component of the atmospheric circulation and are closely linked with weather and climate phenomena such as storm tracks, precipitation, and extreme events ( Koch et al. 2006 ; Harnik et al. 2016 ; Mann et al. 2017 , and references therein). The UT jets and the tropopause are themselves sensitive to climate change and ozone depletion (e.g., Seidel and Randel 2006 ; Lorenz and DeWeaver 2007 ; McLandress et al. 2011 ; WMO 2011

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Natalie P. Thomas, Michael G. Bosilovich, Allison B. Marquardt Collow, Randal D. Koster, Siegfried D. Schubert, Amin Dezfuli, and Sarith P. Mahanama

( Figs. 6b,d ), reduced sensible heating ( Fig. 7d ), increased cloud cover ( Figs. 8b,c ), and increased humidity and TPW ( Figs. 9b,d ). The Great Plains low-level jet (GPLLJ; Bonner 1968 ) is an important player in the summer hydroclimate of the United States, as it transports heat and moisture from the Gulf of Mexico into the central United States. It is characterized by a wind maximum in the lower troposphere and a diurnal cycle with increased strength at nighttime ( Helfand and Schubert 1995

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Mohar Chattopadhyay, Will McCarty, and Isaac Moradi

temperature ( Fig. 2a ) and the zonal mean wind ( Fig. 2b ) for CTL during the focal period from 2 July to 31 December 2002. The low temperature of 200 K over the tropics at 100 hPa indicates the tropical tropopause. The position of the stratopause at 1 hPa is also resolved by CTL in Fig. 2a . The positions of the tropospheric and stratospheric jets are also represented correctly in CTL as seen in Fig. 2b . The differences between CTL and MERRA-2 for the same fields are shown in Fig. 3 during the same

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Lawrence Coy, Paul A. Newman, Steven Pawson, and Leslie R. Lait

idealized model experiments that showed Rossby waves interacting with the edges of the QBO westerly jet but not changing the magnitude of the jet ( O’Sullivan 1997 ). Given the structure of the anomalous QBO evolution observed during 2015/16, the potential of Rossby waves to significantly affect the QBO needs to reexamined. Another possible QBO disruption mechanism would be barotropic instability in the equatorial region. Shuckburgh et al. (2001) showed extensive regions of potential barotropic

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Richard I. Cullather and Sophie M. J. Nowicki

by Moore et al. (2013) . Moore et al. (2013) identified a southerly near-surface plateau jet along the western side of the ice sheet in summer and a distinct, westerly jet over the northeastern GrIS. A regression analysis of 10-m zonal and meridional components to the melt area is performed and is shown in Fig. 9 . The regression patterns indicate the relation of southerly winds over the western two-thirds of the ice sheet to enhanced melt, which is consistent with the advection of

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Allison B. Marquardt Collow, Michael G. Bosilovich, and Randal D. Koster

shown), the strongest winds in the jet stream are located between 40° and 50°N with a general westerly flow. Two days prior to an extreme precipitation event, a stronger meridional component of the 250-hPa winds is seen along the U.S.–Canada border around Montana and the Great Lakes. On the day before the event, these wind anomalies become stronger and develop a cyclonic pattern centered around Minnesota. Wind speed divergence is seen in the Midwest region, with directional divergence to the

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Lawrence Coy, Krzysztof Wargan, Andrea M. Molod, William R. McCarty, and Steven Pawson

singular vector decomposition. These QBO meridional circulation cells resembled the expected pattern of downward equatorial motion associated with westerly shear regions ( Plumb and Bell 1982 ) with the circulation cells extending out to midlatitudes. The cells were found to be slightly weaker in the Southern Hemisphere. Using ERA-40, Pascoe et al. (2005) noted that the QBO winds can sometimes contain three vertical jet regions as the upper winds begin to increase before the lowest jet has vanished

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Rolf H. Reichle, Clara S. Draper, Q. Liu, Manuela Girotto, Sarith P. P. Mahanama, Randal D. Koster, and Gabrielle J. M. De Lannoy

harmonics) from the NASA Jet Propulsion Laboratory for the 13-yr period from 2003 to 2015 ( http://GRACE.jpl.nasa.gov ; Swenson 2012 ). The TWS retrievals are reasonably accurate (~10–30-mm-error standard deviation) but have coarse resolution in time (monthly) and space (~300–400 km at midlatitudes) ( Rowlands et al. 2005 ; Swenson et al. 2006 ). The retrievals, which are based on measurements of Earth’s gravity field, are independent of the reanalysis data and can thus be used to evaluate the

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Young-Kwon Lim, Robin M. Kovach, Steven Pawson, and Guillaume Vernieres

CP), compared to 1982/83 and 1997/98. The branch of sinking motion in the subtropical latitude (20°–25°N) is also quite well organized, stretching from the surface to the tropopause in 2015/16, whereas the EP El Niño of 1997/98 exhibits lower height of sinking motion. Better organized Hadley circulation over the CP in 2015/16 could reflect changes in jet strength and enhancement of the positive phase of the Pacific–North American (PNA) teleconnection ( Jayawardena et al. 2011 ; Li and Wettstein

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Bin Guan, Duane E. Waliser, and F. Martin Ralph

obtained online from http://apps.ecmwf.int/datasets/data/interim-full-daily/ , and MERRA-2 from https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/ . This research was supported by the NASA Energy and Water cycle Study (NEWS) program, the California Department of Water Resources, and the Office of Naval Research. D.E.W.’s contribution to this study was carried out on behalf of the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. REFERENCES American Meteorological

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