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Stephanie Leroux and Nicholas M. J. Hall

African easterly jet (AEJ). Many studies have focused on these African synoptic-scale perturbations since the 1970s and the Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) campaign (e.g., Burpee 1972 ; Reed et al. 1969). Motivations for a better understanding of easterly waves are strong because these waves are associated with modulation of convection and rainfall over West Africa (e.g., Duvel 1990 ; Fink and Reiner 2003 ; Kiladis et al. 2006 ) and with the genesis

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Rei Chemke and Yohai Kaspi

1. Introduction One of the most robust phenomena in geophysical fluid dynamics is the emergence of jets. These jets have a large impact on the dynamics of the atmosphere and ocean mostly through eddy–mean flow interactions and appear in both terrestrial and gas planets (e.g., Williams 1978 ; Panetta 1993 ; Schneider 2006 ). Because of their strong dependence on temperature gradients and heat fluxes in the atmosphere, these jets shape and feed off the zonal climatic bands on Earth

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Robert M. Banta, Larry Mahrt, Dean Vickers, Jielun Sun, Ben B. Balsley, Yelena L. Pichugina, and Eric J. Williams

not been described in previous SBL studies. Above these two layers turbulence may still be active at higher levels, sometimes associated with low-level jets (LLJs) when present. Existing analyses of the CASES-99 dataset have emphasized the importance of shear-generated turbulence near the LLJ and coupling with the ground surface (e.g., Blumen et al. 2001 ; Poulos et al. 2002 ; Mahrt and Vickers 2002 ; Banta et al. 2002 , 2003 , 2006 ; Newsom and Banta 2003 ; Sun et al. 2002 , 2004

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Jean-Baptiste Gilet, Matthieu Plu, and Gwendal Rivière

1. Introduction Intense storms in the northeastern Atlantic Basin evolve following a variety of complex life cycles. An often observed cycle consists of an appearance in the southern part of an upper-level large-scale jet, eastward translation without significant amplification on this anticyclonic side, and then sudden and intense growth while the depression crosses the jet axis. The Christmas 1999 Lothar storm over Europe is one example ( Rivière and Joly 2006b ). Similar but less spectacular

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Kunio M. Sayanagi, Adam P. Showman, and Timothy E. Dowling

1. Introduction Spacecraft observations of Jupiter reveal ∼30 zonal jets at the cloud level. In the equatorial region, a fast, broad, eastward jet dominates the flow flanked by westward jets to the north and south. Vortices are absent in the equatorial region roughly between ±20° latitudes. Outside of the equatorial region, numerous zonal jets exist up to ±60° latitudes. Many of the jets contain stable vortices that drift in the east–west direction at speeds slightly different from the

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Loïc Robert, Gwendal Rivière, and Francis Codron

1. Introduction Eddy-driven jets and storm tracks have a key role in midlatitude surface weather, and it is important to understand how they might respond to climate change. Results from the Coupled Model Intercomparison Project (CMIP) experiments show a robust poleward shift of the jet in the Southern Hemisphere ( Kidston and Gerber 2010 ), but the picture is more complicated in the Northern Hemisphere ocean basins ( Barnes and Polvani 2013 ; Simpson et al. 2014 ; Vallis et al. 2015 ). In

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Jen-Shan Hsieh and Kerry H. Cook

investigations associate the 3–5-day waves with hydrodynamic instability of the African easterly jet, which forms near 600–700 hPa in the same region and at the same time of year as the waves ( Burpee 1972 ; Rennick 1976 ; Simmons 1977 ; Kwon 1989 ; Thorncroft and Hoskins 1994a , b ). These studies find that the Charney–Stern necessary condition for instability, that is, a reversed meridional gradient of potential vorticity (PV), is met in the vicinity of the jet’s strong wind shears, suggesting that

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Yohai Kaspi and Glenn R. Flierl

1. Introduction Strong zonal winds dominate the atmospheres of the four big outer planets of the solar system. All four planets exhibit latitudinal banding and strong jet streams, where the wind velocities on Saturn are the strongest reaching more than 400 m s −1 near the equator, and Jupiter has the most structure with at least six alternating bands of east–west winds in each hemisphere ( Ingersoll 1990 ; Porco et al. 2003 ). Unlike Earth, the solid centers are small fractions of the giant

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J. Cuxart and M. A. Jiménez

1. Introduction Although the wind near the surface is frequently light or calm at night under clear sky and weak synoptic winds, some tens of meters above the ground level (AGL) the wind speed may have supergeostrophic values. This is a phenomenon called low-level jet (LLJ) or nocturnal jet since, in many cases, it forms during the night and reaches its peak during the predawn hours. As Stull (1988) summarizes (and references therein), there are several conditions that favor the formation of

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Robert M. Banta, Yelena L. Pichugina, and W. Alan Brewer

1. Introduction The nocturnal low-level jet (LLJ) has an important role in the generation of shear in the layer between the jet maximum or “nose” and the earth’s surface. This shear is often an important source of turbulence and turbulent fluxes in the nighttime boundary layer ( Mahrt et al. 1979 ; Lenschow et al. 1988 ; Smedman et al. 1993 , 1995 , 1997 ; Tjernström and Smedman 1993 ; Mahrt 1999 ; Mahrt and Vickers 2002 ; Banta et al. 2002 , 2003 ). Accurate determination of turbulent

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