Search Results

You are looking at 11 - 20 of 19,553 items for :

  • All content x
Clear All
Lindsey N. Williams, Sukyoung Lee, and Seok-Woo Son

1. Introduction One peculiar feature in the atmosphere, which does not seem to have received much attention, is the fact that large-scale westerly jets, at times, take on a spiral form. An example of the spiral jet structure is shown in Fig. 1 , which displays the 275-hPa Southern Hemisphere (SH) zonal wind field, corresponding approximately to a 40-yr calendar mean of 27 April. A more precise description of the data and averaging procedure will be given in section 2 . Starting from the

Full access
P. Berloff, I. Kamenkovich, and J. Pedlosky

1. Introduction The principal phenomenon studied in this paper is the existence of multiple, alternating zonal jets in the oceans. The observational evidence of these jets emerged mostly over the last few years, and their theoretical understanding is incomplete. In this introduction we pose the problem, discuss the background, and describe the ocean model. The phenomenology of the modeled jets is described in section 2 . Section 3 focuses on the kinematical analysis, section 4 on the

Full access
Tim Woollings, Elizabeth Barnes, Brian Hoskins, Young-Oh Kwon, Robert W. Lee, Camille Li, Erica Madonna, Marie McGraw, Tess Parker, Regina Rodrigues, Clemens Spensberger, and Keith Williams

1. Introduction Shifts of the jet streams are the dominant source of variability in weather patterns across much of the midlatitudes (e.g., Hurrell and Deser 2009 ). Jet shifts are associated with altered storm-track paths and with changes in the regions that experience a mild oceanic influence. Several recent seasons of extreme weather were driven by jet shifts as a proximate cause. In the 2009/10 winter, for example, severe cold over both North America and Eurasia was caused by an extreme

Full access
Tapio Schneider and Junjun Liu

1. Introduction The zonal flow in Jupiter’s upper troposphere has been inferred by tracking cloud features, which move with the horizontal flow in the layer between about 0.5 and 1 bar atmospheric pressure ( Ingersoll et al. 2004 ; West et al. 2004 ; Vasavada and Showman 2005 ). In this layer, the zonal flow is organized into a strong prograde (superrotating) equatorial jet and an alternating sequence of retrograde and prograde off-equatorial jets ( Fig. 1a ). This flow pattern has been

Full access
Anandakumar Karipot, Monique Y. Leclerc, and Gengsheng Zhang

1. Introduction Low-level jets are important atmospheric processes frequently observed in the earth’s planetary boundary layer. A low-level jet (LLJ) generally forms during the evening, strengthens during the course of the night, and dissipates shortly after sunrise because of enhanced vertical mixing generated by the warming of the surface. One of the pioneering theories on the LLJ formation is Blackadar’s (1957) inertial oscillation mechanism associated with frictional decoupling during

Full access
Isabella Bordi, Klaus Fraedrich, Frank Lunkeit, and Alfonso Sutera

1. Introduction The most prominent feature of the general circulation is the presence of a mean westerly jet at the tropopause level in the Tropics. Moreover, when we consider, for example, the observed Northern Hemisphere zonally averaged zonal wind standard deviation, we find two relative maxima located in the subtropics and midlatitudes. Thus, a central problem is the finding of the physical mechanisms that originate and maintain these observed features. Since the works of Rossby and Starr

Full access
Antoine Venaille and Freddy Bouchet

, existing theories give no clear explanation of the existence of strong and robust eastward jets in the inertial part of these currents. The classical wind-driven ocean theory and the inertial approach both give an incomplete picture and complement each other. A useful step toward a comprehensive nonequilibrium theory that would combine both approaches is to study midbasin eastward jets in the inertial limit. Such is the focus of this paper. On the one hand, the problem of the self-organization of a

Full access
Adam H. Monahan and John C. Fyfe

a dipole centered at approximately the latitude of the core of the time-mean jet. This structure is generally interpreted as representing meridional displacements of the eddy-driven jet (the so-called zonal index), while higher-order EOFs (when they are considered) are interpreted as reflecting changes in jet strength or width (e.g., Feldstein and Lee 1998 ; Feldstein 2000 ; DeWeaver and Nigam 2000 ; Codron 2005 ; Vallis et al. 2004 ). Wittman et al. (2005) consider numerical simulations

Full access
Qiang Fu and Pu Lin

1. Introduction By examining atmospheric temperature trends since 1979 based on satellite-borne microwave sounding unit (MSU) data, Fu et al. (2006) identified the enhanced stratospheric cooling and tropospheric warming in the 15°–45° latitude belts in both hemispheres. The changes in meridional tropospheric temperature gradients in the vicinity of the jets provide evidence that the subtropical jets have been shifting poleward ( Fu et al. 2006 ). However, no interpretation has been presented

Full access
Adam J. French and Matthew D. Parker

elevated (ingesting parcels from above approximately 500 m), the mechanism responsible for lifting inflowing parcels evolved from a cold pool to a bore. In the interest of simplicity, the simulations of P08 utilized a homogeneous background wind profile that did not include a low-level wind maximum, or low-level jet (LLJ), which is commonly observed in nocturnal MCS environments (e.g., Maddox 1983 ; Cotton et al. 1989 ). While numerous previous studies have highlighted the importance of the LLJ as

Full access