Search Results

You are looking at 1 - 10 of 12 items for :

  • Spontaneous Imbalance x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: All Content x
Clear All
Yonghui Lin and Fuqing Zhang

and organize convection (e.g., Zhang et al. 2001 ), and they are identified as a possible source of clear-air turbulence (e.g., Koch et al. 2005 ). Mountains, convection, wind shear, and adjustment of unbalanced flows related to jet streams and frontal systems are the most important sources of gravity waves ( Hooke 1986 ). Uccellini and Koch (1987) conceptualized the synoptic pattern of gravity wave generation and found that mesoscale waves with amplitudes of 1–15 hPa, horizontal wavelengths of

Full access
Shuguang Wang, Fuqing Zhang, and Chris Snyder

1. Introduction Gravity waves propagating vertically from the lower atmosphere are widely recognized to play important roles in a variety of atmospheric phenomena. Known sources of these gravity waves include mountains, moist convection, fronts, upper-level jets, geostrophic adjustment, and spontaneous generation ( Fritts and Alexander 2003 , and references therein). Among these, jets are often responsible for generating low-frequency inertia–gravity waves with characteristic horizontal

Full access
Chris Snyder, David J. Muraki, Riwal Plougonven, and Fuqing Zhang

1. Introduction Prominent inertia–gravity waves are often found beneath the downstream portion, or exit region, of localized upper-tropospheric jets (see the review by Uccellini and Koch 1987 ). Upward-propagating waves can also appear with a similar relation to the wind speed maximum, but in the stratosphere, above the tropospheric jet (e.g., Guest et al. 2000 ; Plougonven and Teitelbaum 2003 ). While the source of these observed waves is not yet settled, one possibility is that they arise

Full access
Y. D. Afanasyev, P. B. Rhines, and E. G. Lindahl

were performed using the optical thickness of a dyed thin interfacial layer. A natural choice of flow for investigating the spontaneous imbalance is a baroclinic jet. A few recent numerical simulations ( O’Sullivan and Dunkerton 1995 ; Zhang 2004 ; Viudez and Dritschel 2006 ) describe the emission of inertia–gravity waves by unstable baroclinic jet. In simulations by Viudez and Dritschel (2006) the emission is highly localized in space and occurs only “at the largest curvature side of the

Full access
Michael E. McIntyre

made far-reaching contributions to our subject, and both were persons of exemplary warmth, generosity, and scientific integrity. 2. Lighthill’s theory of acoustic imbalance While still a terrifyingly bright young man—fresh from wartime aerodynamics after his journey through pure mathematics with schoolmate Freeman Dyson—James Lighthill (1952) singlehandedly put his finger on a key aspect of the phenomenon of spontaneous imbalance. Addressing the problem of noise emitted by jet aircraft, Lighthill

Full access
Norihiko Sugimoto, Keiichi Ishioka, and Katsuya Ishii

; Fritts and Alexander 2003 ). There are many studies on gravity waves, and several sources for these waves (topography, convection, jets, fronts, cyclones, and so on) have been identified ( Fritts and Nastrom 1992 ; Sato 2000 ). From several observational studies it has been suggested that inertial gravity waves are radiated from strong rotational flows, such as polar night jets ( Yoshiki and Sato 2000 ), subtropical jets ( Uccelini and Koch 1987 ; Kitamura and Hirota 1989 ; Sato 1994 ; Plougonven

Full access
Kaoru Sato and Motoyoshi Yoshiki

frequency approaches zero. Another important finding was the dominance of downward energy flux associated with gravity waves in the polar night jet (PNJ) region, suggesting gravity wave sources in the polar stratosphere. Yoshiki and Sato (2000) examined seasonal variation of gravity waves in the polar stratosphere using operational radiosonde data from 33 stations over a period of 10 yr. It was shown that both potential and kinetic energies of gravity waves per unit mass are maximized in austral spring

Full access
Vladimir Zeitlin

, following Le Sommer et al. (2003) , we consider the 2RSW equations with no y dependence: Here, δ ij is Kronecker delta and g ′ is the reduced gravity: g′ = ( ρ 2 − ρ 1 )/ ρ 2 . Stationary solutions corresponding to the geostrophic equilibria are the exact solutions of the full nonlinear equations and are given by In the case of barotropic and/or baroclinic pressure distributions with compact support variations, the balanced jet solutions arise. A new phenomenon appears at large enough Ro because

Full access
Dong L. Wu and Stephen D. Eckermann

current GW parameterizations is their poorly constrained specifications of lower atmospheric sources (see, e.g., McLandress and Scinocca 2005 ). Although it is recognized that GWs can be excited by flow across mountains, convection, and imbalance/instability within rapidly evolving baroclinic jet/frontal systems (e.g., Fritts et al. 2006 ), the relative contributions of these sources to the GW spectrum encountered in the middle atmosphere remains highly uncertain, particularly with respect to GWs

Full access
John A. Knox, Donald W. McCann, and Paul D. Williams

. Observational experience (e.g., Sorenson 1964 ) has long indicated the following two flow regimes associated with CAT: strongly cyclonic and strongly anticyclonic flows. Cyclonic CAT has been explained and predicted with some success via Kelvin–Helmholtz instability theory ( Dutton and Panofsky 1970 ) related to frontogenesis and deformation (e.g., Ellrod and Knapp 1992 ). These regions sometimes correspond to areas in which spontaneous emission of gravity waves is expected to occur (e.g., fronts and jets

Full access