scholarly journals Observations and Numerical Simulations of Inertia–Gravity Waves and Shearing Instabilities in the Vicinity of a Jet Stream

2004 ◽  
Vol 61 (22) ◽  
pp. 2692-2706 ◽  
Author(s):  
Todd P. Lane ◽  
James D. Doyle ◽  
Riwal Plougonven ◽  
Melvyn A. Shapiro ◽  
Robert D. Sharman
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Jet Stream ◽  
Sheared Flow ◽  
Mesoscale Structure ◽  
Air Turbulence ◽  
Research Aircraft ◽  
Wave Development ◽  
Upper Level ◽  
Inertia Gravity Waves

Abstract The characteristics and dynamics of inertia–gravity waves generated in the vicinity of an intense jet stream/ upper-level frontal system on 18 February 2001 are investigated using observations from the NOAA Gulfstream-IV research aircraft and numerical simulations. Aircraft dropsonde observations and numerical simulations elucidate the detailed mesoscale structure of this system, including its associated inertia–gravity waves and clear-air turbulence. Results from a multiply nested numerical model show inertia–gravity wave development above the developing jet/front system. These inertia–gravity waves propagate through the highly sheared flow above the jet stream, perturb the background wind shear and stability, and create bands of reduced and increased Richardson numbers. These bands of reduced Richardson numbers are regions of likely Kelvin–Helmholtz instability and a possible source of the clear-air turbulence that was observed.

scholarly journals On the Quantification of Imbalance and Inertia–Gravity Waves Generated in Numerical Simulations of Moist Baroclinic Waves Using the WRF Model

2017 ◽  
Vol 74 (12) ◽  
pp. 4241-4263 ◽  
Author(s):  
Mohammad Mirzaei ◽  
Ali R. Mohebalhojeh ◽  
Christoph Zülicke ◽  
Riwal Plougonven
Keyword(s):  
Numerical Simulations ◽  
Gravity Waves ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Baroclinic Waves ◽  
Surface Front ◽  
The Difference ◽  
Upper Level ◽  
Upper Level Jet ◽  
Inertia Gravity Waves

Abstract Quantification of inertia–gravity waves (IGWs) generated by upper-level jet–surface front systems and their parameterization in global models of the atmosphere relies on suitable methods to estimate the strength of IGWs. A harmonic divergence analysis (HDA) that has been previously employed for quantification of IGWs combines wave properties from linear dynamics with a sophisticated statistical analysis to provide such estimates. A question of fundamental importance that arises is how the measures of IGW activity provided by the HDA are related to the measures coming from the wave–vortex decomposition (WVD) methods. The question is addressed by employing the nonlinear balance relations of the first-order δ–γ, the Bolin–Charney, and the first- to third-order Rossby number expansion to carry out WVD. The global kinetic energy of IGWs given by the HDA and WVD are compared in numerical simulations of moist baroclinic waves by the Weather Research and Forecasting (WRF) Model in a channel on the f plane. The estimates of the HDA are found to be 2–3 times smaller than those of the optimal WVD. This is in part due to the absence of a well-defined scale separation between the waves and vortical flows, the IGW estimates by the HDA capturing only the dominant wave packets and with limited scales. It is also shown that the difference between the HDA and WVD estimates is related to the width of the IGW spectrum.

scholarly journals Identification of the sources of inertia-gravity waves in the Andes Cordillera region

2008 ◽  
Vol 26 (9) ◽  
pp. 2551-2568 ◽  
Author(s):  
A. Spiga ◽  
H. Teitelbaum ◽  
V. Zeitlin
Keyword(s):  
Gravity Waves ◽  
Mesoscale Model ◽  
Jet Stream ◽  
Earth Atmosphere ◽  
Jet Streams ◽  
The Andes ◽  
Wave Parameters ◽  
The Earth ◽  
Andes Cordillera ◽  
Inertia Gravity Waves

Abstract. Four major sources of inertia-gravity waves are known in the Earth atmosphere: upper-tropospheric jet-streams, lower-tropospheric fronts, convection and topography. The Andes Cordillera region is an area where all of these major sources are potentially present. By combining ECMWF and NCEP-NCAR reanalysis, satellite and radiosoundings data and mesoscale WRF simulations in the Andes Cordillera region, we were able to identify the cases where, respectively, the jet-stream source, the convective source and the topography source are predominantly in action. We retrieve emitted wave parameters for each case, compare them, and analyse possible emission mechanisms. The WRF mesoscale model shows very good performance in reproducing the inertia-gravity waves identified in the data analysis, and assessing their likely sources.

scholarly journals Inertia-gravity waves in the troposphere and lower stratosphere associated with a jet stream exit region

1999 ◽  
Vol 17 (1) ◽  
pp. 115-121 ◽  
Author(s):  
L. Thomas ◽  
R. M. Worthington ◽  
A. J. McDonald
Keyword(s):  
Gravity Waves ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Vertical Shear ◽  
Jet Stream ◽  
Mesoscale Meteorology ◽  
Perturbation Velocity ◽  
Waves And Tides ◽  
Radar Measurements ◽  
Inertia Gravity Waves

Abstract. Radar measurements at Aberystwyth (52.4° N, 4.1° W) of winds at tropospheric and lower stratospheric heights are shown for 12-13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation.Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; middle atmosphere dynamics; waves and tides)

Damping of inertial motions by parametric subharmonic instability in baroclinic currents

2014 ◽  
Vol 743 ◽  
pp. 280-294 ◽  
Author(s):  
Leif N. Thomas ◽  
John R. Taylor
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Gravity Waves ◽  
Potential Vorticity ◽  
Wind Shear ◽  
Finite Amplitude ◽  
Instability Criterion ◽  
Thermal Wind ◽  
Parametric Subharmonic Instability ◽  
Inertia Gravity Waves

AbstractA new damping mechanism for vertically-sheared inertial motions is described involving an inertia–gravity wave that oscillates at half the inertial frequency, $f$, and that grows at the expense of inertial shear. This parametric subharmonic instability forms in baroclinic, geostrophic currents where thermal wind shear, by reducing the potential vorticity of the fluid, allows inertia–gravity waves with frequencies less than $f$. A stability analysis and numerical simulations are used to study the instability criterion, energetics, and finite-amplitude behaviour of the instability. For a flow with uniform shear and stratification, parametric subharmonic instability develops when the Richardson number of the geostrophic current nears $Ri_{PSI}=4/3+\gamma \cos \phi $, where $\gamma $ is the ratio of the inertial to thermal wind shear magnitude and $\phi $ is the angle between the inertial and thermal wind shears at the initial time. Inertial shear enters the instability criterion because it can also modify the potential vorticity and hence the minimum frequency of inertia–gravity waves. When this criterion is met, inertia–gravity waves with a frequency $f/2$ and with flow parallel to isopycnals amplify, extracting kinetic energy from the inertial shear through shear production. The solutions of the numerical simulations are consistent with these predictions and additionally show that finite-amplitude parametric subharmonic instability both damps inertial shear and is itself damped by secondary shear instabilities. In this way, parametric subharmonic instability opens a pathway to turbulence where kinetic energy in inertial shear is transferred to small scales and dissipated.

Turbulence and Gravity Waves within an Upper-Level Front

2005 ◽  
Vol 62 (11) ◽  
pp. 3885-3908 ◽  
Author(s):  
Steven E. Koch ◽  
Brian D. Jamison ◽  
Chungu Lu ◽  
Tracy L. Smith ◽  
Edward I. Tollerud ◽  
...  
Keyword(s):  
Structure Function ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Function Analysis ◽  
Numerical Models ◽  
Wide Spectrum ◽  
Potential Temperature ◽  
Scale Model ◽  
Air Turbulence ◽  
Upper Level

Abstract High-resolution dropwindsonde and in-flight measurements collected by a research aircraft during the Severe Clear-Air Turbulence Colliding with Aircraft Traffic (SCATCAT) experiment and simulations from numerical models are analyzed for a clear-air turbulence event associated with an intense upper-level jet/frontal system. Spectral, wavelet, and structure function analyses performed with the 25-Hz in situ data are used to investigate the relationship between gravity waves and turbulence. Mesoscale dynamics are analyzed with the 20-km hydrostatic Rapid Update Cycle (RUC) model and a nested 1-km simulation with the nonhydrostatic Clark–Hall (CH) cloud-scale model. Turbulence occurred in association with a wide spectrum of upward propagating gravity waves above the jet core. Inertia–gravity waves were generated within a region of unbalanced frontogenesis in the vicinity of a complex tropopause fold. Turbulent kinetic energy fields forecast by the RUC and CH models displayed a strongly banded appearance associated with these mesoscale gravity waves (horizontal wavelengths of ∼120–216 km). Smaller-scale gravity wave packets (horizontal wavelengths of 1–20 km) within the mesoscale wave field perturbed the background wind shear and stability, promoting the development of bands of reduced Richardson number conducive to the generation of turbulence. The wavelet analysis revealed that brief episodes of high turbulent energy were closely associated with gravity wave occurrences. Structure function analysis provided evidence that turbulence was most strongly forced at a horizontal scale of 700 m. Fluctuations in ozone measured by the aircraft correlated highly with potential temperature fluctuations and the occurrence of turbulent patches at altitudes just above the jet core, but not at higher flight levels, even though the ozone fluctuations were much larger aloft. These results suggest the existence of remnant “fossil turbulence” from earlier events at higher levels, and that ozone cannot be used as a substitute for more direct measures of turbulence. The findings here do suggest that automated turbulence forecasting algorithms should include some reliable measure of gravity wave activity.

scholarly journals Influences of Moist Convection on a Cold-Season Outbreak of Clear-Air Turbulence (CAT)

2012 ◽  
Vol 140 (8) ◽  
pp. 2477-2496 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman ◽  
Todd P. Lane
Keyword(s):  
Gravity Waves ◽  
Cold Season ◽  
Vertical Shear ◽  
Moist Convection ◽  
Flow Perturbation ◽  
Air Turbulence ◽  
Central United States ◽  
Upper Level ◽  
Vertically Propagating ◽  
Upper Level Jet

Abstract The 9–10 March 2006 aviation turbulence outbreak over the central United States is examined using observations and numerical simulations. Though the turbulence occurs within a deep synoptic cyclone with widespread precipitation, comparison of reports from commercial aircraft with radar and satellite data reveals the majority of the turbulence to be in clear air. This clear-air turbulence (CAT) is located above a strong upper-level jet, where vertical shear ranged between 20 and 30 m s−1 km−1. Comparison of a moist simulation with a dry simulation reveals that simulated vertical shear and subgrid turbulence kinetic energy is significantly enhanced by the anticyclonic upper-level flow perturbation associated with the organized convection in regions of observed CAT. A higher-resolution simulation is used to examine turbulence mechanisms in two primary clusters of reported moderate and severe turbulence. In the northern cluster where vertical shear is strongest, the simulated turbulence arises from Kelvin–Helmholtz (KH) instability. The turbulence farther south occurs several kilometers above shallow, but vigorous, moist convection. There, the simulated turbulence is influenced by vertically propagating gravity waves initiated when the convection impinges on a lowered tropopause. In some locations these gravity waves amplify and break leading directly to turbulence, while in others they aid turbulence development by helping excite KH instability within the layers of strongest vertical shear above them. Although both clusters of turbulence occur either above or laterally displaced from cloud, a shared characteristic is their owed existence to moist convection within the wintertime cyclone, which distinguishes them from traditional CAT.

Inertia–Gravity Waves Spontaneously Generated by Jets and Fronts. Part I: Different Baroclinic Life Cycles

2007 ◽  
Vol 64 (7) ◽  
pp. 2502-2520 ◽  
Author(s):  
Riwal Plougonven ◽  
Chris Snyder
Keyword(s):  
Life Cycle ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Baroclinic Instability ◽  
Life Cycles ◽  
Weather Research And Forecasting ◽  
Spontaneous Generation ◽  
Upper Level ◽  
Upper Level Jet ◽  
Inertia Gravity Waves

Abstract The spontaneous generation of inertia–gravity waves in idealized life cycles of baroclinic instability is investigated using the Weather Research and Forecasting Model. Two substantially different life cycles of baroclinic instability are obtained by varying the initial zonal jet. The wave generation depends strongly on the details of the baroclinic wave’s development. In the life cycle dominated by cyclonic behavior, the most conspicuous gravity waves are excited by the upper-level jet and are broadly consistent with previous simulations of O’Sullivan and Dunkerton. In the life cycle that is dominated by anticyclonic behavior, the most conspicuous gravity waves even in the stratosphere are excited by the surface fronts, although the fronts are no stronger than in the cyclonic life cycle. The anticyclonic life cycle also reveals waves in the lower stratosphere above the upper-level trough of the baroclinic wave; these waves have not been previously identified in idealized simulations. The sensitivities of the different waves to both resolution and dissipation are discussed.

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