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.

scholarly journals Mechanisms Influencing Cirrus Banding and Aviation Turbulence near a Convectively Enhanced Upper-Level Jet Stream

2016 ◽  
Vol 144 (8) ◽  
pp. 3003-3027 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman
Keyword(s):  
Gravity Waves ◽  
Structural Characteristics ◽  
Internal Gravity Waves ◽  
Static Stability ◽  
Shear Instability ◽  
Vertical Shear ◽  
Moist Convection ◽  
Shallow Convection ◽  
Upper Level ◽  
Upper Level Jet

Abstract Mechanisms supporting a cold-season aviation turbulence outbreak over the northwest Atlantic Ocean and adjacent coastal regions of North America are investigated using high-resolution numerical simulations. Two distinct episodes of moderate-or-greater turbulence in the upper troposphere are observed, and the simulations suggest the turbulence is linked to eastward-translating mesoscale perturbations of negative potential vorticity (PV) emanating from upstream organized deep convection along the anticyclonic shear side of an upper-level jet. Within the exit region of the jet where the turbulence episodes occur, thermodynamic and kinematic fields in the vicinity of the PV perturbations exhibit structural characteristics of mesoscale inertia–gravity waves. These wavelike perturbations are shown to facilitate turbulence by influencing the vertical shear and static stability, which promotes mesoscale regions of banded cirrus clouds, near or within which the observed turbulence occurs. The simulations also suggest that the turbulence arises from fundamentally different mechanisms in the two episodes. In the first and most severe turbulence episode, mesoscale wave-related vertical shear enhancements lead to Kelvin–Helmholtz instability (KHI) near aircraft cruising altitudes (~8.9–11.2 km MSL). Simulated KHI is most prevalent near relatively isolated areas of shallow, moist convection, where smaller-scale internal gravity waves originating in the middle troposphere in response to the shallow convection may play a role in excitation of the KHI located above. The second turbulence episode is consistent with simulated thermal-shear instability related to wave-induced mesoscale reductions in upper-tropospheric static stability. However, unlike for the earlier episode of enhanced turbulence, cloud-radiative feedbacks are necessary for the instability and mesoscale regions of banded cirrus to develop.

scholarly journals The Role of Vertically Propagating Gravity Waves Forced by Melting-Induced Cooling in the Formation and Evolution of Wide Cold-Frontal Rainbands

2016 ◽  
Vol 73 (7) ◽  
pp. 2803-2836 ◽  
Author(s):  
Masayuki Kawashima
Keyword(s):  
Gravity Waves ◽  
Frontal Zone ◽  
Mesoscale Model ◽  
Wrf Model ◽  
Wave Pattern ◽  
Wave Generation ◽  
Vertical Shear ◽  
Formation And Evolution ◽  
Upper Level ◽  
Vertically Propagating

Abstract Realistic mesoscale model simulations using the Weather Research and Forecasting (WRF) Model and idealized dry simulations were used to study the mechanisms responsible for the formation and evolution of wide cold-frontal rainbands (WCFRs) associated with a wintertime cyclone that moved onto the Washington coast. The WRF simulation reproduced observed characteristics of three successively formed WCFRs, including their spacing and movement as well as the timing of the formation of two WCFRs behind the first. Sensitivity experiments showed that melting-induced cooling in the stratiform precipitation area behind the surface cold front was essential for the formation of the first and second WCFRs, whereas the third WCFR was formed by the release of potential instability within an ascent forced by upper-level frontogenesis. Enhanced frontal updrafts responsible for the first and second WCFRs were created by a superposition of a broad updraft caused by frontal dynamics and upward-propagating gravity waves generated by the melting-induced cooling. The dry simulations forced by specified cooling revealed specific mechanisms for the wave generation and the evolution of the first and second WCFRs. The gravity waves were generated at the intersection of the low-level frontal zone and the melting layer, where strong vertical shear of the cross-front wind and upshear-sloped cooling by melting cooperatively enhanced the wave generation. The formation of the second WCFR behind the first and subsequent dissipation of these WCFRs was attributed to the evolution of a wave pattern associated with the evolution of cross-front flow above the frontal zone.

Numerical Simulations of Interactions between Gravity Waves and Deep Moist Convection

2005 ◽  
Vol 62 (5) ◽  
pp. 1480-1496 ◽  
Author(s):  
Zachary A. Eitzen ◽  
David A. Randall
Keyword(s):  
Gravity Waves ◽  
Deep Convection ◽  
Velocity Versus ◽  
Moist Convection ◽  
Vertical Grid ◽  
Wave Energy Flux ◽  
Deep Moist Convection ◽  
Vertically Propagating ◽  
The Tropics ◽  
The Waves

Abstract This study uses a numerical model to simulate deep convection both in the Tropics over the ocean and the midlatitudes over land. The vertical grid that was used extends into the stratosphere, allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates. A large number of trajectories are used to evaluate the behavior of tracers in the troposphere, and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement. Conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere. In addition, Fourier analysis is used to characterize the waves in the stratosphere; it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers. Finally, this study examines the wave energy flux as a means to provide a link between the tropospheric behavior of the convection and the strength of the waves in the stratosphere.

scholarly journals Characteristics of Explosive Cyclones over the Northern Pacific

2017 ◽  
Vol 56 (12) ◽  
pp. 3187-3210 ◽  
Author(s):  
Shuqin Zhang ◽  
Gang Fu ◽  
Chungu Lu ◽  
Jingwu Liu
Keyword(s):  
Cold Season ◽  
Early Spring ◽  
Occurrence Frequency ◽  
Northwestern Pacific ◽  
Jet Stream ◽  
Central Pacific ◽  
Positive Vorticity ◽  
Northern Pacific ◽  
Upper Level ◽  
Upper Level Jet

AbstractExplosive cyclones (ECs) over the northern Pacific Ocean during the cold season (October–April) over a 15-yr (2000–15) period are analyzed by using the Final (FNL) Analysis data provided by the National Centers for Environmental Prediction. These ECs are stratified into four categories according to their intensity: weak, moderate, strong, and super ECs. In addition, according to the spatial distribution of their maximum-deepening-rate positions, ECs are further classified into five regions: the Japan–Okhotsk Sea (JOS), the northwestern Pacific (NWP), the west-central Pacific (WCP), the east-central Pacific (ECP), and the northeastern Pacific (NEP). The occurrence frequency of ECs shows evident seasonal variations for the various regions over the northern Pacific. NWP ECs frequently occur in winter and early spring, WCP and ECP ECs frequently occur in winter, and JOS and NEP ECs mainly occur in autumn and early spring. The occurrence frequency, averaged maximum deepening rate, and developing and explosive-developing lifetimes of ECs decrease eastward over the northern Pacific, excluding JOS ECs, consistent with the climatological intensity distributions of the upper-level jet stream, midlevel positive vorticity, and low-level baroclinicity. On the seasonal scale, the occurrence frequency and spatial distribution of ECs are highly correlated with the intensity and position of the upper-level jet stream, respectively, and also with those of midlevel positive vorticity and low-level baroclinicity. Over the northwestern Pacific, the warm ocean surface also contributes to the rapid development of ECs. The composite analysis indicates that the large-scale atmospheric environment for NWP and NEP ECs shows significant differences from that for the 15-yr cold-season average. The southwesterly anomalies of the upper-level jet stream and positive anomalies of midlevel vorticity favor the prevalence of NWP and NEP ECs.

scholarly journals Gravity Waves Generated by Sheared Potential Vorticity Anomalies

2010 ◽  
Vol 67 (1) ◽  
pp. 157-170 ◽  
Author(s):  
François Lott ◽  
Riwal Plougonven ◽  
Jacques Vanneste
Keyword(s):  
Gravity Waves ◽  
Potential Vorticity ◽  
Richardson Number ◽  
Large Scale ◽  
Flow Characteristics ◽  
Vertical Shear ◽  
Wave Flow ◽  
Wave Source ◽  
Flow Interactions ◽  
Vertically Propagating

Abstract The gravity waves (GWs) generated by potential vorticity (PV) anomalies in a rotating stratified shear flow are examined under the assumptions of constant vertical shear, two-dimensionality, and unbounded domain. Near a PV anomaly, the associated perturbation is well modeled by quasigeostrophic theory. This is not the case at large vertical distances, however, and in particular beyond the two inertial layers that appear above and below the anomaly; there, the perturbation consists of vertically propagating gravity waves. This structure is described analytically, using an expansion in the continuous spectrum of the singular modes that results from the presence of critical levels. Several explicit results are obtained. These include the form of the Eliassen–Palm (EP) flux as a function of the Richardson number N 2/Λ2, where N is the Brunt–Väisälä frequency and Λ the vertical shear. Its nondimensional value is shown to be approximately exp(−πN/Λ)/8 in the far-field GW region, approximately twice that between the two inertial layers. These results, which imply substantial wave–flow interactions in the inertial layers, are valid for Richardson numbers larger than 1 and for a large range of PV distributions. In dimensional form they provide simple relationships between the EP fluxes and the large-scale flow characteristics. As an illustration, the authors consider a PV disturbance with an amplitude of 1 PVU and a depth of 1 km, and estimate that the associated EP flux ranges between 0.1 and 100 mPa for a Richardson number between 1 and 10. These values of the flux are comparable with those observed in the lower stratosphere, which suggests that the mechanism identified in this paper provides a substantial gravity wave source, one that could be parameterized in GCMs.

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.

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 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 Environment and Mechanisms of Severe Turbulence in a Midlatitude Cyclone

2020 ◽  
Vol 77 (11) ◽  
pp. 3869-3889 ◽  
Author(s):  
Stanley B. Trier ◽  
Robert D. Sharman ◽  
Domingo Muñoz-Esparza ◽  
Todd P. Lane
Keyword(s):  
Gravity Waves ◽  
Wave Breaking ◽  
Deep Convection ◽  
Vertical Shear ◽  
Synoptic Scale ◽  
Helmholtz Instability ◽  
Commercial Aviation ◽  
Central United States ◽  
Jet Streak ◽  
Horizontal Wavelength

AbstractA large midlatitude cyclone occurred over the central United States from 0000 to 1800 UTC 30 April 2017. During this period, there were more than 1100 reports of moderate-or-greater turbulence at commercial aviation cruising altitudes east of the Rocky Mountains. Much of this turbulence was located above or, otherwise, outside the synoptic-scale cloud shield of the cyclone, thus complicating its avoidance. In this study we use two-way nesting in a numerical model with finest horizontal spacing of 370 m to investigate possible mechanisms producing turbulence in two distinct regions of the cyclone. In both regions, model-parameterized turbulence kinetic energy compares well to observed turbulence reports. Despite being outside of hazardous large radar reflectivity locations in deep convection, both regions experienced strong modification of the turbulence environment as a result of upper-tropospheric/lower-stratospheric (UTLS) convective outflow. For one region, where turbulence was isolated and short lived, simulations revealed breaking of ~100-km horizontal-wavelength lower-stratospheric gravity waves in the exit region of a UTLS jet streak as the most likely mechanism for the observed turbulence. Although similar waves occurred in a simulation without convection, the altitude at which wave breaking occurred in the control simulation was strongly affected by UTLS outflow from distant deep convection. In the other analyzed region, turbulence was more persistent and widespread. There, overturning waves of much shorter 5–10-km horizontal wavelengths occurred within layers of gradient Richardson number < 0.25, which promoted Kelvin–Helmholtz instability associated with strong vertical shear in different horizontal locations both above and beneath the convectively enhanced UTLS jet.

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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