An Objective Clear-Air Turbulence Forecasting Technique: Verification and Operational Use

Ellrod, Gary P.; Knapp, David I.

doi:10.1175/1520-0434(1992)007<0150:aocatf>2.0.co;2

Cited by 158 publications

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“…The diagnostics are described in detail by Sharman et al (2006). They include the Colson and Panofsky (1965) index, the Brown (1973) index, and the Ellrod and Knapp (1992) indices. For each diagnostic, greater values are associated with stronger turbulence, where greater here means closer to plus infinity rather than simply greater in magnitude.…”

Section: 2)mentioning

confidence: 99%

Increased light, moderate, and severe clear-air turbulence in response to climate change

Williams

2017

Adv. Atmos. Sci.

105

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Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of the shear instabilities that generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However, the individual responses of light, moderate, and severe clear-air turbulence have not previously been studied, despite their importance for aircraft operations. Here, we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into eddy dissipation rates, we find that the ensembleaverage airspace volume containing light clear-air turbulence increases by 59% (with an intra-ensemble range of 43%-68%), light-to-moderate by 75% (39%-96%), moderate by 94% (37%-118%), moderate-to-severe by 127% (30%-170%), and severe by 149% (36%-188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes.

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Section: 2)mentioning

confidence: 99%

Increased light, moderate, and severe clear-air turbulence in response to climate change

Williams

2017

Adv. Atmos. Sci.

105

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“…The same might be true for the link of STE with DEF, because a highly deformative flow must distort any air parcel. Note that DEF was also associated with indices of CAT (Ellrod and Knapp, 1992), a process that might be of some importance for STE (Jaeger and Sprenger, 2007). On the other hand, a link between VORT and STE might also be inferred from purely thermodynamical considerations.…”

Section: Mechanisms For a Link Between Def Vort And Stementioning

confidence: 96%

“…Many studies start with a specific meteorological phenomenon, e.g. CAT (Jaeger and Sprenger, 2007), and then argue that this phenomenon is linked to some of the flow components (for instance to deformation in the CAT index by Ellrod and Knapp, 1992). In contrast, our starting point is the decomposition of the velocity field, irrespective of the underlying meteorological phenomenon.…”

Section: Introductionmentioning

confidence: 99%

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Vorticity, deformation and divergence signals associated with stratosphere–troposphere exchange

Jaeger

Sprenger

2009

Quart J Royal Meteoro Soc

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ABSTRACT:The dynamical tropopause of the extratropics, defined as an isosurface of potential vorticity, acts as a barrier to stratosphere-troposphere exchange (STE). Therefore, any transport across this barrier is necessarily associated with diabatic or frictional processes such as turbulence, radiative forcing or condensational heating. Most of these processes are linked to distinct flow phenomena and hence with distinct signatures of the velocity field. The focus of this study is on the characteristics of the velocity field at the time and location of the tropopause crossing, as given by the flowcomponents divergence (DIV ), deformation (DEF ) and vorticity (VORT ). Firstly, the prevalence of distinct signals is shown for three case studies. Then a Lagrangian climatology of STE is used to assess the climatological aspects of this link for the year 1990. Methodologically, the flow-field components are traced along the STE trajectories, both derived from ERA-40. Some key results of this study are as follows. (1) DEF, positive values of VORT and negative values of DIV are markedly correlated with stratosphere-to-troposphere transport (STT). Therefore, the typical flow field associated with STT is deformative, cyclonic and convergent. (2) For troposphere-to-stratosphere transport (TST), the link with the flow-field components is less pronounced. DEF, VORT and DIV all show small, but distinct local maxima just before the exchange. The flow field during TST is therefore rather divergent and less cyclonic. (3) Sensitivity studies reveal that these findings are robust with respect to temporal and spatial variability.

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“…An example of a weather system that produced high altitude CAT associated with an upper-air trough over central South Africa and mountain wave turbulence is presented. The role played by the Ellrod Turbulence Index (Ellrod & Knapp, 1992) in predicting the turbulence, derived from numerical weather prediction models, is also given.…”

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Clear air turbulence over South Africa

Villiers

Heerden

2001

Meteorological Applications

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Clear air turbulence (CAT) at high altitude remains a hazard to aviation which can result in passenger injury and aircraft damage. Two limited surveys of CAT events over South Africa, 1993–1995 (inclusive) and 1998, are used to illustrate the most likely synoptic conditions under which CAT can be expected. A case study of CAT associated with an upper‐air trough and a mountain wave is presented. The study also evaluates the effectiveness of the Ellrod Turbulence Index (ETI) derived from model data provided by the UK Met. Office. A forecast of ETI derived from the Global Spectral Model of the United States National Center for Environmental Prediction (NCEP) is also reviewed. Copyright © 2001 Royal Meteorological Society

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An Objective Clear-Air Turbulence Forecasting Technique: Verification and Operational Use

Cited by 158 publications

References 0 publications

Increased light, moderate, and severe clear-air turbulence in response to climate change

Increased light, moderate, and severe clear-air turbulence in response to climate change

Vorticity, deformation and divergence signals associated with stratosphere–troposphere exchange

Clear air turbulence over South Africa

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