Stratospheric control of planetary waves Hitchcock, Peter; Haynes, Peter H.
Geophysical research letters,
28 November 2016, Letnik:
43, Številka:
22
Journal Article
Recenzirano
Odprti dostop
The effects of imposing at various altitudes in the stratosphere zonally symmetric circulation anomalies associated with a stratospheric sudden warming are investigated in a mechanistic circulation ...model. A shift of the tropospheric jet is found even when the anomalies are imposed only above 2 hPa. Their influence is communicated downward through the planetary wave field via three distinct mechanisms. First, a significant fraction of the amplification of the upward fluxes of wave activity prior to the central date of the warming is due to the coupled evolution of the stratospheric zonal mean state and the wave field throughout the column. Second, a downward propagating region of localized wave, mean‐flow interaction is active around the central date but does not penetrate the tropopause. Third, there is deep, vertically synchronous suppression of upward fluxes following the central date. The magnitude of this suppression correlates with that of the tropospheric jet shift.
Key Points
Coupled evolution of the stratospheric mean state and planetary waves drives half of their amplification prior to sudden warmings
Imposing sudden‐warming‐like anomalies creates a downward migrating region of local wave mean‐flow interaction confined to the stratosphere
The dependence of the equatorward shift of the tropospheric jet on the height of the imposed anomalies is quantified
We study the effect of size on the vibrational modes and frequencies of nanoparticles, by applying a newly developed, robust, and efficient first-principles-based method that we present in outline. ...We focus on rutile TiO2, a technologically important material whose bulk exhibits a softening of a transverse acoustic mode close to q = ( 1 2 , 1 2 , 1 4 ) , which becomes unstable with the application of negative pressure. We demonstrate that, under these conditions, nanoparticles above a critical size exhibit unstable localized modes and we calculate their characteristic localization length and decomposition with respect to bulk phonons. We propose that such localized soft modes could initiate coherent structural phase transformations in small nanoparticles above a critical size.
What Workers Say Freeman, Richard B; Boxall, Peter; Haynes, Peter
09/2018
eBook, Book
This book brings together research in the United States, Canada, the United Kingdom, Ireland, Australia, and New Zealand to answer a series of key questions: * What opportunities do employees in ...Anglo-American workplaces have to voice their concerns and what do they seek? * To what extent, and in what contexts, do workers want greater union representation? * How do workers feel about employer-initiated channels of influence? What styles of engagement do they want with employers? * What institutional models are more successful in giving workers the voice they seek at workplaces? * What can unions, employers, and public policy makers learn from these studies of representation and influence? The research is based largely on surveys that were conducted as a follow-up to the influential Worker Representation and Participation Survey (WRPS) reported in What Workers Want , coauthored by Richard B. Freeman and Joel Rogers in 1999 and updated in 2006. Taken together, these studies authoritatively outline workers' attitudes toward, and opportunities for, representation and influence in the Anglo-American workplace. They also enhance industrial relations theory and suggest strategies for unions, employers, and public policy.
To explore the mechanisms linking Arctic sea ice loss to changes in midlatitude surface temperatures, we conduct idealized modeling experiments using an intermediate general circulation model and ...with sea ice loss confined to the Atlantic or Pacific sectors of the Arctic (Barents‐Kara or Chukchi‐Bering Seas). Extending previous findings, there are opposite effects on the winter stratospheric polar vortex for both large‐magnitude (late 21st century) and moderate‐magnitude sea ice loss. Accordingly, there are opposite tropospheric Arctic Oscillation (AO) responses for moderate‐magnitude sea ice loss. However, there are similar strength negative AO responses for large‐magnitude sea ice loss, suggesting that tropospheric mechanisms become relatively more important than stratospheric mechanisms as the sea ice loss magnitude increases. The midlatitude surface temperature response for each loss region and magnitude can be understood as the combination of an “indirect” part induced by the large‐scale circulation (AO) response, and a residual “direct” part that is local to the loss region.
Key Points
Sea ice losses confined to the Atlantic or Pacific sector of the Arctic have opposite effects on the winter stratospheric polar vortex
Tropospheric Arctic Oscillation response is dependent on the sea ice loss region (Atlantic or Pacific sector of the Arctic) and magnitude
Broader Arctic Oscillation‐induced midlatitude surface temperature response is modulated by the local influence of the sea ice loss region
Stratospheric dynamics HAYNES, Peter
Annual review of fluid mechanics,
01/2005, Letnik:
37, Številka:
1
Journal Article
Recenzirano
▪ Abstract The large-scale dynamics of the extratropical stratosphere are reviewed. The role of Rossby waves and vortex dynamics in shaping the winter stratospheric circulation and the dynamics of ...the longitudinal mean flow are first discussed separately. The important effects of two-way interaction between waves and mean flow are then described, with emphasis on how mechanisms discovered in simple models can be followed through to models that are closer to the real stratosphere. A final topic is the possible effect of the stratosphere on the troposphere, with emphasis on dynamical mechanisms for such an effect.
Abstract
Overshoots are convective air parcels that rise beyond their level of neutral buoyancy. A giga-large-eddy simulation (100-m cubic resolution) of “Hector the Convector,” a deep convective ...system that regularly forms in northern Australia, is analyzed to identify overshoots and quantify the effect of hydration of the stratosphere. In the simulation, 1507 individual overshoots were identified, and 46 of them were tracked over more than 10 min. Hydration of the stratosphere occurs through a sequence of mechanisms: overshoot penetration into the stratosphere, followed by entrainment of stratospheric air and then by efficient turbulent mixing between the air in the overshoot and the entrained warmer air, leaving the subsequent mixed air at about the maximum overshooting altitude. The time scale of these mechanisms is about 1 min. Two categories of overshoots are distinguished: those that significantly hydrate the stratosphere and those that have little direct hydration effect. The former reach higher altitudes and hence entrain and mix with air that has higher potential temperatures. The resulting mixed air has higher temperatures and higher saturation mixing ratios. Therefore, a greater amount of the hydrometeors carried by the original overshoot sublimates to form a persistent vapor-enriched layer. This makes the maximum overshooting altitude the key prognostic for the parameterization of deep convection to represent the correct overshoot transport. One common convection parameterization is tested, and the results suggest that the overshoot downward acceleration due to negative buoyancy is too large relative to that predicted by the numerical simulations and needs to be reduced.
A configuration of an idealized general circulation model has been obtained in which a deep, stratospheric, equatorial, westerly jet is established that is spontaneously and quasi-periodically ...disrupted by shallow easterly jets. Similar to the disruption of the quasi-biennial oscillation (QBO) observed in early 2016, meridional fluxes of wave activity are found to play a central role. The possible relevance of two feedback mechanisms to these disruptions is considered. The first involves the secondary circulation produced in the shear zones on the upper and lower flanks of the easterly jet. This is found to play a role in maintaining the aspect ratio of the emerging easterly jet. The second involves the organization of the eddy fluxes by the mean flow: the presence of a weak easterly anomaly within a tall, tropical, westerly jet is demonstrated to produce enhanced and highly focused wave activity fluxes that reinforce and strengthen the easterly anomalies. The eddies appear to be organized by the formation of strong potential vorticity gradients on the subtropical flanks of the easterly anomaly. Similar wave activity and potential vorticity structures are found in the ERA-Interim for the observed QBO disruption, indicating this second feedback was active then.
Flow on a beta‐plane driven by a steady localised anticyclonic forcing of potential vorticity (or equivalently a mass source) is considered as a simple model of the Asian monsoon flow in the upper ...troposphere. Previous authors have noted that the response may be steady, or unsteady, according to the magnitude of the forcing, with the unsteadiness manifested as westward eddy shedding. A detailed study of the transition between steady and eddy‐shedding regimes reveals a third regime ('break up'), for intermediate forcing magnitude, where the flow is steady in the neighbourhood of the forcing, but the westward extending plume of low potential vorticity breaks up into isolated anticyclonic vortices some distance away from the forcing region. A related spatio‐temporal instability problem for flow on a beta plane is specified and analysed. The flow can be stable, convectively unstable or absolutely unstable. It is argued that these three stability regimes correspond to the steady, break‐up and eddy‐shedding regimes for the forced flow and good quantitative correspondence between the regimes is demonstrated by explicit solution of the spatio‐temporal stability problem.
Snapshots of the stream function and potential vorticity response in quasi‐geostrophic single‐layer experiments forced with a steady, localised mass source. The response transitions between different states (steady, break‐up and shedding), defined in terms of temporal and spatial variability, when varying the magnitude F0 or length‐scale r0 of the forcing. The different behaviours can be explained by the spatio‐temporal stability properties of the steady linear response and a transition of the system into an absolutely or convectively unstable regime.
Stratospheric water vapor affects the Earth's radiative balance and stratospheric chemistry, yet its future changes are uncertain and not fully understood. The influence of deep convection on ...stratospheric water vapor remains subject to debate. This letter presents a detailed process‐based model study of the impact of convective ice sublimation on stratospheric water vapor in response to CO2 forced climate change. The influence of convective injection is found to be limited by the vertical profile of temperature and saturation vapor pressure in the tropical tropopause layer, not by the frequency of occurrence. Lagrangian trajectory analysis shows the relative contributions to stratospheric water vapor from sublimation and large‐scale transport are approximately unchanged when CO2 is increased. The results indicate the role of convective ice injection for stratospheric water vapor in a warmer climate remains constrained by large‐scale temperatures.
Plain Language Summary
Trends in stratospheric water vapor impact on both ozone depletion and the climate. Water vapor enters the stratosphere in the tropics and is tightly constrained by the cold temperatures around the tropopause (around 15–17 km altitude). For the present day climate the contribution from the direct injection of ice into the stratosphere by deep convection is thought to be relatively small, but it has been suggested these may increase in a warmer climate. If convection becomes more frequent and stronger under greenhouse gas induced climate change, the response of stratospheric water vapor might be different from that implied simply by changes to tropical tropopause temperatures. This study examines the roles of convection and large‐scale temperatures and transport in determining the water budget in the tropical tropopause region in a climate model. In response to increased atmospheric carbon dioxide the model simulates increased stratospheric water vapor with a substantial contribution coming from more convective injection. However, the relative contribution of convective injection to stratospheric water vapor remains roughly constant as carbon dioxide increases. Therefore, irrespective of whether convection becomes stronger or more frequent, the impact of convective injection of water is found to be constrained by large‐scale temperatures.
Key Points
We present an innovative method to quantify the processes that lead to a modeled increase in stratospheric water vapor from increased CO2
As well as changes in large‐scale temperatures and transport, we find convective injection of ice contributes to stratospheric moistening
The frequency of convective injection increases as CO2 increases, but its relative contribution to stratospheric water vapor does not
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