Hall, T. Waugh, Timescales for the stratospheric circulation derived from tracers. A class of atmospheric constituents used as tracers of stratospheric flow are chemically long-lived in comparison with timescales of interest and exhibit gradients due primarily to time-dependent mixing ratios at the tropopause. In general, the stratospheric transport properties derived from such tracers depend on the nature of their time variation.
To explore the relationship between timescales associated with the propagation of tracer mixing ratio signals and bulk transport properties, we have used two three-dimensional chemical transport models to simulate the age spectrum the distribution of transit times of mass present in air parcels of the stratosphere.
From the age spectrum the stratospheric response to any time-varying tropospheric forcing may be deduced. The modeled age spectra are broad, indicating a range of transit times present in air parcels, and asymmetric, so that the mean transit time, called the mean age, is much larger than the modal transit time.
Furthermore, the phase lag time of an oscillating signal e. Periodic signal phase lags do not represent "mean transit times" and, in general, cannot be readily related to bulk transport properties.
However, if the age spectrum is peaked enough, as it appears to be in the lower tropical stratosphere, periodic signal phase lags approximate the modal time. Get PDF 1. Document is scanned, no OCR. PDF documents require the free Adobe Reader or compatible viewing software to be viewed. AU - Waugh, D. Schmidt Website Curator: Robert B. Schmunk Page updated: Disclaimer: This material is being kept online for historical purposes.
Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic.
Transport from the lower stratosphere to the lower troposphere LT takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere UT to the middle troposphere MTand the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT.
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The governing processes and timescales of stratosphere-to-troposphere transport Liang, Q. DouglassB. DuncanR. Stolarskiand J. WitteThe governing processes and timescales of stratosphere-to-troposphere transport and its contribution to ozone in the Arctic troposphere, Atmos.
PDF of Publication:. Download from publisher's website. Research Program:.Morgenstern, O. Cumulative mixing inferred from stratospheric tracer relationships.
Journal of Geophysical Research-Atmospheres, D5 : Include files Advanced Search Browse. Add to Basket. Released Journal Article Cumulative mixing inferred from stratospheric tracer relationships. External Ressource. Fulltext public. Supplementary Material public. A model integration is performed covering the period from March to August From the tracer relationships in the lower stratosphere we infer relative tracer lifetimes.
Where the model captures the species' sinks properly and where the tracers are largely inert in the lower stratosphere, the model tracer lifetimes compare favorably with literature values. The breakup phases of the polar vortices in the two boreal winters covered by the simulation are studied in some detail. In both winters, before the final warming, separate canonical correlations appear. Mixing manifests itself in a progressive merger of the correlation curves marking the polar vortex and middle latitudes.
We introduce a method to quantify the origins of fractions of simulated air masses based on tracer relationships describing the situation prior to the final warming. In both years, several weeks after the final vortex breakdown of the polar vortex, the method retrieves realistic quantities of former polar vortex air. The findings are verified using idealized tracer advection experiments.
Some important differences between the two winters emerge with regard to the size and longevity of the polar vortex.Hall and Darryn W. A class of atmospheric onstituents used as tracers of stratospheric flow are chemically long-lived in comparison with timescales of interest and exhibit gradients due primarily to time-dependent mixing ratios at the tropopause.
In general, the stratospheric transport properties derived from such tracers depend on the nature of their time wariation. To explore the relationship between timescales associated with the propagation of tracer mixing ratio signals and bulk transport properties, we have used two three-dimensional chemical transport models to simulate the age spectrum the distribution of transit times of mass present in air parcels of the stratosphere.
From the age spectrum the stratospheric response to any time-varying tropospheric forcing may be deduced. The modeled age spectra are broad, indicating a range of transit times present in air parcels, and asymmetric, so that the mean transit time, called the mean age, is much larger than the modal transit time. Furthermore, the phase lag time of an oscillating signal e. Periodic signal phase lags do not represent "mean transit times " and, in general, cannot be readily related to bulk transport properties.
However, if the age spectrum is peaked enough, as it appears to be in the lower tropical stratosphere, periodic signal phase lags approximate the modal time. Documents: Advanced Search Include Citations. HallDarryn W. Citations: 8 - 3 self. Abstract Abstract. Powered by:.Hall, T. The idealized age tracer is commonly used to diagnose transport in ocean models and to help interpret ocean measurements.
In most studies only the steady-state distribution, the result of many centuries of model integration, has been presented and analyzed. However, in principle the transient solution provides more information about the transport. Here it is shown that this information can be readily interpreted in terms of the ventilation histories of water masses. Implications of the relationship are discussed, and the relationship is illustrated with an idealized model.
Natural and anthropogenic tracers have been used to estimate the ventilation history of ocean water masses. Many of these ideas build on previous work intepreting stratospheric tracers Hall and Plumb and recent more general work on transport timescales in geophysical flows Holzer and Hall ; Beckers et al. In this note we restrict attention to the case of stationary transport i.
Some comments concerning the impact of nonstationarity on our analysis are made in the final section. Due to mixing, the clock times of the individual elements comprising the water mass may vary widely. The ideal age is a popular and useful diagnostic in ocean models, but generally only the steady-state solution is reported and analyzed.
However, the transient approach to steady state contains the transport information provided by the steady-state solution and in principle much more. This transient is a useful diagnostic if it can be interpreted physically in a straightforward manner. Recently, mathematical and physical frameworks have been developed in which passive tracer fields can be expressed in terms of transient evolutions that have interpretations as transit time or age distributions Holzer and Hall ; Beckers et al.
In this note we present an example of this connection between a tracer field and an age-related transient that should be of practical interest to ocean modelers. Given the unit uniform source of 1 one has.
Expression 3 is the response at a location r to a spatially distributed source. That is. Therefore, from 4the ideal age is.
This is equivalent to the distribution of times since last boundary contact in the time-forward flow. Expression 8together with the transit time distribution interpretation, is the key result of this work. The transient solution to the ideal age equation and the age spectrum are related in a simple fashion, a result not previously noted, but which follows naturally from the more general Green's function frameworks of Holzer and Hall and Beckers et al.
The transient solution of the ideal age contains valuable transport information—far more, in fact, than the steady-state ideal age alone—and this information is readily interpretable in terms of the ventilation history of the water mass.This app has helped us reduce cost, bu.
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