Climatologies of subtropical mixing derived from 3D models

Eyring, Veronika; Dameris, Martin; Grewe, Volker; Langbein, I.; Kouker, W.

doi:10.5194/acp-3-1007-2003

Cited by 12 publications

(35 citation statements)

References 49 publications

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“…This does not imply that there is no sub-tropical barrier, since horizontal distributions of e.g. N 2 O clearly reveal large gradients and horizontal exchange by wave-breaking events (streamer) (Eyring et al 2003;Grewe 2006). In comparison to the other models within MM2, ATTILA lies at the upper bound of the model range and even surpasses this range at various altitudes and latitudes ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4

2007

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The Lagrangian scheme ATTILA is used to calculate age spectra and the mean age of air in the general circulation model ECHAM4. The advantage of the Lagrangian method is that temporal variation in transport is taken into account and that beyond transport times the actual transport pathways can be investigated. We found a strong seasonal cycle in mean age and age spectra, especially at high latitudes. When plotting polar age spectra against time, it can clearly be seen that the edge of the polar vortex acts as an efficient transport barrier and that exchange with extra-polar air takes place only for a short period of approximately two months after the polar vortex has broken down. Compared to observations the mean age is reproduced satisfactorily below approximately 20 km. Above that level however, the mean age is underestimated, especially at high latitudes. Furthermore, the observed sharp meridional gradient is located too far polewards in the model, which indicates that the subtropical transport barrier is too weak. There is a distinct variation in the shape of the age spectra with latitude. At low latitudes the age spectra consist of one single peak, whereas at higher latitudes secondary peaks appear, which are one year apart and whose positions in the spectrum are independent of the location. At polar latitudes there are even several peaks of approximately equal size. We explain these peaks with two superposing processes. First, the seasonal cycle of the upward mass flux at the tropical tropopause produces a single peak age distribution. And second, at polar latitudes, the temporal evolution of the polar vortex allows mixing of polar and subtropical air only once a year, which results in a superposition of these single peak age distributions. A final investigation of the transport pathways gave indications for predominant routes from the tropics to high latitudes resulting in altitude dependent meridional transport, however, more detailed studies of 3D trajectory data will be needed to clarify this issue.

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Section: Resultsmentioning

confidence: 99%

Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4

2007

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“…Grant, 2000 andLangbein et al, 2001). For the design of this tracer experiment, use of the zonal anomaly method provided the most convincing results in detecting the horizontal shape of the streamers realistically without any shift in the meridional plane and location as was detected in the meridional gradient method by Eyring et al (2003). The vertical gradient method (e.g.…”

Section: Simulation Of Streamersmentioning

confidence: 99%

“…4 that polar vortex streamers are weaker phenomena and are therefore detected less readily in this case study. Different criteria have been tested: the zonal anomaly (this study), the meridional gradient (Eyring et al, 2003) and the vertical gradient methods (e.g. Grant, 2000 andLangbein et al, 2001).…”

Section: Simulation Of Streamersmentioning

confidence: 99%

“…A first climatology of streamers was derived with the mechanistic model KArlsruher SImulation of the Middle Atmosphere (KASIMA) using analyzed winds for the winters 1990 to 1998 (Langbein et al, 2001). This "assimilated" streamer climatology was compared by Eyring et al (2003) with simulations from the coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM (E39/C). In general a good correspondence between the two was found, when applying the same streamer criterion.…”

Section: Introductionmentioning

confidence: 99%

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Climatological features of stratospheric streamers in the FUB-CMAM with increased horizontal resolution

Krüger

Langematz²,

Grenfell³

et al. 2005

Atmos. Chem. Phys.

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Abstract. The purpose of this study is to investigate horizontal transport processes in the winter stratosphere using data with a resolution relevant for chemistry and climate modeling. For this reason the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) with its model top at 83 km altitude, increased horizontal resolution T42 and the semi-Lagrangian transport scheme for advecting passive tracers is used.A new approach of this paper is the classification of specific transport phenomena within the stratosphere into tropical-subtropical streamers (e.g. Offermann et al., 1999) and polar vortex extrusions hereafter called polar vortex streamers. To investigate the role played by these largescale structures on the inter-annual and seasonal variability of transport processes in northern mid-latitudes, the global occurrence of such streamers was calculated based on a 10-year model climatology, concentrating on the existence of the Arctic polar vortex. For the identification and counting of streamers, the new method of zonal anomaly was chosen. The analysis of the months October-May yielded a maximum occurrence of tropical-subtropical streamers during Arctic winter and spring in the middle and upper stratosphere. Synoptic maps revealed highest intensities in the subtropics over East Asia with a secondary maximum over the Atlantic in the northern hemisphere. Furthermore, tropicalsubtropical streamers exhibited a higher occurrence than polar vortex streamers, indicating that the subtropical barrier is more permeable than the polar vortex barrier (edge) in the model, which is in good correspondence with observations (e.g. Plumb, 2002;Neu et al., 2003). Interesting for the total ozone decrease in mid-latitudes is the consideration of the lower stratosphere for tropical-subtropical streamers and the stratosphere above ∼20 km altitude for polar vortex streamers, where strongest ozone depletion is observed at polar latCorrespondence to: K. Krüger (kkrueger@awi-potsdam.de) itudes (WMO, 2003). In the lower stratosphere the FUB-CMAM simulated a climatological maximum of 10% occurrence of tropical-subtropical streamers over East-Asia/West Pacific and the Atlantic during early-and mid-winter.The results of this paper demonstrate that stratospheric streamers e.g. large-scale, tongue-like structures transporting tropical-subtropical and polar vortex air masses into midlatitudes occur frequently during Arctic winter. They can therefore play a significant role on the strength and variability of the observed total ozone decrease at mid-latitudes and should not be neglected in future climate change studies.

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“…ECHAM4.L39(DLR)/CHEM (hereafter: E39/C) is a coupled chemistry-climate model (CCM) which has been used for different studies regarding past and future atmospheric composition and has been compared to observations Schnadt et al, 2002;Eyring et al, 2003;Dameris et al, 2005;Steinbrecht et al, 2006). The model has been participating in detailed assessments of CCMs of the stratosphere (Austin et al, 2003;Eyring et al, 2006).…”

Section: Model Description and Design Of Model Simulationsmentioning

confidence: 99%

Hemispheric ozone variability indices derived from satellite observations and comparison to a coupled chemistry-climate model

et al. 2006

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Climatologies of subtropical mixing derived from 3D models

Cited by 12 publications

References 49 publications

Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4

Investigating lower stratospheric model transport: Lagrangian calculations of mean age and age spectra in the GCM ECHAM4

Climatological features of stratospheric streamers in the FUB-CMAM with increased horizontal resolution

Hemispheric ozone variability indices derived from satellite observations and comparison to a coupled chemistry-climate model

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