Stratospheric age of air computed with trajectories based on various 3D-Var and 4D-Var data sets

Scheele, M. P.; Siegmund, P.; Velthoven, P. F. J. van

doi:10.5194/acp-5-1-2005

Cited by 34 publications

(39 citation statements)

References 13 publications

(23 reference statements)

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“…1, which shows the age of air in the stratosphere calculated using the linearly increasing tracer in comparison with values derived from SF 6 and CO 2 observations (Andrews et al, 1999;Boering et al, 1996;Elkins et al, 1996;Harnisch et al, 1996) and values from other models (Hall et al, 1999). Clearly the model's air in the high latitude lower stratosphere is too young, a feature seen in most GCMs and even in CTMs driven by assimilated meteorological data (Scheele et al, 2005;Schoeberl et al, 2003).…”

Section: Experimental Setup For Model Evaluationmentioning

confidence: 99%

Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI

et al. 2006

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Abstract.A model of atmospheric composition and climate has been developed at the NASA Goddard Institute for Space Studies (GISS) that includes composition seamlessly from the surface to the lower mesosphere. The model is able to capture many features of the observed magnitude, distribution, and seasonal cycle of trace species. The simulation is especially realistic in the troposphere. In the stratosphere, high latitude regions show substantial biases during period when transport governs the distribution as meridional mixing is too rapid in this model version. In other regions, including the extrapolar tropopause region that dominates radiative forcing (RF) by ozone, stratospheric gases are generally well-simulated. The model's stratosphere-troposphere exchange (STE) agrees well with values inferred from observations for both the global mean flux and the ratio of Northern (NH) to Southern Hemisphere (SH) downward fluxes.Simulations of preindustrial (PI) to present-day (PD) changes show tropospheric ozone burden increases of 11% while the stratospheric burden decreases by 18%. The resulting tropopause RF values are −0.06 W/m 2 from stratospheric ozone and 0.40 W/m 2 from tropospheric ozone. Global mean mass-weighted OH decreases by 16% from the PI to the PD. STE of ozone also decreased substantially during this time, by 14%. Comparison of the PD with a simulation using 1979 pre-ozone hole conditions for the stratosphere shows a much larger downward flux of ozone into the troposphere in 1979, resulting in a substantially greater tropospheric ozone burden than that seen in the PD run. This implies that reduced STE due to stratospheric ozone depletion may have offset as much as 2/3 of the tropospheric ozone burden increase from PI to PD. However, the model overestimates the downward flux of Correspondence to: D. T. Shindell (dshindell@giss.nasa.gov) ozone at high Southern latitudes, so this estimate is likely an upper limit.In the future, the tropospheric ozone burden increases by 101% in 2100 for the A2 scenario including both emissions and climate changes. The primary reason is enhanced STE, which increases by 124% (168% in the SH extratropics, and 114% in the NH extratropics). Climate plays a minimal role in the SH increases, but contributes 38% in the NH. Chemistry and dry deposition both change so as to reduce tropospheric ozone, partially in compensation for the enhanced STE, but the increased ozone influx dominates the burden changes. The net RF due to projected ozone changes is 0.8 W/m 2 for A2. The influence of climate change alone is −0.2 W/m 2 , making it a substantial contributor to the net RF. The tropospheric oxidation capacity increases seven percent in the full A2 simulation, and 36% due to A2 climate change alone.

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Section: Experimental Setup For Model Evaluationmentioning

confidence: 99%

Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI

et al. 2006

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“…Radiative heating rates (Q) are applied as vertical velocity in a quasi-isentropic trajectory model in the stratosphere to avoid the noisy (Manney et al, 2005b) and too high vertical velocities of meteorological assimilations (Meijer et al, 2004;Scheele et al, 2005;Monge-Sanz et al, 2007). Such an approach can be employed in the stratosphere, where radiative processes are determining the slow mean meridional circulation (Andrews et al, 1987).…”

Section: Model and Methodsmentioning

confidence: 99%

Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter

2008

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Abstract.A long-term climatology of air mass transport through the tropical tropopause layer (TTL) is presented, covering the period from 1962-2005. The transport through the TTL is calculated with a Lagrangian approach using radiative heating rates as vertical velocities in an isentropic trajectory model. We demonstrate the improved performance of such an approach compared to previous studies using vertical winds from meteorological analyses. Within the upper part of the TTL, the averaged diabatic ascent is 0.5 K/day during Northern Hemisphere (NH) winters 1992-2001. Climatological maps show a cooling and strengthening of this part of the residual circulation during the 1990s and early 2000s compared to the long-term mean. Lagrangian cold point (LCP) fields show systematic differences for varying time periods and natural forcing components. The interannual variability of LCP temperature and density fields is found to be influenced by volcanic eruptions, El Niño Southern Oscillation (ENSO), Quasi-Biennial Oscillation (QBO) and the solar cycle. The coldest and driest TTL is reached during QBO easterly phase and La Niña over the western Pacific, whereas during volcanic eruptions, El Niño and QBO westerly phase it is warmer and less dry.

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“…This is known to affect all CTMs using wind velocities or divergence to obtain the vertical motion (e.g. Scheele et al, 2005;Wohltman and Rex, 2008). SLIMCAT runs are not affected by the same problem as, in this case, above 350 K potential temperature vertical motion is computed from diagnosed heating rates.…”

Section: Source Gas Injectionmentioning

confidence: 99%

Bromoform and dibromomethane in the tropics: a 3-D model study of chemistry and transport

et al. 2010

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Abstract.We have developed a detailed chemical scheme for the degradation of the short-lived source gases bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ) and implemented it in the TOMCAT/SLIMCAT three-dimensional (3-D) chemical transport model (CTM). The CTM has been used to predict the distribution of the two source gases (SGs) and 11 of their organic product gases (PGs). These first global calculations of the organic PGs show that their abundance is small. The longest lived organic PGs are CBr 2 O and CHBrO, but their peak tropospheric abundance relative to the surface volume mixing ratio (vmr) of the SGs is less than 5%. We calculate their mean local tropospheric lifetimes in the tropics to be ∼7 and ∼2 days (due to photolysis), respectively. Therefore, the assumption in previous modelling studies that SG degradation leads immediately to inorganic bromine seems reasonable.We have compared observed tropical SG profiles from a number of aircraft campaigns with various model experiments. In the tropical tropopause layer (TTL) we find that the CTM run using p levels (TOMCAT) and vertical winds from analysed divergence overestimates the abundance of CH 2 Br 2 , and to a lesser extent CHBr 3 , although the data is sparse and comparisons are not conclusive. Better agreement in the TTL is obtained in the sensitivity run using θ levels (SLIMCAT) and vertical motion from diabatic heating rates. Trajectory estimates of residence times in the two model versions show slower vertical transport in the SLIM-CAT θ-level version. In the p-level model even when we switch off convection we still find significant amounts of the SGs considered may reach the cold point tropopause; the Correspondence to: R. Hossaini (chm3rh@leeds.ac.uk) stratospheric source gas injection (SGI) is only reduced by ∼16% for CHBr 3 and ∼2% for CH 2 Br 2 without convection.Overall, the relative importance of the SG pathway and the PG pathway for transport of bromine to the stratospheric overworld (θ >380 K) has been assessed. Assuming a 10-day washout lifetime of Br y in TOMCAT, we find the delivery of total Br from CHBr 3 to be 0.72 pptv with ∼53% of this coming from SGI. Similary, for CH 2 Br 2 we find a total Br value of 1.69 pptv with ∼94% coming from SGI. We infer that these species contribute ∼2.4 pptv of inorganic bromine to the lower stratosphere with SGI being the dominant pathway. Slower transport to and through the TTL would decrease this estimate.

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Stratospheric age of air computed with trajectories based on various 3D-Var and 4D-Var data sets

Cited by 34 publications

References 13 publications

Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI

Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI

Long-term climatology of air mass transport through the Tropical Tropopause Layer (TTL) during NH winter

Bromoform and dibromomethane in the tropics: a 3-D model study of chemistry and transport

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