Modelling deep convection and its impacts on the tropical tropopause layer

Hosking, J. Scott; Russo, M. R.; Braesicke, Peter; Pyle, J. A.

doi:10.5194/acp-10-11175-2010

Cited by 25 publications

(33 citation statements)

References 49 publications

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“…Air in the lower TTL typically comes from the lower troposphere (below 4 km) with rapid upward transport occurring over several days prior to arriving. Though of course we have used three-dimensional wind fields without an explicit representation of convection, this result appears to support the concept that upward transport from the boundary layer occurs in more than one step, with low-level convection feeding rapid transport to the lower TTL from ∼4 km (Hosking et al, 2010). Air in the upper TTL has largely travelled quasi-horizontally through the TTL over the past 15 days.…”

Section: Atmosmentioning

confidence: 76%

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Transport of short-lived species into the Tropical Tropopause Layer

et al. 2012

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Abstract. We use NAME, a trajectory model, to investigate the routes and timescales over which air parcels reach the tropical tropopause layer (TTL). Our aim is to assist the planning of aircraft campaigns focussed on improving knowledge of such transport. We focus on Southeast Asia and the Western Pacific which appears to be a particularly important source of air that enters the TTL. We first study the TTL above Borneo in November 2008, under neutral El Niño/Southern Oscillation (ENSO) conditions. Air parcels (trajectories) arriving in the lower TTL (below ∼15 km) are most likely to have travelled from the boundary layer (BL; <1 km) above the West Pacific. Few air parcels found above ∼16 km travelled from the BL in the previous 15 days. We then perform similar calculations for moderate El Niño (2006) and La Niña (2007) conditions and find yearto-year variability consistent with the phase of ENSO. Under El Niño conditions fewer air parcels travel from the BL to the TTL above Borneo. During the La Niña year, more air parcels travel from the BL to the mid and upper TTL (above ∼15 km) than in the ENSO-neutral year, and again they do so from the BL above the West Pacific. We also find intra-month variability in all years, with day-to-day differences of up to an order of magnitude in the fraction of an idealised shortlived tracer travelling from the BL to the TTL above Borneo. These calculations were performed as a prelude to the SHIVA field campaign, which took place in Borneo during November 2011. So finally, to validate our approach, we consider measurements made in two previous campaigns. The features of vertical profiles of short-lived species observed in the TTL during CR-AVE and TC4 are in broad agreement with calculated vertical profiles of idealised short-lived tracers. It will require large numbers of observations to fully describe the statistical distribution of short-lived species in the TTL. This modelling approach should prove valuable in planning flights for the long-duration aircraft now capable of making such measurements.

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Section: Atmosmentioning

confidence: 76%

“…A range of models suggest that emissions from Southeast Asia and the tropical Western Pacific are more likely to enter the TTL than emissions from other tropical longitudes (e.g. Levine et al, 2007;Aschmann et al, 2009;Hosking et al, 2010;Pisso et al, 2010).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 99%

Transport of short-lived species into the Tropical Tropopause Layer

et al. 2012

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“…Increased oxidation of VSLS by OH in the UT in a future climate could serve to counteract increased stratospheric VSLS loading following enhanced convective lofting into the tropical tropopause layer (TTL) and subsequent transport into the lower stratosphere. The effect could be particularly important over the Maritime Continent, since it is a region characterised by both high deep convective activity and coastal emissions of VSLS (Hosking et al, 2010). These feedbacks add weight to the importance of future changes in LNO x .…”

Section: Consequences For Methane and Other Trace Gasesmentioning

confidence: 99%

Lightning NO<sub>x</sub>, a key chemistry–climate interaction: impacts of future climate change and consequences for tropospheric oxidising capacity

et al. 2014

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Abstract. Lightning is one of the major natural sources of NO x in the atmosphere. A suite of time slice experiments using a stratosphere-resolving configuration of the Unified Model (UM), containing the United Kingdom Chemistry and Aerosols sub-model (UKCA), has been performed to investigate the impact of climate change on emissions of NO x from lightning (LNO x ) and to highlight its critical impacts on photochemical ozone production and the oxidising capacity of the troposphere. Two Representative Concentration Pathway (RCP) scenarios (RCP4.5 and RCP8.5) are explored. LNO x is simulated to increase in a year-2100 climate by 33 % (RCP4.5) and 78 % (RCP8.5), primarily as a result of increases in the depth of convection. The total tropospheric chemical odd oxygen production (P (O x )) increases linearly with increases in total LNO x and consequently, tropospheric ozone burdens of 29 ± 4 Tg(O 3 ) (RCP4.5) and 46 ± 4 Tg(O 3 ) (RCP8.5) are calculated here. By prescribing a uniform surface boundary concentration for methane in these simulations, methane-driven feedbacks are essentially neglected. A simple estimate of the contribution of the feedback reduces the increase in ozone burden to 24 and 33 Tg(O 3 ), respectively. We thus show that, through changes in LNO x , the effects of climate change counteract the simulated mitigation of the ozone burden, which results from reductions in ozone precursor emissions as part of air quality controls projected in the RCP scenarios. Without the driver of increased LNO x , our simulations suggest that the net effect of climate change would be to lower free tropospheric ozone.In addition, we identify large climate-change-induced enhancements in the concentration of the hydroxyl radical (OH) in the tropical upper troposphere (UT), particularly over the Maritime Continent, primarily as a consequence of greater LNO x . The OH enhancement in the tropics increases oxidation of both methane (with feedbacks onto chemistry and climate) and very short-lived substances (VSLS) (with implications for stratospheric ozone depletion). We emphasise that it is important to improve our understanding of LNO x in order to gain confidence in model projections of composition change under future climate.

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“…The Maritime Continent is important because a number of studies have suggested that emissions from this convectively active region may be much more likely to contribute to stratospheric Br y (e.g. Levine et al, 2007;Aschmann et al, 2009;Hosking et al, 2010;Pisso et al, 2010).…”

Section: J Ashfold Et Al: Estimates Of Tropical Bromoform Emissimentioning

confidence: 99%

Estimates of tropical bromoform emissions using an inversion method

et al. 2014

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Abstract. Bromine plays an important role in ozone chemistry in both the troposphere and stratosphere. When measured by mass, bromoform (CHBr 3 ) is thought to be the largest organic source of bromine to the atmosphere. While seaweed and phytoplankton are known to be dominant sources, the size and the geographical distribution of CHBr 3 emissions remains uncertain. Particularly little is known about emissions from the Maritime Continent, which have usually been assumed to be large, and which appear to be especially likely to reach the stratosphere. In this study we aim to reduce this uncertainty by combining the first multiannual set of CHBr 3 measurements from this region, and an inversion process, to investigate systematically the distribution and magnitude of CHBr 3 emissions. The novelty of our approach lies in the application of the inversion method to CHBr 3 . We find that local measurements of a short-lived gas like CHBr 3 can be used to constrain emissions from only a relatively small, sub-regional domain. We then obtain detailed estimates of CHBr 3 emissions within this area, which appear to be relatively insensitive to the assumptions inherent in the inversion process. We extrapolate this information to produce estimated emissions for the entire tropics (defined as 20 • S-20 • N) of 225 Gg CHBr 3 yr −1 . The ocean in the area we base our extrapolations upon is typically somewhat shallower, and more biologically productive, than the tropical average. Despite this, our tropical estimate is lower than most other recent studies, and suggests that CHBr 3 emissions in the coastline-rich Maritime Continent may not be stronger than emissions in other parts of the tropics.

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Modelling deep convection and its impacts on the tropical tropopause layer

Cited by 25 publications

References 49 publications

Transport of short-lived species into the Tropical Tropopause Layer

Transport of short-lived species into the Tropical Tropopause Layer

Lightning NO<sub>x</sub>, a key chemistry–climate interaction: impacts of future climate change and consequences for tropospheric oxidising capacity

Estimates of tropical bromoform emissions using an inversion method

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Modelling deep convection and its impacts on the tropical tropopause layer

Cited by 25 publications

References 49 publications

Transport of short-lived species into the Tropical Tropopause Layer

Transport of short-lived species into the Tropical Tropopause Layer

Lightning NO&lt;sub&gt;x&lt;/sub&gt;, a key chemistry–climate interaction: impacts of future climate change and consequences for tropospheric oxidising capacity

Estimates of tropical bromoform emissions using an inversion method

Contact Info

Product

Resources

About

Lightning NO<sub>x</sub>, a key chemistry–climate interaction: impacts of future climate change and consequences for tropospheric oxidising capacity