scholarly journals Impact of land convection on troposphere-stratosphere exchange in the tropics

2007 ◽  
Vol 7 (2) ◽  
pp. 3269-3300 ◽  
Author(s):  
P. Ricaud ◽  
B. Barret ◽  
J.-L. Attié ◽  
E. Le Flochmoën ◽  
E. Motte ◽  
...  
Keyword(s):  
Transport Model ◽  
Source Region ◽  
Tropical Rainfall Measuring Mission ◽  
Convective Transport ◽  
Chemical Transport Model ◽  
Tropical Tropopause Layer ◽  
Evergreen Forests ◽  
Tropical Tropopause ◽  
Longitudinal Gradients ◽  
The Tropics

Abstract. The mechanism of troposphere-stratosphere exchange in the tropics was investigated from space-borne observations of the horizontal distributions of nitrous oxide (N2O), methane (CH4) and carbon monoxide (CO) at 17 km in March-April-May by the ODIN/Sub-Millimeter Radiometer (SMR), the Upper Atmosphere Research Satellite (UARS)/Halogen Occultation Experiment (HALOE) and the TERRA/Measurements Of Pollution In The Troposphere (MOPITT) instruments in 2002–2004, completed by recent observations of the AURA/Microwave Limb Sounder (MLS) instrument during the same season in 2005. At the top of the Tropical Tropopause Layer (TTL), all gases show significant longitudinal gradients with maximum amounts primarily over Africa and, depending on the species, secondary more or less pronounced maxima above northern South America and South-East Asia. The Maritime continent in the Western Pacific never appears as a source region for the stratosphere. The large longitudinal gradient at latitudes where the circulation is essentially zonal, and the co-location of the maximum tropospheric trace gases concentrations with the overshooting features reported by the Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar, strongly supports that rapid uplift over land convective regions is the dominating process of troposphere-stratosphere exchange. Calculations carried out with the MOCAGE-Climat chemical transport model well capture the location of the maximum gas concentration in the TTL but of lesser amplitude. Although there are obvious misrepresentations of some of the sources in the model, i.e. CH4 emissions by evergreen forests, the main reason for discrepancy appears to be the underestimation of the maximum altitude reached by land convective transport in MOCAGE.

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

2010 ◽  
Vol 10 (2) ◽  
pp. 719-735 ◽  
Author(s):  
R. Hossaini ◽  
M. P. Chipperfield ◽  
B. M. Monge-Sanz ◽  
N. A. D. Richards ◽  
E. Atlas ◽  
...  
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Vertical Motion ◽  
Chemical Transport Model ◽  
Heating Rates ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Modelling Studies ◽  
Vertical Winds ◽  
The Tropics

Abstract. We have developed a detailed chemical scheme for the degradation of the short-lived source gases bromoform (CHBr3) and dibromomethane (CH2Br2) 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 CBr2O 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 CH2Br2, and to a lesser extent CHBr3, 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 SLIMCAT 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 stratospheric source gas injection (SGI) is only reduced by ~16% for CHBr3 and ~2% for CH2Br2 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 Bry in TOMCAT, we find the delivery of total Br from CHBr3 to be 0.72 pptv with ~53% of this coming from SGI. Similary, for CH2Br2 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.

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

2009 ◽  
Vol 9 (4) ◽  
pp. 16811-16851 ◽  
Author(s):  
R. Hossaini ◽  
M. P. Chipperfield ◽  
B. M. Monge-Sanz ◽  
N. A. D. Richards ◽  
E. Atlas ◽  
...  
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Vertical Motion ◽  
Chemical Transport Model ◽  
Heating Rates ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Modelling Studies ◽  
Vertical Winds ◽  
The Tropics

Abstract. We have developed a detailed chemical scheme for the degradation of the short-lived source gases bromoform (CHBr3) and dibromomethane (CH2Br2) 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 CBr2O and CHBrO, but their peak tropospheric abundance relative to the surface 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 and vertical winds from analysed divergence overestimates the abundance of CH2Br2, and to a lesser extent CHBr3, although the data is sparse and comparisons are not conclusive. Better agreement in the TTL is obtained in the run using θ levels and vertical motion from diabatic heating rates. Trajectory estimates of residence times in the two model versions confirm the more realistic transport in the 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; the stratospheric source gas injection is only reduced by ~16% for CHBr3 and ~2% for CH2Br2 without convection. Overall, the relative importance of the SG pathway and the PG pathway for transport of bromine to the stratosphere has been assessed. Assuming a 10-day washout lifetime of Bry we find the delivery of total Br from CHBr3 to be 0.72 pptv with ~53% of this coming from SGI. Similary, for CH2Br2 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.

scholarly journals The NASA Airborne Tropical Tropopause Experiment: High-Altitude Aircraft Measurements in the Tropical Western Pacific

2017 ◽  
Vol 98 (1) ◽  
pp. 129-143 ◽  
Author(s):  
Eric J. Jensen ◽  
Leonhard Pfister ◽  
David E. Jordan ◽  
Thaopaul V. Bui ◽  
Rei Ueyama ◽  
...  
Keyword(s):  
High Altitude ◽  
Active Species ◽  
Convective Transport ◽  
Western Pacific ◽  
Lower Altitude ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Cloud Properties ◽  
The Tropics ◽  
Global Hawk

Abstract The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).

scholarly journals The contribution of natural and anthropogenic very short-lived species to stratospheric bromine

2012 ◽  
Vol 12 (1) ◽  
pp. 371-380 ◽  
Author(s):  
R. Hossaini ◽  
M. P. Chipperfield ◽  
W. Feng ◽  
T. J. Breider ◽  
E. Atlas ◽  
...  
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Chemical Transport Model ◽  
Atmospheric Lifetime ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Atmospheric Observations ◽  
Surface Mixing ◽  
The Impact

Abstract. We have used a global three-dimensional chemical transport model to quantify the impact of the very short-lived substances (VSLS) CHBr3, CH2Br2, CHBr2Cl, CHBrCl2, CH2BrCl and C2H5-Br on the bromine budget of the stratosphere. Atmospheric observations of these gases allow constraints on surface mixing ratios that, when incorporated into our model, contribute ~4.9–5.2 parts per trillion (ppt) of inorganic bromine (Bry) to the stratosphere. Of this total, ~76 % comes from naturally-emitted CHBr3 and CH2Br2. The remaining species individually contribute modest amounts. However, their accumulated total accounts for up to ~1.2 ppt of the supply and thus should not be ignored. We have compared modelled tropical profiles of a range of VSLS with observations from the recent 2009 NSF HIPPO-1 aircraft campaign. Modelled profiles agree reasonably well with observations from the surface to the lower tropical tropopause layer. We have also considered the poorly studied anthropogenic VSLS, C2H5Br, CH2BrCH2Br, n-C3H7Br and i-C3H7Br. We find the local atmospheric lifetime of these species in the tropical tropopause layer are ~183, 603, 39 and 49 days, respectively. These species, particularly C2H5Br and CH2BrCH2Br, would thus be important carriers of bromine to the stratosphere if emissions were to increase substantially. Our model shows ~70–73 % and ~80–85 % of bromine from these species in the tropical boundary layer can reach the lower stratosphere.

scholarly journals Tropical cooling in the case of stratospheric sudden warming in January 2009: focus on the tropical tropopause layer

2011 ◽  
Vol 11 (1) ◽  
pp. 2263-2296 ◽  
Author(s):  
K. Yoshida ◽  
K. Yamazaki
Keyword(s):  
Source Region ◽  
Temperature Drop ◽  
Eastern Africa ◽  
Stratospheric Sudden Warming ◽  
Tropical Tropopause Layer ◽  
Cooling Period ◽  
Wave Forcing ◽  
Tropical Tropopause ◽  
Vertical Heat Flux ◽  
The Tropics

Abstract. Temperature changes in the tropics, especially in the tropical tropopause layer, are investigated at the time of a major stratospheric sudden warming (SSW) event that started on about 16 January 2009. During the SSW, the temperature in the tropical upper stratosphere declined and the cold anomaly propagated downward, while the tropics between 150 and 100 hPa started to cool from 18 January, prior to a temperature drop at 70 hPa. We performed thermodynamical and dynamical analyses with ERA-Interim data. During the SSW event, the tropical stratosphere was cooled by upwelling, and the upwelling was induced by wave forcing in the northern extratropical stratosphere. However, the stratospheric wave forcing generated only weak upwelling in the tropics below 100 hPa. During the cooling period at around 18 January, tropical ascent was the main contributor to cooling of the tropics between 150 and 100 hPa. Subsequently, vertical convergence of the vertical heat flux, which is closely tied to the convection structure, resulted in a gradual decrease in temperature within the tropical uppermost troposphere. Waves that had same source region with the upward-propagating waves that caused the SSW event, propagated from Alaska to the tropics of Eastern South America and Eastern Africa at around 100 hPa, and dissipated in these areas; the associated wave forcing drove the tropical ascent between 150 and 100 hPa.

scholarly journals Tropical cooling in the case of stratospheric sudden warming in January 2009: focus on the tropical tropopause layer

2011 ◽  
Vol 11 (13) ◽  
pp. 6325-6336 ◽  
Author(s):  
K. Yoshida ◽  
K. Yamazaki
Keyword(s):  
Source Region ◽  
Temperature Drop ◽  
Eastern Africa ◽  
Stratospheric Sudden Warming ◽  
Tropical Tropopause Layer ◽  
Cooling Period ◽  
Wave Forcing ◽  
Tropical Tropopause ◽  
Vertical Heat Flux ◽  
The Tropics

Abstract. Temperature changes in the tropics, especially in the tropical tropopause layer, are investigated at the time of a major stratospheric sudden warming (SSW) event that started on about 16 January 2009. During the SSW, the temperature in the tropical upper stratosphere declined and the cold anomaly propagated downward, while the tropics between 150 and 100 hPa started to cool from 18 January, prior to a temperature drop at 70 hPa. We performed thermodynamical and dynamical analyses with ERA-Interim data. During the SSW event, the tropical stratosphere was cooled by upwelling, and the upwelling was induced by wave forcing in the northern extratropical stratosphere. However, the stratospheric wave forcing generated only weak upwelling in the tropics below 100 hPa. During the cooling period at around 18 January, tropical ascent was the main contributor to cooling of the tropics between 150 and 100 hPa. Subsequently, vertical convergence of the vertical heat flux, which is closely tied to the convection structure, resulted in a gradual decrease in temperature within the tropical uppermost troposphere. Waves that had same source region with the upward-propagating waves that caused the SSW event, propagated from Alaska to the tropics of eastern South America and eastern Africa at around 100 hPa, and dissipated in these areas; the associated wave forcing drove the tropical ascent between 150 and 100 hPa.

scholarly journals Bridging the gap between bromocarbon oceanic emissions and upper air concentrations

2012 ◽  
Vol 12 (2) ◽  
pp. 4477-4505 ◽  
Author(s):  
S. Tegtmeier ◽  
K. Krüger ◽  
B. Quack ◽  
I. Pisso ◽  
A. Stohl ◽  
...  
Keyword(s):  
Transport Model ◽  
Degradation Products ◽  
Source Region ◽  
Western Pacific ◽  
Emission Rates ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Oceanic Emissions ◽  
Atmospheric Concentrations ◽  
The Western Pacific

Abstract. Oceanic emissions of halogenated very short-lived substances (VSLS) are expected to contribute significantly to the stratospheric halogen loading and therefore to ozone depletion. Estimates of the amount of VSLS transported into the stratosphere are highly uncertain and based on sporadic observations around the tropical tropopause layer (TTL) and on modeling studies which use prescribed emission scenarios to reproduce observed atmospheric concentrations. Actual measurements of VSLS emissions at the ocean surface have not been linked to the stratospheric halogen loading until now. Here we use observations of oceanic VSLS emissions in the western Pacific and an atmospheric Lagrangian transport model to estimate the direct contribution of bromoform (CHBr3), and dibromomethane (CH2Br2) to the stratospheric bromine loading. Our emission-based estimates of VSLS profiles provide the first link between observed oceanic emissions and in situ TTL measurements. The emission-based and observed profiles of CHBr3 show good agreement, confirming the importance of the western Pacific as a source region. However, CH2Br2 emission-based estimates are considerable smaller than current upper air observations as a result of relatively low western Pacific emissions. We estimate the relative importance of the highly variable emission rates and the surface to stratosphere transport for the contribution of the two bromocarbons to the stratospheric bromine budget. Our results show that stratospheric entrainment of bromine in form of VSLS or their degradation products is highly variable and that this variability is primarily linked to the variability of the observed sea-to-air flux. Together, both bromocarbons contribute to the stratospheric bromine budget with 0.4 pptv on average and 2.3 pptv for cases of maximum emissions.

scholarly journals The contribution of natural and anthropogenic very short-lived species to stratospheric bromine

2011 ◽  
Vol 11 (8) ◽  
pp. 23859-23882
Author(s):  
R. Hossaini ◽  
M. P. Chipperfield ◽  
W. Feng ◽  
T. J. Breider ◽  
E. Atlas ◽  
...  
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Chemical Transport Model ◽  
Atmospheric Lifetime ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Atmospheric Observations ◽  
Surface Mixing ◽  
The Impact

Abstract. We have used a global three-dimensional chemical transport model to quantify the impact of the very short-lived species (VSLS) CHBr3, CH2Br2, CHBr2Cl, CHBrCl2, CH2BrCl and C2H5Br on the bromine budget of the stratosphere. Atmospheric observations of these gases allow constraints on surface mixing ratios that, when incorporated into our model, contribute ~ 4.9–5.2 parts per trillion (ppt) of inorganic bromine (Bry) to the stratosphere. Of this total, ~ 76 % comes from naturally-emitted CHBr3 and CH2Br2. The remaining species individually contribute modest amounts. However, their accumulated total accounts for up to ~ 1.2 ppt of the supply and thus should not be ignored. We have compared modelled tropical profiles of a range of VSLS with observations from the recent 2009 NSF HIPPO-1 aircraft campaign. Modelled profiles agree reasonably well with observations from the surface to the lower tropical tropopause layer. We have also considered the poorly studied anthropogenic VSLS, C2H5Br, CH2BrCH2Br, n-C3H7Br and i-C3H7Br. We find the local atmospheric lifetime of these species in the tropical tropopause layer are ~ 183, 603, 39 and 49 days, respectively. These species, particularly C2H5Br and CH2BrCH2Br, would thus be important carriers of bromine to the stratosphere if emissions were to increase substantially. Our model shows ~ 70–73 % and ~ 80–85 % of bromine from these species in the tropical boundary layer can reach the lower stratosphere.

scholarly journals Tracer measurements in the tropical tropopause layer during the AMMA/SCOUT-O3 aircraft campaign

2010 ◽  
Vol 10 (8) ◽  
pp. 3615-3627 ◽  
Author(s):  
C. D. Homan ◽  
C. M. Volk ◽  
A. C. Kuhn ◽  
A. Werner ◽  
J. Baehr ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Transport Processes ◽  
Gradual Transition ◽  
Tropical Tropopause Layer ◽  
Mixing Ratios ◽  
Tropical Tropopause ◽  
Multidisciplinary Analysis ◽  
The Tropics

Abstract. We present airborne in situ measurements made during the AMMA (African Monsoon Multidisciplinary Analysis)/SCOUT-O3 campaign between 31 July and 17 August 2006 on board the M55 Geophysica aircraft, based in Ouagadougou, Burkina Faso. CO2 and N2O were measured with the High Altitude Gas Analyzer (HAGAR), CO was measured with the Cryogenically Operated Laser Diode (COLD) instrument, and O3 with the Fast Ozone ANalyzer (FOZAN). We analyse the data obtained during five local flights to study the dominant transport processes controlling the tropical tropopause layer (TTL, here ~350–375 K) and lower stratosphere above West-Africa: deep convection up to the level of main convective outflow, overshooting of deep convection, and horizontal inmixing across the subtropical tropopause. Besides, we examine the morphology of the stratospheric subtropical barrier. Except for the flight of 13 August, distinct minima in CO2 mixing ratios indicate convective outflow of boundary layer air in the TTL. The CO2 profiles show that the level of main convective outflow was mostly located at potential temperatures between 350 and 360 K, and for 11 August reached up to 370 K. While the CO2 minima indicate quite significant convective influence, the O3 profiles suggest that the observed convective signatures were mostly not fresh, but of older origin (several days or more). When compared with the mean O3 profile measured during a previous campaign over Darwin in November 2005, the O3 minimum at the main convective outflow level was less pronounced over Ouagadougou. Furthermore O3 mixing ratios were much higher throughout the whole TTL and, unlike over Darwin, rarely showed low values observed in the regional boundary layer. Signatures of irreversible mixing following overshooting of convective air were scarce in the tracer data. Some small signatures indicative of this process were found in CO2 profiles between 390 and 410 K during the flights of 4 and 8 August, and in CO data at 410 K on 7 August. However, the absence of expected corresponding signatures in other tracer data makes this evidence inconclusive, and overall there is little indication from the observations that overshooting convection has a profound impact on gas-phase tracer TTL composition during AMMA. We find the amount of photochemically aged air isentropically mixed into the TTL across the subtropical tropopause to be not significant. Using the N2O observations we estimate the fraction of aged extratropical stratospheric air in the TTL to be 0.0±0.1 up to 370 K during the local flights. Above the TTL this fraction increases to 0.3±0.1 at 390 K. The subtropical barrier, as indicated by the slope of the correlation between N2O and O3 between 415 and 490 K, does not appear as a sharp border between the tropics and extratropics, but rather as a gradual transition region between 10° N and 25° N where isentropic mixing between these two regions may occur.

scholarly journals The role of horizontal model resolution in assessing the transport of CO in a middle latitude cyclone using WRF-Chem

2014 ◽  
Vol 14 (2) ◽  
pp. 609-627 ◽  
Author(s):  
C. A. Klich ◽  
H. E. Fuelberg
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Deep Convection ◽  
Middle Latitude ◽  
Convective Transport ◽  
Vertical Transport ◽  
Squall Line ◽  
Grid Spacing ◽  
Chemical Transport Model ◽  
Hysplit Model

Abstract. We use the Weather Research and Forecasting with Chemistry (WRF-Chem) online chemical transport model to simulate a middle latitude cyclone in East Asia at three different horizontal resolutions (45, 15, and 5 km grid spacing). The cyclone contains a typical warm conveyor belt (WCB) with an embedded squall line that passes through an area having large surface concentrations (> 400 ppbv) of carbon monoxide (CO). Model output from WRF-Chem is used to compare differences between the large-scale CO vertical transport by the WCB (the 45 km simulation) with the smaller-scale transport due to its convection (the 5 km simulation). Forward trajectories are calculated from WRF-Chem output using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. At 45 km grid spacing, the WCB exhibits gradual ascent, lofting surface CO to 6–7 km. Upon reaching the warm front, the WCB and associated CO ascend more rapidly and later turn eastward over the Pacific Ocean. Convective transport at 5 km resolution with explicitly resolved convection occurs much more rapidly, with surface CO lofted to altitudes greater than 10 km in 1 h or less. We also compute CO vertical mass fluxes over specified areas and times to compare differences in transport due to the different grid spacings. Upward CO flux exceeds 110 000 t h−1 in the domain with explicit convection when the squall line is at peak intensity, while fluxes from the two coarser resolutions are an order of magnitude smaller. Specific areas of interest within the 5 km domain are defined to compare the magnitude of convective transport to that within the entire 5 km region. Although convection encompasses only a small portion of the 5 km domain, it is responsible for ~40% of the upward CO transport. We also examine the vertical transport due to a short wave trough and its associated area of convection, not related to the cyclone, that lofts CO to the upper troposphere. Results indicate that fine-scale resolution with explicitly resolved convection is important when assessing the vertical transport of surface emissions in areas of deep convection.

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