scholarly journals Geographic and seasonal distributions of CO transport pathways and their roles in determining CO centers in the upper troposphere

2011 ◽  
Vol 11 (12) ◽  
pp. 32423-32453
Author(s):  
L. Huang ◽  
R. Fu ◽  
J. H. Jiang ◽  
J. S. Wright ◽  
M. Luo
Keyword(s):  
Lower Troposphere ◽  
Convective Transport ◽  
Boreal Winter ◽  
Transport Pathway ◽  
Austral Spring ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Summer Hemisphere ◽  
Winter Hemisphere ◽  
Co Emission

Abstract. Past studies have identified various pathways along which carbon monoxide (CO) in the tropical upper troposphere (UT) may have been transported from the surface. However, the roles that these transport pathways play in determining the locations and seasonality of CO in the tropical UT remain unclear. In particular, UT CO peaks during the spring and fall seasons when surface CO emission and deep atmospheric convection are moderate relative to those observed during winter and summer. We have developed a method to automate the identification of three pathways that transport CO to the UT, which makes joint use of several A-Train satellite measurements. We use this method to show that the locations and seasonality of the major UT CO centers in the tropics during 2007 were largely determined by local convective transport. On average, the "local convection" pathway, in which convection occurred within a fire region, transported significantly more CO to the UT than the "LT advection → convection" pathway, in which CO was advected within the lower troposphere from a fire region to a convective region prior to convection. To leading order, the seasonality of CO concentrations in the tropical UT followed the seasonality of the "local convection" transport pathway. The centers of highest CO peaked over Central Africa during boreal spring and over South America during austral spring, when the "local convection" transport pathway was most prevalent. During boreal winter and summer, surface CO emission and convection were located in opposite hemispheres, limiting the effectiveness of transport to the UT. In these seasons, CO was mainly transported to the UT via the "LT advection → convection" pathway, in which CO was advected within the lower troposphere from fire source regions in the winter hemisphere to convective regions in the summer hemisphere, or via the "UT advection" pathway, in which UT CO was redistributed from the summer hemisphere to the winter hemisphere.

scholarly journals Geographic and seasonal distributions of CO transport pathways and their roles in determining CO centers in the upper troposphere

2012 ◽  
Vol 12 (10) ◽  
pp. 4683-4698 ◽  
Author(s):  
L. Huang ◽  
R. Fu ◽  
J. H. Jiang ◽  
J. S. Wright ◽  
M. Luo
Keyword(s):  
Central Africa ◽  
Lower Troposphere ◽  
Convective Transport ◽  
Boreal Winter ◽  
Transport Pathway ◽  
Austral Spring ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Joint Application ◽  
The Tropics

Abstract. Past studies have identified a variety of pathways by which carbon monoxide (CO) may be transported from the surface to the tropical upper troposphere (UT); however, the relative roles that these transport pathways play in determining the distribution and seasonality of CO in the tropical UT remain unclear. We have developed a method to automate the identification of two pathways ("local convection" and "advection within the lower troposphere (LT) followed by convective vertical transport") involved in CO transport from the surface to the UT. This method is based on the joint application of instantaneous along-track, co-located, A-Train satellite measurements. Using this method, we find that the locations and seasonality of the UT CO maxima in the tropics were strongly correlated with the frequency of local convective transport during 2007. We also find that the "local convection" pathway (convective transport that occurred within a fire region) typically transported significantly more CO to the UT than the "LT advection → convection" pathway (advection of CO within the LT from a fire region to a convective region prior to convective transport). To leading order, the seasonality of CO concentrations in the tropical UT reflected the seasonality of the "local convection" transport pathway during 2007. The UT CO maxima occurred over Central Africa during boreal spring and over South America during austral spring. Occurrence of the "local convection" transport pathway in these two regions also peaked during these seasons. During boreal winter and summer, surface CO emission and convection were located in opposite hemispheres, which limited the effectiveness of transport to the UT. During these seasons, CO transport from the surface to the UT typically occurred via the "LT advection → convection" pathway.

scholarly journals Impacts of fire emissions and transport pathways on the interannual variation of CO in the tropical upper troposphere

2013 ◽  
Vol 13 (10) ◽  
pp. 25567-25615
Author(s):  
L. Huang ◽  
R. Fu ◽  
J. H. Jiang
Keyword(s):  
El Niño ◽  
Interannual Variation ◽  
El Nino ◽  
Southern Oscillation ◽  
Lower Troposphere ◽  
Transport Pathway ◽  
Central Pacific ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Fire Emissions

Abstract. Carbon monoxide (CO) is an important tracer to study the transport of fire-generated pollutants from the surface to the upper troposphere (UT). This study analyzed the relative importance of fire emission, convection and climate conditions on the interannual variation of CO in the tropical UT, by using satellite observations, reanalysis data and transport pathway auto-identification method developed in our previous study. Empirical orthogonal function (EOF) and singular value decomposition (SVD) methods are used to identify the dominant modes of CO interannual variation in the tropical UT and factors that are related to these modes. Results show that the leading EOF mode is dominated by CO anomalies over Indonesia related to El Niño-Southern Oscillation (ENSO). This is consistent with previous findings by directly evaluating CO anomaly field. Transport pathway analysis suggests that the differences of UT CO between different ENSO types over the tropical continents are mainly dominated by the "local convection" pathway, especially the average CO transported by this pathway. The relative frequency of the "advection within the lower troposphere (LT) followed by convective vertical transport" pathway appears to be responsible only for the UT CO differences over the west-central Pacific between El Niño and La Niña years.

scholarly journals Global climate forcing driven by altered BVOC fluxes from 1990–2010 land cover change in maritime Southeast Asia

2018 ◽  
Author(s):  
Kandice L. Harper ◽  
Nadine Unger
Keyword(s):  
Land Cover ◽  
Southeast Asia ◽  
Land Cover Change ◽  
Radiative Forcing ◽  
Large Scale ◽  
Lower Troposphere ◽  
Convective Transport ◽  
Atmospheric Composition ◽  
Land Cover Changes ◽  
Upper Troposphere

Abstract. Over the period 1990–2010, maritime Southeast Asia experienced large-scale land cover changes, including expansion of high-isoprene-emitting oil palm plantations and contraction of low-isoprene-emitting natural forests. The ModelE2-Yale Interactive Terrestrial Biosphere global chemistry–climate model is used to quantify the atmospheric composition changes and, for the first time, the associated radiative forcing induced by the land-cover-change-driven biogenic volatile organic compound (BVOC) emission changes (+6.5 TgC y−1 isoprene, −0.5 TgC y−1 monoterpenes). Regionally, surface-level ozone concentrations largely decreased (−3.8 to +0.8 ppbv). The tropical land cover changes occurred in a region of strong convective transport, providing a mechanism for the BVOC perturbations to affect the composition of the upper troposphere. Enhanced concentrations of isoprene and its degradation products are simulated in the upper troposphere, and, on a global-mean basis, land cover change had a stronger impact on ozone in the upper troposphere (+0.6 ppbv) than in the lower troposphere (

scholarly journals Tropical convective transport and the Walker circulation

2012 ◽  
Vol 12 (5) ◽  
pp. 12229-12244 ◽  
Author(s):  
J. S. Hosking ◽  
M. R. Russo ◽  
P. Braesicke ◽  
J. A. Pyle
Keyword(s):  
Deep Convection ◽  
Walker Circulation ◽  
Convective Transport ◽  
Boreal Winter ◽  
Maritime Continent ◽  
Transport Pathways ◽  
East Pacific ◽  
Upward Transport ◽  
Fast Transport ◽  
The Walker Circulation

Abstract. We introduce a methodology to visualise rapid vertical and zonal tropical transport pathways. Using prescribed sea-surface temperatures in four monthly model integrations for 2005, preferred transport routes from the troposphere to the stratosphere are found in the model over the Maritime Continent (MC) in November and February, i.e., boreal winter. In these months, the ascending branch of the Walker Circulation over the MC is formed in conjunction with strong deep convection, allowing fast transport into the stratosphere. At the same time, the downwelling branch of the Walker Circulation is enhanced over the East Pacific, compared to other months in 2005, reducing locally the upward transport from emissions below. We conclude that the Walker circulation plays an important role in the seasonality of fast tropical transport from the troposphere to the stratosphere and so impacts at the same time the potential supply of surface emissions.

scholarly journals Tropical convective transport and the Walker circulation

2012 ◽  
Vol 12 (20) ◽  
pp. 9791-9797 ◽  
Author(s):  
J. S. Hosking ◽  
M. R. Russo ◽  
P. Braesicke ◽  
J. A. Pyle
Keyword(s):  
Climate Model ◽  
Deep Convection ◽  
Walker Circulation ◽  
Reanalysis Data ◽  
Convective Transport ◽  
Boreal Winter ◽  
Transport Pathways ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
The Walker Circulation

Abstract. We introduce a methodology to visualise rapid vertical and zonal tropical transport pathways. Using prescribed sea-surface temperatures in four monthly model integrations for 2005, we characterise preferred transport routes from the troposphere to the stratosphere in a high resolution climate model. Most efficient transport is modelled over the Maritime Continent (MC) in November and February, i.e., boreal winter. In these months, the ascending branch of the Walker Circulation over the MC is formed in conjunction with strong deep convection, allowing fast transport into the stratosphere. In the model the upper tropospheric zonal winds associated with the Walker Circulation are also greatest in these months in agreement with ERA-Interim reanalysis data. We conclude that the Walker circulation plays an important role in the seasonality of fast tropical transport from the lower and middle troposphere to the upper troposphere and so impacts at the same time the potential supply of surface emissions to the tropical tropopause layer (TTL) and subsequently to the stratosphere.

Global age of air spectrum from the earth surface to the upper troposphere and tropopause: a model study

2020 ◽  
Author(s):  
Aurelien Podglajen ◽  
Edward Charlesworth ◽  
Felix Ploeger
Keyword(s):  
Time Scales ◽  
Atmospheric Chemistry ◽  
Large Scale ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Convective Transport ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Major Player ◽  
Interhemispheric Transport

<p>Transport of air masses from the surface into the atmosphere occurs via a variety of processes (including clear-air turbulence, atmospheric convection and large-scale circulations), which entails a multitude of transport time scales. This complexity can be characterized in an atmospheric transport model by calculating the age of air spectrum (transit time distribution from the surface). Up to now, mainly the slow time scales of stratospheric and interhemispheric transport (>10 days) have thus been studied. Vertical transport through the troposphere, for which convection is the major player, has only been evaluated using a handful of measured compounds (Radon, CO2 and SF6). However, a wealth of chemically relevant species are affected by the detailed structure of the age spectrum. Recent work (Luo et al., 2018) have used this sensitivity in order to gain observational insights into the tropospheric age spectrum, calling for a comparison with models.</p><p>To that end, we derive upper tropospheric and tropopause age spectra in the EMAC (ECHAM/MESSy Atmospheric Chemistry) model using the Boundary Impulse Response (BIR) method. Because of the large range of time scales involved in tropospheric transport, which extend from tens of minutes (convective transport) to years (stratospheric intrusions), we rely on a suite of pulses with variable durations providing hourly resolution for short time scales (< 12 hours) and monthly for long ones (> 1 month). We first describe the age spectra obtained and their diurnal and seasonal variability. Then, we examine the transport properties from a few specific surface regions to the upper troposphere and stratosphere, with an emphasis on fast pathways from the tropical Western Pacific and on interhemispheric transport. Finally, we investigate the sensitivity of different transport pathways to changes in some of the available model parameterizations (convection) and to different set-ups (using nudging or not).</p>

scholarly journals Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

2014 ◽  
Vol 14 (14) ◽  
pp. 20159-20195 ◽  
Author(s):  
S. Fadnavis ◽  
K. Semeniuk ◽  
M. G. Schultz ◽  
A. Mahajan ◽  
L. Pozzoli ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
North American ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Convective Transport ◽  
Pollution Transport ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry–climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide reservoir species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. The model is evaluated with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-E) and aircraft campaigns during the monsoon season (June–September). There are three regions which contribute substantial pollution to the UTLS during the monsoon: the Asian summer monsoon (ASM), the North American Monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection is deeper into the UTLS as compared to NAM and WAM outflow. The circulation in these monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward to partly merge with the ASM plume. Strong ASM convection transports these remote and regional pollutants into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning generation and thereby the emission of NOy species. This will affect the distribution of PAN in the UTLS. The estimates of lightning produced PAN, HNO3, NOx and ozone obtained from control and lightning-off simulations shows high percentage changes over the regions of convective transport especially equatorial Africa and America and comparatively less over the ASM. This indicates higher anthropogenic pollution transport from the ASM region into the UTLS.

scholarly journals Characteristics of intercontinental transport of tropospheric ozone from Africa to Asia

2018 ◽  
Vol 18 (6) ◽  
pp. 4251-4276 ◽  
Author(s):  
Han Han ◽  
Jane Liu ◽  
Huiling Yuan ◽  
Bingliang Zhuang ◽  
Ye Zhu ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Hadley Cell ◽  
Anthropogenic Sources ◽  
Eastern Africa ◽  
Collective Effects ◽  
Transport Pathway ◽  
Upper Troposphere ◽  
Ozone Precursor ◽  
Somali Jet ◽  
Lightning Nox

Abstract. In this study, we characterize the transport of ozone from Africa to Asia through the analysis of the simulations of a global chemical transport model, GEOS-Chem, from 1987 to 2006. The receptor region Asia is defined within 5–60∘ N and 60–145∘ E, while the source region Africa is within 35∘ S–15∘ N and 20∘ W–55∘ E and within 15–35∘ N and 20∘ W–30∘ E. The ozone generated in the African troposphere from both natural and anthropogenic sources is tracked through tagged ozone simulation. Combining this with analysis of trajectory simulations using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we find that the upper branch of the Hadley cell connects with the subtropical westerlies in the Northern Hemisphere (NH) to form a primary transport pathway from Africa to Asia in the middle and upper troposphere throughout the year. The Somali jet that runs from eastern Africa near the equator to the Indian subcontinent in the lower troposphere is the second pathway that appears only in NH summer. The influence of African ozone mainly appears over Asia south of 40∘ N. The influence shows strong seasonality, varying with latitude, longitude, and altitude. In the Asian upper troposphere, imported African ozone is largest from March to May around 30∘ N (12–16 ppbv) and lowest during July–October around 10∘ N (∼ 2 ppbv). In the Asian middle and lower troposphere, imported African ozone peaks in NH winter between 20 and 25∘ N. Over 5–40∘ N, the mean fractional contribution of imported African ozone to the overall ozone concentrations in Asia is largest during NH winter in the middle troposphere (∼ 18 %) and lowest in NH summer throughout the tropospheric column (∼ 6 %). This seasonality mainly results from the collective effects of the ozone precursor emissions in Africa and meteorology and chemistry in Africa, in Asia and along the transport pathways. The seasonal swing of the Hadley circulation and subtropical westerlies along the primary transport pathway plays a dominant role in modulating the seasonality. There is more imported African ozone in the Asian upper troposphere in NH spring than in winter. This is likely due to more ozone in the NH African upper troposphere generated from biogenic and lightning NOx emissions in NH spring. The influence of African ozone on Asia appears larger in NH spring than in autumn. This can be attributed to both higher altitudes of the elevated ozone in Africa and stronger subtropical westerlies in NH spring. In NH summer, African ozone hardly reaches Asia because of the blocking by the Saharan High, Arabian High, and Tibetan High on the transport pathway in the middle and upper troposphere, in addition to the northward swing of the subtropical westerlies. The seasonal swings of the intertropical convergence zone (ITCZ) in Africa, coinciding with the geographic variations of the ozone precursor emissions, can further modulate the seasonality of the transport of African ozone, owing to the functions of the ITCZ in enhancing lightning NOx generation and uplifting ozone and ozone precursors to upper layers. The strength of the ITCZ in Africa is also found to be positively correlated with the interannual variation of the transport of African ozone to Asia in NH winter. Ozone from NH Africa makes up over 80 % of the total imported African ozone over Asia in most altitudes and seasons. The interhemispheric transport of ozone from southern hemispheric Africa (SHAF) is most evident in NH winter over the Asian upper troposphere and in NH summer over the Asian lower troposphere. The former case is associated with the primary transport pathway in NH winter, while the latter case is associated with the second transport pathway. The intensities of the ITCZ in Africa and the Somali jet can each explain ∼ 30 % of the interannual variations in the transport of ozone from SHAF to Asia in the two cases.

scholarly journals Acetylene C<sub>2</sub>H<sub> 2</sub> retrievals from MIPAS data and regions of enhanced upper tropospheric concentrations in August 2003

2011 ◽  
Vol 11 (19) ◽  
pp. 10243-10257 ◽  
Author(s):  
R. J. Parker ◽  
J. J. Remedios ◽  
D. P. Moore ◽  
V. P. Kanawade
Keyword(s):  
Biomass Burning ◽  
Cross Sections ◽  
Asian Monsoon ◽  
Michelson Interferometer ◽  
Convective Transport ◽  
Random Errors ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Fast Processing

Abstract. Acetylene (C2H2) volume mixing ratios (VMRs) have been successfully retrieved from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) Level 1B radiances during August 2003, providing the first global map of such data and ratios to CO in the literature. The data presented here contain most information between 300 hPa and 100 hPa with systematic errors less than 10% at the upper levels. Random errors per point are less than 15% at lower levels and are closer to 30% at 100 hPa. Global distributions of the C2H2 and C2H2/CO ratio confirm significant features associated with both the Asian monsoon anticyclone and biomass burning for this important hydrocarbon in a characteristic summer month (August 2003), showing tight correlations regionally, particularly at lower to medium values, but globally emphasising the differences between sources and lifetimes of CO and C2H2. The correlations are seen to be particularly disturbed in the regions of highest C2H2 concentrations, indicating variability in the surface emissions or fast processing. A strong isolation of C2H2 within the Asian monsoon anticyclone is observed, evidencing convective transport into the upper troposphere, horizontal advection within the anticyclone at 200 hPa, distinct gradients at the westward edge of the vortex and formation of a secondary dynamical feature from the eastward extension of the anticyclone outflow over the Asian Pacific. Ratios of C2H2/CO are consistent with the evidence from the cross-sections that the C2H2 is uplifted rapidly in convection. Observations are presented of enhanced C2H2 associated with the injection from biomass burning into the upper troposphere and the outflow from Africa at 200 hPa into both the Atlantic and Indian Oceans. In the biomass burning regions, C2H2 and CO are well correlated, but the uplift is less marked and peaks at lower altitudes compared to the strong effects observed in the Asian monsoon anticyclone. Ratios of C2H2/CO clearly decay along transport pathways for the outflow, indicating photochemical ageing of the plumes. Overall, the data show the distinctive nature of C2H2 distributions, confirm in greater detail than previously possible features of hydrocarbon enhancements in the upper troposphere and highlight the future use of MIPAS hydrocarbon data for testing model transport and OH decay regimes in the middle to upper troposphere.

scholarly journals Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

2015 ◽  
Vol 15 (11) ◽  
pp. 15087-15135 ◽  
Author(s):  
S. Fadnavis ◽  
K. Semeniuk ◽  
M. G. Schultz ◽  
M. Kiefer ◽  
A. Mahajan ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
North American ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Convective Transport ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Asian Summer ◽  
Transport Patterns

Abstract. The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. Simulated long term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon season (June–September) in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM), the North American Monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS as compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and be lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning and thereby the formation of additional NOx. This also affects the distribution of PAN in the UTLS. According to sensitivity simulations with and without lightning, increase in concentrations of PAN (~ 40%), HNO3 (75%), NOx (70%) and ozone (30%) over the regions of convective transport, especially over equatorial Africa and America and comparatively less over the ASM. This indicates that PAN in the UTLS over the ASM region is primarily of anthropogenic origin.

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