Infrequent, Rapid Transport Pathways to the Summer North American Upper Troposphere and Lower Stratosphere

2020 ◽  
Author(s):  
Xinyue Wang ◽  
William Randel ◽  
Wu Yutian
Keyword(s):  
North American ◽  
Lower Stratosphere ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Rapid Transport

scholarly journals The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

2019 ◽  
Author(s):  
Xiaolu Yan ◽  
Paul Konopka ◽  
Felix Ploeger ◽  
Aurélien Podglajen ◽  
Jonathon S. Wright ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
North American ◽  
Lower Stratosphere ◽  
Atmospheric Composition ◽  
Transport Pathways ◽  
Transport Efficiency ◽  
Upper Troposphere ◽  
Horizontal Transport ◽  
The Tropics ◽  
K Transport

Abstract. Transport of pollutants into the stratosphere via the Asian summer monsoon (ASM) or North American summer monsoon (NASM) may affect the atmospheric composition and climate both locally and globally. We identify and study the robust characteristics of transport from the ASM and NASM regions to the stratosphere using the Lagrangian chemistry transport model CLaMS as driven by the ERA-Interim and MERRA-2 reanalyses. In particular, we investigate the relative influences of the ASM and NASM on stratospheric composition, the transport pathways by which these influences are effected, and the quantitative contributions and efficiencies of transport from different altitudes in these two monsoon regions to the stratosphere. We release artificial tracers in several vertical layers from the middle troposphere to the lower stratosphere in both ASM and NASM source regions during July and August 2010–2013 and track their evolution until the following summer. We find that the magnitude of transport from the ASM and NASM regions to the tropical stratosphere, and even to the Southern Hemispheric stratosphere, is higher when the tracers are released at the 350–360 K level. For tracers released close to the tropopause (370–380 K), transport is primarily into the Northern Hemispheric stratosphere. Results for different vertical layers or air origin reveal two transport pathways from the upper troposphere over the ASM and NASM regions to the tropical pipe: (i) quasi-horizontal transport to the tropics below the tropopause followed by ascent to the stratosphere via tropical upwelling, and (ii) ascent into the stratosphere inside the ASM/NASM followed by quasi-horizontal transport to the tropical lower stratosphere and tropical pipe. The tropical pathway (i) is faster than the monsoon pathway (ii), particularly in the ascending branch. Ultimately, the abundance of air in the tropical pipe that originates in the ASM upper troposphere (350–360 K, ~ 5 %) is comparable to that of air ascending directly from the tropics ten months after the release of the source tracers. By contrast, the air mass contributions from the ASM to the tropical pipe are about three times larger than the corresponding contribution from the NASM (~ 1.5 %). The transport efficiency into the tropical pipe, normalized by the mass of the domain, is greatest from the ASM region at 370–380 K. Transport from the ASM to the tropical pipe is almost twice as efficient as transport from the NASM or tropics to the tropical pipe. Although the contribution from the NASM to the stratosphere is less than that from either the ASM or the tropics, the transport efficiency from the NASM is comparable to that from the tropics.

scholarly journals The efficiency of transport into the stratosphere via the Asian and North American summer monsoon circulations

2019 ◽  
Vol 19 (24) ◽  
pp. 15629-15649 ◽  
Author(s):  
Xiaolu Yan ◽  
Paul Konopka ◽  
Felix Ploeger ◽  
Aurélien Podglajen ◽  
Jonathon S. Wright ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
North American ◽  
Lower Stratosphere ◽  
Atmospheric Composition ◽  
Transport Pathways ◽  
Air Mass ◽  
Transport Efficiency ◽  
Upper Troposphere ◽  
Horizontal Transport ◽  
The Tropics

Abstract. Transport of pollutants into the stratosphere via the Asian summer monsoon (ASM) or North American summer monsoon (NASM) may affect the atmospheric composition and climate both locally and globally. We identify and study the robust characteristics of transport from the ASM and NASM regions to the stratosphere using the Lagrangian chemistry transport model CLaMS driven by both the ERA-Interim and MERRA-2 reanalyses. In particular, we quantify the relative influences of the ASM and NASM on stratospheric composition and investigate the transport pathways and efficiencies of transport of air masses originating at different altitudes in these two monsoon regions to the stratosphere. We release artificial tracers in several vertical layers from the middle troposphere to the lower stratosphere in both ASM and NASM source regions during July and August 2010–2013 and track their evolution until the following summer. We find that more air mass is transported from the ASM and NASM regions to the tropical stratosphere, and even to the southern hemispheric stratosphere, when the tracers are released clearly below the tropopause (350–360 K) than when they are released close to the tropopause (370–380 K). For tracers released close to the tropopause (370–380 K), transport is primarily into the northern hemispheric lower stratosphere. Results for different vertical layers of air origin reveal two transport pathways from the upper troposphere over the ASM and NASM regions to the tropical pipe: (i) quasi-horizontal transport to the tropics below the tropopause followed by ascent to the stratosphere via tropical upwelling, and (ii) ascent into the stratosphere inside the ASM/NASM followed by quasi-horizontal transport to the tropical lower stratosphere and further to the tropical pipe. Overall, the tropical pathway (i) is faster than the monsoon pathway (ii), particularly in the ascending branch. The abundance of air in the tropical pipe that originates in the ASM upper troposphere (350–360 K) is comparable to the abundance of air ascending directly from the tropics to the tropical pipe 10 months after (the following early summer) the release of the source tracers. The air mass contributions from the ASM to the tropical pipe are about 3 times larger than the corresponding contributions from the NASM. The transport efficiency into the tropical pipe, the air mass fraction inside this destination region normalized by the mass of the domain of origin, is greatest from the ASM region at 370–380 K. Although the contribution from the NASM to the stratosphere is less than that from either the ASM or the tropics, the transport efficiency from the NASM is comparable to that from the tropics.

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 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.

scholarly journals Chemical isolation in the Asian monsoon anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS) data

2008 ◽  
Vol 8 (3) ◽  
pp. 757-764 ◽  
Author(s):  
M. Park ◽  
W. J. Randel ◽  
L. K. Emmons ◽  
P. F. Bernath ◽  
K. A. Walker ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Chemical Constituents ◽  
Strong Correlations ◽  
Near Surface ◽  
Upper Troposphere ◽  
Relative Age ◽  
Rapid Transport ◽  
Chemistry Experiment

Abstract. Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer instrument during summer (June–August) of 2004–2006. Carbon monoxide (CO) shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS); these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13–15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl) exhibit decreased values inside the anticyclone between ~12–20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air) suggest relatively rapid transport of fresh emissions up to the tropopause level inside the anticyclone.

scholarly journals In situ observations of CH<sub>2</sub>Cl<sub>2</sub> and CHCl<sub>3</sub> show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and North American summer monsoons

2021 ◽  
Author(s):  
Valentin Lauther ◽  
Bärbel Vogel ◽  
Johannes Wintel ◽  
Andrea Rau ◽  
Peter Hoor ◽  
...  
Keyword(s):  
North American ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
Late Summer ◽  
Anthropogenic Sources ◽  
North American Monsoon ◽  
Transport Pathway ◽  
Transport Pathways ◽  
Mixing Ratios ◽  
The North

Abstract. Efficient transport pathways for ozone depleting very short-lived substances (VSLS) from their source regions into the stratosphere are a matter of current scientific debate, however they have yet to be fully identified on an observational basis. Understanding the increasing impact of chlorine containing VSLS (Cl-VSLS) on stratospheric ozone depletion is important in order to validate and improve model simulations and future predictions. We report on the first transport study using airborne in situ measurements of the Cl-VSLS dichloromethane (CH2Cl2) and trichloromethane (chloroform, CHCl3) to derive a detailed description of the two most efficient and fast transport pathways from (sub-)tropical source regions into the extratropical lower stratosphere (Ex-LS) in northern hemisphere (NH) late summer. The Cl-VSLS measurements were obtained in the upper troposphere and lower stratosphere (UTLS) above Western Europe and the mid latitude Atlantic Ocean in the frame of the WISE (Wave-driven ISentropic Exchange) aircraft campaign in autumn 2017 and are combined with the results from a three-dimensional simulation of a Lagrangian transport model as well as back-trajectory calculations. Compared to background measurements of similar age we find up to 150 % enhanced CH2Cl2 and up to 100 % enhanced CHCl3 mixing ratios in the Ex-LS. We link the measurements of enhanced mixing ratios to emissions in the region of southern and eastern Asia. Transport from this area to the Ex-LS at potential temperatures in the range of 370–400 K takes about 5–10 weeks via the Asian summer monsoon anticyclone (ASMA). Our measurements suggest anthropogenic sources to be the cause of these strongly elevated Cl-VSLS concentrations observed at the top of the lowermost stratosphere (LMS). A faster transport pathway into the Ex-LS is derived from particularly low CH2Cl2 and CHCl3 mixing ratios in the UTLS. These low mixing ratios reflect weak emission sources and a local seasonal minimum of both species in the boundary layer of Central America and the tropical Atlantic. We show that air masses uplifted by hurricanes, the North American monsoon, and general convection above Central America into the tropical tropopause layer to potential temperatures of about 360–370 K are transported isentropically within 1–5 weeks into the Ex-LS. This transport pathway linked to the North American monsoon mainly impacts the middle and lower part of the LMS with particularly low CH2Cl2 and CHCl3 mixing ratios. In a case study, we specifically analyze air samples directly linked to the uplift by the category 5 hurricane Maria that occurred during October 2017 above the Atlantic Ocean. Regionally differing CHCl3 : CH2Cl2 emission ratios derived from our UTLS measurements suggest a clear similarity between CHCl3 and CH2Cl2 when emitted by anthropogenic sources and differences between the two species mainly caused by additional, likely biogenic, CHCl3 sources. Overall, the transport of strongly enhanced CH2Cl2 and CHCl3 mixing ratios from southern and eastern Asia via the ASMA is the main factor for increasing the chlorine loading from the analyzed VSLS in the Ex-LS during NH late summer. Thus, further increases in Asian CH2Cl2 and CHCl3 emissions, as frequently reported in recent years, will further increase the impact of Cl-VSLS on stratospheric ozone depletion.

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 (20) ◽  
pp. 11477-11499 ◽  
Author(s):  
S. Fadnavis ◽  
K. Semeniuk ◽  
M. G. Schultz ◽  
M. Kiefer ◽  
A. Mahajan ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Peroxyacetyl Nitrate ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Asian Summer ◽  
Emission Change ◽  
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 peroxyacetyl nitrate (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 compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere (UT). Remote transport also occurs in the extratropical UT where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. Sensitivity experiments with ECHAM5–HAMMOZ for simultaneous NOx and non-methane volatile organic compounds (NMVOCs) emission change (−10 %) over ASM, NAM and WAM confirm similar transport. Our analysis shows that a 10 % change in Asian emissions transports ~ 5–30 ppt of PAN in the UTLS over Asia, ~ 1–10 ppt of PAN in the UTLS of northern subtropics and mid-latitudes, ~ 7–10 ppt of HNO3 and ~ 1–2 ppb of ozone in UT over Asia. Comparison of emission change over Asia, North America and Africa shows that the highest transport of HNO3 and ozone occurs in the UT over Asia and least over Africa. 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. Simulations with and without lightning show an increase in the concentrations of PAN (~ 40 %), HNO3 (75 %), NOx (70 %) and ozone (30 %) over the regions of convective transport. Lightning-induced production of these species is higher over equatorial Africa and America compared to the ASM region. This indicates that the contribution of anthropogenic emissions to PAN in the UTLS over the ASM is higher than that of lightning.

scholarly journals Chemical Isolation in the Asian monsoon anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS) data

2007 ◽  
Vol 7 (5) ◽  
pp. 13839-13860 ◽  
Author(s):  
M. Park ◽  
W. J. Randel ◽  
L. K. Emmons ◽  
P. F. Bernath ◽  
K. A. Walker ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Chemical Constituents ◽  
Strong Correlations ◽  
Near Surface ◽  
Upper Troposphere ◽  
Relative Age ◽  
Rapid Transport ◽  
Chemistry Experiment

Abstract. Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer instrument during summer (June–August) of 2004–2006. Carbon monoxide (CO) shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS); these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13–15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl) exhibit decreased values inside the anticyclone between ~12–20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air) suggest relatively rapid transport of fresh emissions up to tropopause level inside the anticyclone.

Comparison of Aura MLS Water Vapor Measurements with GFS and NAM Analyses in the Upper Troposphere–Lower Stratosphere

2010 ◽  
Vol 27 (2) ◽  
pp. 274-289 ◽  
Author(s):  
Le Van Thien ◽  
William A. Gallus ◽  
Mark A. Olsen ◽  
Nathaniel Livesey
Keyword(s):  
Water Vapor ◽  
North American ◽  
Lower Stratosphere ◽  
Model Analysis ◽  
Weather Research And Forecasting ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Four Seasons ◽  
Gfs Model ◽  
The Tropics

Abstract Water vapor mixing ratios in the upper troposphere and lower stratosphere measured by the Aura Microwave Limb Sounder (MLS) version 2.2 instrument have been compared with Global Forecast System (GFS) analyses at five levels within the 300–100-hPa layer and North American Mesoscale (NAM) model analyses at six levels within the 300–50-hPa layer over the two years of 2005 and 2006 at four analysis times (e.g., 0000, 0600, 1200, and 1800 UTC). Probability density functions of the vapor mixing ratios suggest that both analyses are often moister than Aura MLS values, but NAM model analyses agree somewhat better with Aura MLS measurements than GFS model analyses over the same North American domain at the five common levels. Examining five subsets of the global GFS domain, the GFS model analysis is moister than Aura MLS estimates everywhere but at 150 and 100 hPa in all regions outside of the tropics. NAM model analysis water vapor mixing ratios exceeded the Aura MLS values at all levels from 250 to 150 hPa in all four seasons of both years and some seasons at 100 and 50 hPa. Moist biases in winter and spring of both years were similar at all levels, but these moist biases in summer and fall were smaller in 2005 than in 2006 at all levels. These differences may be due to the change in the NAM from using the Eta Model to using the Weather Research and Forecasting model (WRF) in June 2006.

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