Investigating the roles of the Asian monsoon, the North American monsoon, and Hurricanes for efficient transport of chlorinated short-lived species to the UTLS based on in situ observations

2021 ◽  
Author(s):  
Valentin Lauther ◽  
Johannes Wintel ◽  
Emil Gerhardt ◽  
Andrea Rau ◽  
Peter Hoor ◽  
...  
Keyword(s):  
High Altitude ◽  
Central America ◽  
North American ◽  
Asian Summer Monsoon ◽  
North American Monsoon ◽  
Mixing Ratios ◽  
The North ◽  
Asian Summer ◽  
Efficient Transport

<p>Chlorinated very short-lived substances (Cl-VSLS) are not controlled by the Montreal Protocol but the recent emission increase of the Cl-VSLS CH<sub>2</sub>Cl<sub>2</sub> (Dichloromethane) and CHCl<sub>3</sub> (Chloroform) is believed to significantly increase the stratospheric chlorine loading from VSLS. Provided efficient transport of Cl-VSLS from the source region into the stratosphere further emission increases could ultimately even cause a significant delay of the predicted recovery date of the ozone layer to pre-1980 values. During the WISE (Wave-driven ISentropic Exchange) campaign in autumn 2017 excessive probing of the UTLS (upper troposphere lower stratosphere) region above Western Europe and the Atlantic Ocean was conducted from aboard the HALO (High Altitude and Long range) research aircraft. We use real-time in situ WISE measurements of CH<sub>2</sub>Cl<sub>2</sub> and CHCl<sub>3</sub> from HAGAR-V (High Altitude Gas AnalyzeR – 5 channel version) in correlation with N<sub>2</sub>O from UMAQS (University of Mainz Airborne QCL Spectrometer), as well as CLaMS (Chemical Lagrangian Model of the Stratosphere) global 3-dimensional simulations of air mass origin tracers and backward trajectories to identify the most efficient transport mechanisms for Cl-VSLS entering the LS region in northern hemispheric summer.</p><p>The WISE measurements reveal two distinct transport pathways into the UTLS region of particularly CH<sub>2</sub>Cl<sub>2</sub>-rich and CH<sub>2</sub>Cl<sub>2</sub>-poor air. CH<sub>2</sub>Cl<sub>2</sub>-rich air could be identified to be transported by the Asian summer monsoon within about 4-10 weeks from its source regions in Asia into the stratosphere above the Atlantic Ocean at around 380 K and above. CH<sub>2</sub>Cl<sub>2</sub>-poor air could be identified to be mainly uplifted to potential temperatures of about 365 K by the North American monsoon above the region of Central America with transport times of only 2-5 weeks. In addition, we could link backward trajectories of CH<sub>2</sub>Cl<sub>2</sub>-poor air in the LS region to be uplifted by the category 5 hurricane Maria in September 2017. Based on all analyzed WISE measurements, we found that almost all young (transport time < 4 months) air masses were uplifted either above Asia or above Central America, emphasizing not only the impact of the Asian summer monsoon on the stratospheric tracer distribution but also that of the North American monsoon and hurricanes.</p><p>The measurements of both CH<sub>2</sub>Cl<sub>2</sub> and CHCl<sub>3</sub> show the lowest stratospheric mixing ratios originating in the region of Central America and enhanced mixing ratios from Asia (enhancements > 100 % and > 50 %, respectively). However, the source distribution of CHCl<sub>3</sub> is much less clear than that of CH<sub>2</sub>Cl<sub>2</sub> and inconspicuous CH<sub>2</sub>Cl<sub>2</sub> measurements can also contain enhanced CHCl<sub>3</sub> mixing ratios. Nevertheless, the anthropogenic impact on CHCl<sub>3</sub> -rich air from Asia is clearly visible in the measurements and we believe it is likely that a future increase of Asian CHCl<sub>3</sub> emissions could lead to similarly large stratospheric enhancements as already observed for CH<sub>2</sub>Cl<sub>2</sub>. Consequently, this would further increase ozone depletion from stratospheric chlorine deposition of VSLS.</p>

scholarly journals Thunderstorms and upper troposphere chemistry during the early stages of the 2006 North American Monsoon

2012 ◽  
Vol 12 (7) ◽  
pp. 16407-16455 ◽  
Author(s):  
M. C. Barth ◽  
J. Lee ◽  
A. Hodzic ◽  
G. Pfister ◽  
W. C. Skamarock ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North American ◽  
Rocky Mountains ◽  
Gulf Coast ◽  
North American Monsoon ◽  
Chemical Production ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The North

Abstract. In this study, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is applied at 4 km horizontal grid spacing to study the meteorology and chemistry over the continental US and Northern Mexico region for the 15 July to 7 August 2006 period, which coincides with the early stages of the North American Monsoon. Evaluation of model results shows that WRF-Chem reasonably represents the large-scale meteorology and strong convective storms, but tends to overestimate weak convection. In the upper troposphere, the WRF-Chem model predicts ozone and carbon monoxide (CO) to within 10–20% of aircraft and sonde measurements. However, the frequency distribution from satellite data indicates that WRF-Chem is lofting too much CO from the boundary layer (BL). Because ozone mixing ratios agree well with these same satellite data, it suggests that chemical production of O3 in the model is overpredicted and compensates for the excess convective lofting of BL air. Analysis of different geographic regions (West Coast, Rocky Mountains, Central Plains, Midwest, and Gulf Coast) reveals that much of the convective transport occurs in the Rocky Mountains, while much of the UT ozone chemical production occurs over the Gulf Coast and Midwest regions where both CO and volatile organic compounds (VOCs) are abundant in the upper troposphere and promote the production of peroxy radicals. In all regions most of the ozone chemical production occurs within 24 h of the air being lofted from the boundary layer. In addition, analysis of the anticyclone and adjacent air indicates that ozone mixing ratios within the anticyclone region associated with the North American Monsoon and just outside the anticyclone are similar. Increases of O3 within the anticyclone are strongly coincident with entrainment of stratospheric air into the anticyclone, but also are from in situ O3 chemical production. In situ O3 production is up to 17% greater within the anticyclone than just outside the anticyclone when the anticyclone is over the Southern US indicating that the enhancement of O3 is most pronounced over regions with abundant VOCs.

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.

Results from a comparison of HCN measurements and Lagrangian backtrajectory analyses in the Asian Summer Monsoon Anticyclone

2020 ◽  
Author(s):  
Yun Li ◽  
Bärbel Vogel ◽  
Felix Plöger ◽  
Silvia Bucci ◽  
Bernard Legras ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Atmospheric Composition ◽  
Convective Activity ◽  
Mixing Ratios ◽  
Research Aircraft ◽  
Asian Summer ◽  
Good Tracer

&lt;p&gt;The StratoClim aircraft field campaign took place from Kathmandu, Nepal, in summer 2017 in&lt;br&gt;order to study the atmospheric composition, chemistry, and dynamics in the Asian Summer&lt;br&gt;Monsoon Anticyclone (ASMA) which is known to transport surface emissions to the mid-latitude&lt;br&gt;lower stratosphere and the stratosphere worldwide. Hydrogen cyanide (HCN) which is primarily&lt;br&gt;emitted from biomass burning and has a UTLS lifetime on the order of 1-2 years is a good tracer for&lt;br&gt;biomass burning import into the lower and free stratosphere.&lt;br&gt;HCN in the ASM Upper Troposphere and Lower Stratosphere (UTLS) was measured in-situ&lt;br&gt;employing the Chemical-Ionization Time-of-Flight Mass Spectrometer FUNMASS on board the&lt;br&gt;high-altitude research aircraft M55-Geophysica. The observed HCN mixing ratios in and above the&lt;br&gt;ASMA exhibit interesting vertical and horizontal signatures around the tropopause as well as in the&lt;br&gt;LS probably resulting from convective activity or air mass origin (AMO). We here compare&lt;br&gt;measured HCN to Lagrangian simulations by the ClaMS and TRACZILLA models which employ&lt;br&gt;two different approaches to represent higher-reaching convective events. The simulations succeed to&lt;br&gt;track some of the observed HCN features back to convective activity or AMO. The quality of the&lt;br&gt;reproduction and further outcomes on the atmospheric relevance will be discussed in the&lt;br&gt;presentation.&lt;/p&gt;

Synthesis of Results from the North American Monsoon Experiment (NAME) Process Study

2007 ◽  
Vol 20 (9) ◽  
pp. 1601-1607 ◽  
Author(s):  
Wayne Higgins ◽  
David Gochis
Keyword(s):  
United States ◽  
Central America ◽  
North American ◽  
The United States ◽  
Background Information ◽  
North American Monsoon ◽  
The North ◽  
Process Study ◽  
Monsoon System ◽  
United States Mexico

Abstract An international team of scientists from the United States, Mexico, and Central America carried out a major field campaign during the summer of 2004 to develop an improved understanding of the North American monsoon system leading to improved precipitation forecasts. Results from this campaign, which is the centerpiece of the North American Monsoon Experiment (NAME) Process Study, are reported in this issue of the Journal of Climate. In addition to a synthesis of key findings, this brief overview article also raises some important unresolved issues that require further attention. More detailed background information on NAME, including motivating science questions, where NAME 2004 was conducted, when, and the experimental design, was published previously by Higgins et al.

scholarly journals Trace gas composition in the Asian summer monsoon anticyclone: A case study based on aircraft observations and model simulations

2016 ◽  
Author(s):  
Klaus-D. Gottschaldt ◽  
Hans Schlager ◽  
Robert Baumann ◽  
Heiko Bozem ◽  
Veronika Eyring ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Atmospheric Chemistry ◽  
Asian Summer Monsoon ◽  
Trace Gas ◽  
Gas Composition ◽  
Back Trajectories ◽  
Air Masses ◽  
Mixing Ratios ◽  
Asian Summer

Abstract. We present in-situ measurements of the trace gas composition of the upper tropospheric (UT) Asian summer monsoon anticyclone (ASMA) performed with the High Altitude and LOng range (HALO) research aircraft in the frame of the Earth System Model Validation (ESMVal) campaign. Air masses with enhanced O3 mixing ratios were encountered after entering the ASMA at its southern edge at about 150 hPa on 18 September 2012. This is in contrast to previous studies, reporting that the anticyclone's interior is dominated by recently uplifted air with low O3 in the monsoon season. We also observed enhanced CO and HCl in the ASMA, tracers for boundary layer pollution and tropopause layer (TL) air or stratospheric inmixing, respectively. In addition, reactive nitrogen was enhanced in the ASMA. Along the HALO flight track across the ASMA boundary, strong gradients of these tracers separate anticyclonic from outside air. Lagrangian trajectory calculations using HYSPLIT show that HALO sampled three times a filament of UT air, which included air masses uplifted from the lower or mid troposphere north of the Bay of Bengal. The trace gas gradients between UT and uplifted air masses were preserved during transport within a belt of streamlines fringing the central part of the anticyclone (fringe), but are smaller than the gradients across the ASMA boundary. Our data represent the first in-situ observations across the southern and downstream the eastern ASMA flank, respectively. Back-trajectories starting at the flight track furthermore indicate that HALO transected the ASMA where it was just splitting into a Tibetan and an Iranian part. The O3-rich filament is diverted from the fringe towards the interior of the original anticyclone, and at least partially bound to become part of the new Iranian eddy. A simulation with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model is found to reproduce the observations reasonably well. It shows that O3-rich air is entrained by the outer streamlines of the anticyclone at its eastern flank. Back-trajectories and increased HCl mixing ratios indicate that the entrained air originates in the stratospherically influenced TL. Photochemical ageing of air masses in the ASMA additionally increases O3 in originally O3-poor, but CO-rich air. Simulated monthly mean trace gas distributions show decreased O3 in the ASMA centre not in general, but only at the 100 hPa level in July and August, as also reported by previous studies. However, at lower altitudes and in September the ASMA is dominated by increased O3, indicating that the above processes are more important for the ASMA trace gas budgets than previously thought.

scholarly journals Trace gas composition in the Asian summer monsoon anticyclone: a case study based on aircraft observations and model simulations

2017 ◽  
Vol 17 (9) ◽  
pp. 6091-6111 ◽  
Author(s):  
Klaus-D. Gottschaldt ◽  
Hans Schlager ◽  
Robert Baumann ◽  
Heiko Bozem ◽  
Veronika Eyring ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Trace Gas ◽  
Gas Composition ◽  
Back Trajectories ◽  
Air Masses ◽  
Mixing Ratios ◽  
Asian Summer ◽  
In Situ Observations

Abstract. We present in situ measurements of the trace gas composition of the upper tropospheric (UT) Asian summer monsoon anticyclone (ASMA) performed with the High Altitude and Long Range Research Aircraft (HALO) in the frame of the Earth System Model Validation (ESMVal) campaign. Air masses with enhanced O3 mixing ratios were encountered after entering the ASMA at its southern edge at about 150 hPa on 18 September 2012. This is in contrast to the presumption that the anticyclone's interior is dominated by recently uplifted air with low O3 in the monsoon season. We also observed enhanced CO and HCl in the ASMA, which are tracers for boundary layer pollution and tropopause layer (TL) air or stratospheric in-mixing respectively. In addition, reactive nitrogen was enhanced in the ASMA. Along the HALO flight track across the ASMA boundary, strong gradients of these tracers separate anticyclonic from outside air. Lagrangian trajectory calculations using HYSPLIT show that HALO sampled a filament of UT air three times, which included air masses uplifted from the lower or mid-troposphere north of the Bay of Bengal. The trace gas gradients between UT and uplifted air masses were preserved during transport within a belt of streamlines fringing the central part of the anticyclone (fringe), but are smaller than the gradients across the ASMA boundary. Our data represent the first in situ observations across the southern part and downstream of the eastern ASMA flank. Back-trajectories starting at the flight track furthermore indicate that HALO transected the ASMA where it was just splitting into a Tibetan and an Iranian part. The O3-rich filament is diverted from the fringe towards the interior of the original anticyclone, and is at least partially bound to become part of the new Iranian eddy. A simulation with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model is found to reproduce the observations reasonably well. It shows that O3-rich air is entrained by the outer streamlines of the anticyclone at its eastern flank. Back-trajectories and increased HCl mixing ratios indicate that the entrained air originates in the stratospherically influenced TL. Photochemical ageing of air masses in the ASMA additionally increases O3 in originally O3-poor, but CO-rich air. Simulated monthly mean trace gas distributions show decreased O3 in the ASMA centre only at the 100 hPa level in July and August, but at lower altitudes and in September the ASMA is dominated by increased O3. The combination of entrainment from the tropopause region, photochemistry and dynamical instabilities can explain the in situ observations, and might have a larger impact on the highly variable trace gas composition of the anticyclone than previously thought.

scholarly journals Thunderstorms and upper troposphere chemistry during the early stages of the 2006 North American Monsoon

2012 ◽  
Vol 12 (22) ◽  
pp. 11003-11026 ◽  
Author(s):  
M. C. Barth ◽  
J. Lee ◽  
A. Hodzic ◽  
G. Pfister ◽  
W. C. Skamarock ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Satellite Data ◽  
North American ◽  
Rocky Mountains ◽  
Gulf Coast ◽  
North American Monsoon ◽  
Chemical Production ◽  
Upper Troposphere ◽  
The North

Abstract. To study the meteorology and chemistry that is associated with the early stages of the North American Monsoon, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is applied for the first time at high resolution (4 km grid spacing, allowing for explicit representation of convection) over a large region (continental US and northern Mexico) for a multi-week (15 July to 7 August 2006) integration. Evaluation of model results shows that WRF-Chem reasonably represents the large-scale meteorology and strong convective storms, but tends to overestimate weak convection. In the upper troposphere, the WRF-Chem model predicts ozone (O3) and carbon monoxide (CO) to within 10–20% of aircraft and sonde measurements. Comparison of UT O3 and CO frequency distributions between WRF-Chem and satellite data indicates that WRF-Chem is lofting CO too frequently from the boundary layer (BL). This excessive lofting should also cause biases in the WRF-Chem ozone frequency distribution; however it agrees well with satellite data suggesting that either the chemical production of O3 in the model is overpredicted or there is too much stratosphere to troposphere transport in the model. Analysis of different geographic regions (West Coast, Rocky Mountains, Central Plains, Midwest, and Gulf Coast) reveals that much of the convective transport occurs in the Rocky Mountains, while much of the UT ozone chemical production occurs over the Gulf Coast and Midwest regions where both CO and volatile organic compounds (VOCs) are abundant in the upper troposphere and promote the production of peroxy radicals. In all regions most of the ozone chemical production occurs within 24 h of the air being lofted from the boundary layer. In addition, analysis of the anticyclone and adjacent air indicates that ozone mixing ratios within the anticyclone region associated with the North American Monsoon and just outside the anticyclone are similar. Increases of O3 within the anticyclone are strongly coincident with entrainment of stratospheric air into the anticyclone, but also are from in situ O3 chemical production. In situ O3 production is up to 17% greater within the anticyclone than just outside the anticyclone when the anticyclone is over the southern US indicating that the enhancement of O3 is most pronounced over regions with abundant VOCs.

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