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

Wang, Xinyue; Randel, William J.; Wu, Yutian

doi:10.1029/2020gl089763

Cited by 3 publications

(3 citation statements)

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“…Further, a study of satellite measured water vapor and radar observed convection occurring over the continental US has demonstrated the importance of the NAMA circulation mediating the convective hydration of the lower stratosphere (Yu et al., 2020). Several trajectory analyses of satellite identified cross‐tropopause convection have shown that the NAMA circulation contains outflow over North America with significant contributions from convection over the Sierra Madres and the tropics (Clapp et al., 2019; X. Wang et al., 2021). Finally, the NAM has also been shown in a modeling study to have a transport efficiency of air into the stratosphere comparable to the efficiency of the tropics, though less than that of the Asian monsoon (Yan et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

et al. 2021

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Section: Introductionmentioning

confidence: 99%

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

et al. 2021

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“…For instance, Wang et al. (2021) finds that tropospheric tracers are transported to the UTLS via rapid pathways over the Gulf of Mexico and the eastern Pacific, and that these pathways may be a source of UTLS water vapor as well. In addition to low‐latitude convective transport, regulation of the large‐scale temperature due to low‐latitude convection may also play a role in the hydration of this area, as Randel et al.…”

Section: Resultsmentioning

confidence: 99%

“…This suggests that additional sources of stratospheric water vapor outside the range of the U.S. NEXRAD network, such as OC occurring along the Sierra Madre Occidental in western Mexico or around the Panama Bight (Clapp et al, 2019;Liu & Liu, 2016), may contribute to the low-latitude North American water vapor feature. For instance, Wang et al (2021) finds that tropospheric tracers are transported to the UTLS via rapid pathways over the Gulf of Mexico and the eastern Pacific, and that these pathways may be a source of UTLS water vapor as well. In addition to low-latitude convective transport, regulation of the large-scale temperature due to low-latitude convection may also play a role in the hydration of this area, as Randel et al (2015) showed that weaker monsoonal convection leads to increased large-scale temperature and in turn a locally wetter lower stratosphere.…”

Section: Large-scale Transport Of Convectively Influenced Airmentioning

confidence: 99%

Transport and Confinement of Plumes From Tropopause‐Overshooting Convection Over the Contiguous United States During the Warm Season

2023

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Tropopause‐penetrating overshooting convection (OC) can transport tropospheric air into and affect the composition of the lower stratosphere. During the warm season, OC occurs frequently over the contiguous United States, and the transport of plumes from these events is modulated by the flow over North America, which throughout June to August is characterized by a large‐scale anticyclone in the upper troposphere and lower stratosphere. This study uses data from the Next Generation Weather Radar and the ERA5 reanalysis to locate OC during May–August of 2008–2020. Evidence of convective transport is found well above the 380 K isentrope, which is the top of the “lowermost stratosphere” and also the top of the stratospheric middleworld. By initializing massless particles within the volume of OC above the tropopause, we perform trajectory calculations to simulate the transport of OC plumes. With three‐dimensional diabatic trajectory modeling in isentropic coordinates using winds from ERA5, we quantify the confinement within the anticyclone and the number of trajectories transported into the tropical and extratropical stratosphere. By evaluating the trajectory residence time in the North American region, we find that July exhibits the strongest confinement, with about a quarter of trajectories staying in the region for more than 11 days. It is shown that, together with sufficient injection height, convective injection that occurs south of the jet and/or into anticyclonic regimes increases the chances of air remaining in the stratosphere. After 30 days, 45% of all air masses injected above the tropopause remain in the global stratosphere.

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In situ observations of CH2Cl2 and CHCl3 show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon

Lauther

Vogel²,

Wintel

et al. 2022

Atmos. Chem. Phys.

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Abstract. Efficient transport pathways for ozone-depleting very short-lived substances (VSLSs) 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 VSLSs (Cl-VSLSs) on stratospheric ozone depletion is important in order to validate and improve model simulations and future predictions. We report on a transport study using airborne in situ measurements of the Cl-VSLSs dichloromethane (CH2Cl2) and trichloromethane (chloroform, CHCl3) to derive a detailed description of two transport pathways from (sub)tropical source regions into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) in the Northern Hemisphere (NH) late summer. The Cl-VSLS measurements were obtained in the upper troposphere and lower stratosphere (UTLS) above western Europe and the midlatitude 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 extratropical lower stratosphere (Ex-LS). We link the measurements of enhanced CH2Cl2 and CHCl3 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 6–11 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 emissions 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 5–9 weeks from the boundary layer 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. CH2Cl2 and CHCl3 have similar atmospheric sinks and lifetimes, but the fraction of biogenic emissions is clearly higher for CHCl3 than for the mainly anthropogenically emitted CH2Cl2; consequently lower CHCl3 : CH2Cl2 ratios are expected in air parcels showing a higher impact of anthropogenic emissions. The observed CHCl3 : CH2Cl2 ratio suggests clearly stronger anthropogenic emissions in the region of southern and eastern Asia compared to those in the region of Central America and the tropical Atlantic. Overall, the transport of strongly enhanced CH2Cl2 and CHCl3 mixing ratios from southern and eastern Asia via the ASMA is the main factor in increasing the chlorine loading from the analyzed VSLSs in the Ex-LS during the 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-VSLSs on stratospheric ozone depletion.

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

Abstract: Observations and modeling studies have shown that the summer monsoon circulations are effective gateways of tropospheric air into the stratosphere (e.g.,

Cited by 3 publications

References 59 publications

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

Transport and Confinement of Plumes From Tropopause‐Overshooting Convection Over the Contiguous United States During the Warm Season

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 the North American summer monsoon

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

Abstract: Observations and modeling studies have shown that the summer monsoon circulations are effective gateways of tropospheric air into the stratosphere (e.g.,

Cited by 3 publications

References 59 publications

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

Identifying Outflow Regions of North American Monsoon Anticyclone‐Mediated Meridional Transport of Convectively Influenced Air Masses in the Lower Stratosphere

Transport and Confinement of Plumes From Tropopause‐Overshooting Convection Over the Contiguous United States During the Warm Season

In situ observations of CH&lt;sub&gt;2&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt; and CHCl&lt;sub&gt;3&lt;/sub&gt; show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon

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About

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 the North American summer monsoon