Comparison of aerosol extinction between lidar and SAGE II over Gadanki, a tropical station in India

Abstract. An extensive comparison of aerosol extinction has been performed using lidar and Stratospheric Aerosol and Gas Experiment (SAGE) II data over Gadanki (13.5° N, 79.2° E), a tropical station in India, following coincident criteria during volcanically quiescent conditions from 1998 to 2005. The aerosol extinctions derived from lidar are higher than SAGE II during all seasons in the upper troposphere (UT), while in the lower-stratosphere (LS) values are closer. The seasonal mean percent differences between lidar and SAGE II aerosol extinctions are > 100% in the UT and < 50% above 25 km. Different techniques (point and limb observations) played the major role in producing the observed differences. SAGE II aerosol extinction in the UT increases as the longitudinal coverage is increased as the spatial aerosol extent increases, while similar extinction values in LS confirm the zonal homogeneity of LS aerosols. The study strongly emphasized that the best meteorological parameters close to the lidar measurement site in terms of space and time and Ba (sr−1), the ratio between aerosol backscattering and extinction, are needed for the tropics for a more accurate derivation of aerosol extinction.

Download Full-text

Ship-borne lidar measurements showing the progression of the tropical reservoir of volcanic aerosol after the June 1991 Pinatubo eruption

10.5194/essd-2020-81 ◽

2020 ◽

Cited By ~ 1

Author(s):

Juan-Carlos Antuña-Marrero ◽

Graham W. Mann ◽

Philippe Keckhut ◽

Sergey Avdyushin ◽

Bruno Nardi ◽

...

Keyword(s):

Lower Layer ◽

Extinction Ratio ◽

Stratospheric Aerosol ◽

Original Text ◽

Aerosol Extinction ◽

Volcanic Aerosol ◽

Tropical Reservoir ◽

Aerosol Cloud ◽

Pinatubo Eruption ◽

The Tropics

Abstract. A key limitation of volcanic forcing datasets for the Pinatubo period, is the large uncertainty that remains with respect to the extent of the optical depth of the Pinatubo aerosol cloud in the first year after the eruption, the saturation of the SAGE-II instrument restricting it to only be able to measure the upper part of the aerosol cloud in the tropics. Here we report the recovery of stratospheric aerosol measurements from two ship-borne lidars, both of which measured the tropical reservoir of volcanic aerosol produced by the June 1991 Mount Pinatubo eruption. The lidars were on-board two Soviet vessels, each ship crossing the Atlantic, their measurement datasets providing unique observational transects of the Pinatubo cloud across the tropics from Europe to the Caribbean (~ 40° N to 8° N) from July to September 1991 (the Prof Zubov ship) and from Europe to south of the Equator (8° S to ~ 40° N) between January and February 1992 (the Prof Vize ship). Our philosophy with the data recovery is to follow the same algorithms and parameters appearing in the two peer-reviewed articles that presented these datasets in the same issue of GRL in 1993, and here we provide all 48 lidar soundings made from the Prof. Zubov, and 11 of the 20 conducted from the Prof. Vize, ensuring we have reproduced the aerosols backscatter and extinction values in the Figures of those two papers. These original approaches used thermodynamic properties from the CIRA-86 standard atmosphere to derive the molecular backscattering, vertically and temporally constant values applied for the aerosol backscatter to extinction ratio and the correction factor of the aerosols backscattering wavelength dependence. We demonstrate this initial validation of the recovered stratospheric aerosol extinction profiles, providing full details of each dataset in this paper's Supplement S1, the original text files of the backscatter ratio, the calculated aerosols backscatter and extinction profiles. We anticipate the data providing potential new observational case studies for modelling analyses, including a 1-week series of consecutive soundings (in September 1991) at the same location showing the progression of the entrainment of part of the Pinatubo plume into the upper troposphere and the formation of an associated cirrus cloud. The Zubov lidar dataset illustrates how the tropically confined Pinatubo aerosol cloud transformed from a highly heterogeneous vertical structure in August 1991, maximum aerosol extinction values around 19 km for the lower layer and 23–24 for the upper layer, to a more homogeneous and deeper reservoir of volcanic aerosol in September 1991. We encourage modelling groups to consider new analyses of the Pinatubo cloud, comparing to the recovered datasets, with the potential to increase our understanding of the evolution of the Pinatubo aerosol cloud and its effects. Data described in this work are available at https://doi.pangaea.de/10.1594/PANGAEA.912770 (Antuña-Marrero et al., 2020).

Download Full-text

Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere

Atmospheric Measurement Techniques ◽

10.5194/amt-6-91-2013 ◽

2013 ◽

Vol 6 (1) ◽

pp. 91-98 ◽

Cited By ~ 26

Author(s):

P. Achtert ◽

M. Khaplanov ◽

F. Khosrawi ◽

J. Gumbel

Keyword(s):

Lower Stratosphere ◽

Thermal Structure ◽

Atmospheric Temperature ◽

Temperature Measurements ◽

Integration Time ◽

Aerosol Extinction ◽

Temperature Profiles ◽

Backscatter Coefficient ◽

Upper Troposphere ◽

532 Nm

Abstract. The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange (68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the new pure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution is 150 m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements, the aerosol extinction coefficient and the aerosol backscatter coefficient at 532 nm can be measured independently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 km height), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratosphere with daylight capability.

Download Full-text

Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-11209-2017 ◽

2017 ◽

Vol 17 (18) ◽

pp. 11209-11226 ◽

Cited By ~ 12

Author(s):

Daniele Visioni ◽

Giovanni Pitari ◽

Valentina Aquila ◽

Simone Tilmes ◽

Irene Cionni ◽

...

Keyword(s):

Radiative Forcing ◽

Lower Stratosphere ◽

Stratospheric Ozone ◽

Radiation Absorption ◽

Coupled Models ◽

Upper Troposphere ◽

Aerosol Scattering ◽

Intercomparison Project ◽

Planetary Albedo ◽

The Tropics

Abstract. Sulfate geoengineering (SG), made by sustained injection of SO2 in the tropical lower stratosphere, may impact the CH4 abundance through several photochemical mechanisms affecting tropospheric OH and hence the methane lifetime. (a) The reflection of incoming solar radiation increases the planetary albedo and cools the surface, with a tropospheric H2O decrease. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-to-upper troposphere, thus reducing the amount of NOx and O3 production. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rate perturbation is highly latitude dependent, producing a stronger meridional component of the Brewer–Dobson circulation. The net effect on tropospheric OH due to the enhanced stratosphere–troposphere exchange may be positive or negative depending on the net result of different superimposed species perturbations (CH4, NOy, O3, SO4) in the extratropical upper troposphere and lower stratosphere (UTLS). In addition, the atmospheric stabilization resulting from the tropospheric cooling and lower stratospheric warming favors an additional decrease of the UTLS extratropical CH4 by lowering the horizontal eddy mixing. Two climate–chemistry coupled models are used to explore the above radiative, chemical and dynamical mechanisms affecting CH4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH4 lifetime may become significantly longer (by approximately 16 %) with a sustained injection of 8 Tg-SO2 yr−1 starting in the year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.10 W m−2 in the 2040–2049 decade and +0.15 W m−2 in the 2060–2069 decade).

Download Full-text

In situ detection of electrified aerosols in the upper troposphere and in the stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-7061-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 7061-7079 ◽

Cited By ~ 2

Author(s):

J.-B. Renard ◽

S. N. Tripathi ◽

M. Michael ◽

A. Rawal ◽

G. Berthet ◽

...

Keyword(s):

Lower Stratosphere ◽

Lower Troposphere ◽

Stratospheric Aerosol ◽

Balloon Flight ◽

Model Calculations ◽

Upper Troposphere ◽

Charged Aerosols ◽

In Situ Detection ◽

Aerosol Counter

Abstract. Electrified aerosols have been observed in the lower troposphere and in the mesosphere, but have never been detected in the stratosphere and upper troposphere. We present measurements of aerosols during a balloon flight to an altitude of ~24 km. The measurements were performed with an improved version of the STAC aerosol counter dedicated to the search for charged aerosols. It is found that most of the aerosols are charged in the upper troposphere for altitudes below 10 km and in the stratosphere for altitudes above 20 km. On the contrary, the aerosols seem to be uncharged between 10 km and 20 km. Model calculations are used to quantify the electrification of the aerosols with a stratospheric aerosol-ion model. The percentages of charged aerosols obtained with model calculations are in excellent agreement with the observations below 10 km and above 20 km. On the other hand, the model cannot reproduce the absence of detected electrification in the lower stratosphere, such that a distinct unknown process in this altitude range inhibits electrification. The presence of sporadic transient layers of electrified aerosol in the upper troposphere and in the stratosphere could have significant implications for sprite formation.

Download Full-text

A Global Space-based Stratospheric Aerosol Climatology (Version 2.0): 1979–2018

10.5194/essd-2020-56 ◽

2020 ◽

Cited By ~ 1

Author(s):

Mahesh Kovilakam ◽

Larry Thomason ◽

Nicholas Ernest ◽

Landon Rieger ◽

Adam Bourassa ◽

...

Keyword(s):

Lower Stratosphere ◽

Stratospheric Aerosol ◽

Aerosol Extinction ◽

Data Set ◽

Angstrom Exponent ◽

Global Space ◽

Ångström Exponent ◽

Version 2.0 ◽

532 Nm ◽

Ångstrom Exponent

Abstract. A robust stratospheric aerosol climate data record enables the depiction of the radiative forcing of this highly variable component of climate. Since stratospheric aerosol also plays a key role in the chemical processes leading to ozone depletion, stratosphere is one of the crucial parameters in understanding climate change in the past and potential changes in the future. As a part of Stratospheric-tropospheric Processes and their Role in Climate (SPARC) Stratospheric Sulfur and its Role in Climate (SSiRC) activity, the Global Space-based Stratospheric Aerosol Climatology (GloSSAC) was created (Thomason et al., 2018) to support the World Climate Research Programme (WCRP)’s Coupled Model Intercomparison Project Phase 6 (CMIP6) (Zanchettin et al., 2016). This data set is a follow-on to one created as a part of Stratosphere-Troposphere Process and their Role in Climate Project (SPARC)’s Assessment of Stratospheric Aerosol Properties (ASAP) activity(SPARC, 2006) and a data created for Chemistry-Climate Model Initiative (CCMI) in 2012 (Eyring and Lamarque, 2012). Herein, we discuss changes to the original release version including those as a part of v1.1 that was released in September 2018 that primarily corrects an error in the conversion of Cryogenic Limb Array Etalon Spectrometer (CLAES) data to Stratospheric Aerosol and Gas Experiment (SAGE) II wavelengths, and the new release, v2.0. Version 2.0 is focused on improving the post-SAGE II era (after 2005) with the goal to mitigate elevated aerosol extinction in the lower stratosphere at mid and high latitudes noted in v1.0 as noted in Thomason et al. (2018). Changes include the use of version 7.0 of Optical Spectrograph and InfraRed Imaging System(OSIRIS), the recently released Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Lidar Level 3 Stratospheric Aerosol profile monthly product, and the new addition of SAGE III/ISS. Although, the version 7.0 OSIRIS data is substantially improved at its native wavelength of 750 nm, conversion to 525 nm using a constant Angstrom exponent often results in disagreements with SAGEII/ SAGE III/ISS overlap measurements. We, therefore use an observed relationship between OSIRIS extinction at 750 nm and SAGEII/SAGE III/ISS extinction at 525 nm to derive Altitude-Latitude based monthly climatology of Angstrom exponent to compute extinction at 525 nm, resulting in a better agreement between OSIRIS and SAGE measurements. We employ a similar approach to convert OSIRIS 750 nm extinction to 1020 nm extinction for the post-SAGEII period. Additionally, we incorporate the recently released standard CALIPSO stratospheric aerosol profile monthly product into GloSSAC with an improved conversion technique of 532 nm backscatter coefficient to extinction using an observed relationship between OSIRIS 525 nm extinction and CALIPSO 532 nm backscatter. We also investigate for any cloud contamination in OSIRIS/standard CALIPSO stratospheric aerosol product, which may have caused apparent enhancement in the aerosol extinction particularly in the lower stratosphere. SAGE III/ISS data is also incorporated in GloSSAC to extend the climatology to the present and to test the approach used to correct OSIRIS/CALIPSO data. The GloSSAC v2.0 netcdf file is accessible at https://doi.org/10.5067/glossac-l3-v2.0 (Thomason, 2020).

Download Full-text

Asymmetry and pathways of inter-hemispheric transport in the upper troposphere and lower stratosphere

10.5194/acp-2020-1153 ◽

2020 ◽

Author(s):

Xiaolu Yan ◽

Paul Konopka ◽

Marius Hauck ◽

Aurélien Podglajen ◽

Felix Ploeger

Keyword(s):

Lower Stratosphere ◽

Asian Summer Monsoon ◽

Boundary Surface ◽

Lagrangian Model ◽

Boreal Summer ◽

Upper Troposphere ◽

Source Regions ◽

Mass Fractions ◽

Asian Summer ◽

The Tropics

Abstract. Inter-hemispheric transport may strongly affect the trace gas composition of the atmosphere, especially in relation to anthropogenic emissions which originate mainly in the Northern Hemisphere. This study investigates the transport from the boundary surface layer of the Northern Hemispheric (NH) extratropics (30–90° N), Southern Hemispheric (SH) extratropics (30–90° S), and tropics (30° S–30° N) into the global upper troposphere and lower stratosphere (UTLS) using simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS). In particular, we diagnose inter-hemispheric transport in terms of the air mass fractions (AMF), age spectra, and the mean age of air (AoA) calculated for these three source regions. We find that the AMFs from the NH extratropics to the UTLS are about five times larger than the corresponding contributions from the SH extratropics and almost twenty times smaller than those from the tropics. The amplitude of the AMF seasonal variability originating from the NH extratropics is comparable to that from the tropics. The NH and SH extratropics age spectra show much stronger seasonality compared to the seasonality of the tropical age spectra. The transit time of NH extratropical origin air to the SH extratropics is longer than vice versa. The asymmetry of the inter-hemispheric transport is mainly driven by the Asian summer monsoon (ASM). Both ASM and westerly ducts affect the cross hemispheric transport of the NH extratropical air to the SH, and it is an interplay between the ASM and westerly ducts which triggers such cross-equator transport from boreal summer to fall, mainly westerly ducts over the eastern Atlantic.

Download Full-text

Asymmetry and pathways of inter-hemispheric transport in the upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-6627-2021 ◽

2021 ◽

Vol 21 (9) ◽

pp. 6627-6645

Author(s):

Xiaolu Yan ◽

Paul Konopka ◽

Marius Hauck ◽

Aurélien Podglajen ◽

Felix Ploeger

Keyword(s):

Lower Stratosphere ◽

Asian Summer Monsoon ◽

Boundary Surface ◽

Lagrangian Model ◽

Boreal Summer ◽

Upper Troposphere ◽

Source Regions ◽

Mass Fractions ◽

Asian Summer ◽

The Tropics

Abstract. Inter-hemispheric transport may strongly affect the trace gas composition of the atmosphere, especially in relation to anthropogenic emissions, which originate mainly in the Northern Hemisphere. This study investigates the transport from the boundary surface layer of the northern hemispheric (NH) extratropics (30–90∘ N), southern hemispheric (SH) extratropics (30–90∘ S), and tropics (30∘ S–30∘ N) into the global upper troposphere and lower stratosphere (UTLS) using simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS). In particular, we diagnose inter-hemispheric transport in terms of the air mass fractions (AMFs), age spectra, and the mean age of air (AoA) calculated for these three source regions. We find that the AMFs from the NH extratropics to the UTLS are about 5 times larger than the corresponding contributions from the SH extratropics and almost 20 times smaller than those from the tropics. The amplitude of the AMF seasonal variability originating from the NH extratropics is comparable to that from the tropics. The NH and SH extratropical age spectra show much stronger seasonality compared to the seasonality of the tropical age spectra. The transit time of NH-extratropical-origin air to the SH extratropics is longer than vice versa. The asymmetry of the inter-hemispheric transport is mainly driven by the Asian summer monsoon (ASM). We confirm the important role of ASM and westerly ducts in the inter-hemispheric transport from the NH extratropics to the SH. Furthermore, we find that it is an interplay between the ASM and westerly ducts which triggers such cross-Equator transport from boreal summer to fall in the UTLS between 350 and 370 K.

Download Full-text

Lower-stratospheric aerosol measurements in eastward shedding vortices over Japan from the Asian summer monsoon anticyclone during the summer of 2018

10.5194/acp-2020-980 ◽

2020 ◽

Author(s):

Masatomo Fujiwara ◽

Tetsu Sakai ◽

Koichi Shiraishi ◽

Yoichi Inai ◽

Sergey Khaykin ◽

...

Keyword(s):

Summer Monsoon ◽

Forest Fires ◽

Lower Stratosphere ◽

Asian Summer Monsoon ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Aerosol Layer ◽

Upper Troposphere ◽

Asian Summer ◽

The Japanese Archipelago

Abstract. Eastward airmass transport from the Asian summer monsoon (ASM) anticyclone in the upper troposphere and lower stratosphere (UTLS) often involves eastward shedding vortices, which can cover most of the Japanese archipelago. We investigated the aerosol characteristics of these vortices by analysing data from two lidar systems in Japan, at Tsukuba (36.1° N, 140.1° E) and Fukuoka (33.55° N, 130.36° E), during the summer of 2018. We observed several events with enhanced particle signals at Tsukuba at 15.5–18 km altitude (at or above the local tropopause) during August–September 2018, with a backscattering ratio of ~1.10 and particle depolarization of ~5 % (i.e., not spherical, but more spherical than ice crystals). These particle characteristics may be consistent with those of solid aerosol particles, such as ammonium nitrate. Each event had a timescale of a few days. During the same study period, we also observed similar enhanced particle signals in the lower stratosphere at Fukuoka. The upper troposphere is often covered by cirrus clouds at both lidar sites. Backward trajectory calculations for these sites for days with enhanced particle signals in the lower stratosphere and days without indicate that the former airmasses originated within the ASM anticyclone, and the latter more from edge regions. Reanalysis carbon-monoxide and satellite water-vapour data indicate that eastward shedding vortices were involved in the observed aerosol enhancements. Satellite aerosol data confirm that the period and latitudinal region were free from the direct influence of documented volcanic eruptions and high latitude forest fires. Our results indicate that the Asian Tropopause Aerosol Layer (ATAL) over the ASM region extends east towards Japan in association with the eastward shedding vortices, and that lidar systems in Japan can detect at least the lower stratospheric portion of the ATAL during periods when the lower stratosphere is undisturbed by volcanic eruptions and forest fires. The upper tropospheric portion of the ATAL is either depleted by tropospheric processes (convection and wet scavenging) during eastward transport or is obscured by much stronger cirrus cloud signals.

Download Full-text

Lower-stratospheric aerosol measurements in eastward-shedding vortices over Japan from the Asian summer monsoon anticyclone during the summer of 2018

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3073-2021 ◽

2021 ◽

Vol 21 (4) ◽

pp. 3073-3090

Author(s):

Masatomo Fujiwara ◽

Tetsu Sakai ◽

Tomohiro Nagai ◽

Koichi Shiraishi ◽

Yoichi Inai ◽

...

Keyword(s):

Summer Monsoon ◽

Forest Fires ◽

Lower Stratosphere ◽

Asian Summer Monsoon ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Aerosol Layer ◽

Upper Troposphere ◽

Asian Summer ◽

The Japanese Archipelago

Abstract. Eastward air-mass transport from the Asian summer monsoon (ASM) anticyclone in the upper troposphere and lower stratosphere (UTLS) often involves eastward-shedding vortices, which can cover most of the Japanese archipelago. We investigated the aerosol characteristics of these vortices by analysing data from two lidar systems in Japan, at Tsukuba (36.1∘ N, 140.1∘ E) and Fukuoka (33.55∘ N, 130.36∘ E), during the summer of 2018. We observed several events with enhanced particle signals at Tsukuba at 15.5–18 km of altitude (at or above the local tropopause) during August–September 2018, with a backscattering ratio of ∼ 1.10 and particle depolarization of ∼ 5 % (i.e. not spherical, but more spherical than ice crystals). These particle characteristics may be consistent with those of solid aerosol particles, such as ammonium nitrate. Each event had a timescale of a few days. During the same study period, we also observed similar enhanced particle signals in the lower stratosphere at Fukuoka. The upper troposphere is often covered by cirrus clouds at both lidar sites. Backward trajectory calculations for these sites for days with enhanced particle signals in the lower stratosphere and days without indicate that the former air masses originated within the ASM anticyclone and the latter more from edge regions. Reanalysis carbon monoxide and satellite water vapour data indicate that eastward-shedding vortices were involved in the observed aerosol enhancements. Satellite aerosol data confirm that the period and latitudinal region were free from the direct influence of documented volcanic eruptions and high-latitude forest fires. Our results indicate that the Asian tropopause aerosol layer (ATAL) over the ASM region extends east towards Japan in association with the eastward-shedding vortices and that lidar systems in Japan can detect at least the lower-stratospheric portion of the ATAL during periods when the lower stratosphere is undisturbed by volcanic eruptions and forest fires. The upper-tropospheric portion of the ATAL is either depleted by tropospheric processes (convection and wet scavenging) during eastward transport or is obscured by much stronger cirrus cloud signals.

Download Full-text

Global large-scale stratosphere-troposphere exchange in modern reanalyses

10.5194/acp-2016-788 ◽

2016 ◽

Cited By ~ 1

Author(s):

Alexander C. Boothe ◽

Cameron R. Homeyer

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Radiative Properties ◽

Lapse Rate ◽

Polar Regions ◽

Transport Mechanisms ◽

Upper Troposphere ◽

Long Term Changes ◽

The Tropics

Abstract. Stratosphere-troposphere exchange (STE) has important and significant impacts on the chemical and radiative properties of the upper troposphere and lower stratosphere. This study presents a 15-year climatology of global large-scale STE from four modern reanalyses: ERA-Interim, JRA-55, MERRA-2, and MERRA-1. STE is separated into four categories for analysis to identify the significance of known transport mechanisms: 1) vertical stratosphere-to-troposphere transport (STT), 2) vertical troposphere-to-stratosphere transport (TST), 3) lateral STT (that occurring between the tropics and the extratropics and across the tropopause "break"), and 4) lateral TST. In addition, this study employs a method to identify STE as that which crosses the lapse-rate tropopause (LRT), while most previous studies have used a potential vorticity (PV) isosurface as the troposphere-stratosphere boundary. PV-based and LRT based STE climatologies are compared using the same reanalysis output (ERA-Interim). The comparison reveals quantitative and qualitative differences, particularly in the geographic representation of TST in the polar regions. Based upon spatiotemporal integrations, we find STE to be STT-dominant in ERA-Interim and JRA-55 and TST-dominant in the MERRA reanalyses. Time series during the 15-year analysis period show long-term changes that are argued to correspond with changes in the Brewer-Dobson circulation.

Download Full-text