scholarly journals Impact of a moderate volcanic eruption on chemistry in the lower stratosphere: balloon-borne observations and model calculations

2016 ◽  
Author(s):  
Gwenaël Berthet ◽  
Fabrice Jégou ◽  
Valéry Catoire ◽  
Gisèle Krysztofiak ◽  
Jean-Baptiste Renard ◽  
...  
Keyword(s):  
Volcanic Eruption ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Volcanic Eruptions ◽  
Measurement Model ◽  
Stratospheric Aerosol ◽  
Volcanic Plume ◽  
Volcanic Aerosol ◽  
Model Calculations ◽  
Aerosol Loading

Abstract. The major volcanic eruption of Mount Pinatubo in 1991 has been shown to have significant effects on stratospheric chemistry and ozone depletion even at mid-latitudes. Since then, only "moderate" but recurrent volcanic eruptions have modulated the stratospheric aerosol loading such as the eruption of the mid-latitude Sarychev volcano which injected 0.9 Tg of sulfur dioxide (about 20 times less than Pinatubo) in June 2009. In this study, we investigate the chemical impacts of the enhanced liquid sulfate aerosol loading resulting from this moderate eruption using data from a balloon campaign conducted in northern Sweden (Kiruna-Esrange, 67.5° N, 21.0° E) in August-September 2009. Balloon-borne observations of NO2, HNO3 and BrO from infrared and UV-visible spectrometers are compared with the outputs of a three-dimensional (3-D) Chemistry-Transport Model (CTM). It is shown that differences between observations and model outputs are not due to transport calculation issues but rather reflect the chemical impact of the volcanic plume below 19 km in altitude. Good measurement-model agreement is obtained when the CTM is driven by volcanic aerosol loadings derived from in situ or space-borne data. As a result of enhanced N2O5 hydrolysis in the Sarychev volcanic aerosol conditions, the model calculates reductions of ~ 45 % and increases of ~ 11 % in NO2 and HNO3 amounts respectively over the summer 2009 period. The decrease in NOx abundances is limited due to the expected saturation effect for high aerosol loadings. The links between the various chemical catalytic cycles involving chlorine, bromine, nitrogen and HOx compounds in the lower stratosphere are discussed. The increased BrO amounts (~ 22 %) compare rather well with the balloon-borne observations when volcanic aerosol levels are accounted for in the CTM and appear to be mainly controlled by the coupling with nitrogen chemistry rather than by enhanced BrONO2 hydrolysis. Simulated effects of the Sarychev eruption on chlorine activation and partitioning are very limited in the high temperature conditions in the stratosphere at the period considered, inhibiting the effect of ClONO2 hydrolysis. As a consequence, the simulated ozone loss due to the Sarychev aerosols is low with a reduction of 1.1 % of the ozone budget at 16.5 km. Some comparisons with the reported Pinatubo chemical impacts are also provided and overall the Sarychev aerosols have led to less chemical effects than the Pinatubo event.

scholarly journals Impact of a moderate volcanic eruption on chemistry in the lower stratosphere: balloon-borne observations and model calculations

2017 ◽  
Vol 17 (3) ◽  
pp. 2229-2253 ◽  
Author(s):  
Gwenaël Berthet ◽  
Fabrice Jégou ◽  
Valéry Catoire ◽  
Gisèle Krysztofiak ◽  
Jean-Baptiste Renard ◽  
...  
Keyword(s):  
High Temperature ◽  
Ozone Depletion ◽  
Volcanic Eruption ◽  
Lower Stratosphere ◽  
Volcanic Eruptions ◽  
Volcanic Aerosol ◽  
Model Calculations ◽  
Stratospheric Chemistry ◽  
Temperature Conditions

Abstract. The major volcanic eruption of Mount Pinatubo in 1991 has been shown to have significant effects on stratospheric chemistry and ozone depletion even at midlatitudes. Since then, only moderate but recurrent volcanic eruptions have modulated the stratospheric aerosol loading and are assumed to be one cause for the reported increase in the global aerosol content over the past 15 years. This particularly enhanced aerosol context raises questions about the effects on stratospheric chemistry which depend on the latitude, altitude and season of injection. In this study, we focus on the midlatitude Sarychev volcano eruption in June 2009, which injected 0.9 Tg of sulfur dioxide (about 20 times less than Pinatubo) into a lower stratosphere mainly governed by high-stratospheric temperatures. Together with in situ measurements of aerosol amounts, we analyse high-resolution in situ and/or remote-sensing observations of NO2, HNO3 and BrO from balloon-borne infrared and UV–visible spectrometers launched in Sweden in August–September 2009. It is shown that differences between observations and three-dimensional (3-D) chemistry-transport model (CTM) outputs are not due to transport calculation issues but rather reflect the chemical impact of the volcanic plume below 19 km altitude. Good measurement–model agreement is obtained when the CTM is driven by volcanic aerosol loadings derived from in situ or space-borne data. As a result of enhanced N2O5 hydrolysis in the Sarychev volcanic aerosol conditions, the model calculates reductions of ∼ 45 % and increases of ∼ 11 % in NO2 and HNO3 amounts respectively over the August–September 2009 period. The decrease in NOx abundances is limited due to the expected saturation effect for high aerosol loadings. The links between the various chemical catalytic cycles involving chlorine, bromine, nitrogen and HOx compounds in the lower stratosphere are discussed. The increased BrO amounts (∼ 22 %) compare rather well with the balloon-borne observations when volcanic aerosol levels are accounted for in the CTM and appear to be mainly controlled by the coupling with nitrogen chemistry rather than by enhanced BrONO2 hydrolysis. We show that the chlorine partitioning is significantly controlled by enhanced BrONO2 hydrolysis. However, simulated effects of the Sarychev eruption on chlorine activation are very limited in the high-temperature conditions in the stratosphere in the period considered, inhibiting the effect of ClONO2 hydrolysis. As a consequence, the simulated chemical ozone loss due to the Sarychev aerosols is low with a reduction of −22 ppbv (−1.5 %) of the ozone budget around 16 km. This is at least 10 times lower than the maximum ozone depletion from chemical processes (up to −20 %) reported in the Northern Hemisphere lower stratosphere over the first year following the Pinatubo eruption. This study suggests that moderate volcanic eruptions have limited chemical effects when occurring at midlatitudes (restricted residence times) and outside winter periods (high-temperature conditions). However, it would be of interest to investigate longer-lasting tropical volcanic plumes or sulfur injections in the wintertime low-temperature conditions.

scholarly journals Long-range transport of volcanic aerosol from the 2010 Merapi tropical eruption to Antarctica

2018 ◽  
Author(s):  
Xue Wu ◽  
Sabine Griessbach ◽  
Lars Hoffmann
Keyword(s):  
Long Range ◽  
Lower Stratosphere ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Long Range Transport ◽  
Volcanic Plume ◽  
Volcanic Aerosol ◽  
The South ◽  
Range Transport ◽  
The Antarctic

Abstract. Volcanic sulfate aerosol is an important source of sulfur for Antarctica where other local sources of sulfur are rare. Mid- and high latitude volcanic eruptions can directly influence the aerosol budget of the polar stratosphere. However, tropical eruptions can also enhance polar aerosol load following long-range transport. In the present work, we analyze the volcanic plume of a tropical eruption, Mount Merapi in October 2010, using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC), Atmospheric Infrared Sounder (AIRS) SO2 observations and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aerosol observations. We investigate the pathway and transport efficiency of the volcanic aerosol from the tropical tropopause layer (TTL) to the lower stratosphere over Antarctica. We first estimated the time- and height-resolved SO2 injection time series over Mount Merapi during the explosive eruption using the AIRS SO2 observations and a backward trajectory approach. Then the SO2 injections were tracked for up to 6 months using the MPTRAC model. The Lagrangian transport simulation of the volcanic plume was compared to MIPAS aerosol observations and showed good agreement. Both of the simulation and the observations presented in this study suggest that a significant amount of aerosols of the volcanic plume from the Merapi eruption was transported from the tropics to the south of 60 °S within one month after the eruption and even further to Antarctica in the following two months. This relatively fast meridional transport of volcanic aerosol was mainly driven by quasi-horizontal mixing from the TTL to the extratropical lower stratosphere, which was facilitated by the weakening of the subtropical jet during the seasonal transition from austral spring to summer and linked to the westerly phase of the quasi-biennial oscillation (QBO). When the plume went to southern high latitudes, the polar vortex was displaced from the south pole, so the volcanic plume was carried to the south pole without penetrating the polar vortex. Based on the model results, the most efficient pathway for the quasi-horizontal mixing was in between the isentropic surfaces of 360 and 430 K. Although only 4 % of the initial SO2 load was transported into the lower stratosphere south of 60 °S, the Merapi eruption contributed about 8800 tons of sulfur to the Antarctic lower stratosphere. This indicates that the long-range transport under favorable meteorological conditions enables tropical volcanic eruptions to be an important remote source of sulfur for the Antarctic stratosphere.

scholarly journals A tropical West Pacific OH minimum and implications for stratospheric composition

2014 ◽  
Vol 14 (9) ◽  
pp. 4827-4841 ◽  
Author(s):  
M. Rex ◽  
I. Wohltmann ◽  
T. Ridder ◽  
R. Lehmann ◽  
K. Rosenlof ◽  
...  
Keyword(s):  
Transport Model ◽  
Source Region ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
The West ◽  
Model Calculations ◽  
West Pacific ◽  
Stratospheric Composition ◽  
The Impact

Abstract. Most of the short-lived biogenic and anthropogenic chemical species that are emitted into the atmosphere break down efficiently by reaction with OH and do not reach the stratosphere. Here we show the existence of a pronounced minimum in the tropospheric column of ozone over the West Pacific, the main source region for stratospheric air, and suggest a corresponding minimum of the tropospheric column of OH. This has the potential to amplify the impact of surface emissions on the stratospheric composition compared to the impact when assuming globally uniform OH conditions. Specifically, the role of emissions of biogenic halogenated species for the stratospheric halogen budget and the role of increasing emissions of SO2 in Southeast Asia or from minor volcanic eruptions for the increasing stratospheric aerosol loading need to be reassessed in light of these findings. This is also important since climate change will further modify OH abundances and emissions of halogenated species. Our study is based on ozone sonde measurements carried out during the TransBrom cruise with the RV Sonne roughly along 140–150° E in October 2009 and corroborating ozone and OH measurements from satellites, aircraft campaigns and FTIR instruments. Model calculations with the GEOS-Chem Chemistry and Transport Model (CTM) and the ATLAS CTM are used to simulate the tropospheric OH distribution over the West Pacific and the transport pathways to the stratosphere. The potential effect of the OH minimum on species transported into the stratosphere is shown via modeling the transport and chemistry of CH2Br2 and SO2.

scholarly journals Changes in stratospheric aerosol extinction coefficient after the 2018 Ambae eruption as seen by OMPS-LP and ECHAM5-HAM

2020 ◽  
Author(s):  
Elizaveta Malinina ◽  
Alexei Rozanov ◽  
Ulrike Niemeier ◽  
Sandra Peglow ◽  
Carlo Arosio ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Retrieval Algorithm ◽  
Volcanic Plume ◽  
Second Phase ◽  
Aerosol Extinction ◽  
Aerosol Loading ◽  
Aerosol Extinction Coefficient

Abstract. Stratospheric aerosols are an important component of the climate system. They not only change the radiative budget of the Earth but also play an essential role in ozone depletion. Most noticeable those effects are after volcanic eruptions when SO2 injected with the eruption reaches the stratosphere, oxidizes and forms stratospheric aerosol. There have been several studies, where a volcanic eruption plume and the associated radiative forcing were analyzed using climate models. Besides, volcanic eruptions were studied using the data from satellite measurements; however, studies combining both models and measurement data are rare. In this paper, we compared changes in the stratospheric aerosol loading after the 2018 Ambae eruption observed by satellite remote sensing measurements and by a global aerosol model. We use vertical profiles of aerosol extinction coefficient at 869 nm retrieved at IUP Bremen from OMPS-LP (Ozone Mapping and Profiling Suite – Limb Profiler) observations. Here, we present the retrieval algorithm as well as a comparison of the obtained profiles with those from SAGE III/ISS (Stratospheric Aerosol and Gas Experiment III onboard International Space Station). The observed differences are within 25 % for the most latitude bins, which indicates a reasonable quality of the retrieved limb aerosol extinction product. The volcanic plume evolution is investigated using both: monthly mean aerosol extinction coefficients and 10-day averaged data. The measurement results were compared with the model output from ECHAM5-HAM. In order to simulate the eruption accurately, we use SO2 injections estimates from OMPS and OMI for the first phase of eruption and TROPOMI for the second phase. Generally, the agreement between the vertical and geographical distribution of the aerosol extinction coefficient from OMPS-LP and ECHAM is quite remarkable, in particular, for the second phase. We attribute the good consistency between the model and the measurements to the precise estimation of injected SO2 mass and height as well as through nudging to ECMWF reanalysis data. Additionally, we compared the radiative forcing (RF) caused by the increase of the aerosol loading in the stratosphere after the eruption. After accounting for the uncertainties from different RF calculation methods, the RFs from ECHAM and OMPS-LP agree quite well. We estimate the tropical (20° N to 20° S) RF from the second Ambae eruption to be about −0.13 W/m2.

Detection of an enhanced stratospheric aerosol layer above Europe one year after the eruption of the volcano Raikoke

2021 ◽  
Author(s):  
Laura Tomsche ◽  
Andreas Marsing ◽  
Tina Jurkat-Witschas ◽  
Johannes Lucke ◽  
Katharina Kaiser ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Lower Stratosphere ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Sulfate Aerosol ◽  
Aerosol Layer ◽  
Volcanic Aerosol ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass

<p>Extreme volcanic eruptions inject significant amounts of sulfur-containing species into the lower stratosphere and sustain the stratospheric aerosol layer which tends to cool the atmosphere and surface temperatures.</p><p>During the BLUESKY campaign in May/June 2020, the aerosol composition and its precursor gas SO2 were measured with a time-of-flight aerosol mass spectrometer onboard the research aircraft HALO and with a atmospheric chemical ionization mass spectrometer onboard the DLR Falcon. While SO2 was slightly above background levels in the lower stratosphere above Europe, the aerosol mass spectrometer detected an extended aerosol layer. This sulfate aerosol layer was observed on most of the HALO flights and the sulfate mixing ratio increased significantly between 10 and 14 km altitude. Back trajectory calculations show no recent transport of polluted boundary layer air or ground-based emissions into the lower stratosphere. Therefore, we suggest that the stratospheric sulfate aerosol layer might be attributed to the aged stratospheric plume of the volcano Raikoke in Japan. In June 2019, Raikoke injected huge amounts of SO2 into the lower stratosphere, which were converted to sulfate and contributed to the stratospheric aerosol layer. This decaying volcanic aerosol layer was observed with the aerosol mass spectrometer over Europe a year after the eruption. The long-term volcanic remnants enhance the total stratospheric aerosol surface area, facilitate heterogeneous reactions on these particles and provide additional cloud condensation nuclei in the UTLS. They further offset some of the reduced sulfur burden from aviation that was observed during the COVID-19 lockdown in 2020. <br>The sensitive and highly time resolved airborne measurements of composition and size of stratospheric aerosol from an explosive volcanic eruption help to better constrain sulfur chemistry in the lower stratosphere, validate satellite observations near their detection threshold and can be used to evaluate dispersion and chemistry-climate models on long-term effects of volcanic aerosol. </p>

scholarly journals Effect of volcanic aerosol on stratospheric NO<sub>2</sub> and N<sub>2</sub>O<sub>5</sub> from 2002–2014 as measured by Odin-OSIRIS and Envisat-MIPAS

2016 ◽  
Author(s):  
Cristen Adams ◽  
Adam E. Bourassa ◽  
Chris A. McLinden ◽  
Chris E. Sioris ◽  
Thomas von Clarmann ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Pearson Correlation ◽  
Michelson Interferometer ◽  
Correlation Coefficients ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Volcanic Aerosol ◽  
Quasi Biennial Oscillation ◽  
El Chichón ◽  
El Chichon

Abstract. Following the large volcanic eruptions of Pinatubo in 1991 and El Chichón in 1982, decreases in stratospheric NO2 associated with enhanced aerosol were observed. The Optical Spectrograph and InfraRed Imaging Spectrometer (OSIRIS) likewise measured widespread enhancements of stratospheric aerosol following seven volcanic eruptions between 2002 and 2014, although the magnitudes of these eruptions were all much smaller than the Pinatubo and El Chichón eruptions. In order to isolate and quantify the relationship between volcanic aerosol and NO2, NO2 anomalies were calculated using measurements from OSIRIS and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). In the tropics, variability due to the quasi-biennial oscillation was subtracted from the timeseries. OSIRIS profile measurements indicate that the strongest relationships between NO2 and volcanic aerosol extinction were for the layer ~ 3–7 km above the tropopause, where OSIRIS stratospheric NO2 partial columns for ~ 3–7 km above the tropopause were found to be smaller than baseline levels during these aerosol enhancements by up to ~ 60 % with typical Pearson correlation coefficients of R ~ −0.7. MIPAS also observed decreases in NO2 partial columns during periods of affected by volcanic aerosol, with percent differences of up to ~ 25 %. An even stronger relationship was observed between OSIRIS aerosol optical depth and MIPAS N2O5 partial columns, with R ~ −0.9, although no link with MIPAS HNO3 was observed. The variation of OSIRIS NO2 with increasing aerosol was found to be quantitatively consistent with simulations from a photochemical box model in terms of both magnitude and degree of non-linearity.

scholarly journals Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere

2009 ◽  
Vol 9 (5) ◽  
pp. 18511-18543 ◽  
Author(s):  
J. Aschmann ◽  
B. M. Sinnhuber ◽  
E. L. Atlas ◽  
S. M. Schauffler
Keyword(s):  
Large Scale ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Three Dimensional ◽  
Chemical Transport Model ◽  
Heating Rates ◽  
Model Calculations ◽  
Upper Troposphere ◽  
Mass Fluxes ◽  
Tropical Upper Troposphere

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.

scholarly journals Reactive bromine chemistry in Mount Etna's volcanic plume: the influence of total Br, high-temperature processing, aerosol loading and plume–air mixing

2014 ◽  
Vol 14 (20) ◽  
pp. 11201-11219 ◽  
Author(s):  
T. J. Roberts ◽  
R. S. Martin ◽  
L. Jourdain
Keyword(s):  
High Temperature ◽  
Volcanic Plume ◽  
Plume Dispersion ◽  
Emission Flux ◽  
Volcanic Aerosol ◽  
Model Simulations ◽  
Aerosol Loading ◽  
Initial Rise ◽  
Air Mixing ◽  
Volcanic Emission

Abstract. Volcanic emissions present a source of reactive halogens to the troposphere, through rapid plume chemistry that converts the emitted HBr to more reactive forms such as BrO. The nature of this process is poorly quantified, yet is of interest in order to understand volcanic impacts on the troposphere, and infer volcanic activity from volcanic gas measurements (i.e. BrO / SO2 ratios). Recent observations from Etna report an initial increase and subsequent plateau or decline in BrO / SO2 ratios with distance downwind. We present daytime PlumeChem model simulations that reproduce and explain the reported trend in BrO / SO2 at Etna including the initial rise and subsequent plateau. Suites of model simulations also investigate the influences of volcanic aerosol loading, bromine emission, and plume–air mixing rate on the downwind plume chemistry. Emitted volcanic HBr is converted into reactive bromine by autocatalytic bromine chemistry cycles whose onset is accelerated by the model high-temperature initialisation. These rapid chemistry cycles also impact the reactive bromine speciation through inter-conversion of Br, Br2, BrO, BrONO2, BrCl, HOBr. We predict a new evolution of Br speciation in the plume. BrO, Br2, Br and HBr are the main plume species near downwind whilst BrO and HOBr are present further downwind (where BrONO2 and BrCl also make up a minor fraction). BrNO2 is predicted to be only a relatively minor plume component. The initial rise in BrO / SO2 occurs as ozone is entrained into the plume whose reaction with Br promotes net formation of BrO. Aerosol has a modest impact on BrO / SO2 near-downwind (< ~6 km, ~10 min) at the relatively high loadings considered. The subsequent decline in BrO / SO2 occurs as entrainment of oxidants HO2 and NO2 promotes net formation of HOBr and BrONO2, whilst the plume dispersion dilutes volcanic aerosol so slows the heterogeneous loss rates of these species. A higher volcanic aerosol loading enhances BrO / SO2 in the (> 6 km) downwind plume. Simulations assuming low/medium and high Etna bromine emissions scenarios show that the bromine emission has a greater influence on BrO / SO2 further downwind and a modest impact near downwind, and show either complete or partial conversion of HBr into reactive bromine, respectively, yielding BrO contents that reach up to ~50 or ~20% of total bromine (over a timescale of a few 10 s of minutes). Plume–air mixing non-linearly impacts the downwind BrO / SO2, as shown by simulations with varying plume dispersion, wind speed and volcanic emission flux. Greater volcanic emission flux leads to lower BrO / SO2 ratios near downwind, but also delays the subsequent decline in BrO / SO2, and thus yields higher BrO / SO2 ratios further downwind. We highlight the important role of plume chemistry models for the interpretation of observed changes in BrO / SO2 during/prior to volcanic eruptions, as well as for quantifying volcanic plume impacts on atmospheric chemistry. Simulated plume impacts include ozone, HOx and NOx depletion, the latter converted into HNO3. Partial recovery of ozone occurs with distance downwind, although cumulative ozone loss is ongoing over the 3 h simulations.

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

2013 ◽  
Vol 13 (3) ◽  
pp. 7061-7079 ◽  
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.

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

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.

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