scholarly journals Long-term (1999–2019) variability of stratospheric aerosol over Mauna Loa, Hawaii, as seen by two co-located lidars and satellite measurements

2020 ◽  
Author(s):  
Fernando Chouza ◽  
Thierry Leblanc ◽  
John Barnes ◽  
Mark Brewer ◽  
Patrick Wang ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Atmospheric Composition ◽  
Mauna Loa ◽  
Quiescent Period ◽  
Level 3 ◽  
Ground Based Lidar ◽  
The Impact ◽  
Good Agreement

Abstract. As part of the Network for the Detection of Atmospheric Composition Change (NDACC), ground-based measurements obtained from the Jet Propulsion Laboratory (JPL) stratospheric ozone lidar and the NOAA stratospheric aerosol lidar at Mauna Loa, Hawaii over the past two decades were used to investigate the impact of volcanic eruptions and pyro-cumulonimbus smoke plumes on the stratospheric aerosol load above Hawaii since 1999. Measurements at 355 nm and 532 nm conducted by these two lidars revealed Ångström exponents of −1.6 for background plumes and −0.6 for a PyroCb plume recorded on September 2017. Measurements of the Nabro plume by the JPL lidar in 2011/2012 showed a lidar ratio of (64 ± 12.7) sr at 355 nm around the center of the plume. The new GloSSAC, CALIOP Level 3 and SAGE III-ISS stratospheric aerosol datasets were compared to the ground-based lidar datasets. The intercomparison revealed a generally good agreement, with vertical profiles of extinction coefficient within 50 % of discrepancy between 17 km and 23 km above sea level (ASL), and 25 % above 23 km ASL. The stratospheric aerosol depth derived from all these datasets shows good agreement, with the largest discrepancy (20 %) being observed between the new CALIOP Level 3 and the other datasets. All datasets consistently reveal a relatively quiescent period between 1999 and 2005, followed by an active period of multiple eruptions (e.g., Nabro) until early 2012. Another quiescent period, with slightly higher aerosol background, lasted until mid-2017, when a combination of extensive wildfires and multiple volcanic eruptions caused a significant increase in stratospheric aerosol loading. This loading maximized at the very end of the time period considered (fall 2019) as a result of the Raikoke eruption, the plume of which ascended to 26 km altitude in less than three months.

scholarly journals Long-term (1999–2019) variability of stratospheric aerosol over Mauna Loa, Hawaii, as seen by two co-located lidars and satellite measurements

2020 ◽  
Vol 20 (11) ◽  
pp. 6821-6839 ◽  
Author(s):  
Fernando Chouza ◽  
Thierry Leblanc ◽  
John Barnes ◽  
Mark Brewer ◽  
Patrick Wang ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Atmospheric Composition ◽  
Orthogonal Polarization ◽  
Mauna Loa ◽  
Quiescent Period ◽  
Level 3 ◽  
The Impact ◽  
Good Agreement

Abstract. As part of the Network for the Detection of Atmospheric Composition Change (NDACC), ground-based measurements obtained from the Jet Propulsion Laboratory (JPL) stratospheric ozone lidar and the NOAA stratospheric aerosol lidar at Mauna Loa, Hawaii, over the past 2 decades were used to investigate the impact of volcanic eruptions and pyrocumulonimbus (PyroCb) smoke plumes on the stratospheric aerosol load above Hawaii since 1999. Measurements at 355 and 532 nm conducted by these two lidars revealed a color ratio of 0.5 for background aerosols and small volcanic plumes and 0.8 for a PyroCb plume recorded on September 2017. Measurements of the Nabro plume by the JPL lidar in 2011–2012 showed a lidar ratio of (64±12.7) sr at 355 nm around the center of the plume. The new Global Space-based Stratospheric Aerosol Climatology (GloSSAC), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Level 3 and Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III-ISS) stratospheric aerosol datasets were compared to the ground-based lidar datasets. The intercomparison revealed a generally good agreement, with vertical profiles of extinction coefficient within 50 % discrepancy between 17 and 23 km above sea level (a.s.l.) and 25 % above 23 km a.s.l. The stratospheric aerosol depth derived from all of these datasets shows good agreement, with the largest discrepancy (20 %) being observed between the new CALIOP Level 3 and the other datasets. All datasets consistently reveal a relatively quiescent period between 1999 and 2006, followed by an active period of multiple eruptions (e.g., Nabro) until early 2012. Another quiescent period, with slightly higher aerosol background, lasted until mid-2017, when a combination of extensive wildfires and multiple volcanic eruptions caused a significant increase in stratospheric aerosol loading. This loading maximized at the very end of the time period considered (fall 2019) as a result of the Raikoke eruption, the plume of which ascended to 26 km altitude in less than 3 months.

scholarly journals Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 eruption cloud compared to in-situ and satellite observations

2017 ◽  
Author(s):  
Thibaut Lurton ◽  
Fabrice Jégou ◽  
Gwenaël Berthet ◽  
Jean-Baptiste Renard ◽  
Lieven Clarisse ◽  
...  
Keyword(s):  
Particle Size ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Particle Growth ◽  
Climate Impact ◽  
Stratospheric Aerosol ◽  
Stratospheric Chemistry ◽  
The Impact ◽  
Sarychev Peak

Abstract. Volcanic eruptions impact climate through the injection of sulfur dioxide (SO2), which is oxidized to form sulfuric acid aerosol particles that can enhance the stratospheric aerosol optical depth (SAOD). Besides large-magnitude eruptions, moderate-magnitude eruptions such as Kasatochi in 2008 and Sarychev Peak in 2009 can have a significant impact on stratospheric aerosol and hence climate. However, uncertainties remain in quantifying the atmospheric and climatic impacts of the 2009 Sarychev Peak eruption due to limitations in previous model representations of volcanic aerosol microphysics and particle size, whilst biases have been identified in satellite estimates of post-eruption SAOD. In addition, the 2009 Sarychev Peak eruption co-injected hydrogen chloride (HCl) alongside SO2, whose potential stratospheric chemistry impacts have not been investigated to date. We present a study of the stratospheric SO2-particle-HCl processing and impacts following Sarychev Peak eruption, using the CESM1(WACCM)-CARMA sectional aerosol microphysics model (with no a priori assumption on particle size). The Sarychev Peak 2009 eruption injected 0.9 Tg of SO2 into the upper troposphere and lower stratosphere (UTLS), enhancing the aerosol load in the Northern hemisphere. The post-eruption evolution of the volcanic SO2 in space and time are well reproduced by the model when compared to IASI (Infrared Atmospheric Sounding Interferometer) satellite data. Co-injection of 27 Gg HCl causes a lengthening of the SO2 lifetime and a slight delay in the formation of aerosols, and acts to enhance the destruction of stratospheric ozone and mono-nitrogen oxides (NOx) compared to the simulation with volcanic SO2 only. We therefore highlight the need to account for volcanic halogen chemistry when simulating the impact of eruptions such as Sarychev on stratospheric chemistry. The model-simulated evolution of effective radius (reff), reflects new particle formation followed by particle growth that enhances reff to reach up to 0.2 µm on zonal average. Comparisons of the model-simulated particle number and size-distributions to balloon-borne in-situ stratospheric observations over Kiruna, Sweden, in August and September 2009, and over Laramie, U.S.A., in June and November 2009 show good agreement and quantitatively confirms the post-eruption particle enhancement. We show that the model-simulated SAOD is consistent with that derived from OSIRIS (Optical Spectrograph and InfraRed Imager System) when both the saturation bias of OSIRIS and the fact that extinction profiles may terminate well above the tropopause are taken into account. Previous modelling studies (involving assumptions on particle size) that reported agreement to (biased) post-eruption estimates of SAOD derived from OSIRIS likely underestimated the climate impact of the 2009 Sarychev Peak eruption.

scholarly journals Evaluation of a method for converting Stratospheric Aerosol and Gas Experiment (SAGE) extinction coefficients to backscatter coefficients for intercomparison with lidar observations

2020 ◽  
Vol 13 (8) ◽  
pp. 4261-4276
Author(s):  
Travis N. Knepp ◽  
Larry Thomason ◽  
Marilee Roell ◽  
Robert Damadeo ◽  
Kevin Leavor ◽  
...  
Keyword(s):  
Stratospheric Aerosol ◽  
Aerosol Extinction ◽  
Extinction Coefficients ◽  
Mauna Loa ◽  
Quiescent Period ◽  
Table Mountain ◽  
Ground Based Lidar ◽  
Aerosol Backscatter ◽  
Lidar Observations ◽  
Major Eruption

Abstract. Aerosol backscatter coefficients were calculated using multiwavelength aerosol extinction products from the SAGE II and III/ISS instruments (SAGE: Stratospheric Aerosol and Gas Experiment). The conversion methodology is presented, followed by an evaluation of the conversion algorithm's robustness. The SAGE-based backscatter products were compared to backscatter coefficients derived from ground-based lidar at three sites (Table Mountain Facility, Mauna Loa, and Observatoire de Haute-Provence). Further, the SAGE-derived lidar ratios were compared to values from previous balloon and theoretical studies. This evaluation includes the major eruption of Mt. Pinatubo in 1991, followed by the atmospherically quiescent period beginning in the late 1990s. Recommendations are made regarding the use of this method for evaluation of aerosol extinction profiles collected using the occultation method.

scholarly journals CALIPSO Level 3 Stratospheric Aerosol Product: Version 1.00 Algorithm Description and Initial Assessment

2019 ◽  
Author(s):  
Jayanta Kar ◽  
Kam-Pui Lee ◽  
Mark A. Vaughan ◽  
Jason L. Tackett ◽  
Charles R. Trepte ◽  
...  
Keyword(s):  
Space Station ◽  
Volcanic Eruptions ◽  
Satellite Observation ◽  
Stratospheric Aerosol ◽  
Initial Assessment ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Stratospheric Dynamics ◽  
Level 3 ◽  
Good Agreement

Abstract. In August 2018, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) project released a new level 3 stratospheric aerosol profile data product derived from nearly 12 years of measurements acquired by the space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). This monthly averaged, gridded level 3 product is based on version 4.2 of the CALIOP level 1 and level 2 data products, which feature significantly improved calibration that now makes it possible to reliably retrieve profiles of stratospheric aerosol extinction and backscatter coefficients. This paper describes the science algorithm and data handling techniques that were developed to generate the CALIPSO version 1.00 level 3 stratospheric aerosol profile product. Further, we show that the retrieved extinction profiles capture the major stratospheric perturbations over the last decade resulting from volcanic eruptions, extreme smoke events, and signatures of stratospheric dynamics. Initial assessment of the product by inter-comparison with the stratospheric aerosol retrievals from the Stratospheric Aerosol and Gas Experiment III (SAGE III) on the International Space Station (ISS) indicates good agreement in the tropical stratospheric aerosol layer (30° N–30° S), where the average difference between zonal mean extinction profiles is typically less than 25 % between 20 km and 30 km. However, differences can exceed 100 % in the very low aerosol loading regimes found above 25 km at higher latitudes.

scholarly journals Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 eruption cloud compared to in situ and satellite observations

2018 ◽  
Vol 18 (5) ◽  
pp. 3223-3247 ◽  
Author(s):  
Thibaut Lurton ◽  
Fabrice Jégou ◽  
Gwenaël Berthet ◽  
Jean-Baptiste Renard ◽  
Lieven Clarisse ◽  
...  
Keyword(s):  
Particle Size ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Volcanic Eruptions ◽  
Climate Impact ◽  
Stratospheric Aerosol ◽  
Stratospheric Chemistry ◽  
The Impact ◽  
Sarychev Peak

Abstract. Volcanic eruptions impact climate through the injection of sulfur dioxide (SO2), which is oxidized to form sulfuric acid aerosol particles that can enhance the stratospheric aerosol optical depth (SAOD). Besides large-magnitude eruptions, moderate-magnitude eruptions such as Kasatochi in 2008 and Sarychev Peak in 2009 can have a significant impact on stratospheric aerosol and hence climate. However, uncertainties remain in quantifying the atmospheric and climatic impacts of the 2009 Sarychev Peak eruption due to limitations in previous model representations of volcanic aerosol microphysics and particle size, whilst biases have been identified in satellite estimates of post-eruption SAOD. In addition, the 2009 Sarychev Peak eruption co-injected hydrogen chloride (HCl) alongside SO2, whose potential stratospheric chemistry impacts have not been investigated to date. We present a study of the stratospheric SO2–particle–HCl processing and impacts following Sarychev Peak eruption, using the Community Earth System Model version 1.0 (CESM1) Whole Atmosphere Community Climate Model (WACCM) – Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics model (with no a priori assumption on particle size). The Sarychev Peak 2009 eruption injected 0.9 Tg of SO2 into the upper troposphere and lower stratosphere (UTLS), enhancing the aerosol load in the Northern Hemisphere. The post-eruption evolution of the volcanic SO2 in space and time are well reproduced by the model when compared to Infrared Atmospheric Sounding Interferometer (IASI) satellite data. Co-injection of 27 Gg HCl causes a lengthening of the SO2 lifetime and a slight delay in the formation of aerosols, and acts to enhance the destruction of stratospheric ozone and mono-nitrogen oxides (NOx) compared to the simulation with volcanic SO2 only. We therefore highlight the need to account for volcanic halogen chemistry when simulating the impact of eruptions such as Sarychev on stratospheric chemistry. The model-simulated evolution of effective radius (reff) reflects new particle formation followed by particle growth that enhances reff to reach up to 0.2 µm on zonal average. Comparisons of the model-simulated particle number and size distributions to balloon-borne in situ stratospheric observations over Kiruna, Sweden, in August and September 2009, and over Laramie, USA, in June and November 2009 show good agreement and quantitatively confirm the post-eruption particle enhancement. We show that the model-simulated SAOD is consistent with that derived from the Optical Spectrograph and InfraRed Imager System (OSIRIS) when both the saturation bias of OSIRIS and the fact that extinction profiles may terminate well above the tropopause are taken into account. Previous modelling studies (involving assumptions on particle size) that reported agreement with (biased) post-eruption estimates of SAOD derived from OSIRIS likely underestimated the climate impact of the 2009 Sarychev Peak eruption.

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

2013 ◽  
Vol 13 (11) ◽  
pp. 28869-28893 ◽  
Author(s):  
M. Rex ◽  
I. Wohltmann ◽  
T. Ridder ◽  
R. Lehmann ◽  
K. Rosenlof ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Source Region ◽  
Chemical Species ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Seaweed Farming ◽  
West Pacific ◽  
Stratospheric Composition ◽  
The Impact

Abstract. Hundreds of biogenic and anthropogenic chemical species are emitted into the atmosphere. Most break down efficiently by reaction with OH and do not reach the stratosphere. Here we show the existence of pronounced minima in the tropospheric columns of ozone and OH over the West Pacific, the main source region for stratospheric air. We show that this amplifies the impact of surface emissions on the stratospheric composition. Specifically, emissions of biogenic halogenated species from natural sources and from kelp and seaweed farming can have a larger effect on stratospheric ozone depletion. Increasing anthropogenic emissions of SO2 in South East Asia or from minor volcanic eruptions can play a larger role for the stratospheric aerosol budget, a key element for explaining the recently observed decrease in global warming rates (Solomon et al., 2011).

scholarly journals A new Geoengineering Model Intercomparison Project (GeoMIP) experiment designed for climate and chemistry models

2014 ◽  
Vol 7 (4) ◽  
pp. 5447-5464 ◽  
Author(s):  
S. Tilmes ◽  
M. J. Mills ◽  
U. Niemeier ◽  
H. Schmidt ◽  
A. Robock ◽  
...  
Keyword(s):  
Model Comparison ◽  
Stratospheric Aerosol ◽  
Atmospheric Composition ◽  
Model Intercomparison ◽  
Data Set ◽  
Aerosol Forcing ◽  
Input Dataset ◽  
Intercomparison Project ◽  
Total Burden ◽  
The Impact

Abstract. A new Geoengineering Model Intercomparison Project (GeoMIP) experiment "G4 specified stratospheric aerosols" (short name: G4SSA) is proposed to investigate the impact of stratospheric aerosol geoengineering on atmospheric composition, climate, and the environment. In contrast to the earlier G4 GeoMIP experiment, which requires an emission of sulphur dioxide (SO2) into the model, a prescribed aerosol forcing file is provided to the community, to be consistently applied to future model experiments between 2020 and 2100. This stratospheric aerosol distribution, with a total burden of about 2 Tg S has been derived using the ECHAM5-HAM microphysical model, based on a continuous annual tropical emission of 8 Tg SO2 year−1. A ramp-up of geoengineering in 2020 and a ramp-down in 2070 over a period of two years are included in the distribution, while a background aerosol burden should be used for the last 3 decades of the experiment. The performance of this experiment using climate and chemistry models in a multi-model comparison framework will allow us to better understand the significance of the impact of geoengineering and the abrupt termination after 50 years on climate and composition of the atmosphere in a changing environment. The zonal and monthly mean stratospheric aerosol input dataset is available at https://www2.acd.ucar.edu/gcm/geomip-g4-specified-stratospheric-aerosol-data-set.

scholarly journals CALIPSO level 3 stratospheric aerosol profile product: version 1.00 algorithm description and initial assessment

2019 ◽  
Vol 12 (11) ◽  
pp. 6173-6191 ◽  
Author(s):  
Jayanta Kar ◽  
Kam-Pui Lee ◽  
Mark A. Vaughan ◽  
Jason L. Tackett ◽  
Charles R. Trepte ◽  
...  
Keyword(s):  
Space Station ◽  
Volcanic Eruptions ◽  
Satellite Observation ◽  
Stratospheric Aerosol ◽  
Initial Assessment ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Stratospheric Dynamics ◽  
Level 3 ◽  
Lidar Ratio

Abstract. In August 2018, the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) project released a new level 3 stratospheric aerosol profile data product derived from nearly 12 years of measurements acquired by the spaceborne Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP). This monthly averaged, gridded level 3 product is based on version 4 of the CALIOP level 1B and level 2 data products, which feature significantly improved calibration that now makes it possible to reliably retrieve profiles of stratospheric aerosol extinction and backscatter coefficients at 532 nm. This paper describes the science algorithm and data handling techniques that were developed to generate the CALIPSO version 1.00 level 3 stratospheric aerosol profile product. Further, we show that the extinction profiles (retrieved using a constant lidar ratio of 50 sr) capture the major stratospheric perturbations in both hemispheres over the last decade resulting from volcanic eruptions, extreme smoke events, and signatures of stratospheric dynamics. Initial assessment of the product by intercomparison with the stratospheric aerosol retrievals from the Stratospheric Aerosol and Gas Experiment III (SAGE III) on the International Space Station (ISS) indicates good agreement in the tropical stratospheric aerosol layer (30∘ N–30∘ S), where the average difference between zonal mean extinction profiles is typically less than 25 % between 20 and 30 km (CALIPSO biased high). However, differences can exceed 100 % in the very low aerosol loading regimes found above 25 km at higher latitudes. Similarly, there are large differences (≥100 %) within 2 to 3 km above the tropopause that might be due to cloud contamination issues.

scholarly journals Denitrification by large NAT particles: the impact of reduced settling velocities and hints on particle characteristics

2014 ◽  
Vol 14 (20) ◽  
pp. 11525-11544 ◽  
Author(s):  
W. Woiwode ◽  
J.-U. Grooß ◽  
H. Oelhaf ◽  
S. Molleker ◽  
S. Borrmann ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Spherical Particles ◽  
Lagrangian Model ◽  
The Arctic ◽  
Reference Scenario ◽  
Climate Interactions ◽  
Stratospheric Clouds ◽  
The Impact ◽  
Good Agreement

Abstract. Vertical redistribution of HNO3 through large HNO3-containing particles associated with polar stratospheric clouds (PSCs) plays an important role in the chemistry of the Arctic winter stratosphere. During the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) campaign, apparently very large NAT (nitric acid trihydrate) particles were observed by the airborne in situ probe FSSP-100 (Molleker et al., 2014). Our analysis shows that the FSSP-100 observations associated with the flight on 25 January 2010 cannot easily be explained assuming compact spherical NAT particles due to much too short growing time at temperatures below the existence temperature of NAT (TNAT). State-of-the-art simulations using CLaMS (Chemical Lagrangian Model of the Stratosphere; Grooß et al., 2014) suggest considerably smaller particles. We consider the hypothesis that the simulation reproduces the NAT particle masses in a realistic way, but that real NAT particles may have larger apparent sizes compared to compact spherical particles, e.g. due to non-compact morphology or aspheric shape. Our study focuses on the consequence that such particles would have reduced settling velocities compared to compact spheres, altering the vertical redistribution of HNO3. Utilising CLaMS simulations, we investigate the impact of reduced settling velocities of NAT particles on vertical HNO3 redistribution and compare the results with observations of gas-phase HNO3 by the airborne Fourier transform spectrometer MIPAS-STR associated with two RECONCILE flights. The MIPAS-STR observations confirm conditions consistent with denitrification by NAT particles for the flight on 25 January 2010 and show good agreement with the simulations within the limitations of the comparison. Best agreement is found if settling velocities between 100 and 50% relative to compact spherical particles are considered (slight preference for the 70% scenario). In contrast, relative settling velocities of 30% result in too weak vertical HNO3 redistribution. Sensitivity simulations considering temperature biases of ±1 K and multiplying the simulated nucleation rates by factors of 0.5 and 2.0 affect the comparisons to a similar extent, but result in no effective improvement compared to the reference scenario. Our results show that an accurate knowledge of the settling velocities of NAT particles is important for quantitative simulations of vertical HNO3 redistribution.

scholarly journals 35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

2013 ◽  
Vol 13 (10) ◽  
pp. 5205-5225 ◽  
Author(s):  
T. Trickl ◽  
H. Giehl ◽  
H. Jäger ◽  
H. Vogelmann
Keyword(s):  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Saharan Dust ◽  
Positive Trend ◽  
Aerosol Layer ◽  
Mauna Loa ◽  
Background Period ◽  
Lidar Measurements ◽  
Tropopause Region ◽  
Volcanic Impact

Abstract. Lidar measurements at Garmisch-Partenkirchen (Germany) have almost continually delivered backscatter coefficients of stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt Pinatubo (Philippines, 1991). Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa. We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere. Most of them occurred in the mid-latitudes. A key observation for judging the role of eruptions just reaching the tropopause region was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash above the volcano was reported just as 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.3 km. Our analysis suggests for two or three of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, differing from the strong descent of the layers entering Central Europe at low altitudes. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of four to five. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere.

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