A Method for Retrieving Stratospheric Aerosol Extinction and Particle Size from Ground-Based Rayleigh-Mie-Raman Lidar Observations

We report on the retrieval of stratospheric aerosol particle size and extinction coefficient profiles from multi-color backscatter measurements with the Rayleigh–Mie–Raman lidar operated at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in northern Norway. The retrievals are based on a two-step approach. In a first step, the median radius of an assumed monomodal log-normal particle size distribution with fixed width is retrieved based on a color index formed from the measured backscatter ratios at the wavelengths of 1064 nm and 532 nm. An intrinsic ambiguity of the retrieved aerosol size information is discussed. In a second step, this particle size information is used to convert the measured lidar backscatter ratio to aerosol extinction coefficients. The retrieval is currently based on monthly-averaged lidar measurements and the results for March 2013 are discussed. A sensitivity study is presented that allows for establishing an error budget for the aerosol retrievals. Assuming a monomodal log-normal aerosol particle size distribution with a geometric width of S = 1.5, median radii on the order of below 100 nm are retrieved. The median radii are found to generally decrease with increasing altitude. The retrieved aerosol extinction profiles are compared to observations with the OSIRIS (Optical Spectrograph and InfraRed Imager System) and the OMPS-LP (Ozone Mapping Profiling Suite Limb Profiler) satellite instruments in the 60∘ N to 80∘ N latitude band. The extinction profiles that were retrieved from the lidar measurements show good agreement with the observations of the two satellite instruments when taking the different wavelengths of the instruments into account.

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Challenges in retrieving stratospheric aerosol extinction and particle size from ground-based RMR-LIDAR observations

10.5194/amt-2019-267 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jacob Zalach ◽

Christian von Savigny ◽

Arvid Langenbach ◽

Gerd Baumgarten ◽

Franz-Josef Lübken ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Aerosol Particle ◽

Stratospheric Aerosol ◽

The Arctic ◽

Aerosol Extinction ◽

Size Information ◽

Aerosol Particle Size ◽

Log Normal

Abstract. We report on the retrieval of stratospheric aerosol particle size and extinction coefficient profiles from multi-color backscatter measurements with the Rayleigh-Mie-Raman lidar operated at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in northern Norway. The retrievals are based on a two-step approach. In a first step the median radius of an assumed log-normal particle size distribution with fixed width is retrieved based on the color ratio formed from the measured backscatter ratios at wavelenghts of 1064 nm and 532 nm. An intrinsic ambiguity of the retrieved aerosol size information is discussed. In a second step, this particle size information is used to convert the measured lidar backscatter ratio to aerosol extinction coefficients. The retrieval is currently based on monthly-averaged lidar measurements covering the period from the year 2000 to present. A sensitivity study is presented that allows establishing an error budged for the aerosol retrievals. Assuming a log-normal aerosol particle size distribution with a geometric width of S = 1.3, median radii on the order of 100 nm are retrieved. The median radii are found to generally decrease with increasing altitude. The retrieved aerosol extinction profiles are compared to observations with various current and past satellite instruments.

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Stratospheric aerosol particle size information in Odin-OSIRIS limb scatter spectra

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-6-5065-2013 ◽

2013 ◽

Vol 6 (3) ◽

pp. 5065-5099

Author(s):

L. A. Rieger ◽

A. E. Bourassa ◽

D. A. Degenstein

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Imaging System ◽

Stratospheric Aerosol ◽

Retrieval Algorithm ◽

Aerosol Layer ◽

Aerosol Extinction ◽

Model Calculations ◽

Size Information

Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) on-board the Odin satellite has now taken over a decade of limb scatter measurements that have been used to retrieve the Version 5 stratospheric aerosol extinction product. This product is retrieved using a representative particle size distribution to calculate scattering cross sections and scattering phase functions for the forward model calculations. In this work the information content of OSIRIS measurements with respect to stratospheric aerosol is systematically examined for the purpose of retrieving particle size information along with the extinction coefficient. The benefit of using measurements at different wavelengths and scattering angles in the retrieval is studied and it is found that incorporation of the 1530 nm radiance measurement is key for a robust retrieval of particle size information. It is also found that using OSIRIS measurements at different solar geometries simultaneously provides little additional benefit. Based on these results, an improved aerosol retrieval algorithm is developed that couples the retrieval of aerosol extinction and mode radius of a log-normal particle size distribution. Comparison of these results with coincident measurements from SAGE III show agreement in retrieved extinction to within approximately 10% over the bulk of the aerosol layer, which is comparable to Version 5. The retrieved particle size, when converted to Ångström coefficient, shows good qualitative agreement with SAGE II measurements made at somewhat shorter wavelengths.

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Issues related to the retrieval of stratospheric-aerosol particle size information based on optical measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-13-1909-2020 ◽

2020 ◽

Vol 13 (4) ◽

pp. 1909-1920 ◽

Cited By ~ 1

Author(s):

Christian von Savigny ◽

Christoph G. Hoffmann

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Aerosol Particle ◽

Measurement Techniques ◽

Stratospheric Aerosol ◽

Solar Occultation ◽

Lidar Measurements ◽

Aerosol Particle Size ◽

Size Estimates

Abstract. Stratospheric-sulfate aerosols play an important role in the physics and chemistry of the atmosphere. The radiative and chemical effects of stratospheric-sulfate aerosols depend critically on the aerosol particle size distribution and its variability. Despite extensive research spanning several decades, the scientific understanding of the particle size distribution of stratospheric aerosols is still incomplete. Particle size estimates (often represented by the median radius of an assumed monomodal log-normal distribution with a fixed width or by the effective radius) reported in different studies cover a wide range, even under background stratospheric conditions, and particle size estimates retrieved from satellite solar-occultation measurements in the optical spectral range show a tendency to be systematically larger than retrievals based on other optical methods. In this contribution we suggest a potential reason for these systematic differences. Differences between the actual aerosol particle size distribution and the size distribution function assumed for aerosol size retrievals may lead to systematic differences in retrieved aerosol size estimates. We demonstrate that these systematic differences may differ significantly for different measurement techniques, which is related to the different sensitivities of these measurement techniques to specific parts of the aerosol particle population. In particular, stratospheric-aerosol size retrievals based on solar-occultation observations may yield systematically larger particle size estimates (median or effective radii) compared to, e.g., lidar backscatter measurements. Aerosol concentration, on the other hand, may be systematically smaller in retrievals based on occultation measurements compared to lidar measurements. The results indicate that stratospheric-aerosol size retrievals based on occultation or lidar measurements have to be interpreted with caution, as long as the actual aerosol particle size distribution is not well known.

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Stratospheric aerosol particle size information in Odin-OSIRIS limb scatter spectra

Atmospheric Measurement Techniques ◽

10.5194/amt-7-507-2014 ◽

2014 ◽

Vol 7 (2) ◽

pp. 507-522 ◽

Cited By ~ 20

Author(s):

L. A. Rieger ◽

A. E. Bourassa ◽

D. A. Degenstein

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Imaging System ◽

Stratospheric Aerosol ◽

Retrieval Algorithm ◽

Aerosol Layer ◽

Aerosol Extinction ◽

Model Calculations ◽

Size Information

Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) onboard the Odin satellite has now taken over a decade of limb scatter measurements that have been used to retrieve the version 5 stratospheric aerosol extinction product. This product is retrieved using a representative particle size distribution to calculate scattering cross sections and scattering phase functions for the forward model calculations. In this work the information content of OSIRIS measurements with respect to stratospheric aerosol is systematically examined for the purpose of retrieving particle size information along with the extinction coefficient. The benefit of using measurements at different wavelengths and scattering angles in the retrieval is studied, and it is found that incorporation of the 1530 nm radiance measurement is key for a robust retrieval of particle size information. It is also found that using OSIRIS measurements at the different solar geometries available on the Odin orbit simultaneously provides little additional benefit. Based on these results, an improved aerosol retrieval algorithm is developed that couples the retrieval of aerosol extinction and mode radius of a log-normal particle size distribution. Comparison of these results with coincident measurements from SAGE III shows agreement in retrieved extinction to within approximately 10% over the bulk of the aerosol layer, which is comparable to version 5. The retrieved particle size, when converted to Ångström coefficient, shows good qualitative agreement with SAGE II measurements made at somewhat shorter wavelengths.

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Issues related to the retrieval of stratospheric aerosol particle size information based on optical measurements

10.5194/amt-2019-342 ◽

2019 ◽

Author(s):

Christian von Savigny ◽

Christoph Hoffmann

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Aerosol Particle ◽

Measurement Techniques ◽

Stratospheric Aerosol ◽

Particle Sizes ◽

Solar Occultation ◽

Lidar Measurements ◽

Aerosol Particle Size

Abstract. Stratospheric sulfate aerosols play an important role for the physics and chemistry of the atmosphere. Key fundamental properties of the aerosols are their size and particle size distribution. Despite extensive research spanning several decades, the scientific understanding of these properties of stratospheric aerosols is incomplete. The particle sizes reported in different studies cover a wide range – even under background stratospheric conditions – and particle sizes retrieved from satellite solar occultation measurements in the optical spectral range show a tendency to be systematically larger than retrievals based on other optical methods. In this contribution we suggest a potential reason for these systematic differences. Differences between the actual aerosol particle size distribution and the size distribution assumed for aerosol size retrievals may lead to systematic differences in retrieved aerosol size. We demonstrate that these systematic differences may differ significantly for different measurement techniques, which is related to the different sensitivities of these measurement techniques to specific parts of the aerosol particle population. In particular, stratospheric aerosol size retrievals based on solar occultation observations may yield systematically larger particle size estimates compared to, e.g., lidar backscatter measurements. Aerosol concentration – on the other hand – may be systematically smaller in retrievals based on occultation measurements compared to lidar measurements. The results question the overall significance of stratospheric aerosol size retrievals based on optical satellite or lidar measurements, as long as the actual aerosol particle size distribution is not well known.

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Aerosol particle size distribution in the stratosphere retrieved from SCIAMACHY limb measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-11-2085-2018 ◽

2018 ◽

Vol 11 (4) ◽

pp. 2085-2100 ◽

Cited By ~ 7

Author(s):

Elizaveta Malinina ◽

Alexei Rozanov ◽

Vladimir Rozanov ◽

Patricia Liebing ◽

Heinrich Bovensmann ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Aerosol Particle ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Solar Light ◽

Data Set ◽

Aerosol Particle Size ◽

Distribution Parameters

Abstract. Information about aerosols in the Earth's atmosphere is of a great importance in the scientific community. While tropospheric aerosol influences the radiative balance of the troposphere and affects human health, stratospheric aerosol plays an important role in atmospheric chemistry and climate change. In particular, information about the amount and distribution of stratospheric aerosols is required to initialize climate models, as well as validate aerosol microphysics models and investigate geoengineering. In addition, good knowledge of stratospheric aerosol loading is needed to increase the retrieval accuracy of key trace gases (e.g. ozone or water vapour) when interpreting remote sensing measurements of the scattered solar light. The most commonly used characteristics to describe stratospheric aerosols are the aerosol extinction coefficient and Ångström coefficient. However, the use of particle size distribution parameters along with the aerosol number density is a more optimal approach. In this paper we present a new retrieval algorithm to obtain the particle size distribution of stratospheric aerosol from space-borne observations of the scattered solar light in the limb-viewing geometry. While the mode radius and width of the aerosol particle size distribution are retrieved, the aerosol particle number density profile remains unchanged. The latter is justified by a lower sensitivity of the limb-scattering measurements to changes in this parameter. To our knowledge this is the first data set providing two parameters of the particle size distribution of stratospheric aerosol from space-borne measurements of scattered solar light. Typically, the mode radius and w can be retrieved with an uncertainty of less than 20 %. The algorithm was successfully applied to the tropical region (20° N–20° S) for 10 years (2002–2012) of SCIAMACHY observations in limb-viewing geometry, establishing a unique data set. Analysis of this new climatology for the particle size distribution parameters showed clear increases in the mode radius after the tropical volcanic eruptions, whereas no distinct behaviour of the absolute distribution width could be identified. A tape recorder, which describes the time lag as the perturbation propagates to higher altitudes, was identified for both parameters after the volcanic eruptions. A quasi-biannual oscillation (QBO) pattern at upper altitudes (28–32 km) is prominent in the anomalies of the analysed parameters. A comparison of the aerosol effective radii derived from SCIAMACHY and SAGE II data was performed. The average difference is found to be around 30 % at the lower altitudes, decreasing with increasing height to almost zero around 30 km. The data sample available for the comparison is, however, relatively small.

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Aerosol particle size distribution in the stratosphere retrieved from SCIAMACHY limb measurements

10.5194/amt-2017-388 ◽

2017 ◽

Author(s):

Elizaveta Malinina ◽

Alexei Rozanov ◽

Vladimir Rozanov ◽

Patricia Liebing ◽

Heinrich Bovensmann ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Aerosol Particle ◽

Volcanic Eruptions ◽

Stratospheric Aerosol ◽

Solar Light ◽

Data Set ◽

Distribution Width ◽

Aerosol Particle Size

Abstract. Information about aerosols in the Earth’s atmosphere is of a great importance in the scientific community. While tropospheric aerosol influences the radiative balance of the troposphere and affects human health, stratospheric aerosol plays an important role in atmospheric chemistry and climate change. In particular, information about the amount and distribution of stratospheric aerosols is required to initialize climate models, as well as validate aerosol microphysics models and investigate geoengineering. In addition, good knowledge of stratospheric aerosol loading is needed to increase the retrieval accuracy for the key trace gases (e.g. ozone or water vapor), when interpreting remote sensing measurements of the scattered solar light. There are several parameters which are commonly used to describe stratospheric aerosols, such as the aerosol extinction coefficient and Ångström coefficient. However, the use of particle size distribution parameters coupled with the aerosol number density is an unambiguous and more optimal approach. In this manuscript we present a new retrieval algorithm to obtain the particle size distribution of the stratospheric aerosol from space borne observations of the scattered solar light in the limb viewing geometry. While the mode radius and width of the aerosol particle size distribution are retrieved, the aerosol particle number density remains unchanged. The latter is justified by a lower sensitivity of the limb-scattering measurements to changes in this parameter. To our knowledge this the first data set providing two parameters of the particle size distribution of the stratospheric aerosol from space borne measurements of the scattered solar light. Generally, the mode radius and absolute distribution width can be retrieved with the uncertainty of less than 20 %. The algorithm was successfully applied to the tropical region (20° N–20° S) for 10 years (2002–2012) of SCIAMACHY observations in limb viewing geometry, establishing a unique data set. Analysis of this new climatology for the particle size distribution parameters showed clear increases of the mode radius after the tropical volcanic eruptions, whereas no distinct behaviour oft the absolute distribution width could be identified. A tape recorder, which describes the time lag as the perturbation propagates to higher altitudes, was identified for both parameters after the volcanic eruptions. A Quasi Biannual Oscillation (QBO) pattern at upper altitudes (28–32 km) is prominent in the anomalies of the analyzed parameters. A comparison of the aerosol effective radii derived from SCIAMACHY and SAGE II data was performed. The average difference is found to be around 30 % at the lower altitudes decreasing with increasing height to almost zero around 30 km. The data sample available for the comparison is, however, relatively small.

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