Data rescue of stratospheric aerosol observations from lidar at Lexington, MA, and Fairbanks, AK, January 1964 to July 1965.

2021 ◽  
Author(s):  
Juan Carlos Antuña-Marrero ◽  
Graham W. Mann ◽  
John Barnes ◽  
Albeth Rodríguez-Vega ◽  
Sarah Shallcross ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Optical Thickness ◽  
Large Degree ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Aerosol Model ◽  
Scattering Ratio ◽  
Relative Errors

<p>We report the recovery and processing methodology of the first ever multi-year lidar dataset of the stratospheric aerosol layer. A Q-switched Ruby lidar measured 66 vertical profiles of 694nm attenuated backscatter at Lexington, Massachusetts between January 1964 and August 1965, with an additional 9 profile measurements conducted from College, Alaska during July and August 1964.</p><p>We describe the processing of the recovered lidar backscattering ratio profiles to produce mid-visible (532nm) stratospheric aerosol extinction profiles (sAEP<sub>532</sub>) and stratospheric aerosol optical depth (sAOD<sub>532</sub>) measurements.</p><p>Stratospheric soundings of temperature, and pressure generate an accurate local molecular backscattering profile, with nearby ozone soundings determining the ozone absorption, those profiles then used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections were also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements.</p><p>We show the two-way transmittance correction has substantial effects on the retrieved sAEP<sub>532</sub> and sAOD<sub>532</sub>, calculated without the corrections resulting in substantially lower values of both variables, as it was not applied in the original processing producing the lidar scattering ratio profiles we rescued. The combined transmittance corrections causes the aerosol extinction to increase by 67 % for Lexington and 27 % for Fairbanks, for sAOD<sub>532</sub> the increases 66 % and 26 % respectively. Comparing the magnitudes of the aerosol extinction and sAOD with the few contemporary available measurements reported show a better agreement in the case of the two way transmittance corrected values.</p><p>The sAEP and sAOD timeseries at Lexington show a surprisingly large degree of variability, three periods where the stratospheric aerosol layer had suddenly elevated optical thickness, the highest sAOD<sub>532</sub> of 0.07 measured at the end of March 1965. The two other periods of enhanced sAOD<sub>532</sub> are both two-month periods where the lidars show more than 1 night where retrieved sAOD<sub>532</sub> exceeded 0.05: in January and February 1964 and November and December 1964.</p><p>Interactive stratospheric aerosol model simulations of the 1963 Agung cloud illustrate that although substantial variation  in mid-latitude sAOD<sub>532</sub> is expected from the seasonal cycle in the Brewer-Dobson circulation, the Agung cloud dispersion will have caused much slower increase than the more episodic variations observed, with also different timing, elevated optical thickness from Agung occurring in winter and spring.</p><p>The abruptness and timing of the steadily increasing sAOD from January to July 1965 suggests this variation was from a different source than Agung, possibly from one or both of the two VEI3 eruptions that occurred in 1964/65: Trident, Alaska and Vestmannaeyjar, Heimey, south of Iceland.</p><p>A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted, relative errors of 54 % for Fairbanks and 44 % Lexington for the uncorrected sAEP<sub>532</sub>, corrected sAEP<sub>532</sub> of 61 % and 64 % respectively.</p><p>The analysis of the uncertainties identified variables that, with additional data recovery and reprocessing could reduce these relative error levels. Data described in this work are available at https://doi.pangaea.de/10.1594/PANGAEA.922105 (Dataset in Review) (Antuña-Marrero et al., 2020).</p>

scholarly journals Recovery of the first ever multi-year lidar dataset of the stratospheric aerosol layer, from Lexington, MA, and Fairbanks, AK, January 1964 to July 1965

2020 ◽  
Author(s):  
Juan-Carlos Antuña-Marrero ◽  
Graham W. Mann ◽  
John Barnes ◽  
Albeth Rodríguez-Vega ◽  
Sarah Shallcross ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Optical Thickness ◽  
Large Degree ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Aerosol Model ◽  
Scattering Ratio ◽  
Relative Errors

Abstract. We report the recovery and processing methodology of the first ever multi-year lidar dataset of the stratospheric aerosol layer. A Q-switched Ruby lidar measured 66 vertical profiles of 694 nm attenuated backscatter at Lexington, Massachusetts between January 1964 and August 1965, with an additional 9 profile measurements conducted from College, Alaska during July and August 1964. We describe the processing of the recovered lidar backscattering ratio profiles to produce mid-visible (532 nm) stratospheric aerosol extinction profiles (sAEP532) and stratospheric aerosol optical depth (sAOD532) measurements, utilizing a number of contemporary measurements of several different atmospheric variables. Stratospheric soundings of temperature, and pressure generate an accurate local molecular backscattering profile, with nearby ozone soundings determining the ozone absorption, those profiles then used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections were also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements. We show the two-way transmittance correction has substantial effects on the retrieved sAEP532 and sAOD532, calculated without the corrections resulting in substantially lower values of both variables, as it was not applied in the original processing producing the lidar scattering ratio profiles we rescued. The combined transmittance corrections causes the aerosol extinction to increase by 67 % for Lexington and 27 % for Fairbanks, for sAOD532 the increases 66 % and 26 % respectively. Comparing the magnitudes of the aerosol extinction and sAOD with the few contemporary available measurements reported show a better agreement in the case of the two way transmittance corrected values. The sAEP and sAOD timeseries at Lexington show a surprisingly large degree of variability, three periods where the stratospheric aerosol layer had suddenly elevated optical thickness, the highest sAOD532 of 0.07 measured at the end of March 1965. The two other periods of enhanced sAOD532 are both two-month periods where the lidars show more than 1 night where retrieved sAOD532 exceeded 0.05: in January and February 1964 and November and December 1964. Interactive stratospheric aerosol model simulations of the 1963 Agung cloud illustrate that although substantial variation in mid-latitude sAOD532 is expected from the seasonal cycle in the Brewer-Dobson circulation, the Agung cloud dispersion will have caused much slower increase than the more episodic variations observed, with also different timing, elevated optical thickness from Agung occurring in winter and spring. The abruptness and timing of the steadily increasing sAOD from January to July 1965 suggests this variation was from a different source than Agung, possibly from one or both of the two VEI3 eruptions that occurred in 1964/65: Trident, Alaska and Vestmannaeyjar, Heimey, south of Iceland. A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted, relative errors of 54 % for Fairbanks and 44 % Lexington for the uncorrected sAEP532, corrected sAEP532 of 61 % and 64 % respectively. The analysis of the uncertainties identified variables that, with additional data recovery and reprocessing could reduce these relative error levels. Data described in this work are available at https://doi.pangaea.de/10.1594/PANGAEA.922105 (Dataset in Review) (Antuña-Marrero et al., 2020a).

scholarly journals Recovery of the first ever multi-year lidar dataset of the stratospheric aerosol layer, from Lexington, MA, and Fairbanks, AK, January 1964 to July 1965

2021 ◽  
Vol 13 (9) ◽  
pp. 4407-4423
Author(s):  
Juan-Carlos Antuña-Marrero ◽  
Graham W. Mann ◽  
John Barnes ◽  
Albeht Rodríguez-Vega ◽  
Sarah Shallcross ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Coupled Model ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Large Variability ◽  
Aerosol Model ◽  
Intercomparison Project ◽  
Relative Errors ◽  
The Tropics

Abstract. We report the recovery and processing methodology of the first ever multi-year lidar dataset of the stratospheric aerosol layer. A Q-switched ruby lidar measured 66 vertical profiles of 694 nm attenuated backscatter at Lexington, Massachusetts, between January 1964 and August 1965, with an additional nine profile measurements conducted from College, Alaska, during July and August 1964. We describe the processing of the recovered lidar backscattering ratio profiles to produce mid-visible (532 nm) stratospheric aerosol extinction profiles (sAEP532) and stratospheric aerosol optical depth (sAOD532) measurements, utilizing a number of contemporary measurements of several different atmospheric variables. Stratospheric soundings of temperature and pressure generate an accurate local molecular backscattering profile, with nearby ozone soundings determining the ozone absorption, which are used to correct for two-way ozone transmittance. Two-way aerosol transmittance corrections are also applied based on nearby observations of total aerosol optical depth (across the troposphere and stratosphere) from sun photometer measurements. We show that accounting for these two-way transmittance effects substantially increases the magnitude of the 1964/1965 stratospheric aerosol layer's optical thickness in the Northern Hemisphere mid-latitudes, then ∼ 50 % larger than represented in the Coupled Model Intercomparison Project 6 (CMIP6) volcanic forcing dataset. Compared to the uncorrected dataset, the combined transmittance correction increases the sAOD532 by up to 66 % for Lexington and up to 27 % for Fairbanks, as well as individual sAEP532 adjustments of similar magnitude. Comparisons with the few contemporary measurements available show better agreement with the corrected two-way transmittance values. Within the January 1964 to August 1965 measurement time span, the corrected Lexington sAOD532 time series is substantially above 0.05 in three distinct periods, October 1964, March 1965, and May–June 1965, whereas the 6 nights the lidar measured in December 1964 and January 1965 had sAOD values of at most ∼ 0.03. The comparison with interactive stratospheric aerosol model simulations of the Agung aerosol cloud shows that, although substantial variation in mid-latitude sAOD532 are expected from the seasonal cycle in the stratospheric circulation, the Agung cloud's dispersion from the tropics would have been at its strongest in winter and weakest in summer. The increasing trend in sAOD from January to July 1965, also considering the large variability, suggests that the observed variations are from a different source than Agung, possibly from one or both of the two eruptions that occurred in 1964/1965 with a Volcanic Explosivity Index (VEI) of 3: Trident, Alaska, and Vestmannaeyjar, Heimaey, south of Iceland. A detailed error analysis of the uncertainties in each of the variables involved in the processing chain was conducted. Relative errors for the uncorrected sAEP532 were 54 % for Fairbanks and 44 % Lexington. For the corrected sAEP532 the errors were 61 % and 64 %, respectively. The analysis of the uncertainties identified variables that with additional data recovery and reprocessing could reduce these relative error levels. Data described in this work are available at https://doi.org/10.1594/PANGAEA.922105 (Antuña-Marrero et al., 2020a).

scholarly journals Nabro volcano aerosol in the stratosphere over Georgia, South Caucasus from ground-based spectrometry of twilight sky brightness

2013 ◽  
Vol 6 (10) ◽  
pp. 2563-2576 ◽  
Author(s):  
N. Mateshvili ◽  
D. Fussen ◽  
G. Mateshvili ◽  
I. Mateshvili ◽  
F. Vanhellemont ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Multiple Scattering ◽  
Optical Depth ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Spectral Measurements ◽  
South Caucasus ◽  
Tropospheric Aerosol ◽  
Sky Brightness

Abstract. Ground-based spectral measurements of twilight sky brightness were carried out between September 2009 and August 2011 in Georgia, South Caucasus. The algorithm which allowed to retrieve the lower stratospheric and upper tropospheric aerosol extinction profiles was developed. The Monte-Carlo technique was used to correctly represent multiple scattering in a spherical atmosphere. The estimated stratospheric aerosol optical depths at a wavelength of 780 nm were: 6 × 10−3 ± 2 × 10−3 (31 August 2009–29 November 2009), 2.5 × 10−3 ± 7 × 10−4 (20 March 2010–15 January 2011) and 8 × 10−3 ± 3 × 10−3 (18 July 2011–3 August 2011). The optical depth values correspond to the moderately elevated stratospheric aerosol level after the Sarychev eruption in 2009, background stratospheric aerosol layer, and the volcanically disturbed stratospheric aerosol layer after the Nabro eruption in June 2011.

scholarly journals Urban Visible/SWIR surface reflectance ratios from satellite and sun photometer measurements in Mexico City

2007 ◽  
Vol 7 (3) ◽  
pp. 8113-8139 ◽  
Author(s):  
A. D. de Almeida Castanho ◽  
R. Prinn ◽  
V. Martins ◽  
M. Herold ◽  
C. Ichoku ◽  
...  
Keyword(s):  
Mexico City ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spatial Resolution ◽  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Sensor Data ◽  
Aerosol Layer ◽  
Surface Reflectance ◽  
Sun Photometer

Abstract. The surface reflectance ratio between the visible (VIS) and shortwave infrared (SWIR) radiation is an important quantity for the retrieval of the aerosol optical depth (τa) from the MODIS sensor data. Based on empirically determined VIS/SWIR ratios, MODIS τa retrieval uses the surface reflectance in the SWIR band (2.1 μm), where the interaction between solar radiation and the aerosol layer is small, to predict the visible reflectances in the blue (0.47 μm) and red (0.66 μm) bands. Therefore, accurate knowledge of the VIS/SWIR ratio is essential for achieving accurate retrieval of aerosol optical depth from MODIS. The heterogeneity of the surface cover in an urban environment increases the uncertainties in the estimation of the surface reflectance and, consequently, τa. We analyzed the surface reflectance over some distinct surface covers in and around the Mexico City metropolitan area (MCMA) using MODIS radiances at 0.66 μm and 2.1 μm. The analysis was performed at 1.5 km×1.5 km spatial resolution. Also, ground-based AERONET sun-photometer data acquired in Mexico City from 2002 to 2005 were analyzed for aerosol optical thickness and other aerosol optical properties. In addition, a network of hand-held sun-photometers deployed in Mexico City, as part of the MCMA-2006 Study during the MILAGRO Campaign, provided an unprecedented measurement of τa in 5 different sites well distributed in the city. We found that the average RED/SWIR ratio representative of the urbanized sites analyzed is 0.73±0.06. This average ratio was significantly different for non-urban sites, which was approximately 0.55. The aerosol optical thickness retrieved from MODIS radiances at a spatial resolution of 1.5 km×1.5 km and averaged within 10 x 10 km boxes were compared with collocated 1-h τa averaged from sun-photometer measurements. The use of the new RED/SWIR ratio of 0.73 in the MODIS retrieval led to a significant improvement in the agreement between the MODIS and sun-photometer results; with the slope, offset, and the correlation coefficient of the linear regression changing from (τaMODIS = 0.91 τa sun-photometer + 0.33 ,R2=0.66) to (τaMODIS = 0.96 τa sun-photometer −0.006, R2=0.87).

scholarly journals Ceilometer Retrieval of the Boundary Layer Vertical Aerosol Extinction Structure

2008 ◽  
Vol 25 (6) ◽  
pp. 928-944 ◽  
Author(s):  
K. M. Markowicz ◽  
P. J. Flatau ◽  
A. E. Kardas ◽  
J. Remiszewska ◽  
K. Stelmaszczyk ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
United Arab Emirates ◽  
Field Measurements ◽  
Lower Atmosphere ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Aerosol Optical Properties

Abstract The CT25K ceilometer is a general-purpose cloud height sensor employing lidar technology for detection of clouds. In this paper it is shown that it can also be used to retrieve aerosol optical properties in the boundary layer. The authors present a comparison of the CT25K instrument with the aerosol lidar system and discuss its good overall agreement for both the range-corrected signals and the retrieved extinction coefficient profiles. The CT25K aerosol profiling is mostly limited to the boundary layer, but it is capable of detecting events in the lower atmosphere such as mineral dust events between 1 and 3 km. Assumptions needed for the estimation of the aerosol extinction profiles are discussed. It is shown that, when a significant part of the aerosol layer is in the boundary layer, knowledge of the aerosol optical depth from a sun photometer allows inversion of the lidar signal. In other cases, surface observations of the aerosol optical properties are used. It is demonstrated that additional information from a nephelometer and aethalometer allows definition of the lidar ratio. Extinction retrievals based on spherical and randomly oriented spheroid assumptions are performed. It is shown, by comparison with the field measurements during the United Arab Emirates Unified Aerosol Experiment, that an assumption about specific particle shape is important for the extinction profile inversions. The authors indicate that this limitation of detection is a result of the relatively small sensitivity of this instrument in comparison to more sophisticated aerosol lidars. However, in many cases this does not play a significant role because globally only about 20% of the aerosol optical depth is above the boundary layer.

scholarly journals Aerosol optical depth measurements by airborne sun photometer in SOLVE II: Comparisons to SAGE III, POAM III and airborne spectrometer measurements

2004 ◽  
Vol 4 (6) ◽  
pp. 7291-7353 ◽  
Author(s):  
P. Russell ◽  
J. Livingston ◽  
B. Schmid ◽  
J. Eilers ◽  
R. Kolyer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Optical Thickness ◽  
Full Range ◽  
Stratospheric Aerosol ◽  
Line Of Sight ◽  
Validation Experiment ◽  
Satellite Sensors ◽  
Beam Transmission ◽  
Polar Ozone

Abstract. The 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) measured solar-beam transmission on the NASA DC-8 during the Second SAGE III Ozone Loss and Validation Experiment (SOLVE II). This paper presents AATS-14 results for multiwavelength aerosol optical depth (AOD), including its spatial structure and comparisons to results from two satellite sensors and another DC-8 instrument. These are the Stratospheric Aerosol and Gas Experiment III (SAGE III), the Polar Ozone and Aerosol Measurement III (POAM III) and the Direct-beam Irradiance Airborne Spectrometer (DIAS). AATS-14 provides aerosol results at 13 wavelengths λ spanning the full range of SAGE III and POAM III aerosol wavelengths. Because most AATS measurements were made at solar zenith angles (SZA) near 90°, retrieved AODs are strongly affected by uncertainties in the relative optical airmass of the aerosols and other constituents along the refracted line of sight (LOS) between instrument and sun. To reduce dependence of the AATS-satellite comparisons on airmass, we perform the comparisons in line-of-sight (LOS) transmission and LOS optical thickness (OT) as well as in vertical OT (i.e., optical depth, OD). We also use a new airmass algorithm that validates the algorithm we previously used to within 2% for SZA<90°, and in addition provides results for SZA≥90°. For 6 DC-8 flights, 19 January–2 February 2003, AATS and DIAS results for LOS aerosol optical thickness (AOT) at λ=400 nm agree to ≤12% of the AATS value. Mean and root-mean-square (RMS) differences, (DIAS-AATS)/AATS, are –2.3% and 7.7%, respectively. For DC-8 altitudes, AATS-satellite comparisons are possible only for λ>440 nm, because of signal depletion for shorter λ on the satellite full-limb LOS. For the 4 AATS-SAGE and 4 AATS-POAM near-coincidences conducted 19–31 January 2003, AATS-satellite AOD differences were ≤0.0041 for all λ>440 nm. RMS differences were ≤0.0022 for SAGE-AATS and ≤0.0026 for POAM-AATS. RMS percentage differences in AOD ([SAGE-AATS]/AATS) were ≤33% for λ<~755 nm, but grew to 59% for 1020 nm and 66% at 1545 nm. For λ>~755 nm, AATS-POAM differences were less than AATS-SAGE differences, and RMS percentage differences in AOD ([AATS-POAM]/AATS) were ≤31% for all λ between 440 and 1020 nm. Unexplained differences that remain are associated with transmission differences, rather than differences in gas subtraction or conversion from LOS to vertical quantities. The very small stratospheric AOD values that occurred during SOLVE II added to the challenge of the comparisons, but do not explain all the differences.

scholarly journals Minimum aerosol layer detection sensitivities and their subsequent impacts on aerosol optical thickness retrievals in CALIPSO level 2 data products

2018 ◽  
Vol 11 (1) ◽  
pp. 499-514 ◽  
Author(s):  
Travis D. Toth ◽  
James R. Campbell ◽  
Jeffrey S. Reid ◽  
Jason L. Tackett ◽  
Mark A. Vaughan ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Aerosol Optical Thickness ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Noise Floor ◽  
Data Products ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Level 2 ◽  
Global Mean

Abstract. Due to instrument sensitivities and algorithm detection limits, level 2 (L2) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) 532 nm aerosol extinction profile retrievals are often populated with retrieval fill values (RFVs), which indicate the absence of detectable levels of aerosol within the profile. In this study, using 4 years (2007–2008 and 2010–2011) of CALIOP version 3 L2 aerosol data, the occurrence frequency of daytime CALIOP profiles containing all RFVs (all-RFV profiles) is studied. In the CALIOP data products, the aerosol optical thickness (AOT) of any all-RFV profile is reported as being zero, which may introduce a bias in CALIOP-based AOT climatologies. For this study, we derive revised estimates of AOT for all-RFV profiles using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) Dark Target (DT) and, where available, AErosol RObotic NEtwork (AERONET) data. Globally, all-RFV profiles comprise roughly 71 % of all daytime CALIOP L2 aerosol profiles (i.e., including completely attenuated profiles), accounting for nearly half (45 %) of all daytime cloud-free L2 aerosol profiles. The mean collocated MODIS DT (AERONET) 550 nm AOT is found to be near 0.06 (0.08) for CALIOP all-RFV profiles. We further estimate a global mean aerosol extinction profile, a so-called “noise floor”, for CALIOP all-RFV profiles. The global mean CALIOP AOT is then recomputed by replacing RFV values with the derived noise-floor values for both all-RFV and non-all-RFV profiles. This process yields an improvement in the agreement of CALIOP and MODIS over-ocean AOT.

scholarly journals Evidence for the predictability of changes in the stratospheric aerosol size following volcanic eruptions of diverse magnitudes using space-based instruments

2020 ◽  
Author(s):  
Larry W. Thomason ◽  
Mahesh Kovilakam ◽  
Anja Schmidt ◽  
Christian von Savigny ◽  
Travis Knepp ◽  
...  
Keyword(s):  
Size Distribution ◽  
Extinction Coefficient ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Global Climate Models ◽  
Aerosol Size Distribution ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Volcanic Event ◽  
Aerosol Extinction Coefficient

Abstract. An analysis of multiwavelength stratospheric aerosol extinction coefficient data from the Stratospheric Aerosol and Gas Experiment II and III/ISS instruments is used to demonstrate a coherent relationship between the perturbation in extinction coefficient in an eruption's main aerosol layer and an apparent change in aerosol size distribution that spans multiple orders of magnitude in the stratospheric impact of a volcanic event. The relationship is measurement-based and does not rely on assumptions about the aerosol size distribution. We note limitations on this analysis including that the presence of significant amounts of ash in the main aerosol layer may significantly modulate these results. Despite this limitation, these findings represent a unique opportunity to verify the performance of interactive aerosol models used in Global Climate Models and Earth System Model and may suggest an avenue for improving aerosol extinction coefficient measurements from single channel observations such the Optical Spectrograph and Infrared Imager System as they rely on a priori assumptions about particle size.

scholarly journals Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

2020 ◽  
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Atmospheric Aerosols ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus candidate mission for anthropogenic CO2 monitoring (CO2M). To this end, we compare aerosol-induced XCO2 errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm, and a spread (defined as half of the 15.9th to the 84.1th percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to a worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise using both MAP and spectrometer measurements of the synthetic scenes delivers XCO2 errors with an overall bias of −0.004 ppm and a spread of 0.54 ppm, implying compliance with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.

scholarly journals Evidence for the predictability of changes in the stratospheric aerosol size following volcanic eruptions of diverse magnitudes using space-based instruments

2021 ◽  
Vol 21 (2) ◽  
pp. 1143-1158 ◽  
Author(s):  
Larry W. Thomason ◽  
Mahesh Kovilakam ◽  
Anja Schmidt ◽  
Christian von Savigny ◽  
Travis Knepp ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Climate Models ◽  
Single Channel ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Global Climate Models ◽  
Aerosol Size Distribution ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Aerosol Extinction Coefficient

Abstract. An analysis of multiwavelength stratospheric aerosol extinction coefficient data from the Stratospheric Aerosol and Gas Experiment II and III/ISS instruments is used to demonstrate a coherent relationship between the perturbation in extinction coefficient in an eruption's main aerosol layer and the wavelength dependence of that perturbation. This relationship spans multiple orders of magnitude in the aerosol extinction coefficient of stratospheric impact of volcanic events. The relationship is measurement-based and does not rely on assumptions about the aerosol size distribution. We note limitations on this analysis including that the presence of significant amounts of ash in the main sulfuric acid aerosol layer and other factors may significantly modulate these results. Despite these limitations, the findings suggest an avenue for improving aerosol extinction coefficient measurements from single-channel observations such as the Optical Spectrograph and Infrared Imager System as they rely on a prior assumptions about particle size. They may also represent a distinct avenue for the comparison of observations with interactive aerosol models used in global climate models and Earth system models.

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