A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements
<p>A series of in situ measurements made by optical particle counters (OPCs) at Laramie, Wyoming, provides size-resolved stratospheric aerosol concentration data over the period 1971–2018. A subset of these data covering the period of 2008–2017 is analyzed in this study for the purpose of asse...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2020-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/13/1071/2020/amt-13-1071-2020.pdf |
| _version_ | 1819116782144716800 |
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| author | E. Nyaku R. Loughman P. K. Bhartia T. Deshler Z. Chen P. R. Colarco |
| author_facet | E. Nyaku R. Loughman P. K. Bhartia T. Deshler Z. Chen P. R. Colarco |
| author_sort | E. Nyaku |
| collection | DOAJ |
| description | <p>A series of in situ measurements made by optical particle counters (OPCs) at Laramie, Wyoming, provides size-resolved stratospheric aerosol concentration data over the period 1971–2018. A subset of these data covering the period of 2008–2017 is analyzed in this study for the purpose of assessing the sensitivity of the stratospheric aerosol phase function to the aerosol size distribution (ASD) model used to fit the measurements. The two unimodal ASD models investigated are the unimodal lognormal (UMLN) and gamma distribution models, with the minimum <span class="inline-formula"><i>χ</i><sup>2</sup></span> method employed to assess how well each ASD fits the measurements. The aerosol phase function (<span class="inline-formula"><i>P</i><sub>a</sub>(Θ)</span>) for each ASD is calculated using Mie theory and is compared to the <span class="inline-formula"><i>P</i><sub>a</sub>(Θ)</span> derived from the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics module. Comparing the <span class="inline-formula"><i>χ</i><sup>2</sup></span> values for the fits at altitudes of 20 and 25 <span class="inline-formula">km</span> shows that the UMLN distribution better represents the OPC measurements; however, the gamma distribution fits the CARMA model results better than the UMLN model when the CARMA model results are subsetted into the OPC measurement bins. Comparing phase functions derived from the UMLN distribution fit to OPC data with gamma distributions fit to CARMA model results at the location of the OPC measurements shows a satisfying agreement (<span class="inline-formula">±5</span> %) within the scattering angle range of limb sounding satellites. This uncertainty is considerably larger if the CARMA data are fit with a UMLN.</p> |
| first_indexed | 2024-12-22T05:22:33Z |
| format | Article |
| id | doaj.art-44b472c6adf24afca6feacc7c5786e5d |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-22T05:22:33Z |
| publishDate | 2020-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-44b472c6adf24afca6feacc7c5786e5d2022-12-21T18:37:41ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482020-03-01131071108710.5194/amt-13-1071-2020A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurementsE. Nyaku0R. Loughman1P. K. Bhartia2T. Deshler3Z. Chen4P. R. Colarco5Center of Atmospheric Science, Hampton University, Hampton, Virginia, USACenter of Atmospheric Science, Hampton University, Hampton, Virginia, USANASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USADepartment of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USAScience Systems and Applications, Inc. (SSAI), 10210 Greenbelt Road, Suite 600, Lanham, Maryland 20706, USANASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA<p>A series of in situ measurements made by optical particle counters (OPCs) at Laramie, Wyoming, provides size-resolved stratospheric aerosol concentration data over the period 1971–2018. A subset of these data covering the period of 2008–2017 is analyzed in this study for the purpose of assessing the sensitivity of the stratospheric aerosol phase function to the aerosol size distribution (ASD) model used to fit the measurements. The two unimodal ASD models investigated are the unimodal lognormal (UMLN) and gamma distribution models, with the minimum <span class="inline-formula"><i>χ</i><sup>2</sup></span> method employed to assess how well each ASD fits the measurements. The aerosol phase function (<span class="inline-formula"><i>P</i><sub>a</sub>(Θ)</span>) for each ASD is calculated using Mie theory and is compared to the <span class="inline-formula"><i>P</i><sub>a</sub>(Θ)</span> derived from the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics module. Comparing the <span class="inline-formula"><i>χ</i><sup>2</sup></span> values for the fits at altitudes of 20 and 25 <span class="inline-formula">km</span> shows that the UMLN distribution better represents the OPC measurements; however, the gamma distribution fits the CARMA model results better than the UMLN model when the CARMA model results are subsetted into the OPC measurement bins. Comparing phase functions derived from the UMLN distribution fit to OPC data with gamma distributions fit to CARMA model results at the location of the OPC measurements shows a satisfying agreement (<span class="inline-formula">±5</span> %) within the scattering angle range of limb sounding satellites. This uncertainty is considerably larger if the CARMA data are fit with a UMLN.</p>https://www.atmos-meas-tech.net/13/1071/2020/amt-13-1071-2020.pdf |
| spellingShingle | E. Nyaku R. Loughman P. K. Bhartia T. Deshler Z. Chen P. R. Colarco A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements Atmospheric Measurement Techniques |
| title | A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| title_full | A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| title_fullStr | A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| title_full_unstemmed | A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| title_short | A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| title_sort | comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements |
| url | https://www.atmos-meas-tech.net/13/1071/2020/amt-13-1071-2020.pdf |
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