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<front>
<journal-meta>
<journal-id journal-id-type="publisher">ACP</journal-id>
<journal-title-group>
<journal-title>Atmospheric Chemistry and Physics</journal-title>
<abbrev-journal-title abbrev-type="publisher">ACP</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">Atmos. Chem. Phys.</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">1680-7324</issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/acp-13-4605-2013</article-id>
<title-group>
<article-title>Improved SAGE II cloud/aerosol categorization and observations of the Asian tropopause aerosol layer: 1989&amp;ndash;2005</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Thomason</surname>
<given-names>L. W.</given-names>
<ext-link>https://orcid.org/0000-0002-1902-0840</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Vernier</surname>
<given-names>J.-P.</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>NASA Langley Research Center, Hampton, Virginia, USA</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Science Systems and Applications, Inc., Hampton, Virginia, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>03</day>
<month>05</month>
<year>2013</year>
</pub-date>
<volume>13</volume>
<issue>9</issue>
<fpage>4605</fpage>
<lpage>4616</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2013 L. W. Thomason</copyright-statement>
<copyright-year>2013</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/3.0/">https://creativecommons.org/licenses/by/3.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://acp.copernicus.org/articles/13/4605/2013/acp-13-4605-2013.html">This article is available from https://acp.copernicus.org/articles/13/4605/2013/acp-13-4605-2013.html</self-uri>
<self-uri xlink:href="https://acp.copernicus.org/articles/13/4605/2013/acp-13-4605-2013.pdf">The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/4605/2013/acp-13-4605-2013.pdf</self-uri>
<abstract>
<p>We describe the challenges associated with the interpretation of extinction
coefficient measurements by the Stratospheric Aerosol and Gas Experiment
(SAGE II) in the presence of clouds. In particular, we have found that
tropospheric aerosol analyses are highly dependent on a robust method for
identifying when clouds affect the measured extinction coefficient. Herein,
we describe an improved cloud identification method that appears to capture
cloud/aerosol events more effectively than early methods. In addition, we
summarize additional challenges to observing the Asian Tropopause Aerosol
Layer (ATAL) using SAGE II
observations. Using this new approach, we perform analyses of the upper
troposphere, focusing on periods in which the UTLS (upper troposphere/lower
stratosphere) is relatively free of
volcanic material (1989–1990 and after 1996). Of particular interest is the
Asian monsoon anticyclone where CALIPSO (Cloud-Aerosol Lidar Pathfinder Satellite Observations) has observed an
aerosol enhancement. This enhancement, called the ATAL, has a similar morphology to observed enhancements in
long-lived trace gas species like CO. Since the CALIPSO record begins in
2006, the question of how long this aerosol feature has been present
requires a new look at the long-lived SAGE II data sets despite significant
hurdles to its use in the subtropical upper troposphere. We find that there
is no evidence of ATAL in the SAGE II data prior to 1998. After 1998, it is
clear that aerosol in the upper troposphere in the ATAL region is
substantially enhanced relative to the period before that time. In addition,
the data generally supports the presence of the ATAL beginning in 1999
and continuing through the end of the mission, though some years (e.g., 2003)
are complicated by the presence of episodic enhancements most likely of
volcanic origin.</p>
</abstract>
<counts><page-count count="12"/></counts>
</article-meta>
</front>
<body/>
<back>
<ref-list>
<title>References</title>
<ref id="ref1">
<label>1</label><mixed-citation publication-type="other" xlink:type="simple">Bourassa, A. E., Robock, A., Randel, W., Deshler, T., Rieger, L., Nicholas, D., Llewellyn, L., and Degenstein, D.: Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport, Science, 337, 78–81, &lt;a href=&quot;http://dx.doi.org/10.1126/science.1219371&quot;&gt;https://doi.org/10.1126/science.1219371&lt;/a&gt;, 2012.</mixed-citation>
</ref>
<ref id="ref2">
<label>2</label><mixed-citation publication-type="other" xlink:type="simple">Kent, G. S., Winker, D. M., Osborn, M. T., McCormick, M. P., and Skeens, K. M.: A model for the separation of cloud and aerosol in SAGE II occultation data, J. Geophys. Res., 98, 20725–20735, 1993.</mixed-citation>
</ref>
<ref id="ref3">
<label>3</label><mixed-citation publication-type="other" xlink:type="simple">Kent, G. S., Winker, D. M., Vaughan, M. A., Wang, P.-H., and Skeen, K. M.: Simulation of Stratospheric Aerosol and Gas Experiment (SAGE) II cloud measurements using airborne lidar data, J. Geophys. Res., 102, 21795–21807, 1997.</mixed-citation>
</ref>
<ref id="ref4">
<label>4</label><mixed-citation publication-type="other" xlink:type="simple">Kent, G. S., Trepte, C. R., and Lucker, P. L., Long-term Stratospheric Aerosol and Gas Experiment I and II measurements of upper tropospheric aerosol extinction, J. Geophys. Res., 103, 28863–28874, 1998.</mixed-citation>
</ref>
<ref id="ref5">
<label>5</label><mixed-citation publication-type="other" xlink:type="simple">Kim, Y. S., Shibata, T., Iwasaka, Y., Shi, G., Zhou, X., Tamura, K., and Ohashi, T.: Enhancements of aerosols near the cold tropopause in summer over Tibetan Plateau: Lidar and balloon borne measurements in 1999 at Lhasa, Tibet, China, Proc. SPIE, 4893, 496{–}503, &lt;a href=&quot;http://dx.doi.org/10.1117/12.466090&quot;&gt;https://doi.org/10.1117/12.466090&lt;/a&gt;, 2003.</mixed-citation>
</ref>
<ref id="ref6">
<label>6</label><mixed-citation publication-type="other" xlink:type="simple">Pitts, M. C., Poole, L. R., and Thomason, L. W.: CALIPSO polar stratospheric cloud observations: second-generation detection algorithm and composition discrimination, Atmos. Chem. Phys., 9, 7577–7589, &lt;a href=&quot;http://dx.doi.org/10.5194/acp-9-7577-2009&quot;&gt;https://doi.org/10.5194/acp-9-7577-2009&lt;/a&gt;, 2009.</mixed-citation>
</ref>
<ref id="ref7">
<label>7</label><mixed-citation publication-type="other" xlink:type="simple">Randel, W. J., Park, M., Emmons, L., Kinnison, D., Bernath, P., Walker, K. A., Boone, C., and Pumphrey, H.: Asian monsoon transport of pollution to the stratosphere, Science, 328, 611{–}613, &lt;a href=&quot;http://dx.doi.org/10.1126/science.1182274&quot;&gt;https://doi.org/10.1126/science.1182274&lt;/a&gt;, 2010.</mixed-citation>
</ref>
<ref id="ref8">
<label>8</label><mixed-citation publication-type="other" xlink:type="simple">Roberts, G., Wooster, M. J., and Lagoudakis, E.: Annual and diurnal african biomass burning temporal dynamics, Biogeosciences, 6, 849–866, &lt;a href=&quot;http://dx.doi.org/10.5194/bg-6-849-2009&quot;&gt;https://doi.org/10.5194/bg-6-849-2009&lt;/a&gt;, 2009.</mixed-citation>
</ref>
<ref id="ref9">
<label>9</label><mixed-citation publication-type="other" xlink:type="simple">SPARC: Assessment of Stratospheric Aerosol Properties (ASAP), SPARC Report No. 4, WCRP-124, WMO/TD-No. 1295, February 2006, edited by: Thomason, L. and Peter, Th.,  2006.</mixed-citation>
</ref>
<ref id="ref10">
<label>10</label><mixed-citation publication-type="other" xlink:type="simple">Thomason, L. W., Kent, G. S., Trepte, C. R., and Poole, L. R.: A comparison of the stratospheric aerosol background periods of 1979 and 1989–1991, J. Geophys. Res., 102, 3611–3616, 1997a.</mixed-citation>
</ref>
<ref id="ref11">
<label>11</label><mixed-citation publication-type="other" xlink:type="simple">Thomason, L. W., Poole, L. R., and Deshler, T. R.: A global climatology of stratospheric aerosol surface area density as deduced from SAGE II: 1984–1994, J. Geophys. Res., 102, 8967–8976, 1997b.</mixed-citation>
</ref>
<ref id="ref12">
<label>12</label><mixed-citation publication-type="other" xlink:type="simple">Thomason, L. W., Herber, A. B., Yamanouchi, T., and Sato, K.: Arctic Study on Tropospheric Aerosol and Radiation: Comparison of tropospheric aerosol extinction profiles measured by airborne photometer and SAGE II, Geophys. Res. Lett., 30, 1328–1331, &lt;a href=&quot;http://dx.doi.org/10.1029/2002GL016453&quot;&gt;https://doi.org/10.1029/2002GL016453&lt;/a&gt;, 2003.</mixed-citation>
</ref>
<ref id="ref13">
<label>13</label><mixed-citation publication-type="other" xlink:type="simple">Thomason, L. W., Burton, S. P., Luo, B.-P., and Peter, T.: SAGE II measurements of stratospheric aerosol properties at non-volcanic levels, Atmos. Chem. Phys., 8, 983–995, &lt;a href=&quot;http://dx.doi.org/10.5194/acp-8-983-2008&quot;&gt;https://doi.org/10.5194/acp-8-983-2008&lt;/a&gt;, 2008.</mixed-citation>
</ref>
<ref id="ref14">
<label>14</label><mixed-citation publication-type="other" xlink:type="simple">Tobo, Y., Iwasaka, Y., Shi, G.-Y., Kim, Y.-S., Ohashi, T., Tamura, K., and Zhang, D.: Balloon{-}borne observations of high aerosol concentrations near the summertime tropopause over the Tibetan Plateau, Atmos. Res., 84, 233{–}241, &lt;a href=&quot;http://dx.doi.org/10.1016/j.atmosres.2006.08.003&quot;&gt;https://doi.org/10.1016/j.atmosres.2006.08.003&lt;/a&gt;, 2007.</mixed-citation>
</ref>
<ref id="ref15">
<label>15</label><mixed-citation publication-type="other" xlink:type="simple">Vernier, J.-P., Thomason, L. W., and Kar, J.: CALIPSO detection of an Asian tropopause aerosol layer, Geophys. Res. Lett., 38, L07804, &lt;a href=&quot;http://dx.doi.org/10.1029/2010GL046614&quot;&gt;https://doi.org/10.1029/2010GL046614&lt;/a&gt;, 2011a.</mixed-citation>
</ref>
<ref id="ref16">
<label>16</label><mixed-citation publication-type="other" xlink:type="simple">Vernier, J. P., Thomason, L. W., Pommereau, J. P., Bourassa, A., Pelon, J., Garnier, A., Hauchecorne, A., Blanot, L., Trepte, C., Degenstein, D., and Vargas, F.: Volcanic origin of the recent stratospheric aerosol trend, Geophys. Res. Lett., 38, L12807, &lt;a href=&quot;http://dx.doi.org/10.1029/2011GL047563&quot;&gt;https://doi.org/10.1029/2011GL047563&lt;/a&gt;, 2011b.</mixed-citation>
</ref>
<ref id="ref17">
<label>17</label><mixed-citation publication-type="other" xlink:type="simple">Wang, P.-H., Minnis, P., McCormick, M. P., Kent, G. S., and Skeens, K. S.: A 6-year climatology of cloud occurrence frequency from SAGE II observations (1985–1990), J. Geophys. Res., 101, 29407–29429, 1996.</mixed-citation>
</ref>
<ref id="ref18">
<label>18</label><mixed-citation publication-type="other" xlink:type="simple">Wang, P.-H., Minnis, P., Wielicki, B. A., Wong, T., Cess, R. D., Zhang, M., Vann, L. B., and Kent, G. S.: Characteristics of the 1997/1998 El Niño cloud distributions from SAGE II observations, J. Geophys. Res., 108, 4009, &lt;a href=&quot;http://dx.doi.org/10.1029/2002JD002501&quot;&gt;https://doi.org/10.1029/2002JD002501&lt;/a&gt;, 2003.</mixed-citation>
</ref>
</ref-list>
</back>
</article>