Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results
<p>We analyze Aura Microwave Limb Sounder (MLS) monthly zonal mean time series of ClO and HOCl between 50<span class="inline-formula"><sup>∘</sup></span> S and 50<span class="inline-formula"><sup>∘</sup></span> N to estimate u...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/4779/2022/acp-22-4779-2022.pdf |
| _version_ | 1811271545225478144 |
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| author | L. Froidevaux D. E. Kinnison M. L. Santee L. F. Millán N. J. Livesey W. G. Read C. G. Bardeen J. J. Orlando R. A. Fuller |
| author_facet | L. Froidevaux D. E. Kinnison M. L. Santee L. F. Millán N. J. Livesey W. G. Read C. G. Bardeen J. J. Orlando R. A. Fuller |
| author_sort | L. Froidevaux |
| collection | DOAJ |
| description | <p>We analyze Aura Microwave Limb Sounder (MLS) monthly zonal mean time series of ClO and HOCl between 50<span class="inline-formula"><sup>∘</sup></span> S and 50<span class="inline-formula"><sup>∘</sup></span> N to estimate upper stratospheric trends in these chlorine species from 2005 through 2020. We compare these observations to those from the Whole Atmosphere Community Climate Model version 6 (WACCM6), run under the specified dynamics configuration. The model sampling follows the MLS coverage in space and local time. We use version 5 MLS ClO zonal mean daytime profiles and similarly binned daytime ClO model profiles from 32 to 1.5 hPa. For MLS HOCl, we use the version 5 offline product derived from daily zonal mean radiances rather than averaged level-2 profiles; MLS HOCl is scientifically useful between 10 and 2 hPa, and the HOCl monthly zonal means are separated into day and night for comparison to WACCM6. We find good agreement (mostly within <span class="inline-formula">∼</span> 10 %) between the climatological MLS ClO daytime distributions and the model ClO climatology for 2005–2020. The model HOCl climatology, however, underestimates the MLS HOCl climatology by about 30 %. This could well be caused by a combination of fairly large systematic uncertainties in both the model-assumed rate constant for the formation of HOCl and the MLS HOCl retrievals themselves.</p>
<p>The model daytime ClO trends versus latitude and pressure agree quite well with those from MLS. MLS-derived near-global upper stratospheric daytime trends between 7 and 2 hPa are <span class="inline-formula">−</span>0.73 <span class="inline-formula">±</span> 0.40 % yr<span class="inline-formula"><sup>−1</sup></span> for ClO and <span class="inline-formula">−</span>0.39 <span class="inline-formula">±</span> 0.35 % yr<span class="inline-formula"><sup>−1</sup></span> for HOCl, with 2<span class="inline-formula"><i>σ</i></span> uncertainty estimates used here. The corresponding model decreases are somewhat faster than observed (although the difference is not statistically significant), with trend values of <span class="inline-formula">−</span>0.85 <span class="inline-formula">±</span> 0.45 % yr<span class="inline-formula"><sup>−1</sup></span> for ClO and <span class="inline-formula">−</span>0.64 <span class="inline-formula">±</span> 0.37 % yr<span class="inline-formula"><sup>−1</sup></span> for HOCl. Both data and model results point to a faster trend in ClO than in HOCl. The MLS ClO trends are consistent with past estimates of upper stratospheric ClO trends from satellite and ground-based microwave data. As discussed in the past, trends in other species (in particular, positive trends in CH<span class="inline-formula"><sub>4</sub></span> and H<span class="inline-formula"><sub>2</sub></span>O) can lead to a ClO decrease that is faster than the decrease in total inorganic chlorine. Regarding trends in HOCl, positive trends in HO<span class="inline-formula"><sub>2</sub></span> can lead to a faster rate of formation for HOCl as a function of time, which partially offsets the decreasing trend in active chlorine.</p>
<p>The decreasing trends in upper stratospheric ClO and HOCl provide additional confirmation of the effectiveness of the Montreal Protocol and its amendments, which have led to the early stages of an expected long-term ozone recovery from the effects of ozone-depleting substances.</p> |
| first_indexed | 2024-04-12T22:23:00Z |
| format | Article |
| id | doaj.art-7f3d678f37424c73b0be27a177e10342 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-12T22:23:00Z |
| publishDate | 2022-04-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-7f3d678f37424c73b0be27a177e103422022-12-22T03:14:17ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-04-01224779479910.5194/acp-22-4779-2022Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model resultsL. Froidevaux0D. E. Kinnison1M. L. Santee2L. F. Millán3N. J. Livesey4W. G. Read5C. G. Bardeen6J. J. Orlando7R. A. Fuller8Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USANational Center for Atmospheric Research, Boulder, Colorado, USAJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USAJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USAJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USAJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USANational Center for Atmospheric Research, Boulder, Colorado, USANational Center for Atmospheric Research, Boulder, Colorado, USAJet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA<p>We analyze Aura Microwave Limb Sounder (MLS) monthly zonal mean time series of ClO and HOCl between 50<span class="inline-formula"><sup>∘</sup></span> S and 50<span class="inline-formula"><sup>∘</sup></span> N to estimate upper stratospheric trends in these chlorine species from 2005 through 2020. We compare these observations to those from the Whole Atmosphere Community Climate Model version 6 (WACCM6), run under the specified dynamics configuration. The model sampling follows the MLS coverage in space and local time. We use version 5 MLS ClO zonal mean daytime profiles and similarly binned daytime ClO model profiles from 32 to 1.5 hPa. For MLS HOCl, we use the version 5 offline product derived from daily zonal mean radiances rather than averaged level-2 profiles; MLS HOCl is scientifically useful between 10 and 2 hPa, and the HOCl monthly zonal means are separated into day and night for comparison to WACCM6. We find good agreement (mostly within <span class="inline-formula">∼</span> 10 %) between the climatological MLS ClO daytime distributions and the model ClO climatology for 2005–2020. The model HOCl climatology, however, underestimates the MLS HOCl climatology by about 30 %. This could well be caused by a combination of fairly large systematic uncertainties in both the model-assumed rate constant for the formation of HOCl and the MLS HOCl retrievals themselves.</p> <p>The model daytime ClO trends versus latitude and pressure agree quite well with those from MLS. MLS-derived near-global upper stratospheric daytime trends between 7 and 2 hPa are <span class="inline-formula">−</span>0.73 <span class="inline-formula">±</span> 0.40 % yr<span class="inline-formula"><sup>−1</sup></span> for ClO and <span class="inline-formula">−</span>0.39 <span class="inline-formula">±</span> 0.35 % yr<span class="inline-formula"><sup>−1</sup></span> for HOCl, with 2<span class="inline-formula"><i>σ</i></span> uncertainty estimates used here. The corresponding model decreases are somewhat faster than observed (although the difference is not statistically significant), with trend values of <span class="inline-formula">−</span>0.85 <span class="inline-formula">±</span> 0.45 % yr<span class="inline-formula"><sup>−1</sup></span> for ClO and <span class="inline-formula">−</span>0.64 <span class="inline-formula">±</span> 0.37 % yr<span class="inline-formula"><sup>−1</sup></span> for HOCl. Both data and model results point to a faster trend in ClO than in HOCl. The MLS ClO trends are consistent with past estimates of upper stratospheric ClO trends from satellite and ground-based microwave data. As discussed in the past, trends in other species (in particular, positive trends in CH<span class="inline-formula"><sub>4</sub></span> and H<span class="inline-formula"><sub>2</sub></span>O) can lead to a ClO decrease that is faster than the decrease in total inorganic chlorine. Regarding trends in HOCl, positive trends in HO<span class="inline-formula"><sub>2</sub></span> can lead to a faster rate of formation for HOCl as a function of time, which partially offsets the decreasing trend in active chlorine.</p> <p>The decreasing trends in upper stratospheric ClO and HOCl provide additional confirmation of the effectiveness of the Montreal Protocol and its amendments, which have led to the early stages of an expected long-term ozone recovery from the effects of ozone-depleting substances.</p>https://acp.copernicus.org/articles/22/4779/2022/acp-22-4779-2022.pdf |
| spellingShingle | L. Froidevaux D. E. Kinnison M. L. Santee L. F. Millán N. J. Livesey W. G. Read C. G. Bardeen J. J. Orlando R. A. Fuller Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results Atmospheric Chemistry and Physics |
| title | Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results |
| title_full | Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results |
| title_fullStr | Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results |
| title_full_unstemmed | Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results |
| title_short | Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results |
| title_sort | upper stratospheric clo and hocl trends 2005 2020 aura microwave limb sounder and model results |
| url | https://acp.copernicus.org/articles/22/4779/2022/acp-22-4779-2022.pdf |
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