Although HOCl is not a major chlorine gas in terms of the atmospheric chlorine budget or ozone destruction, it does play some role in the chemical ozone destruction cycles and there are still significant uncertainties in its rate of formation (from ClO and HO2).
The HOCl Molecule
How it is part of MLS Science Objectives
Although HOCl is not a major chlorine gas in terms of
the chlorine budget or ozone destruction, it does play
some role in the chemical ozone destruction cycles
and there are still significant uncertainties in its rate
of formation (from ClO and HO2). Obtaining global
measurements of this product could help constrain
some of these uncertainties.
How EOS MLS measures HOCl
The standard product for HOCl is taken from the 640 GHz retrievals. Simulations indicate that enhanced
lower stratospheric values of 0.5 to 1 ppbv may be tracked at the 20% level, in single profiles. Real data
systematics for HOCl, however, lead us to recommend a maximum pressure of 10 hPa.
HOCl is a noisy product and its typical stratospheric abundance is expected to be less than ~200 pptv,
except under heterogeneously-enhanced conditions in the lower stratospheric winter polar vortex, where
larger abundances of order 0.5 - 1 ppbv may occasionally be found.
We feel that zonal mean information (e.g., in 10°-wide bins) from one day's worth of MLS data is marginally
useful, although monthly or bi-weekly averages will reduce the noise to more practical levels.
show a reasonable behavior in the upper stratosphere
but have a tendency to be somewhat lower than other
data (balloon data), and lower also (from a
rough comparison) than the MIPAS published values
(Von Clarmann et al., JGR, 2006) for Sep./Oct. 2002.
More progress in the MLS retrievals for HOCl may come
from (off-line) retrievals using averaged radiances
or other methods in the future.
Quick Product Information for data version v4.2
- Swath Name: HOCl
- Status Flag: Only use profiles for which the Status field is an even number.
- Useful Range: 10 - 2.2 hPa
- DAAC Short Name: ML2HOCL
- Precision: Only use values for which the estimated precision is a positive number.
- Quality Threshold: >1.2
- Convergence Threshold: <1.05
|Download EOS Aura MLS HOCl v4.2 data
Publications related to the MLS HOCl data product
- Hegglin, M., S. Tegtmeier, J. Anderson, A. Bourassa, S. Brohede, D. Degenstein, L. Froidevaux, B. Funke, J. Gille, A. Jones, Y. Kasai, E. Kyrola, J. Lumpe, J. Neu, E. Remsberg, A. Rozanov, M. Toohey, J. Urban, T. von Clarmann, K.A. Walker, R. Wang, "The SPARC Data Initiative: Assessment of stratospheric trace gas and aerosol climatologies from satellite limb sounders", SPARC Report 8, https://dx.doi.org/10.3929/ethz-a-010863911, 2017. reprint
- Khosravi, M., P. Baron, J. Urban, L. Froidevaux, A.I. Jonsson, Y. Kasai, K. Kuribayashi, C. Mitsuda, D.P. Murtagh, H. Sagawa, M.L. Santee, T.O. Sato, M. Shiotani, M. Suzuki, T. von Clarmann, K.A. Walker, S. Wang, "Diurnal variation of stratospheric and lower mesospheric HOCl, ClO and HO2 at the equator: comparison of 1-D model calculations with measurements by satellite instruments", Atmospheric Chemistry and Physics 13, 7587-7606, doi:10.5194/acp-13-7587-2013, 2013. reprint
- Damiani, A., B. Funke, D.R. Marsh, M. Lopez-Puertas, M.L. Santee, L. Froidevaux, S. Wang, C.H. Jackman, T. von Clarmann, A. Gardini, R.R. Cordero, M. Storini, "Impact of January 2005 solar proton events on chlorine species", Atmospheric Chemistry and Physics 12, 4159–4179, doi:10.5194/acp-12-4159-2012, 2012. reprint
- Cofield, R.E., P.C. Stek, "Design and field-of-view calibration of 114-660 GHz optics of the Earth Observing System Microwave Limb Sounder", IEEE Transactions on Geoscience and Remote Sensing 44, no. 5, 1166-1181, doi:10.1109/TGRS.2006.873234, 2006. reprint