Aura MLS

HOCl

Contact: Lucien Froidevaux

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).

How it is part of MLS Science Objectives

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). 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.

MLS values 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.

HOCl Information from the Spectroscopy Database

• Product Information
• Line Listing

Quick Product Information for data version v5

• 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 Aura MLS HOCl v5 data