The MLS HOCl Product
Basic Information
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 and help ascertain the role
of this molecule in polar winter/spring, when its
abundance may increase significantly (from enhancements
in ClO and HO2).
How EOS MLS measures HOCl
The standard product for HOCl is taken from the 640 GHz (Core+R4A) retrievals. Simulations indicate that
the weak HOCl signals will lead to v1.5 retrievals that are accurate to no better than 20%, and that small
abundances at pressures larger than 46 hPa will be difficult to obtain. 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 v1.5 HOCl, however, lead us to recommend a maximum pressure of 22 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.
Few results will exist on actual validation for HOCl, given the paucity of such data and the lack of single-profile
sensitivity for MLS. Some balloon-borne profiles exist, and comparisons of MLS zonal means to these over the
recommended vertical range(22 - 2.2 hPa) look encouraging.
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
|
Quick Product Information for data version v2.2
- Swath Name: HOCl
- Vertical Resolution: 6 km
- Useful Range: 10 - 2.2 hPa
- DAAC Short Name: ML2HOCL
|
- Precision: 30 - 80 pptv for monthly 5 deg. zonal means
in the upper stratosphere
- Accuracy: under investigation
|
v2.2 HOCl Averaging Kernel
colored lines are individual kernels; thick dashed line is full width at half maximum, thick solid is integrated kernel value
Publications related to the MLS HOCl data product
2006
- 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", vol 44, num no. 5, pgs. 1166-1181, 2006. Reprint
|
