Revising the retrieval technique of a long-term stratospheric HNO<sub>3</sub> data set: from a constrained matrix inversion to the optimal estimation algorithm
The Ground-Based Millimeter-wave Spectrometer (GBMS) was designed and built at the State University of New York at Stony Brook in the early 1990s and since then has carried out many measurement campaigns of stratospheric O<sub>3</sub>, HNO<sub>3</sub>, CO and N<sub>2...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2011-07-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/29/1317/2011/angeo-29-1317-2011.pdf |
| Summary: | The Ground-Based Millimeter-wave Spectrometer (GBMS) was designed and built
at the State University of New York at Stony Brook in the early 1990s and
since then has carried out many measurement campaigns of stratospheric
O<sub>3</sub>, HNO<sub>3</sub>, CO and N<sub>2</sub>O at polar and mid-latitudes. Its
HNO<sub>3</sub> data set shed light on HNO<sub>3</sub> annual cycles over the Antarctic
continent and contributed to the validation of both generations of the
satellite-based JPL Microwave Limb Sounder (MLS). Following the increasing
need for long-term data sets of stratospheric constituents, we resolved to
establish a long-term GMBS observation site at the Arctic station of Thule
(76.5° N, 68.8° W), Greenland, beginning in January 2009, in order to
track the long- and short-term interactions between the changing climate and
the seasonal processes tied to the ozone depletion phenomenon. Furthermore,
we updated the retrieval algorithm adapting the Optimal Estimation (OE)
method to GBMS spectral data in order to conform to the standard of the
Network for the Detection of Atmospheric Composition Change (NDACC)
microwave group, and to provide our retrievals with a set of averaging
kernels that allow more straightforward comparisons with other data sets.
The new OE algorithm was applied to GBMS HNO<sub>3</sub> data sets from 1993 South
Pole observations to date, in order to produce HNO<sub>3</sub> version 2 (v2)
profiles. A sample of results obtained at Antarctic latitudes in fall and
winter and at mid-latitudes is shown here. In most conditions, v2 inversions
show a sensitivity (i.e., sum of column elements of the averaging kernel
matrix) of 100 ± 20 % from 20 to 45 km altitude, with somewhat worse
(better) sensitivity in the Antarctic winter lower (upper) stratosphere. The
1σ uncertainty on HNO<sub>3</sub> v2 mixing ratio vertical profiles
depends on altitude and is estimated at ~15 % or 0.3 ppbv, whichever
is larger. Comparisons of v2 with former (v1) GBMS HNO<sub>3</sub> vertical
profiles, obtained employing the constrained matrix inversion method, show
that v1 and v2 profiles are overall consistent. The main difference is at
the HNO<sub>3</sub> mixing ratio maximum in the 20–25 km altitude range, which is
smaller in v2 than v1 profiles by up to 2 ppbv at mid-latitudes and during
the Antarctic fall. This difference suggests a better agreement of GBMS
HNO<sub>3</sub> v2 profiles with both UARS/ and EOS Aura/MLS HNO<sub>3</sub> data than
previous v1 profiles. |
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| ISSN: | 0992-7689 1432-0576 |