Improvement of OMI ozone profile retrievals by simultaneously fitting polar mesospheric clouds
The presence of polar mesospheric clouds (PMCs) at summer high latitudes could affect the retrieval of ozone profiles using backscattered ultraviolet (UV) measurements. PMC-induced errors in ozone profile retrievals from Ozone Monitoring Instrument (OMI) backscattered UV measurements are investigate...
Main Authors: | , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2016-09-01
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Series: | Atmospheric Measurement Techniques |
Online Access: | http://www.atmos-meas-tech.net/9/4521/2016/amt-9-4521-2016.pdf |
Summary: | The presence of polar mesospheric clouds (PMCs) at summer high latitudes
could affect the retrieval of ozone profiles using backscattered ultraviolet
(UV) measurements. PMC-induced errors in ozone profile retrievals from Ozone
Monitoring Instrument (OMI) backscattered UV measurements are investigated
through comparisons with Microwave Limb Sounder (MLS) ozone measurements.
This comparison demonstrates that the presence of PMCs leads to systematic
biases for pressures smaller than 6 hPa; the biases increase from
∼ −2 % at 2 hPa to ∼ −20 % at 0.5 hPa on average and are
significantly correlated with brightness of PMCs. Sensitivity studies show
that the radiance sensitivity to PMCs strongly depends on wavelength,
increasing by a factor of ∼ 4 from 300 to 265 nm. It also strongly
depends on the PMC scattering, thus depending on viewing geometry. The
optimal estimation-based retrieval sensitivity analysis shows that PMCs
located at 80–85 km have the greatest effect on ozone retrievals at
∼ 0.2 hPa ( ∼ 60 km), where the retrieval errors range from
−2.5 % with PMC vertical optical depth (POD) of 10<sup>−4</sup> to
−20 % with 10<sup>−3</sup> POD at backscattering angles. The impacts
increase by a factor of ∼ 5 at forward-scattering angles due to
stronger PMC sensitivities. To reduce the interference of PMCs on ozone
retrievals, we perform simultaneous retrievals of POD and ozone with a loose
constraint of 10<sup>−3</sup> for POD, which results in retrieval errors of
1–4 × 10<sup>−4</sup>. It is demonstrated that the negative bias of OMI
ozone retrievals relative to MLS can be improved by including the PMC in the
forward-model calculation and retrieval. |
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ISSN: | 1867-1381 1867-8548 |