A posteriori calculation of δ<sup>18</sup>O and δD in atmospheric water vapour from ground-based near-infrared FTIR retrievals of H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O, and HD<sup>16</sup>O
This paper investigates the scientific value of retrieving H<sub>2</sub><sup>18</sup>O and HDO columns in addition to H<sub>2</sub><sup>16</sup>O columns from high-resolution ground-based near-infrared spectra. We present a set of refined H<sub>2...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-08-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/7/2567/2014/amt-7-2567-2014.pdf |
| Summary: | This paper investigates the scientific value of retrieving H<sub>2</sub><sup>18</sup>O
and HDO columns in addition to H<sub>2</sub><sup>16</sup>O columns from high-resolution ground-based near-infrared spectra. We present a set of refined
H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O, and HDO spectral windows. The
retrieved H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O, and HDO columns are used
for an a posteriori calculation of columnar δD and
δ<sup>18</sup>O. We estimate the uncertainties for the so-calculated
columnar δD and δ<sup>18</sup>O values. These estimations include
uncertainties due to the measurement noise, errors in the a priori data, and
uncertainties in spectroscopic parameters. Time series of δ<sup>18</sup>O
obtained from ground-based FTIR (Fourier transform infrared) spectra are presented for the first time.
<br><br>
For our study we use a full physics isotopic general circulation model
(ECHAM5-wiso). We show that the full physics simulation of HDO and
H<sub>2</sub><sup>18</sup>O can already be reasonably predicted from the
H<sub>2</sub><sup>16</sup>O columns by a simple linear regression model (scatter values
between full physics and linear regression simulations are 35 and
4‰ for HDO and H<sub>2</sub><sup>18</sup>O, respectively). We document
that the columnar δD and δ<sup>18</sup>O values as calculated a
posteriori from the retrievals of H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O, and
HDO show a better agreement with the ECHAM5-wiso simulation than the
δD and δ<sup>18</sup>O values as calculated from the
H<sub>2</sub><sup>16</sup>O retrievals and the simple linear regression model. This
suggests that the H<sub>2</sub><sup>18</sup>O and HDO column retrievals add
complementary information to the H<sub>2</sub><sup>16</sup>O retrievals. However, these
data have to be used carefully, because of the different vertical sensitivity
of the H<sub>2</sub><sup>16</sup>O, H<sub>2</sub><sup>18</sup>O, and HDO columnar
retrievals. Furthermore, we have to note that the retrievals use reanalysis
humidity profiles as a priori input and the results are thus not independent
of the reanalysis data. |
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| ISSN: | 1867-1381 1867-8548 |