Open AccessTropospheric Emission Spectrometer observations of the tropospheric HDO/H 2 O ratio: Estimation approach and characterization
Author(s) -
Worden John,
Bowman Kevin,
Noone David,
Beer Reinhard,
Clough Shepard,
Eldering Annmarie,
Fisher Brendan,
Goldman Aaron,
Gunson Michael,
Herman Robert,
Kulawik Susan S.,
Lampel Michael,
Luo Ming,
Osterman Gregory,
Rinsland Curtis,
Rodgers Clive,
Sander Stanley,
Shephard Mark,
Worden Helen
Publication year - 2006
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005jd006606
Subject(s) - troposphere , water vapor , atmospheric sciences , radiance , environmental science , mixing ratio , latitude , analytical chemistry (journal) , chemistry , physics , meteorology , optics , astronomy , chromatography
We present global, vertical profile estimates of the HDO/H 2 O ratio from the Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS) Aura satellite. We emphasize in this paper the estimation approach and error characterization, which are critical to determining the very small absolute concentration of HDO relative to H 2 O and its uncertainty. These estimates were made from TES nadir‐viewing (downlooking) thermal infrared spectral radiances observed on 20 September 2004. Profiles of HDO and H 2 O are simultaneously estimated from the observed radiances and a profile of the ratio is then calculated. This simultaneous, or “joint,” estimate is regularized with an a priori covariance matrix that includes expected correlations between HDO and H 2 O. This approach minimizes errors in the profile of the HDO/H 2 O ratio that are due to overlapping HDO and H 2 O spectroscopic lines. Under clear‐sky conditions in the tropics, TES estimates of the HDO/H 2 O ratio are sensitive to the distribution of the actual ratio between the surface and about 300 hPa with peak sensitivity at 700 hPa. The sensitivity decreases with latitude through its dependence on temperature and water amount. We estimate a precision of approximately 1% to 2% for the ratio of the HDO/H 2 O tropospheric densities; however, there is possibly a bias of approximately 5% in the ratio due to the HDO spectroscopic line strengths. These global observations clearly show increased isotopic depletion of water vapor at higher latitudes as well as increased depletion in the upper troposphere versus the lower troposphere.