Observation system simulation experiments using water vapor isotope information

TitleObservation system simulation experiments using water vapor isotope information
Publication TypeJournal Article
Year of Publication2014
AuthorsYoshimura K, Miyoshi T., Kanamitsu M
JournalJournal of Geophysical Research-Atmospheres
Date Published2014/07
Type of ArticleArticle
ISBN Number2169-897X
Accession NumberWOS:000340408000005
KeywordsData assimilation; delta-d; forecast system; fractionation; general-circulation model; land-surface model; o-18; precipitation; resolution; transform kalman filter

Measurements of water vapor isotopes (delta O-18 and delta D) have dramatically increased in recent years with the availability of new spectroscopic technology. To utilize these data more efficiently, this study first developed a new data assimilation system using a local transform ensemble Kalman filter (LETKF) and the Isotope-incorporated Global Spectral Model (IsoGSM). An observation system simulation experiment (OSSE) was then conducted. The OSSE used a synthetic data set of vapor isotope measurements, mimicking Tropospheric Emission Spectrometer (TES)-retrieved delta D from the mid-troposphere, SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)-retrieved delta D from the water vapor column, and the virtual Global Network of Isotopes in Precipitation (GNIP)-like surface vapor isotope (both delta D and delta O-18) monitoring network. For TES and SCIAMACHY, we assumed a similar spatiotemporal coverage as that of the real data sets. For the virtual GNIP-like network, we assumed similar to 200 sites worldwide and 6-hourly measurements. An OSSE with 20 ensemble members was then conducted for January 2006. The results showed a significant improvement in not only the vapor isotopic field but also meteorological fields, such as wind speed, temperature, surface pressure, and humidity, when compared with a test with no observations. For surface air temperature, the global root mean square error has dropped by 10%, with 40-60% of the decrease occurring in the east-southeast Asia where the concentration of observations is relatively higher. When there is a conventional radiosonde network, the improvement gained by adding isotopic measurements was small but positive for all variables.

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