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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-230
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Evaluating the Lower Tropospheric COSMIC GPS Radio Occultation Sounding Quality over the Arctic
Xiao Yu1, Feiqin Xie1, and Chi O. Ao2 1Department of Physical and Environmental Sciences, Texas A&M University – Corpus Christi, Corpus Christi, Texas, 78412, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California , 91011, USA
Abstract. Lower tropospheric moisture and temperature measurements are crucial for understanding weather predication and climate change. Global Positioning System radio occultation (GPS RO) has been demonstrated as a high-quality observation with high-vertical-resolution and sub-Kelvin temperature precision from the upper troposphere to the stratosphere. In the tropical lower troposphere, particularly the lowest 2 km, the quality of RO retrievals is known to be degraded and is a topic of active research. However, it is not clear whether similar problems exist in the high latitudes, particularly over the Artic, which is characterized by smooth ocean surface and often negligible moisture in the atmosphere. In this study, three-year (2008–2010) GPS RO soundings from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) over the Arctic (65° N-90° N) show uniform spatial sampling with average penetration depth within 300 m above the ocean surface. Over 70 % soundings penetrate below 300 m in all non-summer seasons but only about 50–60 % in summer, when near-surface moisture and its variation increase. Both structural and parametric uncertainties of GPS RO soundings were also analyzed. The structural uncertainty (due to different data processing approaches) is estimated to be within 0.07 % in refractivity, 0.72 K in temperature and −0.029 g/kg in specific humidity below 10 km, which is derived by comparing RO retrievals from two independent data processing centers. The parametric uncertainty (internal uncertainty of RO sounding) is quantified by comparing GPS RO with near-coincident radiosonde and ECMWF ERA-Interim profiles. A systematic negative bias up to ~ 1 % in refractivity below 2 km is only seen in the summer, which confirms the moisture impact on GPS RO quality.

Citation: Yu, X., Xie, F., and Ao, C. O.: Evaluating the Lower Tropospheric COSMIC GPS Radio Occultation Sounding Quality over the Arctic, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-230, in review, 2017.
Xiao Yu et al.
Xiao Yu et al.
Xiao Yu et al.

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