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Volume 11, issue 4 | Copyright

Special issue: Observing Atmosphere and Climate with Occultation Techniques...

Atmos. Meas. Tech., 11, 2051-2066, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Apr 2018

Research article | 11 Apr 2018

Evaluating the lower-tropospheric COSMIC GPS radio occultation sounding quality over the Arctic

Xiao Yu1, Feiqin Xie1, and Chi O. Ao2 Xiao Yu et al.
  • 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 91109, USA

Abstract. Lower-tropospheric moisture and temperature measurements are crucial for understanding weather prediction and climate change. Global Positioning System radio occultation (GPS RO) has been demonstrated as a high-quality observation technique with high vertical resolution and sub-kelvin temperature precision from the upper troposphere to the stratosphere. In the tropical lower troposphere, particularly the lowest 2km, 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 at high latitudes, particularly over the Arctic, which is characterized by smooth ocean surface and often negligible moisture in the atmosphere. In this study, 3-year (2008–2010) GPS RO soundings from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) over the Arctic (65–90°N) show uniform spatial sampling with average penetration depth within 300m above the ocean surface. Over 70% of RO soundings penetrate deep into the lowest 300m of the troposphere in all non-summer seasons. However, the fraction of such deeply penetrating profiles reduces to 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,  ∼ 0.72K in temperature, and  ∼ 0.05gkg−1 in specific humidity below 10km, 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 European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim profiles. A systematic negative bias up to  ∼ 1% in refractivity below 2km is only seen in the summer, which confirms the moisture impact on GPS RO quality.

Publications Copernicus
Special issue
Short summary
Atmospheric observations from GPS receiver satellites offer uniform spatial coverage over the Arctic. The GPS profiles sensing deep into the lowest 300 m of the atmosphere only reach 50–60 % in summer but over 70 % in other seasons. The profile uncertainty due to different data centers is within 0.07 % in refractivity, 0.72 K in temperature, and 0.05 g kg-1 in humidity below 10 km. A systematic negative bias of 1 % in refractivity below 2 km is only seen in the summer due to moisture impact.
Atmospheric observations from GPS receiver satellites offer uniform spatial coverage over the...