Evaluating the Lower Tropospheric COSMIC GPS Radio Occultation Sounding Quality over the Arctic

Abstract

Abstract. Lower tropospheric moisture and temperature measurements are crucial for understanding weather predication and 10 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 15 (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% 20 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. 25

An Advanced Algorithm to Retrieve Total Atmospheric Water Vapor Content From the Advanced Microwave Scanning Radiometer Data Over Sea Ice and Sea Water Surfaces in the Arctic

“…Unfortunately, the RO sounding often does not reach the surface in the Arctic that limits the RO capabilities to measure WVC in this region. [30].…”