Abstract
Abstract. In this paper, we introduce a bending angle radio occultation climatology (BAROCLIM) based on Formosat-3/COSMIC (F3C) data. This climatology represents the monthly-mean atmospheric state from 2006 to 2012. Bending angles from radio occultation (RO) measurements are obtained from the accumulation of the change in the raypath direction of Global Positioning System (GPS) signals. Best quality of these near-vertical profiles is found from the middle troposphere up to the mesosphere. Beside RO bending angles we also use data from the Mass Spectrometer and Incoherent Scatter Radar (MSIS) model (modified for RO purposes) to expand BAROCLIM in a spectral model, which (theoretically) reaches from the surface up to infinity. Due to the very high quality of BAROCLIM up to the mesosphere, it can be used to detect deficiencies in current state-of-the-art analysis and reanalysis products from numerical weather prediction (NWP) centers. For bending angles derived from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields from 2006 to 2012, e.g., we find a positive bias of 0.5 to 1% at 40 km, which increases to more than 2% at 50 km. BAROCLIM can also be used as a priori information in RO profile retrievals. In contrast to other a priori information (i.e., MSIS) we find that the use of BAROCLIM better preserves the mean of raw RO measurements. Global statistics of statistically optimized bending angle and refractivity profiles also confirm that BAROCLIM outperforms MSIS. These results clearly demonstrate the utility of BAROCLIM.
Highlights
Global data sets of the lower and middle atmosphere provide important information to understand atmospheric dynamics of the Earth’s climate system
Since we aimed at generating a BAROCLIM spectral model, which reaches from the surface to infinity, we extended mean radio occultation (RO) profiles with Mass Spectrometer and Incoherent Scatter Radar (MSIS)
The profile is flagged as bad if the difference between the RO and the European Centre for Medium-Range Weather Forecasts (ECMWF) profile is larger than 20 % in bending angle, 10 % in refractivity, and/or 25 K in temperature
Summary
Global data sets of the lower and middle atmosphere (troposphere to upper mesosphere) provide important information to understand atmospheric dynamics of the Earth’s climate system. Since RO profiles usually do not reach higher than about 120 km (only about 80 km for Metop) and because the true neutral atmospheric bending angle decreases nearly exponentially with height (and measurement noise dominates in a fractional sense in the mesosphere and above), there is an upper limit to which RO data are useful for the generation of a climatology. The MSIS-based bending angles and refractivities contain no information on atmospheric humidity and are given as a function of month, impact height, latitude, and longitude Both spectral models are based on Chebychev polynomials in the vertical and spherical harmonics in the horizontal and were constructed using an approach similar to the one we use for BAROCLIM described in Sect. Retrieved atmospheric profiles were compared to operationally retrieved OPSv5.6 profiles that used ECMWF short-range forecasts as a priori in the statistical optimization (Schwärz et al, 2013)
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