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Open AccessArticle

Variational Assimilation of Radio Occultation Observations into Numerical Weather Prediction Models: Equations, Strategies, and Algorithms

1
Spire Global Inc., 1825 33rd Street, Suite 100, Boulder, CO 80301, USA
2
A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevsky per. 3, Moscow 119017, Russia
3
Hydrometeorological Research Centre of Russian Federation, B. Predtechensky per. 11-13, Moscow 123242, Russia
*
Author to whom correspondence should be addressed.
Remote Sens. 2019, 11(24), 2886; https://doi.org/10.3390/rs11242886
Received: 21 October 2019 / Revised: 25 November 2019 / Accepted: 29 November 2019 / Published: 4 December 2019
We review different approaches to the variational assimilation of radio occultation (RO) observations into models of global atmospheric circulation. We derive the general equation for the bending angle that reduces to the Abel integral for a spherically layered atmosphere. We review the full 3-D observation operator for bending angles, which provides the strictest solution, but is also most computationally expensive. Commonly used is the 2-D approximation that allows treating rays as plane curve. We discuss a simple 1-D approach to the assimilation of bending angles. The observation operator based on the standard form of the Abel integral has a disadvantage, because it cannot account for waveguides. Alternative approaches use 1-D ray-tracing. The most straightforward way is to use the same framework as for the 3-D observation operator, with the refractivity field reduced to a single profile independent from the horizontal coordinates. An alternative 1-D ray-tracing approach uses the form of ray equation in a spherically layered medium that uses an invariant. The assimilation of refractivity has also 1-D and 3-D options. We derive a new simple form of the refractivity-mapping operator. We present the results of numerical tests of different 3-D and 1-D observation operators, based on Spire data. View Full-Text
Keywords: radio occultation; variational assimilation; observation operators for bending angle and refractivity radio occultation; variational assimilation; observation operators for bending angle and refractivity
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MDPI and ACS Style

Gorbunov, M.; Stefanescu, R.; Irisov, V.; Zupanski, D. Variational Assimilation of Radio Occultation Observations into Numerical Weather Prediction Models: Equations, Strategies, and Algorithms. Remote Sens. 2019, 11, 2886.

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