Time series of ocean mass from Swarm, University of Bonn
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The Swarm time series is derived from monthly time-variable gravity fields, which have been computed at the Institute for Geodesy and Geoinformation, University of Bonn.
The gravity fields are derived from kinematic orbits of Swarm A, B and C using the integral equation approach with short arcs (Mayer-Gürr, 2006).
Non-gravitational forces have been modeled to improve the gravity field processing. 

The following orbit products have been used:
December 2013 to March 2015:    ESA level 2 KIN (van den IJssel et al., 2016)
April 2015 to December 2017:    kinematic orbits computed at the Institut für Erdmessung (IfE), Leibniz Universität Hannover, within the DFG-funded project CONTIM of the SPP 1788
January 2018 to July 2015:      ESA level 2 KIN (van den IJssel et al., 2016)
This is an update with respect to Lück et al., 2018, where we only used ESA level 2 KIN data. 
All ESA level 2 KIN orbits will be replaced with the IfE orbits as soon as they are available.

- ocean mass is given in mm of equivalent water height, relative to the GOCO05c static gravity field
- the gravity fields are evaluated up to d/o 12
- a 500 km Gaussian filter has been applied
- a GIA correction has been applied (A et al., 2013)
- all degree 1 coefficients are added (Swenson et al., 2008)
- the c20 coefficients have been replaced with those derived from satellite laser ranging (SLR) (Cheng et al., 2013)

For more information on the gravity field processing see Lück et al. (2018)

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References:
A, G., Wahr, J., and Zhong, S.: Computations of the viscoelastic response of a 3-D compressible Earth to surface loading: an application to Glacial Isostatic Adjustment in Antarctica and Canada, Geophys. J. Int., 192, 557–572, https://doi.org/10.1093/gji/ggs030, 2013.

Cheng, M., Tapley, B. D., and Ries, J. C.: Deceleration in the Earth’s oblateness, J. Geophys. Res.-Sol. Ea., 118, 740–747, https://doi.org/10.1002/jgrb.50058, 2013.

Lück, C., Kusche, J., Rietbroek, R., and Löcher, A.: Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits, Solid Earth, 9, 323-339, https://doi.org/10.5194/se-9-323-2018, 2018. 

Mayer-Gürr, T.: Gravitationsfeldbestimmung aus der Analyse kurzer Bahnbögen am Beispiel der Satellitenmissionen CHAMP und GRACE, Dissertation, Universität Bonn, Bonn, Germany, 2006.

Swenson, S., Chambers, D., and Wahr, J.: Estimating geocenter variations from a combination of GRACE and ocean model output, J. Geophys. Res.-Sol. Ea., 113, b08410, https://doi.org/10.1029/2007JB005338, 2008.

van den IJssel, J., Forte, B., and Montenbruck, O.: Impact of Swarm GPS receiver updates on POD performance, Earth Planets Space, 68, 85, https://doi.org/10.1186/s40623-016-0459-4, 2016.

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This study is supported by the Priority Program 1788 “Dynamic Earth” of the German Research Foundation (DFG).