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Report of the CGMS International Radio Occultation Working Group – IROWG

This report explores the structural uncertainty in radio occultation (RO) climatologies, focusing on GNSS RO radio signals and their measurements. It discusses the properties and quality of RO data, including long-term stability, high vertical resolution and accuracy, global coverage, and all-weather capabilities. The report also highlights the operational backbone of the RO observing system and provides recommendations for future developments. The next workshop on this topic will be held in Seggau Castle in September 2016.

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Report of the CGMS International Radio Occultation Working Group – IROWG

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  1. WG Climate, March 6 – 9, 2016 Paris, France Report of the CGMS International Radio Occultation Working Group – IROWG Ulrich Foelsche Institute for Geophysics, Astrophysics, and Meteorology/Instituteof Physics (IGAM/IP) Wegener Center for Climate and Global Change University of Graz, Austria ulrich.foelsche@uni-graz.at

  2. IROWG Rapporteur: Tony Mannucci, JPL, USA Co-chairs: Sean Healy, ECMWF, UK Ulrich Foelsche, Uni-Graz, Austria Co-chairs until 2015: Axel von Engeln, EUMETSAT, Germany Dave Ector, UCAR/NOAA, USA SCOPE-CM activity RO-CLIM, Hans Gleisner, DMI, DK Focus: structural uncertainty in Radio Occultation climatologies

  3. GNSS Radio Occultation Radio Signals   20 cm Transmitter GPSGALILEOBeiDouGLONASS Receiver MetOp,COSMIC, CHAMP, GRACE, COSMIC-2, FY-3C …

  4. Orbit Information Orbit Information, Ionospheric Correction Bending Angle Atmospheric Delay Abel Transform Refractivity Water Vapor Clausius-Mossotti Relation Density Temperature HydrostaticIntegral Pressure Temperature Ideal Gas Law Water Vapor (Dry) Temperature Radio Occultation Phase Delay Atmospheric Phase Delay ~ 1 mm Mesopause ~ 20 cm Stratopause ~ 20 m Tropopause ~ 1- 2 km Surface or both Stratosphere Upper Troposphere Lower/Middle Troposphere

  5. Observing Climate • Properties of Radio occultation (RO) measurements: • Long-term stability, because RO data are self-calibrated to a very high degree • High vertical resolution and high accuracy • Global coverage, equal obs. density (and quality) over oceans and continents • All-weather capability, day and night measurements • Modest horizontal resolution is not a disadvantage, since data have to be averaged anyway for climate applications, RO data are meanwhile a pillar in NWP, and are the only satellite data, which can be assimilatedwithout bias correction.

  6. RO Data Quality Bending Angle Statistics between 65 km and 80 km “Bias” means – difference to MSIS climatology – very similar for all sats (UCAR data). Annual and semi-annual cycle. No indications for instrument degradation or instationarities in the RO records No (clear) signal of the solar cycle for the CHAMP record Foelsche et al., AMT 2011, Pirscher, PhD Thesis, 2010

  7. Refractivity Consistency Global, monthly refractivity differences relative to the satellite mean Further reduced when the estimated sampling errors are subtracted

  8. Dry Temp. Consistency Global, monthly dry temperature differences relative to satellite mean Sampling errorssubtracted 15 – 20 km, 25 – 30 km Increasing CHAMP-Offset – Stat. Optimization, Background Bias

  9. Observing System Operational Backbone: COSMIC/FORMOSAT-3, 6 sat constellation (USA/Taiwan) sampling the diurnal cycle, launched 2006, near its end GRAS on MetOPs (EUMETSAT), sun-sync Future: EPS-SG (EUMETSAT) COSMIC-2/FORMOSAT-7 equatorial (NOAA, NSPO) 6 sat, 24° inclination, launch late 2016 (?) COSMIC-2 polar, 6 sat 72° inclination (???) Main IROWG recommendation (John, please help!): Ensure that both, equatorial and polar components of COSMIC-2 are fully funded and launched

  10. Next IROWG Workshop IROWG-5 + OPAC-6 Workshop, Seggau CastleSeptember 8 – 14, 2016wegcwww.uni-graz.at/opacirowg2016

  11. Thankyou! Merci!

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