ro-clim (scm-08) radio occultation based gridded climate
TRANSCRIPT
Sustained Coordinated Processing of
Environmental Satellite Data for
Climate Monitoring
SCOPE-CM Executive Panel Meeting
March 24, 2015
RO-CLIM (SCM-08)
Radio Occultation based gridded
climate data sets
Hans Gleisner & the RO-CLIM Project Team
SCOPE-CM Executive Panel Meeting
March 24, 2015
The RO-CLIM project:
• Background: RO measurements, ROtrends collaboration;
• Project and objectives;
• Ongoing activities and current status;
• Updated project plan for 2015.
Outline
SCOPE-CM Executive Panel Meeting
March 24, 2015
t1 t2
t3
GPS
RO receiver
GPS signals:
L1: ≈19 cm
L2: ≈24 cm
Starting point for processing:
i. Measurements of phase and amplitude
that gives a vertical atmospheric profile at
the ray’s tangent point.
ii. Position and velocity of the satellites.
Atmospheric sounding with GNSS RO
SCOPE-CM Executive Panel Meeting
March 24, 2015
Atmospheric sounding with GNSS RO
L ~ 300 km
Z ~ 200 m – 1.5 km
FCDR
TCDR
TCDR
ECV
SCOPE-CM Executive Panel Meeting
March 24, 2015
Characteristics of RO data
microwave frequencies, active sounding:
independent of clouds, surface emissivity, day/night
based on time measurements, not radiances:
intrinsic long-term stability
no inter-calibration between instruments and missions
provides “anchor” point in NWP and re-analysis
limb sounding:
high vertical resolution (0.1-1.0 km from lower troposphere to stratosphere)
low horizontal resolution (300 km along the ray)
global coverage:
sampling all lats & lons, troposphere and stratosphere
“quasi-random” sampling in space and time
These features make RO ideal for climate monitoring – but errors must be under-
stood. Residual ionospheric errors and structural errors (impact of algorithmic
choices and processing assumptions) are two important limiting factors.
SCOPE-CM Executive Panel Meeting
March 24, 2015
Radio occultation missions
Note: Figure from proposal, now outdated for dates > 2014!
See also: Status of the Global Observing System for Radio Occultation (Update 2013), IROWG/DOC/2013/02,available at: http://irowg.org/workshops/irowg-3/
Initial RO-CLIM Focus
Extended RO-CLIM Focus
Continuous RO data since
August 2001.
SCOPE-CM Executive Panel Meeting
March 24, 2015
ROtrends collaboration
RO community started comparison of different processing centres in 2007 (ROtrends). Main aim is to validate RO as a climate benchmark, identifying the impact of processing assumptions (structural uncertainty).
• ROtrends partners: DMI, JPL, GFZ, UCAR, WEGC, and EUMETSAT
• Common focus on CHAMP data, Aug 2001 to Sep 2008
• Aiming at improved understanding of structural uncertainty
• while still keeping the algorithm/software development independent
• 1st Round: profile-to-profile comparison between processing centres main results described in Ho et al. [2012]
• 2nd Round: comparison of monthly mean climatologies main results described in Steiner et al. [2013]
SCOPE-CM Executive Panel Meeting
March 24, 2015
RO-CLIM project partners
From RO-CLIM Project Description, available at:
http://irowg.org/projects/ro-clim-under-scope-cm/
SCOPE-CM Executive Panel Meeting
March 24, 2015
Summary of project
From RO-CLIM Project Description, available at:
http://irowg.org/projects/ro-clim-under-scope-cm/
SCOPE-CM Executive Panel Meeting
March 24, 2015
Initial RO-CLIM data set
• CHAMP zonal monthly mean data: 5 deg x 200 m, 8-30 km, global coverage • To be provided with error characteristics and sampling-error corrected means • To be provided as an ensemble of 5 or 6 data sets • Currently no single community RO data set – discussions ongoing • Planned to be released during 2015 (following re-formatting, documentation, etc) • Current focus: a) multi-mission inter-comparisons, b) high-altitude initialization
SCOPE-CM Executive Panel Meeting
March 24, 2015
Extended RO-CLIM data set
• CHAMP, GRACE, COSMIC, Metop, SAC-C, …
• Continuous since Aug 2001 (lower resolution), since Aug 2006 (higher resolution)
• Current focus: identification of missions, resolutions, gridding/averaging methods
CHAMP, Aug 2001 – Sep 2008 COSMIC, Aug 2006 – onward
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March 24, 2015
Structural uncertainties: differences between centres
• Common CHAMP data
• DMI, WEGC, UCAR, JPL, GFZ
• Refractivity anomalies
• 12-20 km
• 6 latitude bands
• Data within +/- 0.2%
• Trends within +/- 0.02%/10yr
SCOPE-CM Executive Panel Meeting
March 24, 2015
Structural uncertainties: differences between centres
• Common CHAMP data
• DMI, WEGC, UCAR, JPL, GFZ
• Refractivity anomalies
• 20-30 km
• 6 latitude bands
• Data within +/- 0.5%
• Trends within +/- 0.03%/10yr
SCOPE-CM Executive Panel Meeting
March 24, 2015
Structural uncertainties
• Low structural uncertainty in tropics and at mid-latitudes, 8-25 km
• Larger at high latitudes above 25 km
• Primarily due to different upper altitude initialization (Abel integral)
• Uncertainty in trends over the CHAMP period meets GCOS requirements: < 0.02% in bending angle, refractivity < 0.03% in pressure < 3 m geopotential height < 0.02 K (UT), < 0.1 K (LS) over 7-year period
• Persistent and seasonal biases found at high latitudes, and have lead to software updates at several centres, including the implementation of a new climatology (BAROCLIM [Scherllin-Pirscher et al. [2015]) for upper-level initialization of bending angle profiles.
SCOPE-CM Executive Panel Meeting
March 24, 2015
RO-CLIM: status as per March 2015
Administrative, etc.:
• RO-CLIM project roughly proceeding according to plan;
• Change of project lead in March 2014;
• Held 3 telecons + 1 physical meeting during the period;
• Project web page, common access to documents;
• Collected data at an FTP server – will be linked to web site;
• Short contribution to WGClimate report (to SBSTA-21/UNFCCC)
Project work
• Re-assessment of currently implemented processing software (all centres)
• Impacts on re-processing efforts during 2015 (DMI, JPL, WEGC, …)
• Study processing centre differences: high-altitude filtering and initialization (JPL)
• Multi-mission/multi-centre inter-comparisons (WEGC)
• Initial RO-CLIM data set collected, made public during 2015 (DMI)
• Work towards generation of data sets for obs4MIPs (JPL)
SCOPE-CM Executive Panel Meeting
March 24, 2015
Targeted maturity levels
Example from ROM SAF self-assessment, following CORE-CLIMAX guidelines.
Note that maturity is here quantified by ranges, rather than single numbers.