RO-CLIM (SCM-08) Radio Occultation based gridded climate ...

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


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


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


March 24, 2015

Atmospheric sounding with GNSS RO

L ~ 300 km

Z ~ 200 m – 1.5 km

FCDR

TCDR

TCDR

ECV


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.


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Note: Figure from proposal, now outdated for dates 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.

http://irowg.org/projects/rotrends/





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]


March 24, 2015

RO-CLIM project partners

From RO-CLIM Project Description, available at:

http://irowg.org/projects/ro-clim-under-scope-cm/













March 24, 2015

Summary of project

From RO-CLIM Project Description, available at:














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


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


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


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


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.


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)


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.


March 24, 2015

Updated annual project plan for 2015


March 24, 2015

End

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