The Role of GPS Radio Occultation Observations in the Global Observing System for Weather, Water and Climate NOAA Briefing April 1, 2005 Rick Anthes and Chris Rocken University Corporation for Atmospheric Research Boulder, Colorado, USA Thanks to NSF and NOAA for their support of GPS RO!

Purpose of Meeting Update on GPS Radio Occultation results and COSMIC Build NOAA Stakeholder Support for transitioning research into operations –Continue COSMIC for FY08-FY11 –Develop plans for an operational RO constellation following COSMIC

GPS RO-Research to Ops GPS radio occultation is a promising atmospheric observing system for both weather and climate: –Temperature, water vapor, electron density information –High vertical resolution –High accuracy (<1K) –Unaffected by clouds –Self calibrating, no instrument drift or satellite-to-satellite bias (important for climate detection) GPS RO data will be valuable to: –Weather prediction –Climate monitoring and analysis World’s most accurate atmospheric thermometer! –ionospheric research and space weather forecasting –Calibrate/complement/enhance other satellite observing systems Need plan for transition from research into operations

National and International Priorities U.S Climate Change Science Program (CCSP) Global Earth Observing System of Systems (GEOSS) New Priorities for the 21 st Century: NOAA’s Strategic Plan Updated for FY2005-FY2010 World Meteorological Organization –GCOS-92, WMO/TD No. 1219, October 2004 –WMO/CBS/OPAG IOS ET-ODRRGOS Final Report, 6-10 Sept. 2004, Annex VI

Earth Observation Summit I Washington, DC, July 31, 2003 Summit represented a high level governmental/political commitment to move toward a comprehensive, coordinated, global network: Issued declaration to support this concept Launched development of 10-year implementation plan Established the Group on Earth Observations with US Co-Chair 34Nations 20International Organizations Group on Earth bservations Group on Earth bservations

GCOS Implementation Plan for the Global Observing System for Climate October 2004 Action A20 (AF13): GPS RO measurements should be made available in real time, incorporated into operational data streams, and sustained over the long-term. GCOS-92, WMO/TD No. 1219, October 2004

GOS Implementation Plan Draft Rec S12: The opportunities for a constellation of RO sounders should be explored and operational implementation planned. There has been good progress in planning for NRT distribution of METOP/ GRAS and COSMIC data. Action : WMO Space Programme to discuss with space agencies (1) proposal to develop a shared ground network system and (2) operational constellations following COSMIC. WMO/CBS/OPAG IOS ET-ODRRGOS Final Report, 6-10 Sept. 2004, Annex VI

New Priorities for the 21 st Century NOAA’s Strategic Plan Updated for FY2005-FY2010 Understand Climate Variability and Change Improve the quality and quantity of climate observations Serve Societies Needs for Weather and Water Information Weather Space Weather Water “Develop and infuse research results and new technologies more efficiently to improve products and services. Streamline dissemination, and communicate vital information more effectively.” “Increase quantity, quality, and accuracy of satellite data that are processed and distributed within target time.”

GPS RO and COSMIC Update and Recent Results Chris Rocken COSMIC Chief Scientist

GPS Satellite LEO Satellite Radio Signal LEO Orbit Atmosphere GPS Radio Occultation (RO) Deduce atmospheric refractivity based on precise measurement of phase delay and amplitude.

Signals Abundant GPS Glonass Galileo 60–90 Sources in space T. Yunck, JPL

1. High accuracy: (equivalent to <1 K from 5-25 km) Unique Attractions of GPS Radio Occultation 2. Limb sounding geometry complementary to ground and space nadir viewing instruments 3.High vertical resolution (100m near surface - 1km tropopause) 4.All weather-minimally affected by aerosols, clouds or precipitation 5.Independent height and pressure 6.Requires no first guess sounding 7.Independent of radiosonde calibration 8.No instrument drift 9.No satellite-to-satellite bias 10.Profiles ionosphere, stratosphere, troposphere 11.Inexpensive T. Yunck, JPL

Atmospheric Refractivity N N: pressure (P) temperature (T) water vapor pressure (P W ) electron density (n e ) GPS frequency (f)

Observed Atmospheric Volume L~300 km Z~1 km

Issues with GPS RO Representativeness: Horizontal “average” ~300 km Fundamental to measurement Penetration to lower troposphere –GPS/MET median penetration ~500mb CHAMP soundings penetration improved Final resolution of issue requires improved GPS receiver Negative N bias in lower troposphere, tropical regions Causes understood, partially resolved, final resolution requires improved GPS receiver (currently undergoing testing at JPL)

Note: Wave structure above tropopause (gravity waves) Details at Tropopause Temperature inversions near surface

l In preparation for COSMIC GPS/MET, CHAMP, SAC-C mission data are analyzed and compared to NCEP. ECMWF, and radiosondes l Extensive comparisons between analysis centers are conducted RO Validation

latest previous rms bias Continued improvements in retrieval (previous and latest iono. correction) Figure also shows (for Aug. 2002): 1.ECMWF model in southern hemisphere is worse > 20 km than in northern hemisphere (climatology may also be worse) 2.Positive bias at tropical tropopause (due to higher resolution of RO) 3.Negative N-bias most pronounced in tropics Newest RO - ECMWF Refractivity Comparisons

GPS radio occultation missions Mission Launch-Duration # Soundings/day Remarks GPS-MET4/ ~125Proof of Concept CHAMP11/2000 ~5~250Improved receiver, tracking SAC-C11/2000 ~3~300Improved receiver, open loop tracking test GRACE5/2002 ~5~500RO data not yet available COSMIC12/2005 ~5~2500Real time-ops TerraSAR-X7/2005 ~5~400COSMIC RX & Antennas EQUARS7/2006 ~3~400COSMIC RX & CHAMP antennas METOP4/2006 ~5~500Real time - ops COSMIC II ?3/2009 ~5~5000Real time-ops

Observations should cooperate, not compete!

Combined Soundings at CIMSS RMS and bias of temperature profile retrievals from ATOVS alone (blue) and ATOVS plus CHAMP (red) with respect to radiosonde measurements for the months of October 2001, January 2002, April 2002, and July (Borbas et al, CIMSS)

Information content from1D-Var studies IASI (Infrared Atmospheric Sounding Interferometer) RO (Radio Occultation) (Collard+Healy, QJRMS,2003)

Randel et al., 2003 Deseasonalized T anomalies. 4S-4N. Downward prop patterns assoc with QBO. Contours 0.5 K QBO over Equator

UK Met Office Study (Healy et al. 2004) Forecast impact experiment run for 16 days of CHAMP data May/June 2001 ~160 CHAMP profiles/day (0.35% of total data) All other available obs assimilated (ATOVS, sfc,aircraft,radiosonde Sat winds, SSMI winds)-~47,450 total N assimilated for 4<Z<30 km only Healy, Jupp and Marquardt, Geophys.Res.Lett, 2004

RMS temperature differences at 250 mb and 50 mb between Control and GPS RO analyses. (Healy et al., 2004)

250 hPa SH (lat<-20º)50 hPa NH (lat>20º) Mean and RMS fit to radiosonde T observations for control (red) and GPS RO (blue, dashed) experiments.

COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) 6 Satellites launched in late 2005 Three instruments: GPS receiver, TIP, Tri-band beacon Weather + Space Weather data Global observations of: Pressure, Temperature, Humidity Refractivity Ionospheric Electron Density Ionospheric Scintillation Demonstrate quasi-operational GPS limb sounding with global coverage in near-real time Improved retrievals over GPS/MET, CHAMP

COSMIC Program Status

o: EQUARS o: COSMIC Distribution of GPS Occultation events in 24 hrs with EQUARS (2006, inclination angle<20 o ) and COSMIC (2005, 6 LEO satellites at 72 o ) EQUARS Dense data rate in equatorial region COSMIC Global coverage, but less data at low latitudes +

Concluding Remarks GPS radio occultation technique is a very promising atmospheric observing system for both weather and climate: –High vertical resolution –High accuracy –All weather –No instrument drift (important for climate detection) GPS RO data will be valuable to: –climate change analysis, validating of climate simulations –operational weather prediction –ionospheric research and space weather forecasting –calibrate other observing systems (e.g., radiosonde and other satellite obs.) GPS RO technique is here to stay (COSMIC is coming, and more missions are being planned)

Summary and Look Ahead Proof of concept of the potential value of GPS RO observations has been demonstrated (weather, climate, space weather) Operational GPS RO observations called for by WMO studies Augment present and planned satellite remote sensing at a reasonable cost –Support US CCSP, GEOSS, NOAA Strategic Plan Transition COSMIC constellation into full operations beginning in ~ Plan for success!

COSMIC-II (C2) ~2500 (5000) high-quality, independent soundings to complement and improve infrared and microwave soundings Risk reduction Affordable (<$15M/year ongoing costs-total) Launch in 2009 would overlap COSMIC by one year, allowing tests of value of 5000 (7500) vs soundings Major new contribution to GEOSS [Higher number of soundings in ( ) if Galileo included]

C2 baseline concept spacecraft in flight Total Mass Estimate: 24 Kg. Total Orbit Average Power: 29 watts Stowed Size: 50 cm x 40 cm x 10 cm Improved occultation receiver Reduced latency (<25 min) GPS and Galileo tracking

COSMIC II-Summary Transition research into operations- maintain a constellation of small satellites in low Earth orbit producing RO observations to help meet the weather, climate and space weather operational requirements as part of the GEOSS.

Compared to GPS/MET with median cut-off height ~ 500 mb. Improved HW, firmware, and software have extended vertical coverage for RO. “ Depth” of RO Soundings Achieved by CHAMP Penetration of RO into lower troposphere

Radiosonde Stations and Manufacturers Vaisala/Australia IM-MK3/India Shang/China MEISEI/Japan Mars/MRZ VIZ AIR Others From Junhong Wang

Statistics of CHAMP - Radiosonde Comparison Region Sonde Type # of matches IndiaIM-MK / /1.0 RussiaMars / /0.9 JapanMEISEI / /1.1 ChinaShanghai / /1.0 AustraliaVaisala / /0.9

CHAMP - radiosonde comparison India Australia N CR = 0.82%N CR = 0.18%

RO - ECMWF Comparison Data Poor regions Data Rich regions Comparison of RO profiles with ECMWF profiles in data rich (most land masses) and data poor regions (mostly oceanic regions). The better agreement from 5-30 km indicates that superior ECMWF performance in data rich regions

Kelvin waves near the tropopause Bill Randel NCAR

North Pole Mid-latitudes (NH) Strong Polar Climate signal from RO record?