Exploring Earth's Atmosphere and Climate with GPS, GALILEO, and LEO-LEO Occultations

1. ACE+Exploring Atmosphere and Climateof the EarthUsingGPS, GALILEO, and LEO-LEO OccultationsPer Høeg (AIR/DMI)Gottfried Kirchengast (IGAM/UG) EUMETSAT GRAS SAF 2nd User Workshop 2003

2. Objectives • Climate • Monitoring global long-term variations in the climate and the forcings of the atmosphere system giving rise to trends • Atmosphere • Observe and analyze globally the physical condition and state of the atmosphere of the Earth to improve predictions of future state • Space Weather • Monitoring and modeling of ionosphere and plasmasphere electron density structures EUMETSAT GRAS SAF 2nd User Workshop 2003

3. Primary Issue of Concern: Climate Change • Increasing evidence exists that the Earth’s climate is currently changing (e.g., IPCC 2001 Report). The changes are most pronouncedin the most variable component of the Earth system, the atmosphere. • Key indicators: • Humidity and temperature in the troposphere tend to increase • Stratospheric temperatures tend to decrease • Stratospheric humidity tend to increase with drastic changes in the radiation • It is likely that these changes are associated with human-induced • increases of greenhouse gas concentrations in the atmosphere. • Natural variability of the climate system complicates the picture, • rendering proper understanding of climate change very challenging. EUMETSAT GRAS SAF 2nd User Workshop 2003

4. Variability of Atmospheric Water Vapor • Latitude-HeightSlice of Humidity based on ECMWF analysis • (15 Sep 1999, 12UTC, 79°W) • Radiosonde Humidity Profile • (Kauai, Hawaii, 1 Oct 2000, 12UTC) EUMETSAT GRAS SAF 2nd User Workshop 2003

5. Water Vapor Variability • Column Water Vapor Monthly Map January 1994 • Column Water Vapor Monthly Map July 1994 EUMETSAT GRAS SAF 2nd User Workshop 2003

6. Greenhouse Gas Emissionsand Temperature Change Projections • a) CO2 emission paths for several representative IPCC scenarios • b) Corresponding near surface temperature change projections EUMETSAT GRAS SAF 2nd User Workshop 2003

7. Present Observations • Global tropospheric and surface temperature data from different sources • (MSU: MSU satellite data, UKMO: radiosonde-based data, Surface: surface data) • Inset: difference between surface and radiosonde data EUMETSAT GRAS SAF 2nd User Workshop 2003

8. Scientific Objectives • Major goal: • Monitor and describe variations and changes in the global atmospheric temperature and water vapor distribution; • Assess climate changes caused by mass field changes and atmosphere dynamics. • Main objectives: • To establish highly accurate (< 0.025 g/kg and < 3 % in specific humidity) and vertically resolved (< 1 km) global climatology of water vapor in the troposphere; • To establish a highly accurate (< 0.2 K) and vertically resolved (~1 km) global climatology of temperature in the troposphere and the stratosphere; • To perform research on climate variability and climate change together with research in improved atmospheric models as well as advancements in NWP; • To study troposphere structures in polar and equatorial regions; • To support analysis and validation of data from other space missions; • To demonstrate a new and novel active atmospheric sounding technique with the CALL instrument; • To enhance the European observational capability for improved contribution to the international GCOS initiative. • Advances in atmosphere physics and climate change processes: • Global climate warming and increased averaged atmospheric water vapor levels; • Tropical heat and mass exchange with extra-tropical regions; • Transport across subtropical mixing barriers, relevant for information on the lifetime of greenhouse gases; • Stratospheric winds and temperatures and atmospheric wave phenomena; • Polar front dynamics and mass exchange together with tropospheric water vapor feedback on climate stability; • High latitude tropospheric-stratospheric exchange processes related to polar vortex conditions; • Climatology of Rossby waves and atmospheric internal waves. EUMETSAT GRAS SAF 2nd User Workshop 2003

9. Satellite Constellation • 4 micro-satellites • Mass: 130 kg • Power: 80 W • Stable two-plane constellation in 90 degrees inclination • In each plane, counter-rotating orbits with 2 satellites - for optimizing quality of measurements • Two altitudes • Heights 650 km and 850 km – to optimize spatial distribution of occultations • Orbital local time drift • To optimize the temporal and local time distribution of occultations • Instruments • L-band GPS/GALILEO precision receiver • X/K-band LEO-LEO precision transmitter and receiver (2 of each) EUMETSAT GRAS SAF 2nd User Workshop 2003

10. EUMETSAT GRAS SAF 2nd User Workshop 2003

11. Why is measurements ofatmospheric water vapor important ? • Indicator of climate change • Strongest greenhouse gas • Climate positive/negative feedback • Energy reservoir • Impact/feedback on global wind system changes and general atmosphere dynamics • Hydrologic cycle • Highly variable (time and space) EUMETSAT GRAS SAF 2nd User Workshop 2003

12. Global Temperature Deviations EUMETSAT GRAS SAF 2nd User Workshop 2003

13. Forcing residuals in atmospheric models • Estimation of the residual (R) requires availability of high quality observed data. • Forcing residuals can be used to: • identify tendency errors in the differential equations of atmospheric models • detect temporal variations in external forcing of the atmosphere. EUMETSAT GRAS SAF 2nd User Workshop 2003

14. Weak nudging towards the re-analyses Data assimilation via nudging: Discretization in time (assimilation in spectral space): Forcing residual is approximated by the last fraction: EUMETSAT GRAS SAF 2nd User Workshop 2003

15. The ACE+ Experiment EUMETSAT GRAS SAF 2nd User Workshop 2003

16. GRAS+ Temperature Retrieval EUMETSAT GRAS SAF 2nd User Workshop 2003

17. Processing Steps for Water Vapor Retrievals EUMETSAT GRAS SAF 2nd User Workshop 2003

18. GRAS+ Requirements EUMETSAT GRAS SAF 2nd User Workshop 2003

19. Absorption at X/K-band frequencies Frequencies: 10.0-11.5 GHz 17.2-17.3 GHz 22.5-23.5 GHz EUMETSAT GRAS SAF 2nd User Workshop 2003

20. Absorption EUMETSAT GRAS SAF 2nd User Workshop 2003

21. CALL Temperature and Humidity Retrieval EUMETSAT GRAS SAF 2nd User Workshop 2003

22. CALLTemperatureand HumidityRequirements EUMETSAT GRAS SAF 2nd User Workshop 2003

23. Weekly Profile Coverage • Weekly latitudinal distribution of occultations. Longitudinal variations still exist in the seven days simulation. Part of the spread in the plot is due to this effect. • For the 500 x 500 km cells the following statistics can be calculated: • Average number of occultations in a cell: 22.49 • Standard deviation: 10.36 • Average time difference (min) between profiles in each cell as function of latitude. The simulation covers a whole week of data. • Average time difference between the occultations: 482 min [8h 2min] • Standard deviation: 216 min [3h 36min] EUMETSAT GRAS SAF 2nd User Workshop 2003

24. Global Distribution of Occultations EUMETSAT GRAS SAF 2nd User Workshop 2003

25. Distribution of NWP Radiosonde Observations EUMETSAT GRAS SAF 2nd User Workshop 2003

26. Global Distribution of LEO-LEO Occultations EUMETSAT GRAS SAF 2nd User Workshop 2003

27. Global Humidity Fields EUMETSAT GRAS SAF 2nd User Workshop 2003

28. Launch • 2006/2007 • Mission lifetime • 5 years (2006 – 2012) EUMETSAT GRAS SAF 2nd User Workshop 2003