Wenhui Wang 1 & Cheng- Zhi Zou 2 1 IMSG at NOAA/NESDIS/STAR - PowerPoint PPT Presentation

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Wenhui Wang 1 & Cheng- Zhi Zou 2 1 IMSG at NOAA/NESDIS/STAR

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  1. Lower-Tropospheric Temperature (TLT) Climate Data Record Using NOAA/NESDIS/STAR Recalibrated MSU Observations Wenhui Wang1 & Cheng-Zhi Zou2 1IMSG at NOAA/NESDIS/STAR 2NOAA/NESDIS/Center for Satellite Applications and Research IGARSS Vancouver, Canada July 25-29, 2011

  2. Outline • Background • Methods for Developing TLT Product Using NOAA/NESDIS/STAR Recalibrated MSU Radiances • Results and Discussion • Summary and Future Works

  3. Background • Microwave Sounding Unit (MSU, 1978/11-2006/9) • 9 instruments (NOAA TIROS-N – NOAA-14) • 4 channels Channel 2- mid-troposphere (TMT) Channel 3 - upper-troposphere Channel 4 - lower-stratosphere • 11 scan angles: 0 – 47.35° • Widely used in long-term atmospheric Tb trends studies • MSU Lower Tropospheric Temperature (TLT) • TMT Affected by stratosphere cooling effect • TLT: weighted average of TMT Tb at different view angles (Spencer and Christy, 1992,2003; Mears and Wentz, 2009) TLT=T3+T4+T8+T9-0.75(T1+T2+T10+T11) i=1-4, 8-10 scan positions Reduce stratosphere cooling effect

  4. Background • Two MSU TLT products available Using NOAA pre-launch calibrated observations • University of Alabama group (UAH) • Remote Sensing Systems group (RSS) • Major Issues need to addressed • Calibration Errors (Warm Target Contamination) • Orbital Decay Effect • Diurnal Drift Effect • TLT trends have important policy making implications • Purpose of this study • Generate STAR TLT product using NOAA/NESDIS/STAR recalibrated MSU radiances • Comparing STAR TLT with other two research groups

  5. Methods for STAR TLT Product • Using NOAA/NESDIS/STAR Recalibrated MSU Radiances (v1.2) (Zou et al. 2006, 2009, 2010) • Simultaneous Nadir Overpass (SNO) Method to generate consistent climate data records (CDR) http://www.star.nesdis.noaa.gov/smcd/emb/mscat/mscatmain.htm • Remove Warm Target (WT) Contamination at root level • Can reduce inter-satellite bias by an order of magnitude compared to NOAA pre-launch calibration

  6. Methods for STAR TLT Product • Using NOAA/NESDIS/STAR Recalibrated MSU Radiances • NOAA 10 -14 averaged σ of intersatellite biases SNO calibration (curve) SNO + Christy Bias Correction (straight line) Christy Bias Correction is used to removes residual WT contamination after SNO calibration Noises in TLT are 2 times as large as those in MSU channel 2 (TMT)

  7. Methods for STAR TLT Product • Satellite Altitude & Orbital Decay Effect Correction • Satellite altitudes are different (morning versus noon satellites) • Satellite altitude trends to decay over time • Cause view zenith angle changes, effects vary with different limb positions

  8. Methods for STAR TLT Product • Satellite Altitude & Orbital Decay Effect Correction Simulated altitude effect climatology • Community Radiative Transfer Model (CRTM) • NASA MERRA reanalysis • All observations adjusted to 850 km altitude Rate of Tb change with satellite altitude (K/km)

  9. Methods for STAR TLT Product Diurnal Drift Effect Correction same as STAR TMT products (Zou and Wang 2009)Using RSS monthly averaged diurnal anomaly climatology Before Diurnal Correction NOAA 11 - NOAA 10 Adjust the scene radiances at different observation time to the local noon time After Diurnal Correction

  10. Results 5-day averaged MSU global mean TLT & TMT time series Temporal Coverage: 1978/11-2006/9 Spatial Coverage: -82.5° – +82.5 °

  11. Results: Spatial Trend Patterns (1978-2006) TLT After Orbital Drift Effect Correction TMT (channel 2) TLT Without Orbital Decay Effect Corr.

  12. Comparing STAR, UAH (v5.3), RSS (v3.2) MSU TLT Products (1979 - 2003)

  13. Summary and Future Works • Generated MSU TLT product using NOAA/NESDIS/STAR recalibrated channel 2 radiances • STAR TLT shows a global warming trend of 0.145 K/dec (1978-2006), • STAR TLT has the smallest warming trends compared to UAH and RSS TLT products • Larger differences exist during 1979 – 1986 • Next Step • Generate TLT product using recalibrated Advanced Microwave Sounding Unit A (AMSU-A) observations (1998 – present) • Generate MSU/AMSU-A TLT merged Product

  14. Results TLT show similar trend stability as TMT (Zouand Wang, 2010) Christy bias correction (almost horizontal lines) Constant bias correction