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
Outline• Background• Methods for Developing TLT Product Using NOAA/NESDIS/STAR Recalibrated MSU Radiances• Results and Discussion• Summary and Future Works
Background• Microwave Sounding Unit (MSU, 1978/11-2006/9) • 9 instruments (NOAA TIROS-N – NOAA-14) • 4 channels Channel 2- mid-troposphere (TMT) Weighting Function Channel 3 - upper-troposphere (Ocean) 25 Channel 4 - lower-stratosphere NADIR • 11 scan angles: 0 – 47.35° Scan Pos 5 • Widely used in long-term atmospheric Tb trends studies 20 Scan Pos 4 Scan Pos 3• MSU Lower Tropospheric Temperature (TLT) Scan Pos 2 Height (km) 15 Scan Pos 1 – TMT Affected by stratosphere cooling effect TLT – TLT: weighted average of TMT Tb 10 at different view angles (Spencer and Christy, 1992,2003; Mears and Wentz, 2009) 5 TLT=T3+T4+T8+T9-0.75(T1+T2+T10+T11) 0 0 0.05 0.1 0.15 i=1-4, 8-10 scan positions Reduce stratosphere cooling effect
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
Methods for STAR TLT Product1. 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
Methods for STAR TLT Product1. Using NOAA/NESDIS/STAR Recalibrated MSU RadiancesNOAA 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)
Methods for STAR TLT Product 2. Satellite Altitude & Orbital Decay Effect Correction 870 860 • Satellite altitudes are different (morning 850 versus noon satellites) 840 • Satellite altitude trends to decay over timeAltitude (km) 830 • Cause view zenith angle changes, effects vary with different limb positions 820 810 NTN N6 N7 800 N8 N9 N10 N11 N12 N14 790 1978 1983 1988 1993 1998 2003
Methods for STAR TLT Product2. 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)
Methods for STAR TLT Product3. 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
Results 5-day averaged MSU global mean TLT & TMT time series Temporal Coverage: 1978/11-2006/9 Spatial Coverage: -82.5° – +82.5 °
Results: Spatial Trend Patterns (1978-2006) TLT After Orbital Drift Effect CorrectionTLT Without Orbital Drift Effect Correction TMT (channel 2)
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
Results TLT show similar trend stability as TMT (Zou and Wang, 2010) Christy bias correction (almost horizontal lines) Constant bias correction
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