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Lower-Tropospheric Temperature (TLT) Climate Data Record Using NOAA/NESDIS/STAR Recalibrated MSU Observations. Wenhui Wang 1 & Cheng- Zhi Zou 2 1 IMSG at NOAA/NESDIS/STAR 2 NOAA/NESDIS/Center for Satellite Applications and Research. IGARSS Vancouver, Canada July 25-29, 2011. Outline. - PowerPoint PPT Presentation
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Lower-Tropospheric Temperature (TLT) Climate Data Record Using NOAA/NESDIS/STAR
Recalibrated MSU Observations
Wenhui Wang1 & Cheng-Zhi Zou2
1IMSG at NOAA/NESDIS/STAR2NOAA/NESDIS/Center for Satellite Applications and Research
IGARSSVancouver, Canada July 25-29, 2011
• Background
• Methods for Developing TLT Product Using NOAA/NESDIS/STAR Recalibrated MSU Radiances
• Results and Discussion
• Summary and Future Works
Outline
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-troposphereChannel 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
0 0.05 0.1 0.150
5
10
15
20
25
Weighting Function (Ocean)
NADIRScan Pos 5Scan Pos 4Scan Pos 3Scan Pos 2Scan Pos 1TLT
Heig
ht (k
m)
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
1. 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 Product
SNO calibration (curve) SNO + Christy Bias Correction (straight line)
Christy Bias Correction is used to removes residual WT contamination after SNO calibration
Methods for STAR TLT Product
NOAA 10 -14 averaged σ of intersatellite biases
Noises in TLT are 2 times as large as those in MSU channel 2 (TMT)
1. Using NOAA/NESDIS/STAR Recalibrated MSU Radiances
2. Satellite Altitude & Orbital Decay Effect Correction
Methods for STAR TLT Product
1978 1983 1988 1993 1998 2003790
800
810
820
830
840
850
860
870
NTN N6 N7 N8
N9 N10 N11 N12
N14
Altit
ude
(km
)
• 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
2. 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 Product
3. Diurnal Drift Effect Correction same as STAR TMT products (Zou and Wang 2009)Using RSS monthly averaged diurnal anomaly climatology
Before Diurnal Correction
After Diurnal Correction
NOAA 11 - NOAA 10
Methods for STAR TLT Product
Adjust the scene radiances at different observation time to the local noon time
Results
5-day averaged MSU global mean TLT & TMT time seriesTemporal Coverage: 1978/11-2006/9
Spatial Coverage: -82.5° – +82.5 °
TLT Without Orbital Decay Effect Corr.
TLT After Orbital Drift Effect Correction
Results: Spatial Trend Patterns (1978-2006)
TMT (channel 2)
Comparing STAR, UAH (v5.3), RSS (v3.2) MSU TLT Products (1979 - 2003)
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
TLT show similar trend stability as TMT (Zou and Wang, 2010)Christy bias correction (almost horizontal lines) Constant bias correction
Results