wenhui wang 1 & cheng- zhi zou 2 1 imsg at noaa/nesdis/star

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