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

• 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-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

0

5

10

15

20

25

0 0.05 0.1 0.15

He

igh

t (k

m)

Weighting Function (Ocean)

NADIR

Scan Pos 5

Scan Pos 4

Scan Pos 3

Scan Pos 2

Scan Pos 1

TLT

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

790

800

810

820

830

840

850

860

870

1978 1983 1988 1993 1998 2003

Alt

itu

de

(km

)

NTN N6 N7

N8 N9 N10

N11 N12 N14

• 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 series Temporal Coverage: 1978/11-2006/9

Spatial Coverage: -82.5° – +82.5 °

TLT Without Orbital Drift Effect Correction

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