Homogenized SSU Observations Verify the Anthropogenic Global Warming Theory Cheng-Zhi Zou1 Haifeng Qian2, Likun Wang3, Lilong Zhao4

1: NOAA/NESDIS/STAR, College Park, MD,20740 2: Earth Resource Technology, Inc., Columbia, MD, 20707 3: ESSIC, University of Maryland, College park, MD,20740 4. Nanjing Information Science and Technology University, Nanjing, China, 210044

1.IntroductionThe Stratospheric Sounding Unit (SSU) onboard the historical NOAA TIROS-N

Polar Orbiting Environmental Satellite (POES) series was a three-channel infrared radiometer designed to measure temperature profiles in the middle and upper stratospheres (Figure 1). It plays a key role in estimating temperature trends in the middle and upper stratospheres for the period of 1979–2006. However, the SSU observations suffered several instrument specific drifts that have to be corrected to derive homogenized observations for stratospheric trend investigations. STAR scientists have recently developed innovative algorithms to remove instrument biases such as those from cell pressure changes, diurnal drift, changes in atmospheric carbon dioxide concentration, and viewing angle differences. Homogenized stratospheric temperature climate data record (CDR) was developed after removal of these biases. The time series have been used to investigate and understand stratospheric temperature trends and to verify climate model simulations of the anthropogenic global warming effect on the stratosphere. This poster describes recalibration and merging schemes for generation of the NOAA/STAR SSU CDR and presents preliminary results of the SSU verification of the CMIP5 climate model simulations of the stratospheric temperature changes during 1978-2006.

5. References• Zou, C.-Z., H. Qian, W. Wang, L. Wang, and C. Long (2014), Recalibration and merging of SSU

observations for stratospheric temperature trend studies, J. Geophys. Res. Atmos.,119,13,180-13,205, doi:10.1002/2014JD021603

• Wang, L., C.-Z. Zou, and H. Qian (2012), Construction of stratospheric temperature data records from Stratospheric Sounding Units, J. Clim.,25, 2931–2946, doi:10.1175/JCLI-D-11-00350.1.

2. Recalibration of SSU for Generation of Consistent Radiance FCDR

Figure 2 SSU scan and calibration cycle.

SSU was designed with on-orbit calibration capability by viewing calibration targets, a cosmic space ‘cold’ target and an onboard blackbody ‘warm’ target, as calibration references. A two-point linear calibration equation, was used to transfer SSU raw counts data into radiances,

where R is the scene radiance, C represents the raw counts of satellite observations from the Earth and target views, S = Rw/(Cw-Cc-ε) is the slope determined by the two calibration targets. δR is a small calibration offset, and the subscripts E, w, and c refer to the Earth view, onboard blackbody warm target view, and cold space view, respectively. Figure 2 schematically illustrates the SSU scan and calibration cycle, with details in the reference.

This recalibration used measurement from the space-side thermistor to represent the warm target temperature. This temperature was close to the average from all the PRT and thermistors on the blackbody and calibration uncertainty was within 0.05K. The recalibration also applied a space view correction to account for the space view anomalies associated with switching of PRT to a reference mode (equation (1), ε term).

The recalibrated SSU radiances differ from those from the NOAA operational calibration archived in the NOAA/NCDC CLASS since the former applied a space view correction while the later did not. Figure 3 shows their differences for each satellite channel which was nearly constant for the entire operational period of a satellite. These differences will affect assimilation of the data in climate reanalyses.

Anthropogenic global warming theory predicts that the stratosphere has a cooling response to human-induced changes in atmospheric trace gases: ozone depletion is expected to cause the stratosphere to cool, due to less absorption of the ultra-violet radiation from the sun; increases of carbon dioxide and other greenhouse gases are expected to cause stratospheric cooling as more greenhouse gases trap more outgoing infra-red radiation close to the Earth’s surface and emit more radiation into space from the stratosphere, causing a net energy loss in the stratosphere. Such a stratospheric cooling response has been well simulated by climate models in the Coupled Model Intercomparison Project-5 (CMIP5, Figure 6), with input of trace gas variations to the best of human knowledge at the time, although individual models had resulted in slightly different stratospheric cooling rate.

The STAR homogenized SSU time series were used to verify the CMIP5 model simulations of the past climate change and trends during 1978-2006 (Figure 6). Agreement between the homogenized SSU observations and ensemble means of multiple CMIP5 model simulations were found to be extremely well – the agreement was within the uncertainty estimates at least for SSU channels 2 and 3. This excellent agreement represents a significant milestone in verifying anthropogenic global warming theory and climate model capabilities in simulating the past climate changes. It also implies certain reliability of climate models in predicting future climate changes. In addition, it was suggested (Seidel et al. 2011) that time variation of the three SSU channels followed a remarkable relationship—average of the channel 1 and channel 3 anomalies was close to the channel 2 anomalies to within 0.1 K during the entire SSU period from 1979 to 2006 in all chemistry-climate model simulations (Figure 7). This behavior was also verified to be true by the homogenized SSU observations as shown in Figure 8.

Figure 3 Differences of the global mean brightness temperature time series between the recalibrated SSU radiances and those from NOAA operational calibration archived in NCDC CLASS.

Figure 4. Global mean temperature anomalies for each satellite and total trends before (left panels) and after (right panels) the adjustments and merging.

(1)

SSU recalibrated radiances can be used for temperature trend assessment only after adjustments are done for each satellite to remove time-varying inter-satellite biases. Drifts being adjusted included effects from instrument cell pressure changes, diurnal drifts, changes in atmospheric CO2 concentration, and viewing angle differences. Residual inter-satellite biases may still exist after all these adjustments and they were further removed by constant inter-satellite bias corrections applied at each grid cell. After the adjustments and merging, homogenized SSU time series were obtained for all three SSU channels (Figure 4). Inter-sattelite biases were zero for each satellite pair with no bias drift over time after all adjustments (Figure 5). These provided high confidence on the adjustment and merging technologies and reliability of the dataset for stratospheric temperature trend investigation.

3. Adjustment and Merging of SSU Observations

Unadjusted SSU anomaly time series from recalibrated radiances SSU anomaly time series after all adjustments and merging

Figure 1 Weighting function of the three SSU channels under the standard atmospheric conditions

Figure 5 Global mean inter-satellite difference time series for overlapping satellite pairs after all adjustments.

4. Verifying Climate Model Simulations of Anthropogenic Global Warming Effect in the Stratosphere El Chichón

El Chichón

Mt. Pinatubo

Mt. PinatuboSSU2:-0.76K/dec

Model Mean:-0.77K/dec

Figure 6 Comparison of stratospheric temperature time series and trends between homogenized SSU observations and CMIP5 model simulations. Blue lines are STAR homogenized SSU observations, light grey lines are individual CMIP5 model simulations, and black lines are model means from the grey lines. SSU1, SSU2, and SSU3 are the three SSU channels representing layer mean temperatures of the mid-stratosphere, upper-stratosphere, and stratosphere-mesosphere, respectively. Trends are given for each channels at the upper right corner of each panel.

Figure 8 NOAA SSU anomaly time series for (top) the average of channel 1 and channel 3 versus channel 2 and (bottom) their differences

Figure 7 Global mean temperature anomalies simulated by eight Chemistry-Climate models (red lines) for 1979–2005 in the four vertical layers sampled by the three SSU channels and the Microwave Sounding Unit lower stratosphere (MSU LS). The bottom trace is the average of SSU channels 1 (25) and 3 (27) minus channel 2 (26) from the models (red lines).