Recalibration and merging of SSU observations for stratospheric temperature trend studies

Abstract

Long-term observations from the Stratospheric Sounding Unit (SSU) during 1979-2006 onboard NOAA historical polar orbiting satellites were recalibrated for climate change investigation. A two-point linear calibration equation, with cold space and an internal blackbody warm target as end-point references, was used to transfer SSU raw counts data into radiances. The warm target temperature was represented by measurements from the space side thermistor on the blackbody, and the cold space radiance was assumed to be zero. Space view corrections due to an electrical interference were applied. Intersatellite calibration was conducted simultaneously by applying calibration offsets determined from residual intersatellite biases. The recalibration reached an accuracy of 0.1-0.2 K for global means and thus is expected to improve the consistency in stratospheric temperature time series in climate reanalyses. The recalibrated SSU radiances were further adjusted to develop Version 2 of the NOAA stratospheric temperature time series. The effects being adjusted included those from changes in instrument cell pressure and atmospheric carbon dioxide concentration, viewing angle differences, and semidiurnal tides due to orbital drift. Intersatellite biases were carefully removed to ensure smooth transitions between satellite pairs. Differences from Version 1 included improved radiance calibration, improved adjusting schemes for diurnal drift and intersatellite biases, removal of time-varying cell pressure adjustment for NOAA-9 channel 1, and excluding NOAA-7 channel 2 in the time series. In addition to the final merged data set, intermediate synthetic time series corresponding to different adjustments were also created to quantify their impact on the final trend as well as its reliability and uncertainty. Excellent matching between satellite pairs, especially the 7 year overlaps between NOAA-11 and NOAA-14 during 1997-2004, in intermediate as well as the final time series provided strong evidence on the validity of adjustments and thus confidence on the resulting trends. The Version 2 global mean trends for 1979-2006 were À0.69 ± 0.18, À0.77 ± 0.15, and À0.85 ± 0.15 K/decade for SSU channels 1, 2, and 3, representing temperatures of middle stratosphere, upper stratosphere, and stratosphere-mesosphere, respectively. Among these, cooling of channel 2 was stronger and channel 3 weaker than those in UK Met Office (UKMO) data by about 1 K during the entire SSU period from 1979 to 2006. Finally, the average of the channel 1 and channel 3 anomalies in Version 2 was close to channel 2 anomalies to within 0.2 K for the entire 1979-2006 period with identical trends. This feature was found consistent with chemistry-climate model simulations.

Climatology and interannual variability of dynamic variables in multiple reanalyses evaluated by the SPARC Reanalysis Intercomparison Project (S-RIP)

“…The NOAA STAR TLS, SSU1, and SSU2 data sets (Zou et al, 2014;Zou and Qian, 2016) are a much improved CDR than the version used in Thompson et al (2012), which pointed out the dissimilarities between the NOAA and Met Office SSU data records. The comparison between the version used in this paper and the appropriately weighted reanalyses is much better than previous papers using the older version and the Met Office CDR.…”

“…Anomalies from the 30-year period for the TLS, SSU1, and SSU2 are generated. These anomalies are compared against the NOAA STAR SSU v2.0 data set (Zou et al, 2014) and MSU/AMSU mean layer atmospheric temperature v3.0 (Zou and Wang, 2012). The left column of Fig.…”

An upper-branch Brewer–Dobson circulation index for attribution of stratospheric variability and improved ozone and temperature trend analysis

“…5) we additionally consider equatorial ozone from the Global OZone Chemistry And Related trace gas Data records for the Stratosphere (GOZ-CARDS; Froidevaux et al, 2015), Solar Backscatter Ultraviolet Instrument Merged Cohesive (SBUV-Mer. ; Tummon et al, 2015), SBUV Merged Ozone Dataset (SBUV-MOD; Frith et al, 2014) composites and temperature from the Stratospheric Sounding Unit observations (SSU; Zou et al, 2014), and Japanese 55-year Reanalysis (JRA-55) (Ebita et al, 2011) and Modern-Era Retrospective analysis for Research and Applications (MERRA) (Rienecker et al, 2011) reanalyses. All observations are re-gridded onto the SOCOL model pressure levels and latitudes.…”

Global temperature response to the major volcanic eruptions in multiple reanalysis data sets

“…See, e.g. Christy et al (2003), Wang et al (2012), Wang and Zou (2014), Zou et al (2014), and Nash and Saunders (2015) for these satellite temperature measurements.…”