the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 May 2024
Upper Stratospheric Temperature Trends: New Results from OSIRIS
Abstract. Temperature trends in the upper stratosphere, particularly above ~45 km are difficult to quantify due to a deficit of long-term observational data in this region. The recent v7.3 upper stratospheric (35–60 km) temperature data product from the Optical Spectrograph and InfraRed Imager System (OSIRIS) includes over 22 years of observations that can be used to estimate temperature trends. The trends in OSIRIS temperatures over 2005–2021 are compared to those from two other satellite limb instruments: SABER and MLS. We find that the upper stratosphere cooled by ~0.5 to 1 K/decade during this period. Results from the three instruments are generally in agreement. By merging the OSIRIS observations with those from channel 3 of the Stratospheric Sounding Unit (SSU), we find that the stratosphere cooled at a rate of approximately -0.6 K/decade between 1979 and 2021 near 45 km, in agreement with earlier results based on SSU and MLS. The similarity between OSIRIS temperature trends and those from other records improves confidence in observed upper stratospheric temperature changes over the last several decades.
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RC1: 'Comment on egusphere-2024-1252', Anonymous Referee #1, 22 Jun 2024
This manuscript describes a study of temperature trends in the upper stratosphere and lower mesosphere using a new OSIRIS temperature product based on analysis of Rayleigh scattering at the limb. This is an interesting study because the upper stratosphere is expected to cool as a result of increasing CO2 in the atmosphere and there are few datasets available to track temperature trends in this region of the atmosphere, most of which have low vertical resolution. Trends derived from OSIRIS data are compared with those from other space instruments, the two limb sounders SABER and MLS and the operational nadir sounders SSU and AMSU-A, as well as the three most recent meteorological reanalyses ERA5, MERRA-2 and JRA-55. The overall picture is one of fairly good coherence between these different data sets, with cooling of the order of 0.5 to 1K/decade over the last 40 years. This manuscript deserves to be published in EGUsphere after a few corrections presented below.
1) The OSIRIS data are based on a little known technique of deriving the atmospheric density profile and recovering the absolute temperature profile using hydrostatic equilibrium and the ideal gas law. The creation of this dataset is described in detail in Zawada et al (2024). However, a more detailed description of the technique would be useful, outlining in particular the advantages and disadvantages compared with measurement techniques based on the thermal infrared spectrum and microwaves. I recommend also citing other studies based on this technique and in particular the only one that presents a climatology of temperature in the upper stratosphere and mesosphere (Hauchecorne et al., 2019).
2) In the multilinear regression (MLR) model, the quasi-biennial oscillation is represented by two components QBOa and QBOb but without explaining how these components are defined. The MLR model is described in Damadeo et al (2022) but the paper should give sufficient explanation to be consistent.
3) The way in which the merger with SSU and AMSU-A is carried out should be more detailed. It is not enough to say that it is the same method as Bourassa et al. (2014), although it is important to refer to previous work. Again, the document needs to be consistent. Where data is available, for example for OSIRIS and SSU for a given month and latitude, do we simply take the average between the two datasets or use a more sophisticated technique?
4) The temperature trends shown in Figure 8 appear to be more variable with latitude and with greater uncertainty for SSU+OSIRIS than for SSU+AMSU and SSU+MLS. Is this due to less regular sampling with OSIRIS or to greater uncertainties in the OSIRIS data?
Citation: https://doi.org/10.5194/egusphere-2024-1252-RC1 -
RC2: 'Reviewer comments', Anonymous Referee #2, 03 Aug 2024
The paper introduces a new long-term dataset of upper stratospheric temperature profiles from OSIRIS and presents its extensive evaluation as a climate data record. This is a very valuable contribution. The paper is interesting, well written, it contains informative illustrations. My minor comments are in the attached annotated manuscript.
- AC1: 'Comment on egusphere-2024-1252', Kimberlee Dubé, 12 Sep 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-1252', Anonymous Referee #1, 22 Jun 2024
This manuscript describes a study of temperature trends in the upper stratosphere and lower mesosphere using a new OSIRIS temperature product based on analysis of Rayleigh scattering at the limb. This is an interesting study because the upper stratosphere is expected to cool as a result of increasing CO2 in the atmosphere and there are few datasets available to track temperature trends in this region of the atmosphere, most of which have low vertical resolution. Trends derived from OSIRIS data are compared with those from other space instruments, the two limb sounders SABER and MLS and the operational nadir sounders SSU and AMSU-A, as well as the three most recent meteorological reanalyses ERA5, MERRA-2 and JRA-55. The overall picture is one of fairly good coherence between these different data sets, with cooling of the order of 0.5 to 1K/decade over the last 40 years. This manuscript deserves to be published in EGUsphere after a few corrections presented below.
1) The OSIRIS data are based on a little known technique of deriving the atmospheric density profile and recovering the absolute temperature profile using hydrostatic equilibrium and the ideal gas law. The creation of this dataset is described in detail in Zawada et al (2024). However, a more detailed description of the technique would be useful, outlining in particular the advantages and disadvantages compared with measurement techniques based on the thermal infrared spectrum and microwaves. I recommend also citing other studies based on this technique and in particular the only one that presents a climatology of temperature in the upper stratosphere and mesosphere (Hauchecorne et al., 2019).
2) In the multilinear regression (MLR) model, the quasi-biennial oscillation is represented by two components QBOa and QBOb but without explaining how these components are defined. The MLR model is described in Damadeo et al (2022) but the paper should give sufficient explanation to be consistent.
3) The way in which the merger with SSU and AMSU-A is carried out should be more detailed. It is not enough to say that it is the same method as Bourassa et al. (2014), although it is important to refer to previous work. Again, the document needs to be consistent. Where data is available, for example for OSIRIS and SSU for a given month and latitude, do we simply take the average between the two datasets or use a more sophisticated technique?
4) The temperature trends shown in Figure 8 appear to be more variable with latitude and with greater uncertainty for SSU+OSIRIS than for SSU+AMSU and SSU+MLS. Is this due to less regular sampling with OSIRIS or to greater uncertainties in the OSIRIS data?
Citation: https://doi.org/10.5194/egusphere-2024-1252-RC1 -
RC2: 'Reviewer comments', Anonymous Referee #2, 03 Aug 2024
The paper introduces a new long-term dataset of upper stratospheric temperature profiles from OSIRIS and presents its extensive evaluation as a climate data record. This is a very valuable contribution. The paper is interesting, well written, it contains informative illustrations. My minor comments are in the attached annotated manuscript.
- AC1: 'Comment on egusphere-2024-1252', Kimberlee Dubé, 12 Sep 2024
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