the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Assessing the potential of free tropospheric water vapour isotopologue satellite observations for improving the analyses of latent heating events
Abstract. Satellite-based observations of free tropospheric water vapour isotopologue ratios (δD) with good global and temporal coverage have become recently available. We investigate the potential of these observations for constraining the uncertainties of the atmospheric analyses fields of specific humidity (q), temperature (T), and δD and of variables that capture important properties of the atmospheric water cycle, namely the vertical velocity (ω), the latent heating rate (Q2), and the precipitation rate (Prcp). Our focus is on the impact of the δD observations if used in addition to the observation of q and T , which are much easier to be observed by satellites and routinely in use for atmospheric analyses. For our investigations we use an Observing System Simulation Experiment, i.e. simulate the satellite observations of q, T , and δD with known uncertainties, then use them within a Kalman filter based assimilation framework in order to evaluate their potential for improving the quality of atmospheric analyses. The study is made for low latitudes (30° S to 30° N) and for 40 days between mid-July and end of August 2016. We find that the assimilation of q and T observations alone well constrains the atmospheric q and T fields (analyses skills in the free troposphere of up to 60 %), and moderately constrains the fields of δD, ω, Q2, and Prcp (analyses skills of 20 %–40 %). The additional assimilation of δD observations further improves the quality of the analyses of all variables. We use Q2 as proxy for the presence of condensation and evaporation processes, and we show that the additional improvement is rather weak when evaporation or condensation are negligible (additional analyses skills of generally below 5 %), and strongest for high condensation rates (additional skills of about 15 % and above). The very high condensation rates (identified by large positive Q2 values) are rare, but related to extreme events (very high ω and Prcp) that are not well captured in the analyses (for these extreme events also the analyses uncertainties of ω, Q2, and Prcp are very large), i.e. the additional assimilation of δD observations significantly improves the analyses of the water cycle related variables for the events when an improvement is most important. In real world satellite datasets δD observations affected by such strong latent heating events are frequently available, suggesting that the here demonstrated additional δD impact for the simulated world is also a realistic scenario for a real world data assimilation.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1316 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-1121', Anonymous Referee #1, 29 Nov 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1121/egusphere-2023-1121-RC1-supplement.pdf
- AC1: 'Reply on RC1', Matthias Schneider, 15 Apr 2024
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RC2: 'Comment on egusphere-2023-1121', Anonymous Referee #2, 11 Dec 2023
The manuscript evaluates the use of assimilating dD measured by the satellite IASI in addition to traditional meteorological variables like q and T (also measured by IASI) in an Observation System Simulation Experiment (OSSE) with the isotope-enabled climate model IsoGSM. In general, dD adds little but notable skill to the analysis. Since dD carries information about the phase change history of air masses, the assimilation of dD particularly improves the analysis in cases of strong condensation or evaporation (identified by high latent heating/cooling rates). These extreme events usually involve strong precipitation and are therefore societally relevant, but are poorly captured in most analyses. Therefore the improvement for these events is very promising.
The manuscript is well-written and the figures are appropriate. I appreciate that everything is nicely structured and carefully documented. It is easy to follow the authors‘ explanations throughout the manuscript. I have a few comments that can hopefully further improve the manuscript and/or clarify some aspects.
General comments
1) As far as I know IASI does not see through clouds. Were observations in cloudy conditions filtered out before the assimilation? I would expect that strong latent heating events are almost always associated with clouds. If IASI cannot measure dD in these cases, is the improvement of the analysis thanks to dD still realistic?
2) The latent heating rate is defined as the change of specific humidity in an air parcel (material derivative of q) times the latent heat of net condensation (equation 9). However, mixing processes can also lead to a change in specific humidity in air parcels and could therefore bias the analysis. Is there a way to separate mixing from latent heating/cooling, e.g. by diagnosing Q2 directly in the model?
3) I think it might be nice to show also the horizontal spatial distribution (i.e. maps) of the differences in the skills to see the regions where the assimilation does or does not work well. Or is it pretty uniform?
4) Is there a reason why you use daily mean values for the analyses? I would expect that especially the strong latent heating/cooling events are rather short-lived and the improvement could be better on shorter time scales, e.g. 6 hours.
Specific comments
L24: Suggestion: „where latent heat is released or consumed“
L25: impacting on > impacting
L39: As far as I know, it should be D and H in the equation (instead of HD16O and H216O).
L50: There is also an isotope version of NICAM (Tanoue et al., 2023), which might be worth adding here.
L53: clouds or precipitation involving processes > processes involving clouds or precipitation
L83: such assimilation > such an assimilation
L108: What is different in the 96 initializations? Later you write the initial conditions. What exactly is different in the initial conditions?
L155+: Add/Explain somewhere what is a good skill and what is a bad skill? E.g. 100% means perfect, 0% means same bad as the reference.
L157 do do > to do
L162+: This has been said many times already. I think it could be removed here or somewhere else.
L171: „Therefore…“: I don‘t see how this sentence follows from the previous sentence.
L179: … and 17 vertical levels?
L208: 2x between
L257: close the > close to
L281: uncertainty > error
L292: this uncertainties > these uncertainties
L303: Remove „an“
L304: independent on > independent of
L306: quantitatively document > quantify?
L309: How did you define these bins? Why not the same 60 bins as before?
L343: in particularly > in particular / particularly
L346: by the additional assimilating of > by additionally assimilating / by the additional assimilation of
L359: These subset > This subset
L392: I would add NICAM here again.
Figure 1, caption: remove „skill“ after (e). Is „only q“ not also „only one type of observation“ (like „only T“ or „only dD“)?
Reference
Tanoue, M., Yashiro, H., Takano, Y., Yoshimura, K., Kodama, C., & Satoh, M. (2023). Modeling Water Isotopes Using a Global Non‐Hydrostatic Model With an Explicit Convection: Comparison With Gridded Data Sets and Site Observations. Journal of Geophysical Research: Atmospheres, 128(23), e2021JD036419.
Citation: https://doi.org/10.5194/egusphere-2023-1121-RC2 - AC2: 'Reply on RC2', Matthias Schneider, 15 Apr 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-1121', Anonymous Referee #1, 29 Nov 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1121/egusphere-2023-1121-RC1-supplement.pdf
- AC1: 'Reply on RC1', Matthias Schneider, 15 Apr 2024
-
RC2: 'Comment on egusphere-2023-1121', Anonymous Referee #2, 11 Dec 2023
The manuscript evaluates the use of assimilating dD measured by the satellite IASI in addition to traditional meteorological variables like q and T (also measured by IASI) in an Observation System Simulation Experiment (OSSE) with the isotope-enabled climate model IsoGSM. In general, dD adds little but notable skill to the analysis. Since dD carries information about the phase change history of air masses, the assimilation of dD particularly improves the analysis in cases of strong condensation or evaporation (identified by high latent heating/cooling rates). These extreme events usually involve strong precipitation and are therefore societally relevant, but are poorly captured in most analyses. Therefore the improvement for these events is very promising.
The manuscript is well-written and the figures are appropriate. I appreciate that everything is nicely structured and carefully documented. It is easy to follow the authors‘ explanations throughout the manuscript. I have a few comments that can hopefully further improve the manuscript and/or clarify some aspects.
General comments
1) As far as I know IASI does not see through clouds. Were observations in cloudy conditions filtered out before the assimilation? I would expect that strong latent heating events are almost always associated with clouds. If IASI cannot measure dD in these cases, is the improvement of the analysis thanks to dD still realistic?
2) The latent heating rate is defined as the change of specific humidity in an air parcel (material derivative of q) times the latent heat of net condensation (equation 9). However, mixing processes can also lead to a change in specific humidity in air parcels and could therefore bias the analysis. Is there a way to separate mixing from latent heating/cooling, e.g. by diagnosing Q2 directly in the model?
3) I think it might be nice to show also the horizontal spatial distribution (i.e. maps) of the differences in the skills to see the regions where the assimilation does or does not work well. Or is it pretty uniform?
4) Is there a reason why you use daily mean values for the analyses? I would expect that especially the strong latent heating/cooling events are rather short-lived and the improvement could be better on shorter time scales, e.g. 6 hours.
Specific comments
L24: Suggestion: „where latent heat is released or consumed“
L25: impacting on > impacting
L39: As far as I know, it should be D and H in the equation (instead of HD16O and H216O).
L50: There is also an isotope version of NICAM (Tanoue et al., 2023), which might be worth adding here.
L53: clouds or precipitation involving processes > processes involving clouds or precipitation
L83: such assimilation > such an assimilation
L108: What is different in the 96 initializations? Later you write the initial conditions. What exactly is different in the initial conditions?
L155+: Add/Explain somewhere what is a good skill and what is a bad skill? E.g. 100% means perfect, 0% means same bad as the reference.
L157 do do > to do
L162+: This has been said many times already. I think it could be removed here or somewhere else.
L171: „Therefore…“: I don‘t see how this sentence follows from the previous sentence.
L179: … and 17 vertical levels?
L208: 2x between
L257: close the > close to
L281: uncertainty > error
L292: this uncertainties > these uncertainties
L303: Remove „an“
L304: independent on > independent of
L306: quantitatively document > quantify?
L309: How did you define these bins? Why not the same 60 bins as before?
L343: in particularly > in particular / particularly
L346: by the additional assimilating of > by additionally assimilating / by the additional assimilation of
L359: These subset > This subset
L392: I would add NICAM here again.
Figure 1, caption: remove „skill“ after (e). Is „only q“ not also „only one type of observation“ (like „only T“ or „only dD“)?
Reference
Tanoue, M., Yashiro, H., Takano, Y., Yoshimura, K., Kodama, C., & Satoh, M. (2023). Modeling Water Isotopes Using a Global Non‐Hydrostatic Model With an Explicit Convection: Comparison With Gridded Data Sets and Site Observations. Journal of Geophysical Research: Atmospheres, 128(23), e2021JD036419.
Citation: https://doi.org/10.5194/egusphere-2023-1121-RC2 - AC2: 'Reply on RC2', Matthias Schneider, 15 Apr 2024
Peer review completion
Journal article(s) based on this preprint
Data sets
MUSICA IASI water isotopologue OSSE assimilation experiments (used in AMT study) Matthias Schneider, Kinya Toride, and Kei Yoshimura https://radar.kit.edu/radar/en/dataset/DcBNGzfWSFxvkCks?token=HNcZIPnVWFewVDyqQerQ
MUSICA IASI water isotopologue pair product (a posteriori processing version 2) Christopher J. Diekmann, Matthias Schneider, and Benjamin Ertl https://doi.org/10.35097/415
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Matthias Schneider
Kinya Toride
Farahnaz Khosrawi
Frank Hase
Benjamin Ertl
Christopher Johannes Diekmann
Kei Yoshimura
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1316 KB) - Metadata XML