Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim

Krebs-Kanzow, Uta; Rodehacke, Christian B.; Lohmann, Gerrit

doi:https://doi.org/10.5194/egusphere-2023-525

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https://doi.org/10.5194/egusphere-2023-525

Preprints

23 Mar 2023

| 23 Mar 2023

Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

Abstract. We compare the main atmospheric drivers of the melt season over the Greenland Ice Sheet (GrIS) in ERA5 and ERA-Interim (ERAI) in their overlapping period 1979–2018. In summer, ERA5 differs significantly from ERAI, especially in the melt regions: averaged over the lower parts of the GrIS, mean near-surface temperature is 1 K lower, while the mean downward shortwave radiation at the surface is on average 15 Wm⁻² higher than in ERAI. Comparison with observational weather station data shows a significant warm bias in ERAI and for ERA5 a significant positive bias in downward shortwave radiation. Consequently, methods that previously estimated the GrIS surface mass balance from the ERAI surface energy balance need to be carefully recalibrated before converting to ERA5 forcing.

Received: 21 Mar 2023 – Discussion started: 23 Mar 2023

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Journal article(s) based on this preprint

06 Dec 2023

Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

The Cryosphere, 17, 5131–5136, https://doi.org/10.5194/tc-17-5131-2023,https://doi.org/10.5194/tc-17-5131-2023, 2023

Short summary

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-525', Anonymous Referee #1, 07 Apr 2023

Review of
Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim
by Uta Krebs-Kanzow and others
General

This paper issues a warning that researchers that previously used ERA-Interim to estimate Greenland ice sheet (GrIS) surface energy/mass balance (SEB/SMB) must recalibrate their methods when switching to ERA5. The authors find significant differences in near-surface climate, notably near-surface air temperature, and SEB, notably the flux of incoming solar radiation. The paper is generally well written with clear figures but see my technical comments below. The paper is well-timed, as ERA-Interim will be phased out soon at the expense of ERA5. Unfortunately, no interpretation as to why the differences occur between the two products is provided, making the scientific impact of this study somewhat limited.
Major comments

In Figure 1 I assume some of the small-scale features in the marginal ice sheet are associated with the interpolation procedure, in combination with comparing two datasets of different resolutions.
Minor and textual comments
l. 9: persistent warming trend -> persistent positive trend
l. 10: "a mean warming of 5.3 K is projected for the 21st century". This is ambiguous. By "mean" do you mean model mean, or the mean over the (remainder of) the century, or end-of-century? Please be precise. Also, consider presenting a number from a more likely scenario.
l. 11: " The associated reduction in Greenland Ice Sheet’s surface mass balance (SMB) leads to more runoff " It is the other way around: the associated increase in runoff leads to a reduction of the GrIS SMB...Again, please be precise, there is already enough confusion about ice sheet mass balance.
l. 13: Consider replacing "Surface mass balance models" with "Surface energy balance models".
l. 16: near-surface temperature -> near-surface air temperature
l. 33: Reanalysis Era-Interim (ERAI) -> ECMWF Reanalysis - Interim (ERA-Interim, henceforth ERAI)
l. 34: Reanalysis v5 (ERA5) -> ECMWF Reanalysis v5 (ERA5)
l. 34: ERA5 runs from January 1940 to the present
l. 37: For clarity and consistency with previous work, consider using T2m rather than T2M
l. 70: Please use higher/lower temperatures rather than warmer/colder temperatures throughout.
l. 75: stronger -> larger

Citation: https://doi.org/10.5194/egusphere-2023-525-RC1
- AC1: 'Reply on RC1', Uta Krebs-Kanzow, 07 Jul 2023
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-525-AC1
RC2:
'Comment on egusphere-2023-525', Anonymous Referee #2, 09 May 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-525-RC2
- AC2: 'Reply on RC2', Uta Krebs-Kanzow, 07 Jul 2023
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-525-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-525', Anonymous Referee #1, 07 Apr 2023

Review of
Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim
by Uta Krebs-Kanzow and others
General

This paper issues a warning that researchers that previously used ERA-Interim to estimate Greenland ice sheet (GrIS) surface energy/mass balance (SEB/SMB) must recalibrate their methods when switching to ERA5. The authors find significant differences in near-surface climate, notably near-surface air temperature, and SEB, notably the flux of incoming solar radiation. The paper is generally well written with clear figures but see my technical comments below. The paper is well-timed, as ERA-Interim will be phased out soon at the expense of ERA5. Unfortunately, no interpretation as to why the differences occur between the two products is provided, making the scientific impact of this study somewhat limited.
Major comments

In Figure 1 I assume some of the small-scale features in the marginal ice sheet are associated with the interpolation procedure, in combination with comparing two datasets of different resolutions.
Minor and textual comments
l. 9: persistent warming trend -> persistent positive trend
l. 10: "a mean warming of 5.3 K is projected for the 21st century". This is ambiguous. By "mean" do you mean model mean, or the mean over the (remainder of) the century, or end-of-century? Please be precise. Also, consider presenting a number from a more likely scenario.
l. 11: " The associated reduction in Greenland Ice Sheet’s surface mass balance (SMB) leads to more runoff " It is the other way around: the associated increase in runoff leads to a reduction of the GrIS SMB...Again, please be precise, there is already enough confusion about ice sheet mass balance.
l. 13: Consider replacing "Surface mass balance models" with "Surface energy balance models".
l. 16: near-surface temperature -> near-surface air temperature
l. 33: Reanalysis Era-Interim (ERAI) -> ECMWF Reanalysis - Interim (ERA-Interim, henceforth ERAI)
l. 34: Reanalysis v5 (ERA5) -> ECMWF Reanalysis v5 (ERA5)
l. 34: ERA5 runs from January 1940 to the present
l. 37: For clarity and consistency with previous work, consider using T2m rather than T2M
l. 70: Please use higher/lower temperatures rather than warmer/colder temperatures throughout.
l. 75: stronger -> larger

Citation: https://doi.org/10.5194/egusphere-2023-525-RC1
- AC1: 'Reply on RC1', Uta Krebs-Kanzow, 07 Jul 2023
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-525-AC1
RC2:
'Comment on egusphere-2023-525', Anonymous Referee #2, 09 May 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-525-RC2
- AC2: 'Reply on RC2', Uta Krebs-Kanzow, 07 Jul 2023
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-525/egusphere-2023-525-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2023-525-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to minor revisions (review by editor) (18 Jul 2023) by Alexander Robinson

AR by Uta Krebs-Kanzow on behalf of the Authors (30 Aug 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (27 Sep 2023) by Alexander Robinson

To the authors,

The manuscript appears to have improved significantly following your revisions. I believe it is ready for publication after consideration of a few minor points listed below.

Cheers,
Alex

Minor comments:

L17: sea level rise => sea-level rise

L35: focussing => focusing

L46: T2m <= Consider using subscript "T_2m", or removing italics. I assume this name relates directly to its name in the ECMWF dataset. Check for consistency throughout the manuscript.

L48, Eq. 1: Should the "int" subscript appear here? This is a general equation used for both reanalyses right?

L55: "ISMIP6 orography H_ice" <= Are temperatures scaled by H_ice or surface elevation, as the latter would be the more relevant variable. On line 60, surface elevation is even mentioned. Usually H = ice thickness and h = surface elevation (or z_srf, for example would be more direct). Please just double check that you are happy with this choice.

L75: South Eastern margins = > southeastern margins

L80 and rest of section: the term "mean bias" is somewhat confusing in this context, as bias is usually relative to a chosen reference. Here you are comparing ERAI to ERA5 and it is not clear which one you assume then to be the reference. This is also problematic when you refer to the two standard deviations ("The mean bias exceeds two standard deviations") as again the question arises as to which dataset provides the measure of the standard deviation. To solve this, I would add a few sentences to define your metholodogy more clearly. State explicitly which dataset is considered the reference. Or, if you don't mean to define a reference, then change from "bias" to simply "difference". In this case, it should be made clear how the standard deviation is calculated that is used as the measure of variability. Note that when comparing to the AWS data, I see no problem, as clearly the AWS data would be the reference and the renalysis is biased relative to that.

L92: comparrison = > comparison

L94: Fig. 2) => Figure 2 [When starting a setence, the whole word should be used.]

L99: In Fig. 3 height range => In Fig. 3, the elevation range considered

L124: In case => In the case

L124: air temperature => air temperature,

Hide

AR by Uta Krebs-Kanzow on behalf of the Authors (16 Oct 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (18 Oct 2023) by Alexander Robinson

AR by Uta Krebs-Kanzow on behalf of the Authors (18 Oct 2023) Manuscript

Journal article(s) based on this preprint

06 Dec 2023

Brief communication: Surface energy balance differences over Greenland between ERA5 and ERA-Interim

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

The Cryosphere, 17, 5131–5136, https://doi.org/10.5194/tc-17-5131-2023,https://doi.org/10.5194/tc-17-5131-2023, 2023

Short summary

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

Supplement

https://doi.org/10.5194/egusphere-2023-525-supplement

Uta Krebs-Kanzow, Christian B. Rodehacke, and Gerrit Lohmann

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Short summary

We compare components of the surface energy balance from two data sets, ERA5 and ERA-Interim, which can be used to estimate surface mass balance (SMB) on the Greenland Ice Sheet (GrIS). ERA5 differs significantly from ERA-Interim, especially in the melt regions with lower temperatures and stronger shortwave radiation. Consequently, methods that previously estimated the GrIS SMB from the ERA-Interim need to be carefully re-calibrated before converting to ERA5 forcing.


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