the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Apr 2021
Radiative energy budget and cloud radiative forcing in the daytime marginal sea ice zone during Arctic spring and summer
Abstract. Airborne measurements of the surface radiative energy budget (REB) collected in the area of the marginal sea ice zone (MIZ) close to Svalbard (Norway) during two campaigns conducted in early spring and and early summer are presented. From the data, the cloud radiative forcing was derived. The analysis is focussed on the impact of changing atmospheric thermodynamic conditions on the REB and on the linkage of sea ice properties and cloud radiative forcing (CRF). The observed two-mode longwave net irradiance frequency distributions above sea ice are compared with measurements from previous studies. The transition of both states (cloudy and cloud-free) from winter towards summer and the associated broadening of the modes is discussed as a function of the seasonal thermodynamic profiles and the surface type. The influence of cold air outbreaks (CAO) and warm air intrusions on the REB is illustrated for several case studies, whereby the source and sink terms of REB in the evolving CAO boundary layer are quantified. Furthermore, the role of thermodynamic profiles and the vertical location of clouds during on-ice flow is illustrated. The sea ice concentration was identified as the main driver of the shortwave cooling by the clouds. The longwave warming of clouds, estimated to about 75 W m−2, seems to be representative for this region, as compared to other studies. Simplified radiative transfer simulations of the frequently observed low-level boundary layer clouds and average thermodynamic profiles represent the observed radiative quantities fairly well. The simulations illustrate the delicate interplay of surface and cloud properties that modify the REB and CRF, and the challenges in quantifying trends in the Arctic REB induced by potential changes of the cloud optical thickness.
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Interactive discussion
Status: closed
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RC1: 'Comment on acp-2021-279', Anonymous Referee #1, 22 May 2021
In this paper the authors use aircraft observations to study radiation budgets and cloud radiative forcing over sea ice, open water and the marginal ice zone. There is a wealth of very interesting information here and the study appears to be carefully performed carried out. However, the work is not done until its done and this manuscript needs a lot more work. I therefore recommend that it is rejected and encourage the authors to go back to the drawing board and make a new attempt.
The author instructions call for a concise text; this is anything but. It completely lacks organization; I gave up reading around page 20 or 21, still not sure if I actually had come to the results section, or if I were still in the introductory lead-up. Besides it would be about radiation, I still don’t see where this study is leading me and what important new finding it will lead up to. The text is much too long and contains too many different lines of thought without a clear connecting concept. It feels like a pile of detailed but unconnected case studies.
It also has too complicated and poorly explained plots; sometimes more and simpler plots are better than really ingenious constructions that are poorly explained. To top that off, the language is not very good. I get the feeling the authors are making a real effort to write “fancy” English, but the sentence structure is often strange with many short subordinate clauses piled on top of each other (German influence?), and in many cases sentences contains too many ideas. I was once told by a mentor: "One sentence, one thought"! Hard to stick to but useful to think about when writing.
I normally try and provide detailed comments when I review papers to help young scientists; I’m not an expert per see but have gained some experience over the years. But also here I gave up; comments are much too many. I’d be very happy to review a new version of this manuscript and provide detailed help, but it has to be organized and possibly split into more than one manuscript with some cohesive structure.
Make no mistake; I would really like for these resulats to be published! But this manuscript is not ready yet and if I were to recommend major revision, it might never be; hence reject and resubmit.
Citation: https://doi.org/10.5194/acp-2021-279-RC1 -
RC2: 'Comment on acp-2021-279', Anonymous Referee #2, 01 Jun 2021
The study analyzes radiometric data collected from aircraft over the MIZ in the Atlantic sector of the Arctic during spring. The analysis begins with 22 hours of measurements and ends with a new model for the role of clouds and tipping points in Arctic Amplification. The interim is a lengthy and meandering discussion on a variety of topics related to the many atmospheric and surface conditions that influence the radiation budget. There are a number of intriguing discussions, but these do not clearly contribute to a central thesis nor do they stand alone, and there are specific problems within the individual analyses as well. By choosing a specific research question well-suited to the core data set and carrying out a thorough analysis, there are probably several promising starts to papers contained within these pages, but as it stands, I don’t feel this manuscript is ready for publication. I will provide a couple examples of my specific concerns next.
As I read the manuscript, I frequently needed to remind myself of the extremely limited sampling that forms the basis for the study. Twenty-two hours of data, spliced from two campaigns in different years, are meant to represent a springtime transition in the surface radiation balance from March through June. This represents < 1% of a single 4-month period, collected largely near solar noon at an arbitrary altitude in a handful of synoptic cycles that were suitable for flight operations. These things are acknowledged, but that is not license to proceed to overly generalizing the results. While I applaud the author’s efforts to link their measurements to other campaigns (e.g., SHEBA, N-ICE2015), such work demands a focus on understanding how these various perspectives complement one another, but this is largely glossed over in favor of a series of overstated assertions of the behavior of the system. I will provide two examples, focusing on Sections 4.1 and 4.2.
In Section 4.1, the modes of the widely-reported bimodal state are compared with surface measurements and some subtle differences are highlighted. These are interesting differences, but I am skeptical that such subtleties can be interpreted robustly. Even neglecting the sample size or the large leap in relating multiyear ice in the western arctic with the eastern arctic MIZ, there is no attempt to demonstrate that the net longwave radiation from 100 m altitude is sufficiently representative of the surface that the comparison is valid in the first place. Indeed, there are suggestions elsewhere in the manuscript that it is not, such as the first full paragraph on page 5. I’m not even certain if the upwelling longwave that is used in this study is from a pyrgeometer for or if it is derived somehow from the KT-15, and neither would be directly comparable to surface measurements.
In Section 4.2 (Fig. 5), a “four mode structure” is discussed. First, I think that Fig. 5 provides the sort of perspective that takes advantage of the strengths of the core data sets (good spatial sampling). But unfortunately, the limited temporal sampling and use of proxy are creating false impressions. The conclusion is that there are four modes, but if you plotted ACLOUD and AFLUX on top of one another, there would be at least 6 modes. More could perhaps be identified if different conditions were sampled. Even the separation of ACLOUD and AFLUX in panels (a) and (b) are used to link the position of the modes to seasons (P15L26), as if these were static features within the time periods plotted. What would happen if you plotted April/May? In actuality, the values where the bimodal state peaks are dependent on surface and cloud conditions and the figure shows snapshots of this. The figure is revealing of the degree of spatial variability within the set of conditions sampled, and this is what I suggest focusing on. Additionally, the use of albedo as a proxy is a bit deceptive. The net LW is not sensitive to albedo at all, but rather to differences in surface temperature, which albedo separates to first order. I’m guessing these four modes are less distinctive when surface temperature replaces albedo.
Citation: https://doi.org/10.5194/acp-2021-279-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on acp-2021-279', Anonymous Referee #1, 22 May 2021
In this paper the authors use aircraft observations to study radiation budgets and cloud radiative forcing over sea ice, open water and the marginal ice zone. There is a wealth of very interesting information here and the study appears to be carefully performed carried out. However, the work is not done until its done and this manuscript needs a lot more work. I therefore recommend that it is rejected and encourage the authors to go back to the drawing board and make a new attempt.
The author instructions call for a concise text; this is anything but. It completely lacks organization; I gave up reading around page 20 or 21, still not sure if I actually had come to the results section, or if I were still in the introductory lead-up. Besides it would be about radiation, I still don’t see where this study is leading me and what important new finding it will lead up to. The text is much too long and contains too many different lines of thought without a clear connecting concept. It feels like a pile of detailed but unconnected case studies.
It also has too complicated and poorly explained plots; sometimes more and simpler plots are better than really ingenious constructions that are poorly explained. To top that off, the language is not very good. I get the feeling the authors are making a real effort to write “fancy” English, but the sentence structure is often strange with many short subordinate clauses piled on top of each other (German influence?), and in many cases sentences contains too many ideas. I was once told by a mentor: "One sentence, one thought"! Hard to stick to but useful to think about when writing.
I normally try and provide detailed comments when I review papers to help young scientists; I’m not an expert per see but have gained some experience over the years. But also here I gave up; comments are much too many. I’d be very happy to review a new version of this manuscript and provide detailed help, but it has to be organized and possibly split into more than one manuscript with some cohesive structure.
Make no mistake; I would really like for these resulats to be published! But this manuscript is not ready yet and if I were to recommend major revision, it might never be; hence reject and resubmit.
Citation: https://doi.org/10.5194/acp-2021-279-RC1 -
RC2: 'Comment on acp-2021-279', Anonymous Referee #2, 01 Jun 2021
The study analyzes radiometric data collected from aircraft over the MIZ in the Atlantic sector of the Arctic during spring. The analysis begins with 22 hours of measurements and ends with a new model for the role of clouds and tipping points in Arctic Amplification. The interim is a lengthy and meandering discussion on a variety of topics related to the many atmospheric and surface conditions that influence the radiation budget. There are a number of intriguing discussions, but these do not clearly contribute to a central thesis nor do they stand alone, and there are specific problems within the individual analyses as well. By choosing a specific research question well-suited to the core data set and carrying out a thorough analysis, there are probably several promising starts to papers contained within these pages, but as it stands, I don’t feel this manuscript is ready for publication. I will provide a couple examples of my specific concerns next.
As I read the manuscript, I frequently needed to remind myself of the extremely limited sampling that forms the basis for the study. Twenty-two hours of data, spliced from two campaigns in different years, are meant to represent a springtime transition in the surface radiation balance from March through June. This represents < 1% of a single 4-month period, collected largely near solar noon at an arbitrary altitude in a handful of synoptic cycles that were suitable for flight operations. These things are acknowledged, but that is not license to proceed to overly generalizing the results. While I applaud the author’s efforts to link their measurements to other campaigns (e.g., SHEBA, N-ICE2015), such work demands a focus on understanding how these various perspectives complement one another, but this is largely glossed over in favor of a series of overstated assertions of the behavior of the system. I will provide two examples, focusing on Sections 4.1 and 4.2.
In Section 4.1, the modes of the widely-reported bimodal state are compared with surface measurements and some subtle differences are highlighted. These are interesting differences, but I am skeptical that such subtleties can be interpreted robustly. Even neglecting the sample size or the large leap in relating multiyear ice in the western arctic with the eastern arctic MIZ, there is no attempt to demonstrate that the net longwave radiation from 100 m altitude is sufficiently representative of the surface that the comparison is valid in the first place. Indeed, there are suggestions elsewhere in the manuscript that it is not, such as the first full paragraph on page 5. I’m not even certain if the upwelling longwave that is used in this study is from a pyrgeometer for or if it is derived somehow from the KT-15, and neither would be directly comparable to surface measurements.
In Section 4.2 (Fig. 5), a “four mode structure” is discussed. First, I think that Fig. 5 provides the sort of perspective that takes advantage of the strengths of the core data sets (good spatial sampling). But unfortunately, the limited temporal sampling and use of proxy are creating false impressions. The conclusion is that there are four modes, but if you plotted ACLOUD and AFLUX on top of one another, there would be at least 6 modes. More could perhaps be identified if different conditions were sampled. Even the separation of ACLOUD and AFLUX in panels (a) and (b) are used to link the position of the modes to seasons (P15L26), as if these were static features within the time periods plotted. What would happen if you plotted April/May? In actuality, the values where the bimodal state peaks are dependent on surface and cloud conditions and the figure shows snapshots of this. The figure is revealing of the degree of spatial variability within the set of conditions sampled, and this is what I suggest focusing on. Additionally, the use of albedo as a proxy is a bit deceptive. The net LW is not sensitive to albedo at all, but rather to differences in surface temperature, which albedo separates to first order. I’m guessing these four modes are less distinctive when surface temperature replaces albedo.
Citation: https://doi.org/10.5194/acp-2021-279-RC2
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Cited
2 citations as recorded by crossref.
- Analysis of an Arctic cold air outbreak during autumn and related air mass transformations forced by surface changes and advection in higher altitudes B. Kirbus et al. 10.1525/elementa.2023.00079
- Radiative closure and cloud effects on the radiation budget based on satellite and shipborne observations during the Arctic summer research cruise, PS106 C. Barrientos-Velasco et al. 10.5194/acp-22-9313-2022