the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jul 2023
The role of a low-level jet for stirring the stable atmospheric surface layer in the Arctic
Holger Siebert
Olaf Hellmuth
Lise Lotte Sorensen
Abstract. In this study, we analyze the transition of a stable atmospheric boundary layer (ABL) with a low-level jet (LLJ) to a traditional stable ABL with a classic Ekman helix in the late-winter central Arctic. Vertical profiles in the ABL were measured with a hot-wire anemometer on a tethered balloon during a 15 h period in March 2018 in northeast Greenland. The tethered balloon allows high-resolution turbulence observations from the ground to the top of the ABL. The core of the LLJ was observed at about 150 m altitude, and its height and strength were associated with the temperature inversion. Increased turbulence was observed in the vicinity of the LLJ, but most of the turbulence does not reach down to the surface, thus decoupling the LLJ from the surface. Only when the LLJ collapses and the ABL again exhibits a more classical Ekman spiral, a coupling to the surface is re-established. Numerical simulations using an analytical model support these observations and allow conclusions to be drawn about the possible role of an LLJ in the advection of a passive tracer such as aerosol particles or moisture.
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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
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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
Ulrike Egerer et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-567', Anonymous Referee #1, 02 Sep 2023
General Comments
This paper provides an interesting analysis of the evolution of the ABL in the central Arctic over Greenland from a stable ABL with an LLJ to the return of a “standard” stable ABL without an LLJ, and the corresponding evolution of turbulence associated with the LLJ. Through a case study of tethered balloon observations, and an analytical modelling approach, the authors seek to understand how an LLJ and the dissipation of which could contribute to the horizontal and vertical transport of passive tracers such as aerosols and moisture.
Overall, the paper is very well-written and the analysis is very relevant for improving our understanding of the relationship between LLJs and the ABL in the Arctic, which is crucial for the improvement of global climate models and the enhancement of knowledge regarding the interaction between the surface and overlying atmosphere in the central Arctic. To improve this paper, I suggest the authors add some more description of a few aspects of the methods, some chosen terminology, and some figures, as discussed in the minor comments below. After these minor revisions, I would support the publication of this manuscript.
Minor Comments
L13: It should be noted that often the LLJ is above the ABL, rather than always being within it. This can be particularly evident when the LLJ is decoupled from the surface in the case of a stable LLJ, and the formation mechanism is inertial oscillations.
L57: Please include some uncertainties for the two sensor packages described in (i) and (ii).
L60: It is mentioned that the ABL transitioned to being a “more classic stable ABL.” You should include a characterization of the ABL before the transition, so it is well-understood how the ABL changed (aside from just the presence to dissipation of the LLJ).
Figure 1: I am a little confused by panel (a). Please specify what StdMeteo and Hotwire refer to – are these the two sensor packages described in L52-57? You should clarify the abbreviations in the figure legend. Also, it appears the BELUGA doesn’t always fly with both sensor at the same time? Please also clarify why this is and how it was determined in the field that certain profiles only had one or the other sensor in this case study.
L75-78: Your criteria for defining LLJs differ some from the standard literature (e.g., the requirement of the LLJ core being below 250 m, and the LLJ strength being relative to the higher value of the wind minimum above and below the core). Please add some explanation about why you divert from the more standard criteria for an LLJ. For example, include mention of any testing you might have done to determine that these methods provide valid results.
L102: Add a space between 5 and s in “5s-long”
Figure 3: Rather than “the ascends and descends are from the BELUGA” perhaps say “The time-height profiles are from the BELUGA.” Also, for consistency, it would be better to include all temperature measurements in the same units, either temperature or potential temperature, rather than a mix of both.
L122: Somewhere (maybe in the Intro?) you should define what you mean when you say “standard stable ABL” for northern Greenland, as this could be different depending on location, and it shouldn’t be assumed that a reader would know what you mean. Perhaps use wording such as “<description of standard ABL>, which will hereafter be referred to as a “standard stable ABL.”
L31: By “strong surface temperature gradient” do you mean strong surface temperature inversion? Please specify.
L297: Should it be “Therefore, in the following section, the analytical LLJ model…”?
L312: Should be “…discretized in the x-direction…” (discretized is spelled wrong in the manuscript, and you should add “the” before x-direction). Also add “the” before “y-direction” in L314.
Figure 10: For someone unfamiliar with some of the modelling techniques of this study, Figure 10 would be difficult to understand. The paper would benefit from, and would reach a wider audience with, some additional discussion on what is depicted in Figure 10.
L326: In some central Arctic locations, an LLJ is almost ubiquitous, so it is rather the more “normal” case that a stable ABL co-occurs with an LLJ. Please add some discussion (probably in the Intro) of literature which leads to the conclusion that in northeast Greenland, it is more common to not have an LLJ with a stable ABL.
L336: “falsify” is an odd word. Perhaps rather “to test this hypothesis…”
Citation: https://doi.org/10.5194/egusphere-2023-567-RC1 - AC1: 'Reply on RC1', Ulrike Egerer, 27 Oct 2023
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RC2: 'Comment on egusphere-2023-567', Geraint Vaughan, 04 Sep 2023
- AC2: 'Reply on RC2', Ulrike Egerer, 27 Oct 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-567', Anonymous Referee #1, 02 Sep 2023
General Comments
This paper provides an interesting analysis of the evolution of the ABL in the central Arctic over Greenland from a stable ABL with an LLJ to the return of a “standard” stable ABL without an LLJ, and the corresponding evolution of turbulence associated with the LLJ. Through a case study of tethered balloon observations, and an analytical modelling approach, the authors seek to understand how an LLJ and the dissipation of which could contribute to the horizontal and vertical transport of passive tracers such as aerosols and moisture.
Overall, the paper is very well-written and the analysis is very relevant for improving our understanding of the relationship between LLJs and the ABL in the Arctic, which is crucial for the improvement of global climate models and the enhancement of knowledge regarding the interaction between the surface and overlying atmosphere in the central Arctic. To improve this paper, I suggest the authors add some more description of a few aspects of the methods, some chosen terminology, and some figures, as discussed in the minor comments below. After these minor revisions, I would support the publication of this manuscript.
Minor Comments
L13: It should be noted that often the LLJ is above the ABL, rather than always being within it. This can be particularly evident when the LLJ is decoupled from the surface in the case of a stable LLJ, and the formation mechanism is inertial oscillations.
L57: Please include some uncertainties for the two sensor packages described in (i) and (ii).
L60: It is mentioned that the ABL transitioned to being a “more classic stable ABL.” You should include a characterization of the ABL before the transition, so it is well-understood how the ABL changed (aside from just the presence to dissipation of the LLJ).
Figure 1: I am a little confused by panel (a). Please specify what StdMeteo and Hotwire refer to – are these the two sensor packages described in L52-57? You should clarify the abbreviations in the figure legend. Also, it appears the BELUGA doesn’t always fly with both sensor at the same time? Please also clarify why this is and how it was determined in the field that certain profiles only had one or the other sensor in this case study.
L75-78: Your criteria for defining LLJs differ some from the standard literature (e.g., the requirement of the LLJ core being below 250 m, and the LLJ strength being relative to the higher value of the wind minimum above and below the core). Please add some explanation about why you divert from the more standard criteria for an LLJ. For example, include mention of any testing you might have done to determine that these methods provide valid results.
L102: Add a space between 5 and s in “5s-long”
Figure 3: Rather than “the ascends and descends are from the BELUGA” perhaps say “The time-height profiles are from the BELUGA.” Also, for consistency, it would be better to include all temperature measurements in the same units, either temperature or potential temperature, rather than a mix of both.
L122: Somewhere (maybe in the Intro?) you should define what you mean when you say “standard stable ABL” for northern Greenland, as this could be different depending on location, and it shouldn’t be assumed that a reader would know what you mean. Perhaps use wording such as “<description of standard ABL>, which will hereafter be referred to as a “standard stable ABL.”
L31: By “strong surface temperature gradient” do you mean strong surface temperature inversion? Please specify.
L297: Should it be “Therefore, in the following section, the analytical LLJ model…”?
L312: Should be “…discretized in the x-direction…” (discretized is spelled wrong in the manuscript, and you should add “the” before x-direction). Also add “the” before “y-direction” in L314.
Figure 10: For someone unfamiliar with some of the modelling techniques of this study, Figure 10 would be difficult to understand. The paper would benefit from, and would reach a wider audience with, some additional discussion on what is depicted in Figure 10.
L326: In some central Arctic locations, an LLJ is almost ubiquitous, so it is rather the more “normal” case that a stable ABL co-occurs with an LLJ. Please add some discussion (probably in the Intro) of literature which leads to the conclusion that in northeast Greenland, it is more common to not have an LLJ with a stable ABL.
L336: “falsify” is an odd word. Perhaps rather “to test this hypothesis…”
Citation: https://doi.org/10.5194/egusphere-2023-567-RC1 - AC1: 'Reply on RC1', Ulrike Egerer, 27 Oct 2023
-
RC2: 'Comment on egusphere-2023-567', Geraint Vaughan, 04 Sep 2023
- AC2: 'Reply on RC2', Ulrike Egerer, 27 Oct 2023
Peer review completion
Journal article(s) based on this preprint
Ulrike Egerer et al.
Ulrike Egerer et al.
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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
(4956 KB) - Metadata XML