the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jan 2025
Lagrangian single-column modeling of Arctic airmass transformation during HALO-(𝒜𝒞)3
Abstract. In Arctic warm-air intrusions (WAIs), airmasses undergo a series of radiative, turbulent, cloud and precipitation processes, the sum of which constitutes the airmass transformation. During the Arctic airmass transformation, heat and moisture is transferred from the airmass to the Arctic environment, melting the sea-ice and potentially reinforcing feedback mechanisms responsible for the amplified Arctic warming. We tackle this complex, poorly understood phenomenon from a Lagrangian perspective, using the WAI event on 12–14 March captured by the 2022 HALO-(𝒜𝒞)3 campaign. Our trajectory analysis of the event suggests that the intruding airmass can be treated as an undistorted air column, therefore justifying the use of a single-column model. In this study, we test this hypothesis using the Atmosphere-Ocean Single-Column Model (AOSCM). The rates of heat and moisture depletion vary along the advection path due to the changing surface properties and large-scale vertical motion. The ability of the Lagrangian AOSCM framework to emulate elements of the airmass transformation seen in aircraft observations, ERA5 reanalysis and operational forecast data, makes it an attractive tool for future model analysis and diagnostics development. Our findings can benefit the understanding of the timescales and driving mechanisms of Arctic airmass transformation and help determine the contribution of WAIs in Arctic Amplification.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2024-3709', Anonymous Referee #1, 06 Apr 2025
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Summary
In this study, Karalis and coauthors study the transformation of an air mass entering the Atlantic sector of the Arctic during March 2022. They use observations from the HALO-(AC)3 field campaign along with a single-column model to dissect the physical processes occurring within the air mass and validate the model simulations. They find that different physical processes influence the air mass cooling along its path, with near-surface radiative and turbulent cooling dominating over the ocean, and cloud processes and adiabatic cooling becoming more important as the air mass progresses into the marginal ice zone and sea ice areas. They also find that the single-column model generally simulates the air mass transformation realistically, but struggles to reproduce the stable boundary layer and is highly dependent on the vertical motion prescribed by the ERA5 reanalysis data used to force the model.This study provides a unique perspective on Arctic air mass transformation, a process that is still not fully understood but is critically important to understanding the causes of Arctic-amplified warming. The paper is generally well-written and scientifically robust. I have a number of minor comments and technical corrections listed below. Once these comments are addressed, in my evaluation this will be a valuable addition to the literature on Arctic air mass transformation.
Minor comments
- General comment: Is this air mass considered to be "fully transformed" at the end of the 12–14 March 2022 study period, or did it continue cooling after the HALO-(AC)3 sampling ended on 14 March? At the end of the study period, was the air temperature characteristic of a cold Arctic air mass, or was its thermal state more characteristic of an air mass still in transition from mid-latitude to Arctic conditions? If it continued cooling, do the authors expect that the dominant cooling processes at the end of the study period continued to be most important for air mass cooling as the air continued to reside in the Arctic? From Fig. 4 it appears the air mass was still cooling, albeit at possibly a cooler rate, at the end of the study period. I understand that further simulations outside the study period are likely outside of the scope of this study, but it would be useful to provide some discussion about these aspects for context.
- General comment: The authors provide qualitative descriptions of which physical processes were most important for air mass cooling at different stages of its life cycle. Is it possible to integrate these contributions over time to provide a comparison of which processes contributed the most to cooling throughout the entire study period?
- L6: The meaning of "undistorted" air column isn't quite clear here and doesn't become apparent until later in the paper (e.g. L99–101, L112–118, L180–191). I suggest using the word "cohesive" in the abstract (as in L182) to be more clear.
- L150–152: What type of adjustment is needed for the model to be able to produce realistic skin temperature values?
- L145–154: I'm not entirely clear on the mixture of data sources here. So ERA5 is used for SIC, then CMEMS is used to quantify snow on top of sea ice and sea ice thickness? So both the snow on sea ice and the sea ice thickness are taken into account by the AOSCM? This is also unclear in L364–366.
- Fig. 2 and Fig. 3: Are these maps showing instantaneous snapshots of IVT, IWV, LWP, etc.? Or are these quantities integrated over time? Is the (Eulerian) ERA5 regular grid field of these values plotted, or are the values interpolated to the Lagrangian trajectories? I assume the cloud fields (LWP, IWP) and SEB values (SHF, LHF, etc.) are taken from ERA5, is this correct?
- L206–208: This is an interesting hypothesis about the quality controls in the assimilation scheme filtering the profiles out – is there any way to check this?
- L214–219: This paragraph is describing the cloud radiative effect – is it possible to directly calculate the cloud radiative effect and plot it on the maps?
- Fig. 4: I don't quite understand how cloud liquid and ice are represented in Fig. 4. Does the shaded area represent the additional atmospheric water in ice or liquid phase, in addition to the vapor-phase water (IWV)?
- Fig. 4: It is difficult to distinguish between the faded perpendicular lines for AOSCM/ERA5/IFS. Perhaps some could be plotted as dotted or dashed lines to make them easier to tell apart? Does each of these lines represent a timestep, such that the wider spacing of the lines over sea ice can be interpreted as faster air mass cooling and drying? Is appears that the uncertainty range is greater for the AOSCM than the other two products, is that correct?
- L326–327: How was Bulk Richardson number = 0.25 chosen as the threshold for the boundary layer? Is this threshold based on previous studies?
- Fig. 5: Is this figure created by averaging all the trajectories? Also, the uncertainty contours are difficult to see on the figure panels – perhaps they could be plotted with a darker color and/or thicker line.
- L366–368: So are the ERA5 and IFS-OF representation of the boundary considered more reliable than the AOSCM?
- L372: I think the reference to Fig. 5h is actually referring to Fig. 5k,h here? Please also check the other figure references in this paragraph (e.g. reference to Fig. 5i on L374).
- L376: To my eye, it looks like the IFS-OF mostly shows a single-layer cloud structure for about 75% of the MIZ and early sea-ice leg.
- Fig. 6: I don't see several features on this figure that are described in the text. For example, where does AOSCM simulate a drop in temperature below freezing levels (L394–395)? L395 states that dropsondes released over full sea-ice cover show minor surface cooling, but it looks the dropsonde observations are within the envelope of the other temperature profiles in panel (k)?
- Fig. 6: Unless I am missing something, I don't see where the cloud liquid comparisons (right column) are addressed in the text.
- L414–416: It sounds like it would be more accurate to call it the "liquid cloud layer" rather than the "cloud layer".
- Fig. 7: The caption does not describe panels e–g. Please check that all figure captions describe the figures in sufficient detail.
Technical corrections
- L3: "is" --> "are"
- L9: I think "simulate" or "reproduce" would be a better word choice than "emulate" here
- L26: Remove comma after "As"
- L42: "Airborn" --> "Airborne"
- L58: "imporant" --> "important"
- L68: "on" --> "to"
- L134: Add the word "are" after "tracks"
- L197: "dropping" --> "decreasing"
- L211: "air mass" --> "airmass" (to be consistent with the use of this word throughout the manuscript, I would argue that "air mass" is more commonly used in the literature but will leave it up to the authors whether they wish to change it throughout the manuscript)
- L216: Space needed in "ofthe"
- L293: "big" --> "large"
- L303: "uncertainty range ERA5 and IFS-OF curves" --> "uncertainty range of the ERA5 and IFS-OF curves" (?)
- L305: "and" --> "an"
- L307: "heat-to-moisture" --> "heat-to-moisture ratio" (?)
- L345: "while" --> "with" (?)
- L369: "dropping" --> "decreasing"
- L374: "bares" --> "bears"
- L391: "profiles" --> "profiles are" (?)Citation: https://doi.org/10.5194/egusphere-2024-3709-RC1
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