Review of "A comprehensive in-situ and remote sensing data set collected during the HALO–(AC)3 aircraft campaign" by Ehrlich et al.

The paper presents a comprehensive overview of the data collected during a three-aircraft campaign conducted in March and April 2022 in the Atlantic Arctic region between Svalbard, Greenland and the ice-covered Arctic Ocean. The goal of the campaign was to quantify the temporal evolution of air masses, particularly under Cold Air Outbreak or Warm Air Intrusion events, through a lagrangian approach. The meticulous preparation, structuring, documentation, and archiving of data from a diverse array of remote and in-situ sensing instruments were crucial for this endeavor. The paper effectively outlines these processes, detailing the instrumentation and the resultant archived datasets.

To my opinion, the paper fully meets the ESSD criteria. The combination of data sets from three different aircraft, operating in a highly coordinated manner, yields novel, unique, substantial and quite comprehensive data for the analyses of critical Arctic marine weather phenomena during the spring season. The data set description in this article equips potential data users with the necessary information for data utilization and potential discovery of significant findings. My random exploration of some data sets within the PANGAEA data bank revealed well-structured and readily accessible data. The examples provided in the paper, together with other papers describing results from the campaign, underscore the dataset's high quality and usability. Readers are directed also to dedicated software tools for data extraction and specific utilization of this substantial data set.

The paper is well written and the key information are well described. While I have only few minor suggestions and specific comments the overall quality is commendable and the paper is highly suitable for publication.

Some general remarks:

A brief overview of the prevailing meteorological conditions in the Atlantic Arctic during spring 2022 would enhance the paper's context. Was that year exceptional or “on average” with respect to temperatures, occurrence of CAOs and WAIs? (I didn’t find such a description in Wendisch et al., 2024 or elsewhere. If I overlooked, please provide a corresponding reference.) It could be easily introduced towards the end of chapter 1 or as a dedicated paragraph in chapter 2.

This paper describes the data collected from the three aircraft. Ground based observations from the AWIPEV base are mentioned in line 75 to 82, but no further reference to data sets is given, except for the radiosonde observations. It would be useful to add further references, at least for the mentioned tethered balloon data and the ground based remote sensing data sets.

An essential part of the project is the data set of lagrangian matches of air mass trajectories, which have been probed twice, thereby allowing to determine the temporal air mass development. To my understanding the data sets Kirbus et al. 2024a and Kirbus et al. 2024b provide matches of air masses probed by the HALO aircraft only. Wouldn’t it by useful to have also matches between air masses probed by HALO and Polar 5, or 6, at least for the drop sonde data? If not, this should be more clearly mentioned in chapter 3.1.5 and especially in the conclusions (line 730f)

A minor remark on chapter 5.3, line 700:

“Can be applied to validate satellite products”  is only a very general statement. Could you give an example, or a reference, of what could be learned from this combination of passive sensors data?

Line 109 / Figure 2: Figure 2 could be omitted as the main information is well described in the text. Relative flight duration given in % does not seem to be very meaningful to this reviewer.

Some specific remarks and suggestions:

Author list: C. Lüpkes is of AWI not LIM ?

Line 63: wording of “balloon-borne observations in area around Svalbard“

Line 74: wording of “… during one single and along successive flights”

Line 83 and 84: any references available to descriptions of the ISLAS and ACAO campaigns?

Line 94 should read “between two fixed waypoints”

Line 131,132: wording “were operated almost identical setup“

Line 133: should read “devices were extended”

Line 215: I think you want to say that in the stratosphere the accuracy of humidity measurements is low.

Line 269: “two versions of SMART”: what kind of 2 versions are these? One for each plane? What is their difference? See also line 275 where a 1-2 sentence description of SMART would be helpful.

Line 275: “two types of grating spectrometers”: which 2 types are these? see comment in line 269

Lines 278 and 279: should read “wavelengths”

Line 295: double word “depolarization”

Line 412ff: there are two Moser et al. 2023 references in the literature section. Please be specific, which reference is used where (should be 2023a and 2023b)

Line 480: double word “to”

Line 535: “N. and Y., 2010” as well as in reference list: this should be the reference “Moteki and Kondo, 2010” You also need to correct it in the reference list.

Line 547: wording “which not always sufficient,”

Line 560: wording “to investigating”

Line 603: wording: “With the exception of some instruments available in compressed ASCII format, ”

Figure 6 (before Line 680): Please add in the figure caption something like: "Blue line in panel (b) gives flight altitude of Polar 6 for in situ sampling."

Line 731: please write “the meteorological data transferred to GTS”

This paper provides a comprehensive overview of measurements from three research aircraft (HALO, Polar 5, and Polar 6), dedicated to studying Arctic air mass transformations during warm air intrusions (WAIs) and cold air outbreaks (CAO). A detailed description of campaign objectives, instrument setup and conditions (in-situ and remote sensing), and data processing, archive, and publication has been provided. The authors also provide guidance on how to combine datasets from three research aircraft. These novel and high-quality datasets are expected to support future studies, such as the evolution of the thermodynamics and cloud properties during Arctic air mass transformations, cloud-aerosol interaction, and Arctic mesoscale dynamics, which is important for future improvement and validation of satellite retrievals and climate models.

The paper aligns well with the criteria for ESSD, and only a few revisions are suggested before it is ready for publication.

General comments:

1. Sect. 2.1 of general setup: The authors mentioned the ground-based and balloon-borne observations, however, the associated instrumentation, data processing, archive, and publication are not provided. Could authors provide more information related to these observations?

2. Lines 42-43: The authors mentioned that “the HALO–(AC) 3 aircraft campaign was designed to combine different aircraft platforms and aiming for observations in a quasi-Lagrangian approach”. Lines 50-52: The authors also mentioned that “CAOs were characterized in their initial stage close to the sea ice edge with the Polar 5 and Polar 6 research aircraft and in a quasi-Lagrangian perspective jointly with HALO”.

However, in Sect. 3.1.5 and Table 4, the analysis approach and data publication of quasi-Lagrangian matches are described only for HALO aircraft flights. Are quasi-Lagrangian matches analyzed between HALO and Polar 5, or 6 flights? If yes, could authors provide more information related to such as its data publication?

If it is available, could you also provide an example figure of quasi-Lagrangian matches?

3. Section 3.5.3: The analysis method of INP filters is not provided in the manuscript, which is an important part of INP filter methodology. Additionally, the publication of the INP dataset is not provided. Could authors provide more information related to INP filters?

Specific comments:

Page 7, Line 133: “the cloud microphysical devices was extended…” should be “were extended”.

Page 11, Line 180: It will be nice to provide which flight numbers are not available for the Polar 5 and Polar wind data.

Page 12, Line 215: “where the accuracy of measurements is large” should be “where the uncertainty of measurements is large”.

Page 14, Line 249: “Measurements during HALO–(AC)³ are characterized…” should be “were characterized”.

Page 14, Line 251: “the solar leakage effect of the pyrgeometer effecting the…” should be “affecting the…”.

Page 15, Line 269: the authors mentioned that “Spectrally resolved downward (Polar 5, HALO) and upward (Polar 5 only) solar irradiance were measured using two versions of the Spectral Modular Airborne Radiation measurement sysTem (SMART)”. What are the two versions of the SMART and the corresponding versions for HALO and Polar5? What are the differences between the two versions of the SMART?

Page 15, Line 284: The authors mentioned that “the Polar 5 data set was filtered for large SZA and aircraft pitch and roll angle”. Why this filter criteria was not applied to the HALO dataset?

Page 15, Line 295: “particle linear depolarization depolarization”, duplicate “depolarization”.

Page 16, Lines 297-298: “The backscatter profiles are extinction-corrected…” should be “were…”.

Page 16, Lines 304-305: The authors mentioned “The data are considered of good quality if no flag is set, i.e., if the flag is zero. Note that for a non-zero flag, the data value itself is not replaced by a fill-value.” What is the recommended treatment for non-zero-flag value? Nor reliable to use or?

Page 16, Line 308: “at 355 nm and 532 nm wavelength” ---> “wavelengths”.

Page 20, Lines 451-452: The authors mentioned that “Due to the complexity of deriving microphysical properties from OAPs different solutions are included in the data sets, which can be selected depending on the focus of analysis”. What do “different solutions” refer to?

Page 21, Lines 469-470: “The respective enrichment factor (EF) needs to be applied to every instrument sampling CPRs”. Could authors provide a reference or brief introduction about the calculation method of EF?

Page 21, Line 490: “the number concentration of particles larger than 10 nm wass” ---> “was”.

Page 24, Line 560: " to investigating potential" ---> "to investigate"

Page 33, Line 726: “cold air outbreaks (COAs)” should be rephrased to “cold air outbreaks (CAOs)”.