the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Investigating extreme marine summers in the Mediterranean Sea
Gerasimos Korres
Emmanouil Flaounas
Maria Hatzaki
Abstract. The Mediterranean Sea (MS) has been experiencing significant surface warming, particularly pronounced during summers and associated with devastating impacts. Τhis study proposes the concept of Extreme Marine Summers (EMSs) and investigates their characteristics in the MS, using Sea Surface Temperature (SST) reanalysis data spanning 1950–2020. A marine summer may evolve as extreme, in terms of mean summer SST, under different SST substructures. Results suggest that EMSs identified in most of the basin, are formed mainly due to the warmest part of the ranked daily SST distribution being warmer than normal. Areas where the warmest (coldest) part of the ranked daily SST distribution is more variable, experience EMSs primarily due to the contribution of the warmest (coldest) part of the distribution. Marine heatwaves (MHWs) within EMSs are more intense, longer lasting, and more frequent than usual, mainly in northern MS regions. However, the relative contribution of MHWs in EMSs is more pronounced in the central and eastern basin. Furthermore, a metric is proposed to quantify the driving role of air-sea heat fluxes in forming EMSs. Results suggest that surface fluxes primarily drive EMSs in the northern half of the MS, while oceanic processes play a major role in southern regions. Upper ocean preconditioning is also found to contribute to the EMS formation. Finally, a detrended dataset was produced to examine how the SST multi-decadal variability affects the studied EMS features. Despite leading to warmer EMSs basin-wide, the multi-decadal signal does not significantly affect the dominant SST substructures during EMSs. Results also highlight the fundamental role of latent heat flux in modulating the surface heat budget during EMSs, regardless of long-term trends.
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Dimitra Denaxa et al.
Status: open (extended)
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RC1: 'Comment on egusphere-2023-1709', Anonymous Referee #1, 31 Aug 2023
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Please see comments in the attached document
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RC2: 'Comment on egusphere-2023-1709', Anonymous Referee #2, 01 Oct 2023
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The paper untitled “Investigating extreme marine summers in the Mediterranean Sea” - by Dimitra Denaxa Gerasimos Korres, Emmanouil Flaounas, and Maria Hatzaki – investigates Marine Heat Waves (MHW) during “extreme marine summers” in the Mediterranean Sea. The authors use a reanalysis to identify MHW characteristics and understand the main drivers explaining regional differences during particularly hot summers.
In general, I found the paper is well-written with a straightforward general structure. I really appreciated efforts of authors to clearly describe their results, even if some parts could be shortened to reduce the long length of the manuscript.
However, I have several concerns from the beginning of the paper regarding methodological choices:
- I do not understand why the authors decide to only consider 4 events as “extreme marine summers”. Even if Figure 4 gives an idea about the distribution of summer SST, this is only at three locations. The authors need to give a more precise definition of what they call “extreme marine summer” regarding the distribution.
- My second concern is a lack of justification about applying methodologies for each “grid point”. Results gives a very statistical point of view. Is there any criterion about spatial scales? This is confusing as they give physical interpretation associated with regional patterns. I would at least explain why they are not considering EMS composites.
- If I understand Figure 3 correctly, it needs more explanation since patterns might results from one “very extreme” event for instance, and might not be representative of the 4 events. This also might be an issue in other figures.
- It misses a discussion about the interest for the community of this new term “ESM”.
I think these points need to be addressed before introducing this new concept. A major revision is required to clarify these points.
Minor comments:
L128 – “derives from a combination of HadISST2 and OSTIA datasets” – ERA5 SST is based on a reanalysis which includes model and observations datasets. I would reformulate.
L133 – “In addition to ERA5 (reference SST dataset), we use the CMEMS L4 satellite SST product (EU Copernicus Marine Service Product, 2022c) for the period 1982-2019, at 0.05°x0.05° grid spacing, to cross check the quality of the reference dataset against a high-resolution observational SST dataset.” What did you compare? What did you conclude?
L143 – “We then define EMSs, separately at each grid point, as the four summers with the highest average JAS SST, i.e., exceeding the 95th percentile of the 71 available summer periods from 1950 to 2020. “ As the authors want to introduce a new concept, it needs more explanation and justification.
L239 – “we provide examples of different patterns for three grid points of the domain ». Why these points? Are they representative a regional patterns?
Figure 4 – This figure is interesting, but this arises questions. I would imagine with such “Extreme Marine Summer” concept, that the spatial scales would be close to those of the basin. Maybe, the authors should show several plot with seasonal SST anomaly during two or three typical ESM.
L627 – “These values indicate that oceanic processes are primarily responsible for the observed EMS SSTs in these areas “ – You often refer to oceanic processes, but can you give references that support this result.
Citation: https://doi.org/10.5194/egusphere-2023-1709-RC2
Dimitra Denaxa et al.
Dimitra Denaxa et al.
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