the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Jun 2024
Impact of Extratropical Cyclones on Coastal Circulation in a Semi-Enclosed Bay within the Humboldt Current System
Abstract. This study examines the hydrodynamic response of the Gulf of Arauco, a semi-enclosed bay within the Humboldt Current System, to the passage of extratropical cyclones and their associated changes in wind patterns during the austral winter. Characterization of these cyclones over central Chile and their effect on the gulf's meridional wind was conducted using ERA5 atmospheric pressure fields in conjunction with a cyclone tracking algorithm. The hydrodynamic response was assessed through ADCP observations at two strategic sites, providing valuable insights into the currents at the gulf's connections with the open ocean. Measurements were conducted from July to September 2016 and May to July 2018. Additionally, the main modes of subtidal current variability were compared with the local wind through coherence wavelets, revealing a direct influence of cyclones on the modulation of the gulf's currents. Our findings suggests that intense north wind events, associated with the passage of extratropical cyclones, can cause surface water transport into the Gulf, accumulating at the Gulf's head. This results in a pronounced pressure gradient, driving a water outflow through both connections with the open ocean, thereby altering the coastal circulation patterns. As the north wind decreases, the surface inflow in the northwest region attenuates, allowing the water to exit at shallower depths. This mechanism suggests a vital role of cyclones in renewing the waters of semi-enclosed bays such as the Gulf of Arauco, potentially reducing the water residence times. Consequently, these insights provide a broader understanding of wind-driven coastal dynamics, highlighting their significant impacts on marine ecosystems and coastal management in similar semi-enclosed bays globally. By contributing to the broader knowledge of the interaction between atmospheric and oceanic processes in coastal regions, this research offers a comparative perspective applicable to other regions affected by similar atmospheric phenomena.
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RC1: 'Comment on egusphere-2024-1822', Iván Pérez-Santos, 24 Oct 2024
Article title: Impact of Extratropical Cyclones on Coastal Circulation in a Semi-Enclosed Bay within the Humboldt Current System.
The wind regimen plays an essential role in the physical and biogeochemical conditions in the water column along the coastal zone of the Humboldt Current system. Moreover, most of the past and recent publications focused on the wind-favorable upwelling generated by the influence of the southeast Pacific subtropical anti-cyclone (High-pressure systems) during the spring-summer seasons. The present manuscript used a re-analysis data set from ERA5 to evaluate the relationship of extratropical cyclones (low-pressure systems) on the circulation regime of a semi-enclosed bay in central Chile for the first time. The methods and statistical analysis were well applied, and results and discussion allowed the completion of the manuscript goals. Therefore, I recommend the manuscript be published in Ocean Science after minor comments.
General comments:
- The study area is influenced by extratropical cyclones and low atmospheric pressure systems coming through the Subantarctic region, with a primary origin in the Southern Hemisphere westerly wind belt. Adding information in the Introduction section about all the low-pressure systems impacting the study area could benefit the manuscript and also justify the selection of only studying the extratropical cyclones.
- The methodology for detecting extratropical cyclones proposed an origin between 20°-40° S, and trajectories passed from 30°-50°S. The quantification of events is well presented, but it could be exciting to see and present a map of all trajectories (annual), focusing on trajectories during extratropical cyclone seasons (winter).
Specific comments:
Lines 140-141: Please clarify better the origin trajectory criteria used in the manuscript, e.,g. 20°-40°S ?
Lines 161-173: I recommend using a Taylor diagram to better illustrate the comparison between the ERA5 data and the coastal meteorological stations.
Lines 175-191: Adding a map of the trajectories of the extratropical cyclone could be significant to the manuscript, especially to see if there is any influence from the low-pressure systems coming from the Subantarctic region that finally arrive in the Gulf of Arauco.
Figure 4d and 5d. Reduce the y-range to -5 to 25 cm to better show the sea level oscillation.
Line 149. The Gulf of Arauco is affected by hypoxic events impacting the biogeochemical cycles and the ecology. Please add the benefit of the influence and pass of extratropical cyclones from GA to the oxygen variability and biological species in this section.
Citation: https://doi.org/10.5194/egusphere-2024-1822-RC1 -
RC2: 'Comment on egusphere-2024-1822', Anonymous Referee #2, 29 Oct 2024
Comments to the Author:
Summary:
The authors used in-situ current measurements (2 ADCPs) along with sea level pressure and surface wind from an atmospheric Reanalisys product and sea level from an oceanic Reanalisys product to investigate the impact of extratropical cyclones on the circulation of the Gulf of Arauco (Chile) in the Humboldt Current System.The authors found that the intense northerly wind events associated with the passage of extratropical cyclones produce surface water transport into the Gulf, accumulating at the Gulf’s head, resulting in a pressure gradient that drives water outflow through both connections with the open ocean. After, when wind decreases, the surface inflow in the northwest region attenuates, allowing the water to exit at shallower depths, suggesting a vital role of the extratropical cyclones in renewing the waters of the Gulf of Arauco.
The topic is interesting and should appeal to the EGUsphere readers. However, there are issues that the authors should address. Given this and minor concerns regarding the text, I suggest resubmitting the manuscript after revision.
Major corrections
I have only one major correction related to acknowledging the limitations of the sea level data used and, thus, the limitations of the pressure gradient reported as a primary mechanism for changes in circulation patterns inside the Gulf of Arauco when an extratropical cyclone is present. When intense northerly winds blow, wind waves are generated in the same direction and could produce a wave set-up inside the Gulf. However, the oceanic Reanalysis has probably not reproduced this process, which only reproduces the wind set-up. This must be discussed in the manuscript.
Also, does the sea level data from the ocean reanalysis include the inverted barometer effect?
The acceleration of observed currents responds adequately to the pressure gradient obtained from the sea level ocean reanalysis.
Minor corrections
Line 77: GA instead of Gulf of Arauco
Line 131: “It employs atmospheric pressure fields …” should be “It employs sea level pressure fields …”
Line 143: “cyclones with pressures below…” should be “cyclones with central pressures below…”
Lines 156 and 157: I believe there is a severe mistake in using “northward wind” in both these lines. The northward wind is the southerly wind, consistent with anticyclones and NOT cyclones.
Lines 161, 162, and 167: SLP instead of sea level pressure
Lines 170 to 173: This paragraph is confusing. From my point of view, ERA5 underestimates the magnitude of wind because the sign indicates wind direction. Please clarify.
Line 185: Similar to the previous comment, from my point of view, you are using the upper quartile of the northerly winds (view as magnitude). Please clarify.
Figure 2a: The x-axis label should be “Duration (Days).”
Figure 3a and 3c: The x-axis label should be “Meridional wind (m/s)”.
Figure 4d: I believe the y-axis should be modified (maybe ±12 cm) to visualize the difference between sea-level anomalies better.
Line 286: What does “the onset of an extratropical cyclone” mean? When is it generated? When the cyclone enters the selected area ??? or when the meridional wind starts to blow from the north ??? Please clarify.
Line 304: I suggest adding the trajectories of cyclones … “Such shifts modify the preferent tracks of extratropical cyclones and may be influencing its frequency in the region.” (or something like that)
Citation: https://doi.org/10.5194/egusphere-2024-1822-RC2
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