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Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum a standardised geodetic datum that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. Current sea level rise is mainly caused by human-induced climate change. When temperatures rise, mountain glaciers and the polar ice caps melt, increasing the amount of water in water bodies. Because most of human settlement and infras

Effects of entrance conditions on tidal hydrodynamics in idealized prismatic estuaries under sea level rise

Steve Hottinger

Understanding tidal hydrodynamics response to sea level rise (SLR) in estuaries is essential to predict future potential issues such as shoreline erosion, more frequent and intense flooding, coastal wetland threatening, and their economic and ecological associated losses. By going beyond the classic static or “bathtub” approach, this study uses the RMA-2 modelling software to capture the full energy dynamic resulting from SLR and changes in entrance conditions. Indeed, entrance restrictions are seen as a key factor controlling tidal propagation within the entire system and only little knowledge exists on their effects on the flow under SLR. An innovative numerical approach using idealized prismatic estuaries is undertook to fill this gap. More than 150 simulation cases are performed, varying the channels geometry, restrictions dimensions and tidal forcing to capture most of existing prismatic estuarine dynamics. The resulting tidal flow is described using tidal ranges (TR), but also flow velocity, tidal asymmetry, wave types, tidal prism, etc. to find out potential interesting trends. In short channels, tidal reflection is found to be the dominant process influencing tidal propagation while in long channels the flow is mostly controlled by bottom friction. TR are amplified up to 10% per metre SLR, exacerbating the future flooding problematics linked to a higher mean sea level. However, strong TR attenuation is observed when entrance restrictions are implemented, leading to potential insights on SLR effects mitigation using narrower inlets. SLR acts on the flow velocities distribution and on the tidal asymmetry by increasing medium velocities and decreasing flood dominance. Both will impact sediment transport, leading to stronger coastal erosion. This increases therefore the pressure on sensitive ecosystem already struggling to stay in pace with SLR. SLR can bring the channels closer or further from their natural period of sway. This change in tidal resonance can lead to modifications of the flow parameters behaviour. When channels become more resonant with SLR, amplification of the above phenomena are usually seen, while when they are brought away from resonance, attenuation or even reverse effects can be observed. All these issues are not captured by the bathtub approach and arise from changes in tidal dynamics. Furthermore, instead of focusing on specific estuaries as most of the previous studies, this project is using an idealized approach allowing a global evaluation of the future tidal hydrodynamics. Understanding tidal response to sea level rise in estuaries is crucial to develop efficient coastal management plans able to mitigate this threat on estuarine ecosystems and populated areas. In particular, over 130 port cities having a population higher than 1 million people are concerned by SLR issues in estuaries.

2019

In-Situ Observations Of Aerosol Hygroscopicity And Cloud Droplet Formation In Ny-Ålesund, Svalbard, During Fall 2019 And Spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of Spring 2021 compared to those of Fall 2020. In addition, we found filterpack-derived values of the aerosol hygroscopic parameter κ around 0.7. Combined with temperature and pressure data, these results were used as input parameters for the Morales Betancourt and Nenes (2014) parameterization in order to investigate the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., 2021). We found strong variations between the Fall to Winter months, known for pristine-like conditions, and the higher particle concentrations generally found in Spring, known as the arctic haze. Specifically, droplet formation was always limited by the low aerosol concentrations in Fall/Winter, whereas updraft-limited cloud formation occurred in Spring. Reviewing relevant literature tells that the relationship between the limiting droplet number concentration and the updraft velocity during NASCENT agrees with that of various locations worldwide, which tends to confirm the universality of this relationship. Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Ramelli, F., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A., Lohmann, U., and Nenes, A.: On the drivers of droplet variability in alpine mixed-phase clouds, 21, 10993–11012, https://doi.org/10.5194/acp-21-10993-2021, 2021. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Morales Betancourt, R. and Nenes, A.: Droplet activation parameterization: the population-splitting concept revisited, 7, 2345–2357, https://doi.org/10.5194/gmd-7-2345-2014, 2014.

2021

In-situ observations of aerosol-cloud interactions in Ny-Ålesund, Svalbard, during fall 2019 and spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). Specifically, the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., under review), could strongly vary between the fall to winter months, with pristine-like conditions, and the higher particle concentrations generally found in spring, known as the arctic haze. First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of spring 2021 compared to those of fall 2020. In addition, we found relatively low values of the aerosol hygroscopic parameter κ, generally below 0.3, consistently with previous studies in the arctic region (Moore et al., 2011). Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A. and Nenes, A.: On the drivers of droplet variability in Alpine mixed-phase clouds, , 34, under review. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Moore, R. H., Bahreini, R., Brock, C. A., Froyd, K. D., Cozic, J., Holloway, J. S., Middlebrook, A. M., Murphy, D. M. and Nenes, A.: Hygroscopicity and composition of Alaskan Arctic CCN during April 2008, Atmospheric Chemistry and Physics, 11(22), 11807–11825, https://doi.org/10.5194/acp-11-11807-2011, 2011.

2021

In-situ observations of aerosol-cloud interactions in Ny-Ålesund, Svalbard, during fall 2019 and spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). Specifically, the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., under review), could strongly vary between the fall to winter months, with pristine-like conditions, and the higher particle concentrations generally found in spring, known as the arctic haze. First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of spring 2021 compared to those of fall 2020. In addition, we found relatively low values of the aerosol hygroscopic parameter κ, generally below 0.3, consistently with previous studies in the arctic region (Moore et al., 2011). Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A. and Nenes, A.: On the drivers of droplet variability in Alpine mixed-phase clouds, , 34, under review. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Moore, R. H., Bahreini, R., Brock, C. A., Froyd, K. D., Cozic, J., Holloway, J. S., Middlebrook, A. M., Murphy, D. M. and Nenes, A.: Hygroscopicity and composition of Alaskan Arctic CCN during April 2008, Atmospheric Chemistry and Physics, 11(22), 11807–11825, https://doi.org/10.5194/acp-11-11807-2011, 2011.

2021

Effects of entrance conditions on tidal hydrodynamics in idealized prismatic estuaries under sea level rise

Steve Hottinger

2019

In-Situ Observations Of Aerosol Hygroscopicity And Cloud Droplet Formation In Ny-Ålesund, Svalbard, During Fall 2019 And Spring 2020

Paraskevi Georgakaki, Ghislain Gilles Jean-Michel Motos, Athanasios Nenes, Jörg Wieder

2021