Society is facing unprecedented challenges arising from climate change impacts. Among them, marine heat waves (MHWs) are prolonged periods of extreme ocean temperatures with major ecological and socio-economic impacts. The Mediterranean is the largest semi-enclosed sea, with 46.000 km of coastline and many islands, being also considered a hot-spot of biodiversity with many endemic species. It is also one of the most vulnerable regions to climate change and responds rapidly to global warming with strong spatial variations between sub-basins. In this study, we will update and provide new insights on MHWs in the Mediterranean, from sub-regional to local scales, from surface to subsurface, and from the open ocean to coastal waters using multi-platform remote sensing and in situ observations.

Continuous satellite-based sea surface temperature monitoring allows to detect MHWs at the surface and to estimate their spatio-temporal variations at sub-regional and local scales over the last four decades. At the same time, the Mediterranean network of moored buoys installed in shallow waters allows addressing the coastal ocean response to such extreme events over the last 10 years or more. Additionally, profiling floats in the whole basin and ocean gliders along endurance lines in key ‘choke points’ provide valuable information at the subsurface on sub-regional and local scales, respectively, about both the physical and biogeochemical properties from the coast to the open sea. Results on the thermal stress situation will be provided updating the results from Juza et al. (2022) from satellite and profiling floats observations. In particular, we will address the unprecedented MHW recent events (2022 and 2023) characteristics, providing also new insights with the use of coastal moorings and gliders and through the integration of available physical and biogeochemical data.

The multi-platform observations used in this study are open access and distributed by national and European marine data portals such as the Spanish Balearic Islands Coastal Observing and Forecasting System (SOCIB), the U.K. Meteorological Office and the E.U. Copernicus Marine Service. Particularly, historical and near real-time ocean data available in the latter are being also used in the web-based application (www.apps.socib.es/subregmed-marine-heatwaves) implemented by SOCIB. This user-friendly visualization tool helps to detect MHWs in real time and to monitor their long-term variations, aiming at supporting the marine conservation and policy decision-makings for climate change mitigation.

How to cite: Juza, M., De Alfonso, M., Mora-Fernandez, A., Díaz, L., Chevillard, C., Zarokanellos, N., Reyes, E., and Tintoré, J.: Update and new insights on marine heat waves in the Mediterranean, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-305, https://doi.org/10.5194/ems2023-305, 2023.

Ocean evaporation in the subtropics and tropics is the main supplier of moisture to the tropics and is of fundamental importance to the global hydrological cycle, influencing atmospheric and oceanic dynamics and thermodynamics. Ocean evaporation (turbulent latent heat flux) varies on a range of time scales, from the diurnal to longer climatic scales. While previous studies characterize its variability over seasonal-interannual to decadal time scales, here we focus on the subseasonal, and particularly daily-weekly scales, and aim to understand the drivers of this variability. We first show that latent heat flux variability entails transient evaporation hotspots, regionally exceeding 250 W/m², which build up the long-term climatology. We then show indications for the mechanisms governing this variability, and especially the extreme evaporation hotspots. Namely, it is dry air intrusions from the wake of midlatitude cyclones that reach the low latitudes. The relatively dry and cold airmass over the subtropical and tropical oceans dominates the occurrence and variability of intense latent heat flux in these regions. Our findings suggest, however, that the tropics are not zonally homogeneous, in the sense that such intrusions dominate tropical evaporation in particular regions more than others. For example, in the west of south Africa, southern South America and Mexico, evaporation hotspots co-occur with intrusions from the extratropics 70% of the time and more, while in the western South Pacific and Arabian Sea the co-occurrence reaches values of up to 30%. The fact that the variability and extremes of tropical latent heat flux are governed by extratropical dynamics on this scale, suggest that this mechanism should be viewed as a type of extratropical-tropical interaction, having implications for the predictability of tropical evaporation hotspots. 

How to cite: Yaari-Sadeh, T. and Raveh-Rubin, S.: An extratropical driver of evaporation in the tropical and subtropical oceans, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-362, https://doi.org/10.5194/ems2023-362, 2023.

Terra Nova Bay (TNB), in the Ross Sea, is characterized by the presence of persistent ice-free areas during the austral winter, known as polynyas. TNB polynya markedly influences air-sea dynamics and physical oceanography in that region as a major sea ice and salt “factories”, maintained by strong persistent katabatic winds. The role of TNB polynya is important in the formation of High Salinity Shelf Water (HSSW), the densest water mass of the Southern Ocean, occurring during sea ice production that increases the salinity of the subsurface water. The aim of this study is to investigate the processes that occur in the TNB coastal polynya and the role of the air-sea interactions in the determination of its opening and activity. First of all, we analysed the role of the katabatic winds, that are widely recognized to be one of the most relevant meteorological features of Antarctica continental margins. The genesis of these winds can be ascribed to the cooling of the near-surface air on the Antarctic Plateau, which determines a strong pressure gradient force downslope. The topographic forcing provides a strong direction consistency to such winds and can cause strengthening in wind speed near steep-sloped coasts. The impact of katabatic winds has been evaluated analyzing the in-situ meteorological data collected in Terra Nova Bay in the framework of the MeteoClimatological Observatory of Italian National Research Antarctic Program (PNRA). We studied the polynya response to the wind forcing and the katabatic regime, establishing subjective criteria to distinguish these strong and persistent winds from a normal wind’s intensification, and find the moments of distribution of katabatic events over the years from 1995 to 2022 examined during the austral winter season (April to October). The characterization of the detected event has been performed through the following indicators, the duration (DUR), the Severity (SEV) and Intensity (INT). Subsequently, we have computed the frequency (FRE, which is the number of events) and the average DUR, SEV and INT of the events belonging to every single year of the 1995-2022 period. In the second step the open water fractions, detected by the Ice Surface Temperature (IST) imagery derived from the MODIS data, were used to estimate the opening and the activity of the polynya during the winter seasons. Then, we estimated the surface heat budget between ocean and atmosphere, which can be assumed to result directly in ice production considering that ocean column is at its freezing point. Assuming that ice production rate depends on the net heat flux and on the polynya extension, it is possible to calculate the total production of salt released during sea ice formation and HSSW volume.

How to cite: Fusco, G., Aulicino, G., Capozzi, V., Cotroneo, Y., Esposito, M., and Budillon, G.: Katabatic winds and polynya activity in Terra Nova Bay during winter seasons in the period 1995-2022, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-511, https://doi.org/10.5194/ems2023-511, 2023.

Using the general analogies with the descriptive models of the tropical cyclones, some climate change effects identify a significant increase in the Mediterranean sea surface temperature. This phenomenon, in conjunction with its peculiar morphological predisposition, could justify the acceleration, recently observed, and the formation of cyclones at these latitudes, so-called medicanes (“MEDIterranean HurriCANES”). Their observations are based on a typical rotational motion around a low-pressure center in the atmospheric mesoscale, including the air-sea interaction effects.

In this work, different kinds of analyses were carried out about the spatial and temporal evolution of the Ianos medicane (Mediterranean cyclone that developed in 2020 in the middle of the Ionian sea). In particular, we use the Proper Orthogonal Decomposition (POD) method to decompose a database of spatio-temporal data collected by SEVIRI radiometer, onboard the Meteosat Second Generation - 11 geostationary satellite. Within this approach, we study the superposition regions of the rotating air masses, starting from the temperature field, in order to extract important informations about the evolution and distribution of the energy in the different scales of the event. Through this technique, it has been possible to study the turbulent dynamics of Ianos at different scales, obtaining a basis of empirical eigenfunctions along with their relative temporal coefficients. The ability of the POD to capture the maximum energy content in the spectrum, allows to separate different ranges of scales with similar characteristics, suggesting a different origin for the various kinds of emerging structures.

On the other hand, through the use of specific remote sensing techniques, the diagnostics of Ianos were studied using databases obtained from LEO satellites. The capabilities of the VIIRS and MODIS sensors, on board the Suomi NPP and EOS-Terra/Aqua platforms, which have 2D images with higher spatial resolutions, were explored. The aim of this analysis is based on the extraction of some atmospheric parameters, such as the temperature field within the Ianos cloud system, associated with altitude values, and the assessment of the ice pixel percentage using the split window. In addition, a study of atmospheric instability was carried out using the vertical temperature gradient and sea surface temperature, and the pressure field for the characterization of the minimum in the eye of the cyclone. 

How to cite: Ciardullo, G., Primavera, L., Lepreti, F., Ferrucci, F., and Carbone, V.: Satellite-based studies of the evolution of the Ianos medicane dynamics, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-21, https://doi.org/10.5194/ems2023-21, 2023.

An intense Mediterranean tropical-like cyclone (Medicane) known as Ianos developed in the central-eastern Mediterranean Sea in mid-September 2020. The parent cyclone of Ianos initially formed on 14 September and strengthened on 15-16 September. Ianos acquired its tropical characteristics mainly on 17-18 September and it began to gradually lose its energy on 19-20 September while it finally dissipated on 21 September. Although Ianos affected several Mediterranean areas, it significantly influenced Greece with strong winds, high waves, storm surge, coastal inundation, heavy rainfall, flash floods, and landslides, thus having severe socioeconomic implications including four deaths and extensive damages. The impact of Ianos on the sea state was very intense, especially across the coastal areas of the Ionian Sea where the cyclone was characterized by its maximum winds reaching even Category 2 of the Saffir-Simpson scale. Moreover, high waves were observed in the coastal areas of the Ionian Sea during the passage of Ianos. In this framework, this study investigates the coastal wave conditions during Ianos in the Ionian Sea using the open-source tool DNORA (https://github.com/KonstantinChri/dnora) to dynamically downscale the ERA5 reanalysis data applying the spectral wave model SWAN. We use high-resolution bathymetry from the EMODNET database. We analyze the wave conditions using integrated wave parameters such as significant wave height and wave periods as well as wave spectrum. Particular focus is given to the evolution of the 2D wave spectrum during the Medicane Ianos. Preliminary results indicate that such extreme atmospheric events can lead to rapid growth of wind sea conditions with a significant impact on coastal areas.

How to cite: Christakos, K., Varlas, G., and Björkqvist, J.-V.: Coastal wave conditions in the Ionian Sea during the Medicane Ianos (2020)., EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-407, https://doi.org/10.5194/ems2023-407, 2023.

In this work, we have used a hydrodynamic finite element model to study tides, surges and seiches in the Mediterranean Sea. The simulations were performed with and without data assimilation for a two-month period, November and December 2019, in which several intense meteorological events occurred in this area. The observations come from coastal stations along the Mediterranean and have been processed to select tides and surges. Surge simulations were used also to analyse seiche oscillations in the Mediterranean. These oscillations are caused by an initial perturbation and propagate freely with periods corresponding to the barotropic modes of the basin. The periods and the energy have been identified through spectral analysis from the observed data and their forecast improves significantly with data assimilation. Furthermore, data assimilation in reanalysis simulations shows a significantly improving in the results, both for the surge and for the astronomical tide. The error of the results reduces considerably even in areas far from the assimilated stations, such as the Eastern Mediterranean Sea. In the case of the astronomical tide, a comparison with the tide calculated from the harmonic components, extrapolated by altimetric data, demonstrates a considerable improvement not only in the coastal areas but also in the central part of the basin. This study is the first step to set up long-term reanalysis climatological simulations for tides, surges and total sea level in the Mediterranean Sea.

How to cite: Bajo, M., Ferrarin, C., and Umgiesser, G.: Modelling the sea level in the Mediterranean Sea by assimilating data from coastal stations, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-465, https://doi.org/10.5194/ems2023-465, 2023.