Extreme cooling and dense water formation estimates in open and coastal regions of the Adriatic Sea during the winter of 2012

Abstract

Generation of dense waters in the Adriatic Sea during an extreme cooling event in the winter of 2012, including its preconditioning and spreading phases, have been investigated using the one-way coupled ROMS and the ALADIN/HR modeling system. Both climatological and real river fluxes are used in the simulations. Aside from the ''convenient'' dense water formation areas located at the northernmost Adriatic shelf, we found that a similar amount of dense water, with slightly lower density, was formed in the eastern and deeper Adriatic coastal area, which was subjected to extreme heat losses (up to 2000 W/m 2 ) during peak cooling periods. This part of the Adriatic has been known for extreme cooling during wintertime bora outbreaks; nevertheless, no ocean model study has previously reproduced dense water formation in this area. The most likely reason for that was an overestimate of river discharges introduced to ocean models. From newly available data, we estimated that the contribution of eastern Adriatic rivers between the Neretva River and Rijeka Bay is more than six times lower than what has been previously documented. Transport of dense water toward the middle Adriatic had a peak value of about 0.6 Sv, while the speed of initial bottom density current surpassed 40-50 cm/s, which is several times faster than past events. Different pathways of the dense water toward the middle and south Adriatic depressions have also been documented. The contribution of the eastern coastal Adriatic area to the overall north Adriatic dense water formation has been quantified and discussed for average and low freshwater load conditions, indicating that this part of the Adriatic is a common place for dense water generation.

Modeling the ocean and atmosphere during an extreme bora event in northern Adriatic using one-way and two-way atmosphere–ocean coupling

“…1), were included in both POM1w and POM2w using climatologies for the rivers Stella, Tagliamento, Livenza, Piave, Sile, Adige, Reno, Marecchia, Vibrata, Ofanto, Bojana, Drini, Shkumbi and Seman from (Raicich, 1994). Climatologies for rivers Mirna, Raša, Crikvenica, HPP (hydroelectric power plant) Senj, Zrmanja, Krka, Jadro, Cetina, Neretva, Ombla and HPP Dubrovnik were taken from (Janeković et al, 2014). Po River discharges were included using daily means of hourly discharge observations from Pontelagoscuro station.…”

“…Buoyant spreading of their low salinity waters tends to generate a classical coastal current, which, under the influence of Earth's rotation, remains more or less confined to the western Adriatic (Italian) coast where it flows south as a part of Western Adriatic Current. Adriatic river climatological discharges, used ubiquitously in the Adriatic modeling community, were compiled in Raicich (1994), while another, more recent, work investigated circulation, dense water formation and its spreading along the Adriatic basin during the February 2012 bora, using new Croatian river climatologies (based on 2009-2011 river-runoff observations) as hydrological forcings in their circulation model (Janeković et al, 2014). Dominant wind forcings can be separated into two classes: the cold northeasterly bora wind and the warm southeasterly scirocco.…”

“…Consequently, there were several routine (and ad hoc) field campaigns performed in the Gulf of Trieste and in mid-Adriatic immediately before and immediately after the strongest bora episode, and the event itself was subsequently widely reported Mihanović et al, 2013) as well as modeled (Janeković et al, 2014;Benetazzo et al, 2014). Atmospheric forcing caused exceptionally large surface heat fluxes, leading to an almost unprecedented water cooling and dense water formation in the Gulf of Trieste, where the sea temperatures dropped to 4 • C and density anomalies exceeded 30.55 kg m −3 Mihanović et al, 2013).…”

Development of BFMCOUPLER (v1.0), the coupling scheme that links the MITgcm and BFM models for ocean biogeochemistry simulations

“…River contributions were introduced as local boundary conditions, imposing observed daily freshwater flow rates for the major rivers (e.g. Po) and climatological annual flow rates for the others, with spring and autumn maxima and winter and summer minima (Querin et al, 2013;Janeković et al, 2014). The tracer concentrations at the river mouths were constant in space and time (Table 1), and the mass fluxes were calculated by multiplying the concentrations by the flow rate of each river.…”

A multiplatform investigation of Istrian Front dynamics (north Adriatic Sea) in winter 2015

“…An intense Bora wind produces strong surface cooling and intense evaporation, thus making the water denser Lee et al, 2005a, b;Janeković et al, 2014;Vilibić et al, 2016). The resulting dense waters tend to spread out over the whole basin, moving to the southern region (Carniel et al, 2012;Vilibić & Supić, 2005).…”