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General facts
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Depths: The shallowest part
of our sea is in Istria, where the depth does not exceed 50 metres.
From Pula, the seabed mildly drops, making a long, narrow valley
which extends from Zirje towards Italy which is called Jabucka kotlina.
The biggest depth there is about 240 metres. From Jabucka kotlina,
the bottom rises to Palagruza reef where the biggest depth is 130
metres. Towards the south, the bottom drops steeply towards the Juznojadranska
dolina, where the biggest measured depth is about 1,300 metres.
Seabed: The appearance of the underwater relief is the consequence of tectonic
movements, abrasion or erosion which were active several million years ago, in
times when certain parts of the seabed were land or the coastal area. Uneven
areas on the bottom are constantly reduced by sedimentation of detritus from
the land. That process is slow, but constant.
Tides: In the Adriatic, the high and low tides have relatively small amplitudes.
In the southern part, the difference is rarely above some forty centimetres,
while in the northern part it is somewhat bigger, so that it comes to 1 metre
in Istria and the Gulf of Trieste. In some narrow channels and bays, the high
tide can grow considerably during a strong sirocco. That phenomenon is characteristic
for big and deep bays of the southern Adriatic. The tides are of a mixed type,
which means that their rhythm is semidiurnal during the new and full moon, and
of a daily type during the first and the last quarter. Their amplitudes are very
irregular.
Sea Currents: Sea currents occur under the influence of winds, the difference
in pressure, temperature, and the differences in salinity. With respect to the
direction, they can be horizontal or vertical. There are also bottom currents
which appear as the consequence of moving of water from warmer areas to colder
ones, during which the surface layer gets cold and descends towards the seabed.
Currents are weakly observable in the Adriatic.The speed of currents changes
in particular areas, but it also depends on time periods. The average speed of
currents is about 0.5 knots, but they can also reach the speed of 4 knots.
Salinity of Sea: The total quantity of salt dissolved in one kilogram of sea
water is called salinity, which is usually expressed in grams and as the permillage.
The salinity of the Adriatic Sea is 38.30 per mill averagely, i.e. there is 38.30
g of salt dissolved in 1 kg of water. In the northern part, the salinity is somewhat
lower than in the middle and southern part because of the influence of the Po
River.
Sea Temperature: The Adriatic Sea has a very marked annual change of the surface
temperature. The average annual temperature is 11°C. During the winter, the sea
is the coldest and the surface temperature is about 7°C; very seldom, it can
drop below that too. In the spring, the sea becomes warmer, and the surface temperature
rises to 18°C. In the summer the surface of the sea reaches a very high temperature,
of up to 22 to 25°C, and in the southern Adriatic and Istria up to 27°C. In the
Adriatic, thermoclines, i.e. parts of the water column of the same temperature,
are very well distinguished. The thermocline is most evident during the summer,
and, in the winter, the isothermal process arises, i.e. equaling of the temperature
throughout the water column. In the summer, we can notice the first thermocline
at the depth of 3 to 5 metres, the next one is at about 12 metres, and yet another
one at 18 metres, while below 30 metres the temperature is mostly constant throughout
the year.
Waves in the Adriatic: Waves occur primarily as the consequence of the blowing
of winds. The bigger the reach, i.e. the surface across which the wind blows,
the higher the waves will be. Their strength depends on the configuration and
the exposure of the coast. In that way, mixing of the surface layer with water
from the deep is enabled, and the interaction between the atmosphere and the
sea. We distinguish the crest and the trough of a wave. The length of the wave
is the distance between two troughs. Most often, heights of waves in the Adriatic
are between 0.5 and 1.5 metres, and they very rarely exceed 5 metres. Climate
The climate at the Adriatic is typically a Mediterranean one, with mild rainy
winters, and hot and dry summers. The air temperature changes depending on the
area. Thus, summer temperatures in July will be about 34°C in the northern part,
while in the southern part they will rise even to 38°C. In the winter, the coldest
temperatures are noticed in the northern Adriatic (up to -16°C), while they will
not have exceeded 6°C in the southern part.
Winds: At the Adriatic Sea, the bora, sirocco and north-western wind blow most
often. Data About Weather Weather forecasts are made by the State Hydrometeorological
Institute, and they can be heard on VHF frequencies of coastal radio stations
and harbor master's offices. They are also broadcast on FM stations or at the
end of the news or within broadcasts for seamen. Harbor master's offices constantly
send weather reports and warnings on their VHF operating channels, in four languages.
It is possible to get forecasts with the presentation of the synoptical situation
in all the marinas and harbor offices.
Nautical Radio Service and Communications Service: The whole of the Croatian
coast is covered by radio communications rather well. The radio service for protection
of human lives and safety of navigation is provided by Plovput from Split, through
radio stations Split and Dubrovnik, which cover the southern Adriatic, and Rijeka,
which covers the northern part of our sea. According to the standards of the
GMDSS system (Global Maritime Distress and Safety System), the channel for automated
receipt of digitalized distress calls is the channel 70, after which the communication
is transferred to the operating channel of the coastal station, i.e. a harbor
master's office (16 or 10). GMDSS system has been in use since 1 st February
1999, and on the present VHF channel for distress calls, the channel 16, constant
listening will be possible still for some more time. For a direct call to a harbor
master's office, the channel 10 is used.
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