 |
Bay of Biscay and Gulf of Lion : after the heatwave, August 2006
In July, it was the heatwave. In August, it is cold! This summer 2006 shows the ocean variability near our coasts.
By Véronique Landes, with the cooperation of Silvana Buarque-Giordani, Fabrice Hernandez and Eric Greiner, Mercator Océan
2006 is an interesting case of warming/cooling process of the superficial ocean: a never seen before big warming in July then a cooling in August. Processes consist in heat transfer from the atmosphere to the ocean, then from the ocean to the atmosphere. The wind is also able to push warm waters and to cool an ocean area in a few days. This was the case during the beginning of August, in the Gulf of Lion, Mediterranean.
Bay of Biscay
In August, the average sea surface temperatures reaches 19°C to 23°C, from the North-West to the South-East of the Bay of Biscay. The ocean is the hotest in August in this area, with maximas located off the Spanish Basque Country.
This year, the time sequence hasn't been respected. It was in July that the waters were the hotest.
|
|
Average sea surface temperature in July 2006, left, in August 2006, right. In August, the 23°C waters area is less extended and is localized along a very narrow coastal band along the Basque Country. In Galicia, North-West Spain, Northern winds have blowed regularly. The warm surface waters went away causing cold waters upwelling locally. These maps have been made from PSY2V2 Mercator operational system output. |
August 2006 shows normal values for the season: slightly above 19.6°C in average, in the restricted area 43-48.5N / 8W-0E (average value computed from the 10 years MERA-11 reanalysis).
The heat content is represented by the average temperature between 0 and 20 meters. In this layer, the reference average temperature (MERA-11 reference) is 19°C in the area 43-48.5N / 8W-0E.
The figure shows that, except for 2005, oscillating around an average value of 19°C, the 3 other years are above this value. In 2003, the anomaly was 1.2°C. In August 2006, during the first decade, the anomaly is 1.6°C, coming back to a normal value at the end of the month.
 | Heat content in the first 20 meters: average 0-20m temperature evolution between June and November 2006, Bay of Biscay (43-48.5N / 8W-0E). In July, the red curve is above all the others corresponding to the July 2006 heatwave. In August, it's the green curve corresponding to 2003 heatwave.
|
North-West Mediterranean
2 areas are considered: West, the Gulf of Lion, under the northern Mistral and Tramontane winds and Rhone waters influence and East, the Provençal Basin (Côte d'Azur, Gulf of Genoa) with the warm current coming from the Ligurian Sea. A "normal" situation in August shows average temperatures between 22 and 23°C West of Marseille, with a little pocket of water at 21/22°C along the Languedoc coast, and 24 to 25°C East, particularly along the Côte d'Azur. This year, in August, sea surface temperatures drop down to 20°C from the Camargue area to the Provence area.
A spectacular shift
 |
 |
Average sea surface temperature in July 2006, left, in August 2006, right. July situation has been drastically changed in a few days, because of the Mistral. These maps have been made from PSY2V2 Mercator operational system output. |
 | Heat content in the first 20 meters: 0-20m average temperature evolution in the North-West Mediterranean Basin (40-44N / 0-8E). |
|
Surface temperature and current in North-West Mediterranean: animation between 26 July and 9 August 2006. |
Where are the warm waters?
Warm waters haven't totally disappeared but they accumulated partially near the Balearic Sea.
 Heat content evolution in North-West Mediterranean, between 26 July 2006 and 13 September 2006. Heat content is represented by different colours from the blue (weak heat content) to the red (high heat content). Arrows represent the wind stress. |
Figure opposite illustrates the temporal evolution of the heat content in the superficial ocean layers. One of the last cévenol rains episode (harsh rain above the Cévennes, in Autumn), happened on 13 September 2006. Mercator system allowed to localize the high heat content areas available during this period which have given energy to the low atmosphere. They are located North of the Balearic Islands and near Sardinia. These processes are comparable to hurricane tropical processes (see bulletin #12). |
|
|
)
)
)
)
)
)
)
)
)
)
)
)
