Sparr, Miriam (2006) Footprints of extratropical storms in the upper ocean. (Diploma thesis), Christian-Albrechts-Universität, Kiel, Germany, 82 pp.

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Abstract

This diploma thesis analyses the negative change of the SST in the midlatitude on the north hemisphere in spring and summer, which has a connection to the atmospherical condition. The SST rise with incident solar radiation in spring and summer, so that the ocean mixed layer becomes thinner and warmer. And than the SST decreases about 0.5 Kelvin or more in 6 till 48 hours. This temperature subsidence can only explained with the mixing of the ocean mixed layer with colder water from below the mixed layer. When it comes from a atmospherical general conditions, this intermixture arise with the impaced of the wind.The wind stress transmits moment on the ocean and stimulate Ekman circulation and Langmuir circulation. The analyse base on data from a coupled run of the atmosphere circulation model ECHAM with the ocean model Mopy. The wind data and the data of the geopotentical high is used for the analyse. It is analysed in which atmospherical situation a negative change of the SST existed. The hypothesis is that a low in the midlatitude have a connection to the negative change of the SST. To show this, different statistical methods are used. The negative SST change exist in the area between the subtropical high and the lows in the midlatitude. A direct relationship between the SST change and the atmosphere is only found at the wind speed. The wind speed must increase clear compared with the wind speed of the time before. If the wind speed increases, the SST can decrease 0.5 Kelvin or more to the following time. When negative SST change exists, the mean of the wind speed is higher then the mean of the wind speed at all areas and time points. The comparison of the geopotentical height in 1000hPa level doesn't show a typical situation in which the negative SST change exist. The wind speed arises in different areas of a low and also in a high. On the other hand there is a relationship between negative SST change and geopotentical height in 500hPa level. The negative SST change exists often with eopotentical height in 500hPa level which is greater than the mean, that means in the subtropical air respectively is connected with a ridge. The polar front is connected with the ground over the dynamic lows in the midlatitude. The ridge belongs to ridge of high pressure and the warm section of a low. Between the ridge and the trough is the cold front at the ground. After the cold front the trough comes in the high level. The wind speed is weak in the high, so the ocean mixed layer can become thinner and warmer. When the low comes near, the wind speed becomes stronger and the ocean mixed layer is mixed with colder water. So the SST decreases and a negative SST change arises.

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