Monthly mean SST

Monthly mean SST maps were calculated on the basis of all cloud-free pixels of the available scenes (overpasses) during each month. The number of overpasses per month of the two received satellites varied between 60 and 180, which are 2-7 per day and about 30 000 scenes in the entire investigation period. The number of usable pixel per image contributing to the monthly means varied seasonally, depending on the cloud coverage, misinterpretation... 

The monthly mean SSTs of the central Arkona Sea of the years 1990-1998 were compared with the available solar radiation and air temperature of the region (Siegel et al., 1999b). The interannual variations in summer are strongly related. In spring the solar radiation forced the air temperature, and with a delay of one month followed the water temperature. In selected years, the air temperature also delayed by one month. In autumn, the solar radiation decreased first, and the delay of air and water temperature increased because of the heat storage by the water body. 

While the mean maximum of air temperature occurs between July and August, the maximum S ST is reached normally in August, as seen in Fig. 9.2 where seasonal variations of all monthly mean SST for the investigation period and the mean values for the entire period are presented. 

The correlation coefficients between a 10 year monthly mean time series of volatilisation rates and SST, 1 Om wind speed and pollutant concentration are used to elucidate which of the parameters drives the volatilisation rate changes and causes the deviations from the long term mean. All of the parameters do not vary independently. Since both SST and wind speed influence the volatilisation rate in a nonlinear manner, it is not intuitive whether an increase in wind speed leads to an increase in volatilisation rate. A raise in wind speed that coincides with a decrease of the sea surface temperature can lead to a negative linear correlation coefficient between volatilisation rate and wind speed. For that reason the partial correlation coefficient is calculated in addition to the simple linear correlation coefficients. It explains the relation between a dependent and one or more independent parameters with reduced danger of spurious correlations due to the elimination of the influence of a third or fourth parameter, by holding it fixed. One important feature of the partial correlation coefficient is, that it is equal to the linear correlation coefficient if both variables... 

A trend analysis forthe investigated period reflects that the seven warmest years were observed since 1999. The positive trend in the yearly mean SSTs with an increase of 0.97K in 16 years (0.65K/decade) confirms the global observation also for the Baltic Sea. Summer and autumn temperatures mostly contribute to this positive trend. The monthly resolved trend varies between the slightly negative trends in March and the highest positive trends in July in the northern Baltic Sea. The yearly trend of the entire Baltic Sea is stronger than that of the northern hemisphere. 

FIGURE 9.3 Seasonal cycle of SST in different regions compared to the monthly means of the entire Baltic Sea. 

In Siegel et al. (2006), the regional differences were additionally discussed separately for the winter and summer months. In the northern Baltic Sea, particularly in Bothnian Bay, the SST every year in February is below 0°C and the water is often covered by ice. From the western part (Pl) to the northern Gotland Sea (P16), the mean SST is around 2°C. The warmest February was in 1990 with SST between 3 C and 4 C in the main parts. The coldest was in 1996 in the southwestern Baltic and in 2003 in the northern Baltic. The... 

From Figs. 2a, 3a, and 4 it follows that, over the approximately 50-year-long period, the coldest winters in the Black Sea were observed in 1954, 1964, 1976, 1985, 1987, 1992, and 1993. Four of them occurred during the last 20 years. The lowest winter SST was registered in 1993. Starting from 1994, mean monthly winter temperatures have never decreased below 6.6 °C (Fig. 2a). High mean monthly and mean seasonal temperatures in winter were... 

Fig. 2 The peak mean monthly SSTs in the period 1982-2002 a winter minimums, b summer maximums. Hereafter, the bold horizontal segments mark time periods of El Ninos...

The mean annual SST values for the entire sea obtained from averaging mean monthly temperatures in the period 1982-2002 changed within approximately 2 °C (Fig. 5). The lowest mean annual temperatures corre-... 

Fig. 6 Six-month running mean of mean monthly ENSO (solid line) and NAO (dashed line) indices in the period 1950-2003 acquired from the Internet sites (http //www.cpc. NOAA.gov/data/indices/soi, http //www.cpc.NOAA.gov/data/teledoc). The circles indicate years with the anomalous winter SST values the black circles correspond to cold winters, the open circles to warm winters...

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