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Zmiany temperatury wody na Prądzie Zachodniogrenlandzkim w okresie 1982-2003

Zblewski S.

Problemy Klimatologii Polarnej

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2004

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nr 14

29-37

EN

This work deals with the changes in sea surface temperature (SST) in selected grids located along the West Greenland Current (Fig. 1). The West Greenland Current is a warm current, which transports warm waters to the bay/ gulf of the Baffin Sea and in this way has a great influence on the formation of ice cover and on air temperature in this area. The Reynolds's data set, version SST OI v.1., covering values of mean monthly SST in grids 1ox1o has been used as the data source. Yearly temperatures for selected grids have been calculated on the basis of mean monthly temperatures. The Reynolds's data set covers whole years from the period 1982-2002 (21years). This period is especially interesting because during these years (and also at present) an advanced process of sea ice cover degradation and an increase in air temperature has been observed in Arctic. At Greenland, especially during the past few years, an advanced process of ice melting on land was noted - summer ablation reaches the level of 1600-2000m. That is why changes in SST at the same time may also be interesting. Trends in chronological series of mean yearly values of SST in grids located along the West Greenland Current ([59°N, 44°W], [62°N, 52°W], [66°N, 56°W], [70°N, 58°W], [74°N, 60°W] and [76°N, 72°W] ) have been analysed. Such an analysis indicated that in all grids of the West Greenland Current the trends in water temperature prove to be positive and that these trends are statistically relevant (p < 0.05 ) in nearly all grids. An exception to this pattern is the sea area extending around the Cape Farewell (grid [59, 44] - the first part of the West Greenland Current} where the trends are very low and statistically not relevant (Tab. 1). The highest values of trends can be observed in grids [62, 52] (+0.059deg./year) and [74, 60] (+0.051deg./year) resulting in the increase in SST by 1.24°C and 1.07°C over the period of 21 years. These grids are located in the initial and final parts of the West Greenland Current. Far weaker trends were observed in central part of the current [70, 58] - +0.030deg./year and in grid [76, 72] - +0.035 deg/year. Yearly temperatures of water in the West Greenland Current prove to show strong correlation (see Fig. 2). The mean monthly values of SST have also been analysed. The highest values of trends (statistically relevant) were noted in grid [74, 60] in August (+0.193deg/year) and in September (+0.136deg/year) thus giving in the analysed period the increase in SST by 4.05°C and 2.86°C. Such distribution of trends in time indicates that the role of the summer warming of the sea surface has increased. Positive trends in spring and autumn months in grids [62, 52] and [66, 56] are statistically relevant. In grid [70, 58] positive trends are observed both in summer months as well as in winter ones and in the northernmost located grids positive and statistically relevant trends are observed in almost all months during which waters are ice free. Yearly values of SST in the south part of the West Greenland Current prove to show strong negative correlation with the Hurrell NAO index (r~ -0.7; see Fig. 4) the monthly values of SST show delayed correlation with the Hurrell NAO index; correlations which are statistically relevant were noted in the period from June to December, the maximum (r = -0.64 to ?0.74) in the period from August to October. Monthly and yearly values of SST which show statistically relevant correlation with the Hurrell NAO index disappear at latitude 67°N-68°N. In the analysed period the NAO index indicates weak negative trend which is not relevant (-0.052/year), however correlation of yearly SST with NAO index over the analysed period are statistically relevant, e.g. in grid 66°N, 056°W, they explain 45% of the observed changeability in SST (R = 0.69, F(1.19) = 17.6, p< 0.0005).

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Wpływ zmian temperatury wody na Prądzie Norweskim na kształtowanie rocznej temperatury powietrza w atlantyckiej Arktyce i notowane tam ocieplenie w okresie ostatniego 20-lecia

Styszyńska A.

Problemy Klimatologii Polarnej

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2004

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nr 14

69-78

EN

Kruszewski, Marsz and Zblewski (2003) found out that winter temperature of water in the Norwegian Current indicates quite strong, occurring with a delay, correlations with the air temperature at Spitsbergen, Bjornoya, Hopen and Jan Mayen. Strong and statistically significant correlations between the mean sea surface temperature (SST) in the period January-March in grid 2°x2° [67°N, 10°E] and the monthly temperature of July, August and September with SST are marked the same year (3-5 month delay) and with the air temperature in November and December the following year (18-20 month delay). Waters of the Norwegian Current transport warm, of higher salinity Atlantic waters. Winter SST of the Atlantic Ocean characterizes the heat resources in the deeper layers of waters. SST in grid [67,10] in an indirect way characterizes heat resources carried with the Atlantic waters into the Norwegian Sea and farther to the Arctic together with the West Spitsbergen and Nordcap currents. The aim of this work is to describe the influence caused by changes in heat resources transported to the Arctic with the Norwegian Current on the annual temperature of air in the region of Hopen, Spitsbergen and Jan Mayen. The examined period covers the years of 1982?2002 and is marked by great warming in this area. The analysis of spatial distribution of correlation coefficients justifies Kruszewski and others (2003) hypothesis of mechanism causing the delayed influence of changes in water heat resources on the air temperature in this region The observed positive correlations between winter SST in [67,10] grid and air temperature in July, August and September result in the influence of changing water heat resources on atmospheric circulation noted in these months. Positive correlations in November and December in the following year result from the ?onflow? to the Arctic of warmer and of high salinity Atlantic waters. They have influence on the ice formation on the Greenland and Barents seas thus causing that influence of changing heat resources carried with waters on air temperature is much stronger. The analysis of regression made it possible to establish the correlation between annual air temperature at a given station (Ts) and winter water temperature (Tw) in [67,10] grid. Annual temperature in a year k is a function of two variables: Tw of the same year as the temperature Ts (Tw(k)) and Tw from the preceding year (Tw(k-1)): Ts(k) = A + b . Tw(k) + c . Tw(k-1) Table 3 contains the values of constant term and regression coefficients as well as statistical characteristics of formulas for the analysed stations. Both variables Tw from the year k and the year k-1 explain about 40% of the changeability in mean annual air temperature of the observed 20-year period at the analysed stations. This means that only one element, i.e. heat resource in the waters of the Norwegian Current, defined with the value Tw, determines more than 1/3 of the whole annual changeability in air temperature in the region located from Jan Mayen up to Hopen and from Tromso up to Ny Alesund. The station for which maximum explanation may be applied (47.7%) is Hopen, the station where the positive trend in annual temperature is the highest (+0.090°C/year). The values of regression coefficients b and c prove that the inertial factor connected with advection of the Atlantic waters has greater role in the changeability in mean annual temperature of air. The analysis of formula [2] indicates that great increases and decreases in annual temperature at the discussed stations will be observed in a k year if the values of Tw in two following years are significantly higher or lower than the mean ones. That is why the occurrence of positive trend in value of Tw should be followed by relatively systematic increase in annual air temperature at stations located at the described region. A positive trend in annual air temperature was noted at the analysed stations over the period 1982?2002. At Jan Mayen its value is +0.067 (ą0.028)°C/year (p<0.026). When taking the estimated values of regression coefficients in the multiple regression connecting the annual temperature at Jan Mayen with the value of Tw (Table 1) and the same value of trend T equal to +0.023 then the value of annual trend in air temperature at Jan Mayen influenced by trend Tw equals 0.0598°C/year. The obtained result indicates that the whole or almost whole warming observed at Jan Mayen in the years 1983-2002 may be explained by direct and indirect influence of the increase in the value of Tw over that period.

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Wpływ cyrkulacji atmosferycznej na temperaturę wody u polskiego wybrzeża Bałtyku w chłodnej porze roku

Girjatowicz J.

Inżynieria Morska i Geotechnika

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1999

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nr 1

4-7