Klimatyczny wskaźnik aktywności Prądu Labradorskiego

Some of the sea currents show strong activity in climate formation and this fact is well known. Their activity represented as a time function is not stable but proves to be changeable. For this reason it seems quite reasonable to introduce appropriate indexes which could be used to characte-rise activity of a given current and, in an indirect way, to describe heat masses carried with this current. The aim of this article is to present an index which characterises the climatic activity of the Labrador Current. The basis to create such an index is the number of icebergs carried with this current. In consecutive ice seasons (October - September) this number passed south of 48°N of E from New Foundland (data from ?International Ice Patrol?). Changeable from year to year number of icebergs carried to the North Atlantic (see fig. 2) primarily represents the increase or decrease in the intensity of the Labrador Current. As the number of icebergs moved to the Atlantic comprises random component, which is very high, in order to create the index a logarythm was used to reduce the changeability of the amplitude. Formula [ 1 ] has been proposed to be used to calculate the index of intensity of the Labrador Current (WPL): WPL= (ln(G + 1))/2 where: ln - natural logarythm (base = e), G - the number of icebergs noted in a given ice season. Values of WPL index calculated in this way dated in January in ice season over a period 1900?2002 have been presented in Table 2 and their course in Fig. 3. The value of WPL indicates quite strong correlation with both winter (DJFM) and annual NAO indexes (r ~ 0.5), however the analysis showed that NAO is not the only element having influence on the Labrador Current activity. The analysis, carried out at random, of relations between the values of WPL and different climatic and hydroclimatic elements indicated to the fact that most of the relations are shifted/delayed in time - changeability of WPL takes place earlier than changes in these elements. For instance, the air temperature in August the following year in most area of Poland proves to have not too strong but clear correlation with the changes in WPL. Numerous correlations between WPL and occurring later monthly values of air temperature and monthly sums of precipitation at stations in the Atlantic sector of Arctica have been observed. The size of sea ice cover in the Barents Sea in the following year has shown especially high correlation with the changeability of WPL (the changeability of WPL explains ~50% of changeability in the area of the sea ice cover of the Barents Sea in January the following year). In this way WPL seems to be potentially useful in long term predictors of weather forecasts. The delayed activity of WPL can be explained by means of the following cause- and-effect chain of actions: winter (DJFM) atmpspheric circulation over the Davis Strait and the Labrador Sea has influence on the activity of the Labrador Current - the activity of the Labrador Current has influence on the extent and size of the anomalies in SST in the Labrador Sea and in NW part of the Atlantic (MJJA) - the presence of such anomalies in SST has a modifying effect on the atmospheric circulation occurring in the following autumn (SON) and winter (DJFM).