Trenberth, K. E., and D. A. Paolino Jr., 1980: The Northern Hemisphere sea level pressure data set: Trends, errors, and discontinuities. The investigation is devoted to the development of a regional eddy-resolving model of the ocean of the Subpolar North Atlantic in order to reliably reproduce the components and properties of the Subpolar Gyre and the Atlantic meridional overturning circulation. The fluxes correlated to a positive NAO (see Visbeck et al. height: 4px; The bucket temperature cold bias might be larger as there could be ocean stratification at the time, so the in situ temperature of the water collected in the bucket could be a little higher than the intake temperature. The results were also checked using a sea level pressurebased index with no significant differences (see discussion in Trenberth and Paolino 1980). In situ data available before 1992 are described in Reverdin et al. Oceanogr., 33 , 964978. To homogenize the time series we normalize them (to an average standard deviation) before averaging. Rayner, N. A., P. Brohan, D. E. Parker, C. K. Folland, J. J. Kennedy, M. Vanicek, T. J. Ansell, and S. F. B. Tett, 2006: Improved analyses of changes and uncertainties in sea surface temperature measured in situ since the mid-nineteeth century: The HadSST2 dataset. The movement of the world's major ocean gyres helps drive the " ocean conveyor belt ." The ocean conveyor belt circulates ocean water around the entire planet. It could also result from atmospheric forcing. 2006). Averaged over the whole crossing, the errors in these three nonoptimal measurements result in an average additional 0.02C bias. The uncertainty in the averaged time series for a given year is estimated from the rms deviation between the different time series for that year, when only three or less boxes are combined, and from the uncertainties in the individual time series, when at least four boxes are sampled. Measurement of T was usually made within two minutes and the salinity sample was drawn afterward from the same bucket (some times drawn after refilling the bucket). The South Atlantic shows little response and . Richter, T. O., F. J. C. Peeters, and T. C. E. van Weering, 2009: Late Holocene (0-2.4 ka BP) surface water temperature and salinity variability, Feni Drift, NE Atlantic Ocean. (1997); Holliday et al. Smith, T. M., R. W. Reynolds, T. C. Peterson, and J. Lawrimore, 2008: Improvements to NOAAs historical merged landocean surface temperature analysis (18802006). I, 50 , 2352. Both observations and ocean reanalyses show a pronounced seasonality in the strength of the Atlantic meridional overturning circulation (MOC) within the eastern North Atlantic subpolar gyre (eSPG). display: flex; Geophys. Part I: Comparison with HadlSST1 open-ocean surface temperatures and preliminary analysis of long-term patterns and anomalies of SSTs around Iceland. The novelty of this work is the decomposition of the subpolar gyre into a western and an eastern subregion, which is motivated by water mass . Uncertainties are not reported on density but have similar magnitudes to what is plotted on temperature. Surface salinity variability in the northern North Atlantic during recent decades. The winter season (DecemberFebruary) was only sampled regularly for the area close to southern Iceland (but avoiding the shelves) and the eastern box (areas 1 and 2 in Fig. North Atlantic Sub-Polar Gyre Climate Index: A New Approach It should be related to changes in the westerlies south of 60N and, thus, result in changes in airsea fluxes as well as in gyre extension and intensity (Visbeck et al. However, the values for both temperature and salinity trends are well above errors related to sampling and random data errors and seem to be above possible method/systematic errors; thus, the negative sign of the density trend is likely to hold for these sources of uncertainty. NAO variability has almost as much variance at HF as at multidecadal time scales (by a factor of 1.2), whereas ocean signals were smaller. The present analysis presents a larger positive SST trend per century (0.29C) than HadSST2 (0.04C). Rev., 27 , 20412047. The most significant trend is a lowering in surface density. 3.1). Most features are reproduced, with a few differences, most notably in the late 1920s and for the 197090 period when uncertainties are higher. 2004). The SST record of the nearby Westmann Islands also indicated low SSTs in early 1952 (Hanna et al. Close to the Faeroes and west of Scotland, the mix of data is much more complex with additional Swedish and U.K. contributions at different times. Ocean gyre - Wikipedia Dutch and French Ocean Weather Ships (OWS), as well as most research vessels (before the 1980s), used a dedicated iron bucket for drawing the water and measuring temperature, whereas on the U.K. OWS Cumulus water was drawn (and temperature measured) at the intake. Bersch et al. Oceanogr., 41 , 168. The surface waters of the northeastern subpolar gyre are major contributors to the western part of the gyre (Labrador Sea, Irminger Sea) where the deeper waters are formed by winter convection (Lazier 1995; Pickart et al. Possible small (less than 0.1C) positive temperature biases could be present due either to systematic differences of intake temperature with TSG data or to biases in XBT temperatures used to correct the temperatures (Reverdin et al. The heavy line defines the domain over which HadSST2 fields are averaged to define a regional time series. The multidecadal low-frequency variability in salinity is correlated with the one in temperature for lags of 03 yr (S lagging). .ajtmh_container { Hurrell, J. W., and H. van Loon, 1997: Decadal variations in climate associated with the North Atlantic Oscillation. Interestingly, it does not seem to be present at other times except, maybe, for the early 1920s spike. The ones in the early 1920s, early 1950s, and early 1960s, on the other hand, also correspond to temperature signals (the last two were also commented on from hydrographic data by Reverdin et al. Multidecadal components of detrended combined time series for four different seasons. This could be investigated based on a multiple set of time series over the northeastern part of the subpolar gyre straddling hundreds of years with decadal resolution. The difference in the multidecadal T and S for the 1920s (high S but relatively low T) is puzzling, as advective changes for periods of prevailing westerlies are expected to result in covariability. Reverdin, G., F. Marin, B. Bourls, and P. LHerminier, 2009: XBT temperature errors during French research cruises (19992008). 1). The combination of the trend and the multidecadal variability produces the lightest surface waters in recent years (200008, Fig. Krahmann, G., M. Visbeck, and G. Reverdin, 2001: Formation and propagation of temperature anomalies along the North Atlantic Current. Errors due to insufficient spatial sampling are not included in our estimation of uncertainty based only on the scatter in the available data, and therefore the estimated uncertainty in the time series is too small for that year (Fig. Sci. Geosci., 2 , 6772. Wind Gusts 10 mph. Toward estimating climatic trends in SST. The temperature time series both at multidecadal and at higher frequencies are rather similar in our record and HadSST2 (Fig. 2 also suggests variability at decadal or multidecadal time scales both in T and S, but owing to uncertainty resulting from insufficient sampling, they are not well resolved in individual time series. A Lagrangian view of seasonal overturning variability in the eastern 2002). Comparing retrospective predictions of North Atlantic SST with observations, we show that the most state-of-the-art climate models have improved in predicting North Atlantic SST for up to 10 years ahead compared to the previous generation of climate models. The Norwegian vessels in 193139 read temperature from the intake (with a likely positive bias), whereas the water sample was drawn either from the intake or from a small iron bucket. Subpolar North Atlantic Overturning and GyreScale Circulation in the J. The negative correlation with temperature is maximum with the NAO in the same year (previous winter) or taken with a 1-yr lead. On the other hand, the large-scale gridded HadSST2 analysis (not shown) does not present this dip. These mode waters are one of the precursors to the deep waters formed in the North Atlantic. Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 20072008. Changes in the eastward extension of the subarctic front and in the northward penetration of intergyre water are associated with the covariability of T and S. Such changes clearly took place for the well-documented recent positive trend (Bersch et al. Res. HF variability is also portrayed in a similar way in the two analyses of SST (with a correlation coefficient of 0.71 significantly nonzero at the 99% confidence level and very similar rms variability; Fig. The salinity record also clearly presents some of the GSA signals, in particular in the late 1970s and 1980s, that have been related to outflows of freshwater from the Arctic (Belkin et al. Lett., 36 , L17607. 2009) can be used to investigate changes in water masses in the southern part of the Rockall Trough (near 5540N, 14W) but not so much for spring surface temperature, at least on decadal time scales. The difference between T and S in the HF spectral range thus points to different forcing mechanisms. Different types of draw buckets or intake sampling have been used that result in biases both for temperature (T) (see recent review in Rayner et al. 2003). The early 1920s is a period of relatively low sampling and for which there were few comparisons available to correct the surface data (we corrected the Danish S data by 0.05 PSS-78 during 192039). The negative correlation with salinity is maximum for the NAO leading between 0 and 3 yr. For salinity, this average seasonal cycle is not always very accurate because of insufficient sampling of large interannual variability. As an alternative and to estimate uncertainties due to inhomogeneous spatial sampling, we will use HadSST2 monthly gridded SST fields (Rayner et al. Josey, S. A., and R. Marsh, 2005: Surface freshwater flux variability and recent freshening of the North Atlantic in the eastern subpolar gyre. margin: 0; 4). doi:10.1029/2008JC004883. There is also published evidence for a very pronounced salinity minimum in the 1920s farther south in the Rockall Trough (Feni drift, Richter et al. 3). 112, International Council for the Exploration of the Sea, 7794. However, there too the mid-1920s minimum was preceded and followed quickly by much larger values, so it is not clear if it would project on the multidecadal component. In addition, surface data were collected in the 195074 period by the weather ships provided by various European countries (mostly by Dutch, U.K., Norwegian, or French ocean weather ships). 2004; Hurrell and van Loon 1997), although Rogers et al. 2003; Vage et al. ESA - Eduspace EN - Weather and Climate - The North Atlantic Gyre 96 F. RealFeel 102. Exceptionally low North American temperatures and record-breaking precipitation over the British Isles during winter 2013-2014 were interconnected by anomalous ocean evaporation over the North Atlantic subpolar gyre region (SPG). However, there is evidence that the canvas buckets in use on Danish merchant vessels were sometimes much smaller than recommended and that the time delay with the bucket on board before reading the temperature was at times much higher (up to 5 min) than what was requested, so errors on temperature and salinity are expected to have been larger than during our investigation (cf. (top) Map of the area investigated with 200-m, 1000-m-, and 4000-m isobaths plotted. Is Labrador Sea water formed in the Irminger Basin? Both observations and ocean reanalyses show a . An ocean gyre is a large system of circular ocean currents formed by global wind patterns and forces created by Earth's rotation. 2005) to document variability in the North Atlantic subpolar gyre prior to the 1950s.
