Seasonal to decadal temperature variations in the Faroe—Shetland inflow waters

Abstract

A 53 years hind-cast simulation with a regional version of the Nansen Center version of the Miami Isopycnic Coordinate Ocean Model (MICOM) has been conducted to explore the nature of the observed seasonal to inter-annual variations in the temperature of the pole-ward flowing Atlantic Water (AW) crossing the IcelandScotland Ridge (ISR). It is found that the simulated long-term temperature variations closely resemble observations south of the ridge (Rockall Trough), north of the ridge (Svinøy section) and between (Faroe Shetland Channel, FSC). The simulated temperature on the Faroe Shelf is also compared to daily temperature observations from Mykines, revealing realistic long-term temperature variations, seasonal variations and a realistic seasonal modulation. The simulated time series in the FSC indicates that the phase and amplitude of the annual temperature cycle of the AW have varied by almost one month and 0.15 ºC between the 1960s and 2001, illustrating the difficulty in unambiguously removing the seasonal cycle from the, sparsely sampled, time series. It is argued that the simulated time series can be used to complement the observed time series in periods with sparse sampling. Specifically, the observation-based cold anomaly in the late 1960s and the warming in the early 1980s should be treated with caution. Finally, the analysis indicates that it is not advisable to survey the hydrographic section less than four times a year if reliable decadal scale temperature variations are of interest.

Spectral Characteristics of the Response of the Meridional Overturning Circulation to Deep-Water Formation

“…It is based on a regional version of MICOM with 20-km horizontal resolution covering the Atlantic Ocean between 30°and 78°N, nested in a global version of double horizontal resolution and forced by daily fields derived from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalyses from 1948 to 2002. The global simulation is discussed in Bentsen et al (2004); the nesting approach and the regional simulation are discussed in Hátun et al (2005). Although deep convection occurs in the Labrador Sea, the Irminger Sea, and the Greenland, Iceland, and Norwegian (GIN) Seas, we only consider convection in the Labrador Sea.…”

Simulated Variability of the Circulation in the North Atlantic from 1953 to 2003

“…In the regional model only, the mixed layer temperature and salinity fields were linearly relaxed toward the monthly mean climatological values of Levitus and Boyer (1994) and Levitus et al (1994), respectively. The relaxation scheme has been shown to be sufficiently weak to allow for realistic seasonal-to-interannual variations in the simulated hydrography in the northern North Atlantic (Hátún et al 2005).…”

Passive tracers and active dynamics: A model study of hydrography and circulation in the northern North Atlantic

“…It is well known that numerical models in general struggle with simulating hydrography, so our results can be considered suggestive only. Nevertheless, we do know that this model has fared rather well in comparisons with observed hydrography [see, e.g., Nilsen et al, 2003;Hátún et al, 2005aHátún et al, , 2005b. The findings are further evaluated against observations when possible.…”