The Atmospheric Circulation over the North Atlantic as Induced by the SST Field

Abstract

Spectral analyses of the sea surface temperature (SST) in the Simple Ocean Data Analysis (SODA) reanalysis for the past half-century identify prominent and statistically significant interannual oscillations in two regions along the Gulf Stream front over the North Atlantic. A model of the atmospheric marine boundary layer coupled to a baroclinic quasi-geostrophic model of the free atmosphere is then forced with the SST history from the SODA reanalysis.Two extreme states are found in the atmospheric simulations: they consist of (1) an eastward extension of the westerly jet associated with the front, which occurs mainly during boreal winter; and (2) a quiescent state of very weak flow found predominantly in the summer. This vacillation of the oceanic-front-induced jet in the model is found to exhibit periodicities similar to those identified in the observed Gulf Stream SST front itself. In addition, a close correspondence is found between interannual spectral peaks in the observed North Atlantic Oscillation (NAO) index, and the SODA-induced oscillations in the atmospheric model. In particular, significant oscillatory modes with periods of 8.5, 4.2 and 2.8 years are found in both the observed and simulated indices, and shown to be highly synchronized and of similar energy in both time series. These oscillatory modes in the simulations are shown to be suppressed when either (a) the Gulf Stream front or (b) its interannual oscillations are omitted from the SST field. Moreover, these modes also disappear when (c) the SST front is spatially smoothed, thus confirming that they are indeed induced by the oceanic front.

Interannual Variability in the North Atlantic Ocean’s Temperature Field and Its Association with the Wind Stress Forcing

“…Whatever the underlying mechanisms of interannual variability, it is interesting to note that, in a series of increasingly detailed atmospheric models, Feliks et al (2004Feliks et al ( , 2007Feliks et al ( , 2011Feliks et al ( , 2016, Brachet et al (2012) and Deremble et al (2012) have shown that sharp SST gradients, like the Gulf Stream or Kuroshio fronts, can have a strong influence on the overlying atmosphere and its lowfrequency variability. Variations in frontal strength, for example, were shown to modulate the atmospheric jet's intensity; see also Schneider and Qiu (2015) and Kilpatrick et al (2016, and references therein) for details on the Ekman pumping mechanism that mediates the SST front effect on the midlatitude atmosphere.…”

Monte Carlo Singular Spectrum Analysis (SSA) Revisited: Detecting Oscillator Clusters in Multivariate Datasets

“…Feliks et al (2011) identified significant oscillatory modes with periods of 8.5 yr and 10.5 yr in the SST field of the Cape Hatteras and Grand Banks region, respectively, and have shown that these modes spinup in an atmospheric model and become synchronized with a simulated NAO index.…”

“…Feliks et al (2011) identified in either one or both of these two regions, interannual spectral peaks of 8.5 yr, 4.2 yr and 2.8 yr. As discussed in the Introduction, these peaks are similar to those found in the NAO index (Gámiz-Fortis et al 2002;Paluš and Novotná 2004;Feliks et al 2013); hence the possibility of shared mechanisms between the ocean and atmosphere in the North Atlantic basin is worth examining further.…”

“…In the present paper, we follow Feliks et al (2011) and focus on SST data in the Gulf Stream region but combine it with SLP data in the entire North Atlantic region in a joint M-SSA analysis. The cleaner and sharper spectral results obtained herein support the previous authors' findings of very similar interannual peaks in the Gulf Stream SST data and the North Atlantic Oscillation (NAO).…”

Modeling the climatic implications and indicative senses of the Guliya δ<sup>18</sup>O-temperature proxy record to the ocean–atmosphere system during the past 130 ka

“…The similar link may also be indicated in the present climate. For example, the summer North Atlantic SST modulates the Asian precipitation by influencing the Europe-Asia atmosphere circulation on decadal timescales illustrated by modern reanalysis data and simulations (Sutton and Hodson, 2005;Dong et al, 2006;Wang et al, 2009;Feliks et al, 2011). When such physical phenomenon between the North Atlantic SST and Asian precipitation on decadal timescale is consistent with that in UVic Model on a longer timescale, the mechanism in the decadal physical phenomenon may take effect on a longer timescale.…”