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( Lau 1997 ; Alexander et al. 2002 ) and internal atmospheric variability ( Frankignoul 1985 ; Kushnir et al. 2002 ). In fact, Robinson (2000) reported difficulties in atmospheric general circulation model (AGCM) experiments to yield systematic atmospheric responses to prescribed midlatitude SST anomalies. It has been suggested recently (e.g., Taguchi et al. 2012 ), however, that persistent SST anomalies in the North Pacific subarctic frontal zone (SAFZ) can force basin-scale atmospheric
( Lau 1997 ; Alexander et al. 2002 ) and internal atmospheric variability ( Frankignoul 1985 ; Kushnir et al. 2002 ). In fact, Robinson (2000) reported difficulties in atmospheric general circulation model (AGCM) experiments to yield systematic atmospheric responses to prescribed midlatitude SST anomalies. It has been suggested recently (e.g., Taguchi et al. 2012 ), however, that persistent SST anomalies in the North Pacific subarctic frontal zone (SAFZ) can force basin-scale atmospheric
SST anomaly does not move far on monthly time scales.) This definition follows the finding by Sérazin et al. (2015) that in high-resolution models most of the small-scale SSH variability is intrinsic, and intrinsic motions also contribute in a nonnegligible fashion to large-scale variability of SSH. This notion will be expanded upon in a follow-on paper that aims to separate out the contributions of heat content variability due to atmosphere-forcing by air–sea heat fluxes, versus atmosphere
SST anomaly does not move far on monthly time scales.) This definition follows the finding by Sérazin et al. (2015) that in high-resolution models most of the small-scale SSH variability is intrinsic, and intrinsic motions also contribute in a nonnegligible fashion to large-scale variability of SSH. This notion will be expanded upon in a follow-on paper that aims to separate out the contributions of heat content variability due to atmosphere-forcing by air–sea heat fluxes, versus atmosphere
frontal regions, on the other hand, can lead to an equatorward shift of the entire low-level atmospheric circulation system, including the surface westerlies, jet streams, and subtropical high pressure belt ( Sampe et al. 2010 ). By comparing atmosphere-only model simulations forced by prescribed SSTs, Taguchi et al. (2009) showed a reduced storm-track activity in response to a weakened SST gradient forcing due to the decreased meridional gradient of turbulent heat fluxes and moisture fluxes across
frontal regions, on the other hand, can lead to an equatorward shift of the entire low-level atmospheric circulation system, including the surface westerlies, jet streams, and subtropical high pressure belt ( Sampe et al. 2010 ). By comparing atmosphere-only model simulations forced by prescribed SSTs, Taguchi et al. (2009) showed a reduced storm-track activity in response to a weakened SST gradient forcing due to the decreased meridional gradient of turbulent heat fluxes and moisture fluxes across
1. Introduction Owing to greater persistence of SST anomalies than atmospheric anomalies, a robust atmospheric response to oceanic forcing, if any, could contribute to improvement in seasonal forecast skill. Influence of extratropical SST anomalies on the large-scale atmospheric circulation has long been believed to be insignificant, in the presence of a prevailing remote influence from the tropics ( Lau 1997 ; Alexander et al. 2002 ) and large intrinsic atmospheric variability ( Frankignoul
1. Introduction Owing to greater persistence of SST anomalies than atmospheric anomalies, a robust atmospheric response to oceanic forcing, if any, could contribute to improvement in seasonal forecast skill. Influence of extratropical SST anomalies on the large-scale atmospheric circulation has long been believed to be insignificant, in the presence of a prevailing remote influence from the tropics ( Lau 1997 ; Alexander et al. 2002 ) and large intrinsic atmospheric variability ( Frankignoul
, which would then increase the pressure gradient between the straits and drive a stronger Throughflow. Observations show the Throughflow changing in the opposite phase and therefore suggest that some other processes are at work affecting or driving the annual cycle of the Throughflow. b. The mechanism driving the annual cycle How is the annual cycle of the Throughflow induced at the straits? Based on the two aspects mentioned above, specific questions are as follows: What is the primary forcing agent
, which would then increase the pressure gradient between the straits and drive a stronger Throughflow. Observations show the Throughflow changing in the opposite phase and therefore suggest that some other processes are at work affecting or driving the annual cycle of the Throughflow. b. The mechanism driving the annual cycle How is the annual cycle of the Throughflow induced at the straits? Based on the two aspects mentioned above, specific questions are as follows: What is the primary forcing agent
linearized around the basic state. The basic state, which comprises zonal and meridional wind, temperature, and surface pressure, is defined as the 31-day time average around the date for which the forcing is given from the JRA-55 data. Spectral T42 resolution is used in the horizontal directions, and there are 20 vertical levels, using the sigma coordinate. The LBM includes Rayleigh damping and Newtonian cooling. Because the response mostly achieves a steady state by 8 days (see section 4b ), the
linearized around the basic state. The basic state, which comprises zonal and meridional wind, temperature, and surface pressure, is defined as the 31-day time average around the date for which the forcing is given from the JRA-55 data. Spectral T42 resolution is used in the horizontal directions, and there are 20 vertical levels, using the sigma coordinate. The LBM includes Rayleigh damping and Newtonian cooling. Because the response mostly achieves a steady state by 8 days (see section 4b ), the
; Minobe et al. 2008 ; Tokinaga et al. 2009 ). The local imprints of ocean currents, including surface wind, precipitation, and cloud formation, are well represented in satellite data from over a short period of just a few years. Two mechanisms, the vertical mixing mechanism and the pressure adjustment mechanism, have been proposed to explain the processes behind the ocean forcing on the overlying boundary layer at frontal scales. The vertical mixing mechanism attributes the correspondence of the SST
; Minobe et al. 2008 ; Tokinaga et al. 2009 ). The local imprints of ocean currents, including surface wind, precipitation, and cloud formation, are well represented in satellite data from over a short period of just a few years. Two mechanisms, the vertical mixing mechanism and the pressure adjustment mechanism, have been proposed to explain the processes behind the ocean forcing on the overlying boundary layer at frontal scales. The vertical mixing mechanism attributes the correspondence of the SST
1. Introduction Large-scale extratropical ocean–atmosphere interaction has long been recognized as dominated by atmospheric forcing of the ocean ( Davis 1976 ; Frankignoul and Hasselmann 1977 ; Frankignoul 1985 ). However, ocean–atmosphere coupling varies considerably across the midlatitude ocean basins, with oceanic processes likely to be more important to sea surface temperature (SST) variability in the vicinity of the western boundary currents (WBCs) and their associated SST fronts ( Qiu
1. Introduction Large-scale extratropical ocean–atmosphere interaction has long been recognized as dominated by atmospheric forcing of the ocean ( Davis 1976 ; Frankignoul and Hasselmann 1977 ; Frankignoul 1985 ). However, ocean–atmosphere coupling varies considerably across the midlatitude ocean basins, with oceanic processes likely to be more important to sea surface temperature (SST) variability in the vicinity of the western boundary currents (WBCs) and their associated SST fronts ( Qiu
1. Introduction Atmospheric storm tracks are very important for climate dynamics. They indicate regions of maximum transient poleward energy transport and zonal momentum transport ( Chang et al. 2002 ) and play an important role in setting the dynamical response of the midlatitudes to global warming through their radiative forcing ( Voigt and Shaw 2015 ). Storm tracks are generally calculated as the standard deviation of atmospheric data that has been filtered in the time domain to isolate
1. Introduction Atmospheric storm tracks are very important for climate dynamics. They indicate regions of maximum transient poleward energy transport and zonal momentum transport ( Chang et al. 2002 ) and play an important role in setting the dynamical response of the midlatitudes to global warming through their radiative forcing ( Voigt and Shaw 2015 ). Storm tracks are generally calculated as the standard deviation of atmospheric data that has been filtered in the time domain to isolate
in ice concentration and by wind forcings are also included. Finally, we summarize the results in section 5 . 2. Formulation a. Sea ice model We consider equations of freely drifting ice motion driven by steady wind. Since the adjusting time scale is much shorter than the inertial period that is a typical time scale of this problem, we assume to neglect the time derivative term ( Leppäranta 2005 ). The momentum equations of the sea ice drift may be written as follows: where u i is the ice
in ice concentration and by wind forcings are also included. Finally, we summarize the results in section 5 . 2. Formulation a. Sea ice model We consider equations of freely drifting ice motion driven by steady wind. Since the adjusting time scale is much shorter than the inertial period that is a typical time scale of this problem, we assume to neglect the time derivative term ( Leppäranta 2005 ). The momentum equations of the sea ice drift may be written as follows: where u i is the ice
