Does Pacific variability influence the Northwest Atlantic shelf temperature?

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 4110–4131, doi:10.1029/2017JC013414.The relationship between North Pacific variability and sea surface temperature (SST) of the Northwest Atlantic continental shelf is examined over interannual time scale in 1982–2014. Statistically significant negative correlations exist between Pacific Decadal Oscillation (PDO) index and SST in the Gulf of Maine (GoM) in spring and summer. Cross‐correlation analysis further suggests significant negative lead‐lag correlations, with the spring PDO leading the GoM SST by 0–3 months while the summer PDO lags by 1–3 months. These correlations are dominated by the interannual component of the PDO. Statistical relationships are placed in context by further investigating the physical processes controlling the upper ocean mixed layer temperature budget in the GoM. The results reveal contrasting roles between the atmosphere and the ocean in spring and summer, respectively. Local atmospheric forcings, in particular the radiative air‐sea fluxes, are the dominant driver for the interannual variability of springtime SST over the Northwest Atlantic shelf. In contrast, oceanic terms are important in controlling the interannual variability of summertime SST. As a result, reconstructed SST using atmospheric forcings successfully reproduces the statistical relationship with PDO in spring, but not in summer. Furthermore, it is shown that the SST anomalies in the central and eastern North Pacific play a key role in these relationships.National Science Foundation Ocean Science Division Grant Numbers: OCE‐1435602 , OCE‐1558960 , OCE‐1634094; National Oceanic and Atmospheric Administration Climate Program Office MAPP program Grant Number: NA170AR43101112018-12-2

The modulation of Gulf Stream influence on the troposphere by the eddy-driven jet

Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 33(10), (2020): 4109-4120, doi:10.1175/JCLI-D-19-0294.1.This study suggests that the Gulf Stream influence on the wintertime North Atlantic troposphere is most pronounced when the eddy-driven jet (EDJ) is farthest south and better collocated with the Gulf Stream. Using the reanalysis dataset NCEP-CFSR for December–February 1979–2009, the daily EDJ latitude is separated into three regimes (northern, central, and southern). It is found that the average trajectory of atmospheric fronts covaries with EDJ latitude. In the southern EDJ regime (~19% of the time), the frequency of near-surface atmospheric fronts that pass across the Gulf Stream is maximized. Analysis suggests that this leads to significant strengthening in near-surface atmospheric frontal convergence resulting from strong air–sea sensible heat flux gradients (due to strong temperature gradients in the atmosphere and ocean). In recent studies, it was shown that the pronounced band of time-mean near-surface wind convergence across the Gulf Stream is set by atmospheric fronts. Here, it is shown that an even smaller subset of atmospheric fronts—those associated with a southern EDJ—primarily sets the time mean, due to enhanced Gulf Stream air–sea interaction. Furthermore, statistically significant anomalies in vertical velocity extending well above the boundary layer are identified in association with changes in EDJ latitude. These anomalies are particularly strong for a southern EDJ and are spatially consistent with increases in near-surface atmospheric frontal convergence over the Gulf Stream. These results imply that much of the Gulf Stream influence on the time-mean atmosphere is modulated on synoptic time scales, and enhanced when the EDJ is farthest south.For part of this study, R. P. was funded by the Weston Howland Jr. postdoctoral scholarship at Woods Hole Oceanographic Institution. We gratefully acknowledge the support to Y.-O. K. from the NOAA CPO Climate Variability and Predictability program (NA13OAR4310139), the DOE Regional and Global Model Analysis program (DE-SC0014433 and DE-SC0019492), and the NSF AGS Climate and Large-scale Dynamics program and OCE Physical Oceanography program (AGS-1355339). We thank NCAR for allowing access to the NCEP-CFSR dataset, accessible at https://rda.ucar.edu. We thank the editor Hisashi Nakamura and the three reviewers whose comments have helped greatly improve the manuscript.2020-10-1

An enhancement of low-frequency variability in the Kuroshio–Oyashio Extension in CCSM3 owing to ocean model biases

Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 23 (2010): 6221–6233, doi:10.1175/2010JCLI3402.1.Enhanced decadal variability in sea surface temperature (SST) centered on the Kuroshio Extension (KE) has been found in the Community Climate System Model version 3 (CCSM3) as well as in other coupled climate models. This decadal peak has higher energy than is found in nature, almost twice as large in some cases. While previous analyses have concentrated on the mechanisms for such decadal variability in coupled models, an analysis of the causes of excessive SST response to changes in wind stress has been missing. Here, a detailed comparison of the relationships between interannual changes in SST and sea surface height (SSH) as a proxy for geostrophic surface currents in the region in both CCSM3 and observations, and how these relationships depend on the mean ocean circulation, temperature, and salinity, is made. We use observationally based climatological temperature and salinity fields as well as satellite-based SSH and SST fields for comparison. The primary cause for the excessive SST variability is the coincidence of the mean KE with the region of largest SST gradients in the model. In observations, these two regions are separated by almost 500 km. In addition, the too shallow surface oceanic mixed layer in March north of the KE in the subarctic Pacific contributes to the biases. These biases are not unique to CCSM3 and suggest that mean biases in current, temperature, and salinity structures in separated western boundary current regions can exert a large influence on the size of modeled decadal SST variability.Support for L.T. was provided by the NASA sponsored Ocean Surface Topography Science Team, under Contract 1267196 with the University of Washington, administered by the Jet Propulsion Laboratory. Support for Y.-O. K. comes from the NOAA Office of Global Programs (grant to C. Deser and Y.-O. Kwon) and the WHOI Heyman fellowship

Northern hemisphere winter atmospheric transient eddy heat fluxes and the Gulf Stream and Kuroshio–Oyashio Extension variability

Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 26 (2013): 9839–9859, doi:10.1175/JCLI-D-12-00647.1.Spatial and temporal covariability between the atmospheric transient eddy heat fluxes (i.e., υ′T′ and υ′q′) in the Northern Hemisphere winter (January–March) and the paths of the Gulf Stream (GS), Kuroshio Extension (KE), and Oyashio Extension (OE) are examined based on an atmospheric reanalyses and ocean observations for 1979–2009. For the climatological winter mean, the northward heat fluxes by the synoptic (2–8 days) transient eddies exhibit canonical storm tracks with their maxima collocated with the GS and KE/OE. The intraseasonal (8 days–3 months) counterpart, while having overall similar amplitude, shows a spatial pattern with more localized maxima near the major orography and blocking regions. Lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts. Linear regression is used to examine the lead–lag relationship between interannual changes in the northward heat fluxes by the transient eddies and the meridional changes in the paths of the GS, KE, and OE, respectively. One to three years prior to the northward shifts of each ocean front, the atmospheric storm tracks shift northward and intensify, which is consistent with wind-driven changes of the ocean. Following the northward shifts of the ocean fronts, the synoptic storm tracks weaken in all three cases. The zonally integrated northward heat transport by the synoptic transient eddies increases by ~5% of its maximum mean value prior to the northward shift of each ocean front and decreases to a similar amplitude afterward.Support from the National Aeronautics and Space Administration (NASA) Physical Oceanography Program (NNX09AF35G to TJ and Y-OK) and the Department of Energy (DOE) Climate and Environmental Sciences Division (DE-SC0007052 to Y-OK) is gratefully acknowledged.2014-06-1

Interictal fatigue and its predictors in epilepsy patients: A case-control study

AbstractPurposeFatigue impairs the quality of life (QOL) of epilepsy patients, but few studies have investigated this issue and no systematic analysis of the predictors of fatigue in epilepsy patients has been performed. Thus, we investigated the degree and predictors of fatigue in epilepsy patients.MethodsWe enrolled 270 consecutive adult patients with epilepsy and categorized them into three subgroups: uncontrolled epilepsy (UCE), well-controlled epilepsy (WCE), and poorly controlled epilepsy (PCE). All subjects were asked to complete the Korean versions of the Fatigue Severity Scale (K-FSS), the Neurological Disorders Depression Inventory for Epilepsy (K-NDDI-E), the Generalized Anxiety Disorder-7 (K-GAD-7) scale, and the short forms of the Patient-Reported Outcomes Measurement Information System Sleep-Related Impairment (PROMIS-SRI) and Sleep Disturbance (PROMIS-SD) scales. Additionally, 200 normal control subjects who completed the K-FSS, K-NDDI-E, and K-GAD-7 measures were included. The K-FSS scores of the epilepsy subgroups and the control group were compared, and stepwise multiple regression analysis was performed to identify predictors of high scores on the K-FSS among epilepsy patients.ResultsThe K-FSS, K-NDDI-E, and K-GAD-7 scores were higher in the epilepsy patients than in the controls. The K-FSS scores of the UCE subgroup, but not of the PCE and WCE subgroups, were higher than those of the control group. K-FSS scores of epilepsy patients were predicted by PROMIS-SRI and K-NDDI-E scores.ConclusionsFatigue was more severe in epilepsy patients than in healthy controls without epilepsy, especially when seizures were not controlled. Sleep-related impairments and depression aggravated fatigue in epilepsy patients

Adjustment of a wind-driven two-layer system with mid-basin topography

A linear primitive equations model is used to simulate spin-up of a two-layer ocean bisected by a meridional ridge. The ocean is forced with steady zonal winds east of the ridge. When wind-driven barotropic planetary Rossby waves propagate across the ridge, barotropic and baroclinic anomalies are generated as the barotropic flow adjusts. These ridge-generated anomalies propagate westward from the ridge as planetary Rossby waves and their arrival along the basin\u27s western boundary modulates the western boundary current (WBC) transport and vertical structure. Model results suggest that at short (\u3c1 year) and long (\u3e10 years) delay relative to a change in wind stress curl, net WBC transport, TWBC, is that predicted by the Sverdrup balance for a flat ocean, TSv, but at intermediate delay this balance is disrupted by arrival of the additional barotropic ridge-generated anomalies. The magnitude of the anomalous transport, TWBC, depends on the meridional deflection of the flow at the ridge relative to the length-scale over which wind stress curl varies. The timescale, tBT, associated with adjustment at the ridge is a function of latitude, density contrast between layers and ridge width

On the effect of the East/Japan Sea SST variability on the North Pacific atmospheric circulation in a regional climate model

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Atmospheres 119 (2014): 418–444, doi:10.1002/2013JD020523.The East/Japan Sea (EJS) is a semi-enclosed marginal sea located in the upstream of the North Pacific storm track, where the leading modes of wintertime interannual variability in sea surface temperature (SST) are characterized by the basin-wide warming-cooling and the northeast-southwest dipole. Processes leading to local and remote atmospheric responses to these SST anomalies are investigated using the Weather Research and Forecast (WRF) model. The atmosphere in direct contact with anomalous diabatic forcing exhibits a linear and symmetric response with respect to the sign, pattern, and magnitude of SST anomalies, producing increased (decreased) wind speed and precipitation response over warm (cold) SSTs. This local response is due to modulation of both the vertical stability of the marine atmospheric boundary layer and the adjustment of sea level pressure, although the latter provides a better explanation of the quadrature relationship between SST and wind speed. The linearity in the local response suggests the importance of fine-scale EJS SSTs to predictability of the regional weather and climate variability. The remote circulation response, in contrast, is strongly nonlinear. An intraseasonal equivalent barotropic ridge emerges in the Gulf of Alaska as a common remote response independent of EJS SST anomalies. This downstream blocking response is reinforced by the enhanced storm track variability east of Japan via transient eddy vorticity flux convergence. Strong nonlinearity in remote response implies that detailed EJS SST patterns may not be critical to this downstream ridge response. Overall, results demonstrate a remarkably far-reaching impact of the EJS SSTs on the atmospheric circulation.H.S. gratefully acknowledges the support from the Penzance Endowed Fund in support of Assistant Scientists at WHOI. Y.-O.K. acknowledges NSF Climate and Large-Scale Dynamics program (AGS-1035423). H.S. and Y.-O.K. also thank NASA grant (NNX13AM59G)

Interannual variability of winter-spring temperature in the Middle Atlantic Bight : relative contributions of atmospheric and oceanic processes

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 4209–4227, doi:10.1002/2016JC011646.Relative contributions between the local atmospheric and oceanic processes on the interannual variability of winter-spring shelf temperature in the Middle Atlantic Bight (MAB) are investigated based on a regional ocean model. The model demonstrates sufficient capability to realistically simulate the interannual temperature changes during 2003–2014. On interannual time scales, the mean winter/spring temperature in the MAB is determined by the combination of the initial temperature at the beginning of the season and the mean cumulative air-sea flux, while the mean cumulative ocean advective flux plays a secondary role. In spite of the overall importance of air-sea flux in determining the winter and spring temperature, the relative contributions between air-sea flux and ocean advective flux on the evolution of the temperature anomaly in each individual year varies. The predictability of spring (April–June) temperature based on winter (January–March) temperature is weak because the temporal decorrelation time scale changes significantly from year to year. Both the highly variable shelf temperature and its decorrelation time scale are affected by the changes in the relative contributions between the air-sea flux and ocean advective flux.National Science Foundation Grant Number: OCE-14356022016-12-1