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

North Atlantic natural variability modulates emergence of widespread Greenland melt in a warming climate

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 Geophysical Research Letters 45 (2018): 9171-9178, doi:10.1029/2018GL079682.Record‐breaking melt over Greenland in recent decades is linked not only to climate change but also to natural variability, including persistent atmospheric high‐pressure conditions in the negative phase of the North Atlantic Oscillation and warm North Atlantic Ocean temperatures during the positive phase of the Atlantic Multidecadal Oscillation. However, the relative importance of natural variability for Greenland melt under varying degrees of greenhouse forcing is still unclear. Using reanalysis data and a large ensemble of climate model simulations, we find that a negative North Atlantic Oscillation and positive Atlantic Multidecadal Oscillation consistently promote heightened summer melt under various forcing conditions. Moreover, timing of widespread 21st century Greenland melt varies considerably between ensemble members due to different phasing of these modes of natural variability. These results indicate the importance of natural modes of variability across a range of external forcing conditions for interannual melt variability and the emergence of widespread Greenland melt.U.S. National Science Foundation Grant Number: ANS‐1736738; Woods Hole Oceanographic Institution Summer Student Fellow program Grant Number: AGS‐13553392019-03-1