The sensitivity of North Atlantic Deep Water formation to variations in mean surface temperature is explored with a meridional-vertical plane ocean model coupled to an energy balance atmosphere. It ...is found that North Atlantic Deep Water formation is favored by a warm climate, while cold climates are more likely to produce Southern Ocean deep water or deep-decoupling oscillations (when the Southern sinking region is halocline covered). This behavior is traced to a cooling-induced convective instability near the North Atlantic sinking region, that is, to unstable horizontal spreading of a halocline that stratifies part of the region. Under the convective instability it is found that climate cooling is generally equivalent to increased freshwater forcing. This is because in a cold climate, high-latitude water masses approach the temperature of maximum density and the convection-driving, upward thermal buoyancy flux induced by surface cooling becomes insufficient to overcome the stratifying effect of surface freshening (a downward buoyancy flux). An extensive halocline is then formed and this halocline interferes with the heat loss necessary for the steady production of North Atlantic Deep Water.
Storm surge and coastal flooding caused by tropical cyclones (hurricanes) and extratropical cyclones (nor’easters) pose a threat to communities along the Atlantic coast of the United States. Climate ...change and sea level rise are altering the statistics of these extreme events in a rather complex fashion. Here we use a fully coupled global weather/climate modeling system (GFDL CM4) to study characteristics of extreme daily sea level (ESL) along the U.S. Atlantic coast and their response to global warming. We find that under natural weather processes, the Gulf of Mexico coast is most vulnerable to storm surge and related ESL. New Orleans is a striking hotspot with the highest surge efficiency in response to storm winds. Under a 1% per year atmospheric CO₂ increase on centennial time scales, the anthropogenic signal in ESL is robust along the U.S. East Coast. It can emerge from the background variability as soon as in 20 years, or even before global sea level rise is taken into account. The regional dynamic sea level rise induced by the weakening of the Atlantic meridional overturning circulation facilitates this early emergence, especially during wintertime coastal flooding associated with nor’easters. Along the Gulf Coast, ESL is sensitive to the modification of hurricane characteristics under the CO₂ forcing.
Recent laboratory and field studies point to an increase of sea salt aerosol (SSA) emissions with temperature, suggesting that SSA may lower climate sensitivity. We assess the impact of a strong ...(4.2% K
−1) and weak (0.7% K
−1) temperature response of SSA emissions on the climate sensitivity of the coupled climate model CM4. We find that the stronger temperature dependence improves the simulation of marine aerosol optical depth sensitivity to temperature and lowers CM4 Transient Climate Response (‐0.12 K) and Equilibrium Climate Sensitivity (‐0.5 K). At
CO2 doubling, the higher SSA emission sensitivity causes a negative radiative feedback (‐0.125
Wm−2K−1), which can only be partly explained by changes in the radiative effect of SSA (‐0.08
Wm−2K−1). Stronger radiative feedbacks are dominated by more negative low‐level cloud feedbacks in the Northern Hemisphere, which are partly offset by more positive feedbacks in the Southern Hemisphere associated with a weaker Atlantic Meridional Overturning Circulation.
Key Points
Satellite observations support an increase of sea salt emissions with temperature
Increasing sea salt emissions with temperature induces a negative radiative feedback of ‐0.1 W m
−2 K
−1 in CM4
Changes in sea surface temperature and AMOC modulate the sea salt feedback
We examined patients with clinical findings that are concerning for gallbladder malignancy to determine the incidence of pathology-confirmed malignancy and to discover factors that may be used to ...determine which patients may be initially treated with a laparoscopic approach.
All patients referred to a surgical oncologist with preoperative findings that are concerning for gallbladder malignancy who had not undergone previous surgical resection from 2005 to 2011 were reviewed. Variables collected included demographics, imaging, operative findings, and final pathology. Patients were grouped into 3 categories based on preoperative findings: gallbladder mass, irregular wall thickening, and abnormal intraoperative findings on previous diagnostic laparoscopy.
Twenty-nine of 4474 patients evaluated for gallbladder pathology during the study period met the inclusion criteria. Preoperative imaging included computed tomography, ultrasonography, and magnetic resonance imaging. Twelve patients had multiple imaging studies. Eight patients were initially treated with a laparoscopic approach with 3 conversions to an open procedure. Forty-eight percent of patients had pathology-confirmed malignancy. Patients without a discrete mass on imaging were more likely to have benign disease (P = .04).
Our results demonstrate that >50% of patients with suspicious preoperative findings had benign pathology, suggesting that the initial laparoscopic approach in selected patients may be appropriate.
This chapter contains sections titled:
Introduction
Elementary Arctic Climate Dynamics
Arctic Linearity in 21st Century Experiments
Arctic Nonlinearity in Annually Sea Ice‐Free Experiments
EBM ...Interpretation of the Transition to Annually Ice Free
Tethering Effect of Heat Transport
Summary and Discussion
Abstract
The continuing decline of the summertime sea ice cover has reduced the sea ice path that must be traversed to Arctic destinations and through the Arctic between the Atlantic and Pacific ...Oceans, stimulating interest in trans–Arctic Ocean routes. Seasonal prediction of the sea ice cover along these routes could support the increasing summertime ship traffic taking advantage of recent low ice conditions. We introduce the minimum Arctic sea ice path (MIP) between Atlantic and Pacific Oceans as a shipping-relevant metric that is amenable to multidecadal hindcast evaluation. We show, using 1992–2017 retrospective predictions, that bias correction is necessary for the GFDL Seamless System for Prediction and Earth System Research (SPEAR) forecast system to improve upon damped persistence seasonal forecasts of summertime daily MIP between the Atlantic and Pacific Oceans both east and west of Greenland, corresponding roughly to the Northeast and Northwest Passages. Without bias correction, only the Northwest Passage MIP forecasts have lower error than a damped persistence forecast. Using the forecast ensemble spread to estimate a lower bound on forecast error, we find large opportunities for forecast error reduction, especially at lead times of less than 2 months. Most of the potential improvement remains after linear removal of climatological and trend biases, suggesting that significant error reduction might come from improved initialization and simulation of subannual variability. Using a different passive microwave sea ice dataset for calculating error than was used for data assimilation increases the raw forecast errors but not the trend anomaly forecast errors.
The influence of changing ocean currents on climate change is evaluated by comparing an earth system model’s response to increased CO₂ with and without an ocean circulation response. Inhibiting the ...ocean circulation response, by specifying a seasonally varying preindustrial climatology of currents, has a much larger influence on the heat storage pattern than on the carbon storage pattern. The heat storage pattern without circulation changes resembles carbon storage (either with or without circulation changes) more than it resembles the heat storage when currents are allowed to respond. This is shown to be due to the larger magnitude of the redistribution transport—the change in transport due to circulation anomalies acting on control climate gradients—for heat than for carbon. The net ocean heat and carbon uptake are slightly reduced when currents are allowed to respond. Hence, ocean circulation changes potentially act to warm the surface climate. However, the impact of the reduced carbon uptake on radiative forcing is estimated to be small while the redistribution heat transport shifts ocean heat uptake from low to high latitudes, increasing its cooling power. Consequently, global surface warming is significantly reduced by circulation changes. Circulation changes also shift the pattern of warming from broad Northern Hemisphere amplification to a more structured pattern with reduced warming at subpolar latitudes in both hemispheres and enhanced warming near the equator.
The Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) aims to investigate the spread in simulations of sea-level and ocean climate change in response to CO2 forcing by atmosphere–ocean ...general circulation models (AOGCMs). It is particularly motivated by the uncertainties in projections of ocean heat uptake, global-mean sea-level rise due to thermal expansion and the geographical patterns of sea-level change due to ocean density and circulation change. FAFMIP has three tier-1 experiments, in which prescribed surface flux perturbations of momentum, heat and freshwater respectively are applied to the ocean in separate AOGCM simulations. All other conditions are as in the pre-industrial control. The prescribed fields are typical of pattern and magnitude of changes in these fluxes projected by AOGCMs for doubled CO2 concentration. Five groups have tested the experimental design with existing AOGCMs. Their results show diversity in the pattern and magnitude of changes, with some common qualitative features. Heat and water flux perturbation cause the dipole in sea-level change in the North Atlantic, while momentum and heat flux perturbation cause the gradient across the Antarctic Circumpolar Current. The Atlantic meridional overturning circulation (AMOC) declines in response to the heat flux perturbation, and there is a strong positive feedback on this effect due to the consequent cooling of sea-surface temperature in the North Atlantic, which enhances the local heat input to the ocean. The momentum and water flux perturbations do not substantially affect the AMOC. Heat is taken up largely as a passive tracer in the Southern Ocean, which is the region of greatest heat input, while the weakening of the AMOC causes redistribution of heat towards lower latitudes. Future analysis of these and other phenomena with the wider range of CMIP6 FAFMIP AOGCMs will benefit from new diagnostics of temperature and salinity tendencies, which will enable investigation of the model spread in behaviour in terms of physical processes as formulated in the models.
The current GFDL seasonal prediction system achieved retrospective sea ice extent (SIE) skill without direct sea ice data assimilation. Here we develop sea ice data assimilation, shown to be a key ...source of skill for seasonal sea ice predictions, in GFDL’s next-generation prediction system, the Seamless System for Prediction and Earth System Research (SPEAR). Satellite sea ice concentration (SIC) observations are assimilated into the GFDL Sea Ice Simulator version 2 (SIS2) using the ensemble adjustment Kalman filter (EAKF). Sea ice physics is perturbed to form an ensemble of ice–ocean members with atmospheric forcing from the JRA-55 reanalysis. Assimilation is performed every 5 days from 1982 to 2017 and the evaluation is conducted at pan-Arctic and regional scales over the same period. To mitigate an assimilation overshoot problem and improve the analysis, sea surface temperatures (SSTs) are restored to the daily Optimum Interpolation Sea Surface Temperature version 2 (OISSTv2). The combination of SIC assimilation and SST restoring reduces analysis errors to the observational error level (∼10%) from up to 3 times larger than this (∼30%) in the free-running model. Sensitivity experiments show that the choice of assimilation localization half-width (190 km) is near optimal and that SIC analysis errors can be further reduced slightly either by reducing the observational error or by increasing the assimilation frequency from every 5 days to daily. A lagged-correlation analysis suggests substantial prediction skill improvements from SIC initialization at lead times of less than 2 months.
We investigate the influence of ocean component resolution on simulation of climate sensitivity using variants of the GFDL CM2.5 climate model incorporating eddy‐resolving (1/10°) and ...eddy‐parameterizing (1°) ocean resolutions. Two parameterization configurations of the coarse‐resolution model are used yielding a three‐model suite with significant variation in the transient climate response (TCR). The variation of TCR in this suite and in an enhanced group of 10 GFDL models is found to be strongly associated with the control climate Atlantic meridional overturning circulation (AMOC) magnitude and its decline under forcing. We find that it is the AMOC behavior rather than resolution per se that accounts for most of the TCR differences. A smaller difference in TCR stems from the eddy‐resolving model having more Southern Ocean surface warming than the coarse models.
Key Points
Non‐eddying ocean component resolution need not bias TCRGFDL climate model simulations indicate a role for AMOC in TCRSouthern Ocean warming differs with ocean resolution
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