Papers by Jefferson Knight
Sea surface temperatures (SSTs) in the North Atlantic Ocean show multidecadal fluctuations known ... more Sea surface temperatures (SSTs) in the North Atlantic Ocean show multidecadal fluctuations known as the Atlantic Multidecadal Oscillation (AMO) . The AMO has been related to the thermohaline circulation, which implies a strong association to large-scale climate variability. Indeed, the variability of a wide range of climate parameters in the North Atlantic region has been related to the AMO, e.g. temperatures, precipitation, drought and hurricanes. Moreover, the AMO seems to influence the Asian summer monsoon, and South American precipitation. Most of these relationships have been established analyzing the short observational records or from experiments with climate models. In order to establish the stability of the multidecadal oscillation in the AMO as well as the association with climate, it is necessary to extend the record further back in time. Using tree-ring data from the Northern Hemisphere a reconstruction of the AMO, spanning AD 800 to 2000 is presented. The reconstruction suggests anomalously warm North Atlantic SSTs from ca. AD 900 to 1050, coinciding with the "Medieval Warm Period", as well as a phase between 1100 and 1400 with relatively little interdecadal variability. There is a prolonged negative phase of AMO from ca. 1600-1860, i.e. during the "Little Ice Age" (LIA). The multidecadal variability of approximately 40-80 years remains constant throughout the record, except around ca 1500-1700, i.e. during the LIA, when it breaks down.
Central placement of the screw in simulated fractures of the scaphoid waist: a biomechanical study
The Journal of bone and joint surgery. American volume, 2003
Recent reports on internal fixation of acute fractures of the scaphoid waist have demonstrated hi... more Recent reports on internal fixation of acute fractures of the scaphoid waist have demonstrated higher rates of central placement of the screw when cannulated screws were used than when noncannulated screws were used. This cadaveric study was designed to determine whether central placement in the proximal fragment of the scaphoid offers a biomechanical advantage. Eleven matched pairs of scaphoids were removed from fresh cadaveric wrists. Each scaphoid was placed in a custom manufactured jig that was used to create reproducible central and eccentric positioning of the guidewire. Then a linear osteotomy was made followed by placement of a Herbert-Whipple cannulated screw to fix the osteotomy. The specimen was then potted in a holder with use of polymethylmethacrylate with a Kirschner wire passed through the proximal end of the scaphoid and placed into a fixture with a pneumatically driven plunger resting on the surface of the distal pole. The load acting through the plunger was measure...
Day-case paediatric mastoid surgery
International journal of pediatric otorhinolaryngology, 2003
Children have traditionally been kept in hospital overnight after mastoid surgery, but evidence f... more Children have traditionally been kept in hospital overnight after mastoid surgery, but evidence from the US in adults suggests that a substantial number of patients may be suitable for discharge on the day of surgery. We sought to ascertain the proportion of our children having mastoid operations between February 1994 and December 2000 who were suitable for same-day discharge. We also evaluated some of the factors that prevented discharge the same day. A standard proforma was used to record relevant data in 35 children (mean age 10 years 6 months) undergoing consecutive mastoid operations at Mayday University Hospital, London, UK. Operative findings, duration of anaesthesia and time back on ward were recorded as well as details regarding admission, follow-up findings and complications. A bed was booked preoperatively but there was intent to discharge the patient if feasible. Nine out of twelve patients (75%) operated between 1998 and 2000 were suitable for discharge on the day of su...
Journal of Geophysical Research: Atmospheres, 2013
1] The surface response to 11 year solar cycle variations is investigated by analyzing the long-t... more 1] The surface response to 11 year solar cycle variations is investigated by analyzing the long-term mean sea level pressure and sea surface temperature observations for the period 1870-2010. The analysis reveals a statistically significant 11 year solar signal over Europe, and the North Atlantic provided that the data are lagged by a few years. The delayed signal resembles the positive phase of the North Atlantic Oscillation (NAO) following a solar maximum. The corresponding sea surface temperature response is consistent with this. A similar analysis is performed on long-term climate simulations from a coupled ocean-atmosphere version of the Hadley Centre model that has an extended upper lid so that influences of solar variability via the stratosphere are well resolved. The model reproduces the positive NAO signal over the Atlantic/European sector, but the lag of the surface response is not well reproduced. Possible mechanisms for the lagged nature of the observed response are discussed.
International Journal of Pediatric Otorhinolaryngology, 2006
Journal of Hydrometeorology, 2006
Data for water vapor adsorption and evaporation are presented for a bare soil (sandy loam, clay c... more Data for water vapor adsorption and evaporation are presented for a bare soil (sandy loam, clay content 15%) in a southern Spanish olive grove. Water losses and gains were measured using eight high-precision minilysimeters, placed around an olive tree, which had been irrigated until the soil reached field capacity (ϳ0.22 m 3 m Ϫ3 ). They were subsequently left to dry for 10 days. A pair of lysimeters was situated at each of the main points of the compass (N, E, S, W), at a distance of 1 m (the inner set of lysimeters; ILS) and 2 m (the outer set of lysimeters; OLS), respectively, from the tree trunk.
Journal of Geophysical Research, 2007
1] Three prominent quasi-global patterns of variability and change are observed using the Met Off... more 1] Three prominent quasi-global patterns of variability and change are observed using the Met Office's sea surface temperature (SST) analysis and almost independent night marine air temperature analysis. The first is a global warming signal that is very highly correlated with global mean SST. The second is a decadal to multidecadal fluctuation with some geographical similarity to the El Niño-Southern Oscillation (ENSO). It is associated with the Pacific Decadal Oscillation (PDO), and its Pacific-wide manifestation has been termed the Interdecadal Pacific Oscillation (IPO). We present model investigations of the relationship between the IPO and ENSO. The third mode is an interhemispheric variation on multidecadal timescales which, in view of climate model experiments, is likely to be at least partly due to natural variations in the thermohaline circulation. Observed climatic impacts of this mode also appear in model simulations. Smaller-scale, regional atmospheric phenomena also affect climate on decadal to interdecadal timescales. We concentrate on one such mode, the winter North Atlantic Oscillation (NAO). This shows strong decadal to interdecadal variability and a correspondingly strong influence on surface climate variability which is largely additional to the effects of recent regional anthropogenic climate change. The winter NAO is likely influenced by both SST forcing and stratospheric variability. A full understanding of decadal changes in the NAO and European winter climate may require a detailed representation of the stratosphere that is hitherto missing in the major climate models used to study climate change. (2007), Decadal to multidecadal variability and the climate change background,
Journal of Climate, 2008
Observed atmospheric circulation over the North Atlantic-European (NAE) region is examined using ... more Observed atmospheric circulation over the North Atlantic-European (NAE) region is examined using cluster analysis. A clustering algorithm incorporating a "simulated annealing" methodology is employed to improve on solutions found by the conventional k-means technique. Clustering is applied to daily mean sea level pressure (MSLP) fields to derive a set of circulation types for six 2-month seasons. A measure of the quality of this clustering is defined to reflect the average similarity of the fields in a cluster to each other. It is shown that a range of classifications can be produced for which this measure is almost identical but which partition the days quite differently. This lack of a unique set of circulation types suggests that distinct weather regimes in NAE circulation do not exist or are very weak. It is also shown that the stability of the clustering solution to removal of data is not maximized by a suitable choice of the number of clusters. Indeed, there does not appear to be any robust way of choosing an optimum number of circulation types. Despite the apparent lack of preferred circulation types, cluster analysis can usefully be applied to generate a set of patterns that fully characterize the different circulation types appearing in each season. These patterns can then be used to analyze NAE climate variability. Ten clusters per season are chosen to ensure that a range of distinct circulation types that span the variability is produced. Using this classification, the effect of forcing of NAE circulation by tropical Pacific sea surface temperature (SST) anomalies is analyzed. This shows a significant influence of SST in this region on certain circulation types in almost all seasons. A tendency for a negative correlation between El Niño and an anomaly pattern resembling the positive winter North Atlantic Oscillation (NAO) emerges in a number of seasons. A notable exception is November-December, which shows the opposite relationship, with positive NAO-like patterns correlated with El Niño.
Journal of Climate, 2013
2012: A new HadGEM3-A based system for attribution of weather and climate-related extreme events.... more 2012: A new HadGEM3-A based system for attribution of weather and climate-related extreme events. J. Climate. Abstract 26 27 A new system for attribution of weather and climate extreme events has been 28 developed based on the atmospheric component of the latest Hadley Centre model. 29 The model is run with either observational data of sea-surface temperature and sea-ice 30 or with estimates of what their values would be without the effect of anthropogenic 31 climatic forcings. In that way, ensembles of simulations are produced that represent 32 the climate with and without the effect of human influences. A comparison between 33 the ensembles provides estimates of the change in the frequency of extremes due to 34 anthropogenic forcings. To evaluate the new system, reliability diagrams are 35 constructed, which compare the model-derived probability of extreme events with 36 their observed frequency. The ability of the model to reproduce realistic distributions 37 of relevant climatic variables is another key aspect of the system evaluation. Results 38 are then presented from analyses of three recent high-impact events: the
Journal of Climate, 2012
Initial value predictability measures the degree to which the initial state can influence predict... more Initial value predictability measures the degree to which the initial state can influence predictions. In this paper the initial value predictability of six AOGCMs in the North Pacific and North Atlantic is quantified and contrasted by analyzing long control integrations with time invariant external conditions. Through application of analog and multivariate linear regression methodologies, average predictability properties are estimated for forecasts initiated from every state on the control trajectories. For basin wide measures of predictability, the influence of the initial state tends to last for roughly a decade in both basins, but this limit varies widely among the models, especially in the North Atlantic. Within each basin, predictability varies regionally by as much as a factor of ten for a given model, and the locations of highest predictability are different for each model. Model-to-model variations in predictability are also seen in the behavior of prominent intrinsic basin modes. Predictability is primarily determined by the mean of forecast distributions rather than the spread about the mean. Horizontal propagation plays a large role in the evolution of these signals and is therefore a key factor in differentiating the predictability of the various models.
Geophysical Research Letters, 2013
Clinical Otolaryngology and Allied Sciences, 2003
The aim of this study was to ®nd out from patients who had undergone a myringoplasty via either a... more The aim of this study was to ®nd out from patients who had undergone a myringoplasty via either an endaural or postaural approach whether or not they had experienced problems or symptoms relating to their scar, and if these differed depending on which incision had been used. A questionnaire was sent to 91 patients who had undergone myringoplasty between 18 and 62 months earlier. Thirty-four patients who had undergone previous or subsequent ear surgery were excluded. The only statistically signi®cant difference found between groups having either a postauricular or endaural incision was in how likely others were to comment on their scar. There seem to be few long-term sequealae relating to the scar from myringoplasty. From a patient perspective, between 18 and 62 months postoperatively, there was very little difference in symptoms or problems whether or not an endaural or a postaural incision had been used for the surgery.
Geophysical Research Letters, 2005
An ensemble of simulations of 20th Century climate using the HadCM3 coupled climate model forced ... more An ensemble of simulations of 20th Century climate using the HadCM3 coupled climate model forced with estimates of natural and anthropogenic forcings is compared with instrumental temperature data sets. The results show that while external climate forcing can account for most of 20th century climate change, there are also significant multidecadal climate fluctuations that are not produced by forcings. A major part of this variability corresponds to the `Atlantic Multidecadal Oscillation' (AMO), which has been identified in observations, and represents coherent fluctuations in temperature throughout most of the Northern Hemisphere. Using a 1400 year calculation with HadCM3 without external forcings, we show the model produces a quasi-periodic internal mode with a pattern, amplitude and characteristic time scale similar to that of the observed AMO. Further, the model implies the AMO is a genuine long-lived quasi-cyclical climate phenomenon related to large-scale oceanic heat transport variations associated with changes in the strength of the thermohaline circulation (THC) of about 2 Sv (10%). In the simulation, stronger cross-equatorial temperature gradients are associated with the anomalous northward ocean heat transport during a warm AMO phase. This causes a northward displacement of the mean ITCZ, leading to more rainfall and the development of anomalously fresh water in the tropical North Atlantic. These sustained anomalies slowly propagate to the subpolar North Atlantic in about 5 decades, where they act to slow the THC. The results also confirm observed links between the AMO and multidecadal variability in north-east Brazil and Sahel precipitation, and Atlantic hurricane formation. In addition, the simulated link between temperature and the THC allows an estimate of possible past changes in THC strength. Our results imply that the THC has undergone distinct strong and weak phases in the 20th century and has strengthened over recent decades. We also produce a forecast of the natural component of future THC change that shows a likely decline in the next 35 years to levels similar to the lowest levels reconstructed in the 20th century. This would accelerate anthropogenic THC weakening and the associated change in the AMO would offset Northern Hemisphere warming.
A simulated lagged response of the North Atlantic Oscillation to the solar cycle over the period 1960–2009
Environmental Research Letters, May 1, 2015
GloSea5: The new Met office high resolution seasonal prediction system
An improved operational Global Seasonal Forecast System (GloSea5) was introduced by the Met Offic... more An improved operational Global Seasonal Forecast System (GloSea5) was introduced by the Met Office in Spring 2013. The new system has an atmospheric resolution of approximately 40km in mid latitudes and 0.25 degree in the ocean. Hindcast simulations of past years show GloSea5 possesses unprecedented skill in predicting the winter North Atlantic Oscillation (NAO), with an anomaly correlation of 0.6 for the hindcast period. This represents a dramatic improvement over the current generation of seasonal prediction systems, which lack any significant skill in predicting the NAO (anomaly correlations less than 0.2). It suggests that slowly changing components in the climate system (e.g. ocean heat content anomalies) do indeed play an important role in the variability of extratropical atmospheric circulation in winter, as opposed to being predominantly unpredictable weather noise. Importantly, NAO predictability provides predictability of surface winter climate in Europe and the United Sta...
Nature Communications, 2015
Any reduction in global mean near-surface temperature due to a future decline in solar activity i... more Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming. However, variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects. Here, we explore possible impacts through two experiments designed to bracket uncertainty in ultraviolet irradiance in a scenario in which future solar activity decreases to Maunder Minimum-like conditions by 2050. Both experiments show regional structure in the wintertime response, resembling the North Atlantic Oscillation, with enhanced relative cooling over northern Eurasia and the eastern United States. For a high-end decline in solar ultraviolet irradiance, the impact on winter northern European surface temperatures over the late twenty-first century could be a significant fraction of the difference in climate change between plausible AR5 scenarios of greenhouse gas concentrations.
Improved predictions of global climate in the decade ahead using a new version of the Met Office Hadley Centre Decadal Prediction System
ABSTRACT The Met Office Hadley Centre Decadal Prediction System (DePreSys) produced the first ini... more ABSTRACT The Met Office Hadley Centre Decadal Prediction System (DePreSys) produced the first initialised short-term climate prediction in 2007. It showed, for the first time, that climate prediction up to a decade ahead was improved by including an accurate representation of the initial state of the ocean and atmosphere. Decadal predictions have subsequently been produced by a wide range of climate modelling centres, and this activity is an important new feature of IPCC AR5. Here, results from a comprehensively revised version of the Decadal Prediction System (DePreSys version 2) will be presented. The key enhancement is the use of the Met Office's latest climate model HadGEM3 within the forecast system (as opposed to the HadCM3 model used in the original system). This has approximately doubled the horizonal resolution of HadCM3, and quadrupled the number of vertical levels, in both atmospheric and oceanic components. In addition, the atmospheric component has an improved dynamical core, fully revised parameterisations, and is coupled to a different ocean model (NEMO). The initialisation methodology is essentially the same as for DePreSys version 1. Taking a global overview, indices of local predictive skill show significant improvements for key surface variables across a range of timescales relative to the previous system. In particular, there appears to be more skill in predicting multiannual to decadal variability in the Pacific Ocean and regions with which it has teleconnections. A forecast for global climate over the next few years produced by DePreSys version 2 will also be presented.
Tin-bismuth plating for component finishes
2011 IEEE 61st Electronic Components and Technology Conference (ECTC), 2011
... 6. CH Yu, HS Kang, KS Kim, SW Han, and KC Yang, Effects of Postbake on the Microstructure an... more ... 6. CH Yu, HS Kang, KS Kim, SW Han, and KC Yang, Effects of Postbake on the Microstructure and Whisker Growth of Matte Sn Finish, Proceedings of the 12th International Symposium on Advanced Packaging Materials: Processes, Properties, and Interfaces, APM 2007, pp. ...
Geophys. Res. Lett., 2014
Decadal variability in the North Atlantic and its subpolar gyre (SPG) has been shown to be predic... more Decadal variability in the North Atlantic and its subpolar gyre (SPG) has been shown to be predictable in climate models initialized with the concurrent ocean state. Numerous impacts over ocean and land have also been identified. Here we use three versions of the Met Office Decadal Prediction System to provide a multimodel ensemble forecast of the SPG and related impacts. The recent cooling trend in the SPG is predicted to continue in the next 5 years due to a decrease in the SPG heat convergence related to a slowdown of the Atlantic Meridional Overturning Circulation. We present evidence that the ensemble forecast is able to skilfully predict these quantities over recent decades. We also investigate the ability of the forecast to predict impacts on surface temperature, pressure, precipitation, and Atlantic tropical storms and compare the forecast to recent boreal summer climate.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 2010
Two chronic, traumatic brain injury (TBI) cases are presented, where cognitive function improved ... more Two chronic, traumatic brain injury (TBI) cases are presented, where cognitive function improved following treatment with transcranial light emitting diodes (LEDs). At age 59, P1 had closed-head injury from a motor vehicle accident (MVA) without loss of consciousness and normal MRI, but unable to return to work as development specialist in internet marketing, due to cognitive dysfunction. At 7 years post-MVA, she began transcranial LED treatments with cluster heads (2.1" diameter with 61 diodes each -9x633nm, 52x870nm; 12-15mW per diode; total power, 500mW; 22.2 mW/cm 2 ) on bilateral frontal, temporal, parietal, occipital and midline sagittal areas (13.3 J/cm 2 at scalp, estimated 0.4 J/cm 2 to brain cortex per area). Prior to transcranial LED, focused time on computer was 20 minutes. After 2 months of weekly, transcranial LED treatments, increased to 3 hours on computer. Performs nightly home treatments (now, 5 years, age 72); if stops treating >2 weeks, regresses. P2 (age 52F) had history of closed-head injuries related to sports/military training and recent fall. MRI shows fronto-parietal cortical atrophy. Pre-LED, was not able to work for 6 months and scored below average on attention, memory and executive function. Performed nightly transcranial LED treatments at home (9 months) with similar LED device, on frontal and parietal areas. After 4 months of LED treatments, returned to work as executive consultant, international technology consulting firm. Neuropsychological testing (post-9 months of transcranial LED) showed significant improvement in memory and executive functioning (range, +1 to +2 SD improvement). Case 2 reported reduction in PTSD symptoms.
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Papers by Jefferson Knight