Parameter space exploration of an ocean general circulation model using an isopycnal mixing parameterization

In this study we have employed statistical methods to efficiently design experiments and analyze output of an ocean general circulation model that uses an isopycnal mixing parameterization. Full ranges of seven inputs are explored using 51 numerical experiments. Fifteen of the cases fail to reach satisfactory equilibria. These are attributable to numerical limitations specific to the isopycnal model. Statistical approximating functions are evaluated using the remaining cases to determine the dependency of each of the six scalar outputs on the inputs. With the exception of one output, the approximating functions perform well. Known sensitivities, particularly the importance of diapycnal (vertical) eddy diffusivity and wind stress, are reproduced. The sensitivities of the model to two numerical constraints specific to the isopycnal parameterization, maximum allowable isopycnal slope and horizontal background eddy diffusivity, are explored. Isopycnal modelling issues, convection reduction and the Veronis effect, are examined and found to depend crucially on the isopycnal modelling constraints

Climate Change Scenarios for Hudson Bay, Canada, from General Circulation Models

Two generations of a climate model are compared using the impact of a CO2 doubling on the Hudson Bay region as the means of diagnosing differences in model performance. Surface temperature, precipitation, sea-ice coverage, and permafrost distribution are compared. The most striking difference is the response of the sea ice in the two models. In the coupled atmosphere-ocean climate model, sea ice virtually disappears in Hudson Bay. This leads to a substantially higher regional temperature response. We suggest that conductivity of sea ice and thermal diffusivity of seawater are key factors that cause the difference in sea-ice response. It is recommended that a regional model be developed to produce more representative climate change scenarios for the Hudson Bay region.On compare deux générations d'un modèle de climat en calculant l'incidence sur la région de la baie d'Hudson d'une multiplication par deux du taux de CO2 afin de diagnostiquer les différences dans la performance des deux versions du modèle. On compare la température en surface, les précipitations, la couverture de glace de mer et la distribution du pergélisol. La différence la plus marquante apparaît dans la façon dont la glace de mer réagit dans les deux modèles. Dans le modèle de climat avec couplage atmosphère-océan, la glace de mer disparaît pratiquement de la baie d'Hudson. Il en résulte une hausse notable de la température régionale. On suggère que la conductivité de la glace de mer et la diffusivité thermique de l'eau de mer sont des facteurs clés responsables de la différence dans le comportement de la glace de mer. On recommande l'élaboration d'un modèle régional qui créerait des scénarios de changement climatique plus réalistes pour la région de la baie d'Hudson

Isopycnal mixing and the Veronis effect in an ocean general circulation model

In this study we have run a number of numerical simulations to examine the ‘Veronis effect’ in an ocean general circulation model. This effect is characterized by anomalous interior downwelling, east of the western boundary current of an ocean basin. The impact of varying the horizontal diffusivity and the use of an isopycnal mixing parameterization are examined. Several diagnostics are used. The net volume transport for a sector in the southern part of the domain, east of the western boundary is found to be the clearest indicator of the strength of the Veronis effect. This effect is found to depend crucially on the horizontal diffusivity. The use of an isopycnal mixing parameterization significantly mitigates the interior downwelling problem but is constrained by the required use of a background horizontal diffusivity. Thus, in a geopotential coordinate model an isopycnal mixing parameterization enables the use of a significantly reduced horizontal diffusivity while emphasizing the mixing along isopycnals

Trends in the Dates of Ice Freeze-up and Breakup over Hudson Bay, Canada

Hudson Bay experiences a complete cryogenic cycle each year. Sea ice begins to form in late October, and the Bay is usually ice-free in early August. This seasonally varying ice cover plays an important role in the regional climate. To identify secular trends in the cryogenic cycle, we examined variability in the timing of sea-ice formation and retreat during the period 1971– 2003. The dates of ice freeze-up and breakup at 36 locations across Hudson Bay were catalogued for each year from weekly ice charts provided by the Canadian Ice Service. We used the nonparametric Mann-Kendall test to determine the statistical significance of the trends and the Theil-Sen approach to estimate their magnitude. Our results indicate statistically significant trends toward earlier breakup in James Bay, along the southern shore of Hudson Bay, and in the western half of Hudson Bay, and toward later freeze-up in the northern and northeastern regions of Hudson Bay. These trends in the annual ice cycle of Hudson Bay coincide with both the regional temperature record and the projections from general circulation models. If this trend toward a longer ice-free season continues, Hudson Bay will soon face important environmental challenges.Chaque année, la Baie d’Hudson connaît un cycle cryogénique complet. La formation de la glace marine commence en fin d’octobre et la baie est habituellement exempte de glace en début d’août. La présence saisonnière du couvert de la glace de la Baie d’Hudson revêt une importance primordiale sur le climat régional. Dans cet article, on étudie la variabilité des dates de formation et de retrait de la glace marine de la Baie d’Hudson dans le but d’identifier des tendances séculaires durant la période 1971 à 2003. Les dates de formation et de retrait de la glace marine ont été cataloguées pour tous les ans dans le cas de 36 endroits à travers la Baie d’Hudson et la Baie James en utilisant des images hebdomadaires publiées par le Service canadien des glaces. Le test non paramétrique Mann Kendall a été utilisé pour déterminer la signification statistique des tendances alors que la méthode de Theil Sen nous a fourni un estimé de l’ampleur de ces mêmes tendances. Notre analyse statistique nous indique qu’il existe des tendances significatives vers une date de déglacement plus avancée dans la Baie James, le long de la côte sud de la Baie d’Hudson, et dans la partie ouest de la Baie d’Hudson. De plus, des tendances significatives vers un gel plus tardif ont été observées dans les régions du nord et du nord-est de la Baie d’Hudson. Ces tendances dans le cycle annuel de glace de la Baie d’Hudson coïncident avec les tendances des températures de la région de même qu’avec les projections des modèles de circulation générale. Si cette tendance vers une durée plus courte du couvert de glace continue, la région de la Baie d’Hudson relèvera des défis environnementaux importants dans un proche avenir

East-West Asymmetry in Coastal Temperatures of Hudson Bay as a Proxy for Sea Ice

Hudson Bay experiences a complete cryogenic cycle, which has been well documented since 1971. We developed a temperature proxy method to extend the sea ice record back to 1944, using mean temperatures for Churchill and Inukjuak and the difference between these means at two different seasonal periods. This method proved to reproduce the 1971 to 2011 ice-free season length record with an error just over eight days (6%). This relationship was used to hindcast ice-free season length to 1944. This hindcast was subsequently appended to the existing 1971–2011 record to form a 68-year sea ice record. This extended record shows that the recent statistically significant increase in length of the ice-free season was not the result of a natural oscillation of less than 68 years and is consistent with a net warming due to increasing greenhouse gases.La baie d’Hudson connaît un cycle cryogénique complet, et celui-ci est bien répertorié depuis 1971. Nous avons élaboré une méthode d’obtention de données indirectes des températures afin d’étendre les données des températures jusqu’à 1944, en nous servant des températures moyennes pour Churchill et Inukjuak et de la différence entre ces moyennes à deux périodes saisonnières différentes. Cette méthode avait pour but de reproduire le registre des durées de saisons sans glace de 1971 à 2011, avec une marge d’erreur d’un peu plus de huit jours (6 %). Cette méthode a permis de faire la simulation rétrospective de la durée des saisons sans glace jusqu’en 1944. Par la suite, la simulation rétrospective a été appliquée au registre actuel de 1971–2011, ce qui a donné lieu à un registre sur la glace de mer réparti sur 68 années. Ce registre prolongé a permis de démontrer que la récente augmentation statistiquement différente en matière de durée de la saison sans glace ne découlerait pas d’une oscillation naturelle de moins de 68 ans, et qu’elle correspond à un réchauffement net attribuable à l’augmentation des gaz à effet de serre

Earth–Air Heat Exchanger Geo-Climatic Suitability for Projected Climate Change Scenarios in the Americas

Earth–air heat exchangers (EAHE) provide heating and cooling that is intrinsically tied to the climate of the surrounding environment. A climate-based approach was applied to 273 sites for both historical and projected climate conditions, with the latter being defined by three different Representative Concentration Pathways (RCPs) from the CMIP5 collection of Global Circulation Models (GCMs). Changes to heating and cooling degree hours as well as heating and cooling capacity were estimated and used to classify geo-climatic suitability. The analysis revealed cooler climates will retain their ability to provide cooling despite increasing cooling needs driven by warming temperatures. On the other hand, warmer, more tropical, climates will observe reduced suitability as cooling demand grows. The magnitude and variability of the changes in EAHE potential were greatest for the RCP8.5 scenario during the 2061–2090 time period, particularly for regions with a comparable mix of heating and cooling needs. Ultimately, the results demonstrate that future EAHE suitability is climate dependent, with cooler climates being relatively resistant to changes when compared to warmer climates. The results can be used by stakeholders to find useful climate analogs for their sites of interest to consider the potential impact of global climate change on EAHE usability

Collaborative Uses of Geospatial Technology to Support Climate Change Adaptation in Indigenous Communities of the Circumpolar North

A literature review is conducted of geospatial technologies in community-based research on ice and mobility among Indigenous people of the circumpolar north. Numerous studies explore the use of traditional knowledge in the Arctic on sea ice, but limited evidence of community-based research in sub-Arctic communities and in freshwater ice systems is found. Geographical Information Systems (GIS) and remote sensing tools have been applied in a variety of ways in support of community adaptations. These include the production of living memory maps, ice classification systems, and geodatabases that reflect the relationship-building nature of collaborations between Indigenous traditional knowledge holders and scientists. Satellite imagery—particularly synthetic aperture radar (SAR)—is widely used to characterize traditional understandings of ice to help tailor geospatial tools, climate research, and early warning systems, so that they may be used more effectively to address community interests and needs. As numerous mapping platforms have been developed in the circumpolar north, there are important considerations with respect to data management, Indigenous rights, and data sharing. We see opportunities for further research in lake and river ice, and in further developing early warning systems to address the growing problem of unpredictable ice regimes in Arctic and sub-Arctic regions

The effects of sodium bicarbonate supplementation at individual time-to-peak blood bicarbonate on 4-km cycling time trial performance in the heat.

The purpose of this study was to explore the effect of individualised sodium bicarbonate (NaHCO ) supplementation according to a pre-established individual time-to-peak (TTP) blood bicarbonate (HCO ) on 4-km cycling time trial (TT) performance in the heat. Eleven recreationally trained male cyclists (age: 28 ± 6 years, height: 180 ± 6 cm, body mass: 80.5 ± 8.4 kg) volunteered for this study in a randomised, crossover, triple-blind, placebo-controlled design. An initial visit was conducted to determine TTP HCO following 0.2 g.kg body mass (BM) NaHCO ingestion. Subsequently, on three separate occasions, participants completed a 4-km cycling TT in the heat (30 degrees centigrade; °C) (relative humidity ∼40%) following ingestion of either NaHCO (0.2 g.kg body mass), a sodium chloride placebo (0.2 g.kg BM; PLA) or no supplementation (control; CON) at the predetermined individual TTP HCO . Absolute peak [HCO ] prior to the 4-km cycling TT's was elevated for NaHCO compared to PLA (+2.8 mmol.l ;  = 0.002;  = 2.2) and CON (+2.5 mmol.l ;  < 0.001;  = 2.1). Completion time following NaHCO was 5.6 ± 3.2 s faster than PLA (1.6%; CI: 2.8, 8.3;  = 0.001;  = 0.2) and 4.7 ± 2.8 s faster than CON (1.3%; CI: 2.3, 7.1;  = 0.001;  = 0.2). These results demonstrate that NaHCO ingestion at a pre-established individual TTP HCO improves 4-km cycling TT performance in the heat, likely through enhancing buffering capacity

Canopy Interception of Acid Deposition in Southern Ontario

The impact of tree canopies on acid deposition was examined. Differences in the chemical composition of unintercepted precipitation (dustfall) and canopy was intercepted precipitation (throughfall) at 18 southern Ontario forests, collected during the summers of 1995-1996, were chemically analyzed. The methodology of collection and analysis validated using consistency checks for interception loss, maintenance of electrical neutrality and ion correlation. T-test analyses found throughfall fluxes of K+, Ca2+, Mg2+, and NO3- were significantly higher than dustfall flux (p &lt; 0.05), consistent with other studies. Barrie and nearby sites at Orillia and Bracebridge had larger dustfall depositions of base cations and Cl- suggesting a nearby source of these ions. T-tests revealed large exceedances of pH and sulphate concentration in dustfall over throughfall at the two Scarborough sites; a local point source of sulphates in the Greater Toronto Area was suspected

Sodium Bicarbonate Ingestion Improves Time-to-Exhaustion Cycling Performance and Alters Estimated Energy System Contribution:A Dose-Response Investigation

This study investigated the effects of two sodium bicarbonate (NaHCO3) doses on estimated energy system contribution and performance during an intermittent high-intensity cycling test (HICT), and time-to-exhaustion (TTE) exercise. Twelve healthy males (stature: 1.75 ± 0.08 m; body mass: 67.5 ± 6.3 kg; age: 21.0 ± 1.4 years; maximal oxygen consumption: 45.1 ± 7.0 ml.kg.min-1) attended four separate laboratory visits. Maximal aerobic power (MAP) was identified from an incremental exercise test. During the three experimental visits, participants ingested either 0.2 g.kg-1 BM NaHCO3 (SBC2), 0.3 g.kg-1 BM NaHCO3 (SBC3), or 0.07 g.kg-1 BM sodium chloride (placebo; PLA), 60 minutes pre-exercise. The HICT involved 3 x 60 s cycling bouts (90%, 95%, 100% MAP) interspersed with 90 s recovery, followed by TTE cycling at 105% MAP. Blood lactate was sampled after each cycling bout to calculate estimates for glycolytic contribution to exercise. Gastrointestinal (GI) upset was quantified at baseline, 30 minutes and 60 minutes post-ingestion, and 5 minutes post-exercise. Cycling TTE increased for SBC2 (+20.2 s; p =0.045) and SBC3 (+31.9 s; p =0.004) compared to PLA. Glycolytic contribution increased during the TTE protocol for SBC2 (+7.77 kJ; p =0.10) and SBC3 (+7.95 kJ; p =0.07) compared to PLA. GI upset was exacerbated post-exercise after SBC3 for nausea compared to SBC2 and PLA (p 0.05). Both NaHCO3 doses enhanced cycling performance and glycolytic contribution, however, higher doses may maximise ergogenic benefits