Showing papers in "Atmosphere-ocean in 2001"
TL;DR: The UVic Earth System Climate Model as discussed by the authors consists of a three-dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea ice model, an energy-moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land-ice model.
Abstract: A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three‐dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea‐ice model, an energy‐moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land‐ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospher...
653 citations
TL;DR: The International North Water Project (INWP) as discussed by the authors used current meters to study the physical reasons for the existence of the North Water Polynya, a recurrent polynya at the northern end of Baffin Bay.
Abstract: The North Water Polynya is a recurrent polynya at the northern end of Baffin Bay. As part of the International North Water Project, recording current meters were moored within this polynya during 1997–98 to study the physical reasons for its existence. The data demonstrate that the North Water Polynya is dominated by a strong southward flow of cold water and ice from the Arctic Ocean. Although the West Greenland Current directs a modest flow of warmer water towards the polynya from the south‐east, this flow loses much of its heat south of the polynya through re‐circulation into and isopycnal mixing with the Arctic outflow. If an ice jam stops the inflow of ice from the north, the continued drift of ice southward ‘below’ the blockage is sufficient to create a large polynya without oceanic heating. However, upwelling near the Greenland coast can bring relatively warm water to the base of the turbulent surface layer where it is entrained via convection driven by brine growing from ice. The resulting...
193 citations
TL;DR: In this article, two texture feature extraction methods, Gabor filters and Markov random fields (MRF), are studied for image texture interpretation of SAR sea-ice imagery, and it is demonstrated that uniform quantization is a preferred quantization method compared to histogram equalization.
Abstract: Image texture interpretation is an important aspect of the computer‐assisted discrimination of Synthetic Aperture Radar (SAR) sea‐ice imagery. Co‐occurrence probabilities are the most common approach used to solve this problem. However, other texture feature extraction methods exist that have not been fully studied for their ability to interpret SAR sea‐ice imagery. Gabor filters and Markov random fields (MRF) are two such methods considered here. Classification and significance level testing shows that co‐occurrence probabilities classify the data with the highest accuracy, with Gaborfilters a close second. MRF results significantly lag Gabor and co‐occurrence results. However, the MRF features are uncorrelated with respect to co‐occurrence and Gabor features. The fused co‐occurrence/MRF feature set achieves higher performance. In addition, it is demonstrated that uniform quantization is a preferred quantization method compared to histogram equalization.
183 citations
TL;DR: In this article, a statistically significant relationship between seasonal snow cover and winter-time circulation anomalies over mid-high latitudes is demonstrated. But, the potential impact of snow cover anomalies on local and remote atmospheric dynamics is less understood.
Abstract: The importance of snow cover anomalies on the local energy balance is well known, however, the potential impact of snow cover anomalies on local and remote atmospheric dynamics is less understood. We present observational evidence demonstrating a statistically significant relationship between seasonal snow cover and winter‐time circulation anomalies over mid‐high latitudes. To explore snow forcing further, a General Circulation Model is used to test whether the local diabatic changes caused by snow cover can induce large‐scale dynamical responses. A six‐member ensemble, three winter month (DJF) integration is performed for a control case and a case where snow cover is increased as observed during the positive‐anomalous winter of 1977/1978. Snow cover variability results in altered general circulation patterns resembling observed anomaly patterns at mid‐high latitudes in the Northern Hemisphere winter.
117 citations
TL;DR: In this article, two dynamical models are used to perform a series of seasonal predictions, referred to as GCM2 and SEF, for climate studies and numerical weather prediction, respectively.
Abstract: Two dynamical models are used to perform a series of seasonal predictions. One model, referred to as GCM2, was designed as a general circulation model for climate studies, while the second one, SEF, was designed for numerical weather prediction. The seasonal predictions cover the 26‐year period 1969–1994. For each of the four seasons, ensembles of six forecasts are produced with each model, the six runs starting from initial conditions six hours apart. The sea surface temperature (SST) anomaly for the month prior to the start of the forecast is persisted through the three‐month prediction period, and added to a monthly‐varying climatological SST field. The ensemble‐mean predictions for each of the models are verified independently, and the two ensembles are blended together in two different ways: as a simple average of the two models, denoted GCMSEF, and with weights statistically determined to minimize the mean‐square error (the Best Linear Unbiased Estimate (BLUE) method). The GCMSEF winter and...
98 citations
TL;DR: In this paper, an overview of the meteorological and sea ice conditions within the northern portion of Baffin Bay and the region of the North Water (NOW) polynya between Ellesmere Island and Greenland is provided.
Abstract: In this paper we provide an overview of the meteorological and sea‐ice conditions within the northern portion of Baffin Bay and the region of the North Water (NOW) Polynya between Ellesmere Island and Greenland. Our results indicate an east‐west temperature gradient across the NOW and Baffin Bay regions with colder temperatures on the Ellesmere Island coast (‐14°C) and warmer temperatures on the Greenland coast (‐9°C). This is caused by warm air advection (upper level and boundary layer) due to prevailing atmospheric flows. The sea level pressure (SLP) pattern exhibits a pronounced inverted trough in Baffin Bay extending from a quasi‐stationary low south of Greenland. The trough deepens in winter thereby tightening the pressure gradient across the NOW region. This results in maximum winds (northerly) in winter. The trough also creates a mean cyclonic gyre in Baffin Bay, mirroring the spatial pattern of annual ice concentrations. The polynya is formed between November and March as a result of the ...
95 citations
TL;DR: In this article, the authors analyzed derived aerosol optical properties using datasets from the Canadian AEROCAN (AERosol CANada) sunphotometer network, which consists of eight sunphotometers distributed across Canada at sites chosen in order to obtain a diverse sampling of continental, maritime and arctic aerosols.
Abstract: Ground‐based sunphotometry measurements acquired under clear sky conditions can be used to investigate atmospheric aerosol optical properties. Such measurements are not only important in their own right as a technique for monitoring generic aerosol dynamics, but also represent a direct means of evaluating the contribution of aerosol induced radiative forcing in the modelling of climate change. In this paper we analyze derived aerosol optical properties using datasets from the Canadian AEROCAN (AERosol CANada) sunphotometer network. The AEROCAN network currently includes eight sunphotometers distributed across Canada at sites chosen in order to obtain a diverse sampling of continental, maritime and arctic aerosols. Some of these sites have been operational since 1993 as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). These instruments permit standard and automatic multi‐wavelength measurements of solar extinction radiance centred on the solar disk as well as sky radiance scans off the sola...
61 citations
TL;DR: In this paper, the spatial patterns of sea ice cover within the NOW region during the winter, spring and fall of 1998 in the context of polynya formation and maintenance mechanisms were examined.
Abstract: Polynyas represent polar oceanic areas with anomalous low sea‐ice concentrations. The North Water (NOW) Polynya refers to a region at the northern end of Baffin Bay which encompasses three separate polynyas. This paper examines the spatial patterns of sea‐ice cover within the NOW region during the winter, spring and fall of 1998 in the context of polynya formation and maintenance mechanisms. To accomplish this a sea‐ice classification scheme for RADARSAT‐1 ScanSAR imagery, obtained between 21 January and 7 December 1998, was developed and implemented within a Geographic Information System (GIS). The results identify a clear and consistent spatial structure of sea‐ice cover throughout the winter, spring and fall of 1998. Temporally, the polynya opened southward along the Canadian coast and westward away from the Greenland coast. Comparison with parallel oceanographic, atmospheric and ice motion studies suggested that the polynya was primarily controlled by a latent heat mechanism with the exceptio...
54 citations
TL;DR: In this article, a model is used to hindcast temperatures throughout the mainstem Fraser and Thompson Rivers back to 1953, and the average root mean square difference between model temperatures and those observed at Hell's Gate, on the lower Fraser River, is computed to be 1.12°C.
Abstract: In order to provide better estimates of the thermal‐induced stress encountered by salmon migrating to their spawning grounds, a model is used to hindcast temperatures throughout the mainstem Fraser and Thompson Rivers back to 1953. Tributary and headwater temperatures that are not available prior to 1993 are estimated with both linear regression and neural network techniques. The average root mean square difference between model temperatures and those observed at Hell's Gate, on the lower Fraser River, is computed to be 1.12°C. Historical flow and temperature observations are also used to establish patterns and trends for the Fraser River watershed. The Julian day numbers by which one‐third and one‐half of the integrated yearly discharge had occurred were computed and found to be progressing earlier at the rates of 0.11 and 0.09 days per year, respectively. Both values are significant at the 95% level. Average summer Hell's Gate temperatures from 1941 to 1998 are warming at the rate of 0.012°C pe...
53 citations
TL;DR: In this article, physical processes within the North Water (NOW) polynya were investigated and the results showed that the physical processes in NOW polynyas are very similar to ours.
Abstract: (2001). Physical processes within the North Water (NOW) polynya. Atmosphere-Ocean: Vol. 39, No. 3, pp. 163-166.
46 citations
TL;DR: In this paper, the utility of time series RADARSAT•1 Synthetic Aperture Radar (SAR) to detect melt onset (MO) and pond onset (PO) in the North Water (NOW) Polynya was evaluated.
Abstract: This paper evaluates the utility of time series RADARSAT‐1 Synthetic Aperture Radar (SAR) to detect melt onset (MO) and pond onset (PO) in the North Water (NOW) Polynya. SAR detected MO was associated with the approach of the daily average near‐surface air temperature (Tair) toward freezing, the beginning of a daily average surplus in the net all‐wave radiation flux (Q*), and a sharp decrease in the integrated shortwave albedo (α) at the surface. Relationships between microwave scattering and air, snow surface and ice surface temperature, up until MO, proved sensitive to the diurnal acquisition times of RADARSAT‐1. Time series results demonstrate that, despite its ‘uncalibrated’ status, RADARSAT‐1 ScanSAR data unambiguously identifies MO and PO over landfast First‐Year Ice (FYI) within the NOW Polynya. Spatially, results suggest a significantly earlier spring melt on the Greenland coast compared to the Ellesmere coast (10 to 15 days for regions between 77°N and 79°N and up to 45 days for regions ...
TL;DR: In this paper, two statistical methods: Gandin's point-to-point optimal interpolation and Kagan's pointto-area interpolation were applied to monthly, seasonal and annual total precipitation records gathered by a long-term, high quality, nationwide network of Canadian climate stations.
Abstract: Users of climate records frequently require data at geographical locations where no direct measurements of climatological variables are collected. Climatological conditions at the areas or points of interest have to be estimated by interpolating observations from neighbouring stations. An objective of assessing spatial representativeness of a network of observing stations is to outline the areas for which the network is capable of providing sufficiently accurate climatological information, i.e., where interpolation errors do not exceed a value acceptable to the user. Two statistical methods: Gandin's point‐to‐point optimal interpolation and Kagan's pointto‐area interpolation were applied to monthly, seasonal and annual total precipitation records gathered by a long‐term, high quality, nationwide network of Canadian climate stations. Due to substantial differences in seasonal climate conditions in the Arctic versus the rest of the country, the national network had to be split into two subsets: nor...
TL;DR: In this paper, a study of ice kinematics in the North Water (NOW) region was performed using time sequential and spatially overlapping RADARSAT•1 ScanSAR Wide images (January to December 1998) processed by the Canadian Ice Service (CIS) Ice Tracking Algorithm (Tracker).
Abstract: Monitoring ice motion may provide insight into the atmospheric and oceanic forces acting on ice motion and thus the mechanisms that contribute to polynya dynamics. A study of ice kinematics in the North Water (NOW) region was performed using time sequential and spatially overlapping RADARSAT‐1 ScanSAR Wide images (January to December 1998) processed by the Canadian Ice Service (CIS) Ice Tracking Algorithm (Tracker). The objectives of this research were to: 1) validate the NOW region ice motions derived using Tracker; 2) create monthly image‐maps that present ice speeds and directions over the NOW region for an entire year (January to December 1998); 3) compare these results to previous ice motion studies done in the NOW region; and 4) develop initial insights into relations between derived ice motion and latent and sensible heat mechanisms in the NOW Polynya. Tracker ice motions were validated using in situ ice beacons deployed between April and November 1998. Tracker magnitude and direction coef...
TL;DR: In this paper, the role of eddies in eddy-resolving 1 ½ and 2½ layer models with double-gyre wind forcing was investigated and it was shown that divergent part of the eddy flux of potential vorticity is directed down the mean thickness-weighted potential vORTicity gradient.
Abstract: We investigate some of the claims concerning new eddy parametrization schemes for coarse resolution ocean models by analyzing the role of eddies in eddy‐resolving 1½ and 2½ layer models with double‐gyre wind forcing. We find that the divergent part of the eddy flux of potential vorticity is directed down the mean thickness‐weighted potential vorticity gradient. The relationship between the eddy flux of thickness and either the mean thickness or mean thickness‐weighted potential vorticity gradients is less clear. The analysis is complicated by the presence of large rotational fluxes of both thickness and potential vorticity and by the importance of the Reynolds stress terms. We argue that the rotational fluxes have a fundamental role to play and need to be parametrized in a comprehensive parametrization scheme.
TL;DR: In this paper, the effects of clouds on the longwave and shortwave components of the Arctic surface radiation budget were studied using the CCGS Pierre Radisson in the North Water Polynya in spring and summer 1998.
Abstract: Measurements taken from the CCGS Pierre Radisson in the North Water Polynya in spring and summer 1998, are used to study the effects of clouds on the longwave and shortwave components of the Arctic surface radiation budget. The clear‐sky “baseline” is provided by parametrizations taken from the literature, tuned to the clear‐sky measurements taken during the cruise. The effects of clouds are examined in terms of cloud cover, cloud type, solar zenith angle and time of day. A diurnal signal in the cloud cover is found, with minimum values at local noon. The cloud forcing of the surface radiation was found to be mostly negative (i.e., clouds predominantly cool the surface when the sun is in the sky), with strong dependences on the solar zenith angle, cloud amount and whether the sun is obscured by clouds or is in clear sky; the influence of cloud type was secondary to these parameters.
TL;DR: In this article, surface incident radiation is a critical component of the Arctic surface energy balance making it important for sea ice model parametrizations to properly account for these fluxes.
Abstract: Surface incident radiation is a critical component of the Arctic surface energy balance making it important for sea‐ice model parametrizations to properly account for these fluxes. In this article,...
TL;DR: In 1998, the Royal Military College of Canada (BMC) installed a Quorum Advanced Very High Resolution Radiometer (AVHRR) ground station at Canadian Forces Station Alert (82°31'N 62°17'W), situated on the northern tip of Ellesmere Island.
Abstract: As part of an international study of the North Water Polynya, the Royal Military College of Canada (BMC) installed a Quorum Advanced Very High Resolution Radiometer (AVHRR) ground station at Canadian Forces Station Alert (82°31'N 62°17'W), situated on the northern tip of Ellesmere Island. The extreme northern location of the station permitted image reception every 1.7 hours. A total of 1440 images were recorded and stored between March and August 1998. Of particular interest was a rapidly sampled sequence on 16 and 17 June that documented the rapid dissolution of ice in Nares Strait, extending from the Lincoln Sea to Smith Sound. This allowed a systematic investigation of the effect of the time increment in calculating surface flow speeds in an energetic regime. A maximum cross‐correlation (MCC) ice‐tracking algorithm was applied to 10 images to study the southward movement of ice through the strait. The short time span between sequential images, ranging from 1.7 to 6.7 hours, provided a unique d...
TL;DR: An ice core sampling program was conducted during the North Water (NOW) Project 1998 Experiment in northern Baffin Bay during April-May 1998 as mentioned in this paper, where the physical properties of snow and sea ice as well as the microstructure and stable isotopic composition of first year landfast sea ice near the polynya were investigated.
Abstract: An ice core sampling program was conducted during the North Water (NOW) Polynya Project 1998 Experiment in northern Baffin Bay during April‐May 1998. The physical properties of snow and sea ice as well as the microstructure and stable isotopic composition of first‐year landfast sea ice near the polynya were investigated. The thickness of sea ice at the sampling sites ranged between 147 and 194 cm with thinner snow cover during the period between mid‐April and late May. The ice was characterized as typical first‐year landfast sea ice, being composed of a thin granular ice layer at the top and an underlying columnar ice layer towards the bottom of the ice. The samples obtained at a site closer to the ice edge of the polynya contained a thin granular ice layer originating from frazil ice near the ice bottom. Formation of frazil ice was considered to be caused by turbulent processes induced by winds, waves and currents forced from the polynya and also mixing with water masses produced at the polynya.
TL;DR: In this paper, the authors analyzed the dissolution of ice in Nares Strait using Advanced Very High Resolution Radiometer (AVHRR) data from March to August 1998, and found that in a four-day span, the area of open water increased from 400 km2 to 1200 km2.
Abstract: The North Water Polynya is the largest polynya in the Canadian Arctic. Its northern boundary is defined by a blockage, or ice bridge, that spans Smith Sound. The maintenance of the ice bridge, and the polynya itself, is contingent upon the southward flow of ice from the Lincoln Sea through Nares Strait. This paper analyzes the dissolution of ice in Nares Strait using Advanced Very High Resolution Radiometer (AVHRR) data. From March to August 1998, 1440 images were downloaded by a satellite receiver at Canadian Forces Station (CFS) Alert on the northern tip of Ellesmere Island. A preliminary evaluation of the data included a visual assessment of over 300 cloud‐free images. Of most interest were 42 images that revealed a rapid dissolution of ice in Nares Strait during mid‐June. In a four‐day span the area of open water in Nares Strait increased from 400 km2 to 1200 km2. Subsequent analysis of selected scenes included the application of both a sea and ice surface temperature algorithm. Based on the ...
TL;DR: The Canadian (London, Ontario) VHF Atmospheric Radar (CLOVAR) windprofiler radar near London, Ontario is a relatively new tool for atmospheric wind measurements.
Abstract: The Canadian (London, Ontario) VHF Atmospheric Radar (CLOVAR) windprofiler radar near London, Ontario is a relatively new tool for atmospheric wind measurements (Hocking, 1994, 1997a). In order to verify its proper performance, vertical profiles of horizontal winds were compared with other wind estimates available during the period January 1996 to November 1997. Comparisons with co‐located radiosonde flights (a series of 29 flights in May–June 1996, and another of 8 flights in May–July 1997) showed excellent agreement between the two techniques. In addition, comparisons with horizontal winds measured by routine radiosonde balloons launched some 180 km south‐west of London, at White Lake (Detroit), and some 210 km east of London at Buffalo Airport, showed good agreement, considering the meteorological differences which would be expected at these ranges. A further comparison between winds measured with the radar, and winds extracted for London from Canadian Meteorological Centre (CMC) regional anal...
TL;DR: In this article, two integrations of the Canadian Middle Atmosphere Model (CMAM) are compared to assess the effects of parametrized non-orographic gravity waves on the frequency and timing of stratospheric sudden warmings (SSWs), as well as on the potential for polar stratosphere cloud (PSC) formation.
Abstract: Arctic polar vortex variability in the Canadian Middle Atmosphere Model (CMAM) is documented. Two integrations of the CMAM are compared to assess the effects of parametrized non-orographic gravity waves on the frequency and timing of stratospheric sudden warmings (SSWs), as well as on the potential for polar stratospheric cloud (PSC) formation. The first integration does not include parametrized non-orographic gravity waves while the second integration does. The first integration captures the basic features of the observed north- ern hemisphere (NH) winter circulation although the polar night jet (PNJ) is significantly too weak and poleward shifted. Together with the weaker than observed PNJ are SSWs that occur too often and too early, resulting in an unrealistically low early to mid-winter potential for PSC formation. Whereas, by design, the inclusion of param- etrized non-orographic gravity waves in the second integration significantly improves the southern hemisphere (SH) circulation, the strength of the NH PNJ is further reduced relative to the first integration, and the SSW fre- quency and PSC formation potential further degraded. Finally, the synoptic evolution and wavebreaking signa- ture of the simulated and observed SSW events are compared through the application of a composite high resolution contour advection algorithm. RESUME (Traduit par la redaction) La variabilite du tourbillon circumpolaire arctique dans le modele canadien de l'atmosphere moyenne (CMAM) est documentee. Deux integrations du CMAM sont comparees afin d'evaluer les effets des ondes de gravite non orographiques parametrees sur la frequence et le moment d'occurrence des rechauffements stratospheriques soudains (SSW) ainsi que sur le potentiel de formation de nuages stratospheriques polaires (PSC). La premiere integration n'inclut pas les ondes de gravite non orographiques parametrees, tandis que la seconde les inclut. La premiere integration saisit les caracteristiques fondamentales de la circulation hivernale observee dans l'hemisphere Nord quoique le courant-jet polaire (PNJ) soit decidement trop faible et devie vers le nord. Accompagnant le PNJ plus faible qu'observe, il y a les SSW qui se produisent trop frequemment et trop tot, ce qui entraine un faible potentiel non realiste pour la formation de PSC au debut et au milieu de l'hiver. Alors que, par conception, l'inclusion d'ondes de gravite non orographiques parametrees dans la seconde integration ameliore sensiblement la circulation dans l'hemisphere Sud, la force du PNJ dans l'hemisphere Nord est reduite davantage relativement a la premiere integration et la frequence de SSW ainsi que le potentiel de formation de PSC sont de nouveau diminues. Finalement, l'evolution synoptique et la signature de bris d'ondes des evenements de SSW simules et observes sont comparees par l'application d'un algorithme combine d'advection de contours a haute resolution.
TL;DR: In this paper, the temporal variation of sea and land ice backscatter of twenty-four SAR images from the European Remote Sensing satellite (ERS•1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992.
Abstract: Synthetic Aperture Radar (SAR) data has become an important tool for studies of polar regions, due to high spatial resolution even during the polar night and under cloudy skies. We have studied the temporal variation of sea and land ice backscatter of twenty‐four SAR images from the European Remote Sensing satellite (ERS‐1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992. The presence of fast ice in Jones Sound and glaciers and ice caps on the surrounding islands provides an ideal setting for temporal backscatter studies of ice surfaces. Sample regions for eight different ice types were selected and the temporal backscatter variation was studied. The observed backscatter values for each ice type characterize the radar signatures of the ice surfaces. This time series of twenty‐four SAR images over a 3‐month period provides new insights into the degree of temporal variability of each surface. Ice caps exhibit the highest backscatter value of ‐3.9 dB with hig...
TL;DR: In this paper, the mean climatological circulation on the central Scotian Shelf was investigated during the summer (August-September) and late fall (November-December) by applying a diagnostic model coupled with a variational approach.
Abstract: The mean climatological circulation on the central Scotian Shelf was investigated during the summer (August–September) and late fall (November–December) by applying a diagnostic model coupled with a variational approach. Historical Conductivity‐Temperature‐Depth (CTD) profiles, current meter observations and atmospheric climatological data were applied to the model. The reconstructed fields of temperature, salinity and velocity are dynamically balanced and provide estimates of the circulation features on Western Bank for the summer and fall. The availability of new direct current measurements on and around Western Bank enabled us to define the barotropic velocity field and to produce realistic circulation patterns. The primary difference between the summer and fall circulation is the intensification of the surface flow field in the fall. The transport of the Nova Scotia current increases from 0.4 Sv in summer to 0.9 Sv in the fall. At the same time, some qualitative differences were found over We...
TL;DR: In this paper, the impact of the more sophisticated Canadian Land Surface Scheme (CLASS) on the predictability of the fluxes, using the operational configuration of the global model with the force-restore land surface scheme as a baseline for comparison.
Abstract: As part of the Mackenzie GEWEX Study (MAGS), Canadian global spectral forecast model (SEF) monthly simulations of surface water and energy fluxes averaged over the Mackenzie river basin are examined. We study the impact of the more sophisticated Canadian Land‐Surface Scheme (CLASS) on the predictability of the fluxes, using the operational configuration of the global model with the force‐restore land‐surface scheme as a baseline for comparison. The model, connected successively to the current operational force‐restore land surface scheme and to CLASS, generates nine‐member ensemble simulations of one month duration from analyses perturbed with the Monte‐Carlo method, for spring, summer, fall and winter cases. The perturbations are comparable in magnitude to observational errors. The flux predictability is measured by the degree to which the individual forecasts in the ensembles vary from one another. The mean of the ensemble forecasts is compared with monthly accumulations of surface energy and w...
TL;DR: In this paper, the authors show that annual precipitation was essentially constant during the 1918 − 1994 period in the Moose River Basin (MRB), after several inhomogeneities were accounted for.
Abstract: Annual water balance time series (precipitation, runoff, evaporation) for sub‐basins in the southern portion of the Moose River Basin (MRB) of northeastern Ontario and western Quebec previously suggested that both annual evaporation and precipitation increased by ∼2 mm y−1 during the 1918 ‐1994 period. However, summer air temperature data were not consistent with evaporation increases of that magnitude. Suspected inhomogeneities (i.e., non‐climatic steps or trends associated with changes in measurement procedure or site exposure) in precipitation records for the MRB region indicated significant underestimation of annual precipitation prior to 1950. Temporal trends in rehabilitated precipitation datasets obtained from the Meteorological Service of Canada revealed that annual precipitation was essentially constant during the 1918 ‐ 1994 period in the MRB, after several inhomogeneities were accounted for. This contradicts previously reported increases in precipitation for the region, and results ind...
TL;DR: In this article, a steady-state solution of the linearized thermocline equations satisfying prescribed fluxes of heat and salt at the base of the surface Ekman layer, is presented for a semi-infinite ocean of constant depth.
Abstract: In this paper, new steady‐state solutions of the linearized thermocline equations satisfying prescribed fluxes of heat and salt at the base of the surface Ekman layer, are presented for a semi‐infinite ocean of constant depth. A decomposition into vertical modes is used to solve the problem. The solution is first determined in terms of a derivative of the unknown density at the surface and this derivative is then determined from an integral equation arising from applying the surface thermohaline boundary conditions. Solutions forced by wind stress alone, and by wind stress and thermohaline forcing are considered. The wind‐driven solution exhibits a temperature field with many realistic features, such as largest meridional gradients in the sub‐polar gyre, and the latitudinal spreading of isotherms towards the eastern boundary. The wind‐driven salinity field increases towards the poles, contrary to the observed annual mean salinity field. The stability of the sub‐tropical gyre is enhanced, whilst t...
TL;DR: In this article, two variants of the modelled turbulent heat flux vector are presented and their performance in the simulation of the lifting of an atmospheric inversion is discussed, where the turbulent flux is expressed in both algebraic and differential forms.
Abstract: Improved prediction of complex transport processes usually requires an application of advanced turbulence models. In some particular cases, such as environmental flows, where a variety of physical and thermodynamical processes may occur simultaneously, it is not an easy task to apply a consistent approach for all modelled variables of interest. Consequently, this suggests the use of simple model formulations. In seeking an acceptable turbulence model for the computation of buoyancy dominated turbulent flows, two variants of the modelled turbulent heat flux vector are presented and their performance in the simulation of the lifting of an atmospheric inversion is discussed. By these variants the turbulent heat flux is expressed in both algebraic and differential forms. In applying the algebraic heat flux turbulence model, it was necessary to solve the transport equation for temperature variance and retain its explicit influence in the derived algebraic heat flux model in order to obtain results of ...
TL;DR: In this paper, two oceanic mechanisms that might contribute to a resolution of this paradox are examined, one relies upon salinity re-distribution, while the other relies upon the nonlinearity of the equation of state.
Abstract: Paleoclimcite data indicate a climate paradox. In warmer climates the equator to pole temperature gradient is typically less than that of the current climate. However, more northward heat transport is required to maintain this weaker gradient, particularly in tropical, subtropical and midlatitude regions where the ice‐albedo feedback and polar stratification of the atmosphere have little effect. Most heat transport mechanisms decrease with decreased temperature gradient. Two oceanic mechanisms that might contribute to a resolution of this paradox are examined, one relies upon salinity re‐distribution, while the other relies upon the non‐linearity of the equation of state. These are tested in a simply configured ocean general circulation model of the North Atlantic. Both are shown to increase northward heat transport without increasing the meridional temperature gradient. The nonlinearity mechanism is the more significant of the two, but neither of the mechanisms can conclusively resolve the paradox.