Search Results

You are looking at 1 - 10 of 10 items for

  • Author or Editor: Christopher Spence x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
Christopher Spence and Wayne R. Rouse

Abstract

The objective of the study is to determine the local processes that control the partitioning of the energy budget of shield terrain in the western Canadian subarctic. The magnitude of the spring snowmelt and its potential to flood exposed bedrock portions of the landscape control the energy budget in the early part of the summer. In wet years, Bowen ratios are low and increase over the growing season. The high latent heat fluxes early in the year are promoted by water pooled in bedrock depressions and stored in the shallow soil. The high evaporation rates deplete moisture storage by the end of July after which latent heat fluxes decrease so that Bowen ratios exceed unity until the end of the growing season. This regime differs from other subarctic terrain types with similar vegetation. Exposed and shallow Precambrian bedrock keeps water close to the topographic surface and available for evaporation. The low surface resistance of ponded water on the bedrock surface and high vapor pressure deficits are possible causes for the high evaporation rates in June and July. However, in drier years, when ponded snowmelt water is minimal, evaporation is small and sensible heat dominates the early summer energy budget to a much larger degree than is observed elsewhere in the subarctic. It then becomes a very arid landscape. High evaporation-to-precipitation ratios throughout the summer are an important feature of the western Canadian Shield subarctic region, and this feature has significant hydrological implications. It is normal for a moisture deficit to be created each summer. The magnitude of this moisture deficit is the primary control on hillslope runoff response to precipitation later in the summer and autumn.

Full access
Christopher Spence, Wayne R. Rouse, Devon Worth, and Claire Oswald

Abstract

There is a paucity of information on the energy budget of Canada's northern lakes. This research determines processes controlling the magnitude of energy fluxes between a small Canadian Shield lake and the atmosphere. Meteorological instruments were deployed on a floating platform in the middle of a 5-ha lake during the 1999 and 2000 open-water seasons. High attenuation of incoming radiation at shallow depths and the sheltered location of the lake allows a strong thermocline to develop during the summer months, which prevents deeper water from exchanging energy with the atmosphere. Only after the lake becomes isothermal in late August do deeper waters interact with the atmosphere. When the lake is warming, evaporation is controlled by net radiation, but when the lake is cooling, turbulent energy fluxes are mainly influenced by the vapor pressure deficit. An empirically derived logarithmic relationship was identified between the Bowen ratio and the vapor pressure deficit. The Canadian Global Energy and Water Cycle Experiment (GEWEX) Enhanced Study (CAGES) water year was characterized by a cool dry July that prevented the lake from warming to expected normal conditions. With less of the available energy directed to heating the lake, more was available for the turbulent fluxes, but evaporation rates did not increase. Because of the inability of radiation to penetrate to deep water in this lake, it is unlikely that even local extremes in air temperature and incoming solar radiation create the summer isothermal conditions observed in more southern Canadian Shield lakes, which allow more energy to be directed toward evaporation during the summer months.

Full access
Zuohao Cao, Murray D. Mackay, Christopher Spence, and Vincent Fortin

Abstract

Sensible and latent heat fluxes over Lake Superior are computed using a variational approach with a Bowen ratio constraint and inputs of 7 years of half-hourly temporal resolution observations of hydrometeorological variables over the lake. In an advancement from previous work focusing on the sensible heat flux, in this work computations of the latent heat flux are required so that a new physical constraint of the Bowen ratio is introduced. Verifications are made possible for fluxes predicted by a Canadian operational coupled atmosphere–ocean model due to recent availabilities of observed and model-predicted fluxes over Lake Superior. The observed flux data with longer time periods and higher temporal resolution than those used in previous studies allows for the examination of detailed performances in computing these fluxes. Evaluations utilizing eddy-covariance measurements over Lake Superior show that the variational method yields higher correlations between computed and measured sensible and latent heat fluxes than a flux-gradient method. The variational method is more accurate than the flux-gradient method in computing these fluxes at annual, monthly, daily, and hourly time scales. Under both unstable and stable conditions, the variational method considerably reduces mean absolute errors produced by the flux-gradient approach in computing the fluxes. It is demonstrated with 2 months of data that the variational method obtains higher correlation coefficients between the observed and the computed sensible and latent heat fluxes than the coupled model predicted, and yields lower mean absolute errors than the coupled model. Furthermore, comparisons are made between the coupled-model-predicted fluxes and the fluxes computed based on three buoy observations over Lake Superior.

Full access
Daniel Deacu, Vincent Fortin, Erika Klyszejko, Christopher Spence, and Peter D. Blanken

Abstract

The paper presents the incremental improvement of the prediction of the Great Lakes net basin supply (NBS) with the hydrometeorological model Modélisation Environmentale–Surface et Hydrologie (MESH) by increasing the accuracy of the simulated NBS components (overlake precipitation, lake evaporation, and runoff into the lake). This was achieved through a series of experiments with MESH and its parent numerical weather prediction model [the Canadian Global Environmental Multiscale model in its regional configuration (GEM Regional)]. With forcing extracted from operational GEM Regional forecasts, MESH underestimated the NBS in fall and winter. The underestimation increased when the GEM precipitation was replaced with its corrected version provided by the Canadian Precipitation Analysis. This pointed to overestimated lake evaporation and prompted the revision of the parameterization of the surface turbulent fluxes over water used both in MESH and GEM. The revised parameterization was validated against turbulent fluxes measured at a point on Lake Superior. Its use in MESH reduced the lake evaporation and largely corrected the NBS underestimation. However, the Lake Superior NBS became overestimated, signaling an inconsistency between the reduced lake evaporation and the prescribed precipitation. To remove the inconsistency, a new forcing dataset (including precipitation) was generated with the GEM model using the revised flux parameterization. A major NBS simulation improvement was obtained with the new atmospheric forcing reflecting the atmospheric response to the modified surface fluxes over the lakes. Additional improvements resulted by correcting the runoff with a modified snowmelt rate and by insertion of observed streamflows. The study shows that accurate lake evaporation simulation is crucial for accurate NBS prediction.

Full access
Wayne R. Rouse, Claire M. Oswald, Jacqueline Binyamin, Peter D. Blanken, William M. Schertzer, and Christopher Spence

Abstract

This paper addresses interannual and seasonal variability in the thermal regime and surface energy fluxes in central Great Slave Lake during three contiguous open-water periods, two of which overlap the Canadian Global Energy and Water Cycle Experiment (GEWEX) Enhanced Study (CAGES) water year. The specific objectives are to compare the air temperature regime in the midlake to coastal zones, detail patterns of air and water temperatures and atmospheric stability in the central lake, assess the role of the radiation balance in driving the sensible and latent heat fluxes on a daily and seasonal basis, quantify magnitudes and rates of the sensible and latent heat fluxes and evaporation, and present a comprehensive picture of the seasonal and interannual thermal and energy regimes, their variability, and their most important controls. Atmospheric and lake thermal regimes are closely linked. Temperature differences between midlake and the northern shore follow a seasonal linear change from 6°C colder midlake in June, to 6°C warmer in November–December. These differences are a response to the surface energy budget of the lake. The surface radiation balance, and sensible and latent heat fluxes are not related on a day-to-day basis. Rather, from final lake ice melt in mid-June through to mid- to late August, the surface waters strongly absorb solar radiation. A stable atmosphere dominates this period, the latent heat flux is small and directed upward, and the sensible heat flux is small and directed downward into the lake. During this period, the net solar radiation is largely used in heating the lake. From mid- to late August to freeze up in December to early January, the absorbed solar radiation is small, the atmosphere over the lake becomes increasingly unstable, and the sensible and latent heat fluxes are directed into the atmosphere and grow in magnitude into the winter season. Comparing the period of stable atmospheric conditions with the period of unstable conditions, net radiation is 6 times larger during the period of stable atmosphere and the combined latent and sensible heat fluxes are 9 times larger during the unstable period. From 85% to 90% of total evaporation occurs after mid-August, and evaporation rates increase continuously as the season progresses. This rate of increase varies from year to year. The time of final ice melt exerts the largest single control on the seasonal thermal and energy regimes of this large northern lake.

Full access
Wayne R. Rouse, Peter D. Blanken, Normand Bussières, Anne E. Walker, Claire J. Oswald, William M. Schertzer, and Christopher Spence

Abstract

Great Slave Lake and Great Bear Lake have large surface areas, water volumes, and high latitudinal positions; are cold and deep; and are subject to short daylight periods in winter and long ones in summer. They are dissimilar hydrologically. Great Slave Lake is part of the Mackenzie Basin flowthrough system. Great Bear Lake is hydrologically isolated in its own relatively small drainage basin and all of its inflow and outflow derive from its immediate watershed. Great Slave Lake’s outflow into the Mackenzie River is more than 8 times that from Great Bear Lake. Input from the south via the Slave River provides 82% of this outflow volume. These hydrological differences exert pronounced effects on the thermodynamics, hydrodynamics, and surface climates of each lake. The quantitative results in this study are based on limited datasets from different years that are normalized to allow comparison between the two lakes. They indicate that both lakes have regional annual air temperatures within 2°C of one another, but Great Slave Lake exhibits a much longer open-water period with higher temperatures than Great Bear Lake. During the period when the lakes are warming, each lake exerts a substantial overlake atmospheric cooling, and in the period when the lakes are cooling, each exerts a strong overlake warming. This local cooling and warming cycle is greatest over Great Bear Lake. Temperature and humidity inversions are frequent early in the lake-warming season and very strong lapse gradients occur late in the lake-cooling season. Annually, for both lakes, early ice breakup is matched with late freeze-up. Conversely, late breakup is matched with early freeze-up. The magnitudes of midlake latent heat fluxes (evaporation) and sensible heat fluxes from Great Slave Lake are substantially larger than those from Great Bear Lake during their respective open-water periods. The hypothesis that because they are both large and deep, and are located in high latitudes, Great Slave Lake and Great Bear Lake will exhibit similar surface and near-surface climates that are typical of large lakes in the high latitudes proves invalid because their different hydrological systems impose very different thermodynamic regimes on the two lakes. Additionally, such an extensive north-flowing river system as the Mackenzie is subjected to latitudinally variable meteorological regimes that will differentially influence the hydrology and energy balance of these large lakes. Great Slave Lake is very responsive to climatic variability because of the relation between lake ice and absorbed solar radiation in the high sun season and we expect that Great Bear Lake will be affected in a similar fashion.

Full access
Justin R. Minder, W. Massey Bartolini, Christopher Spence, Newell R. Hedstrom, Peter D. Blanken, and John D. Lenters

Abstract

Lake-effect snow (LeS) storms are driven by strong turbulent surface layer (SL) and planetary boundary layer (PBL) fluxes of heat and moisture caused by the flow of cold air over relatively warm water. To investigate the sensitivity of simulated LeS to the parameterization of SL and PBL turbulence, high-resolution simulations of two major storms, downwind of Lakes Superior and Ontario, are conducted using the Weather Research and Forecasting Model. Multischeme and parameter sensitivity experiments are conducted. Measurements of overlake fluxes and downwind snowfall are used to evaluate the simulations. Consistent with previous studies, LeS is found to be strongly sensitive to SL and PBL parameterization choices. Simulated precipitation accumulations differ by up to a factor of 2 depending on the schemes used. Differences between SL schemes are the dominant source of this sensitivity. Parameterized surface fluxes of sensible and latent heat can each vary by over 100 W m−2 between SL schemes. The magnitude of these fluxes is correlated with the amount of downwind precipitation. Differences between PBL schemes play a secondary role, but have notable impacts on storm morphology. Many schemes produce credible simulations of overlake fluxes and downwind snowfall. However, the schemes that produce the largest surface fluxes produce fluxes and precipitation accumulations that are biased high relative to observations. For two SL schemes studied in detail, unrealistically large fluxes can be attributed to parameter choices: the neutral stability turbulent Prandtl number and the threshold friction velocity used for defining regimes in the overwater surface roughness calculation.

Free access
Wayne R. Rouse, Claire J. Oswald, Jacqueline Binyamin, Christopher Spence, William M. Schertzer, Peter D. Blanken, Normand Bussières, and Claude R. Duguay

Abstract

There are many lakes of widely varying morphometry in northern latitudes. For this study region, in the central Mackenzie River valley of western Canada, lakes make up 37% of the landscape. The nonlake components of the landscape are divided into uplands (55%) and wetlands (8%). With such abundance, lakes are important features that can influence the regional climate. This paper examines the role of lakes in the regional surface energy and water balance and evaluates the links to the frequency–size distribution of lakes. The primary purpose is to examine how the surface energy balance may influence regional climate and weather. Lakes are characterized by both the magnitude and temporal behavior of their surface energy balances during the ice-free period. The impacts of combinations of various-size lakes and land–lake distributions on regional energy balances and evaporation cycles are presented. Net radiation is substantially greater over all water-dominated surfaces compared with uplands. The seasonal heat storage increases with lake size. Medium and large lakes are slow to warm in summer. Their large cumulative heat storage, near summer’s end, fuels large convective heat fluxes in fall and early winter. The evaporation season for upland, wetland, and small, medium, and large lakes lasts for 19, 21, 22, 24, and 30 weeks, respectively. The regional effects of combinations of surface types are derived. The region is initially treated as comprising uplands only. The influences of wetland, small, medium, and large lakes are added sequentially, to build up to the energy budget of the actual landscape. The addition of lakes increases the regional net radiation, the maximum regional subsurface heat storage, and evaporation substantially. Evaporation decreases slightly in the first half of the season but experiences a large enhancement in the second half. The sensible heat flux is reduced substantially in the first half of the season, but changes little in the second half. For energy budget modeling the representation of lake size is important. Net radiation is fairly independent of size. An equal area of medium and large lakes, compared with small lakes, yields substantially larger latent heat fluxes and lesser sensible heat fluxes. Lake size also creates large differences in regional flux magnitudes, especially in the spring and fall periods.

Full access
Ayumi Fujisaki-Manome, Lindsay E. Fitzpatrick, Andrew D. Gronewold, Eric J. Anderson, Brent M. Lofgren, Christopher Spence, Jiquan Chen, Changliang Shao, David M. Wright, and Chuliang Xiao

Abstract

Proper modeling of the turbulent heat fluxes over lakes is critical for accurate predictions of lake-effect snowfall (LES). However, model evaluation of such a process has not been possible because of the lack of direct flux measurements over lakes. The authors conducted the first-ever comparison of the turbulent latent and sensible heat fluxes between state-of-the-art numerical models and direct flux measurements over Lake Erie, focusing on a record LES event in southwest New York in November 2014. The model suite consisted of numerical models that were operationally and experimentally used to provide nowcasts and forecasts of weather and lake conditions. The models captured the rise of the observed turbulent heat fluxes, while the peak values varied significantly. This variation resulted in an increased spread of simulated lake temperature and cumulative evaporation as the representation of the model uncertainty. The water budget analysis of the atmospheric model results showed that the majority of the moisture during this event came from lake evaporation rather than a larger synoptic system. The unstructured-grid Finite-Volume Community Ocean Model (FVCOM) simulations, especially those using the Coupled Ocean–Atmosphere Response Experiment (COARE)-Met Flux algorithm, presented better agreement with the observed fluxes likely due to the model’s capability in representing the detailed spatial patterns of the turbulent heat fluxes and the COARE algorithm’s more realistic treatment of the surface boundary layer than those in the other models.

Full access
Mark S. Kulie, Claire Pettersen, Aronne J. Merrelli, Timothy J. Wagner, Norman B. Wood, Michael Dutter, David Beachler, Todd Kluber, Robin Turner, Marian Mateling, John Lenters, Peter Blanken, Maximilian Maahn, Christopher Spence, Stefan Kneifel, Paul A. Kucera, Ali Tokay, Larry F. Bliven, David B. Wolff, and Walter A. Petersen

Abstract

A multisensor snowfall observational suite has been deployed at the Marquette, Michigan, National Weather Service Weather Forecast Office (KMQT) since 2014. Micro Rain Radar (MRR; profiling radar), Precipitation Imaging Package (PIP; snow particle imager), and ancillary ground-based meteorological observations illustrate the unique capabilities of these combined instruments to document radar and concomitant microphysical properties associated with northern Great Lakes snowfall regimes. Lake-effect, lake-orographic, and transition event case studies are presented that illustrate the variety of snowfall events that occur at KMQT. Case studies and multiyear analyses reveal the ubiquity of snowfall produced by shallow events. These shallow snowfall features and their distinctive microphysical fingerprints are often difficult to discern with conventional remote sensing instruments, thus highlighting the scientific and potential operational value of MRR and PIP observations. The importance of near-surface lake-orographic snowfall enhancement processes in extreme snowfall events and regime-dependent snow particle microphysical variability controlled by regime and environmental factors are also highlighted.

Full access