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Alan G. Barr and G. S. Strong

Abstract

Upper-air budget methods can be used to estimate the surface sensible and latent heat flux densities on a regional scale. This study assesses the application of radiosonde-based budget methods above homogeneous cropland. Serial daytime soundings were released from Kenaston and Saskatoon, Canada, on fair-weather days between 24 June and 31 July 1991.

Two independent methods were used to establish ground truth: surface-layer Bowen ratio-energy balance and Priestley-Taylor. This study was the fist to extend the surface-layer Bowen ratio method to conventional upper-air soundings. The two ground-truth methods agreed to within 20% at both locations and gave mean daytime Bowen ratios of 0.33.

The upper-air budget surface flux estimates agreed most consistently with ground truth when the budget was integrated over the atmospheric boundary layer (BL) and used parameterized entrainment with a value for the entrainment parameter AR of 0.4. The BL budget with AR of 0.4 closed the daytime surface energy balance to within 4% at Kenaston and 7% at Saskatoon and gave a mean estimate for the Bowen ratio that agreed to within 20% of the mean ground-truth estimates. However, the BL budget estimates for 2-3-h periods were quite variable, and it was necessary to average the budget estimates over periods of 12 days or longer to produce credible values. Random sampling errors and uncertainty in horizontal advection were partly responsible for the high variability of the budget estimates, but these terms averaged to zero over extended periods. More seriously, the BL budget estimates for the surface latent heat flux were quite sensitive to the method for estimating entrainment. Because the authors were unable to establish a preferred entrainment estimate a priori, the BL budget estimates for the surface latent heat flux were considered to be unreliable. Further study is needed to develop a reliable and independent method for specifying the value for AR.

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E. P. Lozowski and G. S. Strong

Abstract

A model of the vertical collision of a sphere with a hailpad predicts that the dent volume is proportional to the impact kinetic energy, and gives a relationship between dent diameter and sphere diameter for ice spheres. Laboratory calibration experiments confirm the essence of the theory but cast some doubt on the validity of the assumption of a constant resistance pressure. Further experiments simulating windblown ice spheres show that for the conditions we considered, the horizontal partition of energy has a small effect on the minor axis diamter of the dent. Consequently, if the wind speed is unknown, no more than a 10% error may occur if the sphere diameter is determined using the no-wind relation. Finally, field calibration of the hailpads with hailstones falling in a natural hail shaft tend to support both the laboratory calibrations and the model predictions.

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Renée Elio, Johannes De Haan, and G. S. Strong

Abstract

An experienced forecaster can use several different types of knowledge in forcing. First, there is his theoretical understanding of meteorology, which is well entrenched in current numerical models. A second type is his “local knowledge,” gained over years of experience, of how weather is likely to form in his forecast area. This kind of local familiarity is not easily captured with traditional numeric techniques, but might provide additional insights for prediction that someone unfamiliar with the area might not have. A third type of knowledge is how to interpret forecast tools already in use. This might include knowledge of the tool's limitations and how it works in a particular locale. Capturing these types of knowledge is important in building computing systems that can serve as intelligent consultants to forecasters. This paper describes a prototype system, called METEOR, that incorporates all these types of knowledge to predict the location, severity, and motion of convective storms in Alberta; METEOR interprets contoured maps of a synoptic-based instability index and of surface equivalent potential temperature. It also gathers additional information about a variety of ongoing weather conditions from three portions of surface aviation reports: the cloud cover section, the obstructions visibility, and the observations provided in the “remarks” section. Interpreting remarks made by human observers, while useful to a forecaster experienced with local weather conditions, can be too time consuming for people to do in real-time and too complex for traditional computing methods to handle. However, METEOR interprets these remarks and keeps track of where various weather activities are occurring and how they are changing over time. At present, METEOR's final forecast is a prediction of likely areas of storm initiation, direction of motion, and intensity, plus summaries of current conditions and their implications for storm development.

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Energy and Water Cycles in a High-Latitude, North-Flowing River System

Summary of Results from the Mackenzie GEWEX Study—Phase I

W. R. Rouse, E. M. Blyth, R. W. Crawford, J. R. Gyakum, J. R. Janowicz, B. Kochtubajda, H. G. Leighton, P. Marsh, L. Martz, A. Pietroniro, H. Ritchie, W. M. Schertzer, E. D. Soulis, R. E. Stewart, G. S. Strong, and M. K. Woo

The MacKenzie Global Energy and Water Cycle Experiment (GEWEX) Study, Phase 1, seeks to improve understanding of energy and water cycling in the Mackenzie River basin (MRB) and to initiate and test atmospheric, hydrologic, and coupled models that will project the sensitivity of these cycles to climate change and to human activities. Major findings from the study are outlined in this paper. Absorbed solar radiation is a primary driving force of energy and water, and shows dramatic temporal and spatial variability. Cloud amounts feature large diurnal, seasonal, and interannual fluctuations. Seasonality in moisture inputs and outputs is pronounced. Winter in the northern MRB features deep thermal inversions. Snow hydrological processes are very significant in this high-latitude environment and are being successfully modeled for various landscapes. Runoff processes are distinctive in the major terrain units, which is important to overall water cycling. Lakes and wetlands compose much of MRB and are prominent as hydrologic storage systems that must be incorporated into models. Additionally, they are very efficient and variable evaporating systems that are highly sensitive to climate variability. Mountainous high-latitude sub-basins comprise a mosaic of land surfaces with distinct hydrological attributes that act as variable source areas for runoff generation. They also promote leeward cyclonic storm generation. The hard rock terrain of the Canadian Shield exhibits a distinctive energy flux regimen and hydrologic regime. The MRB has been warming dramatically recently, and ice breakup and spring outflow into the Polar Sea has been occurring progressively earlier. This paper presents initial results from coupled atmospheric-hydrologic modeling and delineates distinctive cold region inputs needed for developments in regional and global climate modeling.

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