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- Author or Editor: Tage Andersson x
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Abstract
The diurnal precipitation variation over northerly oceans is studied with the aid of the 3-hr synoptic observations from Weather Ship M at 66N, 02E during the 20-year period 1949–68. The precipitation frequencies possess a maximum in the morning during the whole year and a pronounced daytime minimum during the months March–September. The remaining months have a less pronounced diurnal variation and during September–April there is usually also an evening maximum. January and February even indicate a night minimum of precipitation frequency.
Abstract
The diurnal precipitation variation over northerly oceans is studied with the aid of the 3-hr synoptic observations from Weather Ship M at 66N, 02E during the 20-year period 1949–68. The precipitation frequencies possess a maximum in the morning during the whole year and a pronounced daytime minimum during the months March–September. The remaining months have a less pronounced diurnal variation and during September–April there is usually also an evening maximum. January and February even indicate a night minimum of precipitation frequency.
Abstract
A case with intense convective snowbands over the Baltic Sea is examined using the High-Resolution Limited Area Model. The intention is to gain a better insight into the importance of the shape of the coasts, the orography, and the surface roughness on the formation and evolution of the snowbands. Among the factors studied are the shape of the coast from which the air departs and that to which it arrives. These factors are so important that two new concepts—coast of departure and coast of arrival—are introduced.
Abstract
A case with intense convective snowbands over the Baltic Sea is examined using the High-Resolution Limited Area Model. The intention is to gain a better insight into the importance of the shape of the coasts, the orography, and the surface roughness on the formation and evolution of the snowbands. Among the factors studied are the shape of the coast from which the air departs and that to which it arrives. These factors are so important that two new concepts—coast of departure and coast of arrival—are introduced.
Abstract
Convective snowbands over the Baltic Sea and its bays are examined to gain insight into snowband characteristics and precipitation distribution. A general description of the physical mechanisms responsible for snowband formation there is provided, as well as a discussion of coastal-precipitation maxima. A number of cases during the winters 1984/85–1987/88 are also examined to provide their meteorological characteristics. Recent radar studies suggest that snowfall maxima occur over the water and that observed coastal maxima are only extensions from snowfall maxima over the sea. In addition, strong winds and drifting snow common in convective band situations cause large errors in conventional precipitation measurements. Radar provides a necessary tool for studying the precipitation distribution to overcome difficulties in measuring snowfall.
Abstract
Convective snowbands over the Baltic Sea and its bays are examined to gain insight into snowband characteristics and precipitation distribution. A general description of the physical mechanisms responsible for snowband formation there is provided, as well as a discussion of coastal-precipitation maxima. A number of cases during the winters 1984/85–1987/88 are also examined to provide their meteorological characteristics. Recent radar studies suggest that snowfall maxima occur over the water and that observed coastal maxima are only extensions from snowfall maxima over the sea. In addition, strong winds and drifting snow common in convective band situations cause large errors in conventional precipitation measurements. Radar provides a necessary tool for studying the precipitation distribution to overcome difficulties in measuring snowfall.
Abstract
A new model for making probability forecasts of accumulated spot precipitation from weather radar data is presented. The model selects a source region upwind of the forecast spot. All pixels (horizontal size 2 × 2 km2) within the source region are considered, having the same probability of hitting the forecast-spot. A pixel hitting the forecast spot is supposed to precipitate there a short time (about 10 min.). A drawing is performed, and a frequency distribution of accumulated precipitation during the first time step of the forecast is obtained. A second drawing gives the frequency distribution of accumulated precipitation during the first to second time step, a third one during the first to third, and so on until the end of the forecast period is reached. A number of forecasts for 1-h accumulated precipitation, with lead times of 0, 1, and 2 h, have been performed and verified. The forecasts for 0-h lead time got the highest Brier skill scores, +50% to 60% relative to climatological forecasts for accumulated precipitation below 1 mm.
Abstract
A new model for making probability forecasts of accumulated spot precipitation from weather radar data is presented. The model selects a source region upwind of the forecast spot. All pixels (horizontal size 2 × 2 km2) within the source region are considered, having the same probability of hitting the forecast-spot. A pixel hitting the forecast spot is supposed to precipitate there a short time (about 10 min.). A drawing is performed, and a frequency distribution of accumulated precipitation during the first time step of the forecast is obtained. A second drawing gives the frequency distribution of accumulated precipitation during the first to second time step, a third one during the first to third, and so on until the end of the forecast period is reached. A number of forecasts for 1-h accumulated precipitation, with lead times of 0, 1, and 2 h, have been performed and verified. The forecasts for 0-h lead time got the highest Brier skill scores, +50% to 60% relative to climatological forecasts for accumulated precipitation below 1 mm.
