The Nether1andsAJ.K. Radar, Wavebuoy Experimental Comparison (NURWJX) was a collaborative experim... more The Nether1andsAJ.K. Radar, Wavebuoy Experimental Comparison (NURWJX) was a collaborative experiment between the University of Birmingham, the Dutch Ftijkswaterstaat (RWS), and the Institute of Oceanographic Sciences (IOS), and was designed to assess the availability and accuracy of ocean wave data using the University of Birmingham ground-wave radar. The experiment lasted for two months during which time over 110 h of radar data were collected and transferred to Birmingham for wave-parameter extraction. Estimates of significant wave height are found to have a standard deviation of 15 percent (by comparison with the Datawell WAVEC buoy) if they were less than 2 m, and of 20 percent if greater, although in this case there is a positive bias of 41 percent. A mean difference in first-moment wave period of 0.6 s over the range 3-10 s is found. The long-wave directional spectrum is found to be in good agreement in the limited number of cases for which comparison is appropriate, with differences of 21 percent in height, 6 percent in period, and 15" in direction. The limitations to these measurements are identified, and suggestions are made for improvements in radar operations and for further research.
... basis for probabilistic seasonal predictions of the behaviour of the atmosphere (often 24 ...... more ... basis for probabilistic seasonal predictions of the behaviour of the atmosphere (often 24 ... 8 Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia and 1 Zimbabwe. ... rainfall is the major climatic determinant of vegetation distribution and the availability 19 ...
Red-billed queleas Quelea quelea are major pests of small-grain crops throughout sub-Saharan Afri... more Red-billed queleas Quelea quelea are major pests of small-grain crops throughout sub-Saharan Africa. When conditions permit, birds breed in vast colonies which are targets for control operations. Queleas are intra-African long-distance migrants whose complex movements vary annually according to variations in rainfall patterns. An ability to forecast where and when colonies could be established will greatly improve the efficiency of control measures. We describe such a forecasting model for the southern African subspecies Q. q. lathamii . 2. The model is based on and provides a partial test of the conjectured rainfall-migration model of Ward , whereby quelea movements are determined by rainfall patterns and grass seed availability. We consider that a threshold quantity of rainfall (shown here to be c . 60 mm) within any 2 weeks at the start of the wet season is necessary to cause annual grass seeds to germinate, forcing queleas to emigrate. Only if rainfall exceeds another threshold (240 mm within a 6-week span and at least 6 weeks elapsed after the 60-mm threshold had been exceeded), allowing production of fresh seed, can queleas return and commence breeding. Birds may breed again in the same season by undertaking further long-distance 'breeding migrations' to areas where sufficient rain had fallen even later. 3. Using only estimates of rainfall derived from satellite data, we describe a simple spatio-temporal model for southern Africa to show at weekly intervals those areas where (a) the wet season has not yet started; (b) the early rains migration threshold has been exceeded; (c) the threshold to permit breeding has been exceeded; and (d) conditions are no longer suitable for new colonies to be established. 4. Synthesis and applications. The model was run for three seasons and performed well compared to an expected null distribution of breeding colonies among quarter-degree grid squares. In , quelea colonies were reported significantly more often in grid squares where the model had predicted breeding to be possible. However, in a more refined analysis of a smaller subset of colonies for which precise dates of their establishment were known, their spatio-temporal distribution matched predictions in 95%, 85% and 99% of grid squares, respectively, over the three breeding seasons. These success rates show that predictions from the model, the first of its kind for any African bird, can aid the planning of quelea control strategies.
The Nether1andsAJ.K. Radar, Wavebuoy Experimental Comparison (NURWJX) was a collaborative experim... more The Nether1andsAJ.K. Radar, Wavebuoy Experimental Comparison (NURWJX) was a collaborative experiment between the University of Birmingham, the Dutch Ftijkswaterstaat (RWS), and the Institute of Oceanographic Sciences (IOS), and was designed to assess the availability and accuracy of ocean wave data using the University of Birmingham ground-wave radar. The experiment lasted for two months during which time over 110 h of radar data were collected and transferred to Birmingham for wave-parameter extraction. Estimates of significant wave height are found to have a standard deviation of 15 percent (by comparison with the Datawell WAVEC buoy) if they were less than 2 m, and of 20 percent if greater, although in this case there is a positive bias of 41 percent. A mean difference in first-moment wave period of 0.6 s over the range 3-10 s is found. The long-wave directional spectrum is found to be in good agreement in the limited number of cases for which comparison is appropriate, with differences of 21 percent in height, 6 percent in period, and 15" in direction. The limitations to these measurements are identified, and suggestions are made for improvements in radar operations and for further research.
... basis for probabilistic seasonal predictions of the behaviour of the atmosphere (often 24 ...... more ... basis for probabilistic seasonal predictions of the behaviour of the atmosphere (often 24 ... 8 Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia and 1 Zimbabwe. ... rainfall is the major climatic determinant of vegetation distribution and the availability 19 ...
Red-billed queleas Quelea quelea are major pests of small-grain crops throughout sub-Saharan Afri... more Red-billed queleas Quelea quelea are major pests of small-grain crops throughout sub-Saharan Africa. When conditions permit, birds breed in vast colonies which are targets for control operations. Queleas are intra-African long-distance migrants whose complex movements vary annually according to variations in rainfall patterns. An ability to forecast where and when colonies could be established will greatly improve the efficiency of control measures. We describe such a forecasting model for the southern African subspecies Q. q. lathamii . 2. The model is based on and provides a partial test of the conjectured rainfall-migration model of Ward , whereby quelea movements are determined by rainfall patterns and grass seed availability. We consider that a threshold quantity of rainfall (shown here to be c . 60 mm) within any 2 weeks at the start of the wet season is necessary to cause annual grass seeds to germinate, forcing queleas to emigrate. Only if rainfall exceeds another threshold (240 mm within a 6-week span and at least 6 weeks elapsed after the 60-mm threshold had been exceeded), allowing production of fresh seed, can queleas return and commence breeding. Birds may breed again in the same season by undertaking further long-distance 'breeding migrations' to areas where sufficient rain had fallen even later. 3. Using only estimates of rainfall derived from satellite data, we describe a simple spatio-temporal model for southern Africa to show at weekly intervals those areas where (a) the wet season has not yet started; (b) the early rains migration threshold has been exceeded; (c) the threshold to permit breeding has been exceeded; and (d) conditions are no longer suitable for new colonies to be established. 4. Synthesis and applications. The model was run for three seasons and performed well compared to an expected null distribution of breeding colonies among quarter-degree grid squares. In , quelea colonies were reported significantly more often in grid squares where the model had predicted breeding to be possible. However, in a more refined analysis of a smaller subset of colonies for which precise dates of their establishment were known, their spatio-temporal distribution matched predictions in 95%, 85% and 99% of grid squares, respectively, over the three breeding seasons. These success rates show that predictions from the model, the first of its kind for any African bird, can aid the planning of quelea control strategies.
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