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Discussion of wind - 4
Journal of Wind Engineering and lndustria: Aerodynamics, 41-44 (1992) 507-508 Elsevier
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507
Discussion of Wind. 4 Session chairmen: J. A. B. Wills, BMT Fluid Mechanics Limited, U.K. & K. MeTaggart, Defence Research Establishment Atlantic, Canada Application of the Wind Atlas Method to Extreme Wind Speed Data. J. Abild, N. G. Mortensen & L. Landberg
Comment by K. C. Mehta The uncorrected wind speed data showed that RISO site had higher wind speeds than the Narrows site. After the correction, for some directions, the Narrows site shows higher wind speed than RISO site. Is there a local phenomena to indicate this switch or is that because of natural variation in data or is it because of reliability of correction?
Author's reply The corrected data sets from Rise and Sproge are assumed to be representative for the 70 m level above sea level in the middle of the Great Belt (over-water upstream condition out to a distance of 10 kin). I enclose for your information the figure showing the effects on the raw data of the terrain corrections applied. (Correction factors for data can be found in the full paper). Hence, for optional performance, the corrected data sets should show similar sector distributions of the extreme data. The central question in the study was the behaviour in the westerly sectors where a considerable difference in representation for the raw data was observed. The corrections have apparently improved the overall representation in the westerly sectors. Note, however, that the corrections involve a change in bind direction which occasionally will shift data from one azimuth sector to another. Hence, with a detailed sector division, it must be expected that the Wind Atlas Method will result in a "statistical" uncertainty in the sector representation.
Comment by ,/on Wieringa The distance between Rise and Sproge is comparable to the size. of a severe storm depression. Have you checked whether at such a macro-distance the two stations are representative for each other without bias? If they are, you are lucky; over 100 km distance, the wind climate can change out of recognition, particularly when coastlines or similar geographical changes are crossed.
Author's reply The correlation between contemporary events recorded at different locations in Denmark has been analysed in a report (not yet published): Abild, J. (1991) "Application of the Wind Atlas Method to Extremes of Wind Climatology". Rise - M-2725, In press. The main conclusions of this report are: For severe westerly type storms, there seems to be a high correlation between comparable events even with a horizontal extrapolation of 500 kin. The correlation is found to be less pronounced for more moderate westerly storms and easterly storms. Obviously for storms of local chaz'acter such as thunderstorms, one cannot expect correlation between contemporary events recorded at stations which are 100 km apart.
Statistical Analysis of High Return Period Wind Speeds . S. Lagomarsino, G. Piccardo & G. Solari
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507
Discussion of Wind. 4 Session chairmen: J. A. B. Wills, BMT Fluid Mechanics Limited, U.K. & K. MeTaggart, Defence Research Establishment Atlantic, Canada Application of the Wind Atlas Method to Extreme Wind Speed Data. J. Abild, N. G. Mortensen & L. Landberg
Comment by K. C. Mehta The uncorrected wind speed data showed that RISO site had higher wind speeds than the Narrows site. After the correction, for some directions, the Narrows site shows higher wind speed than RISO site. Is there a local phenomena to indicate this switch or is that because of natural variation in data or is it because of reliability of correction?
Author's reply The corrected data sets from Rise and Sproge are assumed to be representative for the 70 m level above sea level in the middle of the Great Belt (over-water upstream condition out to a distance of 10 kin). I enclose for your information the figure showing the effects on the raw data of the terrain corrections applied. (Correction factors for data can be found in the full paper). Hence, for optional performance, the corrected data sets should show similar sector distributions of the extreme data. The central question in the study was the behaviour in the westerly sectors where a considerable difference in representation for the raw data was observed. The corrections have apparently improved the overall representation in the westerly sectors. Note, however, that the corrections involve a change in bind direction which occasionally will shift data from one azimuth sector to another. Hence, with a detailed sector division, it must be expected that the Wind Atlas Method will result in a "statistical" uncertainty in the sector representation.
Comment by ,/on Wieringa The distance between Rise and Sproge is comparable to the size. of a severe storm depression. Have you checked whether at such a macro-distance the two stations are representative for each other without bias? If they are, you are lucky; over 100 km distance, the wind climate can change out of recognition, particularly when coastlines or similar geographical changes are crossed.
Author's reply The correlation between contemporary events recorded at different locations in Denmark has been analysed in a report (not yet published): Abild, J. (1991) "Application of the Wind Atlas Method to Extremes of Wind Climatology". Rise - M-2725, In press. The main conclusions of this report are: For severe westerly type storms, there seems to be a high correlation between comparable events even with a horizontal extrapolation of 500 kin. The correlation is found to be less pronounced for more moderate westerly storms and easterly storms. Obviously for storms of local chaz'acter such as thunderstorms, one cannot expect correlation between contemporary events recorded at stations which are 100 km apart.
Statistical Analysis of High Return Period Wind Speeds . S. Lagomarsino, G. Piccardo & G. Solari