Seasonal variations of spectra of wind speed and air temperature in the mesoscale frequency range

✍ Scribed by Hiroshi Ishida

• Publisher: Springer
• Year: 1990
• Tongue: English
• Weight: 801 KB
• Volume: 52
• Category: Article
• ISSN: 0006-8314
• DOI: 10.1007/bf00119428

✦ Synopsis

Seasonal variations of the spectra of wind speed and air temperature in the mesoscale frequency range from 1.3 x 10m4 to 1.5 x 10m3 Hz (10 min to 2 h periods) have been studied through observations over land for one year. Spectrographs [time series of isopleths of spectral densities, f* S(f) vs f] of wind speed and air temperature contain occasional peaks that are attributed to shortlived mesoscale atmospheric activity with narrow frequency bands. Significant spectral peaks of wind speed were found in 19% of the total observations in winter, and in 15-16% in the other seasons; for air temperature, they occured in 12% of observations in autumn, and in 1619% in the other seasons. The peaks most often occurred in the period range from 30 min to 1 h; most had durations less than 24 h. Mesoscale fluctuations of wind speed and air temperature were highly correlated, and in most cases, phase differences were 90-180" with air temperature leading wind speed. Significant spectral peaks of wind speed often occurred during northerly seasonal cold winds in winter, and accompanied tropical and/or mid-latitude cyclones in the other seasons. When the peaks occurred, wind speed was usually relatively high and the atmospheric surface layer was unstable.