Small-scale atmospheric structure deduced from measurements of temperature,humidity and refractive index |
| |
| Authors: | D T Gjessing A G Kjelaas E Golton |
| |
| Institution: | (1) Norwegian Defence Research Establishment, Kjeller, Norway;(2) Radio and Space Research Station, Ditton Park, Slough, England |
| |
| Abstract: | Measurements have been made with fast-response multi-channel temperature, humidity and refractive index sensors flown to 2000 m on a tethered balloon to investigate small-scale fluctuations important in radio-wave scattering, their relation to atmospheric parameters, and their spatial variation in both one and three dimensions. Data from the three types of sensors at one point were consistent for frequencies up to about 8 Hz. Power spectra of data at various heights were computed over 0.1 to 10 Hz and generally showed slopes (on a log-log plot) close to - 5/3 above 1 Hz but ranged from –1.5 to – 3.5 at lower frequencies; in this range (f < 1 Hz) slopes were close to – 5/3 for negative Richardson number (Ri), provided temperature gradients were steeper than –1.1 °C 100 m–1 and wind shears > 1.4 x 10–2 s–1 approx. Steeper slopes were generally associated with stable atmospheric conditions but no precise relation to the above parameters was found. Spectral density was a maximum for Ri  –0.75.Cross-correlations of 0.5 were frequently observed between sensors 1 m apart in orthogonal directions; in the vertical, examples of negative correlation of vapour pressure were occasionally found over this spacing. Using four sensors spaced in line over 9 m, cross-spectrum phase calculations of drift speeds were found to be consistent with measured wind speeds. The ratio of  identification distance (coherence=0.6) to scale size of irregularities ranged from 0.25 to 0.5 with no apparent relation to height or meteorological parameters. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
