The rate of ascent of pilot balloons at melbourne

✍ Scribed by E. Kidson; H. M. Treloar

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 786 KB
• Volume: 55
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49705523006

✦ Synopsis

Abstract

1. The wind regime at Melbourne is described, the prevalence of North‐westerly winds at all levels being emphasised.

2. The mean rate of ascent is shown to be above that given by J. S. Dines's formula near the surface but below it above 200 metres.

3. There is an annual variation in the mean rate of ascent, which is highest in summer and lowest in winter.

4. The rate of ascent, as has been found at other places, is very variable, the departures from normal being sufficiently' serious to render the single theodolite method insufficiently accurate for at least some practical purposes. The standard deviation of the height after various intervals from the commencement is given and the distribution of the departures shown.

5. There is evidence that heat turbulence is more effective in increasing the rate of ascent near the surface than the turbulence produced by high winds. This the authors believe to be due to its being on a smaller scale.

6. By far the most important factor causing variations in the rate of ascent is turbulence. The greater the turbulence, the greater the mean rate of ascent. It is believed, however, that with the same amount of turbulence the rate of ascent would be appreciably less in stable than in unstable air.

7. The diurnal variation in the rate of ascent and the variation with different types of weather are complicated and depend chiefly on the development of stable or unstable conditions in the different air layers.

8. There is considered to be evidence of definite ascending currents in the spring months. Except in the case of upward currents of considerable vertical extent, pilot balloon observations are not calculated to give a measure of true vertical currents as distinct from those due to turbulence.