Large-scale turbulence universality and the study of extreme weather events

• Published in: Physics and chemistry of the earth. Part B, Hydrology, oceans and atmosphere Hydrology, oceans and atmosphere, 2000-01, Vol.25 (1), p.35-38
• Main Authors: Eidelman, A., Branover, H., Moiseev, S.S., Gordienko, S.
• Format: Article
• Language: English
• ISSN: 1464-1909
• DOI: 10.1016/S1464-1909(99)00117-3

Extreme weather events (EWE) can be generated in the atmosphere possessing nonzero helicity under the conditions of stratification and rotation. It has been shown by Moiseev et al. (1983) that the origination of large-scale wind disturbances, such as tropical cyclones, are possible due to mean helicity of the atmosphere. In fact, wind observations reveal that helicity is an essential parameter of atmospheric flows. Wind velocity spectra in both synoptic and mesoscale ranges of scales having slopes close to -7/3 and adjacent to -5/3 were revealed by Eidelman et al. (1995). Figure 1 presents spectra obtained in GASP experiments (Nastrom and Gage, 1985) at various latitudes. Here we have drawn straight lines with the slope of -7/3 that approximate well the data of observations for latitudes > 15 degrees in Fig. 1. Wind spectra can have such a slope, if helicity transfer is a determining process in the respective range of scales, and their parameter is the helicity transfer rate eta = dH/dt (Moiseev et al., 1994). This slope was also revealed by Eidelman and Branover (1998) within the scale range from 2 to 20 km in GASP spectra given by Nastrom et al. (1987). An important property of helical turbulence is the suppression of the direct energy transfer over the spectrum from large to small scales. On the contrary, under such conditions, an inverse energy transfer over the spectrum arises directed towards the large-scale range. The latter circumstance represents a realizable mechanism of large-scale wind disturbances generation in the atmosphere. The presence of additional powerful energy input sources in the small-scale range, e.g., convection, promotes this process. The validity of such generation is also confirmed by the studies of the formation of large-scale disturbances in the Jupiter's atmosphere as a result of the falling of fragments of Comet Schoemaker-Levy (Ivanov et al., 1996). The achieved insight into the processes determining the stage of EWE origination is important for their prediction. It is equally important to understand how they are generated in the atmosphere at the following stages and to reveal characteristics of their large-scales. With this purpose, we have carried out a laboratory study of the generation of large-scale velocity disturbances.