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In the present work a statistical analysis of long-lived microbursts (MBs) in the decimetric wavelength range was performed
for the first time. Long-lived microbursts at decimetric wavelengths were observed with one-dimensional scans on the RATAN-600
radio telescope in intensity and circular polarization with a sensitivity of about 5 – 10 Jy. MBs have fluxes in the range
of 0.001 – 0.1 s.f.u. and polarization degrees of 10 – 100%, and the duration of individual bursts is about 1 – 2 s. Microbursts
and background sources exist for several days and appear at the sites of prolonged energy release. In this work MBs were compared
with noise storms (NSs) in the metric wavelength range. Our analysis shows with high confidence that MBs are manifestation
of NSs in the decimetric wavelength range. The reason for the significant difference in flux between MBs and NSs could be
because MBs (unlike NSs) are related to incoherent generation of Langmuir waves. The nature of the MB emission is similar
to the smoothly varying (background) emission of the NSs, butthe MB emission is impulsive because of the high rate of pitch-angle
diffusion. 相似文献
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Leena Järvi Ari-Juhani Punkka David M. Schultz Tuukka Petäjä Harri Hohti Janne Rinne Toivo Pohja Markku Kulmala Pertti Hari Timo Vesala 《Boundary-Layer Meteorology》2007,125(2):343-359
On the afternoon of 3 July 2004 in Hyytiälä (Juupajoki, Finland), convective cells produced a strong downburst causing forest damage. The SMEAR II field station, situated near the damage site, enabled a unique micrometeorological analysis of a microburst with differences above and inside the canopy. At the time of the event, a squall line associated with a cold front was crossing Hyytiälä with a reflectivity maximum in the middle of the squall line. A bow echo, rear-inflow notch, and probable mesovortex were observed in radar data. The bow echo moved west-north-west, and its apex travelled just north of Hyytiälä. The turbulence data were analysed at two locations above the forest canopy and at one location at sub-canopy. At 1412 EET (Eastern European Time, UTC+2), the horizontal and vertical wind speed increased and the wind veered, reflecting the arrival of a gust front. At the same time, the carbon dioxide concentration increased due to turbulent mixing, the temperature decreased due to cold air flow from aloft and aerosol particle concentration decreased due to rain scavenging. An increase in the number concentration of ultra-fine particles (< 10 nm) was detected, supporting the new particle formation either from cloud outflow or due to rain. Five minutes after the gust front (1417 EET), strong horizontal and downward vertical wind speed gusts occurred with maxima of 22 and 15 m s?1, respectively, reflecting the microburst. The turbulence spectra before, during and after the event were consistent with traditional turbulence spectral theory. 相似文献
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