A campaign to study turbulence in the mesosphere, over low latitudes inIndia, using rocket-borne measurements and Indian MST radar, was conductedduring July 2004. A rocket-borne Langmuir probe detected a spectrum ofelectron density irregularities, with scale sizes in the range of about 1 mto 1 km, in 67.5–78.0 km and 84–89 km altitude regions over a lowlatitude station Sriharikota (13.6° N, 80.2° E). A rocket-bornechaff experiment measured zonal and meridional winds about 30 min after theLangmuir probe flight. The MST radar located at Gadanki (13.5° N,79.2° E), which is about 100 km west of Sriharikota, also detected thepresence of a strong scattering layer in 73.5–77.5 km region from whichradar echoes corresponding to 3 m irregularities were received. Based on theregion of occurrence of irregularities, which was highly collisional,presence of significant shears in zonal and meridional components of windmeasured by the chaff experiment, 10 min periodicity in zonal and meridionalwinds obtained by the MST radar and the nature of wave number spectra of theirregularities, it is suggested that the observed irregularities wereproduced through the neutral turbulence mechanism. The percentage amplitudeof fluctuations across the entire scale size range showed that the strengthof turbulence was stronger in the lower altitude regions and decreased withincreasing altitude. It was also found that the amplitude of fluctuationswas large in regions of steeper electron density gradients. MST radarobservations showed that at smaller scales of turbulence such as 3 m, (a)the thickness of the turbulent layer was between 2 and 3 km and (b) and finestructures, with layer thicknesses of about a km or less were also embeddedin these layers. Rocket also detected 3-m fluctuations, which were verystrong (a few percent) in lower altitudes (67.5 to 71.0 km) and small butclearly well above the noise floor at higher altitudes. Rocket and radarresults also point to the possibility of existence of thin layers ofturbulence (450 m). The turbulence parameters estimated fromrocket-borne measurements of electron density fluctuations are consistentwith those determined from MST radar observed Doppler spectra and theearlier works.
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