First mesospheric turbulence study using coordinated rocket and MST radar measurements over Indian low latitude region

A campaign to study turbulence in the meso- sphere, over low latitudes in India, using rocket-borne mea- surements and Indian MST radar, was conducted during July 2004. A rocket-borne Langmuir probe detected a spectrum of electron density irregularities, with scale sizes in the range of about 1 m to 1 km, in 67.5-78.0 km and 84-89 km alti- tude regions over a low latitude station Sriharikota (13.6 N, 80.2 E). A rocket-borne chaff experiment measured zonal and meridional winds about 30 min after the Langmuir probe flight. The MST radar located at Gadanki (13.5 N, 79.2 E), which is about 100 km west of Sriharikota, also detected the presence of a strong scattering layer in 73.5-77.5 km region from which radar echoes corresponding to 3 m irregularities were received. Based on the region of occurrence of irregu- larities, which was highly collisional, presence of significant shears in zonal and meridional components of wind mea- sured by the chaff experiment, 10 min periodicity in zonal and meridional winds obtained by the MST radar and the nature of wave number spectra of the irregularities, it is sug- gested that the observed irregularities were produced through the neutral turbulence mechanism. The percentage ampli- tude of fluctuations across the entire scale size range showed that the strength of turbulence was stronger in the lower al- titude regions and decreased with increasing altitude. It was also found that the amplitude of fluctuations was large in re- gions of steeper electron density gradients. MST radar ob- servations 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 fine structures, with layer thick- nesses of about a km or less were also embedded in these lay- ers. Rocket also detected 3-m fluctuations, which were very strong (a few percent) in lower altitudes (67.5 to 71.0 km) and small but clearly well above the noise floor at higher alti- tudes. Rocket and radar results also point to the possibility of existence of thin layers of turbulence (<450 m). The turbu- lence parameters estimated from rocket-borne measurements of electron density fluctuations are consistent with those de- termined from MST radar observed Doppler spectra and the earlier works.