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

Abstract

Abstract.A campaign to study turbulence in the mesosphere, over low latitudes in India, using rocket-borne measurements 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 altitude 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 irregularities, which was highly collisional, presence of significant shears in zonal and meridional components of wind measured 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 suggested that the observed irregularities were produced through the neutral turbulence mechanism. The percentage amplitude of fluctuations across the entire scale size range showed that the strength of turbulence was stronger in the lower altitude regions and decreased with increasing altitude. It was also found that the amplitude of fluctuations was large in regions of steeper electron density gradients. MST radar observations 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 thicknesses of about a km or less were also embedded in these layers. Rocket also detected 3-m fluctuations, which were very strong (a few percent) in lower altitudes (67.5 to 71.0 km)Correspondence to: H. Chandra (hchandra@prl.res.in) and small but clearly well above the noise floor at higher altitudes. Rocket and radar results also point to the possibility of existence of thin layers of turbulence (<450 m). The turbulence parameters estimated from rocket-borne measurements of electron density fluctuations are consistent with those determined from MST radar observed Doppler spectra and the earlier works.

Spectral characteristics and scatter cross-section of low latitude mesospheric echoes measured by the Indian MST radar at Gadanki

“…Importantly, the spectra of the mesospheric echoes observed in this experiment would experience less shear broadening and broadening due to possible vertical wind variation over the altitude range, compared to previous LLME observations with the Gadanki radar, where the altitude resolution was 2.4 km (e.g. Kumar et al, 2007;Chandra et al, 2008). Thus, such experimental arrangements allow for the elimination of non-turbulent contributions to the spectral width and, finally, correct evaluation of the parameters of turbulence.…”

“…If interpreted as turbulent echoes, they correspond to 20-200 mW kg −1 turbulent energy dissipation rates. Chandra et al (2008) and Uma Das et al (2009) reported energy dissipation rates of 1-100 mW kg −1 for the same altitude range, which were derived from the rocket measurements from Sriharikota located about 100 east of Gadanki. The LLME spectral widths for our three cases are close to those (2-3 m s −1 ) measured by Chandra et al (2008) with the same radar in July 2004.…”

“…Chandra et al (2008) and Uma Das et al (2009) reported energy dissipation rates of 1-100 mW kg −1 for the same altitude range, which were derived from the rocket measurements from Sriharikota located about 100 east of Gadanki. The LLME spectral widths for our three cases are close to those (2-3 m s −1 ) measured by Chandra et al (2008) with the same radar in July 2004. At Jicamarca, Peru, spectral measurements of mesospheric echoes for 37 days made with a 50-MHz MST radar gave mean values of turbulent energy dissipation rates of 5-30 mW kg −1 for altitudes between 67 and 80 km .…”

High resolution mesospheric sodium properties for adaptive optics applications

“…In our measurements, system noise, from laser mode instability and photon shot noise, becomes dominant at frequencies above a few Hz. Rocket measurements (Chandra et al 2008) indicate that the inner scale of turbulence in the mesosphere is of order 10 m. With a typical average wind speed of ∼30 ms −1 , we would thus expect the PSD to turn down above a few Hz. In any case, the power law is not expected to continue much above ∼30 Hz.…”

Rocket-borne Langmuir probe for plasma density irregularities

“…A study of neutral turbulence generated irregularities was made by Chandra et al (2008) and Patra et al (2009) through simultaneous rocket, radar and ionosonde measurements from Sriharikota and Gadanki (13.5…”