Observations on Stratospheric-Mesospheric-Thermospheric temperatures using Indian MST radar and co-located LIDAR during Leonid Meteor Shower (LMS)

International audienceThe temporal and height statistics of the occurrence of meteor trails during the Leonid meteor shower revealed the capability of the Indian MST radar to record large numbers of meteor trails. The distribution of radio meteor trails due to a Leonid meteor shower in space and time provided a unique opportunity to construct the height profiles of lower thermospheric temperatures and winds, with good time and height resolution. There was a four-fold increase in the meteor trails observed during the LMS compared to a typical non-shower day. The temperatures were found to be in excellent continuity with the temperature profiles below the radio meteor region derived from the co-located Nd-Yag LIDAR and the maximum height of the temperature profile was extended from the LIDAR to ~110 km. There are, how-ever, some significant differences between the observed profiles and the CIRA-86 model profiles. The first results on the meteor statistics and neutral temperature are presented and discussed below. Key words. Atmospheric composition and structure (pres-sure, density, and temperature) History of geophysics (at-mospheric sciences) Meteorology and atmospheric dynamics (middle atmosphere dynamics

Climatologies of quasi 2-day and 16-h wind oscillations in the meteor region over Trivandrum

1-14The climatalogies of quasi 2-day and 16-h wind oscillations obtained from the Meteor Wind Radar observations at Trivandrum (8°N, 77°E) are presented. The quasi 2-day oscillation amplitude is 20-30 ms-1, and during some months it is as large as 60 ms-1 at some altitudes. Amplitudes summer are small in contrast to largest summer amplitudes reported from mid-latitudes, the amplitude and phase profiles indicate the simultaneous presence of two wave modes; the stronger mode has large vertical wavelength (> 100 km) and the weaker mode has shorter vertical wavelength of 16 km, consistently during all the months. The amplitudes of both the modes are comparable in the NS and EW winds. The observed vertical wavelength of both the modes was found not to agree with that of wave number 3 Rossby wave, which is identified as the most probable wave mode in mid-latitudes. The 16-h oscillation amplitudes are significant during all the months over Trivandrum. The two significant wave modes of the 16-h oscillation identified could be of the products of interaction between the two quasi 2-day oscillation modes and the 24-h and/or 12-h tidal modes in the mesopause and above, reported earlier at Trivandrum

A self-calibrating facility for atmospheric radars

61-70A Self-calibrating facility, necessary for routine check on the atmospheric radars being built in India, is described. The facility will ensure data of uniformly good quality and also intercomparison of data obtained over long periods

Planetary scale temperature disturbances in the stratosphere over the Indian zone

33-41The radiance data from the NOAA-9 meteorological satellite were recorded at Trivandrum (8.5°N, 76.9°E), and analysed to study the large scale temperature oscillations in the stratosphere over low latitudes. Temperature oscillations of 9-day and I6-day periods are found to be present in the 29-50 km height range with a significant increase in their amplitudes but very small change of their phases with increasing altitudes. The amplitude and phase of each oscillation exhibit substantial changes with latitude, comprising a trend and large fluctuations. The large fluctuations in phase of the oscillations could be due to interference between closeby frequencies because of the finite width of the weighting functions of the NOAA-9 radiances, or the finite width of the spectral components computed when closeby frequencies exist simultaneously. The third possibility is the interference between extra-tropical waves propagating towards the equator interfering with the equatorial waves. From the mean trends of the phase of the two oscillations with latitude, it is inferred that extra-tropical waves propagate towards the equator, and equatorial waves propagate to extratropics beyond 15°N. The propagation of extra-tropical waves towards equator is shown to be possible, when the observed zonal winds in the low latitude stratosphere are westerly

Low frequency oscillations in the tropical stratospheric temperature field during winter time

338-346The present paper is a study on the long period radiance oscillations in the winter time stratospheric temperature field over the Indian subcontinent. The stratospheric radiance data used in this study were recorded at Trivandrum from the stratospheric sounding unit (SSU) on board the NOAA-9 satellite. It has been found that the dominant components of the stratospheric radiances have periods of 32, 15, 11, and 7 days. The altitude and latitude variations of the phase and amplitude of the observed long period oscillations are interpreted in terms of the propagation characteristics of the tropical and extratropical long period temperature oscillations. Making use of the available zonal wind data over Trivandrum (8.5°N) and Balasore (21.5°N) along with the SSU radiance data for the winter time, it is shown that the observed 32, 15, 11 and 7-day oscillations are the winter time disturbances in the midlatitudes penetrating into the low latitudes during weak equatorial westerlies

The variability of time shifts in the spaced fading records

The variations in phase path recorded at three closely spaced points can be used for measuring horizontal drifts at the E-region level. In this communication the variability of time shifts in spaced fading records have been investigated using simultaneous spaced phase path and fading records. The observed variability in time shifts in the spaced fading records can be interpreted as due to continuous changes in the direction of arrival, and interference between more than one signal. Portions of the spaced phase path records influenced by changes in the direction of arrival and interference effects can be easily identified, and reliable horizontal drift measurements can be made from the phase path records that are not contaminated by the above two effects. No such identification is possible in the spaced fading records

Characteristics of travelling ionospheric perturbations over Waltair using phase path technique

The phase path technique is a very sensitive experimental method for detecting travelling ionospheric perturbations in the FZ-region and is capable of giving much information on the various characteristics of the perturbations. The travelling wave perturbations over Waltair, scaled from phase path records of 'O' and 'X' components in the F2-region echoes on 5.6 MHz were found to have periods in the range 3-39 min. Smaller periods were of more frequent occurrence than larger periods and the most frequently observed period was about 9 min. An average wave perturbation in the F2-region could be represented by the equation A = 46.49 K sin 2πt/K where 'A' is in meters, K the period of the disturbances in the general range 3-39 min and 't' is the time in minutes. The phase speed of the perturbations was in the range 2.5-14 km/min. Perturbations with shorter periods were found to travel faster than larger periods. It was shown that the above variation of the speed of the perturbations with period leads to the conclusion that the group speed of the perturbations is twice their phase speed

Anomalous variations in phase path records

Simultaneous records of amplitude and phase path of ionospherically reflected pulsed radio waves received on an E-W aerial under periodic fading conditions show sudden discontinuities in the phase variations, when the amplitude is a minimum. Under random fading conditions also, the sudden discontinuities, frequently observed in the phase variations, are always accompanied by an amplitude minimum. It is shown that when two signals with a phase path difference changing continuously are received simultaneously, the resultant phase of the combined signal changes rather slowly, and shows a discontinuity, when the difference passes through an angle of 180°. The phase path variations recorded at points separated by about 100 m, sometimes show variations in opposite directions. This has been interpreted as due to the changes in the direction of arrival of the downcoming waves