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Spectral characteristics and scatter cross-section of low latitude mesospheric echoes measured by the Indian MST radar at Gadanki
E. Belova, S. Kirkwood, T. Narayana Rao, S. Satheesh Kumar,T. Sergienko
Annales Geophysicae (ANGEO) , 2012,
Abstract: In November 2008 and in March and April 2009 the Indian MST radar (53 MHz) at Gadanki was operated during the daytime in a special experiment, with 600 m altitude resolution, for understanding the characteristics of low-latitude mesospheric echoes (LLME). The data of three days when the echoes were strongest have been analysed in terms of spectral widths and radar volume reflectivities. Spectral widths of LLME show some decrease with altitude, with median values of 4–6 m s 1 at 69–72 km and of 2–4 m s 1 at 73–78 km. This corresponds to 20–200 mW kg 1 turbulent energy dissipation rates. It has been shown that stronger echoes have broader spectra consistent with a turbulent scattering mechanism. For the first time, the volume reflectivities for the strong LLME for Gadanki have also been calculated. They are in the range of 10 17–10 15 m 1, so LLME at Gadanki are somewhat stronger than those reported so far from Jicamarca, Peru (Lehmacher et al., 2009).
Signatures of mesospheric particles in ionospheric data
M. Friedrich, K. M. Torkar, W. Singer, I. Strelnikova, M. Rapp,S. Robertson
Annales Geophysicae (ANGEO) , 2009,
Abstract: The state of the ionosphere during the 2007 ECOMA/MASS campaign is described by in-situ observations by three sounding rockets launched from the And ya Rocket Range and by ground based observations. The ground based measurements included the incoherent scatter radar EISCAT near Troms (both on UHF and VHF), as well as an MF radar, a meteor radar and an imaging riometer all located in the close vicinity of the rocket range. The pronounced electron density bite-outs seen by two of the rockets could not be detected from the ground, but the associated PMSE (Polar Mesospheric Summer Echoes) provide indirect evidence of pronounced perturbations of mesospheric electron densities.
Turbulence characteristics in the tropical mesosphere as obtained by MST radar at Gadanki (13.5° N, 79.2° E)  [PDF]
M. N. Sasi,L. Vijayan
Annales Geophysicae (ANGEO) , 2003,
Abstract: Turbulent kinetic energy dissipation rates (ε) and eddy diffusion coefficients (Kz) in the tropical mesosphere over Gadanki (13.5° N, 79.2° E), estimated from Doppler widths of MST radar echoes (vertical beam), observed over a 3-year period, show a seasonal variation with a dominant summer maximum. The observed seasonal variation of ε and Kz in the mesosphere is only partially consistent with that of gravity wave activity inferred from mesospheric winds and temperatures measured by rockets for a period of 9 years at Trivandrum (8.5° N, 77° E) (which shows two equinox and one summer maxima) lying close to Gadanki. The summer maximum of mesospheric ε and Kz values appears to be related to the enhanced gravity wave activity over the low-latitude Indian subcontinent during the southwest monsoon period (June – September). Both ε and Kz in the mesosphere over Gadanki show an increase with an increase in height during all seasons. The absolute values of observed ε and Kz in the mesosphere (above ~80 km) does not show significant differences from those reported for high latitudes. Comparison of observed Kz values during the winter above Gadanki with those over Arecibo (18.5° N, 66° W) shows that they are not significantly different from each other above the ~80 km altitude. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; tropical meteorology; wave and tides)
Development of the mesospheric Na layer at 69° N during the Geminids meteor shower 2010
T. Dunker, U.-P. Hoppe, G. Stober,M. Rapp
Annales Geophysicae (ANGEO) , 2013,
Abstract: The ECOMA sounding rocket campaign in 2010 was performed to investigate the charge state and number density of meteoric smoke particles during the Geminids meteor shower in December 2010. The ALOMAR Na lidar contributed to the campaign with measurements of sodium number density, temperature and line-of-sight wind between 80 and 110 km altitude over And ya in northern Norway. This paper investigates a possible connection between the Geminids meteor shower and the mesospheric sodium layer. We compare with data from a meteor radar and from a rocket-borne in situ particle instrument on three days. Our main result is that the sodium column density is smaller during the Geminids meteor shower than the winter average at the same latitude. Moreover, during two of the three years considered, the sodium column density decreased steadily during these three weeks of the year. Both the observed decrease of Na column density by 30% and of meteoric smoke particle column density correlate well with a corresponding decrease of sporadic meteor echoes. We found no correlation between Geminids meteor flux rates and sodium column density, nor between sporadic meteors and Na column density (R = 0.25). In general, we found the Na column density to be at very low values for winter, between 1.8 and 2.6 × 1013 m 2. We detected two meteor trails containing sodium, on 13 December 2010 at 87.1 km and on 19 December 2010 at 84 km. From these meteor trails, we estimate a global meteoric Na flux of 121 kg d 1 and a global total meteoric influx of 20.2 t d 1.
The latitude dependence and probability distribution of polar mesospheric turbulence  [PDF]
M. Rapp,E. Becker,B. Strelnikov,F.-J. Lübken
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: We consider in-situ observations and results from a global circulation model to study the latitude dependence and probability distribution of polar mesospheric turbulence. A comparison of summer observations at 69° N and 79° N shows that mesospheric turbulence weakens towards the summer pole. Furthermore, these data suggest that at both latitudes in about ~70% of all samples there are non-turbulent altitude bins in the considered altitude range between 70 and 95 km. The remaining 30% with detectable turbulence show an approximately log-normal distribution of dissipation rates. A low-resolution model version with a gravity wave (GW) parameterization explains the observed latitude dependence as a consequence of a downshift of the breaking levels towards the summer pole and an accompanying decay of turbulent heating per unit mass. When we do not use a GW parameterization but employ a high spatial resolution instead to simulate GW effects explicitly, the model predicts a similar latitudinal dependence with weakening turbulence towards the summer pole. In addition, the model also produces a log-normal distribution of dissipation rates. The simulated probability distribution is more narrow than in the observations since the model resolves at most mid-frequency GWs, whereas real turbulence is also excited by smaller-scale disturbances. The GW resolving simulation suggests a weaker tropospheric GW source at polar latitudes as the dominating mechanism for the latitudinal dependence.
Seasonal variabilities of low-latitude mesospheric winds  [PDF]
R. Rajaram,S. Gurubaran
Annales Geophysicae (ANGEO) , 2003,
Abstract: Observations of mesospheric winds over a period of four years with the partial reflection radar at Tirunelveli (8.7°N, 77.8°E), India, are presented in this study. The emphasis is on describing seasonal variabilities in mean zonal and meridional winds in the altitude region 70–98 km. The meridional winds exhibit overall transequatorial flow associated with differential heating in the Northern and Southern Hemispheres. At lower altitudes (70–80 km) the mean zonal winds reveal easterly flow during summer and westerly flow during winter, as expected from a circulation driven by solar forcing. In the higher altitude regime (80–98 km) and at all altitudes during equinox periods, the mean zonal flow is subjected to the semi-annual oscillation (SAO). The interannual variability detected in the occurrence of SAO over Tirunelveli has also been observed in the data sets obtained from the recent UARS satellite mission. Harmonic analysis results over a period of two years indicate the presence of long-period oscillations in the mean zonal wind at specific harmonic periods near 240, 150 and 120 days. Results presented in this study are discussed in the context of current understanding of equatorial wave propagation. Key words. Meteorological and atmospheric dynamics · General circulation · Middle atmosphere dynamics · waves and tides.
On the secondary charging effects and structure of mesospheric dust particles impacting on rocket probes
O. Havnes ,L. I. N sheim
Annales Geophysicae (ANGEO) , 2007,
Abstract: The dust probe DUSTY, first launched during the summer of 1994 (flights ECT–02 and ECT–07) from And ya Rocket Range, northern Norway, was the first probe to unambiguously detect heavy charged mesospheric aerosols, from hereon referred to as dust. In ECT–02 the probe detected negatively charged dust particles in the height interval of 83 to 88.5 km. In this flight, the lower grid in the detector (Grid 2) measures both positive and negative currents in various regions, and we find that the relationship between the current measurements of Grid 2 and the bottom plate can only be explained by influence from secondary charge production on Grid 2. In ECT–07, which had a large coning, positive currents reaching the top grid of the probe were interpreted as due to the impact of positively charged dust particles. We have now reanalyzed the data from ECT–07 and arrived at the conclusion that the measured positive currents to this grid must have been mainly due to secondary charging effects from the impacting dust particles. The grid consists of a set of parallel wires crossed with an identical set of wires on top of it, and we find that if the observed currents were created from the direct impact of charged dust particles, then they should be very weakly modulated at four times the rocket spin rate ωR. Observations show, however, that the observed currents are strongly modulated at 2ωR. We cannot reproduce the observed large modulations of the impact currents in the dust layer if the currents are due only to the transfer of the charges on the impacted dust particles. Based on the results of recent ice cluster impact secondary charging experiments by Tomsic (2003), which found that a small fraction of the ice clusters, when impacting with nearly grazing incidence, carried away one negative charge 1e, we have arrived at the conclusion that similar, but significantly more effective, charging effects must be predominantly responsible for the positive currents measured by the top grid in ECT–07 and their large rotational modulation at 2ωR. Since the secondary effect is dependent on the size of the impacting dust, this opens up for the possibility of mapping the relative dust sizes throughout a dust layer by comparing the observed direct and secondary currents.
Lidar measurements of mesospheric temperature inversion at a low latitude  [PDF]
V. Siva Kumar,Y. Bhavani Kumar,K. Raghunath,P. B. Rao
Annales Geophysicae (ANGEO) , 2003,
Abstract: The Rayleigh lidar data collected on 119 nights from March 1998 to February 2000 were used to study the statistical characteristics of the low latitude mesospheric temperature inversion observed over Gadanki (13.5° N, 79.2° E), India. The occurrence frequency of the inversion showed semiannual variation with maxima in the equinoxes and minima in the summer and winter, which was quite different from that reported for the mid-latitudes. The peak of the inversion layer was found to be confined to the height range of 73 to 79 km with the maximum occurrence centered around 76 km, with a weak seasonal dependence that fits well to an annual cycle with a maximum in June and a minimum in December. The magnitude of the temperature deviation associated with the inversion was found to be as high as 32 K, with the most probable value occurring at about 20 K. Its seasonal dependence seems to follow an annual cycle with a maximum in April and a minimum in October. The observed characteristics of the inversion layer are compared with that of the mid-latitudes and discussed in light of the current understanding of the source mechanisms. Key words. Atmospheric composition and structure (pressure, density and temperature). Meterology and atmospheric dynamics (climatology)
Mean winds observed with Indian MST radar over tropical mesosphere and comparison with various techniques  [PDF]
M. Venkat Ratnam,D. Narayana Rao,T. Narayana Rao,S. Thulasiraman
Annales Geophysicae (ANGEO) , 2003,
Abstract: Temporal variation of mean winds between the 65 to 85 km height region from the data collected over the course of approximately four years (1995–99), using the Indian MST radar located at Gadanki (13.5° N, 79.2° E), India is presented in this paper. Mesospheric mean winds and their seasonal variation in the horizontal and vertical components are presented in detail. Westward flows during each of the equinoxes and eastward flows during the solstices are observed in the zonal component. The features of the semi-annual oscillation (SAO) and the quasi-biennial oscillation (QBO) in the zonal component are noted. In the meridional component, contours reveal a northward motion during the winter and a southward motion during the summer. Large inter-annual variability is found in the vertical component with magnitudes of the order of ± 2 ms-1 . The MST observed winds are also compared with the winds observed by the MF radar located at Tirunelveli (8.7° N, 77.8° E), India, the High Resolution Doppler Imager (HRDI) onboard the Upper Atmospheric Research Satellite (UARS), and with the CIRA-86 model. A very good agreement is found between both the ground-based instruments (MST radar and MF radar) in the zonal component and there are few discrepancies in the meridional component. UARS/HRDI observed winds usually have larger magnitudes than the ground-based mean winds. Comparison of the MST derived winds with the CIRA-86 model in the zonal component shows that during the spring equinox and the summer, the winds agree fairly well, but there are a lot of discrepancies in the other seasons and the observed winds with the MST radar are less in magnitude, though the direction is same. The strengths and limitations in estimating reliable mesospheric mean winds using the MST radar are also discussed. Key words. Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics; waves and tides)
Tidal signatures in mesospheric turbulence
C. M. Hall, S. Nozawa, A. H. Manson,C. E. Meek
Annales Geophysicae (ANGEO) , 2006,
Abstract: We search for the presence of tidal signatures in high latitude mesospheric turbulence as parameterized by turbulent energy dissipation rate estimated using a medium frequency radar, quantifying our findings with the aid of correlation analyses. A diurnal periodicity is not particularly evident during the winter and spring months but is a striking feature of the summer mesopause. While semidiurnal variation is present to some degree all year round, it is particularly pronounced in winter. We find that the maximum in the summer 24-h variation corresponds to that of the westward phase of the diurnal tide, and that the maximum in the winter 12 h variation corresponds to that of the southward phase of the semidiurnal tide. This information is used to infer the horizontal propagation direction of gravity waves: during the summer the eastward direction is consistent with closure of the summer vortex, while in winter the inferred directions require more complex arguments.
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