The most recent studies on tidal/planetary waves at Arecibo concentrate on the January 1993 10-day campaign period [Deng et al. 1996, Palo et al. 1996, and Zhou et al. 1996]. Zhou et al report an extensive analysis of tidal and planetary waves in the altitude range of 94 km to 144 km, using the temperature and winds measured by the Arecibo incoherent scatter radar (ISR). This is the first time that simultaneous observational results for the 6-8, 12, 24 hr tides and a quasi 2-day planetary wave at E-region heights have been reported at tropical latitudes. In order to derive the major oscillations from the mainly daytime data, they fill the nighttime periods with assumed data values when valid measurements are not obtainable. Simulated results show that such a method is demonstratively better than leaving the nighttime as a gap. The salient features of the tidal analysis results include: 1) Despite their large day-to-day variabilities in amplitude, the 6-8 hr oscillations are shown to be upward propagating tid
Recent studies on gravity waves at Arecibo include those by Djuth et al [1996] and Zhou [1995]. By applying the coded-long-pulse technique developed by Sulzer [Radio Sci. Vol. 21, p. 1033, 1986] to plasma line echoes created by daytime photoelectrons, Djuth et al. [1996] was able to obtain extremely high accurate measurements of electron density (0.01-0.03% error bars) with an altitude resolution of 150 m and a temporal resolution of 2 s. In the lower thermosphere above Arecibo, background gravity waves couple to the ionosphere plasma, typically yielding 1-3% electron density "imprints" of the neutral waves. These ever-present "imprints" are routinely detected 30-50 standard deviations above the noise. These authors have been using the technique to study a wide range of topics, including: gravity wave propagation, ion heating by the neutral wave in the lower thermosphere and electron thermal balance in the F-region. The study reported in Zhou [1995] shows that gravity wave damping by viscous dissipation does
References:
Deng et al., Coordinated global radar observations of tidal and planetary waves in the mesosphere and lower thermosphere during 20-30 January 1993, J. Geophys. Res., in press, 1996.
Djuth, F., M. Sulzer, V. Wickwar, B. Isham, C. Hines and J. Elder, High-resolution studies of atmosphere-ionosphere coupling at Arecibo, Puerto Rico, International Union of Radio Science Program and Abstract, p. 177, Boulder, CO., January 1996.
Palo et al. An intercomparison between the GSWM, UARS and ground based radar observation s: A case study in January 1993., submitted, 1996.
Zhou, Q., M. P. Sulzer, and C. A. Tepley, An analysis of tidal and planetary waves in the neutral winds and temperature observed at the E-region, submitted to J. Geophys. Res., 1996.
Zhou, Q., A simplified Approach to Internal Gravity Wave Damping by Viscous Dissipation, J. Atmo. Terr. Phys., Vol. 57, p. 1009, 1995.
The most recent studies at Arecibo on sporadic Es/metallic atom layers include those by Mathews [1996, 1998], Mathews et al. [1996], Miller and Lemon[1996], Rosado et al.[1996], Zhou[1996], and Zhou and Mathews[1995]. Using a new coding technique, Mathews et al. were able to observe the ionization layers with very high spatial and temporal resolutions (150m and 10 s). Their observations reveal streaks of ionization, which they refer to as "ion rain", descending from 200 km altitude and converge with the intermediate tidal ion layer as it oscillates. Those "ion rains" have a large phase velocity and a period near 12 minutes. Some possible layer generating mechanisms, including instability-generated kilometer-scale E-fields, are discussed in Mathews [1996b]. Rosado et al. [1996] reported that a strong plasma density enhancement was accompanied by field-aligned coherent echoes seen by the Cornell University Portable Radar Interferometer (CUPRI) during the 1992 NASA CRRES El Coqui campaign. These authors suggest t
Miller and Lemon [1996] studied the composition of tidal ion layers in the E-region. Their results suggest that intermediate layers are more likely maintained by ions accumulated by vertical transport than by metallic ions riding along the convergence node. (Presumably, the ions accumulated by vertical transport are molecular ions.) During the January 1993 10-day campaign, a strong quasi-2-day planetary wave was observed. Associated with the planetary wave was an once-every-other-day ion layer at the bottom of the E-region [Zhou, 1996].
On the neutral side of matters (metals in our case), Zhou and Mathews [1995] discussed the generation of sporadic metal layers through gravity wave break down and saturation. When a gravity wave breaks down, its energy is dumped in a narrow altitude range initiating an increase in temperature, which may consequently generate sporadic sodium layers (SSL) through temperature sensitive chemistries. They show that the generation of the largest SSL observed at Arecibo was associated with gravity waves exhibiting very short vertical wavelength. The recent development of a resonant lidar lead by Friedman and Castleberg will provide many exciting research opportunities in this area.
References:
Mathews, J. D., Apparent electrodynamic coupling of ion layers in the 90-270 km altitude region above Arecibo, International Union of Radio Science Program and Abstract, p. 172, Boulder, CO., January 1996.
Mathews, J. D., Sporadic E: Current views and recent progress, JATP, in press, 1998.
Mathews, J. D., M. P. Sulzer, and P. Perillat, Aspects of layer electrodynamics revealed by high resolution ISR observations of the 80-270 km ionosphere, Geophys. Res. Lett., submitted, 1996.
Miller, K. L., and M. Lemon, Composition of tidal ion layers in the E-region, International Union of Radio Science Program and Abstract, p. 171, Boulder, CO., January 1996.
Rosado-Roman, J. M., C. A. Miller, W. E. Swartz, and D. T. Farley, Simultaneous observations of sporadic E layers by coherent and incoherent scatter radar, International Union of Radio Science Program and Abstract, p. 176, Boulder, CO., January 1996.
Zhou, Q. Neutral wind and tidal ion layer observation at E-region heights above Arecibo, International Union of Radio Science Program and Abstract, p. 172, Boulder, CO., January 1996.
Zhou, Q. and J. D. Mathews, Generation of sporadic sodium layers via turbulent heating of the atmosphere? J. Atmo. Terr. Phys., Vol. 57, p. 1309, 1995.
The first UHF meteor study at Arecibo was meant to be a study on sporadic Es. As we trying to characterize Es layers, we had to get rid of numerous strong echoes that do not last longer than about ~20s, the integration time for one profile. Those short echoes were vaguely believed to arise from meteor ablations, and considered to be the worst nuisances for E-region studies. However, as Laozi, the great grandfather of Taoism, would have admonished: be aware, signal is not signal and noise is not noise, these "noisy nuisances" proved to be micrometeors and since became some collectors' item. The first UHF meteor study at Arecibo, employing several years' World Day data, was reported in Zhou et al. [1995].
Subsequently, special meteor observations have been carried out. In order to resolve the meteor duration, it's necessary to take data at the shortest inter-pulse-period possible, i.e. at 1 ms. The devoted meteor observations have been reported in Mathews et al. [1997], Zhou [1996], and Zhou and Kelley [1997]. To summarize, the majority of the meteor-like echoes observed lasted less than 50 ms at one range gate. Most of the meteor echoes in our observations have an effective radar cross-section the order of 3x10**-8 m2, and an estimated electron line density the order of 4x10**9/m. The visual magnitude is approximately +16, which is the faintest meteors observed by any ground instrument. Most unusually, the Arecibo radar appears to pick up head-on meteors more readily than those arriving at an oblique angle, which runs contrary to classical meteor theory. Some possible scattering mechanisms are discussed in Mathews et al. [1997], Zhou and Kelley [1997]. Mathews et al. [1996] studied the orbits of those meteors observed on the morni
References:
Mathews, J. D., K. P. Hunter, D. D. Meisel, V. S. Getman, and Q. Zhou, Very high resolution studies of micrometeors using the Arecibo 430 MHz radar, ICARUS, in press, 1997.
Zhou, Q., C. A. Tepley, and M. P. Sulzer, Meteor observation by the Arecibo 430 MHz ISR I. results from time-integrated observations, J. Atmo. Terr. Phys., vol. 57, p. 421, 1995.
Zhou, Q., Unusual characteristics of meteor echoes observed by the Arecibo 430 MHz radar, Proceedings of the 7th International Workshop on Technical and Scientific Aspects of MST Radar, p.314, 1996
Zhou, Q., and M. C. Kelley, Meteor observation by the Arecibo 430 MHz ISR II. results from time-resolved observations, J. Atmo. Terr. Phys., in press,1997.