Recent publications (1996/1997)
Recent publications (1996/1997)Abstract: The vertical emission profile of the O2 (a¹ Dg) airglow at 1.27 µ m has been measured during the evening twilight near the equator (Alcântara, Brazil; 2.5° S, 44.2° W) using a rocket-borne infrared photometer. The profile is used to derive the vertical distribution of ozone between 60 and 86 km. The ozone profile shows a minimum concentration at 77 km and a secondary maximum of 1.34E8 cm-³ at 82 km. The height of the secondary maximum is lower than observed at midlatitudes, and the 77-km minimum is sharper than that which has been observed at low latitudes by satellite measurements.
Abstract: A study of sporadic sodium (Ns) layers observed at São José dos Campos (23° S, 46° W) shows that during their occurrence the form of the background sodium layer is different to that which it normally takes when Ns layers are absent. During Ns events, peak sodium in the background layer typically occurs below 90 km, whereas the peak of the average layer observed at our location is around 93 km. The observed change could be caused either by a loss of sodium on the topside of the layer, or by a displacement of sodium to lower heights. The consistency of these two mechanisms with our observations, and with the known properties of Ns layers, is examined, but we are unable to determine which of the mechanisms is responsible for the observed phenomenon.
Abstract: A new analysis of atmospheric sodium measurements, made at São José dos Campos (23° S, 46° W) since 1972, confirms the previously detected trend in the centroid height of the layer, and shows the existence of a 10-year solar-cycle related oscillation. The centroid height fell at an average rate of 37 ± 9 m yr-¹ between 1972 and 1994, and the 10-year cycle has an amplitude of 170 ± 110 m. An analysis of the vertical distribution of atmospheric sodium shows that the fall in height of the centroid is caused not by a simple vertical displacement of the sodium profile, but by the growth of a bulge on the bottomside of the layer.
Abstract: The MULTIFOT airglow payload included 4 side-looking instruments which measured the OH(8,3) band and Na D line emissions. For much of the rocket flight the photometers were well above the emission layers, so that the 4 rps rotation of the rocket payload resulted in a raster scan of the emission layers by the fields of view of the side-looking photometers. The combined effects of the mean vehicle motion, payload rotation, and coning, resulted in the scanning of an area more than 600 km in the E-W direction and 800 km in the N-S direction. The airglow intensities show horizontal variations by as much as a factor of two. In the case of the OH emission a localised area of enhanced emission involved an increase in intensity of around 50% over a horizontal distance of only 20 km. The observed horizontal variations do not appear to be associated with gravity wave propagation.
Abstract: A rocket payload designed to measure mesospheric sodium, hydroxyl and oxygen nightglow emissions, in addition to electron density and temperature, was launched from the Alcântara Launch Center(2.3° S, 44.4° W), Brazil, at 23:52 LST on May 31, 1992. The height profiles of the atomic oxygen OI557.7 nm and molecular oxygen Atmospheric (0-0) band emissions showed maxima at 100 ± 3 km and 98 ± 3 km respectively. The emission data are used to calculate the atomic oxygen concentration profiles. The results show the validity for the equatorial region of the empirical parameters proposed by McDade et al. (1986).
Abstract: Simultaneous rocket measurements of the OH Meinel (8-3) band and O2 Atmospheric (0-0) band emission profiles are used to investigate the OH (v=8) loss in the equatorial mesosphere due to collisions with O2 and N2. The O2 Atmospheric (0-0) band emission profile is used to obtain the atomic oxygen concentration. The derived branching ratios, A(8)/A(8-3), and quenching parameters are found to be about a factor of two smaller than those obtained by McDade et al. (1987). Adopting branching ratios A(8)/A(8-3) from the literature, the best agreement between the emission profiles of oxygen and OH is obtained using the Meinel band transition probabilities of Turnbull and Lowe (1989).
Abstract: Simultaneous measurements of the nightglow profiles of the O2 Herzberg I bands, the O2 Atmospheric (0-0) band and the atomic oxygen green line, carried out at Alcântara (2.5° S, 44.4° W), are presented and discussed. This is the first measurement of the vertical profile of the Herzberg I band to be carried out at low latitudes. The atomic oxygen concentration derived from the O2 Atmospheric (0-0) band emission profile is used to test a photochemical scheme to explain the measured O2 (A³ Su+ -- X³ Sg-) nightglow emission based on atomic oxygen recombination. The kinetic analysis is carried out assuming the emission ratio Herzberg I : Herzberg II = 5:1, 10:1 and the extreme case where Herzberg II brightness = 0. For the three cases studied, the quenching rates required to explain the measurements are higher than the values derived from previous airglow measurements.
Abstract: The MULTIFOT airglow photometer payload was launched from Alcântara (2.5° S, 44.4° W) on a SONDA III rocket at 23:52 hrs local time on 31 May 1992. A total of 10 photometers, 6 forward-looking and 4 side-looking, measured the height profiles of the airglow emissions O2 Herzberg band system, OI 557.7 nm, NaD 589.3 nm, OI 630.0 nm, OH(8,3) band R branch at 724.0 nm, O2 Atmospheric (0,0) band at 762.0 nm and the sky background at 578 nm and 710 nm. At the time of launch, a ground based airglow photometer observed the intensity variations of these emissions, together with the rotational temperature of the OH(9,4) band, and a sodium lidar measured atomic sodium concentration from 80 to 110 km.
Abstract: Atomic hydrogen and ozone concentrations are derived from simultaneous measurements of the vertical profiles of upper mesospheric airglow emissions and atmospheric sodium. The airglow profiles were obtained in a sounding rocket experiment launched from Alcântara (2.5° S, 44.2° W) on 31 May 1992. A lidar operating at the launch site was used to measure sodium at the time of the rocket experiment. A total of 10 airglow photometers, 6 forward-looking and 4 side-looking, observed the OI 557.7 nm, O2 Herzberg and Atmospheric (0,0) bands, sodium D lines, OI 630 nm, OH(8,3) band and the airglow continuum. The simultaneous ground-based sodium lidar and on-board sodium airglow measurements made it possible to derive the ozone concentration at heights between 85 and 100 km. The hydrogen concentrations were then calculated from the O2 Atmospheric (0,0), OH(8,3) and the ozone profiles. The results suggest that the hydrogen concentration varied from 1E9 cm-³ at 85 km to 1E8 cm-³ at 100 km, values much higher than those suggested by recent model atmospheres and by some rocket observations at middle and high latitudes. Although the method of obtaining the concentrations of the minor constituents in the upper atmosphere is an indirect optical technique, this is the first time that these concentrations have been measured by rocket in the equatorial region.
Abstract: Lidar observations have been made at São José dos Campos (23 S, 46 W) since 1972. We shall present a history of the stratospheric aerosol at our site until the end of 1995. Until the beginning of 75 the monthly averages of the backscatter integrated from 17 to 35 km showed large variations but at a very low level. From 75 to 78 it was fairly constant at a level of about 8x10-5 SR-1. From 78 to about mid 79 it was low again and then increased to slightlymore than the 75-78 level until early 82 when El Chichon erupted. During the decay of El Chichon there was a minor maximum from June to August, probably due to circulation since there were no injections reported for this time period. El Chichon decayed back to about its pre-eruption value before a series of eruptions raised the level in 87. The integrated backscatter decayed gradually until mid 91 when Pinatubo erupted. Until the end of 95 the integrated backscatter had not reached the pre-eruption level. A visual analysis of the data from 75 to 85 shows that the annual sum of the volcanic explosivity index is correlated much better with significant changes in the integrated backscatter than is the annual sum of the number of significant volcanoes.