I read with interest a recent note in which Rosenberg et al. [1964] described a twilight release of a trail of trimethyl aluminum extending from 80‐ to 170‐km altitude when the earth's shadow height was about 110 km. They observed the emission of a continuum from about 90 to 130 km, and the (0,2), (0,1), (0,0) and (1,0) bands of the A2Σ+ ‐ X2Σ+ transition of AlO from about 130 to 150 km. Armstrong [1963] has reported similar observations of glows caused by the explosion of aluminized grenades used for the United Kingdom's Skylark rocket program for upper atmosphere wind measurement at Woomera. We have been able to make more detailed observations of these glows since November 1962, using a specially built photoelectric spectrophotometer. This note is written to record some observations relevant to the question, raised by Rosenberg et al., of whether the absence of AlO emissions below 130 km was due to atmospheric extinction of the exciting solar rays or to an unfavorable combination of reaction and excitation rates. Our observations show that the effect observed is due to removal of the exciting solar rays by the earth's atmosphere.

SummaryThe spectral energy distribution is given for the glow clouds resulting from the explosion of aluminized grenades in the range of altitude from 100 to 200 km. At night, over much of the spectral range from 300 to 800 nm, the spectrum is a continuum very similar to that of a black body at 4000-5000 o K. At twilight, emissions resulting from resonant scattering of sunlight by AI, K, Ba, Na, and AIO are superimposed on, and dominate, the continuum.

SummaryGlows have been observed at Woomera when grenades ejected from Skylark rockets have been detonated in the altitude range 90-170 km. Using results obtained from these glows by a special scanning photometer located on the ground, an estimate has been made of the diffusion coefficient in the region 120-160 km. The theoretical model which is used to describe the behaviour of the explosion products incorporates the assumptions of molecular diffusion, a Gaussian distribution of particle density, and an optically thin cloud. The effects of consumption of the cloud particles are included in the model.

SummaryRecords of the behaviour of aluminized grenade glow clouds at twilight and at night were obtained using cameras and photometers. From these records the radiance, radiant p~wer, and radiant energy have been deduced for the altitude range 100-200 km. The twilight observations show that the absorption cross section of aluminium monoxide is about 3 X lO-14 cm2• From the night-time results it is concluded that the glow probably arises from a chemiluminescent reaction with atomic oxygen. A set of reactions consistent with the observations above 120 km altitude is AI02 +O -+ AIO+02, AIO+O -+ AI02+hv, AIO+O -+ AI+02, with the rate constants being 5 X 10-12, 1 X 10-13, and 4 X 10-13 cm3 molecule-1 sec-1 respectively.

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