First results on daytime mesopause OH rotational temperatures using ground-based photometry from equatorial latitudes

Daytime mesospheric OH (8,3) rotational temperatures were estimated from th e measurements of the relative intensities of the rotational lines in the s ame vibrational band, using the unique multiwavelength daytime photometer, from Tirunelveli (8.7 degrees N; 77.8 degrees E; 0.5 degrees N dip latitude ), an equatorial station in the Indian zone. On a couple of days when simul taneous measurements were available in the vicinity of the experimental sit e, the estimated temperatures compared well with those measured by the Wind Imaging Interferometer (WINDII) onboard the Upper Atmosphere Research Sate llite (UARS). These results, the first of their kind, revealed: (1) large d ay-today variabilities; (2) oscillatory features with periodicities ranging from 0.5 to 6 h; and (3) large deviations of +/-30-50 K, on occasions, fro m the MSIS-90 model temperatures. Comparisons have also been made with simu ltaneous measurements of neutral winds around mesopause altitudes using the Partial Reflection radar from the same site to look for any possible assoc iation of neutral dynamical parameters with the mesopause temperature varia bilities. These results are presented and discussed. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.