HRDI observations of the O2(0,0) Atmospheric band nightglow: a seven-year climatology

A climatology of an extensive multi-year and near-global data set of O₂(0,0) Atmospheric band nightglow measurements collected by HRDI/UARS is presented. The measurements span all latitudes from 72S to 72N, and data are available for nearly all months from November 1991 through 1999.

Two operational modes on HRDI are used to observe the O₂ nightglow emission layer. A combined wind/photometric mode measured the emission brightness at low horizontal resolution (~500 km) from late 1991 through 1995, and intermittently thereafter. Much higher spatial resolution (~50 km) and a broader range of local time coverage has been achieved since March 1996 by using the HRDI photometer channel and sacrificing the ability to measure nighttime winds.

This seven-year climatology of the monthly averaged O₂ nightglow data greatly extends and expands upon earlier surveys of HRDI nightglow data. We describe the brightness variations with latitude and local time with an emphasis on the seasonal and interannual variability revealed in this data set. In addition to tidal variations in the brightness (i.e. those dependent on latitude and local time), strong non-tidal variations are observed around the globe. A statistical method is used to separate these perturbations from the tidal and seasonal effects. A climatology of these perturbations is presented, and their possible origins in terms of gravity wave and planetary wave forcing are discussed. The daily variations accompanying these global patterns are rendered in fine spatial detail by the high-resolution data. Daily and small-scale variability within the monthly climatological average is assessed by examining periods in which both high- and low-resolution data were gathered on alternating days.