Long-term variation of OH peak emission altitude and volume emission rate over Indian low latitudes

• OH peak emission altitude and peak emission rate are found to be anti-correlated.
• The OH peak emission altitude varies from 83–87 km with mean value of 85.5 km.
• Prominent signatures of SAO, QBO and ENSO are noted with weak AO.
• Solar flux has greater effect on daytime peak emission rates than the nighttime ones.
• A weak decreasing trend is noted in the OH peak emission altitude.

Using 13 (April 2002–December 2014) years of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER/TIMED) 1.6 µm OH airglow emission data, we have studied the long-term variation of OH peak emission altitude and volume emission rate (VER) for 0–10°N latitude and 70–90°E longitude grid. We have noted that, during day time the OH peak emission altitude is varying from 80 to 87 km with mean value of 83.5 km and from 82 to 88 km with mean value of 85 km during night time. The signature of semi-annual oscillation (SAO), annual oscillation (AO) and quasi-biennial oscillation (QBO) in the OH peak emission altitude as well as the VER is evident. Our analysis reveals that the SAO and QBO signatures but not the AO signature are very strong in the equatorial region during night time. Apart from the SAO, AO and QBO signatures, the presence of oscillation related to the El Niño oscillation (ENSO) is also noted. After the removal of these oscillations, we find the evidence of the influence of solar activity and a long term trend in the OH emission layer. It is also found good correlation between the mesospheric and stratospheric variations (ECMWF data).