GRIPS - long-term measurements at the mesopause near 87 km altitude

Overview

The Wuppertal GRound-based Infrared P-Branch Spectrometer (GRIPS) is operated by the atmospheric science team "each" night in order to measure the temperature of the mesopause centered near 87 km (+/-2 km) altitude. GRIPS is a Czerny-Turner grating spectrometer that scans the near infrared between 1,52 - 1,55 micrometer with a spectral resolution of about 450. Measured parameters are the nighttime hydroxyl Meinel band (3,1) rotational temperatures from the [OH*] emission layer. Measurements have been continuously taken since 1980. More than 3500 nightly mean temperatures are available.

In the upper mesosphere, atomic hydrogen reacts with ozone to form excited hydroxyl molecules:

H + O3 -> OH* + O2*

The NIR hydroxyl emissions have been measured in the nightglow since their identification by Meinel 1950. The rotational temperatures of the OH*(3,1) band are near the kinetic temperature of the atmosphere. They can be derived in a fairly simple manner during nighttime from the relative spectral intensities. For details of the instrument and of the data reduction see the corresponding papers in the publications section.

The GRIPS instrument field-of-view in the zenith has a horizontal resolution of 20x20 km2 (with respect to 87 km altitude). One OH* spectrum is measured in 90 seconds (see figure on the right). Rotational temperatures are derived from the relative intensities of the three lines. Hence, the derived temperatures are not affected by changes of spectrometer sensitivity or atmospheric transmission unless such changes are wavelength dependent. Even in that case, influences would be small because the three lines are close together (1.524, 1.533, 1.543 micrometer).

The relative error of nightly mean temperature values is estimated to be 1-2 K. This is derived from measurements during the whole night, and therefore, it still contains some atmospheric variability. Thus, the value must be considered as an upper limit for the relative error. The absolute temperature error is of the same magnitude. Spectral and absolute intensity calibrations are performed about once per year.

Details

Scientific results of the seasonal variation of the mesopause temperature and of trends are provided.

The GRIPS instrument is a part of the Network for the Detection of Mesopause Change (NDMC).

GRIPS-N setup
GRIPS-F setup

Foto: Peter Knieling

Two typical OH* spectra

The solid arrows indicate the three lines used for the analysis.