Manfred Ern

The Response of Atomic Hydrogen to Solar Radiation Changes

The combination of satellite born SCIAMACHY hydroxyl and GOMOS ozone limb measurements allows for the derivation of the global distribution of atomic hydrogen abundance and instantaneous chemical heating rates in the mesopause region. Chemical heating rates show maximum values of 5–10 K/day at 85–90 km; atomic hydrogen densities are 1–5⋅108 cm−3. Signatures of equatorial Kelvin waves, Rossby-gravity waves and Rossby waves are clearly visible in the data. A pronounced latitudinal structure with maxima at the equator and at mid latitudes is observed. Between 2002 and 2008 chemical heating rates decreased and atomic hydrogen density increased, in accordance with model simulations of the 11-year solar cycle.

Calibration procedures and correction of detector signal relaxations for the CRISTA infrared satellite instrument.

Remote sensing from space has become a common method for deriving geophysical parameters such as atmospheric temperature and composition. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument was designed to sound the middle and the upper atmosphere (10-180 km) with high spatial resolution. Atmospheric IR emissions were measured with Si:Ga bulk or Si:As blocked impurity band detectors for a wavelength interval of 4-17 microm and Ge:Ga bulk detectors for 56-71 microm. An overview of the calibration of the instrument and the correction of detector signal relaxations for the Si:Ga detectors are given, both of which are necessary to provide high-quality IR radiance data as input for the retrieval of atmospheric temperature and trace gas mixing ratios. Laboratory and flight data are shown to demonstrate the quality of the results.

Detector signal relaxations and their correction: the Si:Ga bulk detectors of the CRISTA instrument

The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured atmospheric trace gas emissions in the infrared using the limb scanning technique. For the first time three viewing directions were used by a satellite instrument in near-earth orbit (300 km) to obtain an unprecedented spatial density of the daily global measurement net. The high measurement speed needed for an enhanced horizontal resolution was achieved by cooling the instrument with supercritical and subcooled helium and by using Si:Ga bulk or Si:As blocked impurity band (BIB) detectors for the wavelength range 4-17 micrometers and Ge:Ga bulk detectors for longer wavelengths. The detectors were operated at temperatures between 2.5 and 13 Kelvin. Under these conditions the signal of the detectors shows non-stationary effects (relaxation effects) degrading measured spectra to some extent.These effects are difficult to account for as they can only be described by using at least 6 parameters depending on signal height and illumination history. In this paper an empirical model to correct the non-stationary effects of the Si:Ga detectors is presented. The model is based on measured signal responses after step-like illumination changes. Several tests using different data sets show that the model works well under various conditions.