Michael Kaufmann

Zonal asymmetries in middle atmosphere temperatures

Zonal asymmetries are frequently seen in stratospheric temperature or trace gas fields as surf zones, streamers, filaments etc. They are also seen as very small-scale fluctuations, the intensity of which varies with longitude. Similar structures might be expected in the mesosphere as well, and several examples have recently been found. CRISTA 1 large-scale data are presented that indicate a surf zone in the middle mesosphere at the beginning of winter. Very small-scale data are shown from the CRISTA 2 mission. Mesospheric variability is found to be high at all altitudes, latitudes, and longitudes. There are considerable non-zonal structures in these fluctuations. (The duration of the Crista missions was about one week each.) Zonal asymmetries have been known for a long time from comparisons of ground stations measuring the same parameter in the mesosphere/lower thermosphere. As an example, upper mesosphere temperatures derived from OH∗ emissions are compared here for Wuppertal and Moscow (Zvenigorod), which are about 2000 km apart. A systematic and substantial difference in temperature is obtained, with higher temperatures at Wuppertal than at Moscow. The difference appears to follow the solar cycle: it is small at solar maximum and large (up to 28 K) at solar minimum. The reason for this surprising behavior is as yet unknown. The Moscow and Wuppertal temperatures have also been analyzed for long-term trends: a trend discrepancy between the two stations is not seen in the data interval common to the two stations.

The fine structure emission of thermospheric atomic oxygen

Abstract The fine structure emission of thermospheric atomic oxygen at 63 μm wavelength was measured for the first time globally by the CRISTA (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere) experiment in November 1994. The data indicate low atomic oxygen densities throughtout the lower thermosphere during the time period of the experiment. A first analysis of the latitudinal distribution of oxygen atoms at 150 km altitude shows deviations from the respective CIRA-86 model predictions at mid to high northern latitudes. These deviations vary from day to day, and are possibly the result of changes in the geomagnetic activity.

Thermospheric nitric oxide infrared emissions measured by CRISTA

Abstract In November 1994 the CRISTA (Cryogenic Infrared Spectrometers and Telescopes of the Atmosphere) experiment measured mid and far infrared spectra from the Earth limb. One of the spectral channels covered the 5.3 μm (Δv = 1) band of nitric oxide. A first analysis of the data of this channel is presented. Large enhancements of the 5.3 μm band radiances were observed at high northern and at high southern magnetic latitudes. The measured intensities were a factor of 4 – 6 above those found at low latitudes.