G. K. Hartmann

Measurements of O3, H2O and ClO in the Middle Atmosphere Using the Millimeter-Wave Atmospheric Sounder (MAS)

The Millimeter-Wave Atmospheric Sounder (MAS) is a shuttle-based limb-sounding instrument designed for global spectroscopic studies of O3, and constituents important in O3 photochemistry, in the middle atmosphere. It is part of the NASAs Atmospheric Laboratory for Applications and Science (ATLAS) spacelab shuttle mission. This paper presents an overview of the instrument, operation, and data analysis. In addition, as an example of the results, we present zonal average retrievals for O3, H2O and ClO obtained in ATLAS 1. The MAS O3 and H2O measurements are shown to agree well with simultaneous observations made with the UARS MLS instrument.

The electron content of the ionosphere and the Southern boundary of diffuse Aurora

Abstract Measurements of latitudinal dependence of ionospheric electron content over Europe exhibit strong enhancements around 60° geomagnetic latitude, occuring during some winter nights. One of these events — on December 4th, 1977 — could be related to the precipitation of soft electrons (

MAS measurements of the latitudinal distribution of water vapor and ozone in the mesosphere and lower thermosphere

We present measurements of the latitudinal variation of nighttime O3 and H2O in the mesosphere and (for O3) lower thermosphere obtained with the Millimeter-wave Atmospheric Sounder (MAS) instrument during the ATLAS 2 mission (8–15 April 1993). These are the first such measurements that have ever been reported. They indicate an O3 mixing ratio minimum at mid-latitudes in the upper mesosphere, with maxima in the tropics and at high latitudes. The H2O retrievals indicate H2O mixing ratios decreasing toward the poles in both hemispheres in the upper mesosphere. We also present measurements of the diurnal variation of O3 at southern mid-latitudes, at higher vertical resolution than has ever been reported previously. The results are generally consistent with previous measurements and modeling studies.

Middle atmosphere abundances of water vapor and ozone during MAP/WINE

Abstract Water vapor and ozone concentrations measured at mid and high latitudes above Europe during the MAP/WINE Campaign in the winter 1983/1984 are presented. Both water vapor and ozone distributions are found to be variable and structured. On two occasions strong enhancements of mesospheric ozone were recorded, which were probably caused by dynamic effects. The assumption of a photochemical equilibrium for ozone at high latitudes in winter does not appear justified according to the variations measured during MAP/WINE. Water vapor mixing ratios determined in the stratosphere and mesosphere above Scandinavia yield average mixing ratios of near 4 ppmv.

A comparison of several methods of estimating the columnar electron content of the plasmasphere

Abstract Data from several different observation techniques are used to estimate the columnar electron content of the plasmasphere. The estimate is based upon the subtraction of the ionospheric electron content from the total content along the radio path from ground to the geostationary satellite ATS-6. The Radio Beacon Experiment on this satellite allows a very accurate determination of the total electron content up to the height of the satellite. For the ionospheric electron content (ground to appr. 2000 km) the following techniques are used 1. (a) Faraday effect on the ATS-6 signals, 2. (b) Differential Doppler effect on the signals of the low orbiting NNSS satellites, 3. (c) combination of bottomside and topside ionograms, and 4. (d) extrapolation of bottomside ionograms. It is shown that the combination of Group Delay and Faraday effect data on the ATS-6 RBE signals provide the most reliable estimates of the columnar electron content of the plasmasphere. Data from low orbiting satellites support this conclusion.

Interactive text retrieval based on document similarities

In this article we present a prototypical implementation of a software tool for document retrieval which groups/arranges (pre-processed) documents based on a similarity measure. The prototype was developed based on self-organising maps to realise interactive associative search and visual exploration of document databases. This helps a user to navigate through similar documents. The navigation, especially the search for the first appropriate document, is supported by conventional keyword search methods. The usability of the presented approach is shown by a sample search.

Geomagnetic Activity Indices

The predominant part of the geomagnetic field, as observed at the Earth’s surface, originates from sources in the Earth’s core and, to a lesser degree, in the Earth’s crust. Spatial distribution and secular variation of this internal part were described, e.g., by Schmucker (1985). Superimposed, there is a small external part due to large-scale current systems in the ionosphere and magnetosphere finally resulting from the motion of charged particles in the Earth’s magnetic field. Short-term time variations of the external part are governed by solar wave (W) and particle (P) radiation and thus may serve to yield information on solar-terrestrial relationships that otherwise cannot so easily and continuously be achieved.

A multi-station satellite radio beacon study of ionospheric variations during total solar eclipses

Faraday rotation data obtained at Delhi, Kurukshetra, Hyderabad, Bangalore, Waltair, Nagpur and Calcutta during the total solar eclipse of 16 February 1980 and at Delhi during the total solar eclipse of 31 July 1981 have been analysed to detect the gravity waves generated by a total solar eclipse as hypothesized by Chimonas and Hines (1970, J. geophys. Res. 75, 875). It has been found that gravity waves can be generated by a total solar eclipse but their detection at ionospheric heights is critically dependent on the location of the observing station in relation to the eclipse path geometry. The distance of the observing station from the eclipse path should be more than 500 km in order to detect such gravity waves.

Zeeman splitting of the 61 Gigahertz oxygen (O2) line in the mesosphere

Zeeman splitting of O2 molecular states in the Earths upper atmosphere leads to polarized emission spectra. A 61 GHz radiometer operated as part of the Millimeter-wave Atmospheric Sounder (MAS), a core payload instrument of the NASA Space Shuttle ATLAS missions, observed such emissions. This instruments high resolution spectrometer (200 kHz) allows us to verify for the first time Zeeman effect model calculations for the upper atmosphere in some detail. The results suggest some interesting new aspects for the research of the upper atmosphere.

Space-Borne H2O Observations in the Arctic Stratosphere and Mesosphere in the Spring of 1992

We report on stratospheric and mesospheric water vapor (H2O) observations obtained by the Millimeter wave Atmospheric Sounder (MAS) in the Arctic spring of 1992. In the lower stratosphere, the observations show enhanced H2O inside the vortex between 450 K and 625 K, in agreement with other H2O observations. In the upper stratosphere and lower mesosphere, at potential temperatures between 1850 K and 2200 K, we find regions of depressed H2O volume mixing ratio coincident with remnants of high potential vorticity. The depressed mesospheric H2O, as well as the enhanced lower stratospheric H2O, are consistent with wintertime descent. It also suggests effective containment of air up into the lower mesosphere.