AGU journal highlights -- Aug. 1, 2007

Initial observations from the Cassini spacecraft have revealed evidence for interchanging magnetic flux tubes in Saturn's inner magnetosphere. These tubes interchange dense cold plasma with tenuous hot plasma originating from farther out in the magnetosphere. These tubes differ by their magnetic signatures, having a depressed or enhanced magnetic pressure relative to their surroundings. André et al. study interchanging flux tubes with enhanced magnetic pressure, which previous researchers hypothesize as having outward moving mass-loaded or inward moving plasma-depleted properties. Using data from several instruments aboard Cassini, the authors discriminate between the two previous and opposite interpretations of flux tubes with enhanced magnetic pressure. They find that all these flux tubes are in fact plasma-depleted, although they may possess different magnetic signatures. These signatures are associated with the latitude above which they form. Similar flux tubes have also been observed in Jupiter's magnetosphere.

Title: Magnetic signatures of plasma-depleted flux tubes in the Saturnian inner magnetosphere

Authors: N. André: Research and Scientific Support Department, European Space Agency, Noordwijk, The Netherlands;

A, M. Persoon, W. S. Kurth, and D. A. Gurnett: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, U.S.A.;

J. Goldstein, J. L. Burch, F. J. Crary, and D. T. Young: Southwest Research Institute, San Antonio, Texas, U.S.A.;

P. Louarn: Centre d'Etude Spatiale des Rayonnements, Toulouse, France;

A. M. Rymer: Applied Physics Laboratory, The Johns Hopkins University, Laurel, Maryland, U.S.A.;

G. R. Lewis and A. J. Coates: Mullard Space Science Laboratory, University College London, Dorking, U.K.;

E. C. Sittler, Jr.: NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.;

M. F. Thomsen: Los Alamos National Laboratory, Los Alamos, New Mexico, U.S.A.;

M. K. Dougherty: The Blackett Laboratory, Imperial College, London, U.K.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030374, 2007

11. Soil moisture and remote sensing

Soil moisture plays an important role in the exchange of water and heat between land and atmosphere. Although C-band (6-7 gigahertz) passive microwave frequencies have been used to map soil moisture from aircraft and satellites, many studies have suggested that L-band (1.4 gigahertz) is more useful for this application. Unlike other bands, L-band data are less obscured by the presence of vegetation. However, utilizing this frequency from space with conventional technologies requires an antenna size too large for most satellite missions. Problems with antenna size can be overcome with new interferometric technology. Ryu et al. analyze data from an airborne experiment that used this technology to collect L-band data over Alabama in 2003. Data is then compared with simultaneously collected C-band data and with surface soil measurements collected from the ground. The results demonstrate that L-band data provides soil moisture values more accurately than does C-band data. The new interferometric technology will be employed to monitor soil moisture using L-band for the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) satellite mission, scheduled for launch in 2008.