AGU journal highlights - July 2, 2009

Authors: Ken Xiansheng Hao, Hiroyuki Fujiwara, and Taku Ozawa: National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan;

Hongjun Si: Kozo Keikaku Engineering Inc., Tokyo, Japan.

Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL037971, 2009; http://dx.doi.org/10.1029/2009GL037971

3. First direct measurement of Lunar backscatter from solar wind

When the solar wind, made up mostly of ionized hydrogen, hits the Moon, most of it is absorbed, but some is reemitted as energetic neutral atoms. This lunar backscatter and neutralization had been predicted but not directly measured until now. Using NASA's Interstellar Boundary Explorer satellite, launched on 19 October 2008, McComas et al. have for the first time observed energetic neutral atoms scattered off the Moon from the incoming solar wind ion beam. They find that about 10 percent of solar wind ions hitting the Moon result in the emission of neutral atoms, corresponding to about 150 metric tons of hydrogen emitted from the Moon per year. They also show that the energy spectrum and numbers of neutral atoms emitted from the Moon trace the variations in the incident solar wind. The authors suggest that the findings could shed additional light on the solar wind's interactions with other objects in the solar system, such as dust grains, asteroids, and moons of other planets, and could provide clues to the evolution of dust and rocky moons in other planetary systems.

Title: Lunar backscatter and neutralization of the solar wind: First observations of neutral atoms from the Moon

Authors: D. J. McComas and F. Allegrini: Southwest Research Institute, San Antonio, Texas, USA;

P. Bochsler, H. Kucharek, and E. Möbius: Space Science Center, University of New Hampshire, Durham, New Hampshire, USA;

P. Frisch: Department of Astronomy and Astrophysics, University of Chicago, Chicago, Illinois, USA;

H. O. Funsten: Los Alamos National Laboratory, Los Alamos, New Mexico, USA;

M. Gruntman: Astronautics and Space Technology Division, University of Southern California, Los Angeles, California, USA;

P. H. Janzen and D. B. Reisenfeld: Department of Physics and Astronomy, University of Montana, Missoula, Montana, USA;

N. A. Schwadron: Department of Astronomy, Boston University, Boston, Massachusetts, USA.

Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL038794, 2009; http://dx.doi.org/10.1029/2009GL038794

4. Reducing uncertainty in estimates of global sea level rise

Accurate information about long-term sea level changes is important for the study of global climate change. Most estimates of global sea level rise over the past century are based on long tide gauge records. However, these records produce a wide range of estimates of global sea level because they do not generally take into account all of the vertical motions of the land on which the tide gauges are located. Wöppelmann et al. show that they can reduce the uncertainty in global sea level estimates by using GPS observations to correct for vertical land motions. They analyze GPS observations from 227 stations around the world taken from January 1997 to November 2006 to compute vertical velocities and uncertainties in vertical land motion, and use these data to correct long tide gauge records. Their calculations lead to an estimate of global sea level rise of 1.61 ± 0.19 millimeters (0.0634 ± 0.0075 inches) per year over the past century, in good agreement with other recent estimates. The authors believe the method could help scientists improve understanding of sea level rise and variability.