AGU journal highlights -- April 22, 2008

Title: Sensitivity of Southern Hemisphere climate to zonal asymmetry in ozone

Authors: Julia A. Crook and Nathan P. Gillett: Climate Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U.K.;

Sarah P. E. Keeley: Climate Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U.K.; also at Department of Meteorology, University of Reading, Reading, U.K.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032698, 2008; http://dx.doi.org/10.1029/2007GL032698

3. Might surges trigger geomagnetic substorms?

Geomagnetic substorms are driven by variations on the Sun and can disrupt satellite systems, produce aurorae, and increase the radiation dose of astronauts and passengers on transpolar flights. Right before the onset of a geomagnetic substorm, a large upsurge in duskward ion flux occurs that some scientists believe excites cross-field current instabilities and possibly triggers substorm expansion. Saito et al. seek to discover whether this ballooning instability influences the magnetotail near Earth in the late-growth stage of substorms. Using data from the joint Japan/U.S. Geotail satellite, the authors determine that the ballooning instability deforms magnetic field lines in the magnetotail, producing magnetic field fluctuations. Further examination of a set of six substorms that were detected in the vicinity of the magnetic equator reveal that that ballooning mode was identified in cases where plasma flow velocities were high. From this knowledge of the plasma flow velocity, the scientists are able to estimate the wavelength of the instabilities. The authors expect that such studies will help scientists better predict geomagnetic substorms.

Title: Ballooning mode waves prior to substorm-associated dipolarizations: Geotail observations

Authors: M. H. Saito, Y Miyashita, M. Fujimoto, I. Shinohara, and Y. Saito: Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan;

K. Liou: Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, U.S.A.;

T. Mukai: Japan Aerospace Exploration Agency, Tokyo, Japan.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033269, 2008; http://dx.doi.org/10.1029/2008GL033269

4. Model warns early of Indonesia, Australia drought

The Indian Ocean Dipole (IOD) is an air-sea coupled climate oscillation. In the dipole’s positive phase, greater-than-average sea surface temperatures and precipitation occur around the western Indian Ocean and southern India, and waters cool in the eastern Indian Ocean causing drought conditions in Indonesia and Australia. Opposite conditions occur in the negative phase. Although most research synchronizes dipole patterns with El Niño oscillations in the Pacific Ocean, in both 2006 and 2007 during fall in the Northern Hemisphere, two consecutive positive dipole events occurred. One took place during an El Niño condition and the other during a La Niña condition. Luo et al. find that forecasts using a coupled model could have predicted these dipole phases three to four seasons in advance, although the model did not predict the weaker 2007 positive dipole event very robustly. Further analysis reveals that seasonal climate anomalies in the Eastern Hemisphere associated with the two positive dipole events can be predicted one or two seasons ahead, implying that published dipole predictions could help societies better prepare for potential adverse weather.