AGU journal highlights - July 2, 2009

The Earth's climate is driven by exchange of energy among the Sun, Earth, and space. This is affected by greenhouse gases, clouds, surface properties, and aerosols. Several instruments monitor climate, and to help agencies evaluate potential start times of new missions, Loeb et al. investigate how gaps in the record affect scientists' ability to fully understand climate. Focusing on cloud radiative effects, the authors simulate a 30-year climate data record based on the first five years of data from the Clouds and the Earth's Radiant Energy System (CERES) instrument on board NASA's Terra satellites. On the basis of analyses of accuracy and precision errors, the authors find that a gap of any length anywhere in the record will significantly increase the time required to detect a trend above natural variability because data collected prior to and after the gap cannot be combined accurately enough to ensure trend detection at the required level. To avoid gaps, the authors recommend that at least six months of global or one year of tropical overlapping measurements between successive instruments are needed.

Title: Impact of data gaps on satellite broadband radiation records

Authors: Norman G. Loeb, Bruce A. Wielicki, Takmeng Wong, and Peter A. Parker: NASA Langley Research Center, Hampton, Virginia, USA.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD011183, 2009; http://dx.doi.org/10.1029/2008JD011183

7. Glaciers cause seismic activity in Iceland

In volcanic regions, repeating long-period (lp) earthquakes occur often and are sometimes thought to signal an imminent eruption. Recently, however, some of these earthquake events have been found to be associated with ice movement rather than with volcanic activity. To accurately assess volcanic hazards, scientists need to correctly identify the source of earthquake activity. Jónsdóttir et al. analyze climatic and seismic data from Katla volcano, Iceland. Their study, covering more than 13,000 lp events since 2000, indicates that earthquake activity was seasonal and clearly correlated with climatic changes associated with increased ice movement. They also note that the seismic activity has been continuous for years, with no sign of volcanic eruption. They conclude that the lp events recorded in the region were caused by glacial movements, not volcanic activity, as previously thought. Although the results are specific to the Katla volcano region, the authors suggest that global warming could lead to increasing glacier-induced earthquake activity at other glacier-covered volcanoes.

Title: Glacial long period seismic events at Katla volcano, Iceland

Authors: Kristín Jónsdóttir, Roland Roberts, Veijo Pohjola, Björn Lund, Zaher Hossein Shomali, Ari Tryggvason, and Reynir Böðvarsson: Department of Earth Science, Uppsala University, Uppsala, Sweden.

Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL038234, 2009; http://dx.doi.org/10.1029/2009GL038234

8. Features of Medieval Warm Period in China's Tianshan Mountains