AGU journal highlights -- Dec. 31, 2008

1. Surprise drop in carbon dioxide absorbed by East/Japan Sea

The East/Japan Sea in the western North Pacific is ventilated from the surface to the bottom of the ocean over decades. Such short overturning circulation indicates that carbon dioxide (CO₂) from human emissions is able to pervade the East/Japan Sea on similarly short timescales. Three surveys of the East/Japan Sea (conducted in 1992, 1999, and 2007, respectively) have allowed scientists to measure changes in the sea accumulation rate of CO₂ emitted by humans in response to changes in surface conditions. Park et al. analyze data from these surveys and find that the average uptake rate of anthropogenic CO₂ by the East/Japan Sea from 1999 to 2007 was half of what it was for the period between 1992 and 1999. Further, anthropogenic CO₂ absorbed by the water more recently was confined to waters less than 300 meters (984 feet) in depth. Because emissions have in fact accelerated over the past 10 years, the authors conclude that overturning circulation is weakening, slowing down the transport of anthropogenic CO₂ from the surface to the interior of the East/Japan Sea.

Title: Sudden, considerable reduction in recent uptake of anthropogenic CO₂ by the East/Japan Sea

Authors: Geun-Ha Park and Kitack Lee: School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang, Korea;

Pavel Tishchenko: Pacific Oceanological Institute, Far East Division, Russian Academy of Sciences, Vladivostok, Russia.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036118, 2008; http://dx.doi.org/10.1029/2008GL036118

2. Simulations suggest big raindrops favor tornado formation

One of the largest sources of uncertainty in weather prediction involves how microscale structures influence larger-scale phenomena. For instance, previous studies have demonstrated that the structure, dynamics, and evolution of thunderstorms are very sensitive to cloud microphysical parameters. However, those studies used resolutions too coarse to resolve tornadoes or tornado-like circulations and were therefore not able to study the sensitivity of tornadogenesis to microphysics. Snook and Xue have now conducted simulations of severe tornadic thunderstorms using a grid of 100-meter (328-feet) spacing. They find that when the sizes of rain and hail drops are large, weaker cold pools due to reduced evaporative cooling/melting over smaller geographic regions result. Such weak cold pools are found to produce conditions that enhance low-level rotation. The authors' simulations show that strong, sustained vertical updrafts are positioned near and above the low-level circulation centers, providing strong dynamic lifting and vertical stretching to the air at the lower levels, which favors the creation of tornadoes.

Title: Effects of microphysical drop size distribution on tornadogenesis in supercell thunderstorms.

Authors: Nathan Snook and Ming Xue: School of Meteorology and Center for Analysis and Prediction of Storms, University of Oklahoma, Norman, Oklahoma, U.S.A.