Daily Archives: August 1, 2013

Atmospheric model results depend upon the computer used

The results of GCM simulations have now been found to depend on the computer hardware and software used.

Song-You Hong, Myung-Seo Koo, Jihyeon Jang, Jung-Eun Esther Kim, Hoon Park, Min-Su Joh, Ji-Hoon Kang, and Tae-Jin Oh. An Evaluation of the Software System Dependency of a Global Atmospheric Model. Monthly Weather Review. 2013. doi: http://dx.doi.org/10.1175/MWR-D-12-00352.1

This study presents the dependency of the simulation results from a global atmospheric numerical model on machines with different hardware and software systems. The global model program (GMP) of the Global/Regional Integrated Model system (GRIMs) is tested on 10 different computer systems having different central processing unit (CPU) architectures or compilers. There exist differences in the results for different compilers, parallel libraries, and optimization levels, primarily due to the treatment of rounding errors by the different software systems. The system dependency, which is the standard deviation of the 500-hPa geopotential height averaged over the globe, increases with time. However, its fractional tendency, which is the change of the standard deviation relative to the value itself, remains nearly zero with time. In a seasonal prediction framework, the ensemble spread due to the differences in software system is comparable to the ensemble spread due to the differences in initial conditions that is used for the traditional ensemble forecasting.

Click here for full paper (fee).

Assessing exposure, reducing risk to trihalomethanes in drinking water

Chowdhury S. Exposure assessment for trihalomethanes in municipal drinking water and risk reduction strategy. Science of the Total Environment. 2013 Jul 18;463-464C:922-930. doi: 10.1016/j.scitotenv.2013.06.104.

Lifetime exposure to disinfection byproducts (DBPs) in municipal water may pose risks to human health. Current approaches of exposure assessments use DBPs in cold water during showering, while warming of chlorinated water during showering may increase trihalomethane (THM) formation in the presence of free residual chlorine. Further, DBP exposure through dermal contact during showering is estimated using steady-state condition between the DBPs in shower water impacting on human skin and skin exposed to shower water. The lag times to achieve steady-state condition between DBPs in shower water and human skin can vary in the range of 9.8-391.2min, while shower duration is often less than the lag times. Assessment of exposure without incorporating these factors might have misinterpreted DBP exposure in some previous studies. In this study, exposure to THMs through ingestion was estimated using cold water THMs, while THM exposure through inhalation and dermal contact during showering was estimated using THMs in warm water. Inhalation of THMs was estimated using THM partition into the shower air, while dermal uptake was estimated by incorporating lag times (e.g., unsteady and steady-state phases of exposure) during showering. Probabilistic approach was followed to incorporate uncertainty in the assessment. Inhalation and dermal contact during showering contributed 25-60% of total exposure. Exposure to THMs during showering can be controlled by varying shower stall volume, shower duration and air exchange rate following power law equations. The findings might be useful in understanding exposure to THMs, which can be extended to other volatile compounds in municipal water.

Click here for full paper (fee).