Sungbo Shim

Influence of aerosols in multidecadal SST variability simulations over the North Pacific

The influence of aerosol emissions on North Pacific sea surface temperature (SST) variability during the twentieth century is investigated using a comparison between historical simulations with and without anthropogenic aerosol changes. The historical simulations using the Hadley Global Environment Model version 2 show that there is a common externally forced component in relation to the twentieth century North Pacific SST variability. This matches a number of important temporal and spatial characteristics of the observed multidecadal SST variability from the 1920s to 1990s, which is not found in experiments without aerosol changes. This paper explores both direct and indirect aerosol influences, and finds that in this model the aerosol-cloud interactions dominate the total aerosol forcing of the surface energy budget. These aerosol-cloud processes were not commonly included in most models in the previous (Coupled Model Intercomparison Project phase 3) generation, which may explain why the potential role of aerosols in Pacific variability has not been previously discussed. However, unlike recently reported aerosol drivers of Atlantic SST variability, the aerosol surface radiative forcing pattern does not map directly onto the historical spatial surface radiative and SST changes but is instead modulated by circulation changes to the Aleutian Low. These circulation changes share common features with previously reported studies of natural drivers of Pacific variability, suggesting that both forced and internally generated SST variability may be modulated via the same circulation response.

Oxygen-plasma effects of a La0.7Ca0.3MnO3−δ single crystal

A La0.7Ca0.3MnO3−δ single crystal was oxygen-plasma treated at 200 °C. Our electrical and magnetic measurements indicate that the oxygen-plasma treatment can be an effective low temperature method of oxygen stoichiometry modification of colossal magnetoresistance manganites. The oxygen plasma is also shown to introduce structural defects, whose effects are prominent near the Curie temperature (Tc), giving rise to anomalies in the resistivity and magnetic behaviors.

Intercomparison of precipitation datasets for summer precipitation characteristics over East Asia

Precipitation data in the Global Precipitation Climatology Project (GPCP) and in four reanalysis datasets, ERA-Interim, MERRA, NCEP/NCAR, and JRA, are compared against the CPC Merged Precipitation (CMAP) in the cyclostationary empirical orthogonal function (CSEOF) space to evaluate these datasets in representing the summer precipitation characteristics over East Asia. CSEOF analysis is applied to each dataset, and regression analysis is performed in the CSEOF space with the CMAP data as the target. The regression analysis establishes one-to-one correspondence between the CSEOF loading vectors of the target variable and those of the predictors, i.e., GPCP and the four reanalysis datasets. The loading vectors of the GPCP data coincide almost exactly with those of the CMAP data, i.e., the two observation-based precipitation datasets represent practically identical summer precipitation characteristics over East Asia. The reanalysis datasets also reproduce the first five CSEOF modes reasonably; however, performance of NCEP/NCAR is notably lower than others. The re-constructed precipitation using the first five regressed CSEOF modes of the reanalysis datasets are well correlated with that of the CMAP data with reasonably large correlation coefficients, suggesting that these reanalysis precipitation products reliably simulate the major summer precipitation characteristics in East Asia. All of the four reanalysis products commonly show noticeable errors in representing the summer rainfall over the mid-latitude ocean to the south of Japan, the tropical western Pacific, tropical/subtropical regions including the Indochina Peninsula, India, the Maritime Continent, and regions of complex terrain especially those characterized by strong orographic slopes around the Tibetan Plateau. The errors over the regions of complex orography and coastal lines may be partially due to the inability of reanalysis models in simulating the effects of complex terrain and the lack of observations in these sparsely populated regions.

Impact of Fossil Fuel Organic Carbon Emission on the 20th Century Climate

Aerosols play the important role as scatter or absorb solar radiation, which consequently modifies the radiative balance of the atmosphere. Aerosol and its effects, especially its indirect effects, on climate have drawn increasing attention in recent years. Understanding of interactions of aerosols and climate is important to better prediction of future climate change. In this study, the direct and indirect effect of fossil fuel organic carbon aerosol (OC) and its impacts on the climate during the period of the early of 20th century (1901~1920) and the end of 20th century (1986~2005) were investigated. we examine changes in aerosol emission during 20th century. Using HadGEM2-AO (Hadley Centre Global Environmental Model version 2, Atmosphere and Ocean), historical experiments are carried out with and without anthropogenic aerosol emissions (HIST, FIXA) from 1860 to 2005. Fossil fuel organic carbon aerosol (OCFF) emission fixed at 1860 is added. Due to the large emission of OC, thick optical depth of the OC appears over Asia, western Europe and eastern north America. The direct effect due to increasing OC influences negative radiative effect at the surface, which leads to a cooling effect on the surface. The OC shows direct effect and indirect effect as well. The variation of total amount of clouds are affected by the OC aerosols emission.