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C.-H. Ho, S.-J. Park, S.-J. Jeong, J. Kim, and J.-G. Jhun

Abstract

The impacts of harvested cropland in the double cropping region (DCR) of the northern China plains (NCP) on the regional climate are examined using surface meteorological data and the satellite-derived normalized difference vegetation index (NDVI) and land surface temperature (LST). The NDVI data are used to distinguish the DCR from the single cropping region (SCR) in the NCP. Notable increases in LST in the period May–June are found in the area identified as the DCR on the basis of the NDVI data. The difference between the mean daily maximum temperature averaged over the DCR and SCR stations peaks at 1.27°C in June. The specific humidity in the DCR is significantly smaller than in the SCR. These results suggest that the enhanced agricultural production by multiple cropping may amplify regional warming and aridity to further modify the regional climate in addition to the global climate change. Results in this study may also be used as a quantitative observed reference state of the crop/vegetation effects for future climate modeling studies.

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H. K. Ha, A. K. Wåhlin, T. W. Kim, S. H. Lee, J. H. Lee, H. J. Lee, C. S. Hong, L. Arneborg, G. Björk, and O. Kalén

Abstract

The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by the Dotson trough (DT), leading from the outer shelf to the deep basins on the inner shelf. During the measurement period, warm deep water was observed to flow southward on the eastern side of DT in approximate geostrophic balance. A northward outflow from the shelf was also observed along the bottom in the western side of DT. Estimates of the flow rate suggest that up to one-third of the inflowing warm deep water leaves the shelf area below the thermocline in this deep outflow. The deep current was 1.2°C colder and 0.3 psu fresher than the inflow, but still warm, salty, and dense compared to the overlying water mass. The temperature and salinity properties suggest that the cooling and freshening process is induced by subsurface melting of glacial ice, possibly from basal melting of Dotson and Getz ice shelves. New heat budgets are presented, with a southward oceanic heat transport of 3.3 TW on the eastern side of the DT, a northward oceanic heat transport of 0.5–1.6 TW on the western side, and an ocean-to-glacier heat flux of 0.9–2.53 TW, equivalent to melting glacial ice at the rate of 83–237 km3 yr−1. Recent satellite-based estimates of basal melt rates for the glaciers suggest comparable values for the Getz and Dotson ice shelves.

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A. K. Wåhlin, O. Kalén, K. M. Assmann, E. Darelius, H. K. Ha, T. W. Kim, and S. H. Lee

Abstract

Mooring data from the western flank of Dotson trough, Amundsen Sea shelf region, show the presence of barotropic oscillations with a period of 40–80 h. The oscillations are visible in velocity, temperature, salinity, and pressure and are comparable to tides in magnitude. The period of the oscillations corresponds to topographic Rossby waves of low group velocity and a wavelength of about 40 km, that is, the half-width of the channel. It is suggested that these resonant topographic Rossby waves cause the observed peak in the wave spectra. The observations show that sparse CTD data from this region should be treated with caution and need to be complemented with moorings or yo-yo stations in order to give a representative picture for the hydrography.

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Shakti P. C.,, M. Maki, S. Shimizu, T. Maesaka, D.-S. Kim, D.-I. Lee, and H. Iida

Abstract

Two approaches to correcting the partial beam blockage of radar reflectivity in mountainous areas were evaluated using X-band dual polarization radar data from the Hakone mountain region, Kanto, Japan. The comparatively simple digital elevation model (DEM) method calculates the power loss in the received signal based on the geometrical relationship between radar beams and a DEM. The second approach, the modified DEM method, attempts to account for unknown power losses related to ground clutter, hardware calibration errors, etc. Comparison between ground data and reflectivity data corrected by both methods suggests that the DEM method alone was insufficient to correct beam blockage problems but that the modified DEM data were in generally good agreement with the ground data. The authors also estimated 10-min rainfall amounts using reflectivity corrected by the modified DEM method and compared these with data from a network of rain gauges in the mountainous region. In general, the results show good agreement between radar estimates and rain gauge measurements. On the basis of their results, the authors conclude that the modified DEM method offers a suitable solution to the problem of beam blockage in mountainous regions, provided that the beam blockage rate is less than 80%.

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A. K. Wåhlin, O. Kalén, L. Arneborg, G. Björk, G. K. Carvajal, H. K. Ha, T. W. Kim, S. H. Lee, J. H. Lee, and C. Stranne

Abstract

The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transport warm dense water onto the shelf, channeled by bathymetric troughs leading to the deep inner basins. A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar Deep Water (CDW) toward the ice shelves in the bottom layer. This bottom-intensified flow appears to be driven by buoyancy forces rather than the shelfbreak wind. The years of 2010 and 2011 were characterized by a comparatively stationary Amundsen Sea low, and hence there were no strong eastward winds during winter that could drive an upwelling of warm water along the shelf break. Regardless of this, there was a persistent flow of lower CDW in the bottom layer during the two years. The average heat transport toward the ice shelves in the trough was estimated from the mooring data to be 0.95 TW.

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H. J. Lee, M. O. Kwon, S.-W. Yeh, Y.-O. Kwon, W. Park, J.-H. Park, Y. H. Kim, and M. A. Alexander

Abstract

Arctic sea ice area (SIA) during late summer and early fall decreased substantially over the last four decades, and its decline accelerated beginning in the early 2000s. Statistical analyses of observations show that enhanced poleward moisture transport from the North Pacific to the Arctic Ocean contributed to the accelerated SIA decrease during the most recent period. As a consequence, specific humidity in the Arctic Pacific sector significantly increased along with an increase of downward longwave radiation beginning in 2002, which led to a significant acceleration in the decline of SIA in the Arctic Pacific sector. The resulting sea ice loss led to increased evaporation in the Arctic Ocean, resulting in a further increase of the specific humidity in mid-to-late fall, thus acting as a positive feedback to the sea ice loss. The overall set of processes is also found in a long control simulation of a coupled climate model.

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Y. P. Kim, S-G. Shim, K. C. Moon, C-G. Hu, C. H. Kang, and K. Y. Park

Abstract

Gaseous species and total suspended particles were measured at Kosan, Cheju Island, Korea, between 11 March and 19 April 1994. The concentrations of nonsea salt (nss) ions were higher than those measured in clean marine areas of Japan and other background marine areas of the world. In particular, the nss sulfate concentration was comparable to that measured in Seoul. The average SO2 and NOx concentrations were approximately 0.97 and 3.5 ppb, respectively, which were lower than those at other urban areas in Korea but higher than those of other remote areas in the world. In contrast, the average O3 concentration was approximately 55 ppb, which is comparable to or higher than those at remote sites in Japan that were influenced by long-range transport of air pollutants. Half of the air parcels during the period were from northern China and about 30% of the air parcels from southern China. The main difference of air pollutant levels between the two areas was higher crustal species and lower nss sulfate concentrations for air parcels from northern China. The nss SO2−4 concentrations had a strong correlation with nss K+, NH+4, and O3 concentrations. In addition, the nss Ca2+ concentrations had a strong correlation with the nss K+ and nss Mg2+ concentrations. It was suggested that nss K+ had two sources:anthropogenic and crustal.

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A. H. Lynch, F. S. Chapin III, L. D. Hinzman, W. Wu, E. Lilly, G. Vourlitis, and E. Kim

Abstract

The progress made in the Land–Atmosphere–Ice Interactions Flux Study over the past 4 yr to fully characterize the biophysical fluxes in the snow-free tundra ecosystem and their relationship to climate and climate change is described. This paper is the result of a synthesis effort to bring together the measurements of surface fluxes at various sites on the North Slope of Alaska in the snow-free period of 1995 with the results of modeling efforts for this region. It is found that methodological and site dissimilarities contribute to measurement differences at least as much as instrument and sampling error, even for closely collocated and similarly vegetated sites. The regional climate model employed in this study generally simulates fluxes that are within the range of measured fluxes, but tends to overestimate both net radiation and latent heat fluxes. The regional model also captures site to site variations quite well, which appear to be more sensitive to mesoscale meteorological conditions than on specifics of site characteristics. The active layer model employed in this study performs well in estimating ground heat flux but rather more poorly in simulating turbulent fluxes. The global climate model is unable to capture the broad-scale response of the land surface sensible heat flux and net radiation, although it performs rather better in the simulation of latent and ground heat fluxes. Finally, the intended purposes and applications of both data and model simulations have a strong impact on their applicability to other studies.

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J. M. Warnock, T. E. VanZandt, W. L. Clark, S. J. Franke, H. S. Kim, G. D. Nastrom, and P. E. Johnston

Abstract

An experimental field campaign to measure synoptic-scale vertical velocities was conducted from 5 to 11 January 1991 in the Urbana-Champaign, Illinois, region, which is in very flat terrain far from mountains. Both the Flatland and the Urbana wind-profiling radars, which are separated by 23.1 km, participated in the campaign. Meteorological sounding balloons were also launched from the Flatland Observatory site. In this study, lime averages are compared of the vertical wind velocity measured directly by both radars in order to help verify the capability of wind-profiling radars to measure synoptic-scale vertical velocities. This comparison, of course, also provides an opportunity to evaluate the performance of both radars.

The variance of the vertical velocity observed by the Flatland radar has been previously shown to be dominated by short-period fluctuations with most of the variance occurring at periods less than 6 h. Also, since March 1987 when the Flatland radar began operating nearly continuously, the vertical velocity measurements showed a nearly constant downward mean value of several centimeters per second in the troposphere. After bandpass filtering, the time-series measurements of vertical velocity to obtain 6-b and 1-day means, the filtered signal is compared to similar measurements made by the newly constructed Urbana radar. Both the 6-b and 1-day time averages of vertical velocity measured by the radars displayed large variations in time and height. Variations of 1.0–1.5 cm s−1 occurred frequently, which are considerably larger than the expected measurement error. Good to excellent agreement is generally found in the shape of height profiles measured by the two radars. These results suggest that wind-profiling radars located in very flat terrain are capable of measuring synoptic-scale vertical velocity profiles with useful precision.

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D. S. Gutzler, H. - K. Kim, R. W. Higgins, H. - M. H. Juang, M. Kanamitsu, K. Mitchell, K. Mo, P. Pegion, E. Ritchie, J. - K. Schemm, S. Schubert, Y. Song, and R. Yang
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