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C. P. Kim and J. N. M. Stricker

Abstract

This paper investigates the treatment of the soil water budget of two parametric models currently used in atmospheric models for climate studies. Because the parametric models are intended to represent areally averaged behavior, results of the water budget for both models are compared to output of a well-tested physically based, one-dimensional unsaturated flow model with spatially heterogeneous soil hydraulic properties. Computations are performed for the three models using two datasets of soil hydraulic properties and three separate years of daily average meteorological conditions. Neglecting the percolation process in land-surface parameterizations can lead to very unrealistic results in evapotranspiration estimates. Evapotranspiration efficiencies of the parametric models show more rapid time fluctuations compared to the physically based model. Furthermore, it appears that a selected reference set of soil hydraulic properties behaves similar to the areally distributed properties for soil water balance computation in the absence of surface runoff.

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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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Y. C. Sud, W. K-M. Lau, G. K. Walker, J-H. Kim, G. E. Liston, and P. J. Sellers

Abstract

Two 3-year (1979–1982) integrations were carried out with a version of the GLA GCM that contains the Simple Biosphere Model (SiB) for simulating land-atmosphere interactions. The control case used the usual SiB vegetation cover (comprising 12 vegetation types), while its twin, the deforestation case, imposed a scenario in which all tropical rainforests were entirely replaced by grassland. Except for this difference, all other initial and prescribed boundary conditions were kept identical in both integrations.

An intercomparison of the integrations shows that tropical deforestation

• decreases evapotranspiration and increases land surface outgoing longwave radiation and sensible heat flux, thereby warming and drying the planetary boundary layer. This happens despite the reduced absorption of solar radiation due to higher surface albedo of the deforested land.

• produces significant and robust local as well as global climate changes. The local effect includes significant changes (mostly reductions) in precipitation and diabatic heating, while the large-scale effect is to weaken the Hadley circulation but invigorate the southern Ferrel cell, drawing larger air mass from the indirect polar cells.

• decreases the surface stress (drag force) owing to reduced surface roughness of deforested land, which in turn intensifies winds in the planetary boundary layer, thereby affecting the dynamic structure of moisture convergence. The simulated surface winds are about 70% stronger and are accompanied by significant changes in the power spectrum of the annual cycle of surface and PBL winds and precipitation.

• Our results broadly confirm several findings of recent tropical deforestation simulation experiments. In addition, some global-scale climatic influences of deforestation not identified in earlier studies are delineated.

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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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Ryan C. Bunker, Ariel E. Cohen, John A. Hart, Alan E. Gerard, Kim E. Klockow-McClain, and David P. Nowicki

Abstract

Tornadoes that occur at night pose particularly dangerous societal risks, and these risks are amplified across the southeastern United States. The purpose of this study is to highlight some of the characteristics distinguishing the convective environment accompanying these events. This is accomplished by building upon previous research that assesses the predictive power of meteorological parameters. In particular, this study uses the Statistical Severe Convective Risk Assessment Model (SSCRAM) to determine how well convective parameters explain tornado potential across the Southeast during the months of November–May and during the 0300–1200 UTC (nocturnal) time frame. This study compares conditional tornado probabilities across the Southeast during November–May nocturnal hours to those probabilities for all other November–May environments across the contiguous United States. This study shows that effective bulk shear, effective storm-relative helicity, and effective-layer significant tornado parameter yield the strongest predictability for the November–May nocturnal Southeast regime among investigated parameters. This study demonstrates that November–May southeastern U.S. nocturnal predictability is generally similar to that within other regimes across the contiguous United States. However, selected ranges of multiple parameters are associated with slightly better predictability for the nocturnal Southeast regime. Additionally, this study assesses conditional November–May nocturnal tornado probabilities across a coastal domain embedded within the Southeast. Nocturnal coastal tornado predictability is shown to generally be lower than the other regimes. All of the differences highlight several forecast challenges, which this study analyzes in detail.

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T. H. Chen, A. Henderson-Sellers, P. C. D. Milly, A. J. Pitman, A. C. M. Beljaars, J. Polcher, F. Abramopoulos, A. Boone, S. Chang, F. Chen, Y. Dai, C. E. Desborough, R. E. Dickinson, L. Dümenil, M. Ek, J. R. Garratt, N. Gedney, Y. M. Gusev, J. Kim, R. Koster, E. A. Kowalczyk, K. Laval, J. Lean, D. Lettenmaier, X. Liang, J.-F. Mahfouf, H.-T. Mengelkamp, K. Mitchell, O. N. Nasonova, J. Noilhan, A. Robock, C. Rosenzweig, J. Schaake, C. A. Schlosser, J.-P. Schulz, Y. Shao, A. B. Shmakin, D. L. Verseghy, P. Wetzel, E. F. Wood, Y. Xue, Z.-L. Yang, and Q. Zeng

Abstract

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m−2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (±10 W m−2). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models’ neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of30 W m−2 and 25 W m−2, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W m−2 for sensible heat flux and 10 W m−2 for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to groundwater, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.

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Anne S. Daloz, S. J. Camargo, J. P. Kossin, K. Emanuel, M. Horn, J. A. Jonas, D. Kim, T. LaRow, Y.-K. Lim, C. M. Patricola, M. Roberts, E. Scoccimarro, D. Shaevitz, P. L. Vidale, H. Wang, M. Wehner, and M. Zhao

Abstract

A realistic representation of the North Atlantic tropical cyclone tracks is crucial as it allows, for example, explaining potential changes in U.S. landfalling systems. Here, the authors present a tentative study that examines the ability of recent climate models to represent North Atlantic tropical cyclone tracks. Tracks from two types of climate models are evaluated: explicit tracks are obtained from tropical cyclones simulated in regional or global climate models with moderate to high horizontal resolution (1°–0.25°), and downscaled tracks are obtained using a downscaling technique with large-scale environmental fields from a subset of these models. For both configurations, tracks are objectively separated into four groups using a cluster technique, leading to a zonal and a meridional separation of the tracks. The meridional separation largely captures the separation between deep tropical and subtropical, hybrid or baroclinic cyclones, while the zonal separation segregates Gulf of Mexico and Cape Verde storms. The properties of the tracks’ seasonality, intensity, and power dissipation index in each cluster are documented for both configurations. The authors’ results show that, except for the seasonality, the downscaled tracks better capture the observed characteristics of the clusters. The authors also use three different idealized scenarios to examine the possible future changes of tropical cyclone tracks under 1) warming sea surface temperature, 2) increasing carbon dioxide, and 3) a combination of the two. The response to each scenario is highly variable depending on the simulation considered. Finally, the authors examine the role of each cluster in these future changes and find no preponderant contribution of any single cluster over the others.

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M. Goldberg, G. Ohring, J. Butler, C. Cao, R. Datla, D. Doelling, V. Gärtner, T. Hewison, B. Iacovazzi, D. Kim, T. Kurino, J. Lafeuille, P. Minnis, D. Renaut, J. Schmetz, D. Tobin, L. Wang, F. Weng, X. Wu, F. Yu, P. Zhang, and T. Zhu

The Global Space-based Inter-Calibration System (GSICS) is a new international program to assure the comparability of satellite measurements taken at different times and locations by different instruments operated by different satellite agencies. Sponsored by the World Meteorological Organization and the Coordination Group for Meteorological Satellites, GSICS will intercalibrate the instruments of the international constellation of operational low-earth-orbiting (LEO) and geostationary earth-orbiting (GEO) environmental satellites and tie these to common reference standards. The intercomparability of the observations will result in more accurate measurements for assimilation in numerical weather prediction models, construction of more reliable climate data records, and progress toward achieving the societal goals of the Global Earth Observation System of Systems. GSICS includes globally coordinated activities for prelaunch instrument characterization, onboard routine calibration, sensor intercomparison of near-simultaneous observations of individual scenes or overlapping time series, vicarious calibration using Earth-based or celestial references, and field campaigns. An initial strategy uses high-accuracy satellite instruments, such as the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Atmospheric Infrared Sounder (AIRS) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)'s Centre National d'Études Spatiales (CNES) Infrared Atmospheric Sounding Interferometer (IASI), as space-based reference standards for intercalibrating the operational satellite sensors. Examples of initial intercalibration results and future plans are presented. Agencies participating in the program include the Centre National d'Études Spatiales, China Meteorological Administration, EUMETSAT, Japan Meteorological Agency, Korea Meteorological Administration, NASA, National Institute of Standards and Technology, and NOAA.

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A. Roiger, J.-L. Thomas, H. Schlager, K. S. Law, J. Kim, A. Schäfler, B. Weinzierl, F. Dahlkötter, I. Krisch, L. Marelle, A. Minikin, J.-C. Raut, A. Reiter, M. Rose, M. Scheibe, P. Stock, R. Baumann, I. Bouarar, C. Clerbaux, M. George, T. Onishi, and J. Flemming

Abstract

Arctic sea ice has decreased dramatically in the past few decades and the Arctic is increasingly open to transit shipping and natural resource extraction. However, large knowledge gaps exist regarding composition and impacts of emissions associated with these activities. Arctic hydrocarbon extraction is currently under development owing to the large oil and gas reserves in the region. Transit shipping through the Arctic as an alternative to the traditional shipping routes is currently underway. These activities are expected to increase emissions of air pollutants and climate forcers (e.g., aerosols, ozone) in the Arctic troposphere significantly in the future. The authors present the first measurements of these activities off the coast of Norway taken in summer 2012 as part of the European Arctic Climate Change, Economy, and Society (ACCESS) project. The objectives include quantifying the impact that anthropogenic activities will have on regional air pollution and understanding the connections to Arctic climate. Trace gas and aerosol concentrations in pollution plumes were measured, including emissions from different ship types and several offshore extraction facilities. Emissions originating from industrial activities (smelting) on the Kola Peninsula were also sampled. In addition, pollution plumes originating from Siberian biomass burning were probed in order to put the emerging local pollution within a broader context. In the near future these measurements will be combined with model simulations to quantify the influence of local anthropogenic activities on Arctic composition. Here the authors present the scientific objectives of the ACCESS aircraft experiment and the the meteorological conditions during the campaign, and they highlight first scientific results from the experiment.

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A. G. Slater, C. A. Schlosser, C. E. Desborough, A. J. Pitman, A. Henderson-Sellers, A. Robock, K. Ya Vinnikov, J. Entin, K. Mitchell, F. Chen, A. Boone, P. Etchevers, F. Habets, J. Noilhan, H. Braden, P. M. Cox, P. de Rosnay, R. E. Dickinson, Z-L. Yang, Y-J. Dai, Q. Zeng, Q. Duan, V. Koren, S. Schaake, N. Gedney, Ye M. Gusev, O. N. Nasonova, J. Kim, E. A. Kowalczyk, A. B. Shmakin, T. G. Smirnova, D. Verseghy, P. Wetzel, and Y. Xue

Abstract

Twenty-one land surface schemes (LSSs) performed simulations forced by 18 yr of observed meteorological data from a grassland catchment at Valdai, Russia, as part of the Project for the Intercomparison of Land-Surface Parameterization Schemes (PILPS) Phase 2(d). In this paper the authors examine the simulation of snow. In comparison with observations, the models are able to capture the broad features of the snow regime on both an intra- and interannual basis. However, weaknesses in the simulations exist, and early season ablation events are a significant source of model scatter. Over the 18-yr simulation, systematic differences between the models’ snow simulations are evident and reveal specific aspects of snow model parameterization and design as being responsible. Vapor exchange at the snow surface varies widely among the models, ranging from a large net loss to a small net source for the snow season. Snow albedo, fractional snow cover, and their interplay have a large effect on energy available for ablation, with differences among models most evident at low snow depths. The incorporation of the snowpack within an LSS structure affects the method by which snow accesses, as well as utilizes, available energy for ablation. The sensitivity of some models to longwave radiation, the dominant winter radiative flux, is partly due to a stability-induced feedback and the differing abilities of models to exchange turbulent energy with the atmosphere. Results presented in this paper suggest where weaknesses in macroscale snow modeling lie and where both theoretical and observational work should be focused to address these weaknesses.

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