Publications by KASA Members : 2003

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¡Ü Lee, M-I.,I.-S.Kang, and B.E. Mapes, 2003: Impacts of cumulus convection parameterization on aqua-planet AGCM simulations of tropical intraseasonal variability. J. Meteorol. Soc. Japan, 81, 5, 963-992.

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¡Ü Baik, Jong-Jin, J.-J. Kim, and J. S. Fernando, 2003: A CFD model for simulating urban flow and dispersion.  Journal of Applied Meteorology, 42(11), 1636-1648.

¡Ü Ha, So-Young, Y.-H. Kuo, Y.-R. Guo, and G.-H. Lim, 2003: Variational Assimilation of Slant-Path Wet Delay Measurements from a Hypothetical Ground-Based GPS Network. Part I: Comparison with Precipitable Water Assimilation. Monthly Weather Review, 131(11),  2635–2655.

ABSTRACT

With the recent advance in Global Positioning System (GPS) atmospheric sensing technology, slant wet delay along each ray path can be measured with a few millimeters accuracy. In this study, the impact of slant wet delay is assessed on the short-range prediction of a squall line. Since the current GPS observation network in the central United States is not of high enough density to capture the mesoscale variation of moisture in time and space, a set of observing system simulation experiments is performed to assimilate slant wet delay data from a hypothetical network of ground-based GPS receivers using the four-dimensional variational data assimilation technique. In the assimilation of slant wet delay data, significant changes in moisture, temperature, and wind fields within the boundary layer were found. These changes lead to a stronger surface cold front and stronger convective instability ahead of the front. Consequently, the assimilation of slant wet delay produces a considerably improved 6-h forecast of a squall line in terms of rainfall prediction and mesoscale frontal structure. Previous studies have shown that the assimilation of GPS-derived precipitable water data can improve moisture analysis and rainfall prediction. In order to assess the additional value of slant wet delay data assimilation, a parallel experiment is performed in which precipitable water data is assimilated. The assimilation of slant wet delay data is demonstrated to be superior in recovering water vapor information between receiver sites and in short-range precipitation forecast both in terms of rainfall distribution and intensity. As revealed by atmospheric soundings in the vicinity of the squall line, the assimilation of slant wet delay data more accurately retrieves the temperature and moisture structure in the convectively unstable region.

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¡Ü Shin, Dong-Bin, and C. Kummerow, 2003: Parametric Rainfall Retrieval Algorithms for Passive Microwave Radiometers. J. Appl. Meteor., 42(10), 1480-1496.

ABSTRACT

A methodology is described to construct fully parametric rainfall retrieval algorithms for a variety of passive microwave sensors that exist today and are planned for the future. The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) is used to retrieve nonraining geophysical parameters. The method then blends these background geophysical parameters with three-dimensional precipitation fields obtained by matching the TRMM precipitation radar (PR) reflectivity profiles with cloud-resolving model simulations to produce a consistent three-dimensional atmospheric description. Based upon this common description, radiative transfer simulations corresponding to specific microwave sensors are then employed to compute radiances from clear and rainy scenes, as might be seen by any specified microwave radiometer. Last, a Bayesian retrieval methodology is used in conjunction with this database to derive the most likely surface rainfall as well as its vertical structure. By avoiding any dependencies on specific channels or channel combinations, the technique can readily be adapted to different sensor configurations. The algorithm performance is tested for a variety of sensor designs using synthetic retrievals to demonstrate its capability for consistent rainfall estimates. Whereas actual retrievals would be sensitive to the details of the a priori database construction, results from this study indicate that even modest radiometers can retrieve unbiased rainfall rates when constrained by an a priori database constructed from the TRMM satellite. Random errors are correlated to unobserved variations in the vertical and horizontal structure of the precipitation and, thus, depend upon sensor design specifications. The fidelity of these synthetic retrievals is briefly examined by comparing the simulated brightness temperature (T_b) generated in this study with direct observations by the TRMM TMI. Good physical consistency between the simulated and TRMM observed T_bs is found in precipitating regions for frequencies at which emission processes dominate the radiometric signal. The consistency is poor for higher-frequency microwave channels for which ice scattering is important. Greater consistency between the computed and observed T_bs should be sought before replacing current operational algorithms with the parametric equivalent.

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¡Ü Sohn, Byung-Ju, and E. A. Smith, 2003: Explaining sources of discrepancy in SSM/I water vapor algorithms. J. Climate, 16(20), 3229-3255.

ABSTRACT

This study examines a mix of seven statistical and physical Special Sensor Microwave Imager (SSM/I) passive microwave algorithms that were designed for retrieval of over-ocean precipitable water (PW). The aim is to understand and explain why the algorithms exhibit a range of discrepancies with respect to measured PWs and with respect to each other, particularly systematic regional discrepancies that would produce substantive uncertainties in water vapor transports and radiative cooling in the context of climate dynamics. Data analysis is used to explore the nature of the algorithm differences, while radiative transfer analysis is used to explore the influence of several environmental variables (referred to as tangential environmental factors) that affect the PW retrievals. These are sea surface temperature (SST), surface wind speed (U_s), cloud liquid water path (LWP), and vertical profile structure of water vapor [q(z)]. The main datasets include the Wentz matched radiosonde–SSM/I point database consisting of 42 months of globally distributed oceanic radiosonde profiles paired with coincident SSM/I brightness temperatures, and globally compiled instantaneous orbit-swath maps of SSM/I brightness temperatures for January and July 1990.

Results demonstrate that the seemingly good agreement found in past studies and herein, within the conventional framework of scatter diagram analysis that ignores regional classification, gives way to poor agreement in the framework of monthly and zonally averaged differences. It is shown how much of the disagreement inherent to statistical algorithms is due to disjoint training datasets used in deriving algorithm regression coefficients. The investigation also explores how tangential environmental factors composed of variations in SST, U_s, cloud LWP, and q(z) structure impart dissimilar errors to retrieved PWs, according to the design of the retrieval algorithms. A discussion on implications of the discrepancies vis-à-vis the Global Energy and Water Cycle Experiment program is given, with suggestions on mitigating discrepancies in algorithm designs.

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¡Ü Kim, Jinwon, and Jung-Eun Lee, 2003: A Multiyear Regional Climate Hindcast for the Western United States Using the Mesoscale Atmospheric Simulation Model. Journal of Hydrometeorology, 4(5), 878-890.

ABSTRACT

In preparation for studying the effects of increased CO₂ on the hydrologic cycle in the western United States, an 8-yr hindcast was performed using a regional climate model (RCM) driven by the large-scale forcing from the NCEP–NCAR reanalysis. The simulated precipitation characteristics agree well with observations, especially in the winter. The simulated precipitation compares with rain gauge data at similar accuracy as the NCEP reanalysis, but the RCM-generated precipitation is more accurate than the reanalysis data at the scales of individual basins. Important characteristics of the hydrologic cycle of the region, such as seasonal snowfall, frequency of heavy and extreme daily precipitation events, and interannual variations of precipitation associated with the North American monsoon are also well represented in the hindcast. Compared to the Climate Research Unit, University of East Anglia (CRU), analysis, the simulated low-level air temperatures show cold biases except in summer. The temperature biases are difficult to quantify, however, due to suspected warm biases in the CRU data. The RCM overestimates surface insolation and outgoing longwave radiation at the top of the atmosphere (OLR-TOA). The errors in the simulated radiation are smaller over the land than the ocean. Both simulated and observed OLR-TOA suggest strong influence of low-level temperatures on the seasonal variations of OLR-TOA in the region. The results suggest that the RCM employed in this study possesses reasonable skill for studying regional climate change signals in the western United States

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¡Ü Kim, K.-Y, J. J. O'Brien, and A. I. Barcilon, 2003: The Principal Physical Modes of Variability over the Tropical Pacific. Earth Interactions, 7, Paper 3.

ABSTRACT

The structures of the two principal modes of sea surface temperature (SST) variability were extracted by conducting cyclostationary EOF (CSEOF) analysis and regression analysis on several key variables. The CSEOF analysis extracts two dominant modes of SST variability that are distinct in nature. The first CSEOF is stochastic in nature and represents a standing mode of SST variability associated with a basinwide change in the surface wind. The second CSEOF exhibits a strong deterministic component describing a biennial oscillation between a warm phase and a cold phase. The surface wind directional change in the far-western Pacific appears to be instrumental for the oscillation between the two phases. Because of the distinct nature of evolution, dynamical and thermodynamical responses of the two modes are different. Further, the predictability of the two modes is different. Specifically, the biennial mode is more predictable because of the strong deterministic component associated with its evolution. The distinction of the two modes, therefore, may be important for predicting ENSO. The irregular interplay of the two modes seems to explain some inter-ENSO variability, namely, variable duration of ENSO events, approximate phase-locking property, and irregular onset and termination times.

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¡Ü An, S.-I., 2003: Conditional Maximum Covariance Analysis and Its Application to the Tropical Indian Ocean SST and Surface Wind Stress Anomalies. Journal of Climate, 16 (17), 2932–2938.

ABSTRACT

This study introduces the conditional maximum covariance analysis (CMCA). The normal maximum covariance analysis (MCA) is a method that isolates the most coherent pairs of spatial patterns and their associated time series by performing an eigenanalysis on the temporal covariance matrix between two geophysical fields. Different from the normal MCA, the CMCA not only isolates the most coherent patterns between two fields but also excludes the unwanted signal by subtracting the regressed value of each employed field that depends on the unwanted signal.

To evaluate the usefulness of the CMCA, it is applied to the tropical Indian Ocean sea surface temperature and surface wind stress anomalies, from which the El Niño–Southern Oscillation (ENSO) signal is removed. Results show that the first mode of the CMCA represents an east–west contrast pattern in SST and a monopole pattern in the zonal wind stress centered at the equatorial central Indian Ocean. The corresponding expansion coefficients are completely uncorrelated with the ENSO index. On the other hand, in the normal MCA, the expansion coefficients are correlated with both the ENSO index and the Indian Ocean east–west contrast pattern index. Thus, the CMCA method effectively detected the coherent patterns induced by the local air–sea interaction without the ENSO signal considered as an external factor, whereas the normal MCA detected the coherent patterns, but the effects of local and external factors cannot be separated.

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¡Ü Kar, S. K., and K.-J. Ha, 2003: Characteristic Differences of Rainfall and Cloud-to-Ground Lightning Activity over South Korea during the Summer Monsoon Season. Mon. Wea. Rev., 131 (10), 2312–2323.

ABSTRACT

In this paper the characteristic variations of cloud-to-ground (CG) lightning and total precipitation during the Korean summer monsoon (June–August) season have been extensively analyzed for different climate regimes. The data used in this study consist of the monthly CG lightning flash count as detected by the lightning detection network installed at the Korean Meteorological Administration (KMA) and the monthly precipitation data from 23 meteorological observatories spread over the Korean peninsula for a period of 10 yr from 1988 to 1997. Temporal and spatial scales of 1 month and 10² km², respectively, were considered to determine the seasonal values of rain yield or rain volume per CG flash (defined as the ratio of total precipitation to CG flash count over a common area). Seasonal values of rain yield have been compared with that of monthly values separately. The results of variation of the rain yield during the different months constituting the monsoon season are also presented. Results show that the variation of rain yield for the monsoon season closely resembles that of July indicating that July, rather than the other two monsoon months, dominates the overall monsoon pattern. The maximum values of rain yield are observed in the east coast of the Korean peninsula, particularly in the region east of Tae-back Mountain, with a mean value of 3 ¡¿ 10⁵ m³ fl^-1 while the minimum value is seen in the west of Tae-back Mountain, with an average value of 8 ¡¿ 10⁴ m³ fl^-1. The method for separating convective rain designed on broad heterogeneity similar to the Petersen and Rutledge method shows on average 82% of the total rainfall is convective in nature at the west coast stations, 53% is convective at the middle of the peninsula, and 46% is convective at the east coast stations. Maximum convective rain occurred at Kanghwa in the northwest, while the minimum was seen at Ulsan in the southeast. The correlation coefficient between the total precipitation and CG lightning during the summer monsoon season is 0.54, which is not very high since in most cases total precipitation persists longer than CG lightning. This may be due to the occasional development of mesoscale convective systems (MCSs), which produce light stratiform precipitation during their dissipation stage or might have been contaminated by the upslope precipitation or by nonlightning producing frontal precipitation. This low correlation coefficient could also be due to the episodic presence of warm rain convection or a ¡°low-echo centroid¡± precipitation system.

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¡Ü Lee, M.-S., and D.-K. Lee, 2003: An application of a weakly constrained 4DVAR to satellite data assimilation and heavy rainfall simulation.  Mon. Wea. Rev., 131(9), 2151-2176.

ABSTRACT

In this paper a simple weakly constrained four-dimensional variational data assimilation (4DVAR) technique (W4DVAR) is used in the assimilation of retrieved satellite data for a heavy rainfall simulation. The W4DVAR and the strongly constrained 4DVAR (S4DVAR) were compared through the assimilation of retrieved satellite data. In the assimilation of the retrieved satellite data, the W4DVAR technique provided an optimal initial condition for the MM5 model in the simulation of a heavy rainfall event. The W4DVAR reduced both boundary errors during 4DVAR assimilation and the large retrieval errors of Television Infrared Observational Satellite Operational Vertical Sounder (TOVS) sounding data near the surface. It was found that TOVS sounding data were useful for the simulation of typhoons and mesoscale convective systems over the ocean. The satellite data assimilated by W4DVAR contributed to favorable conditions for a heavy rainfall event by providing increased and balanced water vapor transport in the lower troposphere. The improvement in precipitation prediction using satellite data and W4DVAR was attributed to the improved spinup of moist physics processes due to the fast production of cloud water near the initial time. The moisture and temperature fields generated by W4DVAR were a significant factor in producing optimal initial data for the heavy rainfall prediction. The simulated precipitation indicated that the incremental approach was also useful for providing the initial data for a high-resolution forecast model obtained from low-resolution 4DVAR results. It is also suggested that it would be useful to employ W4DVAR in the assimilation of retrieved asynoptic satellite data over data-void areas.

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¡Ü Song, I.-S., H.-Y. Chun, and T. P., Lane, 2003: Generation mechanisms of convectively forced internal gravity waves and their propagation to the stratosphere.  J. Atmos. Sci., 60(16),  1960-1980.

ABSTRACT

Characteristics of gravity waves induced by mesoscale convective storms and the gravity wave sources are investigated using a two-dimensional cloud-resolving numerical model. In a nonlinear moist (control) simulation, the convective system reaches a quasi-steady state after 4 h in which convective cells are periodically regenerated from a gust front updraft. In the convective storms, there are two types of wave forcing: nonlinear forcing in the form of the divergences of momentum and heat flux, and diabatic forcing. The magnitude of the nonlinear source is 2 to 3 times larger than the diabatic source, especially in the upper troposphere. Three quasi-linear dry simulations forced by the wave sources obtained from the control (CTL) simulation are performed to investigate characteristics of gravity waves induced by the various wave source mechanisms. In the three dry simulations, the magnitudes of the perturbations produced in the stratosphere are comparable, yet much larger than those in the CTL simulation. However, the sum of the quasi-linear perturbations generated by the nonlinear and diabatic sources compare well with the mesoscale circulations and gravity waves in the CTL simulation.  Through the spectral analysis, it is found that the stratospheric gravity waves in all simulations have similar vertical wavelengths (6.6–9.9 km), horizontal wavelengths (10–100 km), and periods (8–80 min). Also, the magnitudes of gravity waves in the quasi-linear dry simulations are comparable with each other in spite of the differences in the magnitude of the nonlinear and diabatic sources. This is because the vertical propagation condition of linear internal gravity waves, in both the troposphere and stratosphere, restricts wave sources in the horizontal wavenumber (k) and frequency () domain, and therefore all of the forcing cannot generate gravity waves that can propagate up to the stratosphere. Compared with the diabatic sources, the nonlinear sources are inefficient in generating linear gravity waves that can propagate vertically into the stratosphere. These results suggest that wave generation mechanisms cannot be accurately understood without examining the vertical propagation condition of the gravity waves. Also, the ¡°effective¡± wave sources are of comparable magnitude, yet mostly out of phase. Therefore, although the wave amplitudes produced by simulations

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¡Ü Newchurch, M.J., D. Sun, J.H. Kim, and X. Liu, Tropical tropospheric ozone derived using Clear-Cloudy Pairs (CCP) of TOMS measurements, Atmos. Chem. Phys., 3, 187-223, 2003. 

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¡Ü Liu, X, Newchurch, M.J., J.H. Kim, Occurance of ozone anomolies over cloudy areas TOMS Version-7 Level-2 data, Atmos. Chem. Phys., 3, 683-695, 2003.

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¡Ü Gao, B.-C., P. Yang, G. Guo, S.K. Park, W. J. Wiscombe, and B. Chen, 2003: Measurements of water vapor and high clouds over the Tibetan plateau with the Terra MODIS instrument. IEEE Trans. Geosci. Remote Sensing, 41, 895-900.

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¡Ü Park, S.K., and D. Zupanski, 2003: Four-dimensional variational data assimilation for mesoscale and storm-scale applications. Meteor. Atm. Phys., 82, 173-208.

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¡Ü Sukyoung Lee and Hyun-kyung Kim, 2003: The Dynamical Relationship between Subtropical and Eddy-Driven Jets. J. Atmos. Sci., 60(12), 1490-1503.

Abstract

To address the relationship between the North Pacific and tropical SST anomalies on decadal and interannual timescales, we analyzed observed SST during the period 1950–2000. The SST variability in the North Pacific has two fairly well separated timescales: (1) decadal and (2) interannual, and each has a markedly different relationship with tropical variability. Both the decadal and interannual variability in the North Pacific is connected to the evolution of tropical SST variability with different lead-lag relationships. The decadal SST variability in the North Pacific is found to lead tropical decadal variability by approximately 5 ~ 7 years; however, the interannual SST variability is in the North Pacific in equilibrium with the tropical interannual variability. It is also shown that the spatial structure of the decadal variability in the North Pacific is significantly different from the interannual variability.

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Abstract

We present evidence showing that the nonlinear dynamic heating (NDH) in the tropical Pacific ocean heat budget is essential in the generation of intense El Niño events as well as the observed asymmetry between El Niño (warm) and La Niña (cold) events. The increase in NDH associated with the enhanced El Niño activity had an influence on the recent tropical Pacific warming trend and it might provide a positive feedback mechanism for climate change in the tropical Pacific.

Abstract

A near-annual coupled ocean-atmosphere mode in the equatorial Pacific is studied using the NCEP ocean assimilation data set. This fast mode of tropical Pacific climate variability is superimposed on the slow 3–5 year El Niño-Southern Oscillation (ENSO) phenomenon. Anomalous zonal advection plays a crucial role in generating this fast mode. It is suggested that this fast mode can be understood in terms of a coupled Pacific basin mode. It is responsible for the occurrence of some minor El Niño and La Niña events and has implications for the prediction of ENSO events.

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¡Ü Yign Noh, Woo Geun Cheon, and Siegfried Raasch, 2003: The Role of Preconditioning in the Evolution of Open-Ocean Deep Convection, Journal of Physical Oceanography, 33(6), 1145–1166.

Abstract

Large-eddy simulation of open-ocean deep convection shows that the evolution of convection appears in a fundamentally different pattern, depending on the precondition of the ocean and the magnitude of the surface buoyancy flux. As the intensity of the cyclonic gyre in the ocean under the cooling increases, the pattern of convection is transformed from ¡°distributed convection¡± to ¡°localized convection.¡± In localized convection the typical pattern of open-ocean deep convection appears, such as the generation of baroclinic instability and large lateral buoyancy transfer, secondary circulation, restratification, and the breakup of the original cyclonic gyre. On the other hand, in distributed convection small-scale convective plumes appear uniformly over the whole surface similarly to the convective boundary layer without generating the typical features of open-ocean deep convection. Hence, an enormous difference in the generated eddy kinetic energies exists between the two cases. It is also found that a stronger cooling at the sea surface suppresses the transition from distributed convection to localized convection. Dimensional analysis provides the parameters to characterize the pattern of convection, and the critical condition for the transition is estimated by analyzing the numerical results.

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¡Ü L. Wu, Z. Liu, R. Gallimore, R. Jacob, Dong Eun. Lee and Y. Zhong, 2003: Pacific Decadal Variability: The Tropical Pacific Mode and the North Pacific Mode. Journal of Climate, 16(8), 1101–1120.

Abstract

Pacific decadal variability is studied in a series of coupled global ocean–atmosphere simulations aided by two ¡°modeling surgery¡± strategies: partial coupling (PC) and partial blocking (PB). The PC experiments retain full ocean–atmosphere coupling in selected regions, but constrain ocean–atmosphere coupling elsewhere by prescribing the model climatological SST to force the atmospheric component of the coupled system. In PB experiments, sponge walls are inserted into the ocean component of the coupled model at specified latitudinal bands to block the extratropical–tropical oceanic teleconnection.

Both modeling and observational studies suggest that Pacific decadal variability is composed of two distinct modes: a decadal to bidecadal tropical Pacific mode (TPM) and a multidecadal North Pacific mode (NPM). The PC and PB experiments showed that the tropical Pacific mode originates predominantly from local coupled ocean–atmosphere interaction within the tropical Pacific. Extratropical–tropical teleconnections, although not a necessary precondition for the genesis of the tropical decadal variability, can enhance SST variations in the Tropics. The decadal memory in the Tropics seems to be associated with tropical higher baroclinic modes. The North Pacific mode originates from local atmospheric stochastic processes and coupled ocean–atmosphere interaction. Atmospheric stochastic forcing can generate a weaker NPM-like pattern in both the atmosphere and ocean, but with no preferred timescales. In contrast, coupled ocean–atmosphere feedback can enhance the variability substantially and generate a basin-scale multidecadal mode in the North Pacific. The multidecadal memory in the midlatitudes seems to be associated with the delayed response of the subtropical/subpolar gyre to wind stress variation in the central North Pacific and the slow growing/decaying of SST anomalies that propagate eastward in the Kuroshio Extension region. Oceanic dynamics, particularly the advection of the mean temperature by anomalous meridional surface Ekman flow and western boundary currents, plays an important role in generating the North Pacific mode.

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¡Ü Lifeng Luo, Alan Robock, Konstantin Y. Vinnikov, C. Adam Schlosser, Andrew G. Slater, Aaron Boone, Harald Braden, Peter Cox, Patricia de Rosnay, Robert E. Dickinson, Yongjiu Dai, Qingyun Duan, Pierre Etchevers, Ann Henderson-Sellers, Nicola Gedney, Yevgeniy M. Gusev, Florence Habets, Jinwon Kim, Eva Kowalczyk, Kenneth Mitchell, Olga N. Nasonova, Joel Noilhan, Andrew J. Pitman, John Schaake, Andrey B. Shmakin, Tatiana G. Smirnova, Peter Wetzel, Yongkang Xue, Zong-Liang Yang, and Qing-Cun Zeng, 2003: Effects of Frozen Soil on Soil Temperature, Spring Infiltration, and Runoff: Results from the PILPS 2(d) Experiment at Valdai, Russia. Journal of Hydrometeorology, 4(2), 334–351.

Abstract

The Project for Intercomparison of Land-Surface Parameterization Schemes phase 2(d) experiment at Valdai, Russia, offers a unique opportunity to evaluate land surface schemes, especially snow and frozen soil parameterizations. Here, the ability of the 21 schemes that participated in the experiment to correctly simulate the thermal and hydrological properties of the soil on several different timescales was examined. Using observed vertical profiles of soil temperature and soil moisture, the impact of frozen soil schemes in the land surface models on the soil temperature and soil moisture simulations was evaluated.

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¡Ü Cho, H.-K, Myeong J., Jeong, Jhoon Kim, and Young J. Kim, 2003: Dependence of diffuse photosynthetically active solar irradiance on total optical depth. JOURNAL OF GEOPHYSICAL RESEARCH, 108(D9), 4267, doi:10.1029/2002JD002175.

Abstract

Photosynthetically active solar irradiance (PAR, 400–700 nm) data measured with a rotating shadowband radiometer at Yonsei University, Seoul (37.57¡ÆN, 126.97¡ÆE) from 1996 through 1997 have been analyzed to investigate statistical features in components of the horizontal PAR and the dependence of the diffuse PAR on total optical depth (TOD) for visible range. Based on our measurements, it is found that the seasonal and sky conditional percentages of the global PAR for the direct and diffuse components depend considerably on the magnitude of the TOD. Annual mean diffuse PAR at Seoul appears to be 51% of the global-horizontal PAR (5.12 ¡¾ 1.27 M J m^-2 d^-1) for all-sky conditions with a TOD of 1.02 ¡¾ 0.32. However, the diffuse PAR are 39% of the global PAR (6.10 ¡¾ 2.27 M J m^-2 d^-1) under clear-sky conditions (cloud amount 2/10) with a TOD of 0.47 ¡¾ 0.23 and 73% of the global PAR (2.99 ¡¾ 2.07 M J m^-2 d^-1) under cloudy sky conditions (cloud amount 8/10) with a TOD of 1.80 ¡¾ 0.45, respectively. Simple statistical models are presented for the determination of direct and diffuse-horizontal PAR as a function of TOD, which is fitted by a curvilinear regression at a given solar zenith angle (SZA). Overall, there was reasonable agreement between predicted and measured values of two PAR components. On the basis of the statistical models for direct and diffuse PAR, we found that the four parameters of the maximum diffuse PAR, the TOD corresponding to the maximum diffuse PAR, the PAR and TOD when direct and diffuse PAR have the same value, decrease all with increasing SZA. It is of interest to note that these all four parameters can be expressed as simple linear functions of SZA.

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¡Ü Lee, K.-M.; Park, J. H.; Kim, Y.; Choi, W.; Cho, H.-K.; Massie, S. T.; Sasano, Y.; Yokota, T., 2003: Properties of polar stratospheric clouds observed by ILAS in early 1997. J. Geophys. Res.  108(D7), doi:10.1029/2002JD002854.

Abstract

The relative extinction coefficients for Arctic polar stratospheric clouds (PSCs) are determined using a transmittance-ratio technique from spectral data observed in early 1997 by the Improved Limb Atmospheric Spectrometer (ILAS). The observed relative extinction coefficients are compared with theoretical coefficients calculated by the Mie theory for single mode lognormal size distributions of PSCs. The observed PSCs are then classified into three types: nitric acid droplets (HNO₃/H₂O), and nitric acid trihydrate (NAT) solid particles in the form of -NAT and -NAT. However, the definitive detection of -NAT is difficult due to uncertainties of atmospheric temperature measurements and laboratory determination of refractive indices.

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¡Ü Shin, D. W., and T. N. Krishnamurti, 2003: Short- to medium-range superensemble precipitation forecasts using satellite products: 1. Deterministic forecasting.  J. Geophys. Res.  108(D8), doi:10.1029/2001JD001510.

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Abstract

As a comprehensive extension of the previous multimodel/multianalysis superensemble (SE) studies of rainfall forecasts, the benefits and prospects of the SE precipitation forecasts are explored using satellite products. Three different precipitation ensemble configurations are first established from a great number of numerical experiments. These configurations are multianalysis (MA), multicumulus-scheme (MC), and multimodel (MM) configurations. A set of MA ensemble comes from the use of several different satellite-derived rain rates through the physical initialization procedure within the Florida State University Global Spectral Model (FSUGSM) system. Six different state-of-the art cumulus parameterization schemes are incorporated into the FSUGSM in order to introduce the MC ensemble configuration. The MM configuration is composed of an FSU control forecast and those provided by five operational numerical weather prediction centers. In addition to the original technique, a possible deterministic SE enhancement technique (regression dynamic linear model) is then proposed and applied to the above three configurations of ensemble members as well as all of them together. The impact of a higher resolution family of models on the performance of SE forecasts is extensively investigated by repeating the above procedure with T170 resolution precipitation forecasts. Results show that short- to medium-range SE forecasts are generally superior in skill to various conventional forecasts. A notably improved (~20%) quantitative precipitation forecast is exhibited by the newly proposed SE technique. The MM configuration proved to be the most effective ensemble prediction system. Although a higher-resolution SE forecast requires a large amount of computing time, it turns out that the impact is significant not only in skill scores but also in resolving mesoscale-based convective disturbances.

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¡Ü Shin, D. W., and T. N.  Krishnamurti, 2003: Short- to medium-range superensemble precipitation forecasts using satellite products: 2. Probabilistic forecasting. J. Geophys. Res.  108(D8), doi: 10.1029/2001JD001511.

Abstract

Short- to medium-range probabilistic precipitation forecasts over the global tropics are explored using satellite products, from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Special Sensor Microwave/Imager (SSM/I) instruments. In addition to the conventional probability of precipitation (POP) forecast, superensemble (SE) POP forecasts are introduced and applied to the multianalysis, multicumulus-scheme, and multimodel ensemble configurations in two different horizontal resolution forecasts. It is shown that an ensemble system using a single model has a more consistent bias, which can at least partially be removed by a simple bias correction. With the aid of properly prepared ensemble members, meaningful POP forecasts have much longer forecast lead times. Results also show that a family of higher-resolution forecasts has a greater ability in removing model biases. The advantage of the SE approach is found to be evident in making POP forecasts, compared to the conventional method. The skills of SE POP are 10 to 20 percent better than those of the bias-corrected.

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¡Ü Young-Joon Kim, Stephen D. Eckermann and Hye-Yeong Chun, 2003: An Overview of the Past, Present and Future of Gravity-Wave Drag Parametrization for Numerical Climate and Weather Prediction Models. Atmosphere-Ocean, 41(1), pp 65-98.

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¡Ü Byung-Ju Sohn, Eui-Seok Chung, Johannes Schmetz, and Eric A. Smith, 2003: Estimating Upper-Tropospheric Water Vapor from SSM/T-2 Satellite Measurements. Journal of Applied Meteorology, 42(4), pp. 488-504.

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¡Ü Y. Noh , W. G. Cheon , S. Y. Hong , S. Raasch, 2003: Improvement of the K-profile Model for the Planetary Boundary Layer based on Large Eddy Simulation Data. Boundary Layer Meteorology, 107(2), pp. 401-427  

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¡Ü Heo, Bok-Haeng, S. Jacoby-Koaly, Kyung-Eak Kim, B. Campistron, B. Benech, and Eun-Sil Jung, 2003: Use of the Doppler Spectral Width to Improve the Estimation of the Convective Boundary Layer Height from UHF Wind Profiler Observations. Journal of Atmospheric and Oceanic Technology, Vol. 20, No. 3, pp. 408-424.

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¡Ü Boehm, M. T., and Sukyoung Lee, 2003: The implications of tropical Rossby waves for tropical tropopause cirrus formation and for the Equatorial upwelling of Brewer-Dobson circulation. Journal of Atmospheric Sciences, 60(2), pp. 247-261.

Oey, L.-Y., and H.-C. Lee, 2002: Deep Eddy energy and topographic Rossby waves in the Gulf of Mexico. Journal of Physical Oceanography, 32(12), pp. 3499–3527.

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¡Ü Kwon, Hyuk Joe, Seong-Hee Won, Myung-Hwan Ahn, Ae-Sook Suh, and Hyo-Sang Chung, 2002: GFDL-Type Typhoon Initialization in MM5. Monthly Weather Review, 130(12), pp. 2966–2974.

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¡Ü Lim, Young-Kwon, Kwang-Yul Kim, and Hee-Sang Lee, 2002: Temporal and Spatial Evolution of the Asian Summer Monsoon in the Seasonal Cycle of Synoptic Fields. Journal of Climate: Vol. 15, No. 24, pp. 3630–3644.

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¡Ü Kim, Si-Wan and Soon-Ung Park, 2003: Coherent Structures near the Surface in a Strongly Sheared Convective Boundary Layer Generated by Large-Eddy Simulation. Boundary-Layer Meteorology, 106 (1), pp. 35-60.