Tuning of length-scale and observation-error for radar data assimilation using four dimensional variational (4D-Var) method

The effects of tuning of length-scale and observation-error on heavy rainfall forecasts are investigated. Length scale and observation error are tuned based on observation minus background (O - B) covariances and theoretically expected cost function values, respectively. Tuned length scale and observation error are applied to radar data assimilation using the Four Dimensional Variational (4D-Var) method. Length-scale tuning leads to improved Quantitative Precipitation Forecast (QPF) skill for heavy precipitation, better analyses, and reduced errors of wind, temperature, humidity, and hydrometeor forecasts. The effects of observation-error tuning are not as significant as those of length-scale tuning, and they are limited to improvements in QPF skill. This is because tuned observation errors are close to pre-assumed values. Proper tuning of length-scale and observation-error is essential for radar data assimilation using the 4D-Var method

A Study on Optimized Management Options for the Wolsong Low-and Intermediate - Level Waste Disposal Center in Korea -13479

ABSTRACT The safe and effective management of radioactive waste is a national task required for sustainable generation of nuclear power and for energy self-reliance in Korea. Currently, for permanent disposal of low-and intermediate-level waste (LILW), the Wolsong LILW Disposal Center (WLDC) is under construction. It will accommodate a total of 800,000 drums at the final stage after stepwise expansion. As an implementing strategy for cost-effective development of the WLDC, various disposal options suitable for waste classification schemes would be considered. It is also needed an optimized management of the WLDC by taking a countermeasure of volume reduction treatment. In this study, various management options to be applied to each waste class are analyzed in terms of its inventory and disposal cost. For the volume reduction and stabilization of waste, the vitrification and plasma melting methods are considered for combustible and incombustible waste, respectively

Satellite radiance data assimilation for binary tropical cyclone cases over the western North Pacific

A total of three binary tropical cyclone (TC) cases over the Western North Pacific are selected to investigate the effects of satellite radiance data assimilation on analyses and forecasts of binary TCs. Two parallel cycling experiments with a 6 h interval are performed for each binary TC case, and the difference between the two experiments is whether satellite radiance observations are assimilated. Satellite radiance observations are assimilated using the Weather Research and Forecasting Data Assimilation (WRFDA)'s three-dimensional variational (3D-Var) system, which includes the observation operator, quality control procedures, and bias correction algorithm for radiance observations. On average, radiance assimilation results in slight improvements of environmental fields and track forecasts of binary TC cases, but the detailed effects vary with the case. When there is no direct interaction between binary TCs, radiance assimilation leads to better depictions of environmental fields, and finally it results in improved track forecasts. However, positive effects of radiance assimilation on track forecasts can be reduced when there exists a direct interaction between binary TCs and intensities/structures of binary TCs are not represented well. An initialization method (e.g., dynamic initialization) combined with radiance assimilation and/or more advanced DA techniques (e.g., hybrid method) can be considered to overcome these limitations

Tropical Temperature Variability in the UTLS: New Insights from GPS Radio Occultation Observations

AbstractGlobal positioning system (GPS) radio occultation (RO) observations, first made of Earth's atmosphere in 1995, have contributed in new ways to the understanding of the thermal structure and variability of the tropical upper troposphere–lower stratosphere (UTLS), an important component of the climate system. The UTLS plays an essential role in the global radiative balance, the exchange of water vapor, ozone, and other chemical constituents between the troposphere and stratosphere, and the transfer of energy from the troposphere to the stratosphere. With their high accuracy, precision, vertical resolution, and global coverage, RO observations are uniquely suited for studying the UTLS and a broad range of equatorial waves, including gravity waves, Kelvin waves, Rossby and mixed Rossby–gravity waves, and thermal tides. Because RO measurements are nearly unaffected by clouds, they also resolve the upper-level thermal structure of deep convection and tropical cyclones as well as volcanic clouds. Their low biases and stability from mission to mission make RO observations powerful tools for studying climate variability and trends, including the annual cycle and intraseasonal-to-interannual atmospheric modes of variability such as the quasi-biennial oscillation (QBO), Madden–Julian oscillation (MJO), and El Niño–Southern Oscillation (ENSO). These properties also make them useful for evaluating climate models and detection of small trends in the UTLS temperature, key indicators of climate change. This paper reviews the contributions of RO observations to the understanding of the three-dimensional structure of tropical UTLS phenomena and their variability over time scales ranging from hours to decades and longer

"Offset" as an instrument of national industrial policy

Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1991.Includes bibliographical references (leaves 153-154).by Joowan Kim.Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1991

The role of dynamics in the formation and maintenance of the tropical cold-point tropopause

This thesis examines characteristics of the tropical cold-point tropopause (CPT)and associated dynamic mechanisms using observations, idealized model, and generalcirculation model simulations. Fine-scale structure of the CPT is investigated usingnewly available high-resolution temperature data. Then, the dynamic mechanism ofthe CPT formation is rigorously tested and examined using a dry primitive equationmodel under the framework of transformed Eulerian-mean. Finally, the characteristicsof the CPT are examined in the state-of-art climate models that participated inthe Coupled Model Intercomparison Project Phase 5 (CMIP5). The current climatemodels' capability to reproduce the CPT features is evaluated and discussed.In the observational study, climatology, seasonal cycle, and intraseasonal variabilityof three CPT properties (temperature, pressure, and sharpness) are examinedusing high-resolution temperature profiles derived from COSMIC global positioningsystem (GPS) radio occultation (RO) measurements. The climatology obtained fromthe GPS RO data captures the characteristic structure of the CPT successfully. Thethree CPT properties show coherent seasonal cycle in the tropics that the CPT iscolder, higher (lower in pressure) and sharper in boreal winter compared to that inboreal summer. This seasonality is consistent with that of the large-scale tropopauseupwelling, which is largely driven by near-tropopause processes. The variability onintraseasonal timescales is more likely controlled by the tropical deep convectionand associated tropical waves. Particularly, intraseasonal variability of the CPTproperties shows clear signature of Kelvin waves, with a secondary contribution byMadden-Julian Oscillation in the deep tropics.The formation mechanism of the CPT is further investigated using a dry primitiveequation general circulation model with a simplified thermal forcing. The simpledynamic system reproduces a distinct cold level at the top of the tropical troposphere,which is analogous to the CPT in the real atmosphere. The modeled CPT is primarilymaintained by adiabatic cooling due to upwelling at the tropical tropopause,and synoptic-scale wave forcing in the subtropical lower stratosphere is found as theprimary driver of the upwelling. Further investigation on the evolution mechanismsuggests that the formation of the CPT is a part of balancing process between waveforcings and mean flow response in the tropics, and this is likely an important processthat decides the vertical extent of the subtropical jet in the lower stratosphere.The thermal characteristics of the CPT examined in CMIP5 models exhibitreasonable agreements with observations. Historical simulations successfully capturethe spatio-temporal structure of the CPT on annual and seasonal timescales. The interannualvariability associated with El Ni˜no Southern Oscillation and intraseasonalvariability associated with equatorial waves are also roughly reproduced. However,many of the models still have overall warm bias near the CPT and non-negligiblebiases in the amplitude of variability in intraseasonal to interannual timescales. Inthe future projections based on the Representative Concentration Pathway (RCP)8.5 scenario, the models predict robust warming both at the 100-hPa and zero-lapseratelevels (estimated CPT), but cooling at the 70-hPa level. A weakened seasonalcycle in the temperature is also found in most models at both the 100- and 70-hPalevels, which could have an important implication for the stratosphere-troposphereexchange and related climate variability.Cette thèse examine les caractéristiques du point froid de la tropopause tropicale, "tropical cold-point tropopause" (CPT) et les mécanismes dynamiques associés en utilisant des observations, un modèle idéalisé ainsi qu'on model de circulation globale. La fine structure du CPT est évaluée en utilisant de nouvelles mesures de températures à haute résolution. Ensuite, les mécanismes dynamiques de la formation du CPT sont testées de manière rigoureuse et examinées en utilisant un model sec basé sur les équations primitives dans le cadre du "Transformed Eulerian Mean". Finalement, les caractéristiques du CPT sont examinées avec les modèles climatiques de pointe du "Coupled Model Intercomparions Project Phase 5" (CMIP5). La capacité actuelle de ces modèles de reproduire les caractéristiques du CPT sont par la suite évaluées.Dans l'étude observationnelle, la climatologie, le cycle saisonnier et la variabilité intra-saisonnière de trois propriétés du CPT (température, pression et finesse) sont examinées en utilisant des profils de température haute-résolution dérivés du system de mesure par radio occultation gps COSMIC. La climatologie obtenue par COSMIC capture la structure caractéristique du CPT avec succès. Les trois propriétés du CPT montrent une évolution saisonnière cohérente dans les tropiques : le CPT est plus haut, plus froid, et plus fin lors de l'hiver boréal compare à l'été boréal. Cette saisonnalité est consistante avec les mouvements verticaux de large échelle qui sont principalement générées par des procédés locaux à la tropopause. La variabilité intra saisonnière est plus vraisemblablement contrôlée par la convection tropicale profonde et les ondes tropicales associées. Particulièrement, la variabilité saisonnière du CPT montre clairement une signature d'onde Kelvin, avec une contribution secondaire de la Madden-Julian Oscillation dans les tropiques. Les mécanismes de formation du CPT sont par la suite évalués en utilisant un model basé sur les équations primitives avec un forçage thermal simplifie. Le système dynamique simple reproduit un niveau froid distinct au sommet de la troposphère tropicale, qui est analogue au CPT de l'atmosphère terrestre. Le CPT modelé est principalement maintenu par de refroidissement adiabatique par ascension à la tropopause tropicale. Le forçage par onde synoptiques dans la basse stratosphère subtropicale est le mécanisme dominant régissant ce refroidissement par ascension. Une évaluation plus poussée suggère que la formation du CPT fait partie d'un processus de stabilisation entre le forçage d'onde et la réponse de la circulation moyenne dans les tropiques et que ce processus est vraisemblablement important pour décider de l'étendue verticale du courant jet subtropical dans la basse stratosphère.Les caractéristiques thermales du CPT observées dans les modèles CMIP5 démontrent une correspondance raisonnable avec les observations. Les simulations historiques capturent avec succès la structure spatio-temporelle du CPT sur des bases annuelles et saisonnières. La variabilité interannuelle associée avec le « El Nino-Southern Oscillation» et la variabilité intra saisonnière associée avec les ondes équatoriales sont reproduites avec succès. Cependant, plusieurs des modèles présentent une erreur chaude près du CPT et des erreurs non-négligeables dans l'amplitude de la variabilité intra saisonnière et interannuelle. Dans la projection future basée dur le scenario « Representative Concentration Pathway » (RCP) 8.5, les modèles prédisent un réchauffement au niveau du CPT, mais un refroidissement à 70 hPa. Un cycle saisonnier de températures plus faible est aussi observé dans la plupart des modèles au niveau de 100 et 70 hPa, ce qui pourrait avoir des implications importantes pour les échanges stratosphère troposphère et la variabilité climatique associée

Spatio-temporal variability of cloud top and tropopause heights over the Arctic from 10-year CALIPSO, GPSRO and MERRA-2 datasets

© 2022The characteristics of cloud top heights (CTHs) and tropopause heights (TPHs) over the Arctic and their relationship were investigated using Cloud-Aerosol Lidar Infrared Pathfinder Satellite (CALIPSO) observations and Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) data for approximately 10 years from June 2006 to March 2016. Global positioning system radio occultation (GPSRO) measurements were also used to validate the TPHs derived from the MERRA-2 reanalysis data. Results of the composite analysis indicate that CTHs over the Arctic generally constitute the low-top (lower than ~3 km) and high-top (higher than ~7 km) categories in all seasons. The high CTHs above approximately 8 km show a close relationship with TPHs in all seasons, with an especially strong positive correlation in winter. In general, both CTH and TPH for each season revealed by composite analysis exhibited a zonally symmetric pattern with greater heights at lower latitudes, except for the winter when significantly high CTHs and TPHs were observed in the Greenland Sea, Atlantic, and Scandinavian regions. The proportion of high CTHs in these regions was higher than that in other regions. Notably, CTH values in the range of approximately 9.7–10.5 km over these regions are slightly higher than the climatological TPHs in winter. From a detailed analysis of Atlantic storm tracks, we conclude that the Atlantic windstorms make a significant contribution to the higher CTHs and TPHs over the Norwegian, Greenland, Kara-Barents Seas, and Northwest Russian regions of the Arctic.N