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Riyu Lu, Baohua Ren, and Hyo-Sang Chung

Abstract

In this study, based on the cases of strong and weak June–August (JJA) mean convection over the tropical western North Pacific, composite analyses are performed by using the satellite-observed outgoing longwave radiation (OLR) data for the 23-yr period from 1979 to 2001, and the contrast features of the composite seasonal evolution of the convection between the strong and weak cases are examined. Anomalous annual cycle and 30–60-day oscillations, that is, two components of the seasonal evolution, and their relative contributions to the anomalous seasonal evolution is analyzed.

The authors find that in the composite sense, convection exhibits a larger (smaller) seasonal change during the strong (weak) JJA mean convection summers. The strong (weak) JJA mean convection corresponds to enhanced (suppressed) convection of the annual cycle from the beginning of the year to September, and such a difference in the annual cycle between strong and weak cases is most significant from May to August. On the other hand, the composite 30–60-day oscillations for the strong cases have greater amplitudes than the weak cases, and the phases of the 30–60-day oscillations tend to be more consistent for the strong cases than for the weak cases. Both annual cycle and 30–60-day oscillations contribute to the interannual variation of the seasonal evolution.

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H. Joe Kwon, Seong-Hee Won, Myung-Hwan Ahn, Ae-Sook Suh, and Hyo-Sang Chung

Abstract

The Geophysical Fluid Dynamics Laboratory (GFDL) hurricane initialization algorithm is implemented in the community fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). This work is applied to the MM5-based Regional Data Assimilation and Prediction System model (RDAPS), the Korea Meteorological Administration's regional forecast model. The bogus procedure starts by initializing the winds within the bogus area. The main difficulty lies in the generation of other variables, such as humidity, temperature, geopotential, etc., which are dynamically consistent with the prescribed wind. However, it was found that there is a simple and practical way of tropical cyclone (TC) initialization. It is achieved by the use of the built-in function of MM5, the four-dimensional data assimilation (FDDA). In order to do so, a miniature RDAPS is constructed. After the initialization of wind within the filter region, all other variables are generated by the model through a strong 24-h nudging to the prescribed wind.

It is found after careful analyses that there is an improvement over the no-bogus model. Failures are mostly due to the fake vortex or the spurious deepening of the vortex, which have been problems of the original RDAPS model. The bogus RDAPS never cures the failure of the original model.

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Youngsin Chun, Hi-Ku Cho, Hyo-Sang Chung, and Meehye Lee

The observation of dust events in Korea must have been important through its long history because of its geographical and meteorological setting. Descriptions about dust events were well documented in historical archives, such as Samguk sagi (57 BC–AD 938), Goryeo sa (918–1392), Joseon wangjosillok (1392–1853), and Munhuenbigo (~1776). In this study, records of Asian dust events were compiled from the above historical archives, covering the period of the second to the eighteenth century. These historical records were investigated along with the recent data (1915–2005) of dust event days in Seoul, Korea. The first record was made in AD 174 in Silla during the period of the Three Kingdoms. A dust event, now called hwangsa, was commonly written down as Woo-Tou or Tou-Woo standing for “dustfall” in the historical archives. Asian dust events took place most frequently during spring from March to May and there was almost no occurrence in summer. The main seasonal feature of the historical dust events was found to be in good agreement with that of the last 90 yr. The result suggests that the past seasonal mechanism of the dust event occurrence and transport in northeast Asia is not significantly different from the present.

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Andrew M. E. Grose, Eric A. Smith, Hyo-Sang Chung, Mi-Lim Ou, Byung-Ju Sohn, and F. Joseph Turk

Abstract

A rainfall nowcasting system is developed that identifies locations of raining clouds on consecutive infrared geosynchronous satellite images while predicting the movement of the rain cells for up to 10 h using cloud-motion-based winds. As part of the analysis, the strengths and weaknesses of various kinds of cloud wind filtering schemes and both steady and nonsteady storm advection techniques as forecast operators for quantitative precipitation forecasting are evaluated. The first part of the study addresses the development of a probability matching method (PMM) between histograms of equivalent blackbody temperatures (EBBTs) and Special Sensor Microwave Imager (SSM/I)–derived rain rates (RRs), which enables estimating RRs from instantaneous infrared imagery and allows for RR forecasts from the predicted EBBT fields. The second part of the study addresses the development and testing of the nowcasting system built upon the PMM capability and analyzes its success according to various skill score metrics. Key processes involved in the nowcasting system include the retrieved cloud-motion wind field, the filtered cloud-motion wind field, and the forecasting of a future rain field by storm advection and EBBT tendencies. These processes allow for the short-term forecasting of cloud and rain locations and of rain intensity, using PMM-based RRs from different datasets of infrared Geostationary Meteorological Satellite (GMS) and Geostationary Operational Environmental Satellite (GOES) imagery. For this study, three convective rain sequences from the Caribbean basin, the Amazon basin, and the Korean peninsula are analyzed. The final part of the study addresses the decay of forecast accuracy with time (i.e., the point at which the asymptotic limit on forecast skill is reached). This analysis indicates that the nowcasting system can produce useful rainfall forecast information out to approximately 6 h.

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